ES 96 2010 HVAC Final Report

Rethinking Heating, Ventilation & Air Conditioning (HVAC) in Harvard

University’s River Houses

HARVARD COLLEGE ENGINEERING SCIENCES 96 FINAL REPORT

HVAC Group: Mason Brunnick, Hayden Burgoyne, Ben Chiel,

Shomesh Chaudhuri, Or Gadish

May 6, 2010

ES96 Final Report Brunnick, Burgoyne, Chaudhuri, Chiel, Gadish

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Table of Contents Executive Summary .................................................................................................................. 7

1. Introduction ........................................................................................................................ 8 1.1. The Role of ES 96 ............................................................................................................................................ 8

1.1.1. The general problem............................................................................................................................... 8 1.1.2. HVAC Group.......................................................................................................................................... 8 1.1.3. HVAC 2009 vs. 2010............................................................................................................................. 9

1.2. HVAC Group’s solutions .............................................................................................................................. 9 1.2.1. Re-thinking HVAC................................................................................................................................ 9 1.2.2. Breaking up the system into components ........................................................................................10 1.2.3. Beyond temperature and moving air.................................................................................................11 1.2.4. Four-tiered solutions ............................................................................................................................12 1.2.5. Reconsidering HVAC as TCAQ.......................................................................................................14

1.3. Methods for generating solutions...............................................................................................................15 1.3.1. Looking to nature..................................................................................................................................15 1.3.2. Cell model...............................................................................................................................................15 1.3.3. Human Body model .............................................................................................................................16 1.3.4. Solutions that transcend time.............................................................................................................16

2. Background........................................................................................................................ 17 2.1. Thermal Comfort and Air Quality ............................................................................................................17 2.2. Standards..........................................................................................................................................................17

2.2.1 Temperature............................................................................................................................................17 2.2.2. Humidity.................................................................................................................................................17 2.2.3. Air Movement........................................................................................................................................18 2.2.4. Carbon Dioxide .....................................................................................................................................18 2.2.5. Carbon Monoxide.................................................................................................................................18

2.3. Methods for analysis of solutions ...............................................................................................................18 2.3.1. Baseline system.......................................................................................................................................19 2.3.2. Analysis Metrics.....................................................................................................................................19

3. Baseline .............................................................................................................................. 21 3.1. Goals and Justification of the Baseline ......................................................................................................21 3.2. Components of the Baseline........................................................................................................................21

3.2.1. Heating: Blackstone..............................................................................................................................21 3.2.2. Cooling: Chilled Water Plant ............................................................................................................22 3.2.3. Distribution: Fan Coils........................................................................................................................23 3.2.4. Ventilation: Air Handler .....................................................................................................................25

4. Active Ventilation: ............................................................................................................ 27 4.1. Standards for Active Ventilation................................................................................................................27 4.2. Solutions Involving Active Ventilation.....................................................................................................27

4.2.1. Fan Coils with External Louvers........................................................................................................27 4.2.2. Heat Recovery Ventilators ..................................................................................................................28

5. Natural Ventilation ........................................................................................................... 31 5.1. Introduction.....................................................................................................................................................31 5.2. Natural Ventilation Feasibility Assessment .............................................................................................31 5.3. Operating Industry Standards.....................................................................................................................36


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5.4. Strategies for Natural Ventilation ..............................................................................................................37 5.4.1. Single-Sided Ventilation ......................................................................................................................38 5.4.2. Wind-Driven Cross-Ventilation .......................................................................................................39 5.4.3. Buoyancy-Driven Stack Ventilation Combined with Wind Ventilation..................................40

5.5. Cooling Potential............................................................................................................................................43 5.6. Concluding Strategies ....................................................................................................................................44

6. Passive Solar Heating ......................................................................................................... 46 6.1. Justification for Passive Solar Heating ......................................................................................................46 6.2. Windows..........................................................................................................................................................46 6.3. Southern Facing Window Analysis............................................................................................................47 6.4. Southern Facing Window Results..............................................................................................................48 6.5. Southern Facing Window Conclusions....................................................................................................48

7. Seasonal Heat Storage in Outer Walls ............................................................................... 50 7.1. Justification for Seasonal Heat Storage .....................................................................................................50 7.2. Seasonal Heat Storage Analysis...................................................................................................................50 7.3. Seasonal Heat Storage Results.....................................................................................................................52 7.4. Seasonal Heat Storage Conclusions ...........................................................................................................52

8. Ground Source Heat Pumps ............................................................................................. 54 8.1. Justification for Ground Source Heat Pumps .........................................................................................54 8.2. Ground Source Heat Pumps Analysis .......................................................................................................54 8.3. Ground Source Heat Pumps Results and Conclusions .........................................................................56

9. Plants ................................................................................................................................. 58 9.1. Justification for Studying Plants .................................................................................................................58 9.2. Exploring the Two Methods .......................................................................................................................58

9.2.1. Option 1: Substituting Plants for Active Ventilation..................................................................58 9.2.2. Option 2: Incorporating Plants into an Active Ventilation System ..........................................60

10. Phase Change Materials for Thermal Storage ................................................................ 62 10.1. Phase Change Materials Background......................................................................................................62 10.2. Incorporating PCM into Building Materials ........................................................................................62

11. Variable Refrigerant Flow Air Conditioning ................................................................. 64 11.1. Benefits ..........................................................................................................................................................64 11.2. Disadvantages ...............................................................................................................................................64 11.3. Conclusion....................................................................................................................................................65

12. Double Skin Façade......................................................................................................... 66 12.1. Benefits ..........................................................................................................................................................66 12.2. Disadvantages ...............................................................................................................................................66 12.3. Conclusion....................................................................................................................................................67

13. Biomimicry ...................................................................................................................... 68 13.1. Avian respiration .........................................................................................................................................68

13.1.1. The system in nature ..........................................................................................................................68 13.1.2. Applications .........................................................................................................................................69

13.2. The Termite Mound...................................................................................................................................70 13.2.1. The system in nature ..........................................................................................................................70 13.2.2. Applications .........................................................................................................................................70


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13.3. Biomimicry Conclusions ...........................................................................................................................71

Conclusion and Recommendations....................................................................................... 72

References............................................................................................................................... 75

Appendices ............................................................................................................................. 79


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List of Figures Figure 1.1 – Simplistic view of the purpose of HVAC systems......................................................... 10

Figure 1.2 – More complex understanding the purpose and role of HVAC.................................. 10

Figure 1.3 – Four tiered solutions ............................................................................................................ 12

Figure 1.4 – The over-arching idea that this group proposes............................................................. 15

Figure 3.1 – Schematic of baseline system.............................................................................................. 26

Figure 4.1 – Snorkel vents in brick .......................................................................................................... 28

Figure 4.2 – Schematic diagram of thermal coupling of air streams................................................. 29

Figure 5.1 – Historical temperature data for 02139 ............................................................................ 32

Figure 5.2 – Psychometric range for natural ventilation..................................................................... 33

Figure 5.3 – Ozone pollution data ........................................................................................................... 34

Figure 5.4 – Operable window types ....................................................................................................... 35

Figure 5.5 – Heating. cooling, ventilation regimes............................................................................... 36

Figure 5.6 – Temperature driven single-sided ventilation.................................................................. 38

Figure 5.7 – Single-sided cubic feet per minute potential................................................................... 39

Figure 5.8 – Neutral pressure level........................................................................................................... 40

Figure 5.9 – Strategies for changing neutral pressure level ................................................................. 41

Figure 5.10 – Stack effects for windows.................................................................................................. 42

Figure 5.11 – Stack effects of chimney openings .................................................................................. 42

Figure 5.12 – Effects of window placement on indoor airspeed ....................................................... 43

Figure 5.13 – Combined strategies for natural ventilation ................................................................ 44

Figure 7.1 – Thermal model diagram for outer wall ............................................................................ 50

Figure 7.2 – Thermal wall effect............................................................................................................... 52

Figure 8.1 –Ground source heat pumps cost versus natural gas price .............................................. 56

Figure 8.2 – Natural gas prices over last decade .................................................................................... 57

Figure 8.3 – Ground source heat pumps cost versus cost of carbon dioxide .................................. 57

Figure 9.1 – Typical shoulder height indoor Areca Palm ................................................................... 58

Figure 9.2 – Costs of plant program........................................................................................................ 59

Figure 9.3 – Costs savings plant program............................................................................................... 60

Figure 10.1 – Microencapsulated paraffin wax ..................................................................................... 63

Figure 13.1 – The avian respiration system............................................................................................ 69


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Figure 13.2 – Termite mound schematic ............................................................................................... 71

Figure 14.1 – Plot of cost-savings vs. Greenhouse gas savings for solutions.................................... 73


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Executive Summary To be at the forefront of reducing greenhouse gas emissions while minimizing cost, Harvard must be at the forefront of heating, ventilation and air conditioning (HVAC) technologies. HVAC corresponds to a large part of the greenhouse gas emissions and maintenance cost of the Harvard Houses and will amount to a large part of the capital cost invested in the upcoming renovations of the river Houses. In this report, the ES96 HVAC group rethought the framework for HVAC and analyzed various possible solutions, as a result.

The HVAC group recommends that Harvard consider the four major solutions found to be appropriate for implementation in the current renovation project: natural ventilation, passive heating, ground source heating pumps, and plant use. Furthermore, we recommend looking into implementation of other technologies in the future. Such technologies could be implemented after the major renovations are complete and include the use of phase change materials and passive ventilation technologies modeled after avian respiration. In order to be able to effectively combine and use the technologies described above – most likely in conjunction with more conventional technologies, such as those described in the baseline system, as well – Harvard must also rethink HVAC. Conventional treatment of HVAC suggests a monolithic solution that involves heating, ventilating, and cooling the residence. We have found that it is more useful to consider the goal of HVAC systems as thermal comfort and air quality (TCAQ) and to build a system of solutions around it. The system can be such that solutions treat the various aspects of TCAQ to differing amounts. Such a system can, furthermore, be optimized by a control network to match the changing environment and the needs of the student throughout the 80-year lifespan of the renovated Houses. Within this framework Harvard can not only choose a single solution that we have recommended, but implement a variety of solutions including, but not limited to, those recommended in this report. We believe that this will allow for the most robust and efficient system, leading to a minimization of cost and greenhouse gas emissions, while providing Harvard with flexibility throughout its future.


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1. Introduction 1.1. The Role of ES 96

1.1.1. The general problem In the spring of 2010, the students of Engineering Sciences 96 were charged with

assessing Harvard College’s renovation plans for the Harvard River House (HRH) dormitories that are nearing or are over one hundred years of age. The class, specifically, was trying to find creative ways to bring down the cost of the renovations and further maintenance, imagine the needs of the new houses looking forward to their desired 80-year life span and to the lower the green house gas emissions of the new dorms – an objective in line with the general goals of Harvard University President Drew Faust. To help focus the class’ projects, Stephen Needham, Director of Capital Projects at Harvard, asked two very important questions of the class:

1. How to provide year round thermal comfort in line with engineering standards, while meeting or exceeding the University’s sustainability goals?

2. How to meet the electrical demands of current and future students while meeting or exceeding the University’s sustainability goals?i

Furthermore, it was explained that Winthrop House would be the first HRH to undergo renovations and that it would act as the pilot for various novel projects. As such, we have projected all of our analyses onto Winthrop House to gain a better understanding for feasibility of our proposed solutions and our analyses in general. 1.1.2. HVAC Group

In response to Mr. Needham’s questions, the HVAC group decided that it could best tackle the problem at hand by thinking about solutions to the first question. The first idea that comes from engineers thinking about thermal comfort solutions is usually in the area of Heating, Ventilation, and Air Conditioning (HVAC) systems.

The reason, then, for choosing to think about heating, ventilation and air conditioning was two-fold. Firstly, this immediately tackles Mr. Needham’s first question, seeing as how HVAC systems are usually responsible for the majority of thermal comfort in residential buildings today. Secondly, HVAC systems are also responsible for a great deal of the Greenhouse Gas (GHG) emissions at Harvard, responsible for up to 67% of carbon emissions in Winthrop Houseii.

The advantages of tackling the problem of redesigning the HVAC systems of the HRH to better match the University’s sustainability goals, engineering standards, and satisfaction by Harvard’s most numerous clients, the students, are far-reaching and long-lasting. The HVAC system is part of the basic design of a building and, as such, may be hard to change without


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major renovations. This is, therefore, the best chance to redesign the system, include the most innovative advances that are feasibly available, thinking ahead to how the building would have to serve students for the entirety of its proposed 80-year lifespan.

1.1.3. HVAC 2009 vs. 2010

It is important to distinguish this report from the 2009 ES96 HVAC reportiii. Last year’s group focused primarily on potential methods for implementing air conditioning in the HRH. While this year’s group still believes that expanding the HRH’s HVAC systems to be able to provide air conditioning is important, we felt that it was more important to rethink HVAC entirely, providing an innovative look at such a key part of residences in general. The recommendations of last year’s report, however, can be taken into consideration together with this year’s report, understanding that they are not conflicting, but rather, complimentary, tackling different aspects of the project.

1.2. HVAC Group’s solutions 1.2.1. Re-thinking HVAC

The group began by seeking novel technologies that would not only provide a big step towards reducing Harvard’s GHG emissions and improving living conditions in the HRH, but also put Harvard at the forefront of dormitory technologies. We quickly found, however, that such technologies were either too far from being technologically feasible, or were not feasible under the current economic conditions.

We had to, therefore, rethink heating, ventilation, and air condition entirely. The purpose of HVAC systems is, most literally to heat, ventilate and cool the environment in which they are applied. This definition, however, is very limiting in assuming that one system is able to raise or lower temperatures and move air around appropriately. Fully redesigning the HRH’s HVAC systems requires questioning this basic assumption.

The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has a definition: HVAC&R1 systems mediate “the interaction between people and the indoor and outdoor environment.”iv It is important to understand, as ASHRAE has already understood, that HVAC cannot be thought in the simplistic manner diagram by Figure 1.1. Rather, HVAC mediates interactions that will continue to exist even beyond the introduction of an HVAC system. Such a system is, thus, better diagrammed by Figure 1.2. Analyzing the roots of the basic assumptions underlying the development of HVAC systems, both historically and at present, has brought forth the innovative solutions provided in this report. More so than just redesigning the HVAC system in the HRH, this group found that it was important to rethink the role of HVAC in general and the treatment of such roles. From these considerations have arisen a set of guidelines and recommendations that should be considered.

1 ASHRAE has already rethought the role of HVAC and have added a fourth component: refrigeration, yielding HVAC&R.


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Figure 1.1 – The most simplistic view of the purpose of HVAC systems. The three colored arrows signify heating, ventilation, and air condition, respectively.

Figure 1.2 – A more complex understanding the purpose and role of HVAC as discussed by ASHRAE. The colored lines represent the transfer of heat and air. The dashed lines indicate relationships that fall outside the scope of an HVAC system but should be understood when designing any such system.

1.2.2. Breaking up the system into components

The most efficient way of accomplishing heating, ventilation, and air condition is not by providing one single, monolithic solution. Instead, it is better to separate the various purposes of HVAC into distinct aspects, each of which is treated by components tailored to maximize the efficiency of several aspects.

Furthermore, components make the system as a whole extendible and more flexible, adapting to the changing needs and conditions of the future. Due to the difficulty of predicting changes in HVAC-related needs, it is necessary to be able to match these changes without major reconstruction, as will only be done in these initial stages of the HRH lifespan. Components allow us to add and remove pieces that are not an integral part of the building structure to satisfy these changing needs.

Moreover, reducing the HRH’s reliance on one particular HVAC solution prevents it from running the risk of failing to properly match appropriate living conditions while still meeting sustainability codes. With this in mind, Harvard could implement innovative, yet removable solutions and take a smaller risk of failure than if the system were a monolithic. By doing so, Harvard could provide adequate living conditions, meet sustainability codes, and be at the forefront of HVAC technology.

H

V

A

C

Unpleasant

Environment

Pleasant

Environment

HVAC

C

People

Indoor

Environment

Outdoor

Environment


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Breaking the system into components also allows an increased-resolution control system. According to Jason Halmen, Consulting Sales Engineer at Distribution Corporation of New England (DCNE), the future of successful and green HVAC systems is hybrid systems that can allow for an intelligent, secure control network.v A component-based approach is inherent to such hybrid systems. From such systems stem the ability to create a successful control system, each component being able to be optimized separately based on the dynamic parameters. A successful and up-to-date model can use data about the environment (e.g. temperature, student occupancy, student needs, and CO2 levels in Boston air) and the economy (e.g. cost of electricity, steam, and natural gas) to increase and decrease the influence and activity of components of the system to optimize cost-effectiveness while providing appropriate student living conditions and meeting sustainability codes. Implementation of such control systems may require an initial capital and periodic maintenance cost, the basis of such a model (using eQuest) has already been developed by the collegevi and such a dynamic investment is a low-risk one. 1.2.3. Beyond temperature and moving air

The problem that HVAC treats is much complex than simply temperature fluctuations and moving air. It involves all the various aspects of the dynamic relationships between people, the indoor environment, and the outdoor environment. While this aspect-based analysis is similar in theory to the component-based solutions, the relationship is not one-to-one, but rather many-to-many. That is, one component solution may target various aspects of the HVAC problem and one aspect may be targeted by many components of the solution. This relationship is diagrammed in Figure 1.4. While it might be ideal, for the optimization of a control system, to set up a one-to-one system, the aspects are interrelated such that affecting one may greatly affect another.

HVAC is not the proper way to think about the problem because it limits the solution space to that defined by “heating, ventilation, and air condition”. This methodology does not do a good job of treating a major aspect of the people-environment relationship: air quality. While moving air (ventilation) is one method of improving air quality, it falls very short of addressing the issue of air quality. The United States Environmental Protection Agency (EPA) says that “indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes.”vii While they mention ventilation as a part of the solution, it is clear that it is not the only part. Air quality is an even bigger problem in an environment like that of dormitories, in which confined spaces and daily contact between people greatly promote the spread of diseases and pollutants. Studies by Arda et al (Turkey)viii, Barksey et al (USA)ix and Stein-Zamir et al (Israel)x all detail the enhancing effect of dormitories on the spread of particular diseases. Infectious disease specialist Dr. Vivek Kak details the effects of confined spaces on the spread of diseases, likening dormitories, in this sense, to cruise ships and military barracks.xi These and many other studies indicate the great importance of this problem in dormitories and the reason for it being a large section of our analysis of the problem. Finally it is also important to understand that many aspects of air quality are highly interrelated with small changes in conditions affecting many of such aspects. For example, we must remember that the decrease in natural infiltration due to extreme


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improvements in the ability to reduce heat loss can negatively affect air qualityxii and must be adjusted for. 1.2.4. Four-tiered solutions

FOUR-TIERED SOLUTIONS

Requires Little Renovation Requires Major Renovation

Feasible Now

• Plants • Passive Heating • Natural Ventilation

I

• Ground Source Heat Pumps

• Natural Ventilation II

Possibly Feasible in the Future

III • Phase Change Materials • Passive Ventilation (based

on Avian Respiration)

IV • Thermal Walls • Variable Refrigerant Flow • Double-skinned façade • Passive Cooling (based on

Termite Mounds) Figure 1.3 – A grid that categorizes the solutions researched into four categories based on renovation requirements and current feasibility. The dark red indicates solutions that should be pursued in the upcoming renovation process; the light red indicates solutions that may be implemented when they become feasible in the future; and the white indicates the solutions that are not feasible for the current renovations.

In order to take advantage of the component-based idea for HVAC solutions, it is important to understand how our solutions will fit into such a framework. In Figure 1.3, above, are four different tiers of solution types. The solutions that our group researched are categorized within each box. The four tiers are arranged to describe two important metrics used to analyze our solutions: feasibility and renovation requirement. In general, this allows an understanding of what solutions can be looked at now, what solutions can be kept in mind for the future and what solutions are not likely to be useful for Harvard’s renovation project.

Tiers I & II – Solutions that can be implemented in the upcoming renovations:

Current feasibility, as determined by analyses of costs, GHG emissions, and technological development, leads to the understanding that the solutions in Tiers I and II should be strongly considered for the upcoming renovations. The details of the feasibility analyses of each solution will be described in later sections.

The solutions in Tier I are those that could be implemented on existing structures because they do not require invasive access to the building. That is, they do not require installation of ductwork, piping, or changing aspects of the architecture of the building. The solutions we researched that fit in this category are the use of plants to improve air quality and passive heating through improved window qualities.


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Solutions in Tier II, while feasible now, can only be implemented upon major renovations because they may require the addition of ductwork, piping, or access to the building skeleton. Such solutions must be considered to be implemented in the initial phase as it will be very complicated to add them later. The solution we looked at from this category is the use of ground source heat pumps (GSHP). The heat pumps may require major construction both because they require proper ductwork, and because they require major construction and renovations in the ground where they will be implemented. If, for example, the appropriate ductwork exists for another technology, it may be possible to add GSHP technology after the initial renovation stage.

Some technologies fall in two categories because of the requirement for implementation. Natural ventilation is one such technology. In order to optimally design a building to allow for natural ventilation, one should take advantage of a major renovation project, such as the one in question, to do so. Nevertheless, natural ventilation technologies could still be implemented on an existing building. If the existing chimneys in the HRH, for example, were opened up, such that they were not a security hazard, they could serve as sources of natural ventilation. Furthermore, many aspects go beyond just architecture and design, involving, for example, opening windows.

The qualities of the solutions presented in Tiers I and II make them prime candidates for technologies to be implemented in the upcoming renovation project. Other solutions that are not considered in this report but fall into one of these two categories – such as earth-to-air heat exchangers (EAHX)2, which would follow GSHP in its categorization – should also be considered. Tier III – Solutions that should be considered for future implementation:

Tier III solutions require little renovation, like those in Tier I, but which this group predicts will not be feasible by the end of the current renovation project. The lack of feasibility stems from an unsatisfactory cost-benefit analysis and/or lacking technological advancement. Nevertheless, these solutions are likely to become feasible in the 80-year future of the HRH and, furthermore, could be implemented at that point because they do not require major renovations. The inadequate conditions for feasibility may be mediated in the future by different electricity, steam, and oil cost scenarios, the possibility of a tax on GHG emissions, and by technological developments.

Solutions of this category include phase change materials for thermal storage and passive ventilation systems modeled on avian respiration. For the specific case of these two solutions, lack of technological progress is holding the feasibility of their implementation back. With the improvement of these technologies, the solutions may become feasible and could be implemented then. As such, they should be considered in the design of the building, but not as a critical component of the immediate renovations. Tier IV – Solutions that should not be considered:

2 EAHX are not analyzed in this report as they have been discussed in the 2009 ES 96 HVAC report and has been researched extensively by the Blackstone Power Plant.


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Solutions in fourth tier are those that require major renovations to implement them, but are unlikely to be feasible in the near future. Despite their technologically interesting nature, they are unlikely to be plausible solutions for the renovations. Advances in research or major changes in cost scenarios may change the feasibility of implementing such solutions during renovations, but the current situation suggests not considering these solutions. It is important, nevertheless, to keep track of the technological development of such solutions, but they would be hard to implement after the major renovation phase is over. These include double-skinned buildings, thermal wall technology, variable refrigerant flow, and passive cooling modeled on the architecture of termite mounds. The technological developments and cost-benefit analyses of these solutions will be discussed for the purposes of explaining why our group concluded that they would not be appropriate solutions. The Tier system:

If Harvard were to tackle HVAC with a component-based approach, as we are

suggesting, it would be able to take advantage of the development of the solutions in tiers I and III and implement both during the initial stages of the renovation and throughout the lifespan of the HRH. Furthermore, Harvard could use the pilot HRH as the place in which to conduct trials with the various technologies that can be implemented and removed. This quality reduces the overall capital risk in implementing advanced HVAC technologies.

1.2.5. Reconsidering HVAC as TCAQ

Thinking of the problem and solution as each broken down into pieces leads to a reanalysis of the term HVAC. The real problems that HVAC systems treat are Thermal Comfort and Air Quality (TCAQ). Thus, instead of describing the system based on the technologies (antiquated as such a categorization might be) – HVAC – our categorization describes the system based on the problem it is meant to solve – TCAQ – a labeling that is invariant with the changing technological developments. As the technologies, behaviors, and needs of people change over the next 80 years, the need for thermal comfort and air quality as the basic standard for living conditions will remain. Thus, TCAQ better describes what HVAC is more conventionally used to describe: both the set of technologies that are used to mediate the relationships between people and their environments and the particular aspects of the problem. Figure 1.4, below, diagrams this idea.


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Figure 1.4 – The over-arching idea that this ES 96 group proposes: a restructuring of the purpose and implementation of HVAC. Instead of treating HVAC with a monolithic solution (left), the problem is broken down (right), into its two major pieces: Thermal Comfort (TC) and Air Quality (AQ). These, in turn are treated by various solutions working in tandem to treat the many aspects of each of these pieces. Green and dark blue lines and coloring represent components that treat air quality aspects, while red and light blue coloring represent components that treat thermal comfort aspects. Most components will have a large overlap, indicated both by the colored connections and the coloring of each solution.

1.3. Methods for generating solutions Having a better understanding of the true nature of the problem, allows one to take a

step back from the conventional treatment of HVAC designs and approach solving the problem in novel ways. We drew inspirations from two main sources: analogies available from nature and looking back at history, the present situation, and, of course, at the future.

1.3.1. Looking to nature

Using nature as a model for engineering is not a new topic, although it has seen very little of the technological spotlight so far. Nevertheless, Janine Benyus of the Biomimicry Institute has instilled such ideas in the minds of the engineers and scientists working with her under the mission of “nurtur[ing] and grow[ing] a global community of people who are learning from, emulating, and conserving life’s genius to create a healthier, more sustainable planet.”xiii That is, the different elements of nature have evolved to develop extremely efficient systems. The goal is to learn how nature makes these systems so efficient and to emulate such processes. While such technologies may not yet be feasible under current economic scenarios and technological developments, it is extremely worthwhile to approach the problem from such a standpoint and consider how nature treats the problem. 1.3.2. Cell model

Analyzing the building as a cell leads most directly to a comparison of the cell membrane and the building envelope. The main principle to be learned from the cell in this aspect is: in order to stay alive, it must properly control the movement of nutrients in and out and the tempering of other environmental conditions. Furthermore, it wants to fully utilize any nutrients that it gets, maximizing the path by which these nutrients travel before discarding any waste.

HVA

C

Monolithic

Solution

A

Q

T

C

Component-

based

Solution


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It is important to realize that the cell’s envelope is not an airtight seal, and while the tendency of building technologies is to tend towards improvement of the building’s envelope to allow less heat to escape, that may not be the best solution. In a discussion with Paul Eldrenkamp, owner of sustainable remodeling company Byggmeister, he outlined a negative consequence of overly sealing the building’s envelope. In Harvard’s case, for example, if one were to insulate the envelope from the inside (since Harvard is not allowed to remodel the exterior, due to constraints by the Cambridge Historical Commissionxiv) one would have to find a way to account for the humidity that would accumulate in between the old envelope and the new insulated one. Such humidity would normally evaporate due to heat losses from the building, but if the building were completely void of heat loss through the envelope, such humidity would remain liquid and would cause mold. Eldrenkamp emphasized that while we need to keep in mind account for the negative consequences of super-insulation, he promoted dealing with all heat losses through the envelope.xv The cell’s double membrane provides a unique approach to such a problem. This may be one of the sources of inspiration for the double façade buildings, a solution to be discussed later. 1.3.3. Human Body model

Thinking of the suite as a cell in a multi-cellular building allows us to consider the human body as a model, especially considering the extreme health aspects of air quality. Looking at the way cells interact with their immediate vicinity leads to ideas that may be beneficial for HVAC solution implementation.

One such idea is that of the transom, a small porthole above the door frame which allows for some passage of air between suites, rooms, or between a suite and a hallway within the residence. The hole is too small to be a security hazard, but is large enough to provide the pressure differences that encourage passive ventilation. The specifications of such a solution are detailed in the ES 96 2009 HVAC reportxvi and thus not detailed here.

Overall, observing the body leads us to one major conclusion. Although the blood system may be the one major way in which thermal comfort and nutrients are distributed, the source of these nutrients and thermal comfort is a very complex system of various components that complement each other. The body’s component system is much like the system recommended in this report. It allows for extendibility (evolution in the case of the body) and for swapping of components. These qualities allow our bodies to survive radical changes in conditions, and may allow us to develop technologies that withstand various residential environments – architectural, technological and human.

1.3.4. Solutions that transcend time

It is helpful to look backwards and see what assumptions have been made in order to properly look forward. This is a cornerstone idea that has allowed us to question the basic assumptions regarding HVAC solution development. Looking at the history of HVAC, before the development of the monolith system idea, developed during the industrial revolution allows us to properly assess current technologies, near-future technological advances, and technologies that are not feasible at present but provide innovative ideas to look ahead to.


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2. Background

2.1. Thermal Comfort and Air Quality In order to understand how to treat thermal comfort, it is important to understand that

thermal comfort is not simply about temperature. It is, largely, about the human perception of the conditions. ASHRAE Standard 55, describes thermal comfort as the state of mind that expresses satisfaction with the thermal conditions of the environment.xvii Humidity, for example, is also an important factor in our perception of thermal comfort: David Cook of the Atmospheric Research Section at the Argonne National Laboratory “said that “high humidity makes it seem colder when the temperature is below 53 degrees F and warmer when the temperature is above 53 degrees F.”xviii Thus, it is important to control all aspects of thermal comfort.

Air quality, like thermal comfort, goes beyond the most obvious definition of movement and ventilation of air. One must account for all of the aspects of the health of the air that students live in, for this is directly tied to their health (as discussed above). The specific standards for thermal comfort and air quality are detailed below.

2.2. Standards 2.2.1 Temperature

ASHRAE Standard 55-2004 defines an indoor environment to be acceptable for thermal comfort if 80% of sedentary or mildly active individuals are comfortable.xix While Standard 62 does not specifically recommend a maximum allowable temperature variation between rooms in a residence,xx Standard 55-2004 “notes that for thermal comfort purposes, temperature could range from between approximately 67 and 82 °F.”xxi Standard 55-2004 does acknowledge that further specification of temperature ranges are highly dependent on properties specific to the building and conditions of that point in time. ASHRAE Standard 62 recognizes the variability of comfort levels between rooms and states that “Areas or rooms having dissimilar load characteristics … should be controlled individually.”xxii This, again, shows how important it can be to use component solutions that can be adjusted separately. 2.2.2. Humidity

The recommendations of ASHRAE Standard 55-2004 correspond to a maximum humidity of 80% at low dry bulb temperatures. This upper limit changes based on temperature conditions. The standard also requires that any system that controls humidity must be able to maintain a dew-point temperature of 62.2oF. Standard 62.1-2007 expands on the requirement, recommending that humidity be “controlled to less than 65% to reduce the likelihood of conditions leading to microbial growth.”xxiii


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2.2.3. Air Movement The air movement standards relevant for this project are the ASHRAE ventilation

standards. Ventilation involves the purposeful movement of air. Assuming that the insulation in the building envelope will be substantially improved, the rate of movement of air through the building envelope, also known as infiltration, will be minimal. As such, this report refers mostly to ventilation, either active or passive (natural). The standards specific to active and passive ventilation will be discussed in sections 4.1 and 5.3, respectively.

ASHRAE Standard 62 sets a minimum air exchange rate of 15 cubic feet per minute (cfm).xxiv This is the bare minimum necessary to provide the United States Environmental Protection Agency (EPA) air quality standards, described below. Since the group’s report dealt mostly with residential spaces not including laundry rooms, bathrooms, or kitchen areas, the standards relevant to such spaces will not be mentioned.

It is important to note that the movement of air affects thermal comfort significantly. ASHRAE states that air flow of velocity greater than 50 feet per minute (fpm) may negatively affect thermal comfort as perceived by residents. As such, ASHRAE Standard 55 suggests “a linear relationship between temperature and air flow.”xxv As mentioned various times above, it is important, when considering each of these aspects of TCAQ to remember how they are interrelated. 2.2.4. Carbon Dioxide

Carbon dioxide recommendations are intimately related to ventilation standards, with ASHRAE Standard 62 requiring CO2 levels to be within 0.07% of that outside. According to the standard concentrations in outdoor air typically range from 300 to 500 ppm. They say, however, that “CO2 concentrations of 1000 to 1200 ppm in spaces housing sedentary people is an indicator that a substantial majority of visitors entering the space will be satisfied with respect to human bioeffluents (body odor).”xxvi Such aspects are very important when considering indoor air quality. The absolute upper limit for CO2 concentrations in residential spaces is 5000ppm, as this can cause serious health risks. 2.2.5. Carbon Monoxide

Standards for the lesser-found (yet more lethal in many cases) substances vary widely across different health organizations. These substances are very important, however, when considering indoor air quality and the health of the inhabitants. Carbon monoxide being a major contaminant behind carbon dioxide, its standards have been discussed here.

The US EPA sets outdoor maximal levels for carbon monoxide at 35 ppm, while the World Health Organization limits the levels based on exposure time. A 15-minute exposure has a maximum concentration of 90 ppm, while a prolonged, 8-hour exposure has a maximum concentration of 10 ppm. Any and all sources of carbon monoxide must be minimized to below these levels as it greatly affects the health and performance of the students.xxvii

2.3. Methods for analysis of solutions


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2.3.1. Baseline system In order to analyze the solutions, the group looked to compare all of the solutions with

themselves and with a baseline system that the group developed to represent what the renovated HRH might look like with conventional technologies and renovations that met the standards required, as detailed above.

The group assumed that fan coil units would be the method of heating and cooling, based on conversations with Mr. Needhamxxviii and Mr. Halmen.xxix In order to satisfy the students’ desire to have control over their room temperature, the assumption was made that one fan-coil unit would be installed in each room, with additional units installed in the public spaces in the HRH. The group assumed the building would be ventilated in the most conventional manner: using an air handler that met the ASHRAE standards discussed above. Finally, to provide cooling in the summer months, the group assumed the new buildings would have access to a nearby chilled-water plant.

It is important to understand how energy usage in the developed baseline system compares to that in the current HRH. Winthrop House, upon which the baseline system was based, uses approximately 10 GBtu/yr of steam to satisfy its HVAC needs. The steam is dispersed to radiators in each room and is also used to provide hot water. The only form of air movement is through natural infiltration through the building envelope. As such, Winthrop House does not currently use any electricity for HVAC purposes.

By comparison, we assumed the baseline system would use approximately the same amount of steam at 10GBtu/yr and 0.638GBtu/yr (187 MWh/yr) of electricity due to the fan coil units and air handlers. The detailed specifications of the baseline and the assumptions that led to these numbers are provided in section 3. 2.3.2. Analysis Metrics

The group also developed points of analysis by which to compare and categorize the various solution ideas generated. The two most important metrics for analysis were cost and Greenhouse Gas emissions. The former was analyzed by averaging the total cost to implement the system over 30 years, including initial capital cost and maintenance costs. The latter was calculated in Metric Tons of Carbon Dioxide Emitted (MTCDE) per year. Each of these was calculated separately for each solution in the situation in which that solution was most likely to be implemented.

After the solutions passed the two most important metrics, they were analyzed for flexibility in implementation, renovation requirement, and technological development and reliability. Solutions that allowed for flexibility – they could be implemented in both an electrical system and a steam system – are valuable because they don’t require forecasting the situation of electricity, steam, oil, and allow us to continue using the steam provided by the Blackstone Power Plant, through existing infrastructure, until replaced. Solutions requiring heavy renovations were only considered if feasible for the current renovations, while solutions that didn’t require heavy renovations were considered beyond the scope of the immediate renovations, as analyzed above in Figure 1.3. Finally technologies that had not been developed to the point of a successful real-world implementation were not recommended for implementation in the renovations, but were investigated and discussed. Such discussion allows for the discussion of technologies in Tier III beyond the scope of the immediate renovations.


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All the solutions were judged on the basis of all the aforementioned principles and recommendations resulted from that analysis.


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3. Baseline 3.1. Goals and Justification of the Baseline

In order to evaluate the efficacy of our solutions, we needed a baseline system to judge them against. This section will lay out what we believe to be the current standard for an HVAC system in contemporary buildings. We believe this baseline will be the most likely implementation to be used in the renovations. Our solutions will then be compared to this base as a means of objectively evaluating them. The baseline system can be split into four distinct parts, the two energy sources for heating and cooling, the distribution method of that energy within the rooms, and the ventilation system.

• An energy source for heating already exists in the form of the Blackstone steam

plant, but we investigated the economic and technological advantages and disadvantages of changing the source.

• As a cooling source, the non-residential buildings at Harvard currently use two large chilled water plants below the Science Center and below Northwest Labs. It is likely that if cooling were to be implemented for the house renovations, a new chilled water plants would be built in a central location near the housesxxx.

• The current distribution source within the rooms is steam radiators and it looks very likely that these will be changed. Fan coil units have been installed in the newest Harvard residential buildings and based on our brief discussion with Mr. Steve Needham, it is most effective to use fan coils as our baseline on which to improve.

• Most modern buildings use a central air handler ducted to the hallways and large common spaces. The air handler tempers and filters the air as well as ensures appropriate humidity. The fresh air is ducted to hallways and central spaces and then permeates through the building under doorways and through vents.

3.2. Components of the Baseline 3.2.1. Heating: Blackstone

The Blackstone Steam Plant is owned and operated by Harvard and supplies steam to the entire campus except for Radcliffe Yard and the Quad. They heat the steam using natural gas and fuel oil burners and they have one steam turbine generator to harvest electricity from the high-pressure steam before it is distributed to the campus. The main consumers of the steam are the scientific laboratories at the northern end of the campus and although this does introduce inefficiencies due to the long distance the steam must travel, it does force the main distribution lines to pass right by the houses. It therefore requires very little additional infrastructure to bring this energy source to the houses. The Blackstone plant runs at 72% efficiency, transferring the energy from the natural gas it burns into the steam it supplies to the


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campusxxxi. After the initial capital costs of buying the plant, they recently added the $8 Million steam turbine generator and they plan to see a return on that investment within three years. In our discussion with the directors of University Operations Services, they laid out their vision for the future of the energy production at Harvard. They first addressed their concern with the issue of the main users being so far away from the source. In order to solve this, they believed that it is possible for smaller, more specialized plants to be constructed closer to the main energy consumers. For example, across the river in Alston, plans are already in progress to build a natural gas turbine to generate electricity and use the waste heat to create steam and hot water for the new Alston campus. While the Blackstone plant generates steam with electricity as a byproduct, the Alston plant would generate electricity with steam as a byproduct. Therefore, while the Blackstone Plant is most efficient when steam is needed in the winter months, the Alston plant would be most efficient in the summer months when the most electricity is needed. Their outputs would be tied together in order to augment one another. This network of connected and complimentary, modular energy generation was their vision for the future, with a new plant using the most modern technology being added about every decade. Specific costs and efficiencies for the next generation of cogeneration plants are unobtainable at this time because University Operations Services plans on using the most technologically advanced option available at the time of the addition of each of the new plants. Many of our calculations rely on the assumption that steam will always be available to use for heating. However because the future vision includes electricity generation, some of our solutions utilize added electricity as well. Many of our analyses take into account the fact that the price of steam and electricity may fluctuate dramatically as the University’s energy generation landscape is transformed and modernized. 3.2.2. Cooling: Chilled Water Plant

The university has two large chilled water plants at the north end of campus which supply all of the science labs, classroom buildings and the yard. They run very efficient electric chillers, averaging .688 kW/tonxxxii, where one ton of cooling is the equivalent of 12,000 Btu/hr (or the amount of cooling provided by 1 ton of ice). This corresponds to a coefficient of performance, the measure of a heat pump’s efficiency at turning electrical energy into cooling, of 5.11. Nevertheless, those plants do not have the capacity or the infrastructure to bring chilled water to the houses and therefore a new dedicated chiller plant would have to be built. Using just the square footage of Winthrop house and a rule of thumb supplied by an air conditioning contractorxxxiii, a plant capable of supplying 260 tons of cooling would be required to cool Winthrop house. We can assume that any system implemented would have similar efficiencies and similar costs to the current plants. Using the conclusion from the 2009 HVAC group’s report we can estimate that cooling would be required 64 days of the year and would be running during the day for an average of 12 hours per dayxxxiv. The University Operations Services currently charges $10.08 per ton per day, which would translate into a yearly cost of $83,866. Pricing for a chilled water system of this size is around $2800 per tonxxxv so a system large enough to handle the load from Winthrop house would incur an initial capital cost of $840,000. Because cooling is not currently employed in the houses, there are no potential savings involved. Cooling would purely be implemented to increase occupant comfort.


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3.2.3. Distribution: Fan Coils

In the renovation of the river houses that is expected to take place in the near future, fan coil units will be the technology that Harvard chooses to install. Fan coil units will be installed in the house common spaces, stairways, and hallways in addition to each individual room to provide sufficient heating, and possible cooling, to the residents. Fan coil units have the capacity for cooling, a feature that Harvard does not currently support in the majority of its dormitories. Depending on how Harvard chooses to address the issue of personal comfort, the option for cooling may see more use than it currently does in this future scenario. Regardless of what Harvard decides to do in the forthcoming years, the technology exists in fan coils to allow for both heating and cooling to occur simultaneously. This feature will be very beneficial in allowing Harvard to deal with any potential changes relating to heating ventilation and air conditioning. This dual aspect associated with fan coil units will eliminate the need to have a new technology installed in order to address any cooling needs. Fan coils units are a technology that is prepared to deal with a changing landscape that Harvard will be faced with in the future.

Fan coil units are devices that have either a heating or cooling coil in addition to an internal fan. They can remove or add heat from the air through the process of heat transfer. Fan coils can be installed independently of any ductwork that would be needed in a different technology, while doing the same operations. It is because fan coil units do not bring in outside air, which is what the presence of air handling units are for, that they do not require ductwork. Fan coils units come in several different models, including wall mounted, freestanding units, and ceiling mounted models. There is a wide range of models for Harvard to choose from, but the vertical fan coil units, which most closely resemble the radiators that are installed now, should be the model that Harvard chooses. The vertical fan coils can be placed against a wall beneath a window as a way to maximize the personal space of the student, while minimizing aesthetic losses. Fan coils can come in ceiling mounted models, but this may serve as a problem for some students who have difficulty reaching high areas. A ground mounted unit will thus be accessible to all students.

Fan coil units come in either a two-pipe system or a four-pipe system. The two-pipe system only allows for either hot or cold water to flow in and out of the system at any given time, allowing the system to heat or cool the air. In Harvard’s case, heating occurs throughout most of the year, and is shut off during the months that are designated warm enough to not require heating. In the two pipe system, one pipe supplies the fan coil with the manner in which it receives its energy, while the other pipe returns the water or steam back to the plant. In the four pipe model, both hot and cold water can flow into the fan coil at any given time. This allows for more user comfort, as heating or cooling can be obtained at any given time, but this option will be more expensive to run than the traditional manner of heat or nothing at all that Harvard abides by. If Harvard adopts a method of cooling, then both hot and cold water, and possibly steam, will circulate through the coils. Fan coil units allow the user to have more control over the temperature in the specified space than the radiators currently do. The students at Harvard have some control over the current radiators in use, but these devices are out of date and the variation of temperature they provide is not sufficient for student comfort.

Each fan coil unit contains an internal fan that helps distribute the heating or cooling to the designated space, but it does it much more efficiently than a radiator because there is a


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force actually moving the treated air around. Fan coil units draw power to blow the air around rather than passively heating the surrounding air in the case of a radiatorxxxvi. Thus, through the use of the fan, the user can control the flow of the energy. While more air is moving around through the use of a fan coil, it will be more expensive to operate than a radiator because additional power is required to operate each unit. This will definitely increase the price that Harvard must pay to maintain the temperature in each dorm. As this is already the prescribed baseline, Harvard knows about the exchange of paying more for increased user comfort that will arise through this technology.

In the process of learning about the baseline for fan coil units that Harvard will pursue, the HVAC group met with Mr. Halman, a consulting engineer for DCNE. Mr. Halman discussed that a possible strategy to further increase user comfort, in allowing for even more control over the units, would be to draw in outside air to each unit. This possibility is investigated later in this report.

In order to provide sufficient heating to each student, a 300-400 cubic feet per minute (cfm) unit would be needed in each roomxxxvii. The units that Harvard would purchase, from companies such Trane, Carrier, and McQuay, cost in the range of $400-500 a unit. Due to its relatively cheap installation cost, and price per unit, installing fan coil units saves more money than installing technologies that require extensive ductwork or piping. Based upon the suggestion from Mr. Halman to allow for more user comfort in the rooms, he concluded that additional piping would be required in order to make this idea work. Adding piping will require hiring a union pipe fitter to come in, which will run Harvard around $30-40 an hourxxxviii. The process of evaluating the needed renovation and the actual process of installing the piping may take a lot longer than projected, due to the fact that much investigation is required by the pipe fitter. Having individual units in each room as compared to one unit serving multiple rooms will require more piping to be installed. It is possible to use one fan coil unit per suite, but the size of the fan coil would have to increase.

Staying true to a baseline established by the HVAC group on what Harvard will do in regards to installing fan coils in the renovated dormitories, and from the information that the group received, it has been concluded that there will be approximately 825 fan coil units installed in Winthrop house. Winthrop House is the dormitory that is being addressed because at this point in time, it is where the pilot project will take place. Winthrop House roughly consists of 200,000 square feet of space. In Winthrop House, there are approximately 75 rooms on each floor. For the two buildings that comprise Winthrop House, there are five floors in each building. This totals to approximately 750 rooms in Winthrop House. Not all of these rooms are bedrooms, as many of them are in suite common rooms. Harvard will automatically need at least 750 fan coil units for Winthrop House to satisfy heating and cooling needs for bedrooms. There is approximately one stairwell per floor, in addition to hallways on all five levels. This leads to the requirement of around 50 additional fan coil units. Addressing the square footage and space that the house common rooms take up, including the dining hall, 25 additional units will be required. Thus from this evaluation of the necessary fan coil units to heat Winthrop House, the total comes to 825. The cost to purchase 825 units will run Harvard around $330,000 minimum.

Harvard currently uses 10 GBtu/yr of steam, or 330 kW. Estimating that each fan coil uses 17.1 W a day of energy, and that all 825 fan coil units operate every day throughout the


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year, the 14.1 kW required to run all of the fan coils will total to 123.5 MWh over a year. Air handling units will be needed to provide ventilation, so using similar calculations, these air handlers will use an additional 64 MWh a year. The cost of steam is $0.15/kWh and this equates to roughly $20,000 a year to run the fan coil units in Winthrop House.

The factor of student safety falls alongside personal comfort pertaining to importance. In order to prevent the possible tampering with units that may occur, an encasement would be necessary to increase the life of the unit in addition to the personal safety of the inhabitantsxxxix. Several companies sell vertical fan coils that are already encased, but Harvard may choose to have a casing designed to more appropriately match the interior of the historic river houses. In addition, a specific color scheme may be chosen to prevent these devices from taking away from interior aesthetics of the rooms that Harvard places such an important emphasis on. 3.2.4. Ventilation: Air Handler

Further discussion of ventilation needs can be found in the active and natural ventilation sections, but in general 20 cubic feet per minute of fresh air is suggested per personxl. This translates to an air handler requirement of 10,000 cfm for the building, giving 0.375 air changes per hour. A typical air handler of this size built by AAON, cost around $20,000 and requires about 7 kW of electricity on average for operationxli. This translates into an operating cost of about $10,000 per year at current electricity prices. Furthermore, since the air handler brings in outside air, it needs to be tempered and brought to a comfortable temperature before it can be distributed to the building. 20 cfm of air is equivalent to 11.33 g/sec and using the specific heat of air and taking the difference between the average temperature in Boston and the typical room temperature, we get an estimate for the power that would need to be supplied to heat the incoming air for one person.

!

˙ Q = ˙ m " c " #T = 11.33 g/sec( ) 1 J/gK( ) 8 K( ) = 90.6 W 90.6 W is equivalent to 2.71 MBtu per person per year, which at current prices for steam heating from Blackstone would add an additional $75 per person per year, $37,500 total or nearly 10% of the current steam billxlii. However, since fresh air was being supplied to the rooms through a ventilation system as opposed to the current system, which relies purely on infiltration of air through the building envelope, it can be expected that when the building is renovated, the steam heating cost will be very different than current usage. When fresh air is being actively brought into the building, the envelope can be made much tighter than is current is, allowing for a reduction in standard heating costs to offset the cost of tempering the outside air that the air handler is supplying to the building.


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3.3. Summary of Baseline

Requirement

Baseline Solution

Installation Cost

Usage Cost (per year)

Energy Usage

GHG Emissions

Heat Source

Steam, Blackstone

$0

$280,000

9.54 GBtu/yr

737.5 tons

Cooling Source Chilled Water, new plant

~$840,000

$83,000

2.1 GBtu/yr

47.8 tons

Distribution Method

Fan Coil units, one per room

~$330,000

$20,000

123 MWh

13.60 tons

Ventilation

Air handler

~50,000

$10,000

64 MWh

21.70 tons

Figure 3.1: Schematic of Baseline System


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4. Active Ventilation:

4.1. Standards for Active Ventilation Fresh air supplied to the Houses is essential to maximize cognitive ability and support

the happiness of students. High levels of carbon dioxide have been shown to inhibit learning and problem solving and indoor pollutants can exacerbate allergy symptomsxliii. ASHRAE Standard 62 requires 15 cubic feet per minute (cfm) per student and HVAC professionals recommend 15-20 cfm to ensure occupant comfort. Using Winthrop House as a baseline, we assume the 200,000 ft2 is divided evenly among the 500 student occupants, giving us 400 ft2 per person, which then gives us .281-.375 air changes per hour with outside air. Furthermore, the U.S. Department of Housing and Urban Development (HUD) gives a guideline of .35 air changes per hour, validating our assumption. Making student comfort the priority we will assume that Harvard will implement a system capable of 20 cfm per person or equivalently, .05 cfm per ft2. There are many options available to achieve this goal of 20 cfm per person.

4.2. Solutions Involving Active Ventilation 4.2.1. Fan Coils with External Louvers

Commercial Fan Coil units generally have the capability to be fitted with outside air intakes that allow for up to 10-25% fresh air to be mixed with recirculated air from the roomxliv. Since a typical Fan Coil unit has a fan capable of at least 200 cfmxlv, this is more than sufficient to provide adequate ventilation from outdoor air:

Since this outside air is being brought directly into the distribution source for thermal energy, this solution can provide extremely good thermal comfort and satisfy all ventilation requirements. Also since it doesn’t require any additional ventilators or air handlers, it has very low operational costs. If another ventilation system were installed, student would still be running the fans on their fan coils for thermal comfort needs. This solution uses a single fan to provide all the requirements of an HVAC system. It can therefore more efficient, requiring only the electrical energy for the fan coils accounted for in the baseline. Using only the fan coils as the ventilation source and the distribution method for thermal comfort is also highly compatible with whichever energy sources could be used in future scenarios. It does not matter what the source of steam, hot water or chilled water is, the fan coil will be able to provide thermal comfort and all the ventilation requirements of the occupants at a very high level of personal control.

However, this solution does require direct access to the outside air. This would easily be accomplished on any other building by adding a duct through the exterior wall and attaching a louver. But due to restrictions by the Cambridge Historical Commission, any attempt to modify the exterior of the building would have to be unnoticeable from the street. This could


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be achieved by hiding the louvers in an unseen location such as under a windowsill, or below a gutter. But the simplest solutions would be removing the mortar between some bricks and attaching an internal grate, or adding many small snorkel vents between bricks such as figure 4.1, below. Holes could also be drilled through a few select brick to have those bricks act as the vents.

Furthermore, since the outside air is being brought directly into the building there

would be some issues with the air quality of the incoming air. An air handler such as the one discussed in the baseline, controls for other air quality factors besides just temperature such as humidity and pollutant. A fan coil that distributed outside air directly into the rooms would not be able to control those factors. In addition, the fan coils would have to be run continuously to provide consistent ventilation to the room, thus increasing energy costs and creating potential noise issues.

While there are a few issues yet to be solved with this solution, it is extremely cost effective. There would be very limited additional cost to implementing this solution. Only the cost of creating the paths to the exterior would expand construction costs, but the addition would be negligible compared to the cost of the entire physical renovations. On the other hand, because the Cambridge Historical Commission approves each exterior modification on a case-by-case basis, this solution cannot be taken for granted as the most feasible method. If fan coils are used in the house renovation it is highly suggested that a proposal for this solution is brought to the Historical Commission due to the simplicity, low cost, and efficiency of this solution. 4.2.2. Heat Recovery Ventilators

In the event that the Historical Commission denies any modification to the exterior what so ever, another solution using centralized mechanically forced air would have to be implemented. In the baseline we discussed typical air handling units, but a promising alternative in this situation are Heat Recovery Ventilators (HRVs).

HRVs are the most efficient way of providing tempered air without actively conditioning it. An HRV thermally couples the inlet and exhaust air streams without allowing them to mix. Therefore, HRVs can very efficiently retain heat in the building while simultaneously bringing in outside air for ventilation. Also since the main use of the HRV is to

Figure 4.1: Snorkel Vents in brick, unnoticeable from the street


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maintain temperatures inside the building, it doesn’t not matter what sources provide the heat or cooling and is therefore very flexible to future scenarios.

An HRV system would require sufficient ductwork to supply air to every room. It also needs a well-designed, linear path for the flow for the incoming and outgoing air supplies. If there are blockages along the path of airflow, or if the source is too close to the return air supplies, there will be pressure differentials or poorly ventilated portions of the building. This task of designing and building the ductwork would have to be done by a specialist given the limited free space in the interiors of the houses.

Since providing ductwork to the entire building may be difficult during the proposed

renovations, we may have to think of novel ways to allow for the flow of air. Many of the proposals for introducing natural and passive ventilation will be applicable for encouraging the permeation of mechanically force air. One solution proposed as a means of introducing natural ventilation was to use the chimneys, and that idea can be applied here as well. A large HRV can consistently supply 1500 cfmxlvi which would be enough airflow to supply an entire entry way or two. It would be possible to use the chimney systems of two adjacent entryways as the source and the return. Their airstreams could then be connected through the HRV in an attic or basement space between the two entryways, or on the roof. To achieve the desired 20 cfm of outside air per student, we could use a large HRV to supply a few entryways. Typical units of this size cost about $3/cfm, with the costs of specially designing the ducts, installing the ductwork and performing maintenance bringing the total costs to at most $10/cfmxlvii. The blower motors generally require about 1 W/cfm as well. Therefore a typical HRV system would cost $200 per person in initial costs and would require 175.2 kWh per person of electricity yearly, or $26.82 at current electricity prices. However, since the typical HRV is recovering about 55-70% of heatxlviii, it is saving energy compared to a system where the same amount of outside air was being introduced without being tempered.

Figure 4.2: Schematic diagram of thermal coupling of air streams in an HRV unitxvii.


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Recall our estimate from the baseline for the power that would need to be supplied to heat the incoming air. We calculated it to be 90.6 W, or equivalently 2.71 MBtu per year, which at current prices for steam heating from Blackstone would add an additional $75 per person per year. However by using HRVs instead of the baseline air handler or simply non-heat recovering exhaust fans we save at least 55% of the heat that would otherwise be lost. Therefore we would only require 1.49 MBtu per year for an HRV ventilation system, about $41 per person per year. Given that exhaust fans cost about $.05 per cfm, but would still require the same ductwork, installation costs and electricity usage, the savings from an HRV ventilation system over one that just used exhausts fans would justify the additional capital costs in just 4.8 years. Baseline Exhaust Fans HRVs Implementation Air handler, steam

tempers air then ducted around

Outside air pulled into building, heated after

Thermally couples air steams, tempered and ducted around

Comfort Extremely good Poor thermal consistency

Nearly as consistent as the baseline

Installation Cost $120,000 $70,000 $100,000 Total Usage Cost $47,000 $50,000 $33,600 Electricity Usage 64 MWh 87.6 MWh 87.6 MWh Heating Usage 1.355 GBtu 1.355 GBtu 0.745 GBtu GHG Emissions over the baseline

0 0 44.99 MTCDE


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5. Natural Ventilation

5.1. Introduction Natural ventilation is far from new technology, having been used throughout the ages for both ventilation and comfort cooling. From town streets along the Mediterranean oriented to “bring the coolness of the sea breezes into the heart of the city,” to Persian houses with large openings (iwanis) designed to match natural air direction; from wind scoops in India, to roof ventilators (mulqaf) in Egypt, to direction-insensitive wind towers (barjeel/badjeer) in Dubai–the use of natural ventilation for promoting indoor air quality and cooling among peoples of the past is well documented.xlix The colonial architecture of the Southern US reflects principles of natural ventilation, with Thomas Jefferson’s house in Monticello featuring open verandas, cupolas, and specially designed closets that were naturally ventilated to forestall stuffy clothing. Open stairwells and high, domed ceilings to ventilate rising hot air are other features of naturally ventilated historical structures.l The current infrastructure of the Harvard River Houses (HRH) is not incompatible with this legacy, having cupolas, roof dormers, and chimneys. The very nature of the Harvard House redesign–leaving the outside architecture intact to maintain the historical character of the buildings–motivates creative insight in repurposing the current infrastructure.

The ubiquity of mechanical air-conditioning during the last century has shaped industry conventions and codes, necessitating quantitative analyses in assessing the feasibility of natural ventilation. Natural ventilation creates much smaller pressure differentials–essential for moving air–relative to mechanical ventilation, theoretically limiting its capacity to match standards. Interestingly, however, current industry codes allow for the possibility of greater flexibility in naturally ventilated structures, as will be detailed. While a complete, computational analysis of the feasibility of natural ventilation is beyond the scope of this section, important preliminary steps and guiding principles are presented, indicating that natural ventilation may very well be of interest during the renovations of the HRH.

5.2. Natural Ventilation Feasibility Assessment A general assessment of the viability for natural ventilation or mixed-mode systems is desirable. The following section identifies the current state of the art in this respect and proceeds to characterize the HRH using these guidelines. Much of the literature is characterized by two extreme approaches–expansive or limited views. The 2009 ASHRAE Fundamentals Handbook characterizes natural ventilation as being able to “effectively control both temperature and contaminants in mild climates,” under “some circumstances,” but “is not considered practical in hot and humid climates or cold climates.” On the other end of the spectrum, recent literature presents elaborate degree-day models that conclude that natural ventilation has the potential to be used for cooling, especially in Northern Europe,” and, with proper design, can overcome noise and pollution effects.li Of note, there is


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an important distinction to be made between the ventilation and the cooling potential of natural ventilation strategies, but the range of opinions regarding natural ventilation generally is clear. Furthermore, there is concern that envelope openings defeat the use of advanced insulation, creating additional heating and cooling loads that undermine an energy-efficient thermal comfort system. While useless holes in insulation would be problematic, carefully designed and controlled intentional openings, which replace air handling units and fans for air movement, should balance out energetically, and be far more cost effective than installing and continuously running ducted fan systems. A recent (2008) paper published in the ASHRAE Journal identifies a number of key issues to be raised, drawing on real-life natural ventilation case studies. The questions can generally be divided into two categories: location-specific and building design-specific.lii The table below highlights a number of the questions (adapted slightly), and assesses the applicability of HRH using these criteria. The questions not discussed in this report relate to building envelope solar gain, internal heat loads, and specific questions about the potential for night “purge” and radiant cooling, which are either part of the larger design process, or irrelevant. It becomes clear that based on this preliminary examination, natural ventilation may be viable for the HRH.

Question Preliminary Answer for HRH

Are there at least 6 months where monthly maximum temperature is less than 80 F but mean minimum higher than 32 F?

Yes. There are exactly 6 months that meet both conditions for Cambridge.

Figure 5.1 Historical Temperature Data for 02139 (Source: Weather.com)liii


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Does psychometric data (a combination of temperature and humidity data) demonstrate feasibility?

Yes. The original question was tailored towards commercial buildings occupied during the daytimeliv, requiring adaptation.

Figure 5.2 Psychometric Range For Nat. Ventilation (Modified from Givoni p. 41lv)

The availability of psychometric data specific to Boston was dated to 1997, which revealed that the metrics relevant for ventilation–Wet Bulb and Mean Coincident Dry Bulb (WB/MCDB), and Dew Point and Mean Coincident Dry Bulb (DP/MCDB)–indicate that even when accounting for 0.4% design specification deviation (the best available), the relative humidity (RH%) values were within the correct regime on the psychometric chart as defined by the question.lvi (Source: PsyCalc98lvii)


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Is the surrounding environment suitable for direct intake of air from the outside (no security, noise, proximity to street, air pollution concerns)?

Yes. A natural ventilation system making use of windows and existing chimney stacks / wind catchers would have no additional security, noise, or pollution concerns from the present situation. The exemplary standing of Boston air quality has been documented by the Massachusetts Department of Environmental Protection (MassDEP):

Ozone is the only pollutant for which Massachusetts monitors indicate violations…. Massachusetts is in attainment for the other criteria pollutants, including carbon monoxide, lead, nitrogen dioxide, sulfur dioxide, and particulate matter (including PM10 and PM2.5)lviii

Regarding Ozone, the trend shows clear improvement over the past two decades as well, indicating that outdoor air quality is likely to remain in compliance with national standards.

Figure 5.3 Ozone Pollution Data (Source: MassDEP)

While some of the HRH have windows facing streets (including Memorial Drive), these are generally not in violation of ASHRAE 62.1 regarding proximity to street-level.


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Can windows open to the equivalent of 4-5% of total floor area (e.g., for a floor of 150 square ft., is there at least 6-7.5 square ft. of open-able window area)?

Yes. The large sliding windows in each room currently open to around 6.5 sq. ft., which represents nearly 4.3% of the sq. ft. of the average size room (150 sq. ft.), and a significantly higher percentage for smaller bedrooms (up to 6.5%).

Figure 5.4 Operable Window Types (Source: Ghiaus p. 159)

Replacement of sliding models with bottom or side hinged models would enable using the entire window frame, giving an area of roughly 15.5 sq. ft., or over 10% of the square footage of the average room.


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5.3. Operating Industry Standards Having motivated an investigation of natural ventilation for the HRH, the next

question becomes what, if any, industry standards and codes are relevant, including implications for LEED. Drawing again from the recent (2008) ASHRAE Journal paper, a number of useful tables are reproduced in the appendices. It is important to distinguish between natural ventilation as used for IAQ, in which case ASHRAE Standard 62.1-2007 is relevant, as opposed to humidity or temperature, where ASHRAE Standard 55-2004 comes to the fore. Standard 55-2004 clearly notes that “no specific guidance for naturally conditioned spaces is included in this standard,” as evidenced by the exceptions of the standard where “occupants will tend to accept a wider range of indoor comfort temperatures as compared to those limits established as acceptable for typical environments,” referring to “naturally

Can one rely on wind-driven effects for cooling, and is there a direct airflow path from bottom to top of naturally ventilated area?

Likely yes to both. While the literature about which temperatures require cooling varies, and includes assumptions reflected in industry standards–people are more willing to put up with larger temperature fluctuations in naturally ventilated environments with user-operable windows (see graph)–there is certainly potential for cooling.

Figure 5.5 Heating. Cooling, Ventilation Regimes (Source: Ghiaus p. 202)lix

The existence of a clear airflow path is, once again, design-dependent, and numerous strategies exist, including the use of open stairways, concealed vertical ducts, and bathroom exhaust plenums.

Does the climate have regular outside air temperatures over 80 F (in this case, “no” is preferable)?

Rarely (meaning that investigation of exposed thermal mass is unnecessary, which would be somewhat difficult given the outside construction constraints).


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conditioned spaces.”lx This is consistent with research that has indicated that introducing outdoor air with a given speed can provide a “physiological cooling effect”, even if this causes an increase in the indoor air temperature, as on a warm summer day.lxi Standard 62.1§5.1 notes that “an engineered natural ventilation system when approved by the authority having jurisdiction need not meet the requirements” outlined elsewhere in the standard. The definition of an “engineered” solution is interpreted to refer to the CIBSE Applications Manual AM10, Natural Ventilation in Non-Domestic Buildings, which is apparently used by LEED for new construction guidelines. Although this might appear to be the wrong standard for the HRH project, the guidelines there are fairly typical: making use of “envelope flow models, computational fluid dynamics (CFD), combined thermal and ventilation models, and physical scale models.”lxii Thus, the future steps for analyzing natural ventilation are:

1. Multizonal simulations (heat transfer, bulk airflow) using available software, which eases the process of calibrating temperatures, envelope geometry/materials and openings, pressure coefficients, etc. This usually requires iterative testing to ensure appropriate modeling.

2. Next, assuming the above step confirms the feasibility of natural ventilation, use CFD software (Navier-Stokes equations-based), which will represent the room volume as air cells, graphically display airflow patterns, and highlight problematic flow areas that should be fixed. These models can be reviewed by the relevant building authorities, and are “often accepted as proof of concept to meet the definition of ‘an engineered natural ventilation system” under Standard 62.1§5.1.”lxiii

A program that includes both of these features, and specifically accounts for natural ventilation is DesignBuilder.lxiv An initial investigation revealed that this program provides a nice GUI built on top of eQuest for modeling the entire building for heating, cooling, and ventilation loads. An undergraduate was able to build a rudimentary model of the building in an afternoon, indicating feasibility for a professional engineer.

Looking at the current standards, it becomes clear that natural ventilation falls between the creases of certain requirements, enabling added potential creativity for meeting both code and LEED (as outlined in the tables reproduced in the appendices).

Having noted this, the conventional industry standard for ventilation is on the order of

15-20 cubic feet per minute (CFM) per person, which was used as a baseline in assessing the feasibility of natural ventilation methods.

5.4. Strategies for Natural Ventilation Devising a building-wide strategy and creating an accurate model for analyzing the

effects of natural ventilation motivates a brief overview of standard natural ventilation techniques. These range from the simplicity of opening windows, to harnessing the power of chimneys, to roof dormer-specific strategies. What will become clear is that different strategies work better in different parts of a building, motivating a consideration of hybrid strategies that make use of a combination of different methods.


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Note: For all formulas and assumptions used in calculations, see appendices.

5.4.1. Single-Sided Ventilation

This refers to the phenomenon of open windows simultaneously circulating air into and out of a room, when there is sufficient wind speed and temperature difference between the inside and outside environments.

Figure 5.6 Temperature Driven Single-Sided Ventilation (Source Ghiaus p. 137)

An empirical model of this effect (detailed in the appendices) is modeled by a function

of inside and outside temperature difference, and window height (window size in this project is fixed). The following graphs depict the variation in cubic feet per minute (CFM) during the course of the year for the bottom floor (least effective) and top floor (most effective). Despite a theoretical dependence on windward versus leeward side of the building, temperature differences drive the majority of airflow. As shown in the graph, the CFM potential of leaving windows completely open is astounding, even during the summer months.3

3 It should be noted here that the wind speed used (14 mph) was NOT converted using ASHRAE standard 24.3, since this expression calls for meteorological data (Ghiaus p. 139). However, even after applying the ASHRAE 24.3 conversion, the resultant wind speed is still 12.1 mph, so on the same order of magnitude as the original 14 mph as reported by PsyCalc.


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Figure 5.7 Single-Sided CFM Potential for Completely Open (left) and Partially Open (right) windows

Since People are unlikely to leave their windows completely open during the entire year, the right column shows that even if windows are open to just 2% of the total open-able area (cracked open), the ventilation potential throughout the year is still nearly sufficient to achieve the normally mandated 15 CFM, if there is one person per window (although, as noted above, this rate may be above what is needed for naturally ventilated buildings). It is thus clear that user-operable windows can provide significant ventilation year-round, assuming that leaving them cracked open is acceptable from a heating-load perspective. This also motivates a mention of different window types (bottom/side hung, depicted in the table above) that help avoid draftiness during the winter, since those windows facilitate additional air mixing before the outside air reaches occupants. 5.4.2. Wind-Driven Cross-Ventilation

This method makes use of cross-breezes to induce positive pressure on the windward side, and negative pressure on the leeward side, creating a pressure difference, and thereby ventilation. While in certain applications this can have notable effects, its dependence on building openings being correctly oriented with respect to predominant wind, and dependence on constant wind flow make its application to the HRH resident rooms potentially limited. Various strategies exist to induce cross-ventilation, including transoms, or false ceilings over hallways, though there are varying degrees of noise and privacy concernslxv, in addition to potential fire code issues. It may be usable for large areas, such as dining halls or common rooms; that analysis is beyond the scope of this discussion.


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5.4.3. Buoyancy-Driven Stack Ventilation Combined with Wind Ventilation This form of Ventilation makes use of the fact that warm, humid air tends to be lighter

than cold, dry air. This results in warm air rising, with cool air potentially venting in as a result of the induced pressure difference. Buoyancy, or stack ventilation thus occurs in all buildings, but few applications attempt to use its effects for actual ventilation. There are a few, significant difficulties associated with both calculating and relying on stack effects for ventilation: (1) identification and stability of the neutral pressure level (NPL), (2) proper design to complement, and not oppose wind effects, (3) dependence on dedicated architecture. Identification and instability of NPL

As shown in figure 5.8, below, there is a point in a building where the inward and outward pressure effects balance, resulting in zero airflow, and above which there is limited potential for circulating stack ventilation. Since this location is dependent on other pressure effects in the building, identification of this point is especially challenging, with the best estimates of experts ranging from half way up the building to potentially being above the building entirely, depending on architecture. Furthermore, because of this dependence, other openings in the envelope, whether user-operable or computer controlled, will change the location of the NPL, further complicating design.

Figure 5.8 NPL (Source: ASHRAE 16.9 2009)

This limitation, while significant, may not be as problematic in application to the HRH, assuming proper design is used. The existence of chimney and fireplace shafts throughout the buildings have potential to raise the NPL to be permanently above occupancy height; thus, even if every user-operable window was opened, the NPL would remain above the highest residences.lxvi Additionally, as shown in the figure 5.9, below, there are other clever strategies for overcoming NPL shift. This point relates to the issue of architectural dependence for stack ventilation (3) as well, requiring careful design, but giving the HRH potential for overcoming those limitations.


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Figure 5.9 Strategies for Changing NPL (Source: Ghiaus p. 141)

Inevitably, overcoming the issues of complementing and not competing with effects is also a design question, and requires designing stack vents (whether directional vents concealed in the chimneys, or otherwise) that open toward the leeward side of the building. Wind direction data for Boston indicates that there are changes in wind direction, with wind mainly heading in a WNW orientation during cold conditions (January), and shifting to ESE during warm conditions (August), although other data indicate less of a significant shift, being from NWN to W during the summer and winter, respectively.lxvii This would require careful design to ensure that critical stack ventilation in chimneys can be counted on over the course of the year. Although this could be problematic with respect to historical commission regulations, some of the river house chimneys have been stopped up by adding cement to the top, indicating a possibility of adding directional control on top of existing chimneys. An order of magnitude estimate for flow from both windows and chimneys as a result of thermal and wind forces was calculated, based on ASHRAE formulae (detailed in the appendices). The resulting values for airflow through windows accounting for wind effects were calculated to be 3.1x10^3 CFM if the windows were left completely open, and 62.1 CFM if the windows are cracked open to 2% of total open-able area.

In assessing the effects caused by temperature as related to the stack effect, there was no ventilation available for floors with windows above the NPL (estimated to be at 60% of the total building height):


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Figure 5.10 Stack Effects for Windows (Bottom Three Floors)

Although the location of the NPL limits the availability of stack ventilation from thermal effects to the lower three floors, the CFM available from both full window openings (minimum of roughly 4000 CFM) as well as cracking the window open to 2% (roughly 80 CFM) is substantial.

Figure 5.11 Stack Effects of Chimney Openings

With respect to the chimneys their useful duct size was estimated at 1.5 by 1.5 feet.lxviii

Using the same expressions as before, but changing the wind coefficient slightly to reflect diagonal instead of perpendicular winds, the CFM available from wind effects was 577.8 CFM.


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Looking at temperature related effects, the available CFM are at a minimum value (during the heat of summer) of 3580 CFM. As a result of this analysis, the stack effects of the chimneys are substantial, considering that there is roughly a chimney above every entryway in the HRH, and each entryway requires on the order of 1000 CFM. The results of this analysis confirm the feasibility of natural ventilation for ventilation purposes of HRH throughout the year, though for the summer months, higher stories will have more difficulty relying on stack effects. This conclusion largely adheres to industry suggestions regarding natural ventilation.

5.5. Cooling Potential With respect to cooling, a more complete CFD analysis is warranted. In essence, the

goal is to maintain reasonable speed of the interior air–on the order of 4-5 mph–which can be complicated by building orientation with respect to predominant winds, as well as window designs/placement. A number of studies have been done which indicate optimal window placement and design for transferring wind speed from outside, as depicted in figure, 5.12, below.

Figure 5.12 Effects of Window Placement on Indoor airspeed (meter/sec). Vi is Average Interior Air Speed as

Percentage of Outdoor Wind Speed (Source: Givoni p. 46)

Furthermore, the successes of using courtyards, solar chimneys, and wind towers for promoting comfort cooling using natural ventilation is well documentedlxix, being another promising possibility once more accurate CFD models are developed. Finally, there is a vast amount of literature concerning diurnal or nocturnal ventilation, where a building is cooled at night for the following day; the relevance of this technique for residential buildings is somewhat questionable.


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5.6. Concluding Strategies The most widespread applications of natural ventilation, as highlighted in the case studies, implement multiple natural ventilation strategies working together. The image below depicts one such strategy. As shown in the data presented above, some natural ventilation effects can compensate for others, as the relative strength of single-sided ventilation and thermal stack effects are inversely proportional. The major concern areas remain rooms that are on high floors on the leeward side, possibly with limited window access as well. What is important, however, is considering natural ventilation strategies generally, and then implementing additional conditioning as needed in limited situations.

Figure 5.13 Combined Strategies for Natural Ventilation (Source: Ghiaus p. 146)

Of note, in many projects, natural ventilation strategies are part of a larger, partially mechanical system that includes intelligent automation able to incorporate active mechanical pressure systems (such as exhaust fans), making use of occupancy sensors (either infrared (IR) or CO2), to ensure that constant ventilation comfort is maintained (see LEED guidelines in appendices). There are current limitations to accurate and cost-effective CO2 monitors, though with increasing demand, the technology should be more readily available.lxx As noted above, the placement and types of windows chosen can greatly influence comfort, both in inducing greater air mixing for greater comfort throughout the room, as well as preventing occupants from experiencing discomfort by being in direct line of sight to window openings (ameliorated by side/bottom hung model).


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The potential for natural ventilation for satisfying both ventilation and cooling needs throughout much of the year seems promising, motivating serious consideration and further investigation.


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6. Passive Solar Heating

6.1. Justification for Passive Solar Heating After designing the new Houses to have a reduced heating load through the employment of a high performance thermal envelope, the next major consideration should be to provide as much of the remaining heating load with passive solar heating as possible. This passive solar heating occurs through the direct absorption of sunlight making it a free source of energy when available with negligible maintenance costs. The Commission of the European Communities has shown examples of buildings from the 1980s that obtained up to 68% of their heating requirements through combinations of insulation, performance windows, thermal mass, shading methods and the redistribution of solar heatlxxi . The energy savings available using this technique in the Harvard houses is significant, and the goal of this section of the report is to provide ways of harnessing this solar energy for heating and quantifying the savings.

6.2. Windows When considering what kind of windows to install, two of the most important

parameters to consider are the window's U-value and the solar heat gain coefficient (SHGC). The U-value of a window relates to how well it conducts heat, with a low U-value being characteristic of a good insulatorlxxii. The SHGC of a window is the fraction of incoming solar irradiance that the window transmits with 0 representing no transmissionlxxiii.

A window with a low U-value leads to large reductions in heat loss in winter but only a small reduction in the summer cooling load because of the smaller difference in indoor and outdoor temperatures. Also, low U-value windows tend to have smaller SHGCs because increased number of panes and low-e coating increase the amount of light reflected by the window. This small SHGC contributes to a significant reduction in the cooling load in the summer, however it reduces the solar heat gain of the window in the winter. The conventional recommendation for windows in the Boston area is a window with a low U-value and a low SHGClxxiv.

At the latitude that Harvard University is situated in the northern hemisphere (42.4°N), this loss of solar heat gain for east, west and north facing windows due to the smaller SHGC is relatively small because there is not much solar irradiance on these walls in the winter. Thus for east, west and north facing walls one should install conventional windows with low U-values and low SHGCs. Since southern walls face the equator, the solar irradiance that hits them is strongest in the winter when the northern hemisphere is tilted away from the sun and weakest in the summer when the northern hemisphere is more directly facing the sun. This creates a trade-off between the southern facing window’s U-value and SHGC such that conventional windows may not be the most cost-effectivelxxv.


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6.3. Southern Facing Window Analysis This section will look at two windows with similar prices to analyze the trade-off in southern facing windows. Both windows are from the manufacturer Steindl Glass. The unconventional window (medium U-value, medium SHGC) will be a double glazed window with argon gas between the panes. The conventional window (low U-value, low SHGC) will be a triple glazed window with argon gas between the panes. The properties of these windows are summarized in Table 6.1. Each of these windows has a face area of 1m2.

U-value (W/m2/K) SHGC

Unconventional Window 1.4 0.58

Conventional Window 0.6 0.44

Table 6.1: Properties of the unconventional window and the conventional windowlxxvi

By analyzing the heating and cooling degree days (a unit of measurement equal to a difference of one degree between the mean outdoor temperature on a certain day and a baseline temperature [17]), with a baseline heating temperature of 65°F (temperatures below this value need heating) and a baseline cooling temperature of 75°F (temperatures above this value need cooling) it was approximated that solar heat gain would be beneficial between the months of November and March, and undesirable between the months of June and August. The analysis of the windows will focus upon these time periods. The three modes of heat transfer across a window are convection, conduction and radiation. The convection rate is not related to the U-value or the SHGC so it will be considered the same between the two windows and ignored. To estimate the heat conduction, 'q conduction', across the window, the following simplified equation will be usedlxxvii:

(1)

In equation (1) 'T' is the daily average outdoor temperature, '!t' is the step size of one day and U is the window’s U-value. The daily average temperature in Fahrenheit in the Boston area can be represented by equation (2) where 't' is the number of days since January 1stlxxviii:

(2)

To estimate the solar heat gain from radiation the average solar irradiance will be multiplied by time and the SHGC. This is assuming that the efficiency of converting light into heat within the building is 1 and that there is no shading. In this analysis, the average solar irradiance was calculated at 50°N, and since Harvard University is located at a latitude of 42.4°N the numbers are slightly off but still make a good approximation. The average solar irradiance on a vertical southern facing wall is 214W/m2 between November and March, and it is 185W/m2 between June and Augustlxxix. Table 6.2 gives a summary of the results.

Unconventional Window Conventional Window


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Heating (Nov-Mar)

Cooling (Jun-Aug)

Heating (Nov-Mar)

Cooling (Jun-Aug)

Solar heat gain potential (kBTU)

2628 1363 2628 1363

SHGC 0.58 0.58 0.44 0.44 Actual solar heat gain (kBTU) +1524 +791 +1156 +600 U-Value (W/m2/K) 1.4 1.4 0.6 0.6 Conduction (kBTU) -343.7 -6.4 -147.3 -2.8 Total Energy Through Window (kBTU)

+1180.3 +784.6 +1008.7 +597.2

Convert Total Energy Through Window to Savings if Energy was Provided by Baseline Equipment Performance 1 5.11 1 5.11 Total Secondary Energy (kBTU) 1180.3 153.5 1008.7 116.9 Supply Efficiency 0.72 0.72 0.72 0.72 Total Primary Energy (kBTU) 1639.3 213.2 1401 162.4 Savings ($) 6.8 -0.88 5.81 -0.67 Total Savings ($) 5.92 5.14

Table 6.2: Comparison of unconventional window and conventional window in Cambridge, MA. Each window is 1m2 and faces due south. Note: For this analysis the price of burning natural gas was estimated to be $4.15/MMBTUlxxx. Heat transfer into the building was positive and heat transfer out of the building was negative. Also heat transfer into the building is a savings during the winter and a cost during the summer.

6.4. Southern Facing Window Results From table 6.2 it can be seen that the unconventional window saves $0.78 more per m2

per year than the conventional window. Even though the conventional window is better at reducing the heat that is transfered outside through conduction, the unconventional window more than offsets this difference by having a larger heat gain in the summer. Also, even though the unconventional window has a larger heat gain than the conventional window in the summer, this does not become a significant factor because there are fewer cooling days than heating days, and the cooling system is more efficient converting primary energy into cooling BTUs because the baseline chiller has a coefficient of performance (COP—the number of thermal energy units output from one unit of electrical energy input) of 5.11. Since burning 109 BTUs (1 GBTU) of natural gas emits approximately 53.1 metric tons of CO2 equivalent (MTCDE), the unconventional window also reduces greenhouse gas emissions by about 0.01MTCDE/m2 more than the conventional windowlxxxi.

6.5. Southern Facing Window Conclusions This analysis concludes that southern facing windows at Harvard with a high SHGC have an energy and cost advantage over windows with low SHGCs. Even when there is a trade-off between having a window with a low U-value and a low SHGC, and a window having a higher SHGC at the expense of having a higher U-value, the latter window can still be more


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cost effective if the window faces south. Thus Harvard University should install low U-value, low SHGC windows on walls that face east, west and north, and medium U-value, medium SHGC windows on walls that face south to maximize energy benefits.


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7. Seasonal Heat Storage in Outer Walls

7.1. Justification for Seasonal Heat Storage The outer walls of a building can act as a heat sink in the summer and a heat source in

the winter if they have enough thermal mass. This occurs because thermal energy from warm days will be stored in the walls long enough to be re-radiated into the building during colder days and the cooling of the walls during cold days will cause thermal energy to be transferred from within the building to the walls on warmer days. The following analysis will demonstrate this effect and show under what scenarios this idea would be cost-effective.

7.2. Seasonal Heat Storage Analysis Using equation (1) as the outside temperature, and setting the inside temperature to 72°F (22°C) we can find the temperature profile within the wall as a function of space and time. Figure 7.1 illustrates this situation:

Figure 7.1: Thermal model diagram for outer wall

For this analysis the outer wall will be made from cement-bonded wood fiber bricks, a

form of insulating concrete. Cement-bonded wood fiber is known to be used in LEED-certified projects and other green buildings. It is composed of recycled waste wood which has been chipped into wood fiber, mineralized, and bonded together with cementlxxxii. Cement-bonded wood fiber has the following propertieslxxxiii:

!

Density = " = 600kg /m2

Thermal Conductivity = k = 0.083W /(m #K)

Specific Heat Capacity = c =1500J /(kg #K)

For a vertical wall in air the convective heat transfer coefficient is approximately

4W/(m2K). Here, the wall will be assumed to be at least 0.3m thick. The Biot number, the ratio of convective heat loss to conductive heat loss, can be calculated as:


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Since the Biot number is larger than 10, it means that the majority of thermal resistance is found within the walls and so we can estimate that the temperature is constant beyond the wall. The heat transfer at the boundary of the outer wall with the inside of the building can be found by solving equations (3) and (4) where 'T' is the temperature, 't' is time, 'x' is the distance from the outside of the wall and 'q' is the thermal heat transfer per m2:

!

"T

"t=k

#c$" 2T

"x 2 (3)

!

q = "k #$T

$x (4)

Note that in equation (3), the dimensions of the diffusion constant have to be changed from m2/s to m2/day to agree with unit of time being days in the temperature equation. To solve these partial differential equations the following boundary conditions are used and correspond to the fact that at the boundary of the wall and the outside air the temperature corresponds to equation (2), and at the boundary of the wall and the inside air the temperature is a constant 295K (22°C):

!

T(x = 0,t) = 283.8 "12.0722cos((# /180)(t " 27.6)) (5)

!

T(X = L,T) = 295K (6)

Note that equation (5) is equation (2) written in units of Kelvin instead of Fahrenheit and that 'L' is the width of the wall. For the initial condition the temperature profile at time 0 days is considered linear. Solving these equations numerically, we find that only wall thicknesses of 2m and greater have significant seasonal thermal storage. Calculating the heat flux into the room from equation (4) for a 2m thick wall, we get the result of the thermal mass effect as seen in figure 7.2.


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Figure 7.2: The outside temperature and the heat transfer from a high thermal mass wall to the inside of the

building graphed against the number of days since January 1st. A wall that had less thermal mass, would not have this buffer against the fluctuations of the outside temperature because the temperature would diffuse through it easier and so the heat flux profile would follow the outside temperature profile more closely. Also, as the wall gets thinner, the effects of convective heat transfer become larger further increasing the rate at which the outside temperature diffuses through the wall.

7.3. Seasonal Heat Storage Results This result shows that only walls 2m or thicker have significant seasonal thermal

storage. By increasing the thermal mass of the outer walls by increasing its width to 2m, one can delay the effects of the temperature difference between the inside of the building and the outside by about one month. This would be most beneficial during the transitional seasons of spring and fall. In the spring, when it is getting warm, one would not have to begin cooling as soon because the walls would be cooling at a rate of one month previous. Similarly in the fall, when it is getting cold, you would not have to start heating as early because your walls would be cooling at a smaller rate because of the warm outside temperature one month earlier.

7.4. Seasonal Heat Storage Conclusions Assuming that you could save approximately 15 full days of cooling in May and 15 full days of heating in October by building a 2m thick thermal mass walls, this would result in a savings of about 560 MMBTU of cooling and 385 MMBTU of heating for Winthrop House. Assuming a chiller COP of 5.11, a Blackstone efficiency of 0.72lxxxiv and a natural gas price of $4.15/MMBTUlxxxv this would be equivalent to a saving's of $3000/yr. With one 14" by 12" by 24" block of cement-bonded wood fiber costing about $15lxxxvi, the total cost of installing the


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extra thickness of wall around Winthrop House would be about $3,000,000. Since Harvard University would likely make more money through other investments, assuming a real interest of 4%, this extra thermal wall would not be cost effective unless the cost of installing the walls decreased to $75,000, which would mean that the price of a cement-bonded wood block would have to decrease to about $0.40. This solution is unpractical, since the walls are far too thick and it costs far too much. However, if in the future a material with a smaller thermal heat diffusivity, k/(!c), was invented and was not very expensive then this solution would begin to become feasible.


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8. Ground Source Heat Pumps

8.1. Justification for Ground Source Heat Pumps Heat pumps can be used for both heating and coolinglxxxvii. As coefficients of performance increase, they are becoming a more attractive component of HVAC systems in the New England region. The two main types of heat pumps are Air Source Heat Pumps (ASHPs) and Ground Source Heat Pumps (GSHPs). In an ASHP the outside air serves as a thermal reservoir while in a GSHP the ground serves as a thermal reservoir for the building. The goal of this section of the report is to determine how ground source heat pumps can be used for heating and cooling in the Houses and under what scenarios they would be most economic. Ground source heat pumps typically use less energy than conventional HVAC systems and can significantly reduce greenhouse gas emissions by utilizing the thermal energy stored in the ground. GSHPs are also up to 44% more efficient than air source heat pumpslxxxviii. Other advantages of GSHPs are lower maintenance costs compared to conventional HVAC systems since their parts are not exposed to outside weather, and have fewer moving parts. They are also noiseless and hidden so they would not infringe upon the rules of the city of Cambridge or the Cambridge Historic Commissionlxxxix. Harvard's first LEED platinum building at 46 Blackstone St, the home of the university's operations services uses two, 1500 ft deep geothermal wells to provide its coolingxc. Like all other existing GSHPs at Harvard, these wells are open loop, standing column wells. They use an underground water source as both the heat source and heat sink for the buildingxci. As this type of well has been determined as the most practical given the local conditions, it will be the kind used in the following analysis.

8.2. Ground Source Heat Pumps Analysis The pumps in these GSHPs would be located 110 feet below the surface and would have a maximum pump capacity of 180 gallons per minute. They would be equipped with variable frequency drives to allow them to run at partial capacity, reducing the electric energy cost to run themxcii. Monitors would also have to be installed to measure the rate of corrosion in the piping in the heat exchangers since the local groundwater has been found to be brackish and contain iron. In cooling mode—during the summer—well water, at ground temperatures between 64-91°F, exchanges heat in a heat pump and helps to cool the chilled distribution water in the building from 55°F down to 44°F. The well water returns to the ground at a higher temperature, between 74-101°F, where it is re-cooled or replaced by the thermal reservoir water in the well. In heating mode—during the winter—well water, at ground temperatures between 60-70°F, exchanges heat in a heat pump and helps to heat the hot distribution water in the building from 100°F up to 110°F. The well water returns to the ground at a lower temperature, between 52-62°F, where it is re-heated or replaced by the thermal reservoir water in the wellxciii. A detailed schematic of this process is provided in Appendix 4. The amount of heat that is rejected from the ground source in winter should be the same as the amount of heat injected into the ground source in the summer so that the temperature of the thermal reservoir does not change over years and the system remains


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efficientxciv. The number of days that require cooling in Cambridge is on average 64xcv. Assuming that the wells only operate for 12 hours per day when there is a demand for cooling, then the total energy withdrawn from a well can be calculated. Assuming a pump rate of 90 gallons per minute and a temperature difference between ground water and return water of 23°F (88°F return, 65°F ground) in the summer and 8°F (57°F return, 65°F ground) in the winter, then the heat injected into the ground in summer and rejected in winter can be calculated:

!

Qsummer = ˙ m " time " c " #T (7)

The heat injected into the ground in the summer is the limiting heat transfer value since there is a 6:1 heating to cooling degree day ratio in Cambridgexcvi. Since the heat transfer into the ground in summer has to equal the heat transfer out of the ground in winter:

!

Qwinter = 796,000kBTU = ˙ m " time " c " #T (8)

(9)

Equation (9) shows that the GSHPs can only operate in heating mode for 92 full days in the winter. However, because there is water flow in the ground that is not being accounted for in this analysis, the net energy balance, Qsummer = Qwinter, does not have to hold. This means that the wells would be able to run longer in the winter and not affect the ground temperature substantially. Therefore, equation (9) is a lower limit on the use of the wells in winter because they could be used for more than 92 full days. Table 8.1 compares the performance and costs if these GSHPs were used for heating and cooling instead of the baseline scenario of using steam from Blackstone for heating and a new chiller for cooling. Winthrop House was used as the model for this analysis.

Baseline GSHPs Heating Cooling Heating Cooling

Annual Load (GBTU) 9.54 2.4 9.54 2.4 Equipment Performance 1 5.11 3.2 5.4 Annual Energy (GBTU) 9.54 0.47 2.98 0.44 Supply Efficiency 0.72 0.72 0.72 0.72 Annual Primary Energy (GBTU) 13.9 4.75 CO2 emissions (MTCDE/yr) 738 252 Total Annual Energy Cost ($) 57,685 19,713 Investment Cost ($) 728,000 1,800,000 Annual Financing Cost ($) 42,100 104,094 Total Annual Cost ($) 99,785 123,807 Table 8.1: Operating and cost characteristics of a ground source heat pumps and the baseline of steam from the co-generation Blackstone plant and a new chiller for building. Note: Winthrop House was estimated to operate at a full cooling capacity of 260 tons, where 1 ton=12000 BTU/hr, and that it would require 12 GSHPs to heat and cool Winthrop House. The conversion rate for burning natural gas and emitting greenhouse gases was 53.1 MTCDE/GBTUxcvii. The price of burning natural gas was


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estimated to be $4.15/MMBTUxcviii. The real interest rate was assumed to be 4% and the lifespan of both systems was estimated to be 30 years.

8.3. Ground Source Heat Pumps Results and Conclusions From table 8.1, it is apparent from the total annual cost of both systems that the GSHPs would cost about $24,000 per year more than the baseline system. However, there are two scenarios under which the GSHPs would become cost effective: • The price of natural gas increased above $6.78/MMBTU (figure 8.1) • There was a cost of $49.43 or greater for each MTCDE (figure 8.3)

Figure 8.1: The annual cost of the baseline system and the ground source heat pumps versus the price of natural gas. They intersect at a price of $6.78/MMBTU and a annual cost of $136 000.

As seen in figure 8.2, the historical data of the price of natural gas in the US over the past ten years, natural gas prices are volatile and have climbed over $6.78/MMBTU in the past decade. According to market forecasts (which are only predictions) the price of natural gas will rise past $7/MMBTU and continue to rise by 2015 which would suggest that GSHPs may become cost effectivexcix.


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Figure 8.2: Henry Hub natural gas prices on the NYMEX (New York Mercantile Exchange) over the past decadec. The second scenario where GSHPs become cost effective is when there is a cost on

emitting greenhouse gases. Two economists have tried to estimate the price of emitting one MTCDE by taking into account the costs of global warming and climate change. Yale economics professor Bill Nordhaus estimated the price should be $30/MTCDE and British economist Nicholas Stern estimated it should be $300/MTCDEci. If there was to be a carbon tax imposed by the US government and if its magnitude was on the order of either of these estimated prices, then GSHPs would become cost effective. Specifically if there was a tax of $50/MTCDE or greater, GSHPs would be cost effective.

Figure 8.3: The annual cost of the baseline system and the ground source heat pumps versus the price of a MTCDE. They intersect at a price of $49.43/MTCDE and an annual cost of $136,000.


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9. Plants 9.1. Justification for Studying Plants A few decades ago NASA was very interested in using plant life for air pollutant filtering and for restoring carbon dioxide and oxygen levels for use on the International Space Station. However, their results can be applied in dorm rooms as well. Their studies showed that the plants and microorganisms associated with them in the soil were very efficient at removing some of the most common pollutants from the aircii. If houseplants were to be considered an alternative to providing outside air, the most efficient candidate would be the Areca Palm (Areca catechu). Not only was the palm one of the most effective filters, it is also very efficient at exchanging carbon dioxide for oxygen. According to Kamal Meattle of GreenSpaces, only four shoulder high Areca palms in indoor conditions with consistent watering are necessary to provide all the fresh air for a person performing normal physical activitiesciii. Therefore there are two options to consider: four plants could be provided to the students as a substitute for a ventilation system or plants could be used to supplement a ventilation system, allowing for system to be used at reduced capacity. 9.2. Exploring the Two Methods 9.2.1. Option 1: Substituting Plants for Active Ventilation

In order to evaluate the cost effectiveness of the houseplant ventilation option we look at the initial capital costs and the maintenance costs of the two systems.

The cost of each palm is around $10civ. If we assume that each student is given four palms each year and is able to keep them all alive for the entire year, the cost of the trees will be

Figure 9.1: Left shows a typical shoulder height indoor Areca Palm. Right shows Areca Palm seedlingsxvii.


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$40 per person per year. We assume that the cost of the water to sustain the trees is negligible. Therefore each year, the cost is fixed at $40 per person per year.

Heat Recovery Ventilators (HRVs) large enough to supply a space about the size of an entryway cost about $10 per cfm for the unit and installation and require about 1 Watt per cfm to runcv. HRVs are only up to 80% efficient at transferring heat between incoming and exiting air, but if we assume a reasonable infiltration rate, the additional heat loss through the ventilation will be negligible compared to the inevitable heat lost through the building envelope. Therefore the initial cost of the system and the electrical cost to run it are the only significant expenses involved in using HRVs to provide ventilation. In order to provide the necessary air quality, we assume the HRV is running the entire year continuously. This translates to an electricity usage of 175.2 kWh or at current electricity prices, $26.28. The average yearly cost of the ventilation system is therefore, the price of the electricity consumption plus the initial capital cost that becomes less significant the longer the system runs.

The effective yearly cost of the system is the cumulative spending divided by the number of years in operation. The yearly cost of the HRV system asymptotically approaches the operating cost of the electricity it consumes while the cost of the plant program remains fixed assuming the price of the plants remains fixed. After 7.3 years, the yearly cost of the HRV system becomes less than the fixed $40 for the plants. Therefore at current electricity prices, it would not be cost effective to replace a standard mechanical ventilation system with a plant program. However, electricity prices do not have to change dramatically to make this idea more feasible. If electricity were $0.20/kWh, it would take 20.2 years for the HRV system to become less expensive. And in the limit where the years in operation go to infinity (meaning that the impact of initial costs of the HRV system vanishes), it would only require the price of electricity to reach $0.228 for the plant program to remain less expensive forever. Furthermore, if when

Figure 9.2: Left shows average yearly costs per student of an HRV system with current electricity costs versus the

costs per person of a plant program. Right shows the yearly costs per person at various electricity prices.


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buying in bulk the university was able to get a significant discount, the plant program would also become cost effective if the price for each plant was $6.50. 9.2.2. Option 2: Incorporating Plants into an Active Ventilation System

The second option is to use plant life as a supplement to an active ventilation system. Since ASHRAE standards and Massachusetts building laws require air changes with outside air, an air handling system capable of delivering the necessary air would most likely be installed. However, the use of plant life could enable the system to only run part time. While this would not affect the installation and system costs because the system would still have to be sized to meet the requirements, it would decrease consumption costs.

We have seen before that systems that include plant life do not become cost effective unless the price of electricity increases. However if were to add a plant program in addition to the installation of an HRV system, we could assume that for every plant provided, the HRV system could run less, cutting one quarter of its duty cycle for each plant. It is helpful to graph potential savings from the incorporation of a plant program versus the price of electricity.

By taking the yearly effective cost of the HRV system and subtracting the yearly

effective cost of a system with a given number of plants alleviating some of the load, we can see the dynamics of the system. At the crossover point at $0.228/kWh, there are no savings no matter how many plants are provided because operating costs are equal. When electricity prices go above the crossover point, plants become more cost effective and the savings increase linearly with each plant. However with electricity currently below the crossover point, there are no savings to be gleaned and the losses of the plant program increase linearly with each plant. Therefore if a plant program were to be implemented immediately in order to increase the air

Figure 9.3: Electricity Prices in dollars/kWh versus the savings per person in dollars for different amounts of

plants


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quality and comfort of occupants, a single plant would be sufficient to provide most the benefits and would be the most cost effective. However if electricity prices rise past the crossover point, supplying additional plants would begin to lower ventilation costs.


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10. Phase Change Materials for Thermal Storage

10.1. Phase Change Materials Background The principles behind using Phase Change Materials (PCMs) for thermal storage have

been utilized for many centuries. While a material is changing state, in this application most commonly from solid to liquid or vice versa, its temperature remains constant. When a substance is melting, the constant temperature is a consequence of energy being required to force the molecule out of the lower energy crystal structure. And in the case of freezing, the constant temperature is a consequence of energy being expelled as the molecules form the crystal. This idea allows for ice to be used to maintain a cold temperature because even as the ice melts, its temperature stays nearly constant until all the ice has melted. It therefore acts as a thermal buffer, providing additional thermal mass throughout the phase change process. This idea is now being rethought and applied in contemporary HVAC systems. The two most important properties to consider for a PCM are its melting point and its latent heat of fusion. The heat of fusion is a measure of how much energy is required to complete the phase change and is dependent on how well structured the resulting crystal is. While water has a very high heat of fusion, it has a poor melting point for HVAC applications. The PCM only adds thermal inertia at temperatures close to its melting point. Since water’s melting point is so low, it can only hold temperatures close to 32° F. However a few extremely good candidate have been found, for example Sodium Acetate Trihydrate [NaC2H3O2(H2O)3]cvi. It has a latent heat of fusion of 264-289 kJ/kg, comparable to water’s 333.6 kJ/kg. However its melting point is 58° F, making it much more suitable for PCM applications. While it is theoretically possible to provide all the heating necessary just through PCM, it has never been attempted. If we wanted the crystallization of Sodium Acetate Trihydrate to provide the total yearly heating requirements of Winthrop house we would need to generate 36 million kilograms of “ice.” Given that Sodium Acetate costs about $15 per kilogram, that translates into a cost about two thousand times higher than the price of steam heating the house for a year. Also given the density of 1.45 g/cm3, the ice would require 25,000 m3, nearly half the volume of Winthrop House itself. This amount of “ice” would have no problem providing heating and cooling to keep the temperature of the building a constant 58° F the entire year. Also, given that the thermal properties remain nearly constant over a huge amount of phase changes, the PCM would remain effective for an extremely long time and would therefore only require a huge initial capital cost, but nearly no operating costs. However, the volume requirements make it unreasonable to expect that a PCM thermal storage system could be implemented to exclusively maintain thermal comfort.

10.2. Incorporating PCM into Building Materials Building components containing PCMs are beginning to be implemented but are still

too untested to be considered for current designs. DuPont recently announced a line of wall panels that have microencapsulated paraffin wax enclosed in aluminum casings which they call Energain Panelscvii. They can be installed similarly to any standard wall panel and then can have


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drywall fixed to them. Paraffin wax is another good PCM with a melting point of 72° F and a heat of fusion of 70 kJ/kg. It is especially forgiving to work with since it is essentially candle wax with a few proprietary polymers added by DuPont. Each panel is about 11 square feet and given the amount of PCM enclosed, each has a total thermal capacity of 67.36 Btu/ft2 of wall area covered with panels in a temperature range of 57-86° F. Given that the surface area of the building is nearly 100,000 ft2, if every wall and the entire roof had an Energain panels, at least 5 MBtus could be supplied or sunk from the House each time the temperature cycled past it’s freezing point. This would constitute an $150 savings each time the temperature cycled. However, once the temperature goes below the freezing point and stays below the freezing point, it no longer works to increase the thermal mass. Therefore, while the PCMs do significantly contribute to maintaining building temperature on temperate days, they do not work effectively when the building needs the maximum heating or cooling on the hottest and coldest days. Furthermore, since these materials are relatively untested and a price is not available yet, there is no way to rigorously analyze the cost versus benefit of retrofitting a building with these materials.

Figure 10.1: DuPont Energain Panels showing microencapsulated Paraffin waxxxi


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11. Variable Refrigerant Flow Air Conditioning

As previously mentioned, during the renovation process of the river houses, by default Harvard will put in fan coil units for each room. A possible alternative that should be addressed is the option of installing a variable refrigerant flow (VRF) system. Variable refrigerant flow systems react to changes in the needs of heating and cooling through the process of varying the refrigerant flow to each unit as a way to meet instantaneous needs of the userscviii.

Variable refrigerant flow systems operate using individual units in a similar manner that fan coils are used. To maximize user comfort, one unit per room should be installed. The individual units that will be placed inside the houses to maintain the temperature in the rooms operate on their own refrigerant loop, but they are all controlled by a common system: a condensing unit. These condensing units can operate up to twenty individual units and need to be stored outsidecix. As compared to fan coils, variable refrigerant flow is a much more complex technology.

11.1. Benefits The installation required for variable refrigerant flow systems is minimal compared to

other alternatives. A major VRF distributor, Mitsubishi Electric, claims that the process of installing a VRF system is a fairly simple processcx. As a ductless technology, variable refrigerant flow systems avoid the need for tearing out the walls and ceilings to install new ductwork. This absence of ductwork actually increases the efficiency of the system. Without the need for ducts, variable refrigerant flow systems eliminate duct losses that would be associated with other systems requiring them. Duct losses are estimated to be around 10-20% of the total airflow in a systemcxi.

In the case of Harvard undergraduate dorms going off steam from Blackstone, or Blackstone switching to all electric energy, VRF would be equipped to cope with this changecxii. For a school that is constantly looking forward into the future, the variable refrigerant flow system would allow Harvard to maximize its control over an uncertain future. To allow for more student activities comfort, VRF allows for simultaneous heating and coolingcxiii. To reach the goal of having satisfactory student comfort, and meeting any heating and cooling needs, VRF would be an appropriate solution.

In addition to student comfort, the implementation of these systems would create little impact on the daily lives of the students and faculty at Harvard. According to Mitsubishi Electric, the individual indoor units operate around 24 dB, and the condensing units that operate outdoors are around 56 dBcxiv. 24 dB is around the magnitude of a quiet whisper, and 56 dB is around the magnitude of a normal conversation. Other than the visible indication that the units are present, the VRF systems would otherwise be unnoticeable.

11.2. Disadvantages Variable refrigerant flow systems have a very high upfront cost to purchase them. A

payoff is not likely to be seen for a few years after the system is up and running. The amount of money that Harvard is willing to spend in the renovation process will be a major factor in


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determining if this is a feasible technology to pursue. Based on the current financial market, this technology will most likely not be seen implemented by Harvard for some time. Once VRF is more widely accepted, and the cost to purchase this technology has decreased, Harvard may then choose to implement it.

Ventilation is not provided from the VRF systems, so an additional form of ventilation is necessary to ensure that the system runs properlycxv. This will equate to installing more hardware to allow for ventilation, or at least improving the existing ventilation systems in each house. Regardless, this will add to a higher installation cost than just adding the VRF alone. The usage of air handling units may address this problem. With the installation of fan coil units, air handling units will be needed too.

As previously mentioned, one outdoor condenser can support around 20 individual units. There are a lot more than twenty rooms in each upperclassmen dormitory, so at least 20 outdoor condensers will be needed for each house. This means that a farm of condensers will practically be needed to maintain each housecxvi. In order to allow for a farm of condensers, Harvard would need to designate a large space to hold these units. Choosing to place these units outside may prove to be unreasonable because that space may not exist in Cambridge, at least for every single house. Placing the condenser units inside is not an option, as they need to be outside in order to properly run.

11.3. Conclusion In an unpredictable climate such as Cambridge, where it may be sunny and warm one day and snowing the next, this lure of reacting to the changing environment that the VRF system proposes is very appealing. As stressed earlier, it will be very important for Harvard to be prepared for a changing landscape, and variable refrigerant flow systems can appropriately prepare Harvard for this adaptability.


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12. Double Skin Façade The double-skin façade was first introduced to the United States in the 1970s. The

introduction was during the first energy crisis, as the technology was implemented to help improve building performance. The double-skin system is made up of two glass skins placed in the building and allows for the air to flow between the two skins. The distance between the two skins can vary anywhere from 20 centimeters to 2 meters. Due to the presence of air flowing between the two skins, a method of ventilation must also be achieved in order to circulate the air and prevent mold and stagnant air. The methods of ventilation used can be natural, fan supported or mechanical. For Harvard, utilizing the current ventilation already installed would help make the process of choosing the method of ventilation easier.

12.1. Benefits In a cold climate such as Cambridge, in order to offset the heat requirements, the solar

gain that is harnessed within the cavity can be circulated to the nearby space. Due to the opening to the external environment that the double skin façade presents, natural ventilation is possible. Natural ventilation has great potential and is further touched upon in the natural ventilation section of this report. In addition to natural ventilation from the openings, natural cooling throughout the nighttime is also feasiblecxvii. The process of natural cooling will see a lot of use throughout the year, but a way to maintain this technique will need to be looked into further to guarantee that the buildings do not get cooled beyond a reasonable amount, especially in a climate such as Cambridge.

Due to the fact that the distance between the internal and external environment is much larger than it is in most buildings, the double-skin protects the indoor environment from external noisescxviii. This would be a very beneficial aspect to have considering the amount of noise some students have to encounter, whether it is garbage trucks, shuttles, or parties. Double-skin façades also address problems of ventilation well. A supply of fresh air of 17 cfm can be obtained without cross-ventilation by just tilting the interior windows at an angle so that they are partially opencxix. Humans need between 15 and 20 cfm an hour, so this cross-ventilation strategy will sufficiently address the problem. Through the installation of this technology, Harvard would passively enhance its benefits, and possibly find a way to get rid of other forms of technology that were previously required.

12.2. Disadvantages Double-skin façades will yield some annual savings in heating and cooling costs, but the initial installation cost is very high compared to the savings the technology will eventually yield. The cost per square meter has been projected in the range of $135-680 depending on the projectcxx. The perimeter of one of the buildings of Winthrop House is 276.5 meters, and the other has a perimeter of 311 meters. Each building is roughly 15 meters tall, so the area of the exterior is approximately 4147.5 m2 for the first building, and 4665 m2 for the second. As previously mentioned in the report, the cost to purchase 875 fan coil units will be $300,000 and


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it would be reasonable to cover approximately 10% of Winthrop House with the double-skin technology for the same price. Thus, it would be less economically sound to invest in this technology, as the total cost would be close to $3 million to renovate just one house. Having thicker walls, as the double skin ranges from 20 centimeters up to 2 meters on every side of a building, would dramatically decrease the floor space in each room. Most rooms will only sacrifice the space on one side of the room, but if a room is ten feet wide and loses close to two meters for the extent of that side, the room is decreased by up to twenty square feet. Most bedrooms are on the order of 100-200 square feet in size, so a 10-20% loss in space would arise from only one side being fitted with the double-skin technology. Corner bedrooms will see a decrease up to 25% because two sides are affected. Students may not be willing to sacrifice a significant amount of the small spaces they already have for marginally better comfort levels.

In order to protect the internal cavities that are present through the use of the double-skin, solar shading devices are often installed in the cavity between the two skins. This helps to protect the double-skin during the cooling period, which for Cambridge, is most of the academic yearcxxi. In addition to the already outrageously expensive double-skin per square meter, these solar shading devices will additionally increase the installation cost, thus the double-skin façade may not be the right answer at this point in time.

To provide sufficient ventilation for the houses, the air pathways that exist between the skins should not be more than two floors highcxxii. As most Harvard dorms are taller than two floors, this will make for a complicated task. More than one pathway will be required for each side of the building. If not properly ventilated, condensation may pose a problem with the double-skin façades. Letting this problem go untreated will result in the façade being damaged and poses a risk for certain health problems. Overheating between the skins may occur as the ventilation rate through the windows is reducedcxxiii.

12.3. Conclusion The double-skin façade is a very interesting idea, but would not be something that

Harvard would actively pursue in the forthcoming years. Once the technology is more cost effective, and the proposed renovations are complete, it would be reasonable for Harvard to invest in double-skin façades.


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13. Biomimicry

Many researchers have found it very important to use nature as a model for engineering, seeking to “learn from, emulate, and conserve”cxxiv nature to such ends. Janine Benyus and the Biomimicry Institute have researched and supported various projects that aim to improve our design of real-world solutions. While such designs may not yet be feasible, changed economic circumstances and increasing technological developments could make such developments useful to follow and understand. Two researched designs in particular are worthwhile to look further into as their technology advances and their ideas might be able to be implemented in future renovations. The first models the avian respiration system as it has evolved to take in unidirectional, high velocity air flow and still maintain a proper level of filtration and ventilation to keep it alive.cxxv The second comes from observation of the natural air conditioning found in termite mounds. This principle has already been implemented on a large scale in the Eastgate Centre building in Harare, Zimbabwe.cxxvi

13.1. Avian respiration 13.1.1. The system in nature

Human respiratory systems are designed such that all the air that gets to the alveoli and whose nutrients are filtered into the blood stream must then return by the exact same path. This means that exchange of nutrients only occurs during one half of the cycle. The high-efficiency respiratory systems of birds have developed such that the air that they intake is constantly undergoing filtration. Figure 13.1 shows a cartoon schematic of the avian respiration cycle.


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Figure 13.1 – The avian respiration system. Figure A is a physiological schematic. Figure B and C are schematics of the inhalation and exhalation phases, respectively.cxxvii Figure 13.1(B) is a schematic of the inhalation phase. Figure 13.1(C) is a schematic of the exhalation phase. The yellow box is the lung which contains all of the alveoli that filter the air and extract its nutrients. The arrows are moving along the lung in the same direction in both phases. The bird uses two sets of air sacs (colored shades of pink and shades of aquamarine) to maintain this system going. This highly efficient system can be used as a model on which to build a ventilation system and air filtration system for the house that only requires one inlet/exhaust. 13.1.2. Applications

The common way to design a ventilation system is to have a separate intake and outtake system. Using avian respiration as the model, first and foremost, it allows for a compact system that can theoretically achieve the same as a much larger system, using only one inlet/outlet. Secondly, it allows for the incorporation of exchangers (of heat or air pollutants) in a small system that doesn’t require lots of extra piping.

This particular solution may find a specific niche in the future of Harvard dorm renovations. The only main access to outside air for natural ventilation (assuming, as we have, that the building envelope to have negligible infiltration) is through the chimneys. The chimneys, however, are too small to include both an intake and exhaust system. If one were able to develop an efficient single intake-exhaust system modeled on avian respiration, it would be possible to implement such a system in the chimneys without affecting the external appearance of the building, and thus complying with the codes set forth for Harvard by the Cambridge Historical Commissioncxxviii.

As explained in section 1.2.4, useful solutions, such as those mentioned, would be Tier III solutions that could be implemented at a later stage, after the renovation project. Such a


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project, however, would require that the chimneys already be a part of the air distribution system.

13.2. The Termite Mound 13.2.1. The system in nature

Despite the conventional misconception that termite mounds are the residences of termite colonies, they are actually “accessory organs of gas exchange, which serve the respiratory needs of the subterranean colony, located about a meter or two below the mound.”cxxix The termites use the thermal properties of the soil and architecture of the mound to provide a system for the movement of air that passively facilitates heating, cooling, and air quality, all in one. It achieves this not by one technologic monolith, but by smart architecture that harbors wind energy to ventilate the nest. Gould and Gould (2007) summarize the advanced technology of termite mounds:

"Heat generated by the termites and their gardens in the core of the nest flows into the collecting pipes and rises in the chimneys at a rate of about five inches per minute. As this humid CO2-rich air flows up the chimneys it draws cooler air in through the cellar area under the nest, where it begins to flow up into the various chambers…The buttresses are riddled with tiny holes too small even for the termites but large enough for the warm stale air to diffuse out while cooler fresh air percolates in."cxxx

13.2.2. Applications Taking advantage of such technology is not beyond the scope of today’s technology. The design of the Eastgate Centre shopping center and office building in Harare, Zimbabwe is modeled upon the design of the termite mound. The building is “passively cooled and does not require a fuel-based air conditioning system.” Furthermore, the building saved almost $4 million on up-front costs (10% of the $35 million dollar building) by not purchasing an active ventilation air conditioning system.cxxxi Such large savings are clearly very attractive, but such improvements require large improvements on the exterior. Limited by the constraints of the CHC, however, reaching such savings would likely not be possible. Furthermore, this Tier IV, solution is one that requires consideration during major renovation. Due its early stages of development, it is highly unlikely to be appropriate for the Harvard renovations. Nevertheless, it is important for the architects and engineers to consider these ideas when designing the new building.


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A

B

Figure 13.2 – Figure A (left) is a schematic of the Eastgate Centre office building and shopping center in Harare, Zimbabwe. Many aspects of the diagramed architecture are tied to the architecture of the termite mound. Note that a large part of it involves the same ideas that natural ventilation are based on, such as the stack effect.cxxxii Figure B (right) is a schematic of the cross section of a termite mound. The living area of the mound is indicated by a dashed circle. The tall airways on top of the living area take advantage of the stack effect, as well as other design elements.cxxxiii

13.3. Biomimicry Conclusions Modeling HVAC technologies after nature’s technologies might not be the

conventional method by which to approach HVAC remodeling, but it allows for an innovative approach to the problem and, possibly, and innovative solution. A biomimetic solution would put Harvard at the forefront of HVAC technologies, likely be highly efficient, and very conservative on Greenhouse Gas emissions. Therefore, even if such solutions are not available right now, they must be considered by Harvard – both for future implementation of biomimetic solutions of Tier III and for future renovation projects.


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14. Conclusion and Recommendations After an in-depth analysis of the framework, the existing implementation, and conventional solutions for heating, ventilation, and air-conditioning (HVAC) in the Harvard River Houses (HRH), the ES96 HVAC group arrived at various conclusions. Firstly, we believe that in order to achieve Harvard’s goals of lowering Greenhouse Gas (GHG) emissions and minimizing cost for the upcoming HRH renovations, Harvard must rethink HVAC, in general, as discussed in detail in section 1.2. The main problem that HVAC solutions treat is thermal comfort and air quality (TCAQ). Highlighting the problem as TCAQ, instead of HVAC, ensures that both air quality and thermal comfort are treated as equally important. Furthermore, we may arrive at some solutions that lay outside the realm of HVAC – at least as simplistically thought of as controlling temperature and moving air – such as the use of plants to improve air quality. Hand in hand with rethinking problem, it is also important to rethink the solutions. To facilitate attaining Harvard’s goals and developing a robust system that is flexible enough to handle the changing landscape of the HRH, Harvard must consider a component-based system, as discussed in section 1.2.2. Such a system replaces the common, monolithic approach to HVAC systems and allows for greater flexibility and better results. It will allow Harvard, for example, to combine an implementation of the solutions discussed in this report to varying degrees, matching the needs of each HRH as necessary. The flexibility of such a system is greatly increased if a control network is developed that allows to adjust the degrees to which each system treats TCAQ at any particular time. Throughout the 80-yr lifespan of the HRH it is expected that conditions will change, and such a network will allow the TCAQ solutions to change with those needs. Having understood the improved method of analyzing HVAC, the group evaluated various possible solutions. The group discovered that good metrics by which to analyze solutions are cost (maintenance and initial investment), GHG emissions, flexibility, the requirement for major renovations, and the level of technological development of the solutions. Furthermore, it was necessary to compare the innovative solutions against the conventional baseline system that the group assumed would be implemented in a standard renovation (described in detail in section 3). By doing a cost-benefit analysis of the novel solutions, we were able to select a few ones that we believe Harvard would be interested in implementing so as to reach its goals. Next, the renovation requirement metric allowed us to categorize solutions within four tiers based on the two axes of current feasibility and major renovation requirement. This four-tier categorization is provided in figure 1.3 in section 1.2.4 and shows how the solutions analyzed fit into the categories.

The most feasible solutions for implementation during the current renovations are those of tier I and II: natural ventilation (section 5), passive heating (section 6), ground source heat pumps (section 8), and plants (section 9). To better understand the benefits of these solutions, we compared the solutions to each other and to the baseline system in terms of relative cost savings (initial investment and maintenance cost averaged over 30 years) vs. relative GHG savings, with the baseline system at the origin. The result of this can be seen below in Figure 14.1.


73

Figure 14.1 – A semi-log plot of cost savings vs. GHG savings. The positive y-axis corresponds to economic savings, and the positive x-axis corresponds to GHG savings (i.e. lowered GHG emissions). The cost is the 30-yr average of capital investment and maintenance cost. This figure allows for a better understanding of at what cost these four technologies lower Harvard’s GHG emissions. As can be seen, the group estimates increased savings in both cost and GHG emissions for natural ventilation and passive heating. Plants and ground source heat pumps require extra investment, but provide greater GHG savings. Based on this, the HVAC group recommends that Harvard consider all these four solutions found to be appropriate for implementation.

We have also found that some solutions, while not feasible now, are likely to become feasible within the 80 year lifespan of the HRH and may be implemented before the next major renovation project. These are the solutions of Tier III and include the use of phase change materials (section 10) and passive ventilation technologies modeled after avian respiration (section 13.1). Changes in the economic landscape and further technological development of these solutions are necessary for their feasibility to increase.

While the solutions of tier IV may become feasible in the future makes their implementation during the current renovation period or before the next major renovation cycle unsuitable. The details of the analysis of such solutions are provided in this report, but the group does not believe that they should be a part of the current renovation project. Within the newly-considered framework of component-based solutions that treat TCAQ, Harvard can not only choose a single solution that we have recommended, but implement a variety of solutions including, but not limited to, those recommended in this report.


74

Furthermore, it will likely be most beneficial for Harvard to combine these novel solutions with conventional solutions in varying degrees. We believe that this will allow for the most robust and efficient system, leading to a minimization of cost and greenhouse gas emissions, while providing Harvard with flexibility throughout its future.


75

References

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Cambridge. 19 Feb. 2010. Presentation. ii Needham. “Steve Needham: ES96 Client Presentation” iii Berenshteyn, Yakov, Alissa Cooperman, Andrew Dane, Hernan Gatpandan, Alice Wang, and Pawel Zimoch. A

Comparison of Cooling Techniques for Harvard Undergraduate Dormitories. Engineering Sciences 96 Final Report. Harvard College -- School of Engineering and Applied Sciences, 11 May 2009. 25 Jan. 2010

iv "Navigation for a Sustainable Future." ASHRAE Research Strategic Plan 2005-2010. ASHRAE.org: Research. American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), 17 Apr. 2006. Web. 21 Apr. 2010. <http://www.ashrae.org/technology/page/39>.

v Halmen, Jason. "Interview with Jason Halmen of DCNE." Personal interview. 14 Apr. 2010. vi Needham. “Steve Needham: ES96 Client Presentation” vii "An Introduction to Indoor Air Quality." Indoor Air Quality (IAQ). US Environmental Protection Agency, 27

Oct. 2009. Web. 22 Apr. 2010. <http://www.epa.gov/iaq/ia-intro.html>. viii Arda, B; Pullukcu, H; Yamazhan, T; Sipahi, OR; Tamsel, S; Demirpolat, G; Korkmaz, M. 2009. “Prevalence of

Echinococcus granulosus detected using enzyme immunoassay and abdominal ultrasonography in a group of students staying in a state dormitory in Turkey.” Turkish Journal of Medical Sciences 39 (5): 791-794.

ix Barskey, AE; Glasser, JW; LeBaron, CW. 2009. “Mumps resurgences in the United States: A historical perspective on unexpected elements.” Vaccine 27 (44): 6186-6195.

x Stein-Zamir, C; Shoob, H; Abramson, N; Tallen-Gozani, E; Sokolov, I; Zentner, G. 2009. “Mumps outbreak in Jerusalem affecting mainly male adolescents.” Eurosurveillance 14 (50): 12-14.

xi Kak, V. 2007. “Infections in confined spaces: Cruise ships, military barracks, and college dormitories.” Infectious Disease Clinics of North America 21 (3): 773

xii Spengler, John D., and Demetrios J. Moschandreas. "Indoor Air Pollution." Editorial. Environment International 1982: 3-4. Web of Science. Web. 21 Apr. 2010.

xiii "The Biomimicry Institute: '06 to '09." The Biomimicry Institute. Web. 21 Apr. 2010. <http://www.biomimicryinstitute.org/>.

xiv Massachusetts. City of Cambridge. Cambridge Historical Commission. Ordinances and General Laws. Web. 3 May 2010. <http://www.cambridgema.gov/~Historic/ordinances.html>.

xv Eldrenkamp, Paul. "Presentation by Paul Eldrenkamp of Byggmeister." Engineering Sciences 96. Harvard University, Cambridge. 4 Mar. 2010. Presentation.

xvi Berenshteyn et al Engineering Sciences 96 Final Report. 2009 xvii ASHRAE Fundamentals Handbook. American Society of Heating, Refrigerating and Air-Conditioning

Engineers, Inc., Atlanta, 2001. (qtd in Berenshteyn et al Engineering Sciences 96 Final Report. 2009) xviii Cook, David R. "Humidity and Temperature Perception." NEWTON. Argonne National Laboratory, 21 May

2002. Web. 22 Apr. 2010. <http://www.newton.dep.anl.gov/askasci/wea00/wea00133.htm>. xix "Technical FAQs." ASHRAE: Technology. American Society of Heating, Refrigerating and Air-Conditioning

Engineers (ASHRAE). Web. 22 Apr. 2010. <http://www.ashrae.org/technology/page/336>. xx ibid xxi ibid xxii ibid xxiii ibid xxiv ASHRAE Fundamentals Handbook 2001 (qtd in Berenshteyn et al Engineering Sciences 96 Final Report. 2009) xxv ibid xxvi "Technical FAQs." ASHRAE: Technology xxvii ibid xxviii Needham. “Steve Needham: ES96 Client Presentation” xxix Halmen. "Interview with Jason Halmen of DCNE.” 2010 xxx Manning and Garron, Interview with Robert Manning and Doug Garron, directors of University Operations

Services xxxi Manning and Garron


76

xxxii ibid xxxiii Interview with Arnold Stein, retired residential air conditioning contractor xxxiv Berenshteyn et al Engineering Sciences 96 Final Report. 2009 xxxv Email from Robert Manning xxxvi Halmen. “Interview with Jason Halmen of DCNE.” 2010 xxxvii ibid xxxviii ibid xxxix ibid xl ASHRAE Fundamentals Handbook 2001 (qtd in Berenshteyn et al Engineering Sciences 96 Final Report. 2009) xli AAON H2/V2, 10000 cfm Air Handler Installation and Operation Manual/Product Data Sheet xlii UOS Building Summary for Winthrop House 2006-2009, www.uos.harvard.edu xliii Control of CO2 in a naturally ventilated classroom, Griffiths and Eftekhari xliv Halmen. "Interview with Jason Halmen of DCNE” xlv Carrier 42V series Fan Coil product data sheet xlviFan Tech KHP 20000 Data Sheet xlvii ibid xlviii ibid xlix Heat & Cold: Mastering the Great Indoors, Donaldson & Nagengast, 1994 (ASHRAE), p. 19 l Ibid. li Building Ventilation: The State of the Art, Edited by Santamouris & Wouters, 2006 pp. 16-35 lii “Mixed Mode Ventilation: Finding the Right Mix,” McConahey, ASHRAE Journal, September 2008. liii http://www.weather.com/weather/wxclimatology/monthly/graph/02139, Accessed on 4/21/10 liv “Does the frequency of occurrence psychometric chart for occupied hours have more than 30% of the time

between 60 F and 80 F and less than 70% relative humidity?” lv Modified from Passive and low energy cooling of buildings, Givoni, 1994 p. 41 lvi WB/MCDB: Wet Bulb: 75.00 F, 57.77 RH%; DP/MCDP: Dew Point 72.00 F, 76.63 RH% lvii PsyCalc (http://www.linric.com/psyc_98.htm) Linric Company, collection of 1997 ASHRAE Climatic Design

Information lviii Commonwealth of Massachusetts 2007 Air Quality Report, MassDEP

(http://www.mass.gov/dep/air/priorities/07aqrpt.pdf) lix Natural Ventilation in the Urban Environment: Assessment and Design, Edited by Ghiaus and Allard 2005, p.

202 lx McConahey, Mixed Mode Ventilation lxi Givoni, p. 38 lxii McConahey, Mixed Mode Ventilation lxiii ibid lxiv http://www.designbuilder.co.uk/ lxv Givoni, p. 43 lxvi Ghiaus, p. 141 lxvii http://www.windfinder.com/windstats/windstatistic_boston_logan_airport.htm#. Compare with results of

PsyCalc from Linric lxviii Based on discussion with Eliot House manager Francisco Medeiros lxix Santamouris & Wouters, Chapter 8, p. 224-226. lxx Santamouris & Wouters, Chapter 7, thoroughly addresses Hybrid Ventilation techniques. lxxi CEC (Commission of the European Communities) (1991) Solar Architecture in Europe: Design, Performance,

and Evaluation, Prism Press, Dorset, UK lxxii Handbook on low-energy buildings lxxiii http://www.nfrc.org/documents/SolarHeatGain.pdf lxxiv http://www.energy.gov/insulationairsealing.htm lxxv Handbook on low-energy buildings lxxvi ibid lxxvii ibid


77

lxxviii Berenshteyn et al Engineering Sciences 96 Final Report. 2009 lxxix Handbook on low-energy buildings lxxx http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp lxxxi http://isites.harvard.edu/fs/docs/icb.topic710320.files/HU-Grnhse-FY07Report.pdf lxxxii http://www.durisolbuild.com/Webdocs/Durisol%20Material%20Properties.pdf lxxxiii http://www.durisolbuild.com/material.shtml lxxxiv Interview with Robert Manning lxxxv http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp lxxxvi http://buildingconstruction.editme.com/files/ICFCompositesUnitCosts/US-Price.pdf lxxxvii Handbook on low-energy buildings lxxxviii Blackstone geothermal wells - lessons learned http://green.harvard.edu/theresource/tech-

prod/documents/GSHP_lessons_3-08.pdf lxxxix ibid xc http://www.uos.harvard.edu/blackstone/tour/ xci Blackstone geothermal wells - lessons learned xcii ibid xciii http://www.uos.harvard.edu/blackstone/geothermal_well.pdf xciv Handbook on low-energy buildings xcv Berenshteyn et al Engineering Sciences 96 Final Report. 2009 xcvi http://www.degreedays.net/#generate xcvii http://isites.harvard.edu/fs/docs/icb.topic710320.files/HU-Grnhse-FY07Report.pdf xcviii http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp xcix http://quotes.ino.com/exchanges/contracts.html?r=NYMEX_NG c http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp ci Ec 10 lecture on carbon tax values by Professor Mankiw cii http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930073077_1993073077.pdf ciiihttp://www.ted.com/index.php/talks/kamal_meattle_on_how_to_grow_your_own_fresh_air.html civ http://www.amazon.com/2-Pots-Areca-Palm-

Seedlings/dp/B0035W1108/ref=sr_1_8?ie=UTF8&s=garden&qid=1271728820&sr=1-8 cv http://www.fantech.net/hrv_erv.htm, Interview with Arnold Stein, April 19th cvi http://intraweb.stockton.edu/eyos/energy_studies/content/docs/FINAL_PAPERS/8B-4.pdf cvii http://energain.co.uk/Energain/en_GB/news_events/recent_releases.html cviii Siddens, Scott. Refrigerant Systems Make for Zone HVAC Control. cix Goetzler, William. “Variable Refrigerant Flow Systems.” ASHRAE Journal, April 2007. American Society of

Heating, Refrigerating and Air-Conditioning Engineers, Inc. cx Siddens. Refrigerant Systems Make for Zone HVAC Control. cxi Goetzler “Variable Refrigerant Flow Systems.” 2007 cxii Halmen. “Interview with Jason Halmen of DCNE.” 2010 cxiii ibid cxiv Siddens. Refrigerant Systems Make for Zone HVAC Control. cxv Goetzler “Variable Refrigerant Flow Systems.” 2007 cxvi Halmen. “Interview with Jason Halmen of DCNE.” 2010 cxvii Allard, Francis and Cristian Ghiaus. Natural Ventilation in the Urban Environment. cxviii ibid cxix ibid cxx Roth, Kurth. “Double-skin Façades.” ASHRAE Journal, October 2007. American Society of Heating,

Refrigerating and Air-Conditioning Engineers, Inc. cxxi Allard, Francis and Cristian Ghiaus. Natural Ventilation in the Urban Environment. cxxii ibid cxxiii ibid cxxiv "The Biomimicry Institute: '06 to '09."


78

cxxv "Air Flow System, Sacs Provide Efficient Gas Exchange: Birds." Ask Nature - the Biomimicry Design Portal. The

Biomimicry Institute. Web. 17 Apr. 2010. cxxvi "Eastgate Centre Building." Ask Nature - the Biomimicry Design Portal. The Biomimicry Institute. Web. 17

Apr. 2010. <http://www.asknature.org/product/373ec79cd6dba791bc00ed32203706a1>. cxxvii Ritchison, Gary. "Avian Respiration." BIO 554/754: Ornithology. Eastern Kentucky University. Web. 17 Apr.

2010. <http://people.eku.edu/ritchisong/birdrespiration.html>. cxxviii Cambridge Historical Commission. Ordinance and General Laws cxxix Turner, Scott. "Mounds as Organs of Extended Physiology." Scott Turner's Research. SUNY College of

Environmental Science and Forestry. Web. 22 Apr. 2010. <http://www.esf.edu/efb/turner/termite/termhome.htm>.

cxxx Gould, James L; Gould, Carol Grant. 2007. Animal architects: building and the evolution of intelligence. New York: Basic Books. 324. (qtd in "Ventilated Nests Remove Heat and Gas: Mound-building Termites." Ask Nature)

cxxxi "Ventilated Nests Remove Heat and Gas: Mound-building Termites." Ask Nature - the Biomimicry Design Portal. The Biomimicry Institute. Web. 17 Apr. 2010. <http://www.asknature.org/strategy/8a16bdffd27387cd2a3a995525ea08b3>

cxxxii <http://2.bp.blogspot.com/_2vzGharhETE/SSDIdDxjzSI/AAAAAAAAABE/qZ34tOqOX_8/s400 /termite1.jpg> 05 May 2010. cxxxiii <http://inhabitat.com/files/eastgateharare.jpg> 05 May 2010.

Appendices

1 Useful Natural Ventilation Tables from (2008) ASHRAE

Journal Paper1

Keyword

Ventilation

Natural

Ventilation

Mixed Mode

Systems

Naturally

Ventilated

Spaces

Naturally

Conditioned

Spaces

Typical Indoor

Environment

Method for

Thermal

Comfort

Adaptive

Model of

Thermal

Comfort

Definition

"The process of supplying air to or removing air from a space for the purpose of

controlling air contaminant levels, humidity or temperature within the space."

"... ventilation provided by therma!, wind, or diffusion effects through doors, w'm-dows, or other intentional openings in the building."

"... refers to a hybrid approach to space conditioning that uses a combination of nat-

ural ventilation from operable windov\/s (either manually or automatically controlled),

and mechanical systems that include air-distribution equipment and refrigeration

equipment for cooling,"

"... shall be permanently open to and within 8 m (25 ft) of operable wall or roof

openings to the outdoors, the openable area of which is a minimum of 4% of the net

occupiable floor area.... "

"The means to open required operable openings shall be readily accessible to the

building occupants whenever the space is occupied."

"... are those spaces where the thermal conditions of the space are regulated primar-

ily by the occupants through opening and closing of windows."

".. a simplified graphical method for determining the comfort zone that may be used

for many typical appiications...

'The range of operative temperatures presented in Figure 5,2.1.1 [from Standard 55-

2004] are for 80% occupant acceptability."

"... Field experiments have shown that occupants' thermal responses in [occupant

controlled naturally conditioned spaces] depend in part on outdoor climate and may

differ from thermal responses in buildings with centralized HVAC systems primar-

ily because of the different thermal experiences, changes in clothing, availability of

control, and shifts in occupant expectations.

"... Allowable indoor operative temperatures for spaces that meet these criteria may

be determined from Figure 5.3 [from Standard 55-2004]."

Standard 62,1-2007,

Section 3

Standard 62.1-2007,

Section 3

Mixed Mode Web Site of

the Center for the Built

Environment at the University

of California, Berkeley^

Standard 62.1-2007,

Sections 5,1.1, 5.1.2

Standard 55-2004,

Section 5.3

Standard 55-2004,

Section 5.2

Standard 55-2004,

Section 5.3

Table I: Definitions related to natural ventilation.

The potential for natural ventilation as a viable means of

comfort conditioning often re]ies on mixed mode approaches

that use natural ventilation for most ofthe year, but re]y on me-

ehanieal eoo]ing tor peak loading conditions. Commonly mixed

mode systems are categorized as one ofthe following:'

• Concurrent (same spaee. same time);

• Chatigeover (same space, different times); or

• Zoned (different spaces, same time).

Additionally, it is neeessary to define exactly how natural

ventilation is used. Windows often are provided as a user ame-

nity within fiilly air-conditioned spaees to give the oeeupants

a connection to the outdoors and some level of control over

increased localized ventilation. This case is not covered by any

code or standard, as the natural ventilation is not necessary for

human health or comfort. In the case where natural ventilation

is used as a primary ventilation or cooiing mechanism, it is

necessary to differentiate between natural ventilation for indoor

air quality (lAQ) or natural ventilation for controlling humid-

ity or temperature, as Standard 62.1 -2007 governs the former,

while Standard 55-2004 addresses the latter. As the focus of

Standard 62.1-2007 is indoor air quality, "naturally ventilated

space" per the standard's Seetion 5,1.1 is primarily meant to

fulfill the IAQ purpose alone.

Therefore, the use of natural airflows to condition spaces

September 2008

falls under the definition of "naturally conditioned spaces"

per Standard 55-2004. This document defines two sets of cri-

teria for acceptable thermal eonditions, one for typical indoor

environments (using the laboratory-based PMV-PPD model)

and another optional method for naturally eonditioned spaces

(using the field-based adaptive thermal eomfort model). A

eomparison of Figures 5.2.1.1 and 5.3 in Standard 55-2004

show that: "in naturally eonditioned spaees, occupants will

tend to accept a wider range of indoor comfort temperatures as

compared to those limits established as acceptable for typical

indoor environments."

A number of explicit limitations in Standard 55-2004 reduce the

applicability ofthe extended eomfort range to only those periods

of time when no mechanical conditioning is provided (Tuhle 2).

Tlierefore, eoncuiTent mixed mode systems .should meet the PMV-

PPD based typieal indoor environment comfort criteria throughout

the year. Zoned and changeover systems should do so wherever

and whenever mechanical conditioning is provided.

Design Guidance, or Lack Thereof

Standard 55-2004 states that "no specific guidance for natu-

rally conditioned spaces is included in this standard." Standard

62.1-2007. Section 5.1, explicitly states that "an engineered

natural ventilation system when approved by the authority

ASHRAE Journal 37

Figure 1: Useful Definitions Related to Natural Ventilation

1“Mixed Mode Ventilation: Finding the Right Mix”, By Erin McConahey, P.E.

Figure 2: LEED Considerations for Natural Ventilation

2 Natural Ventilation Formula Appendix

Note: the numerical values used in the following formulas are detailed in the Assumptions Appendix

2.1 Single Sided Ventilation

The formula used to determine the cubic feet per minute (CFM) available from windows basedsolely on single-sided ventilation effects is defined as:

Total[CFM ] = 0.5 ∗Aw ∗ veff ∗ ConvFactor

Where:Aw represents the windows area (empirically measured).

ConvFac is defined as the conversion factor between meter/second and ft./min ( 196.85ft/min

1m/s).

The 0.5 term represents the fact that roughly half of the opening is for air in, half for air out.veff is defined by the following expression:2

veff = (c1v2r + c2H ∗∆T + c3)1/2

where c1 ≈ 0.001, c ≈ 0.0035, c3 = 0.01 are window opening, buoyancy, and wind constants, vr[m/s]is the mean wind speed, H[m] is the height of the opening, and ∆T is the mean temperature dif-

2de Gidds and Phaff, 1982, quoted in Natural Ventilation, Ghiaus and Allard, p. 136

ference between inside and outside.

2.2 Buoyancy-Driven Stack Ventilation3

Flow caused by wind only: Q = CvAU

where Cv ≈ 0.5 for perpendicular winds (windows) and 0.25 for diagonal winds (chimneys), A isthe area of inlet opening, and U is the properly calculated wind speed.

As defined by ASHRAE (Fundamentals 2009 section 24.3) adjusted U (UH), is given by: UH =Umet

�δmetHmet

�amet�H

δ

�a

where the various δ and a terms are used to convert from wind speed measured at different condi-tions at the meteorological station (airport) to the actual site (urban environment).

Flow Caused by Thermal Forces Only: Q = CDA

�2g∆HNPL(Ti − T0)/Ti

where CD is a discharge coefficient for opening, and ∆HNPL is the height from the midpoint oflower opening to NPL, and Ti and To are indoor and outdoor temperatures, respectively.

3 Natural Ventilation Assumptions Appendix

All temperature distributions made use of the trigonometric function described in last year’s (2009)HVAC report for quantifying daily average temperatures.

As a reference comfort indoor temperature, 70 F was chosen.

The mean airspeed used was 14 mph, based on the Boston data in the PsyCalc98 program.

There was no attempt to determine windward versus leeward specific natural ventilation, since thatlevel of specificity it best handled using computer software (such as DesignBuilder).

The height of the bottom of the first floor window was estimated at 1.5 m, or roughly 5 ft. Windowson subsequent stories were assumed to be 10 ft. above that, up to the fifth floor.

All window sizes were assumed to be uniform at having 38.5” x 23.5” (6.3 sq. ft.) open-ablearea.

For calculating the adjusted wind speed from the 14 mph, the parameters for meteorological datawere assumed to be terrain category 3, with a = 0.14 and delta = 900 ft., and the site terrain wascategory 2, with a = 0.22, δ = 1200 ft. (Outlined in section 24.3 in 2009 ASHRAE Fundamentals,and 16.3 in 2005 ASHRAE Fundamentals).

The overall height of Winthrop was estimated at 50 ft., with maximum chimney height being at 60ft.

3All formulas in this section from AHSRAE Fundamentals 16.13 (2009) unless otherwise stated

Cv for windows was 0.5, on the lower end of ASHRAE guidelines for perpendicular wind (2009Fundamentals 16.13). Cv for chimneys was 0.25, on the low end of the ASHRAE guidelines fordiagonal wind (Ibid.).

NPL of Winthrop was .6 of the height. Based on the arguments from the literature, the NPL isusually at the midpoint of the structure or higher, and with the chimneys that should push theNPL a bit higher as well. Though the higher the NPL the better, it was reasoned that .6 was likelyto be within the right regime, and if anything underestimate stack effects.

CD was chosen as 0.65 for both windows and chimneys. There is a wealth of literature aboutthe complexities of determining this properly, and it was determined that if a natural ventilationstrategy is pursued, the standards in ASHRAE 16.13 (2009 Fundamentals) would be satisfied,namely that there would be other openings, and unidirectional flow could be assumed.

Each entryway is estimated to have 50 people (based on assuming 500 total occupants and counting10 entryways). Requiring 20 cfm/person equates to 1000 cfm per entryway.

4 Geothermal Well Appendix

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etur

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Com

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Con

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Coo

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igh

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arva

rd C

olle

ge

Figure 3: GSHP operating at Blackstone under heating and cooling modes

ES 96 2010 HVAC Final Report

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