-
Energy Savings in MEP Systems - Building Design Course No:
M02-010
Credit: 2 PDH
Steven Liescheidt, P.E., CCS, CCPR
Continuing Education and Development, Inc. 9 Greyridge Farm
Court Stony Point, NY 10980 P: (877) 322-5800 F: (877) 322-4774
[email protected]
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37
GREENING FEDERAL FACILITIESAn Energy, Environmental, and
Economic Resource Guide for Federal Facility Managers and
Designers
Part IV
BUILDING DESIGN
SECTION PAGE
4.1 Integrated Building Design
..................................... 38
4.1.1 Passive Solar Design ....................................
40
4.1.2 Daylighting Design .......................................
42
4.1.3 Natural Ventilation
....................................... 44
4.2 Building Envelope
...................................................... 46
4.2.1 Windows and Glazing Systems................... 48
4.2.2 Insulation
........................................................ 50
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38
4.1 Integrated Building Design
The graph below suggests that the earlier design inte-gration
becomes a part of the process, the more suc-cessful the results
will be. Conversely, if a building isdesigned as usual and then
green technologies areapplied to it as an afterthought, the results
will prob-ably be poorly integrated into the overall building
de-sign objectives, and the greening strategies will likelybe
expensive to implement.
In existing buildings, opportunities for improved build-ing
design integration exist whenever a major replace-ment or
renovation of a building component or systemis being planned. For
example, if a large chiller sys-tem is to be replaced, investments
in reducing the cool-ing loads through daylighting, improved
glazing, andmore efficient electric lighting may significantly
reducethe size and cost of the new chiller. In some cases,
costsavings from the new chiller may be greater than in-vestments
in the load-reduction strategies, so the an-cillary benefits of
improved lighting and lower energyconsumption are obtained for
freeor even at a nega-tive cost.
Technical Information
Consider integrated building design strategies for allaspects of
green design: improving energy efficiency,planning a sustainable
site, safeguarding water, cre-ating healthy indoor environments,
and using environ-mentally preferable materials. Major design
issuesshould be considered by all members of the designteamfrom
civil engineers to interior designerswhohave common goals that were
set in the building pro-gram. The procurement of A&E services
should stress a
Integrated building design is a process of design inwhich
multiple disciplines and seemingly unrelatedaspects of design are
integrated in a manner that per-mits synergistic benefits to be
realized. The goal is toachieve high performance and multiple
benefits at alower cost than the total for all the components
com-bined. This process often includes integrating greendesign
strategies into conventional design criteria forbuilding form,
function, performance, and cost. A keyto successful integrated
building design is the partici-pation of people from different
specialties of design:general architecture, HVAC, lighting and
electrical,interior design, and landscape design. By working
to-gether at key points in the design process, these par-ticipants
can often identify highly attractive solutionsto design needs that
would otherwise not be found. Inan integrated design approach, the
mechanical engi-neer will calculate energy use and cost very early
inthe design, informing designers of the energy-use im-plications
of building orientation, configuration, fen-estration, mechanical
systems, and lighting options.
Opportunities
Although integrated building design can be part of al-most any
Federal facilities project, it is most suitablefor the design of
new whole buildings or significantrenovation projects. Integrated
building design is mosteffective when key issues are addressed
early in thefacility planning and design process. Opportunities
aremost easily identified through an open process of ex-ploring how
to combine low-energy-use and othergreening strategies to achieve
the best results.
DESIGN PROCESS
Implementation Phase
Leve
l
Predes
ign
Schem
atics
Devel
opment
Constr.
Do
cs
Constru
ction
Level ofDesign Effort
Opportunitiesto ImplementCost-EffectiveEnergy Savings
Source: ENSAR Group
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39
team-building approach, and provisions for integrateddesign
should be clearly presented in the statement ofwork (SOW). For
example, the SOW should stipulatefrequent meetings and a
significant level of effort frommechanical engineers to evaluate
design options.
The design and analysis process for developing inte-grated
building designs includes:
Establishing a base casefor example, a perfor-mance profile
showing energy use and costs for atypical facility that complies
with Federal energystandards and other measures for the project
type,location, size, etc.
Identifying a range of solutionsall those thatappear to have
potential for the specific project.
Evaluating the performance of individualstrategiesone by one
through sensitivity analy-sis or a process of elimination
parametrics.
Grouping strategies that are high performersinto different
combinations to evaluate performance.
Selecting strategies, refining the design, andreiterating the
analysis throughout the process.
Finding the right building design recipes through anintegrated
design process can be challenging. At first,design teams often make
incremental changes that areeffective and result in
high-performance buildingsand often at affordable costs. However,
continuing toexplore design integration opportunities can
sometimesyield incredible results, in which the design teambreaks
through the cost barrier.
Whenever one green design strategy can provide morethan one
benefit, there is a potential for design inte-gration. For example,
windows can be highly cost-ef-fective even when they are designed
and placed to pro-vide the multiple benefits of daylight, passive
solarheating, summer-heat-gain avoidance, natural venti-lation, and
an attractive view. A double-loaded centralcorridor, common in
historic buildings, provides day-light and natural ventilation to
each room, and tran-som windows above doors provide lower levels of
lightand ventilation to corridors. Building envelope andlighting
design strategies that significantly reduceHVAC system requirements
can have remarkable re-sults. Sometimes the most effective
solutions also havethe lowest construction costs, especially when
they arepart of an integrated design.
References
Wilson, Alex, et al., Rocky Mountain Institute,
GreenDevelopment: Integrating Ecology and Real Estate,John Wiley
and Sons, New York, NY, 1998.
Designing Low-Energy Buildings, Sustainable Build-ings Industry
Council, Washington, DC, 1997.
U.S. Air Force Environmentally Responsible FacilitiesGuide,
Government Printing Office, 1999.
Anderson, Bruce, Solar Building Architecture, MITPress,
Cambridge, MA, 1990.
Contacts
Green Development Services, Rocky Mountain Insti-tute, 1739
Snowmass Creek Road, Snowmass, CO81654; 970/927-3807;
www.rmi.org.
Sustainable Buildings Industry Council, 1331 H Street,NW, Suite
1000, Washington, DC 20005; (202) 628-7400, (202) 393-5043 (fax);
www.sbicouncil.org.
The Way Station (above) is an institu-tional building created
for mental health
care in Frederick, Maryland. The integrated build-ing design
used in creating it included carefulsiting, climate-responsive
building form, energy-efficient envelope design, daylighting,
passivesolar heating, cooling-load reduction
strategies,high-performance glazings, high-efficiency light-ing and
HVAC equipment, and healthy buildingdesign strategies. The net
increase in construc-tion cost for this package of measures
was$170,000, and the annual energy savings total$38,000a
return-on-investment of 22%.
Source: ENSAR Group
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40
4.1.1 Passive Solar Design
in occupied spaces and thermal mass to smooth outtemperature
fluctuations. A Trombe wall puts the ther-mal mass (e.g., tile
floors) directly behind the glazingto reduce glare and overheating
in the occupied space.A sunspace keeps the glass and mass separate
fromthe occupied space but allows for the transfer of usefulheat
into the building by convection or a common masswall; temperatures
in a sunspace are allowed to fluc-tuate around the comfort
range.
Highlight passive solar as a project goal. Manyagencies,
including GSA and DOD, already encouragethe use of passive solar
design and renewables in newconstruction and major renovation. A
good general proj-ect goal is to produce a beautiful, sustainable,
cost-effective building that meets its program, enhances
pro-ductivity, and consumes as little nonrenewable energyas
possible, through the use of passive solar design, en-ergy
efficiency, and the use of other renewable resources.
Incorporating energy performance goals into theprogramming
documents conveys the seriousnessof energy consumption and the use
of passive solar asa design issue. For small offices, warehouses,
and othersmaller projects10,000 sq ft (930 m2) or
lessfacilitymanagers or their contractors can develop energy
bud-gets easily using software such as Energy-10. For
largermulti-zone projects (for example, laboratories or high-rise
office buildings), national average energy consump-tion data by
building type can be cited as targets to beexceeded, or more
complex analyses can be run by con-sultants. The building program
should describe an ar-ticulation that allows passive solar
strategies to be ef-fective (for example, large multistory core
zones arehard to reach with passive solar). The building pro-gram
should also describe requirements, such as pri-vacy and security,
that may influence the type of pas-sive solar heating system that
can be used.
Thirty to fifty percent energy cost reductionsbelow national
averages are economically real-istic in new office design if an
optimum mix of energyconservation and passive solar design
strategies is ap-plied to the building design. Annual savings of
$0.45to $0.75 per sq ft ($5 to $8/m2) is a reasonable estimateof
achievable cost savings.
Passive solar design considers the synergy ofdifferent building
components and systems.For example:
Can natural daylighting reduce the need for elec-tric light?
If less electric light generates less heat, will therebe a lower
cooling load?
If the cooling load is lower, can the fans be smaller?
Passive solar systems make use of natural energy flowsas the
primary means of harvesting solar energy. Pas-sive solar systems
can provide space heating, cooling-load avoidance, natural
ventilation, water heating, anddaylighting. This section focuses on
passive solar heat-ing, but the other strategies also need to be
integratedand coordinated into a whole-building design.
Passivesolar design is an approach that integrates
buildingcomponentsexterior walls, windows, and buildingmaterialsto
provide solar collection, heat storage, andheat distribution.
Passive solar heating systems aretypically categorized as
sun-tempered, direct-gain,sunspaces, and thermal storage walls
(Trombe walls).In most U.S. climates, passive solar design
techniquescan significantly reduce heating requirements for
resi-dential and small commercial buildings.
Opportunities
New construction offers the greatest opportunity
forincorporating passive solar design, but any renovationor
addition to a building envelope also offers opportu-nities for
integration of passive methods. It is impor-tant to include passive
solar as early as possible in thesite planning and design process,
or when the addi-tion or building is first conceived. Ideally, an
energybudget is included in the building design specifications,and
the RFPs require the design team to demonstratetheir commitment to
whole-building performance andtheir ability to respond to the
energy targets. This com-mitment is emphasized during programming
andthroughout the design and construction process.
For retrofit projects, consider (1) daylighting strate-gies,
such as making atria out of courtyards or addingclerestories, along
with modification of the electric light-ing system to ensure energy
savings; (2) heat controltechniques, such as adding exterior shades
or overhangs;and (3) using passive solar heating strategies to
allowmodification of HVAC systemsperhaps down-sizingif the passive
strategies reduce energy loads sufficiently.
Many buildings in the Federal inventory have passivefeatures
because they were built before modern light-ing and HVAC
technologies became available. Whenrenovating older buildings,
determine whether passivefeatures that have been disabled can be
revitalized.
Technical Information
Terminology. Sun tempering is simply using windowswith a size
and orientation to admit a moderate amountof solar heat in winter
without special measures forheat storage. Direct gain has more
south-facing glass
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41
Will natural ventilation allow fans and other cool-ing equipment
to be turned off at times?
Passive solar design is often more challenging thandesigning a
mechanical system to accomplish the samefunctions. Using the
building components to regulatetemperature takes a rigorous
analytical approach tooptimize performance while avoiding such
problemsas overheating and glare.
Buildings properly designed using pas-sive solar systems and
strategies are
generally more comfortable for the occupants,resulting in
productivity benefits that are greatrelative to the building
cost.
Generic design solutions or rules of thumb areof limited value.
Rules of thumb may be useful inanticipating system size and type,
but only early inthe design process. Computer simulation
providesmuch more accurate guidance because of the complex-ity of
system combinations and in-teractions. Some of the variables
in-volved include:
Climate (sun, wind, air tempera-ture, and humidity);
Building orientation (glazingand room layout);
Building use type (occupancyschedules and use profiles);
Lighting and daylighting (elec-tric and natural light
sources);
Building envelope (geometry, in-sulation, fenestration, air
leak-age, ventilation, shading, ther-mal mass, color);
Internal heat gains (from light-ing, office equipment,
machin-ery, and people);
HVAC (plant, systems, and controls); and
Energy costs (fuel source, demand charges, conver-sion
efficiency).
An hourly simulation analysis combines all of theseparameters to
evaluate a single figure-of-merit, suchas annual energy use or
annual operating cost.
The integrated interaction of many energy-effi-cient strategies
is considered in passive solar design.These include: passive solar
heating, glazing, thermalmass, insulation, shading, daylighting,
energy-efficientlighting, lighting controls, air-leakage control,
naturalventilation, and mechanical system options such as
economizer cycle, exhaust air heat recovery, high-effi-ciency
HVAC, HVAC controls, and evaporative cooling.
Passive solar design is an integrated de-sign approach
optimizing total building
performance rather than a single building sys-tem. This is the
key to green building design.
Cost and technical analyses are conducted at thesame time in
passive solar design to optimize invest-ments for maximum energy
cost savings. It is rarelyfeasible to meet 100% of the building
load with pas-sive solar, so an optimum design is based on
minimiz-ing life-cycle cost: the sum of solar system first-costand
life-cycle operating costs. Means Assemblies CostData is a good
source of cost information for thermalstorage walls (Trombe walls)
and other selected strat-egies. It is difficult to separate the
cost of many pas-sive solar systems and components from other
buildingcosts because passive solar features serve other build-ing
functionse.g., as windows and wall systems.
References
Olgyay, Victor, Design with Climate:Bioclimatic Approach to
Architec-tural Regionalism, Princeton Uni-versity Press, Princeton,
NJ, 1963.
Watson, Donald, and KennethLabs, Climatic Design:
Energy-Ef-ficient Building Principles andPractices, McGraw-Hill,
New York,NY, 1983.
Designing Low-Energy Buildings,Sustainable Buildings
IndustryCouncil, Washington, DC, 1997.
Means Assemblies Cost Data 2000,R. S. Means Company, Inc.,
King-ston, MA, 2000.
Contacts
FEMP offers a course on passive solar design, Design-ing
Low-Energy Buildings. Call (800) DOE-EREC (363-3732) for course
information.
Sustainable Buildings Industry Council (SBIC), 1331H Street, NW,
Suite 1000, Washington, DC 20005 (202)628-7400; www.sbicouncil.org.
SBIC sponsors work-shops on low-energy building design and
marketsEnergy-10, the software developed by NREL to aid inthe
evaluation of passive measures in residential andsmall, single-zone
commercial buildings.
The Trombe wall at the NREL VisitorsCenter in Golden, Colorado,
providespassive heating and daylighting to theexhibit hall. Photo:
Warren Gretz
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42
4.1.2 Daylighting Design
Achieving good daylighting is often more of an art thana
technical, engineered solution. The eyes perceptionof light is a
key part of visibility. The amount of light(typically measured in
foot-candles) in a space is onlyone small part of the equation. The
brightness of sur-faces within the field of view directs the eyes
percep-tion of visibility. If the brightness difference
(luminanceratio) of surfaces being viewed is too great, the
darkerareas seem underlit even when the amount of light iswithin
desirable ranges.
The quality of daylight and the human need for con-nection to
daylight cannot be emphasized enough. Hu-man health and
productivity can be enhanced withsound daylighting designs. Some
studies have indicatedsignificant increases in productivity (up to
15%) andreduced absenteeism for office workers through the useof
effective daylighting. Recent studies in Californiademonstrate a
strong statistical correlation betweendaylighting and improved
sales in retail stores. Simi-larly, daylit classrooms are being
shown to result infaster learning and healthier students.
The form-givers relating to daylighting design arebuilding
geometry (architectural form of interior spacesand the building as
a whole), glazing strategies (size,orientation, type, location),
daylighting controls (lightshelves, blinds, fins), and surfaces
(textures, colors). Adouble-loaded corridor provides access to
daylight fromone wall in each room, with a lower level of
borrowedlight in the central corridor.
Daylighting is the effective use of natural light in build-ings
to minimize the need for electric light during day-light hours.
When properly designed, daylighting canprovide high-quality
architectural lighting and canbalance the thermal consequences of
additional glaz-ing. Since many Federal buildings use significant
en-ergy for electric lighting (often 30 to 50% of annualenergy
use), daylighting can be a very important de-sign strategy to
consider.
Opportunities
In almost all cases where lighting is needed in a build-ing on a
regular basis during the day, daylighting canbe an effective
solution for at least some of the lightingrequirements. Daylighting
should be considered inbuildings such as offices, laboratories,
schools, foodservice facilities, and other daytime-use spaces. In
ex-isting buildings, daylighting potential is greatest closeto
perimeter window walls.
A baseline lighting profile will help establish thepotential
opportunities for daylighting. The graph belowillustrates the
lighting profile baseline of an officebuilding on average days for
each month on a 24-hourbasis. The energy saved because of
daylighting is plot-ted in the lower negative curve. This profile
indicatesthat daylighting provides considerable savings inthis
building and thus is a good candidate for furtherconsideration.
Technical
Information
Windows are provided inmost buildings for daylight,view, and
architectural aes-thetics, as well as to satisfya basic human need
to con-nect with nature. However,the art and science of design-ing
effective, high-qualitydaylighting systems goes be-yond simply
adding windowsin a wall. Glazing strategiesresponding to size,
location,orientation, type, sun control,and building geometry all
af-fect the quality and effective-ness of a daylighting design.
The energy saved monthly as a result of daylighting in a Denver
Federal office build-ing is shown graphically in the bottom (black)
profiles. Source: ENSAR Group
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43
Contacts
Windows and Daylighting Group, Lawrence BerkeleyNational
Laboratory, Berkeley, CA; 510/486-6845,www.lbl.gov. Tips for
Daylighting with Windows isavailable as a pdf file.
Center for Buildings and Thermal Systems, NationalRenewable
Energy Laboratory, Golden, CO; www.nrel.gov/buildings_thermal/.
Daylighting Collaborative, Energy Center of Wiscon-sin, 595
Science Drive, Madison, WI 53711; (608) 238-4601;
www.daylighting.org.
Pacific Gas & Electric Daylighting Initiative,
www.pge.com/pec/daylight/.
Building 33 at the Navy Shipyard in Washington, D.C., isa
retrofit of a historic building where daylighting wasemployed
through skylights and windows.
There is a tremendous amount of lightoutdoors, and even small
windows let in
enough lightan important objective is to mini-mize the
difference between the lightest anddarkest points of the room.
A key component of any daylighting strategy, particu-larly for a
large building, is careful integration withelectric lighting. After
all, even the best daylightingdesign will save energy only if it
reduces the amountof electricity used for artificial lighting.
Daylight con-trols can dim fluorescent lighting if luminaires are
fit-ted with dimming electronic ballasts. Controlling banksof
luminaires along window walls separately from in-terior lights
enables perimeter lights to be dimmedwhen natural light levels are
adequate, thus yieldingsignificant savings.
Beyond the basics, advanced daylighting systems, suchas light
pipes, light shelves with specular surfaces fordeep directional
daylighting to the building core, fiberoptics, tracking daylight
apertures, and other tech-niques can provide ample daylighting when
simple ap-proaches wont solve the problem. Most of these
ap-proaches, however, will increase overall costs.
Bring daylight in high in the space,bounce daylight off
surfaces, filter day-
light with vegetation and architectural compo-nents, and
integrate daylighting design with elec-tric lighting, HVAC, and
architectural systems.
Avoid ceiling reflections and direct sun-light or skylight in
areas where extreme
brightness isnt useful.
References
Evans, Benjamin H., AIA, Daylight in Architecture,McGraw-Hill,
New York, NY, 1981.
Ander, Gregg D., AIA, Daylighting: Performance andDesign, Van
Nostrand Reinhold, New York, NY, 1995.
Source: ENSAR Group
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OBSTACLES TO THE USE OFNATURAL VENTILATION
Smoke control in case of fire is more difficultand may require
special equipment and/or vari-ances in codes.
Outdoor noise is difficult to manage in a build-ing that relies
on operable windows or vents.
Acoustic separation between spaces can bedifficult to
achieve.
Low pressure differences often require largeapertures for
desired airflow rates.
Outdoor air must be clean enough to intro-duce directly into
occupied space. If filtrationis required, mechanical ventilation is
necessary.
4.1.3 Natural Ventilation
or stack ventilation. Wind ventilation supplies air froma
positive pressure through apertures on the windwardside of a
building and exhausts air to a negative pres-sure on the leeward
side. Shutters and louvres can alsobe positioned to maximize
wind-induced airflowthrough the building. Airflow rate depends on
the windspeed and direction as well as the size of
apertures.Wind-driven turbine extractors are common in indus-trial
buildings to provide natural ventilation.
In summer, the indoor-outdoor temperature differenceis not high
enough to drive buoyancy ventilation, andwind is used to supply as
much fresh air as possible.In winter, however, the indoors is much
warmer thanoutdoors, providing an opportunity for buoyancy
ven-tilation. Also, ventilation is normally reduced to
levelssufficient to remove excess moisture and pollutants inwinter.
For buoyancy ventilation, warm air in the roofrises and exhausts
out of a high aperture, while cooleroutdoor air comes in through an
aperture at a lowerelevation. Airflow rate depends on the size of
these ap-ertures, the height difference between them, and theindoor
and outdoor temperatures. A solar chimneymay be added to the
exhaust to enhance the stack ef-fect. An improvement sometimes used
in arid climatesis to add an evaporative cooler on top of a cool
towerthis precools and pressurizes the inlet air and helpsexhaust
warm air high in the conditioned space orthrough the solar
chimney.
Natural ventilation as a primary cooling and ventila-tion
strategy is appropriate only under certain condi-tions. Temperate
climates with low average humidity
Natural ventilation is the use of wind and tempera-ture
differences to create airflows in and through build-ings. These
airflows may be used both for ventilationair and for passive
cooling strategies. Natural ventila-tion is often strongly
preferred by building occupants,especially if they have some
control over it, as withoperable windows. Studies have shown that
most oc-cupants will readily tolerate a wider range of
ambientconditions if they have such control.
Before the advent of mechanical ventilation, all build-ings were
naturally ventilated. Since that time, cli-mate-control
expectations have risen significantly, andmost building programs,
codes, and regulations arebased on the expectation of mechanical
systems. Nev-ertheless, well-designed natural ventilation can
oftenbe used in conjunction with mechanical systems, cre-ating a
mixed mode building. Mixed-mode buildingsmay be designed around
mechanical systems that aresupplemented by natural ventilation or
vice versa. Thebuilding may be designed to use both systems
simul-taneously or to switch from one to the other based onclimate
conditions or occupant demand. In a few situ-ations, natural
ventilation approaches can replace me-chanical cooling and
ventilation systems entirely.
Opportunities
Buildings constructed before about 1950 were almostalways
designed for natural ventilation, and it oftenmakes sense to retain
that function when renovatingsuch buildings. Building types with
less stringent cli-mate-control requirements are the best
candidates fornatural ventilation, whether renovated or newly
de-signed. Temperate climates with low relative humid-ity, such as
in the northwestern United States, are bestsuited to natural
ventilation.
Natural ventilation is most effective in increasing occu-pant
satisfaction when it is combined with daylightingand when occupants
are at least partially in control ofthe conditions. Unfortunately,
giving control to occu-pants makes energy use by mechanical systems
diffi-cult to predict. Natural ventilation is most effective asan
energy conservation strategy when combined withother passive
cooling and cooling load reduction strat-egies, such as night
flushing and effective shading.
Technical Information
There are two basic types of natural ventilation ef-fects:
buoyancy and wind. Buoyancy ventilation ismore commonly referred to
as temperature-induced
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45
levels are the best candidates. In cold climates, mixed-mode
buildings are viable, with natural ventilation asthe primary source
of outdoor air on a seasonal basis.Hot, humid climates tend to have
the fewest days inwhich natural ventilation can be used without the
riskof compromising comfort.
When natural ventilation is a priority for a new build-ing or
renovation, performance requirements shouldnot include strict
limits on acceptable indoor tempera-ture and humidity conditions;
this is because extremeweather conditions are difficult to predict.
Instead,clear guidelines should be established for an
allowablepercentage of time to stray from certain conditions.
Themore broadly these conditions are defined, and thelarger the
acceptable amount of time out of compli-ance, the greater the
possibilities for reducing mechani-cal system size and usage.
Naturally ventilated and mixed-mode buildings typi-cally have
floor plates less than 40 feet (12 m) widethe floor plates of
typical new large office buildingsare too big for air to move
reliably across them. Cool-ing-load reduction strategiese.g.,
shading, heat-re-jecting glazing, and the use of thermal mass to
dampentemperature swingsare essential to maintaining
$
comfortable conditions in buildings relying on
naturalventilation.
Mixed-mode buildings may be designed to switch frommechanical to
natural ventilation within the samespace, or they may have both
types of ventilation oc-curring simultaneously in separate spaces.
Runningboth natural and mechanical ventilation simulta-neously in
the same space will usually lead to exces-sive energy use,
especially if mechanical cooling orheating is active. In humid
climates, switching backand forth between mechanical and natural
ventilationmay increase energy use, as the mechanical coolingsystem
has to work harder to remove latent heat (mois-ture) that
accumulates in the air and in materials inthe building.
Design for passive airflow is complex, especially in
largebuildings. Specialized computational fluid dynamics(CFD)
software is valuable in understanding airflowunder different
conditions, but such software is expen-sive and time-consuming to
learn. Engineering firmswith expertise in natural ventilation
should have CFDsoftware or access to it. The design of simple
struc-tures, such as livestock barns, often relies on simplebut
effective hand calculations to size the natural ven-tilation
apertures.
For any building type, an understanding of local cli-mate
conditions is essential for good natural ventila-tion design. The
free Climate Consultant software fromthe University of California
at Los Angeles providesgraphic displays of temperature and humidity
condi-tions for most U.S. locations. It can be downloaded
fromwww.aud.ucla.edu/energy-design-tools/.
Mixed-mode buildings tend to be more ex-pensive than either
mechanically venti-
lated or naturally ventilated buildings becauseof the
duplication of air movement systems.
References
Allard, Francis, ed., Natural Ventilation in Buildings,James and
James, London, 1998.
Givoni, Baruch, Climate Considerations in Buildingand Urban
Design, John Wiley & Sons, New York, NY,1998.
Passive down-draft cool towers at the Visitor Center inZion
National Park (in Springdale, Utah) help bring tem-peratures down
by cooling hot air with water at the top ofthe tower. This cooled
air then falls into the building andonto the patio. Photo: Paul
Torcellini
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46
4.2 Building Envelope
The building envelope is a critical component of anyfacility
since it both protects the building occupantsand plays a major role
in regulating the indoor envi-ronment. Consisting of the buildings
roof, walls, win-dows, and doors, the envelope controls the flow of
en-ergy between the interior and exterior of the building.The
building envelope can be considered the selectivepathway for a
building to work with the climatere-sponding to heating, cooling,
ventilating, and naturallighting needs.
Opportunities
For a new project, opportunities relating to the build-ing
envelope begin during the predesign phase of thefacility. An
optimal design of the building envelope mayprovide significant
reductions in heating and coolingloadswhich in turn can allow
downsizing of mechani-cal equipment. When the right strategies are
integratedthrough good design, the extra cost for a
high-perfor-mance envelope may be paid for through savingsachieved
by installing smaller HVAC equipment.
With existing facilities, facility managers have muchless
opportunity to change most envelope components.Reducing outside air
infiltration into the building byimproving building envelope
tightness is usually quitefeasible. During reroofing, extra
insulation can typi-cally be added with little difficulty. Windows
and insu-lation can be upgraded during more significant build-ing
improvements and renovations.
Technical Information
WINDOWS
Glazing systems have a huge impact on energy con-sumption, and
glazing modifications often present anexcellent opportunity for
energy improvements in abuilding. Appropriate glazing choices vary
greatly, de-pending on the location of the facility, the uses of
thebuilding, and (in some cases) even the glazings place-ment on
the building. In hot climates, the primarystrategy is to control
heat gain by keeping solar en-ergy from entering the interior space
while allowingreasonable visible light transmittance for views
anddaylighting. Solar screens that intercept solar radia-tion, or
films that prevent infrared and ultraviolettransmission while
allowing good visibility, are usefulretrofits for hot climates.
In colder climates, the focus shifts from keeping so-lar energy
out of the space to reducing heat loss to theoutdoors and (in some
cases) allowing desirable solarradiation to enter. Windows with two
or three glazing
By taking an integrated approach tocombining building envelope
and lighting
components, even greater energy savings and in-creased occupant
comfort can be attained. Thephotos above show dynamically
controlled win-dow and lighting systems implemented by theLawrence
Berkeley National Laboratory at theOakland, California, Federal
Building. The blindsadjust, and electric lights dim, in response
toreal-time variations in sun and sky conditions.Lighting energy
savings were 20% in winter and3050% in summer. Overall cooling
savings forthe summer were 515%.
Source: Lawrence Berkeley National Laboratory
layers that utilize low-emissivity coatings will mini-mize
conductive energy transmission. Filling the spacesbetween the
glazing layers with an inert low-conduc-tivity gas, such as argon,
will further reduce heat flow.Much heat is also lost through a
windows frame. Foroptimal energy performance, specify a
low-conductiv-ity frame material, such as wood or vinyl. If
metal
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47
only systems that include a drainage layer to accom-modate small
leaks that may occur over timeavoidbarrier-type systems.
Roof insulation can typically be increased relativelyeasily
during reroofing. At the time of reroofing, con-sider switching to
a protected-membrane roofing sys-tem, which will allow reuse of the
rigid insulation dur-ing future reroofingthus greatly cutting down
onlandfill disposal.
While we think of insulation as a strategy for coldclimates, it
makes sense in cooling climates as well.The addition of insulation
can significantly reduce airconditioning costs and should be
considered during anymajor renovation project. Roofs and attics
should re-ceive priority attention for insulation retrofits
becauseof the ease and relative low cost.
Insulation is a guideline item under RCRA 6002and should be
purchased with recycled content. Fed-erally funded projects are
required to use insulationmaterials with minimum recycled content
that variesdepending on the type of insulation. Also consider
theozone-depletion potential of rigid insulation materials.Most
extruded polystyrene and polyisocyanurate in-sulation is produced
with ozone-depleting hydrochloro-fluorocarbons (HCFCs), though
ozone-safe alternativesare beginning to appear.
Contacts
Oak Ridge National Laboratory, Bldg 3147, P.O. Box2008 MS6070,
Oak Ridge, TN 37831; (423) 574-5207;www.ornl.gov/roofs+walls. DOE
Insulation Fact Sheetavailable online.
ENERGY STAR Roof Products Program, Office of Air andRadiation,
U.S. Environmental Protection Agency,Washington, DC 20460;
202/564-9124; www.epa.gov/energystar.
frames are used, make sure the frame has thermalbreaks. In
addition to reducing heat loss, a good win-dow frame will help
prevent condensationeven high-performance glazings may result in
condensation prob-lems if those glazings are mounted in
inappropriateframes or window sashes.
Fenestration can be a source of discomfort whensolar gain and
glare interfere with work station vis-ibility or increase contrast
and visual discomfort foroccupants. Daylighting benefits will be
negated if glareforces occupants to close blinds and turn on
electriclights, for example, to perform visual tasks optimally.
Facility managers should choose appropriatewindow technology
that is cost-effective for the cli-mate conditions. Computer
modeling, using a tool suchas DOE-2 or Energy-10, will help
determine which glaz-ing system is most appropriate for a
particular climate.In coastal California, for example, single
glazing maybe all that can be economically justified, while in
bothhotter and colder climates, more sophisticated glazingsare
likely to be much more effective.
WALLS AND ROOFS
For buildings dominated by cooling loads, itmakes sense to
provide exterior finishes with high re-flectivity or wall-shading
devices that reduce solar gain.Reflective roofing products help
reduce cooling loadsbecause the roof is exposed to the sun for the
entireoperating day. Specify roofing products that carry theENERGY
STAR roof labelfor low-slope roofing products,these have an initial
reflectivity of at least 65%. ENERGYSTAR roof products are widely
available with single-plyroofing, as well as various other roofing
systems.
Wall shading can reduce solar heat gain signifi-cantlyuse roof
overhangs, window shades, awnings,a canopy of mature trees, or
other vegetative plant-ings, such as trellises with deciduous
vines. To reducecooling loads, wall shading on the east and west is
mostimportant, though especially for buildings with year-round
cooling loads, south walls will benefit from shad-ing as well. In
new construction, providing architec-tural features that shade
walls and glazings should beconsidered. In existing buildings,
vegetative shadingoptions are generally more feasible.
INSULATION
With new buildings, adding more wall insulationthan normal can
be done for a relatively low-cost pre-mium. Also consider thermal
bridging, which can sig-nificantly degrade the rated performance of
cavity-fillinsulation that is used with steel framing. With
steelframing, consider adding a layer of rigid insulation.
Boosting wall insulation levels in existing build-ings is
difficult without expensive building modifica-tions. One option for
existing buildings is adding anexterior insulation and finish
system (EIFS) on theoutside of the current building skin. With
EIFS, use
Photo: Craig Miller Productions and DOE
Installation of light-colored roofing to better reflect
sun-light and reduce interior temperature.
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48
4.2.1 Windows and Glazing Systems
U-factors, as specified by the National FenestrationRating
Council (NFRC). These unit values account forthe glazing, frame,
and glazing spacers in insulated-glass units. The lower the
U-factor (Btu/ft2Fhr), thebetter the performance. U-factor is the
inverse of R-value (U=1/R). The U-factor of double clear glazing
isabout 0.5 (R-value about 2).
Types of glazing include clear, tinted, reflective,
low-emissivity (low-e), and spectrally selective. Some low-e
coatings are on suspended plastic films (Heat Mir-ror). There are
also some advanced high-tech glazingsystems available or under
development, includingelectrochromic (tinted by applied voltage),
photochro-mic (tinted by light intensity), thermochromic (tintedby
heat), photovoltaic (power-generating), and trans-parent
insulating.
Low-e coatings have revolutionized glazing designin the past
twenty years, dramatically boosting energyperformance. These very
thin coatings of metal (typi-cally silver or tin oxide) allow
short-wavelength sun-light through but block the escape of
longer-wavelengthheat radiation. There are two types of low-e
coatings:soft-coat (vacuum-deposited) coatings that have to
beprotected within a sealed insulated glass unit; andhard-coat
(pyrolytic) coatings that are applied whenthe glass is still molten
and are durable enough to beused on single-pane glazings. Soft-coat
low-e coatingsgenerally block heat loss better, but they also
blockmore of the solar heat gain and thus arent as good
forsouth-facing glazing on passive solar buildings.
Spectrally selective glazings are a special type ofglazing used
mostly in commercial buildings. Theseshould be specified in
climates where solar gain in thesummer creates large cooling loads
and where daylightalso is desired. The coatings allow visible
portions ofthe solar energy spectrum to be transmitted, but
theyblock infrared and ultraviolet portions of the spectrumthat
introduce heat primarily.
The gap between multiple panes of glass also in-fluences heat
flow. The space may be filled with air ora high-conductivity gas
such as argon or krypton. Be-cause these gases have lower thermal
conductivity thanair, they result in lower U-values. While krypton
is sig-nificantly better than argon, it is also a lot more
ex-pensive and therefore rarely used. Low-conductivitygas fills are
particularly important when low-e coat-ings are used on the glass,
because the coatings resultin a higher difference in temperature
across theinterpane space.
In renovationsparticularly of historic buildingsaluminum, metal,
and vinyl panning and receptor sys-tems provide a weathertight,
finished covering for
Windows, and glazing systems in general, can providedaylighting,
passive solar heat gain, natural ventila-tion, and views. Glazings
can be vertical or sloped, wall-mounted or roof-mounted. While a
vitally importantbuilding component, glazing systems can also be
theweakest point in the building enveloperelative to heatloss,
unwanted heat gain, moisture problems, and noisetransmission.
Through proper design, careful analy-sis, and proper installation,
glazing systems allowbuildings to work with the climate to reduce
energyuse as well as enhance human comfort and productivity.
Opportunities
Opportunities to ensure that glazing systems will beeffective
and climate-responsive are greatest very earlyin the planning and
design process both for new build-ings and for existing buildings
undergoing renovation.Renovations afford opportunities for
replacing older,single-glazed, and either clear or darkly tinted
windows.Window and glazing modifications can be
consideredindependently of other building changes, but changeswill
be most cost-effective when carried out as part ofa broader upgrade
of the whole building. Improvingthe energy performance of windows
without replacingthe window units themselves may be feasible by
add-ing shading devices on the exterior, an extra glazinglayer
(storm panel) on the interior or exterior, or win-dow treatments
(such as shades, drapes, shutters, orwindow films) on the
interior.
Technical Information
Windows and glazings are specified by solar heatgain coefficient
(SHGC), U-factor (thermal transferrate), air-leakage rate, visible
light transmittance, andmaterials of construction. The glazing
configuration,frame materials, and quality of construction will
de-termine the environmental impact, maintenance, du-rability, and
potential for disassembly for reuse or re-cycling at the end of its
life.
Issues to be considered in the selection of windowsand glazings
include the glazing system (see below),framing materials and
design, finishes used on fram-ing components, window operation (for
operable units),and how windows or glazing units are sealed at
thetime of installation to ensure a weather-tight envelope.
Windows and glazings allow heat movement viaconduction across
the glazing and the frame, via airleakage at the frame gaps and
between the frame andwall, and via the transmission of solar and
heat radia-tion through the glazing. Window thermal
performanceshould be compared by using the whole-window
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49
placement over existing wood frames. This simplifiesinstallation
of new units and eliminates the removalof old frames. Separate
interior or exterior glazing pan-els can also often be added to
single-pane windows inhistoric buildings to boost energy
performance with-out significantly altering the buildings
appearance.
Wood frames may be a better materialfrom an environmental
standpoint (if the
wood is from a certified well-managed forest),but they may have
greater life-cycle costs be-cause of their shorter life, and higher
mainte-nance costs compared with metal, vinyl (PVC),and fiberglass
windows. When selecting framematerials, weight heavily the thermal
perfor-mance and maintenancenot just the initial en-vironmental
impacts of the material.
To select windows for the best overall energyperformance, first
conduct an analysis that accountsfor inward and outward energy
flows throughout the
year. Various computer software tools can be used forthis
analysis, including DOE-2 and Energy-10.
Sound-control (acoustical) performance of win-dows can be
improved by ensuring that windows areairtight, increasing the
thickness of the glass, addingadditional glazing layers, and
specifying laminatedglass with a plastic interlayer.
The choice of either fixed glazing units or oper-able units
should be based on site-specific and climate-specific opportunities
and constraints. Casement, piv-oting, and awning windows offer the
greatest openingarea for natural ventilation and utilize
compressionseals that provide the best method of sealing the
jointbetween sash and frame. Fixed windows provide thebest thermal
performance because of fixed seals; thesecan be designed to satisfy
acoustical and security con-cerns as well.
Glazings that insulate poorly and framesthat are highly
conductive will have a cold
interior surface during winter months, and con-densation may
occur on the inside of the glassand frames. This can damage window
frames,sills, wallboard, paint, and wall coverings. A morethermally
efficient window and a nonconductiveframe with thermal breaks are
less likely to re-sult in condensation. Avoid metal frames thatlack
thermal breaks.
References
Carmody, John, Steve Selkowitz, and Lisa Heschong,Residential
Windows, W. W. Norton & Company, NewYork, NY, 1996.
Franta, Greg, et al., Glazing Design Handbook, TheAmerican
Institute of Architects, Washington, DC, 1996.
Certified Products Directory: Energy Performance Rat-ings for
Windows, Doors, Skylights, 9th Edition, Na-tional Fenestration
Rating Council, Washington, DC,December 1999.
Contacts
The FEMP Help Desk, (800) DOE-EREC (363-3732)can provide window
evaluation software developed byLawrence Berkeley National
Laboratory.
The National Fenestration Rating Council (NFRC),1300 Spring
Street, Suite 500, Silver Spring, MD20910; (301) 589-6372;
www.nfrc.org. (Both printed andonline versions of NFRC Certified
Product Directoryare available.)
Photo: Warren Gretz
NRELs Solar Energy Research Facility is designed to usenatural
lighting. South-, east-, and west-facing windowsare specially
coated with six different, graduated glazingsto mitigate unwanted
heat or glare from the sun. Windowsfacing east and west are also
outfitted with smart, mo-torized window shades. Each shade has a
photovoltaic sen-sor to detect the suns intensity and automatically
raise orlower the shade to prevent glare and heat gain.
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50
4.2.2 Insulation
rating, pest-resistance, and product standards of ASTMand
others. ASHRAE 90.1 specifies insulation require-ments for various
building envelope components, de-pending on heating degree-days and
other factors.
R-value depends on the properties of the material, thethickness
of the insulation layer, and the packing den-sity. Though R-values
per inch of thickness vary con-siderably, the table shows
representative values for sev-eral common insulating materials.
Minimum recycled content of different types of in-sulation is
specified in the recycled-content procure-ment guidelines of RCRA
6002. Insulation used inFederally funded projects exceeding $10,000
must meetthese standards.
The ozone-depletion potential of rigid boardstockand
foamed-in-place insulation has been reduced bymanufacturing
innovations and materials. The chlo-rofluorocarbons (CFCs) used as
blowing agents in mostfoam insulation have been replaced either
with HCFCs,which are about 10% as damaging to ozone, or
withhydrocarbons, which do not deplete ozone. The HCFC-141b used in
some polyisocyanurate and spray poly-urethane should be phased out
by Jan. 1, 2003; theHCFC-142b used in some extruded polystyrene
(XPS)should be phased out by 2020, with a production capin 2010.
Ozone-safe polyisocyanurate and spray poly-urethane appeared in the
late 1990s.
Fiberglass insulation has a high recycled glass con-tent and
includes post-industrial recycled glass culletfrom window
manufacturing. An increasing percent-age is recycled glass from
beverage containers. Somefiberglass insulation batting is
encapsulated in plasticwrap. This insulation is available without a
phenolformaldehyde binder.
Insulation ranks as one of the best means of savingenergy in
buildings, reducing utility bills, and improv-ing air quality.
Insulation provides resistance to theflow of heat from a buildings
exterior to its interior,and vice versa. Thermal resistance is
measured inR-value, the inverse of U-factor (the measure of
heatflow through a material in Btu per square foot per hourfor each
F difference in temperature). Insulation isprimarily either
loose-fill, batt, rigid boardstock, orfoamed-in-place. Along with
air barriers and vaporretarders, insulation controls the passage of
sensibleand latent heat and prevents condensation within walland
ceiling cavities. Though we take it for granted, onlysince the
1950s has insulation become widely avail-able, inexpensive, easy to
install, fire-retardant, resis-tant to pests, and able to retain
these properties overtime. It represents only a small portion of
buildingcosts, but insulation has a major impact on operatingcosts.
So, selecting the proper insulation is one of themost economical
and effective ways to reduce theoperating costs and environmental
impacts of aFederal facility.
Opportunities
Facility planners should specify R-values that mini-mize
life-cycle costs for all new construction. Codes andstandards
dictate minimums, but it can be cost effec-tive to use more.
Improving the insulation in existingbuildings, especially older
ones, can also be cost effec-tive and beneficial to occupants
health and comfort.Insulation can easily be added to attics or
under floors,but retrofitting cavity insulation in walls is
usuallyexpensive and disruptive. It is less disruptive to addwall
insulation on the exteriorfor example, with anexterior insulation
and finish systemgiving a dilapi-dated exterior a new look. The
best time to considerupgrading wall insulation is during a
renovation. Inreroofing, for example, insulation levels can easily
beincreased when exterior, low-slope insulation is beingremoved and
reapplied (see Section 7.1.4, Low-SlopeRoofing). Tapered insulation
provides the desired slopeto drains, increasing the roof membranes
life.Gasketing and caulking are integral to insulating en-velopes
for energy efficiency; they can be done eitherindependently or
during insulation upgrades.
Technical Issues
Selection issues for insulation include R-value per-formance
(including changes over time), environmen-tal impacts during
manufacture, recycled content,whether HCFCs were used in
manufacture, durabil-ity, waste generated, and potential health
hazards. Theinsulation selected should conform to the relevant
fire
R-VALUES FOR SOME COMMONINSULATING MATERIALS
Material R-value per Inch Thickness(F-ft2-h/Btu/inch)Mineral
Fiber 3.3 to 4.3Glass fiber 4.0Perlite 2.8 to 3.7Polystryrene 3.8
(expanded)
5.0 (extruded)Cellular Polyisocyanurate 5.6 to 7.0Cellulose,
loose fill 3.1 to 3.7Polyurethane,spray-applied foam 5.6 to
6.2Cotton, batt 3.4Source: 1997 ASHRAE Fundamentals Handbook;
cotton data from Environmental BuildingNews, Vol. 9, No. 11
(November 2000).
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51
Mineral wool insulation is made from either iron-ore blast
furnace slag (slagwool) or natural rock(rockwool). Mineral wool is
fire-resistant and effectiveat blocking sound.
Cellulose insulation contains post-consumer recyclednewspaper
and fire-retardant borates and ammoniumsulfate.
Cotton insulation is made from recycled cloth. Bo-rates are
added for fire- and pest-resistance.
Expanded polystyrene (EPS) insulation containsno ozone-depleting
substances and can be made withrecycled polystyrene. Though usually
produced at lowdensityabout 1 lb/ft3 (16 kg/m3)higher density EPSis
also available. In those cases, structural and R-valueproperties
are closer to those of XPS. Below-grade EPSis widely used for
insulated concrete-form products.
Spray-in open-cell polyurethane insulation ispopular in
lightframe construction. It can also be usedfor filling masonry
block. Open-cell polyurethane con-tains neither ozone-depleting
blowing agents norformaldehyde.
There are diminishing economic returns as in-sulation thickness
increases. Designers or facilitymanagers should analyze life-cycle
costs (LCC) to de-termine optimal insulation levels for minimizing
LCCcosts.
Thermal bypasses in the building can significantlyreduce the
effectiveness of insulation, which is whythe R-value of wall
insulation used with steel studs issignificantly lower (see the
table below).
Settling, dust, and moisture accumulation reducethe R-value of
loose-fill and batt insulation, especiallyin vertical wall
cavities. Skilled, careful installationshould avoid or minimize
problems.
Measures to protect both the installer and the insu-lation must
be taken during any installation, and a
continuous barrier (e.g., drywall) should be installedbetween
the insulation and the occupied space to pro-tect building
occupants.
Be aware of the health hazards associated withasbestos. Asbestos
is a proven carcinogen. It is pro-hibited in new construction; when
found in existingbuildings, it is usually left in place and
encapsulated.When asbestos must be removed, all regulations
andmethods for removal, transportation, and disposalshould be
followed.
Moisture in the exterior wall cavity occurs when wa-ter is
trapped in the cavity by impermeable surfaces.Condensation can
occur if the dew point temperatureoccurs anywhere within the
cavity. Managing moisturein the building envelope requires an
understanding ofthe climate, the drying potential of wall cavities,
andthe interior space conditioning method. In northern(cold)
climates, the interior side of wall cavities shouldbe less
permeable than the exterior side; just the op-posite is true in
warm climates with mechanicallycooled buildings. Using rigid
insulation on the exte-rior side of wall framing is one effective
way to dealwith moisture.
References
Lstiburek, Joseph, P. Eng., and John Carmody, Mois-ture Control
Handbook, Oak Ridge National Labora-tory, Oak Ridge, TN, 1991.
Wilson, Alex, Insulation Materials: EnvironmentalComparisons,
Environmental Building News, Vol. 4,No. 1, January 1995;
BuildingGreen, Inc., Brattleboro,VT.
Contacts
Building Thermal Envelope Systems and Materials(BTESM) Program,
Oak Ridge National Laboratory,P.O. Box 2008 MS6070, Oak Ridge, TN
37831-6070;(423) 574-5207; www.ornl.gov/walls+roofs/.
IMPACT OF FRAMING ON WALL R-VALUES
Combined Insulation & Framing R-ValueFraming Material &
Spacing Insulation R-Value Wood-Framed Walls Steel-Framed Walls
2x4 16 on-center R-11 (RSI-1.9) R-9.0 (RSI-1.6) R-5.5
(RSI-0.1)R-13 (RSI-2.3) R-10.1 (RSI-1.8) R-6.0 (RSI-1.0)
2x6 16 on-center R-19 (RSI-3.3) R-15.1 (RSI-2.7) R-7.1
(RSI-1.2)R-21 (RSI-3.7) R-16.2 (RSI-2.9) R-7.4 (RSI-1.3)
2x6 24 on-center R-19 (RSI-3.3) R-16.0 (RSI-2.8) R-8.6
(RSI-1.5)R-21 (RSI-3.7) R-17.2 (RSI-3.0) R-9.0 (RSI-1.6)
Notes: Assumes C-channel steel studs; steel-framing data from
ASHRAE Standard 90.1; wood-framing valuescalculated using
parallel-path method. Source: Environmental Building News, Vol. 3,
No. 4 (July/August 1994)