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 info@cedengineering.com

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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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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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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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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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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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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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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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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

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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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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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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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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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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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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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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)