Sweetwater Spectrum Community Zero Net Energy Monitoring … · 2020. 1. 2. · Sweetwater Spectrum is a planned community of four single-story 3,250 ft² residences and a 2,990 ft²

PG&E’s Emerging Technologies Program ET13PGE1031

Sweetwater Spectrum Community

Zero Net Energy Monitoring Performance

Evaluation Report

ET Project Number: ET13PGE1031

Project Managers: Peter Turnbull & Mananya Chansanchai Pacific Gas and Electric Company Prepared By: Davis Energy Group 123 C St Davis, CA, 95616

Issued: December 19, 2014

Copyright, 2014, Pacific Gas and Electric Company. All rights reserved.

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ACKNOWLEDGEMENTS

Pacific Gas and Electric Company’s (PG&E) Emerging Technologies Program is responsible for this project. It was developed as part of Pacific Gas and Electric Company’s Emerging Technologies – Technology Assessments program under internal project number ET13PGE1031. Davis Energy Group conducted this technology evaluation for Pacific Gas and Electric Company with overall guidance and management from Anna LaRue at Resource Refocus LLC and Loralyn Perry at Energy Matters. For more information on this project, contact Peter Turnbull at [email protected].

LEGAL NOTICE

This report was prepared for Pacific Gas and Electric Company (PG&E) for use by its employees and agents. Neither Pacific Gas and Electric Company nor any of its employees and agents:

(1) makes any written or oral warranty, expressed or implied, including, but not limited to those concerning merchantability or fitness for a particular purpose;

(2) assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, process, method, or policy contained herein; or

(3) represents that its use would not infringe any privately owned rights, including, but not limited to, patents, trademarks, or copyrights.

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ABBREVIATIONS AND ACRONYMS

AHRI Air-Conditioning, Heating, & Refrigeration Institute

CEC California Energy Commission

DC Direct current

DDC Direct digital control

DEG Davis Energy Group

DOE Department of Energy

EER Energy efficiency ratio

HERS Home Energy Rating System

HSPF Heating seasonal performance factor

HVAC Heating, ventilation, and air conditioning

kW Kilowatt

kWh Kilowatt-hour

LEED Leadership in Energy and Environmental Design

PV Photovoltaic

RTD Resistance temperature device

SEER Seasonal energy efficiency ratio

SHGC Solar heat gain coefficient

TDV Time dependent valuation

ZNE Zero net energy

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FIGURES Figure 1: Monthly electricity consumption and PV generation –

Residential Building ........................................................ 16

Figure 2: Monthly electricity consumption and PV electricity

generation – Community Building .................................... 17

Figure 3: Distribution of annual electricity consumption by end use

– Residential Building ..................................................... 17

Figure 4: Distribution of annual electricity consumption by end use

– Community Building .................................................... 18

Figure 5: Daily total energy usage and PV generation – Residential

Building ........................................................................ 19

Figure 6: Daily total energy usage and PV generation –

Community Building ....................................................... 20

Figure 7: Annual electricity use by end use compared to Title-24

software estimates – Residential Building ......................... 21

Figure 8: Measured vs. simulated monthly electricy use by end use

– Residential Building ..................................................... 22

Figure 9: Annual electricity use by end use compared to Title-24

software estimates – Community Building ........................ 23

Figure 10: Measured vs. Simulated monthly electricity use by end

use – Community Building .............................................. 23

Figure 11: EER* vs. Outdoor Temperature – Residential Building .... 25

TABLES Table 1: Building Efficiency Specifications ................................. 6

Table 2: Sweetwater Project Monitoring System History ......... 10

Table 3: Measurement Points – Residence Building #3 ........... 11

Table 4: Measurement Points – Community Building ............... 12

Table 5: Sensor Specifications ................................................. 13

Table 6: Percentage of Space Conditioning Load Supplied by

Radiant Delivery ......................................................... 16

Table 7: Measured Heat Pump Efficiency – Residence

Building 3 ................................................................... 25

Table 8: Measured Heat Pump Efficiency – Community

Building ...................................................................... 26

Table 9: Annual Electric Loads vs. PV Generation .................... 26

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CONTENTS

ABBREVIATIONS AND ACRONYMS _____________________________________________ II

FIGURES _______________________________________________________________ III

TABLES ________________________________________________________________ III

CONTENTS _____________________________________________________________ IV

EXECUTIVE SUMMARY _____________________________________________________ 1

INTRODUCTION __________________________________________________________ 4

BACKGROUND __________________________________________________________ 4

EMERGING TECHNOLOGY __________________________________________________ 5

Thermal Envelope .............................................................. 5 Mechanical Systems ........................................................... 5 Lighting and Appliances ...................................................... 8 Photovoltaic System ........................................................... 9

ASSESSMENT OBJECTIVES __________________________________________________ 9

TECHNOLOGY EVALUATION ________________________________________________ 9

TECHNICAL APPROACH/TEST METHODOLOGY _________________________________ 10

Field Testing of Technology .................................................... 10

Test Plan .............................................................................. 11

Measurements and Monitoring System Commissioning .......... 11

Instrumentation Plan ............................................................. 13

Data logger Specifications ................................................. 13 Sensor Types and Specifications......................................... 13

RESULTS_______________________________________________________________ 15

Data Analysis ........................................................................ 15

Occupant Feedback .......................................................... 15 Overall Building Performance ............................................. 15

EVALUATIONS __________________________________________________________ 21

Comparison of Predicted to Measured Site Energy ..................... 21

Residential Building 3 ....................................................... 21 Community Building ......................................................... 22 Projected TDV Savings ...................................................... 24

Heat Pump Performance Analysis ............................................ 24

Approach to Zero Net Site Energy Use ..................................... 26

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CONCLUSIONS & RECOMMENDATIONS _______________________________________ 27

APPENDIX _____________________________________________________________ 29

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EXECUTIVE SUMMARY

PROJECT GOAL

The primary objective of this project was to evaluate how closely the Sweetwater

Spectrum buildings achieved the design goals of attaining zero net energy

performance over the course of 12 months, and to compare original modeling

estimates to actual monitored data for the occupied buildings.

PROJECT DESCRIPTION

Sweetwater Spectrum is a planned community of four single-story 3,250 ft²

residences and a 2,990 ft² community center located in Sonoma, CA (CA Climate

Zone 2). The facility is designed to serve adults with autism spectrum disorders.

Each residence has four occupants in individual suites, with a shared kitchen, dining

and living-space. The buildings were completed in December, 2012, with full-time

occupancy starting January, 2013. A large portion of the architectural design was

structured with sensitivity to the occupants in mind, as was the location and

acoustical requirements of the mechanical equipment.

The community center includes a large community room, exercise room, kitchen,

office, and art supply room. In addition to supplying community building loads, the

meter for this building serves external loads including spas, swimming pool, well

pumps, a greenhouse facility and exterior site lighting.

The buildings were initially intended to exceed Title 24 by at least 25% and to

achieve LEED™ Gold certification. The owners elected not to pursue LEED

certification at the conclusion of the project. As a cost-saving measure, the size of

the solar photovoltaic (PV) arrays described in the construction documents was

reduced by 50%.

High performance building features include 2x6 walls with R-21 wall insulation, R-48

ceiling insulation, high performance windows, and slab-on-grade construction with

in-floor radiant heating and cooling delivery and supplemental forced air delivery.

Each building is provided with two Daikin “Altherma” water-to-air heat pumps (13

SEER/ 11 HSPF) which supply hot and chilled water to the radiant and forced-air

distribution systems. Though it is likely that single heat pumps would have met the

heating and cooling loads, the redundancy serves as a hedge against equipment

failure. A demand-controlled ventilation system is also described in the construction

documents. The buildings are “all electric”, that is no natural gas was used for space

conditioning or water heating.

The Sweetwater Spectrum project was initiated as one of several zero net energy

demonstrations and provided the opportunity to evaluate the use of innovative HVAC

system solutions in a managed residential care facility. One of the problems in such

facilities is efficiently delivering comfort to multiple spaces, which this design has

overcome by providing zoned radiant floor heating and cooling and also forced air

distribution.

Two buildings were monitored between August 1, 2013 and July 31, 2014: one of the

four residential buildings (Building 3) and the community building. A total of 31 data

points were collected for the residential building and 23 for the community building.

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PROJECT FINDINGS/RESULTS

As originally designed, the residence and community buildings were intended to

meet the zero net energy goal of generating as much energy as required by the

buildings on an annual basis. Cost-cutting measures reduced the area of the PV array

by 50%. For the year that the project was monitored, the community building PV

system generated slightly more electricity than the building required, but only 35%

of the electricity consumed when the outbuilding loads were included. These loads

include spas, swimming pool, well pumps, greenhouse and exterior site lighting. The

PV system for Residence Building 3 generated 53% of the total energy consumed by

that building. Had the size of the array for the residential building not been reduced

it is likely it would have achieved the ZNE goal.

An EnergyPro evaluation using inputs updated to as-built conditions indicates

approximately 25% Time Dependent Valuation (TDV) savings relative to the 2008

standards. TDV estimates of energy savings using measured data were not

completed for this all-electric project.

Site energy use for the residential building was 70% higher than predicted by the as-

built EnergyPro evaluation. The higher than predicted energy use for the residential

buildings is mostly attributed to lighting and plug loads, which are much higher than

assumed by the initial model for typical residential occupancies. The type of

occupancy of the residential buildings is not well reflected by the assumptions used

in the Title 24 ACM Manual for residential occupancies. The four different buildings

each serve a different spectrum of autism and require different levels of care. The

occupants of Building 3 require significant care, and the building is staffed 24 hours

per day. High internal gains from lighting and plug loads in the residential building

contributed to its high cooling energy use. Issues related to the commissioning of

HVAC systems also may have been responsible for increased energy use.

The community building (excluding outbuilding loads) site energy use was 83% lower

than predicted. This building is used for daytime activities and houses Sweetwater

staff offices. The lower than predicted energy use for the community building may

also have been a consequence of Title 24 assumptions that are inconsistent with the

types of use in practice, as well as its good design.

PROJECT RECOMMENDATIONS

The high plug and lighting loads seen in the residential building should be

investigated and could be reduced by better use of controls and operation

management. Outbuilding loads should also be evaluated. Replacement of the

swimming pool pump with a variable speed pump should be strongly considered.

Control of the HVAC fans in both the residential and the community buildings was

seen to be inconsistent, varying between no use and continuous operation over the

monitoring period. Control improvements have been addressed during the post

occupancy commissioning period, which spanned from July – November 2014. Fans

should be controlled to provide the proper amounts of ventilation in accordance with

ASHRAE Standards 62.2 (residential) and 62.1 (community building). Demand

controlled ventilation using CO2 sensors is not an option under Standard 62.2, but

may be appropriate the residential buildings given the high occupancy density and

full time staffing. There are also opportunities to use the existing equipment (fans

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and dampers) to reduce cooling energy use by providing nighttime cooling with

outside air and to provide humidity control.

Controlling humidity would allow more cooling to be delivered from the radiant

system, which would improve heat pump performance.

Reasons for the excessive fan operation were identified through the commissioning

process. Maintenance staff has made corrections to control functions for the fans and

replaced faulty sensors. Since then, temperature and humidity control has been

improved.

Performance of the Daikin Altherma heat pumps was reasonably consistent with

performance ratings, and in some cases better. Though only one of the two heat

pumps provided per building would likely meet the load requirements, having

redundant equipment may prove valuable in the future. The building owners could

experiment with shutting one of the units off, or alternating their use, to extend the

lifetime of both units. (Building managers indicated that they do alternate operation

of the pairs of heat pumps.)

This project provides a good template for the design of similar facilities that strive to

achieve zero net energy use. Development of cost studies and occupant feedback on

comfort would better inform future applications of this design strategy.

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INTRODUCTION This report describes the results of a year-long evaluation of two occupied buildings

located in the Sweetwater Spectrum community, a home for adults with autism. This

project monitored one residential building that is representative of the four identical

residential buildings, as well as a community center building. The all-electric

buildings were designed with numerous energy efficiency measures to reduce

heating, cooling, and water heating loads, improve the efficiency of the HVAC

systems, and to offset usage by utilizing on-site renewables (PV and solar water

heating).

BACKGROUND Sweetwater Spectrum is a planned community of four single-story 3,250 ft²

residences and a 2,990 ft² community center located in Sonoma, CA (CA Climate

Zone 2). The facility is designed to serve adults with autism spectrum disorders.

Each residence has four occupants in individual suites, with a shared kitchen, dining

and living-space. The buildings were completed in December, 2012, with full-time

occupancy starting January, 2013. A large portion of the architectural design was

structured with sensitivity to the occupants in mind, as was the location and

acoustical requirements of the mechanical equipment.

The community center includes a large community room, exercise room, kitchen,

office, and art supply room. In addition to supplying community building loads, the

meter for this building serves external loads including spas, swimming pool, well

pumps, a greenhouse facility and exterior site lighting.

The Sweetwater Spectrum project was initiated as one of several zero net energy

demonstrations and provided the opportunity to evaluate the use of innovative HVAC

system solutions in a managed residential care facility. One of the problems in such

facilities is efficiently delivering comfort to the multiple residential zones, which this

design addressed by providing zoned hydronic radiant heating as well as forced air

distribution.

The buildings in this all-electric community were initially intended to exceed Title 24

by at least 25% and to achieve LEED™ Gold certification. The owners elected not to

pursue LEED certification at the conclusion of the project. As a cost-saving measure,

the size of the solar photovoltaic (PV) arrays described in the construction

documents was reduced by 50%.

Prior work supported by PG&E related to this project included three tasks, (1)

completion of a design review, (2) development of a commissioning plan, and (3)

preparation of a monitoring plan. The design review and monitoring plan were

completed1. As a result of construction delays and other issues, the commissioning

task was cancelled. The monitoring plan developed in the first phase of work was

implemented as this separate project beginning in May 2013.

1 Interim Report: Sweetwater Spectrum Community. Submitted to the Benningfield Group and PG&E, December 31, 2012.

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EMERGING TECHNOLOGY The design applied several high performance building features, including 2x6 walls

with R-21 wall insulation, R-48 ceiling insulation, high performance windows, and

slab-on-grade construction with in-floor radiant heating and cooling delivery and

supplemental forced air delivery. Each building is provided with two Daikin

“Altherma” water-to-air heat pumps (13 SEER/ 11 HSPF) which supply hot and

chilled water to the radiant and forced-air distribution systems. Though it is likely

that single heat pumps would have met the heating and cooling loads, the

redundancy serves as a hedge against equipment failure. A demand-controlled

ventilation system is also described in the construction documents. The buildings are

“all electric”, that is no natural gas was used for space conditioning or water heating.

Details of the efficiency measures included in the completed buildings are listed in

Table 1, along with a comparison to a baseline building built to minimum 2008 Title-

24 standards. No information on incremental costs is available for this project.

Following is detailed information on individual measures that were selected.

THERMAL ENVELOPE

Walls and Roof: The exterior wall construction is 2x6 framing, 24 inches on center.

The stud cavities were filled with fiberglass batt insulation. The cavity between the

roof joist members was sprayed with foam and then insulated with fiberglass to

provide a tight seal. Ceiling finishes were installed directly to the underside of the

joists, and the use of spray foam avoided the need to vent the ceiling cavity as

would otherwise be required by code. Most of the roof is covered with standing seam

metal roofing (AEP Span Cool Weathered Copper), which has a solar reflectance of

0.34 and an emittance of 0.87

Slab: It is a mandatory measure to insulate the perimeter of slab foundations that

incorporate radiant heating to an R-value of 5. These buildings were insulated at the

perimeter to R-7.5, and also at the underside to R-10. As a result the distribution

efficiency of the radiant system should be greater than 90%, with few losses going to

the ground.

Windows: The Pella windows installed at the residence buildings have a U-value of

0.29 and a solar heat gain coefficient (SHGC) of 0.28.

Air Tightness: Given the slab foundation and use of spray foam insulation at the roof,

the structure probably exceeds the current Title 24 assumption of 5 ACH50, however

no testing was performed. Since ducts were installed within the joist bays and below

the foam sprayed roof deck, most duct leakage is likely to the inside of the building

enclosure. However, no duct test data are available; duct testing was not a

mandatory measure under the 2008 standards.

MECHANICAL SYSTEMS

Heating and Cooling:

Because radiant floor distribution systems can utilize relatively cool water (~110°F)

for heating and relatively warm water (~60°F) for cooling (compared to forced air

distribution), the heat pumps do not need to work as hard as conventional heat

pumps due to the reduced “thermal lift” between the evaporator and the condenser.

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Unfortunately, the primary-secondary loop configuration used in the Sweetwater

design does not take full advantage of this characteristic. Primary-secondary piping

is common in high temperature gas heat systems where boiler efficiency is not highly

dependent on water temperature, but can be detrimental to heat pump systems for

which efficiency is reduced by high condensing temperatures. In this case, the

variable speed capability of the heat pumps can adjust to varying loads and they are

capable of supplying hot and chilled water directly to the slabs, eliminating the need

for additional primary-secondary loop pump and improving efficiency.

Table 1: Building Efficiency Specifications

BUILDING COMPONENT

EFFICIENCY FEATURE BASE CASE

ZNE DESIGN - "AS-BUILT"

NOTES

ENVELOPE

Roofing Asphalt Shingle, standard

Standing seam metal (Reflectance 0.36

emmitance 0.87) & built-up

Prem comp shingle

Roof (attic) Vented attic, R-30 blown

No attic, joist bays insulated to R-47.8

Combination of

spray foam and fiberglass batt

Radiant Barrier Yes No

Wall (Exterior) 2x4 16"o.c., R-13 batt

2x6 24"o.c., cavities

filled with R-21 fiberglass batt insulation

Quality Insulation

Installation Verified (HERS)

No No

Foundation Type Slab-on-grade, no insulation

Slab-on-grade, R-7.5

foam at edge, R-10 foam underneath

5” slab with ½”

tubing installed 6” on-center

Exposed Thermal Mass N/A Slab floor Marmoleum

and carpet tile floor coverings

Envelope Leakage Verified (ACH50) (HERS)

No (5.0 assumed) Not tested

Windows (U-factor / SHGC)

U-value = 0.40

SHGC = 0.40

U-value = 0.29 SHGC = 0.28

HERS Measures Tight ducts

Radiant heating and cooling distribution with some forced air

deliver through ducts in semi-conditioned space

Duct leakage not tested but ducts are

mostly within the thermal envelope

HVAC SYSTEM

System Type Single speed heat pump

Two 4.5 ton air-to-water variable speed heat pumps per building

Daikin Altherma EBLQ054BA6VJU

Cooling 13 SEER / 10 EER 13 SEER 13 is nominal

value for Title

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BUILDING COMPONENT



NOTES

24 compliance

Furnace (AFUE) / Heat Pump (HSPF)

7.7 14.0 HSPF (from CF-1R)

11 is nominal

value for Title 24 compliance

Duct Location Attic

In joist bays and

below foam insulation applied to underside of roof deck

DUCT LEAKAGE - TESTED <

6% LEAKAGE (HERS) YES Not tested

Duct Insulation (R-value) R-6 R-4.5 (in conditioned space)

From specs

Verified Refrigerant Charge (HERS)

No No Factory charged

Verified Adequate Airflow (HERS)

No No

Verified Fan Watt/cfm < 0.58W/cfm (HERS)

No No

Nighttime Ventilation Cooling

None None Possible but

not implemented

Mechanical Ventilation Exhaust fan, continuous

Demand-controlled

using air handlers & dampers

WATER HEATING

Water Heating System Standard 50gal Gas, 0.62 EF

Solar thermal with

electric resistance backup, 0.9 EF

Solar DHW: Solar Fraction

N/A 68% (from Title 24 CF-1R)

Solar used on

residence buildings only

Distribution Type Kitchen Pipes Insulated

Recirculation, all hot water pipes insulated

Pump runs continuously

LIGHTING

LED% / CFL% / Incandescent

0% / 35% / 65% Linear fluorescent + LED

Controls None Vacancy sensors

OTHER ENERGY

EFFICIENCY FEATURES

EnergyStar Appliances None

Energy Star

dishwasher, refrigerator, and clothes washer

Cooking Gas Induction Electric

Clothes Dryer Electric Electric

Fireplace, yes/no & fuel No No

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BUILDING COMPONENT



NOTES

type

Home Energy Management System

N/A Siemens

% Better than 2008 Base Case

N/A 66.4%

ON-SITE GENERATION

Solar Photovoltaic System

None

Residences: 8.6 kW DC

Community Bldg: 14.4 kW DC

PV size reduced

by 50% from original specifications

The variable speed capability of the Altherma heat pump and coupling to massive

radiant heating/cooling panels makes it possible to eliminate a storage tank to

prevent short-cycling, which simplifies the system and saves cost. Also, efficiency

increases as the speed is reduced. It is difficult to develop standardized performance

ratings for variable speed air-to-water heat pumps with hydronic distribution because

the performance varies with speed, and the water temperatures supplied can vary

significantly depending on the application and load conditions. In 2012 Daikin came

to agreement with the California Energy Commission (CEC) on performance values

appropriate for the Altherma, settling on a SEER of 13 and an HSPF of 112. The Title

24 compliance calculations submitted for the project list an SEER of 13 and an HSPF

of 14.

Fresh Air Ventilation: Each building is provided with a central ventilation system that

consists of a constant volume fan coil that is ducted to all of the major rooms. The

residential fan coil is specified as 1825 CFM and the community building unit is

specified as 3500 CFM. Each coil is connected to the hydronic system so that

ventilation air can be tempered to avoid comfort problems, and each is “demand

controlled” by a CO2 sensor. Dampers were provided to allow mixing of recirculated

and outside air.

Water Heating: Closed loop solar water heaters serve each of the residential

buildings. Primary water heating for each building is provided by electric resistance

storage type water heaters. Hot water recirculation pumps are controlled to operate

continuously.

LIGHTING AND APPLIANCES

The 2008 California Title 24 standards for residential lighting require a certain

percentage of high efficacy fluorescent fixtures in kitchens, but allow either

fluorescent fixtures or incandescent fixtures with vacancy sensors (or dimmers in

some rooms) in other locations. The specifications for the Sweetwater buildings call

for a combination of T8 linear fluorescent fixtures for general illumination and LED

fixtures for spotlights and exterior lighting. Some of the lights are controlled on

2 Final Evaluation Report - Proposed Compliance Option for: Altherma Air-to-Water Source Heat Pump for the Residential Energy Efficiency Standards. California Energy Commission staff report # CEC‐400‐2011‐010‐SF, March 2012.

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automatic dimmers. Except for the swimming pool heater, no natural gas is used on

site.

PHOTOVOLTAIC SYSTEM

The shed-type standing seam metal roofs are designed to face nearly due south,

presenting a near ideal orientation and surface for mounting the PV modules. Initial

plans show the residence buildings equipped with 72 240 W modules each, and 120

240 W modules mounted on the community building. The sizes of the PV arrays

ultimately mounted on the buildings were reduced by 50%, resulting in an 8.6 kW

array installed on each of the resident buildings and a 14.4 kW array installed on the

community building.

ASSESSMENT OBJECTIVES The main objective of this project is to evaluate how closely the Sweetwater project

achieved the zero net energy design goal, and to compare modeled energy use to

the measured energy use. While the project has aggressive energy efficiency goals,

the 50% reduction from the original PV surface area significantly reduced the

likelihood of achieving zero net energy. However, the project also offers the unique

opportunity to assess the performance of air-to-water heat pumps with zoned radiant

heat distribution applied to communal living establishments such as retirement

homes and limited care facilities. The combination of high performance building

enclosure, high efficiency HVAC system (as used in these buildings), and

appropriately sized PV systems could represent a best practices pathway to zero net

energy in these building types.

TECHNOLOGY EVALUATION This project provided monitoring and evaluation to determine whole building

performance for the residential building and the community building. Specific end

uses including HVAC systems (heat pump units, circulating pumps, and fan coils),

water heating energy, and PV energy delivered to the buildings and the grid were

also monitored. Miscellaneous end uses such as lighting, appliances, and plug loads

were measured by subtracting HVAC end uses from whole house power, which was

measured at the main panel. When it was discovered that the panel for the

community building included extraneous power for the spa and swimming pool

equipment and greenhouse, monitoring of these circuits was added.

In order to qualify the results, outdoor temperature and indoor temperatures at

multiple locations were also measured. Monitoring of water flows and temperatures

also enabled the calculation of energy delivered by the heat pumps, as well as heat

pump efficiency. A detailed list of monitoring points is included in the Test Plan

section which follows.

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California uses a Time Dependent Valuation (TDV) based definition of zero net

energy. The TDV approach assigns higher values to energy used during high

demand periods. To evaluate energy use using this definition, a prior project report3

used a somewhat complex process to estimate the time dependent value of

measured energy consumption and to compare it to the TDV energy predicted by the

compliance model. Compliance models calculate TDV energy by applying a

conversion factor to site electric (and gas) energy use that considers the societal

value at each hour of the day. This prior method related TDV values for the climate

zone to particular temperature conditions in the weather file, created bins of site

energy use corresponding to those weather conditions, and applied TDV multipliers

to the binned data. Results were then compared to the TDV quantities reported by

the energy compliance model (EnergyPro). As the Sweetwater project did not

approach the ZNE goal, due to the reduction in size of the PV systems and the large

outbuilding loads, this exercise was deemed to be unnecessary. Instead, measured

site energy use was directly compared to predicted site energy use obtained from the

Title 24 compliance software (EnergyPro).

TECHNICAL APPROACH/TEST METHODOLOGY

FIELD TESTING OF TECHNOLOGY Long-term monitoring followed by data analysis was employed to identify building

and system performance over the 12 month evaluation period. Power monitors were

used to measure true RMS power for the end uses listed in Tables 2 and 3. HVAC

energy delivery was measured using water side measurements (from flow and

temperature differences), which were then used to calculate seasonal efficiency of

the heat pumps. Water heating system performance was also measured using flows

and temperature differences for the residential building only, including contributions

from the solar water heater. Electricity use by the community building electric water

heater is included in building miscellaneous loads. Gas energy use by the swimming

pool heater was not monitored.

Monitoring data was carefully reviewed and analyzed in an effort to respond to the

research goals of this project. Table 2 chronicles the problems encountered with the

monitoring equipment, the site visits, and any changes that may have affected the

monitoring data.

Table 2: Sweetwater Project Monitoring System History

DATE DESCRIPTION

6/28/13 The data logger for the community building was non-responsive.

7/2/13 – 7/12/13 Inspected the community center logger and

found that channels were blown, possibly a result of an accidental short caused by the project electrician. Replaced the logger with a

3 ”Cottle House Zero Net Energy Home Monitoring” (2014) - http://www.etcc-ca.com/reports/cottle-house-zero-net-energy-home-monitoring

11


DATE DESCRIPTION

borrowed unit and resumed monitoring.

7/15/13 Discovered that the Dent PowerScout 18 power

monitors were reporting instantaneous, not averaged power. Also discovered that the Dent was not correctly communicating via the Modbus link to the data logger, resulting in out of sync time stamps. Remedial actions were taken.

9/18/13 Replaced the borrowed logger with the repaired original logger.

Due to ongoing commissioning efforts by the controls contractor which produced

irregular system operation as verified by indoor temperature readings, as well as the

loss of data in July, the project team pushed back the official start of monitoring

reporting. Accordingly, the effective monitoring period was shifted to cover August 1,

2013 to August 1, 2014.

TEST PLAN Each of the two buildings, Residence Building #3 and the community center building,

were equipped with data loggers and modems for continuously collecting, storing,

and transferring data via cellular communications. Sensors were scanned every 15

seconds, and data was summed or averaged (as appropriate) and stored in data

logger memory every 15 minutes.

MEASUREMENTS AND MONITORING SYSTEM COMMISSIONING

Short term measurements were made on site to verify readings from the various

sensors, including temperature sensors and power monitors. More detailed

information on commissioning procedures is provided in the Interim Report. Table 3

and 4 list the measurement points that were monitored on a continuous basis for the

residence and community buildings, respectively.

Table 3: Measurement Points – Residence Building #3

Name Description Location Sensor Type

TAI1 Temp, air, indoor, Zone 1 Near Z1 T-stat RTD, 4-20ma

RHI1 RH, air, indoor, Zone 1 "" RH, 4-20ma








TWFS Temp, Water, Entering Fan Coil Mechanical Room Immersion TT

TWFR Temp, Water, Leaving Fan Coil Mechanical Room Immersion TT

TWZS Temp, Water, Entering Zones Mechanical Room Immersion TT

TWZR Temp, Water, Leaving Zones Mechanical Room Immersion TT

TWH Temp, Water, DHW Supply Mechanical Room Immersion TT

12


TWCS Temp, Water, Cold Water Supply Mechanical Room Immersion TT

TWSE Temp, Water, Entering Solar Mechanical Room Immersion TT

TWSL Temp, Water, Leaving Solar Mechanical Room Immersion TT

FWZ Flow, Floor Zones Mechanical Room Flow meter

FFC Flow, Fan Coil Mechanical Room Flow meter

FWS Flow, Solar System Mechanical Room Flow meter

FWD Flow, Domestic Hot Water Mechanical Room Flow meter

EHSE Energy, Total House Main Service Panel Power Meter

EPV Energy, PV Main Service Panel Power Meter

EGEN Energy, Generated to Grid Main Service Panel Power Meter

SRP Status, Recirc Pump Mechanical Room Relay

EHP1 Energy, Heat Pump Mechanical Room Power Meter

EFC Energy, Fan Mechanical Room Power Meter

EP7 Energy, Pump Mechanical Room Power Meter

EP1 Energy, Pump (Zone) Mechanical Room Power Meter

EWH Energy Water Heater Mechanical Room Power Meter

ESP Energy Solar Loop Pump Mechanical Room Power Meter

Table 4: Measurement Points – Community Building

Name Description Location Sensor Type

TAO Temp, air, outdoor NorthFace RTD, 4-20ma

RHO RH, air, outdoor "" RH, 4-20ma








TWFS Temp, Water, Entering Fan Coil Mechanical Room Immersion TT

TWFR Temp, Water, Leaving Fan Coil Mechanical Room Immersion TT

TWZS Temp, Water, Entering Zones Mechanical Room Immersion TT

TWZR Temp, Water, Leaving Zones Mechanical Room Immersion TT

FWZ Flow, Floor Zones Mechanical Room Flow meter

FFC Flow, Fan Coil Mechanical Room Flow meter

EHSE Energy, Total House Main Service Panel Power Meter

EPV Energy, PV Main Service Panel Power Meter

EGEN Energy, Generated to Grid Main Service Panel Power Meter

EHP4 Energy, Heat Pump Mechanical Room Power Meter

EFC Energy, Fan Mechanical Room Power Meter

EP9 Energy, Pump Mechanical Room Power Meter

EP3 Energy, Pump (Zone) Mechanical Room Power Meter

EOB Energy, Outbuildings Main Service Panel Power Meter

13


INSTRUMENTATION PLAN

DATA LOGGER SPECIFICATIONS

Data Electronics Model DT-800 data loggers were used to collect and store

monitoring data. Analog inputs were single-ended type (all referenced to ground).

Digital inputs were used for power monitors and status signals; high speed counter

inputs were used with water flow meters. The data loggers were provided with an

RS232 communications interface and battery backup. They also included integral

cold junction circuitry for direct measurement of Type T thermocouples. The table

below provides detailed specifications for the data logger.

Manufacturer: dataTaker, Inc.

Model: DT-85

Analog Inputs: Up to 32 single-ended

Digital Inputs: 8 bidirectional + 4 high speed counters (100 kHz)

Analog Accuracy: 0.1%

Memory: 128 MB flash, approx. 10,000,000 data points

Communications: Ethernet, USB, RS232/485, Modbus

SENSOR TYPES AND SPECIFICATIONS

Standard specifications for the sensor types used are listed in Table 5: 5. Sensor

selection was based on functionality, accuracy, cost, reliability, and durability. Signal

ranges for temperature sensors correspond approximately to listed spans.

Table 5: Sensor Specifications

TYPE APPLICATION MFG/MODEL SIGNAL SPAN ACCURACY

RTD Outdoor temp and RH

RM Young 41372VF 0-10V -50 – 150°F ±1F

0 – 100% +1%RH

RTD Indoor temperature / RH

General Eastern

MRHT 3-2-1 4-20 mA

50 - 90ºF ±1.5F

0 – 100% +2%RH

RTD Duct temperature / RH – HRV

Vaisala HMD60Y 4-20 mA -4 - 176ºF ±1.5F

0 – 100% ±2%RH

RTD Duct temperature / RH – Air Handler

General Eastern

MRHT 3-2-1 4-20 mA

32 - 132ºF ±1.5F

0 – 100% ±2%RH

RTD Indoor temperature – Attic, Crawlspace

LM34 10 mV /°F

50 - 90ºF ±1F

Type T Thermocouple

Surface / Air temperatures

Omega -99 to 500ºF 0.4%

24VAC Relay Fresh air Damper

Status, zone damper status

Omron Dry contact

n/a n/a

14


Power monitor

All circuits except those listed below

Dent Instruments PowerScout 18

Modbus Varies by circuit

±0.5%

Power monitor

PV power to grid and outbuildings (pool, etc.)

Watt Node WNB-3-D-240-PV

Pulse CTA/40 ±0.5%

Pressure Transducer

Air Pressure SETRA 4-20mA 0-0.5inWC ±1%FS

Gas Pulse Meter

Water Heater IMAC Pulse 10 pulses/cuft

15


RESULTS The following data summaries are presented for the 12 month period between

August 1, 2013 and July 31, 2014.

DATA ANALYSIS

OCCUPANT FEEDBACK

No direct feedback was provided by occupants. Building managers initially expressed

concerns about indoor temperatures that were outside comfort expectations in some

zones. This was corrected over a period of time by Siemens, the contactor for the

direct digital controls (DDC) system.

OVERALL BUILDING PERFORMANCE

MONTHLY AND ANNUAL ENERGY USE

The energy performance of the two Sweetwater buildings was evaluated to

determine site energy use and energy supplied to the grid. In addition, measured

site energy use for HVAC and water heating was compared to site energy use

predicted by EnergyPro. Modifications were made to the EnergyPro input files that

were used for compliance (obtained from the mechanical engineer) to update wall

and roof U-values and window U-value and SHGC. An HSPF of 14 was used in the

compliance assumptions; in the updated as-built model, this was corrected to the

HSPF 11 value that the Energy Commission stipulated should be used for Altherma

heat pumps.

Figure 1 and Figure 2 display monthly electricity consumption for the Residence

Building 3 and the Community Building, respectively, for each major end use. PV

production is shown as negative values below the x-axis. In Figures 2 and 3 monthly

net electricity is displayed by the solid line in the graph. Figures 3 and 4 show the

breakdown of annual electricity end use for the two buildings.

For the residential building, 53% of total site electricity usage was offset by the 8.6

kW DC rated PV system over the 12 month monitoring period. For the community

building the 14.4 kW DC PV system offset 35% of the total annual electricity use.

However, if outbuilding loads are excluded, the PV system generated about 200 kWh

more than the 19,723 kWh consumed by the community building.

Observations of monitoring data suggest that adjustments were being made to the

HVAC systems throughout the year. In particular, there was inconsistency in the

operation of fans and in temperature control settings that were likely occurring as

control systems were being commissioned and adjusted.

Cooling system operation was observed in both buildings from August through

October of 2013 and from April through July of 2014, with some overlapping of

heating and cooling, particularly in shoulder months. Heating and cooling were

supplied by both the radiant floors and the fan coils. The percentages that radiant

delivery contributed to heating and cooling demand are listed in Table 6.

16


Table 6: Percentage of Space Conditioning Load Supplied by Radiant

Delivery

Building Heating Cooling

Residential 85% 33%

Community 67% 58%

FIGURE 1: MONTHLY ELECTRICITY CONSUMPTION AND PV GENERATION – RESIDENTIAL BUILDING

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

2,500

Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Jul-14

Mo

nth

ly E

lect

rici

ty C

on

sum

pti

on

(kW

h)

PV Space Cooling Space Heating Plug Loads+Misc Water Heating Monthly Net

17


FIGURE 2: MONTHLY ELECTRICITY CONSUMPTION AND PV ELECTRICITY GENERATION – COMMUNITY BUILDING

FIGURE 3: DISTRIBUTION OF ANNUAL ELECTRICITY CONSUMPTION BY END USE – RESIDENTIAL BUILDING

-3,000

-2,000

-1,000

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

Aug-13 Sep-13 Oct-13 Nov-13 Dec-13 Jan-14 Feb-14 Mar-14 Apr-14 May-14 Jun-14 Jul-14Mo

nth

ly E

lect

rici

ty C

on

sum

pti

on

(kW

h)

PV Space Cooling Space Heating Plug Loads+Misc Outbuildings Monthly Net

18


FIGURE 4: DISTRIBUTION OF ANNUAL ELECTRICITY CONSUMPTION BY END USE – COMMUNITY BUILDING

DAILY ENERGY USE

Error! Reference source not found.5 and 6 display daily electricity consumption

or the residential and community buildings, respectively. Average daily electricity

consumption for the residential building was 64.2 kWh and for the community

building was 154.8 kWh.

These figures show very little seasonal variation, which reflects the fact that HVAC

energy use only represents 35% and 19% of total energy use for the residential and

community buildings, respectively. Also, fan energy for both fresh air ventilation and

heating/cooling constituted 20% of HVAC energy use in the residential building and

9% of HVAC energy use in the community building.

MECHANICAL SYSTEM OBSERVATIONS

Each building is served by two heat pumps. The pairs of heat pumps were monitored

using a single current transducer, so it was not possible to determine from the data

whether one or two were operating at any given time, but the control strategy

outlined in the drawings suggests they are staged. Monthly heat pump energy

consumption was apportioned by multiplying heat pump electrical use by the fraction

of measured heating or cooling delivered for each month. Monitored water

temperatures were used to determine whether the heat pumps were operating in

heating or cooling mode at any given time.

The fan coil in the residential building was cycled coincident with the heat pump part

of the year and was out of commission most of February 2014. The community

building fan coil did not operate at all August through November 2013 or in March of

2014, but ran continuously through part of the remainder of the year.

19


Construction documentation indicates that the fans would be “demand controlled”

using a CO2 sensor. This type of ventilation control is typically used in commercial

buildings, but is inconsistent with the residential ventilation standard, ASHRAE 62.2,

which prescribes continuous or intermittent ventilation at rates that are a function of

the building conditioned floor area and number of bedrooms. It was not clear from

the available documentation what specific control strategy would be adopted for the

fans and for control of the dampers which mix outdoor and return air, and the fan

control strategy appeared to vary through the year with some continuous operation

and some cycling with heat pump operation. For this analysis fan energy was

apportioned to heating or cooling, depending on the season.

Water heating was only monitored as a separate end use for the residential building.

The residential water heating system consists of two flat-plate collectors

(approximately 48 ft2 total) connected to an 80 gallon storage tank with an included

heating element for supplemental heat. A closed glycol loop transfers heat from the

collectors to the storage tank via a heat exchanger integrated with the tank. A pump

that recirculates hot water to the fixtures was apparently operated continuously.

Water heater electrical use in Building 3 averaged 9 kWh per day. Hot water use

ranged from a low of 41 gallons per day in July 2014 to a high of 140 gallons per day

in August 2013, and averaged 92 gallons per day.

If standby loss from the solar storage tank and recirculation piping losses are

considered as part of the hot water load, the calculated annual contribution of the

solar water heater to total water heating energy use was 25%. Including energy

used by the solar collector pump, the effective energy factor (hot water delivered

divided by electrical energy input in Btu’s) averaged 1.33 over the year, and ranged

from 0.86 to 2.55. Given the hot water load and collector area, this result is not

surprising.

FIGURE 5: DAILY TOTAL ENERGY USAGE AND PV GENERATION – RESIDENTIAL BUILDING

20


FIGURE 6: DAILY TOTAL ENERGY USAGE AND PV GENERATION – COMMUNITY BUILDING

21


EVALUATIONS

COMPARISON OF PREDICTED TO MEASURED SITE ENERGY

RESIDENTIAL BUILDING 3

EnergyPro files were obtained from the project mechanical engineer for Residence Building 3

and the community building. Upon review it was found that inputs for wall and roof R-

values, and window U-value and solar heat gain coefficients were inconsistent with as-built

conditions. In general, these adjustments would improve the modeled building performance.

However, the compliance documents listed an HSPF value of 14 for the Altherma heat

pump, whereas the CEC ruling established an HSPF of 114. Also, the input files included a

68% solar fraction, which given the size of the collectors relative to the hot water load

appeared excessive. Instead, a value of 25%, which is consistent with what was measured,

was substituted in the EnergyPro model. The modified EnergyPro input files were used to

generate monthly estimates of site energy use for space heating, cooling, water heating,

and miscellaneous use (lighting, appliances, and plug loads). It should be recognized that

model results were not normalized to actual year weather.

Figure 7 illustrates the significant difference between energy use predicted by EnergyPro

(simulated) vs. monitored energy use for the residential building. Cooling energy use was

160% higher, heating 57% higher, and lighting and miscellaneous uses 114% higher than

predicted. Only water heating was close, at 13% lower than predicted. Overall energy use

was 70% higher than predicted.

FIGURE 7: ANNUAL ELECTRICITY USE BY END USE COMPARED TO TITLE-24 SOFTWARE ESTIMATES – RESIDENTIAL

BUILDING

4 Final Evaluation Report – Proposed Compliance Option for Altherma Air-to-Water Source Heat Pump for the Residential Energy Efficiency Standards. CEC‐400‐2011‐010‐SF. March 2012.

22


There are several circumstances that explain the high usage relative to the Title 24

residential compliance model results. The compliance model calculates internal heat gain

from people, lights, and appliances by assuming 20,000 Btu/day for each dwelling unit plus

15 Btu/day for each square foot of conditioned floor area. Building 3 houses residents who

require around-the-clock staff engagement. Therefore, each building is occupied by 32

people in each 24-hours period, far more than a typical residence of similar size. Lastly,

HVAC systems were not fully commissioned during the majority of time the building was

monitored.

Figure 8 compares measured and simulated end uses for the residential building on a

monthly basis. Cooling and heating energy use varies seasonally as expected in both cases,

but the magnitudes are significantly different. Overall, lighting, plugs, and other

miscellaneous uses are responsible for the greatest magnitude in the discrepancy between

measured and simulated use. As noted, the type of occupancy, operating schedule, and

number of occupants helps account for this difference.

FIGURE 8: MEASURED VS. SIMULATED MONTHLY ELECTRICITY USE BY END USE – RESIDENTIAL BUILDING

COMMUNITY BUILDING

The community building site energy use was also considerably different than what was

estimated by EnergyPro, but with significantly less energy used than was predicted by the

model. Figure 10 compares monitored and simulated energy use for all end uses except the

outbuildings. The outbuildings are included on the meter for the building, but since they are

not considered in the Title 24 calculations this energy use was not shown in the Figure 10

comparison. Excluding the outbuildings, the community building alone used 19,723 kWh

over the one year period, 83% less than predicted by the model. The outbuildings, which

include the swimming pool, spa, welcome center, and greenhouse, used 36,780 kWh.

The model predicted high fan energy use (13,402 kWh) for the commercial building which,

as for the residential building was allocated to heating and cooling in proportion to the

respective loads. Monitored fan energy use was only 707 kWh. If modeled fan energy were

substituted for the measured value, the discrepancy between measured and simulated

energy use would fall from 83% to just 18%. Since much of the heating and cooling is

Measured Simulated

23


Measured Simulated

delivered from the radiant floor, the Title 24 model would tend to over predict fan energy

use in this case.

FIGURE 9: ANNUAL ELECTRICITY USE BY END USE COMPARED TO TITLE-24 SOFTWARE ESTIMATES – COMMUNITY

BUILDING

Figure 10 compares the distribution of energy use for measured vs. simulated data by

month. For the reason described above, outbuilding energy use was not included in these

graphs. Again, the high fan energy assumption in the Title 24 model is largely responsible

for the relatively high heating and cooling energy in the simulated data.

FIGURE 10: MEASURED VS. SIMULATED MONTHLY ELECTRICITY USE BY END USE – COMMUNITY BUILDING

24


PROJECTED TDV SAVINGS

Using the corrected EnergyPro Version 5 input files, TDV energy savings of 26.2% and

23.5% were calculated for the residence and community buildings, respectively. Given these

margins, the buildings would likely comply under the 2013 standards, though this analysis

was not completed.

HEAT PUMP PERFORMANCE ANALYSIS The key emerging technologies utilized in the Sweetwater project are the air source heat

pumps coupled to radiant distribution systems that provide the majority of heating and a

significant amount of cooling (as seen in Table 6). There are some challenges to identifying

the performance of the heat pumps from the data collected and comparing measured data

to manufacturer’s rated conditions as well as to efficiencies of other equipment types.

In the absence of an AHRI test procedure for air source

heat pumps, the CEC issued an evaluation report (cited

above in Footnote 4) that established performance values

for use in completing compliance calculations for the

Altherma, prescribing a SEER of 13 and HSPF of 11.

European Standard EN14511 was used to determine a COP

under similar rating conditions as used for air-to-air heat

pumps, based on a leaving water temperature of 95°F and

an outdoor temperature of 44°F. As described by

Francisco5, the AHRI test method for HSPF applies three

different temperature conditions (17°F, 35°F, and 45°F),

and takes into account defrost cycle losses and electric

resistance heating needed to maintain comfort during

defrost cycles and under outdoor temperature conditions

that require supplemental heating. The CEC used the

range of COP’s provided by Daikin to choose a COP of 4.2, which when converted to HSPF

using the method from the standards6, yields the HSPF of 11. Because Standard EN14511

does not include an SEER test method, the current federal minimum SEER value of 13 was

somewhat arbitrarily assigned.

In theory, air-to-water heat pumps with radiant distribution should perform well because of

the relatively low temperatures required for heating and high temperatures required for

cooling when used with radiant distribution. The floor serves to provide a very large heat

transfer surface area compared to what is typically found in finned coils, allowing more

moderate temperatures to be used in meeting heating and cooling needs. The resulting

moderate evaporator (in cooling) and condenser (in heating) temperatures mean “thermal

lift” is reduced and compressors in these systems should not have to work as hard to raise

or lower the temperature of the heat transfer medium (air or water). Other factors include

lower power required by pumps vs. fans, the variable speed capability of the Altherma

which should result in improved efficiency at lower speeds, and the elimination of the need

for electric resistance heating for defrost cycles.

5 Francisco, P., L. Palmiter, D. Baylin (2004). Understanding Heating Seasonal Performance Factor for Heat Pumps. Proceedings, 2004 ACEEE Summer Study. 6 HSPF = 3.2 x COP – 2.4

Typical Daikin Altherma Heat Pump

(Source: Davis Energy Group photo)

25


In an effort to identify correlations between heat pump performance and outdoor

temperature, the “application EER” (EER*)for the residential building was calculated using

the equation below and plotted as shown in Figure 11.

EER* = Qdel / (Ehp + Epump)

Where: Qdel = rate of cooling energy delivered in kBtu/hr

Ehp = heat pump electricity demand in kW

Epump = pump electricity demand in kW

The data show no clear trends; in fact the EER appears to be rising instead of falling with

increasing outdoor temperature. The wide scatter is likely a result of operation at a variety

of speeds and part load conditions. Since a single circuit serving both heat pumps was

monitored it was not possible to distinguish whether one or both were operating at any

given time.

To calculate seasonal performance values, heating and cooling energy supplied were divided

by heat pump energy for both buildings, resulting in the values listed in Tables 7 and 8. To

account for all related energy uses, performance values are shown with and without pumps

and fans. HSPF’s were calculated using the Title 24 standards formula for ground source

heat pumps (see footnote 5).

FIGURE 11: EER* VS. OUTDOOR TEMPERATURE – RESIDENTIAL BUILDING

Table 7: Measured Heat Pump Efficiency – Residence Building 3

Components COP HSPF EER

HP only 6.9 19.6 16.6

HP + Pumps 5.8 16.1 14.5

HP+ Pumps & Fans 4.9 13.4 11.3

26


Table 8: Measured Heat Pump Efficiency – Community Building

Components COP HSPF EER

HP only 6.2 17.5 16.8

HP + Pumps 4.5 12.1 12.6

HP+ Pumps & Fan 4.3 11.3 11.1

When including pump energy, the averaged measured seasonal EERs are not far from the

13 SEER rated value but the averaged HSPFs are significantly higher than the CEC rating of

11. The lower heat pump performance seen for the community building may be a result of

greater part load operation, and possibly excessive pump power. Flow rates were seen to be

greater than the recommended 3 gpm per ton generally specified.

A study of another Altherma air-to-water heat pump completed under a Building America

project7 found full load COPs averaging above 4 at an outdoor temperature of 45°F and a

leaving water temperature of 94°F, close to manufacturer’s rated performance at these

conditions. The average seasonal COP was 4.18.

APPROACH TO ZERO NET SITE ENERGY USE Table 9 lists total electrical energy use for each building and separately lists the energy use

of the community building with (total) and without the outbuilding loads included

(community building only). These results show that, excluding the outbuilding loads, the

community building is effectively achieving zero net performance on a site energy basis.

Had the PV system on the residence building not been decreased in size by 50%, it is likely

that it too would have achieved zero net energy.

Table 9: Annual Electric Loads vs. PV Generation

Building/Load

Energy

Use

PV

Generation

PV

Contribution

Residential Building 23,424 12,386 53%

Community Building (only) 19,724 19,942 101%

Community Building (total) 56,504 19,942 35%

7 See http://www.nrel.gov/docs/fy14osti/60135.pdf

27


CONCLUSIONS & RECOMMENDATIONS The 50% reduction in the size of the PV system ruled out the possibility of achieving zero

net energy use for the residential building, but excluding the loads for the pool, spas,

greenhouse, and well pumps, the community building generated about 200 kWh more than

it used for the year. Doubling the output of the community building PV system would have

resulted in it providing about 70% of the annual electricity consumed by the building

including the outbuilding loads. The well pumps and greenhouse were not part of the design

process and not initially considered part of the facility loads.

With updated inputs to reflect as-built conditions, the TDV savings calculated using

EnergyPro Version 5 showed the buildings to perform approximately 25% better than 2008

Title 24 standards. Given the step up in the 2013 code, the buildings evaluated would

probably still comply.

A comparison of monitored performance to the predicted site energy use from the Title 24

compliance model simulations indicated much higher measured energy use for the

residential building and much lower measured use for the community building than

predicted by the simulations. The high use for the residential building stems from the type

of occupancy, the high number of occupants, and 24 hour staffing, all of which are not

characteristic of the assumptions used by the compliance model for single family homes. As

low-rise residential buildings the buildings would not qualify as “non-residential” under the

standards, as would a health care facility. The high plug and lighting loads indicate high

internal gains and hence higher cooling loads than for typical residences. Equipment that

had not been fully commissioned also accounted for the higher than modeled energy use.

Inconsistent operation of fans and other equipment that occurred with the ongoing

commissioning and efforts to adjust comfort conditions during the year may have also

contributed to measured performance that was at variance with predictions8.

Monitoring results suggest that one heat pump would be sufficient to carry the load of each

of the buildings. An analysis completed during the design review phase of this project

suggested that the pumps within the Altherma units may have sufficient capacity to deliver

water to the radiant floor piping. The variable capacity of the Altherma and the thermal

capacitance of the slab foundation would allow future designs to avoid the cost, increased

pumping energy, and probable reduced performance of the primary-secondary piping used

in the Sweetwater design.

The fan coils were intended to provide tempered fresh air supplied through slot diffusers

using demand control (CO2 sensors mounted in each of the rooms). The fans were originally

specified to be variable volume, though constant volume fans were installed. There is also a

reference to an economizer function in the design narrative.

For the residential building, fan energy could be reduced and indoor air quality improved by

installing a variable frequency drive (as originally specified) and setting the fan to deliver

constant airflow in accordance with ASHRAE Standard 62.2 (<200 cfm), with sensors used

to boost airflow when CO2 levels are elevated. The fan coil is intended to provide humidity

control. The fan coils and dampers could also be operated to provide supplemental cooling

as needed as well as provide free nighttime cooling. For the community building, the fan

should be operated to deliver fresh air in accordance with ASHRAE Standard 62.1 and

8 Performance model predictions rarely align well with measured performance.

28


similar control strategies could be used as in the residential buildings to reduce energy use

and assure comfort.

The high electric load from the outbuildings (swimming pool, spas, greenhouse, and well

pumps) should be investigated; an audit may discover ways that this load can be

decreased. One observation made during the maintenance of the monitoring equipment was

that the swimming pool pump is fixed speed. Replacing it with a variable speed pump could

reduce pumping energy substantially, particularly if the filtration schedule is adjusted to just

meet the requirements of California health regulations, and the payback period could be

very short.

In conclusion, though the residential buildings used more energy than expected for typical

residential occupancies, they may have achieved zero net energy had the originally specified

PV area been installed. Monitoring showed that the community building did produce more

energy than it consumed over the period of monitoring if the external loads (spa, pool,

greenhouse, well pumps) are excluded, despite that its PV area was also reduced by half.

Operational improvements to better control fans and replacing the swimming pool pump

with a variable speed pump are two obvious recommendations that would reduce energy

use below monitored levels. The building owners may also wish to investigate use of fans

for ventilation cooling was well as fresh air ventilation and supplemental heating and

cooling.

29


APPENDIX

Tabulated Monthly End Use Values and PV Production

Site Plan

Original System Schematic

As-Built Modifications to System Schematic

As-Built Solar Water Heating System Schematic

Altherma Performance Curves – Heating

Altherma Performance Curves – Cooling

30


Monthly End Use Values and PV Production

31


Site Plan

32


Original System Schematic from Construction Documents

33


As-Built Modifications to System Schematic

34


As-Built Solar Water Heating System Schematic

35


Altherma Heating Performance Curves – Engineering Data

0

1

2

3

4

5

6

0 50 100 150

Po

we

r (k

W)

Leaving Water Temperature (oF)

Altherma OADB=68

Altherma OADB=59

Altherma OADB=54

Altherma OADB=45

Altherma OADB=36

Altherma OADB=25

Altherma OADB=190

1

2

3

4

5

6

0 20 40 60 80

Po

we

r (k

W)

Outdoor Air Temperature (oF)

Altherma LWT=131

Altherma LWT=122

Altherma LWT=113

Altherma LWT=104

Altherma LWT=95

Altherma LWT=86

0

10

20

30

40

50

60

70

0 20 40 60 80

Cap

acit

y (k

Wb

u/h

)


Altherma LWT=131

Altherma LWT=122

Altherma LWT=113

Altherma LWT=104

Altherma LWT=95

Altherma LWT=86

0

1

2

3

4

5

6

7

0 20 40 60 80

CO

P


Altherma LWT=131

Altherma LWT=122

Altherma LWT=113

Altherma LWT=104

Altherma LWT=95

Altherma LWT=86

0

10

20

30

40

50

60

70

0 50 100 150

Cap

acit

y (k

Btu

/h)


Altherma OADB=68

Altherma OADB=59

Altherma OADB=54

Altherma OADB=45

Altherma OADB=36

Altherma OADB=25

Altherma OADB=19

0

1

2

3

4

5

6

7

0 50 100 150

CO

P


Altherma OADB=68

Altherma OADB=59

Altherma OADB=54

Altherma OADB=45

Altherma OADB=36

Altherma OADB=25

Altherma OADB=19

36


Altherma Cooling Performance Curves – Engineering Data