Reducing energy use in the buildings sector: measures, costs, and … energy use in the... · The...

Reducing energy use in the buildings sector: measures, costs,and examples

L. D. Danny Harvey

Received: 17 June 2008 /Accepted: 9 January 2009 / Published online: 6 February 2009# Springer Science + Business Media B.V. 2009

Abstract This paper reviews the literature concerningthe energy savings that can be achieved throughoptimized building shape and form, improved buildingenvelopes, improved efficiencies of individual energy-using devices, alternative energy using systems inbuildings, and through enlightened occupant behaviorand operation of building systems. Cost information isalso provided. Both new buildings and retrofits arediscussed. Energy-relevant characteristics of the build-ing envelope include window-to-wall ratios, insulationlevels of the walls and roof, thermal resistance andsolar heat gain coefficient of windows, degree of airtightness to prevent unwanted exchange of air betweenthe inside and outside, and presence or absence ofoperable windows that connect to pathways for passiveventilation. Provision of a high-performance envelopeis the single most important factor in the design of low-energy buildings, not only because it reduces theheating and cooling loads that the mechanical systemmust satisfy but also because it permits alternative (andlow-energy) systems for meeting the reduced loads. Inmany cases, equipment with significantly greaterefficiency than is currently used is available. However,

the savings available through better and alternativeenergy-using systems (such as alternative heating,ventilation, cooling, and lighting systems) are generallymuch larger than the savings that can be achieved byusing more efficient devices (such as boilers, fans,chillers, and lamps). Because improved buildingenvelopes and improved building systems reduce theneed for mechanical heating and cooling equipment,buildings with dramatically lower energy use (50–75%savings) often entail no greater construction cost thanconventional design while yielding significant annualenergy-cost savings.

Keywords Buildings . Energyuse . Energyefficiency .

Renovations

Introduction

The chapter on energy use in buildings of WorkingGroup III of the Fourth Assessment Report (AR4) ofthe IPCC (Levine et al. 2007) outlines the broadstrategies for reducing energy use in buildings,identifies the major technologies and systems thatcan be used to reduce energy use, and extensivelydiscusses the policies that can be taken to realize thelarge energy-savings potential in the buildings sector.However, space permitted only a limited discussion ofcosts and of quantitative examples of the savingspotential for new buildings and in renovations. This

Energy Efficiency (2009) 2:139–163DOI 10.1007/s12053-009-9041-2

L. D. D. Harvey (*)Department of Geography, University of Toronto,100 St George Street,Toronto M5S 3G3, Canadae-mail: [email protected]

paper reviews the main strategies for reducing energyuse in new and existing buildings and presentsadditional quantitative examples of the savings thathave been achieved in real buildings based, in part, oninformation that has been published since the text ofLevine et al. (2007) was finalized. This paper iscomplemented by Ürge-Vorsatz et al. (2009), whichelaborates upon the policy discussion of Levine et al.(2007).

The report of AR4 Working Group I (Solomonet al. 2007) confirms that the eventual global meanwarming for a doubling of the atmospheric carbondioxide (CO2) concentration, or its radiative equivalent,is highly likely to fall between 2°C and 4°C, whilethe report (Parry et al. 2007) of AR4 Working GroupII (and the summary provided by Parry et al. 2008)makes it quite clear that serious widespread negativeimpacts are likely with only 2–3°C global meanwarming relative to preindustrial times. From this, itfollows that greenhouse gas concentrations equiva-lent to a doubling of preindustrial atmospheric CO2

are dangerous, and that even the current CO2

concentrations can be regarded as dangerous inter-ference in the climatic system (see Harvey (2007a, b)for a more thorough analysis). From this, it followsthat emissions of CO2 need to be reduced with theutmost urgency. Given limits on how fast and towhat extent carbon-free energy sources can bedeployed, it is vital that significant absolute reduc-tions in energy demand be achieved over the comingdecades.

A key conclusion of this paper is that reduc-tions in the energy intensity (annual energy useper unit of floor area) of new buildings by a factorof 3–4 relative to current local practice can beachieved and that reductions in the energy inten-sity of existing buildings by factors of 2–3 can beachieved through comprehensive renovations. Thefollowing sections provide an overview of howthis can be done, while much more detailedinformation can be found in Harvey (2006). Thefinal section of this paper presents scenarios toillustrate the consequences for absolute energy useby buildings and for average building energyintensities through to 2050 of various magnitudesand rates of reduction in the energy intensity ofnew and renovated buildings, in combination withdifferent assumptions concerning the growth intotal floor area between now and 2050.

The importance of a systems approach to buildingdesign

The energy use of buildings depends to a significantextent on how the various energy-using devices(pumps, motors, fans, heaters, chillers, and so on)are put together as systems, rather than depending onthe efficiencies of the individual devices. The savingsopportunities at the system level are generally manytimes what can be achieved at the device level, andthese system-level savings can often be achieved at anet investment-cost savings.

The systems approach requires an IntegratedDesign Process (IDP), in which the building perfor-mance is optimized through an iterative process thatinvolves all members of the design team from thebeginning. However, the conventional process ofdesigning a building is a largely linear process, inwhich the architect makes a number of designdecisions with little or no consideration of theirenergy implications and then passes on the design tothe engineers, who are supposed to make the buildinghabitable through mechanical systems. The design ofmechanical systems is also largely a linear processwith, in some cases, system components specifiedwithout yet having all of the information needed inorder to design an efficient system (given theconstraints imposed by the architect; Lewis 2004).This is not to say that there is no integration orteamwork in the traditional design process but ratherthat the integration is not normally directed towardminimizing total energy use through an iterativemodification of a number of alternative initial designsand concepts so as to optimize the design as a whole.

The steps in the most basic IDP are:

& to consider building orientation, form, andthermal mass

& to specify a high-performance building envelope& to maximize passive heating, cooling, ventilation,

and daylighting& to install efficient systems to meet remaining loads& to ensure that individual energy-using devices are

as efficient as possible and properly sized& to ensure the systems and devices are properly

commissioned

By focusing on building form and a high-performanceenvelope, heating, and cooling loads are minimized,daylighting opportunities are maximized, and me-

140 Energy Efficiency (2009) 2:139–163

chanical systems can be greatly downsized. Thisgenerates cost savings that can offset the additionalcost of a high-performance envelope and the addi-tional cost of installing premium (high efficiency)equipment throughout the building. These stepsalone can usually achieve energy savings on theorder of 35–50% for a new commercial building,compared to standard practice, while utilization ofmore advanced or less conventional approaches hasoften achieved savings on the order of 50–80%. Inthe next section, the key envelope measures, techni-ques for utilizing passive solar energy, and alterna-tive system-level designs are outlined.

Reducing heating and cooling loads

At the early design stages, key decisions—usuallymade by the architect—can greatly influence thesubsequent opportunities to reduce building energyuse. These include building form, orientation, self-shading, height-to-floor-area ratio, window-to-wallarea ratios, insulation levels and window properties,use of thermal mass within the building, and decisionsaffecting the opportunities for and effectiveness ofpassive ventilation and cooling. Many elements oftraditional building designs in both developed anddeveloping countries were effective in reducingheating and cooling loads, but have been discardedin modern designs.

High-performance thermal envelopes combinedwith passive heating

The term thermal envelope refers to the shell of thebuilding as a barrier to the transfer of heat betweenthe inside and outside of the building. The effective-ness of the thermal envelope depends on (1) theinsulation levels in the walls, ceiling, and otherbuilding parts; (2) the thermal properties of windowsand doors; and (3) the rate of uncontrolled exchangeof inside and outside air which, in turn, depends inpart on the air tightness of the envelope.

A high-performance thermal envelope can reduceheat losses to the point where a large fraction of theremaining heat loss can be offset by internal heat gain(from people, lighting, appliances) and passive solarheat gain, with the heating system required only for theresidual. For example, the European Passive House

Standard requires a heating energy use of no more than15 kWh/m2/year, but this is typically achieved byreducing the heat loss to about 45 kWh/m2/year, withone third of the heat loss offset by internal heat gainsand one third offset by passive solar heat gains. Bycomparison, the maximum permitted heating load fornew residential buildings in Germany was 65–100 kWh/m2/year under the 1995 regulations, whilethe average heating requirement of existing buildings isestimated to be 220 kWh/m2/year in Germany and250–400 kWh/m2/year in Eastern Europe (Krapmeierand Drössler 2001; Gauzin-Müller 2002). Thus, thePassive House standard represents a reduction inheating requirements by up to a factor of 25 comparedto typical existing buildings. More generally, a numberof advanced houses have been built in various cold-climate countries around the world that use only 10–25% of the heating energy of houses built according tothe local national building code (Badescu and Sicre2003; Hamada et al. 2003; Hastings 2004).

In countries with mild winters but still requiringheating (including many developing countries), modest(and therefore less costly) amounts of insulation canreadily reduce heating requirements by a factor of 2 ormore, as well as substantially reducing indoor summertemperatures, thereby improving comfort (in theabsence of air conditioning) or reducing summercooling energy use (Taylor et al. 2000; Florides et al.2002; Safarzadeh and Bahadori 2005).

Reducing the cooling load

Reducing the cooling load requires (1) orienting abuilding to minimize the wall area facing east or west(which are the directions most difficult to shade fromthe sun); (2) clustering buildings to provide somedegree of self shading (as in many traditionalcommunities in hot climates); (3) providing fixed oradjustable shading; (4) using highly reflective buildingmaterials; (5) increasing insulation; (6) using win-dows that transmit a relatively small fraction (as littleat 25%) of the total (visible + invisible) incidentsolar energy while permitting a larger fraction of thevisible radiation to enter for daylighting purposes;(7) utilizing thermal mass to minimize daytimeinterior temperature peaks; (8) utilizing nighttimeventilation to remove daytime heat; and (9) mini-mizing internal heat gains by using efficient lightingand appliances. The combination of external insula-

Energy Efficiency (2009) 2:139–163 141

tion, thermal mass, and night ventilation is particu-larly effective in hot-dry climates, as placing theinsulation on the outside exposes the thermal mass tocool night air while minimizing the inward penetra-tion of daytime heat into the thermal mass. Thesemeasures, alone or in combination, can typicallyreduce cooling loads by 50% or more (in many caseseliminating the need for mechanical cooling alto-gether). Low thermal mass and an open design withplenty of cross ventilation is normally recommendedin hot humid climates, although Tenorio (2007) findsthat in humid tropical areas of Brazil, thermal masscombined with night ventilation and selective use ofair conditioning can reduce cooling energy use in atwo-storey house by up to 80% compared to a fullyair-conditioned house.

Passive and low-energy cooling techniques

Having reduced the thermal load through the abovemeasures, usually by a factor of 2 or more, a numberof purely passive cooling techniques (requiring nomechanical energy input) are available. Other techni-ques involve small inputs of mechanical energy toenhance what are largely passive cooling processes.The major passive and passive or low-energy coolingtechniques are discussed below.

Passive ventilation

Passive ventilation reduces the need for mechanicalcooling by directly removing warm air when theincoming air is cooler than the outgoing air, reducingthe perceived temperature due to the cooling effect ofair motion and increasing the acceptable temperaturethrough psychological adaptation when the occupantshave control of operable windows. With regard to thelatter, when the outdoor temperature is 30°C, theaverage preferred temperature in naturally ventilatedbuildings is 27°C, compared to 25°C in mechanicallyventilated buildings (de Dear and Brager 2002).

Passive ventilation requires a driving force, and anadequate number of openings, to produce airflow. Itcan be induced through pressure differences arisingfrom inside–outside temperature differences or fromwind. Design features, both traditional and modern,that create thermal driving forces and/or utilize windeffects include courtyards, atria, wind towers, solar

chimneys, and operable windows (Holford and Hunt2003; Hawkes and Forster 2002). Passive ventilationnot only reduces energy use, but can improve airquality (if the outdoor air is not overly polluted) andgives people what they generally want (a connectionto the outside).

In buildings with good thermal mass exposed tothe interior air, passive ventilation can continue rightthrough the night, sometimes more vigorously thanduring the day due to the greater temperaturedifference between the internal and external air.Nighttime ventilation, in turn, serves to reduce thecooling load by making use of cool ambient air toremove heat.

Evaporative cooling

Evaporation of water cools the remaining liquid waterand air that comes into contact with it. The coldesttemperature that can be achieved through evaporationis called the wetbulb temperature and depends on theinitial temperature and humidity (the higher the initialhumidity, the less evaporation and cooling that canoccur). The wetbulb temperature is sufficiently low(≤20°C) in most of the world most of the time forcooling purposes (see Harvey 2006, Tables 6.7 and6.8). There are two methods of evaporatively coolingthe air supplied to buildings. In a direct evaporativecooler, water evaporates directly into the air stream tobe cooled. In an indirect evaporative cooler, waterevaporates into and cools a secondary air stream,which cools the supply air through a heat exchangerwithout adding moisture. By appropriately combiningdirect and indirect systems, evaporative cooling canprovide comfortable temperature–humidity combina-tions most of the time in most parts of the world.

Evaporative cooling is most effective in dryregions, but water may be a limiting factor in suchregions. However, arid regions tend to have a largediurnal temperature range, so thermal mass withexternal insulation and night ventilation can be usedinstead. Evaporative cooling is not effective in humidclimates, but it can be extended to such climatesthrough the use of desiccants (described below).

Desiccant dehumidification

Desiccant dehumidification and cooling involvesusing a material (desiccant) that removes moisture


from air and is regenerated using heat. Soliddesiccants are a commercially available technology,while liquid desiccants are nearing commercializa-tion. By over-drying the air, there is then room foradding moisture back to the air as a byproduct ofevaporative cooling. Desiccants provide an efficientmeans of air conditioning using solar thermalenergy or waste heat. A 30–50% savings in theprimary energy use for cooling and dehumidifica-tion is possible in large centralized systems, withfirst-costs comparable to those of multi-zone roof-top air conditioners (Harvey 2006, Sections 6.6.4and 7.4.11). A 50–75% savings is possible if waste orsolar heat can be used to regenerate the desiccant,although costs will be greater due to the need for solarthermal collectors.

Earth-pipe cooling

Ventilation air can be precooled by drawing outsideair through a buried air duct. This is referred to asearth-pipe cooling. Good performance depends on theclimate having a substantial annual temperature rangeso that the ground temperature (which will be close tothe mean annual temperature) is comparatively cool.The ratio of the cooling obtained to fan energyrequired to move air through the earth pipe (analo-gous to the coefficient of performance (COP) of aheat pump or air conditioner) in experimental studiesranges from a low as about 5 in Italy (Solaini et al.1998) and 8 in India during the pre-monsoon hotperiod (Thanu et al. 2001) to 30–50 in Germany(Eicker et al. 2006). Up to a 70% reduction in thecooling load in the northern US is possible with earth-pipe cooling (Lee and Strand 2008). By combiningearth pipe cooling with solar chimneys or measures toexploit wind suction, both cooling and ventilation canbe passively driven, with only occasional need forbackup fans, an example being a school in Norway(Schild and Blom 2002)

Heating and cooling equipment

Furnaces and boilers

Commercial buildings, multiunit residences, andmany single-family residences (especially in Europe)use boilers, which produce steam or hot water that is

circulated, generally through radiators. Efficiencies(ratio of heat delivered to fuel use) range from 80% to95%, not including distribution losses. Modernresidential furnaces, which are used primarily inNorth America and produce warm air that is circulat-ed through ducts, have efficiencies ranging from 78%to 96% (again, not including distribution systemlosses). Old equipment tends to have an efficiencyin the range of 60–70%, so new equipment canprovide a substantial savings. Space heating and hotwater for consumptive use (e.g., showers) can besupplied with heat from small wall-hung boilers withan efficiency in excess of 90%.

Heat pumps

A heat pump transfers heat from cold to warm(against the macro-temperature gradient) although ateach point in the system, heat flow is from warm tocold. It relies on the fact that a liquid cools when itevaporates, and the cooling effect is greater the lowerthe pressure of evaporation, while a gas releases latentheat as it condenses and is warmed to a greatertemperature the greater the pressure. A heat pump cantransfer heat from outside to inside (during winter)and from inside to outside (during summer). An airconditioner is a heat pump that operates in only onedirection. The efficiency of cooling equipment isindicated by its COP—the ratio of heat energytransferred to energy input.

The difference between the source temperature(from which heat is drawn) and the sink temperature(to which heat is added) is referred to as thetemperature lift. By drawing heat from the warmestpossible source temperature (such as the ground orexhaust air rather than cold outside air) anddistributing the heat at the lowest possible tempera-ture (as in radiant floors or ceilings) during heatingmode, the temperature lift can be minimized and theCOP increased. Similarly, during cooling mode, thetemperature lift is minimized and COP maximized ifcoldness is distributed at the warmest possibletemperature and the heat rejected at the lowestpossible temperature. Figure 1 shows the variation inthe COP of a heat pump in heating mode and incooling mode for various evaporator–temperaturecombinations. There can easily be a factor of twodifferences in the COP for best- and worst-casesystems.


If the heat pump COP is 3.0 and the efficiencyin producing and delivering the electricity is only33% (both being typical situations), then one unitof energy to the power plant supplies one unit ofheat to the building—about the same as for a highefficiency furnace or boiler. However, if the COPcan be pushed higher, and as more efficient fossilfuel electricity generation comes on line, there willbe a net savings in source energy. If the building iswell insulated and has thermal mass exposed to theinterior, the heat pump could be used preferentiallywhen intermittent carbon-free electricity sources(such as wind) are available in surplus, withtemperatures freely drifting at other times. In thisway, heat pumps can use carbon-free electricityand, by serving as a flexible electricity load, canfacilitate a greater overall use of intermittentrenewable energy sources for electricity.

Air conditioners and chillers

Air conditioners used for houses, apartments, andsmall commercial buildings have a nominal COPranging from 2.2 to 3.8 in North America and Europe,depending on operating conditions, whereas mini-split systems in Japan have COPs of up to 6.2.Chillers are larger cooling devices that producechilled water (rather than cooled air) for use in largeresidential and commercial buildings. Chiller COPgenerally increases with size, with the largest andmost efficient electric chillers having a COP of up to8 under full-load operation and even higher underpart-load operation. This is a factor of 3 better thantypical air conditioners. Although additional energy isused in chiller-based systems for circulating chilledwater and for operating a cooling tower, significantenergy savings are still possible through the choice ofthe most efficient cooling equipment in combinationwith efficient auxiliary systems.

Heating, ventilation, and air conditioning systems

The term HVAC (heating, ventilation, and air condi-tioning) refers to the system that produces anddelivers coldness and warmth as well as fresh airthroughout a building.

Principles of energy-efficient HVAC design

In the simplest HVAC systems, heating or cooling isprovided by circulating a fixed amount of air at asufficiently warm or cold temperature to maintain thedesired room temperature. The rate at which air iscirculated in this case is normally much greater thanthat needed for ventilation to remove contaminants,and is constant. During the cooling season, the air issupplied at the coldest temperature needed in anyzone, and reheated as necessary just before enteringother zones.

There are a number of changes in the design ofHVAC systems that can achieve dramatic savings inthe energy use for heating, cooling, and ventilation.These include,

& using variable-air volume systems with variable-speed fans so as to minimize simultaneous heatingand cooling of air and to reduce fan energy use

0

2

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-20 -15 -10 -5 0 5 10 15

Evaporator Temperature (°C)

He

atin

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OP

30oC

50oC

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Temperature:

nc=0.65

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30 35 40 45 50

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nc=0.65

-5oC

-10oC

a

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Fig. 1 Variation in the COP of a heat pump in heating modeand in cooling mode for various evaporator–temperaturecombinations, assuming a Carnot efficiency (ratio of actual toideal COP) of 0.64. Source, Harvey (2006)


& using heat exchangers to recover heat or coldnessfrom ventilation exhaust air and to supply it to theincoming fresh air

& separating the ventilation from the heating andcooling functions by using chilled or hot water fortemperature control and circulating only thevolume of air needed for ventilation

& implementing a demand-controlled ventilationsystem in which ventilation airflow changes withchanging building occupancy

& separating cooling from dehumidification func-tions through the use of desiccant dehumidifica-tion, with the desiccant preferably regeneratedwith solar heat

& correctly sizing all components& allowing the temperature maintained by the HVAC

system to vary seasonally with outdoor conditions,as a large body of evidence indicates that thetemperature and humidity set-points commonlyencountered in air-conditioned buildings are signif-icantly lower than necessary (de Dear and Brager1998; Fountain et al. 1999).

Hydronic systems (in which water rather than airis circulated), especially floor radiant heating orcooling systems in residential buildings and chilledceiling heating or cooling in commercial buildings,require less energy than forced air systems todistribute a given amount of heat, have low distri-bution heat losses, and do not induce infiltration ofoutside air (as in poorly balanced air distributionsystems). They allow heating and cooling to beprovided at temperatures closer to the desired roomtemperature, which increases the efficiency of heatingand cooling devices.

In many buildings, heating and cooling is providedby circulating a volume of warm or cool air that isseveral times that required for ventilation purposes.To reduce the volume of outside air that needs to beconditioned, it is common to recirculate, say, 80% ofthe internal air on each circuit and replace only 20%with fresh outside air. This spreads contaminantsthroughout the building. If heating and cooling islargely supplied hydronically, the airflow can be setequal to that required for ventilation purposes alonebut then, of necessity, must be completely replacedwith fresh air after each circuit through the building.This forms a dedicated outdoor air supply system and,if combined with displacement ventilation (described

below), allows ceiling heat gains (from lighting orrising thermal plumes and constituting up to 30% of thetotal cooling requirement) to be directly vented to theoutside rather than having to be removed by the chillersbefore the air is recirculated. This is one of the manyexamples of system–level interactions that can lead tolarge energy savings (see Harvey 2008, for other suchexamples).

An optimal combination of the measures listedhere can reduce the HVAC energy use by 30% to75%. These savings are in addition to the savingsarising from reducing heating and cooling loads.Further information on two particularly advantageousfeatures of an efficient HVAC system—chilled-ceiling cooling and displacement ventilation—isgiven below.

Radiant chilled-ceiling cooling

Chilled ceiling (CC) cooling refers to the circulationof chilled water either through panels mountedunderneath the ceiling, or circulating through pipesinside a concrete ceiling. The entire ceiling is chilledin this way, creating a cooling effect largely throughthe reduction in emission of infrared radiation. CCcooling has been used in Europe since at least the mid1970s. Significant energy savings arise because of thegreater effectiveness of water than air in transportingheat and because the chilled water is supplied at 16°Cto 20°C rather than at 5°C to 7°C. This not onlyallows a higher chiller COP when the chiller operatesbut also allows more frequent use of water-side freecooling, in which the chiller is bypassed altogetherand evaporatively cooled water from a cooling toweris used directly for space cooling. Even in the absenceof water-side free cooling, savings of 6–42% havebeen calculated for systems in various US citiescompared to all-air systems (Stetiu and Feustel 1999).

Displacement ventilation

Conventional ventilation relies on turbulent mixing todilute room air with ventilation air. A superior systemis displacement ventilation in which air is introducedat low speed through many diffusers in the floor oralong the sides of a room and is warmed by internalheat sources (occupants, lights, plug-in equipment) asit rises to the top of the room, displacing the airalready present. This allows cooling to be supplied at


a warmer temperature (∼18°C vs. ∼13°C in aconventional mixing ventilation system) and permitssmaller airflows. Savings of 40–60% in coolingenergy use occur in US cities compared to a standardsystem (Sodec 1999; Mumma 2001; Bourassa et al.2002; Howe et al. 2003).

Control systems and commissioning

Building Energy Management Systems are controlsystems for individual buildings or groups of buildingsthat use computers and distributed microprocessorsfor monitoring, data storage, and communication(Levermore 2000). Building commissioning is aquality control process that begins with the earlystages of design. It helps ensure that the designintent is clear and readily tested, that installation issubjected to on-site inspection, and that allsystems are tested and functioning properly beforethe building is accepted. Savings typically rangefrom 15% to 30% at a cost of 1–3% of the HVACsystem and a payback time of 2 years or less(Claridge et al. 2001; Roth et al. 2003; Liu et al.2003; Poulos 2007).

Lighting

Strategies to reduce lighting energy use focus on(1) efficient lighting systems; (2) efficient lightingdevices (ballasts, lamps, luminaires); and (3) optimaluse of daylighting (taking into account additionalcooling loads if excess daylight is supplied). Anexample of an efficient lighting system would be onewith separate controls for different lighting zonesand use of task or ambient lighting (relatively lowbackground light levels where appropriate, supple-mented with greater lighting when and whereneeded). Space limitations do not permit a substan-tial discussion of lighting energy use; an extensivereview in Harvey (2006, Chapter 9) indicates that, inretrofits, a 30–50% savings in electricity use can beroutinely achieved, while a savings of 70–75% issometimes possible with considerable effort. Day-lighting can provide 40–80% savings in lightingenergy use in perimeter offices, 20–33% savingsin combined lighting + cooling energy use, andup to 90% savings deep in rooms using fiberoptics.

Integrated energy savings

There are numerous examples of buildings of alltypes, and in all climate zones, that have achievedenergy savings of 50% to 75% or more compared tothe energy use of buildings built under current localpractice.

Advanced residential buildings

Hamada et al. (2003) summarize the characteristicsand energy savings for 66 advanced houses in 17countries. For the 28 houses where the savings inheating energy use is reported, the savings comparedto the same house built according to conventionalstandards ranges from 23% to 98%, with eight housesachieving a savings of 75% or better.

Several hundred houses that meet the PassiveHouse Standard—a house with an annual heatingrequirement of no more than 15 kWh/m2/yearirrespective of the climate and a total energyconsumption of no more than 42 kWh/m2/year—have been built in Europe. By comparison, theaverage heating load of new residential buildings isabout 60–100 kWh/m2/year in Switzerland andGermany but about 220 kWh/m2/year for theaverage of existing buildings in Germany and 250–400 kWh/m2/year in Central and Eastern Europe.Thus, Passive Houses represent a reduction inheating energy use by a factor of 4–5 compared tonew buildings and by a factor of 10–25 compared tothe average of existing buildings. Technical details,measured performance, design issues, and occupantresponse to Passive Houses in various countries canbe found in Krapmeier and Drössler (2001), Feist etal. (2005), Schnieders and Hermelink (2006), andHastings and Wall (2007a, b), with full technicalreports available at www.cepheus.de.

Parker et al. (1998) shows how a handful of verysimple measures (attic radiant barriers; wider andshorter return-air ducts; use of the most efficient airconditioners with variable speed drives; use of solarhot water heaters; efficient refrigerators, lighting, andpool pumps) can reduce total energy use by 40–45%in single-family houses in Florida compared toconventional practices. These savings are achievedwhile still retaining black asphalt shingle roofs thatproduce roof surface temperatures of up to 82°C!Holton (2002), Gamble et al. (2004), and Rudd et al.


http://www.cepheus.de

(2004) have shown how a series of modest insulationand window improvements can lead to energy savingsof 30–75% in a wide variety of US climates. In allthree studies, alterations in building form to facilitatepassive solar heating, use of thermal mass combinedwith night ventilation to meet cooling requirements(where applicable), or use of features such as earth-pipe cooling, evaporative coolers, or exhaust-air heatpumps are not considered. Thus, the full potential isconsiderably greater. Demirbilek et al. (2000) find,through computer simulation, that a variety of simpleand modest measures can reduce heating energyrequirements by 60% compared to conventionaldesigns for two-storey single-family houses inAnkara, Turkey.

Commercial buildings

Table 1 gives documented examples of new commer-cial buildings in North America, Europe, and Asiathat achieved a minimum of a 50% reduction inoverall energy use compared to current conventionalpractice. Several surveys indicate that these are notunrepresentative examples, but rather, that energysavings of 50–75% can be routinely achieved in newcommercial buildings through maximal implementa-tion of the measures reviewed in this paper.

First, the National Renewable Energy Laboratoryin the US extracted the key energy-related parametersfrom a sample of 5,375 buildings in the 1999Commercial Buildings Energy Consumption Survey,and then used energy models to simulate their energyperformance (Torcellini and Crawley 2006). Theresults of this exercise are as follows,

& average energy use as built is 266 kWh/m2/year& average energy use if complying with the ASH-

RAE 90.1-2004 standard is 157 kWh/m2/year, asavings of 41%

& average energy use would be 92 kWh/m2/yearwith improved electrical lighting, daylight, over-hangs for shading, and elongation of the buildingsalong an east–west axis (applicable only to newbuildings; a savings of 65%)

With implementation of technological improve-ments expected to be available in the future, the grossenergy use is so small that PV panels can generatemore energy than the buildings consume, so that thebuildings would serve as a net source of energy.

Second, in the UK, energy consumption guidelinesindicate that energy use for office buildings is typicallyabout 300–330 kWh/m2/year for standard mechanicallyventilated buildings, 173–186 kWh/m2/year with goodpractice (a savings of about 40–45%), and 127–145 kWh/m2/year for naturally ventilated buildingswith good practice (Walker et al. 2007)—a savings of55–60%.

Third, Voss et al. (2007) present data on themeasured energy use in 21 passively cooled commer-cial and educational buildings in Germany. Thepassive cooling techniques involve earth-to-air heatexchangers (nine cases), slab cooling directlyconnected to the ground via pipes in boreholes orconnected to the groundwater (nine cases), and someform of night ventilation (16 cases), along with alimited window-to-wall ratio (0.27–0.43) and externalsun shading. The buildings also have a high degree ofinsulation and many have triple-glazed windows.Nine of the buildings have total onsite energy use of25–55 kWh/m2/year and ten had 55–110 kWh/m2/yearenergy use, compared to 175 kWh/m2/year for con-ventional designs, so the savings is up to a factor ofseven. Three buildings have a heating energy use lessthan 20 kWh/m2/year and eight have a heating energyuse of 20–40 kWh/m2/year compared to a typicalheating energy use of 125 kWh/m2/year.

Large savings potentials (compared to recentpractice) are not restricted to mid-latitude climates orto industrialized countries. As indicated in Table 1,simulation studies for typical office buildings inMalaysia and Beijing indicate a potential savingsusing simple techniques of about 65–70%, while theTorrent Pharmaceutical Research Centre in Ahmeda-bad, India achieved an electricity savings of 64% anda demonstration office building in Beijing achieved asavings of 60%.

First-cost of deep energy savings in buildings

High performance residential buildings generally costa few percent more than conventional residentialbuildings, whereas high-performance commercialand institutional buildings can sometimes cost slightlyless. In the case of commercial buildings, there is agreater opportunity to offset the cost of a high-performance envelope with lower costs of mechanicalsystems, as mechanical systems are a greater fraction


Tab

le1

Sum

maryof

exem

plary(interm

sof

energy

use)

new

commercial

build

ings

where

baselin

eandreferenceenergy

usehave

been

published

Buildingandlocatio

nEnergyuse

Energy

saving

sReference

for

comparisonof

energy

use

Key

features

Reference

Canadianexam

ples

Green

ontheGrand

(offices),Kitchener,

Ontario

81.2

kWh/m

2/year(design

total)Natural

Gas:43

.1kW

h/m

2/yearElectricity:38

kWh/m

2/year

50.4%

ASHRAE90

.1-198

9Dou

ble-stud

manufacturedwoo

d-fram

ewall;fibreglass-

fram

e,triple-glazed,

doub

le-low

-e,argo

n-filled,

insulatin

g-spacer

windo

ws;redu

cedlig

htingpo

wer

densities;radiantheatingandcoolingpanels,DOASw/

heat

recovery,naturalgasfiredabsorptio

nchiller;

outdoo

rpo

ndreplaces

conv

entio

nalcoolingtower

C-200

0Internal

Program

Reporta

Crestwoo

dCorpo

rate

Centre

BuildingNo.8

62.6

kWh/m

2/year(design

total)Natural

Gas

14.2

kWh/

m2/yearElectricity

48.4

kWh/m

2/year

51.7%

ASHRAE90

.1-198

9Tilt-upconcrete

wallswith

upgraded

airtig

htness

and

insulatio

n;thermally

brok

enAl-fram

edDG

low-e

windo

ws;redu

cedlig

htingpo

wer

densities;high

efficiency

boilerandchiller;4-pipe

fancoilsystem

w/

DOAS

C-200

0Internal

Program

Reporta,b

MECRetailStore

Ottawa

202.8kW

/m2annu

al(design)

Natural

Gas

110.3kW

h/m

2/

year

Electricity

92.5

kWh/

m2/year

56%

MNECB

Upg

radedwallandroof

insulatio

n,DG

low-e

argo

n-filled,

warm

edge

spacer

windo

wsin

clad

woo

dor

TB

Alfram

es;TG

low-e

windo

wson

northfaces;roof

mon

itors

fordaylightingandgreatly

redu

cedconn

ected

lightingpo

wer;high

efficiency

boiler,mid

efficiency

rooftopventilatio

nun

it,ventilatio

nheat

recovery,

upgraded

chiller

efficiency,CO2DCV,variable

speed

fandrives

CBIP

Internal

Techn

ical

Review

Reporta,b

SC3Smith

CarterOffice,

Winnipeg

142.8kW

/m2/year(design)

Electricity

142.8kW

h/m

2/

year

55%

MNECB

Upg

radedinsulatio

nin

wallsandroof;DG

low-e

argo

n-filledwarm

edge

spacer

windo

wsin

TBAlfram

es;

daylightingw/wirelessdigitalandoccupancysensor

controls;exterior

solarshading,

redu

cedconn

ected

lightingpo

wer,combinatio

nbo

ilerandgrou

ndsource

heat

pumpw/GSHPsizedforcooling,

DOASw/

UFA

D

CBIP

Internal

Techn

ical

Review

Reporta

MECRetailStore

Winnipeg

101.5ekW/m

2annu

al(design)

Natural

Gas

41.9

kW/m

2

Electricity

59.6

kWh/m

2

56%

MNECB

Upg

radedinsulatio

nin

wallsandroof,low

fenestratio

n-to-w

allratio

,DG

low-e

argon-filledwarm

edge

spacer

windo

wsin

TB

alum

inum

fram

es;daylightingw/

occupancysensor

controlsandredu

cedconn

ected

lightingpo

wer;mid

efficiency

boiler,DOAS,radiant

slab

andpanelheatingwith

grou

ndwater

cooling

C-200

0Internal

Program

Reporta

FatherMichael

McG

ivney

Secon

dary

Schoo

l14

8kW

h/m

2/year

58%

352kW

h/m

2/year

GSHP,

heat

pipe

type

heat

recovery

unit

GenestandMinea

(200

6)


Tab

le1

(con

tinued)

Buildingandlocatio

nEnergyuse

Energy

saving

sReference

for

comparisonof

energy

use

Key

features

Reference

MECRetailStore,Mon

treal

147.3kW

/m2/year(design)

133kW

/m2/year(actual

2004

)

68%

MNECB

(466

kWh/

m2/year)

High-performance

envelope,daylighting,

GSHP,

DOAS,

radiantslab

heatingandcooling,

earthcoup

ledou

tside

airtempering

.

GenestandMinea

(200

6)

CentreforInteractive

Researchon

Sustainability,

Vancouv

er(propo

sed

design

)

56kW

h/m

2/yearwith

out

BiPVandsolarthermal

(47

kWh/m

2/yearwith

solar)

84%

Typ

ical

existin

gbu

ilding(353

kWh/

m2/year)

High-performance

envelope,adjustable

atrium

shading,

hybrid

ventilatio

n,daylighting,

VSDs,DCV,90

%heat

recovery

effectiveness

Heptin

gandEhret

(200

5)

Sexam

ples

NRELofficesandlabs,

Golden,

Colorado

45%

and

63%

(two

build

ings)

ASHRAE90

.1Murph

y(200

2)

Env

iron

mentalCenter,

Oberlin

College,Ohio

87kW

h/m

2/yearb

48%

ASHRAE90

.1-200

1(169

kWh/m

2/year)

High-performance

envelope,GSHP,

daylighting

Pless

etal.(200

6)60

kWh/m

2/yearwith

recommendedchanges

64%

Federal

Cou

rtho

use,

Denver

50%

ASHRAE90

.1-198

9Tripleglazing,

mod

estinsulatio

n,sunshading

,daylighting,

T5lamps,VAV

displacementventilatio

n,direct

andindirect

evaporativecooling,

VSD

onallair

hand

lers

andpu

mps,BiPV

Mendler

andOdell

(200

0)

Hom

eim

prov

ementstore,

Silv

erthorne,Colorado

124kW

m/m

2/year

54%

ASHRAE90

.1-200

1(296

kWh/m

2/year)

Higher-performance

envelope,hydronic

radiantfloor

heating,

redu

cing

lightingload

anddaylighting,

solar

thermal

collectors.

Torcellini

etal.

(200

4a)

SCJohn

sonWax

Headq

uarters,Racine(W

I)<21

8kW

h/m

2/yeartotal

54%

Ave

new

build

ings

ExistingSJC

build

ings

Daylig

htingwith

automatic

controls,fixedandadjustable

shading,

demand-controlleddesktopperson

alairsupp

lyMendler

andOdell

(200

0)69

%

Academic

build

ing,

U.of

Wisconsin,Green

Bay

60%

Wisconsin

energy

code

WallU

value0.16

W/m

2/K

Roo

fU

value0.11

W/m

2/K

Sky

lightswith

suspendedreflectors

andmotorized

blacko

utpanelsBiPV

Mendler

andOdell

(200

0)

CenterforHealth

and

Healin

gat

theOrego

nHealth

andScience

University,River

Cam

pus

60%

ASHRAE90

.1-199

9Hyb

ridventilatio

n,solarpreheatin

gof

ventilatio

nair,heat

recovery,radiantheating/cooling,

demand-controlled

displacementventilatio

n,PV

mod

ules

asexterior

shading,

commission

ing.

Interface

Eng

ineering

(200

5)

ZionNationalParkVisito

rCentre

85kW

h/m

2/year

62%

Cod

e-compliant

build

ingat22

2kW

h/m2/year

Mod

estly

betterinsulatio

nandwindo

ws,high

thermal

mass,daylightingwith

controls,do

wnd

raftevaporative

cooling

Lon

get

al.(200

6)

Cam

bria

OfficeBuilding,

Ebensbu

rg,Pennsylvania

124kW

h/m

2/year

64%

Reference

build

ings

at32

2kW

h/m

2/year

High-performance

envelope,Und

erfloo

rairdistribu

tion,

heat

recovery

ventilators,GSHP,

daylight

andmotion

sensors

Torcellini

etal.

(200

4b)

Federal

Reserve

Bank,

Minneapolis

<13

4kW

h/m

2/yeartotal9.1

W/m

2conn

ectedlig

hting

load

7.0W/m

2average

74%

ASHRAE90

.1Windo

wUvalue0.74

W/m

2/K

WallUvalue0.2W/m

2/K

Con

ventionalVAV

HVAC

Mendler

andOdell

(200

0)


Tab

le1

(con

tinued)

Buildingandlocatio

nEnergyuse

Energy

saving

sReference

for

comparisonof

energy

use

Key

features

Reference

lightingload

IowaAssociatio

nof

Mun

icipalities

office

107kW

m/m

2/yearsimulated

88–9

1measured

65%

Iowabu

ildingcode

19%

windo

w:wallratio

,high

-perform

ance

envelope,

daylighting,

GSHP,

enthalpy

wheel

forheat

recovery.

McD

ougallet

al.

(200

6)75

%Judson

College

Library,

Illin

ois

69%

fans,

78%

cooling

Mechanically

ventilatedbu

ilding

Designstud

yto

illustrateeffectivenessof

hybrid

ventilatio

nin

redu

cing

coolingandfanenergy

usein

acontinentalclim

ate

Sho

rtandLom

as(200

7)

Science

Museum

ofMinnesota

64kW

h/m

2/yeargross,<0

kWh/m

2/net

usingPVarrays

78%

290kW

h/m

2/yearfor

code-com

pliant

build

ing

Passive

solardesign

,daylighting,

GSHPforheatingand

cooling(w

ithrespectiv

eCOPsof

3.1and3.7)

Steinbo

cket

al.

(200

7)

Env

iron

mentalTechn

olog

yCentre,

Son

omaState

University,California

80%

CaliforniaTitle24

Beeler(199

8)

Europ

eanexam

ples

Brund

tland

Centre,Denmark

50kW

h/m

2/year

70%

Typ

ical

comparable

build

ing(170

kWh/

m2/year)

PrasadandSno

w(200

5)

CenterforSustainable

Building,

Kassel,Germany

16.5

kWh/m

2/yearheating

73%

1995

German

BuildingCod

eTy

picaloffice

build

ing

WallU

value0.11

W/m

2/K,windo

wU

value0.8W/m

2/

K,radiantslab

heatingandcooling,

grou

ndheat

exchanger(COP=

23),hy

brid

ventilatio

n,daylighting

Schmidt(200

2)and

Schmidt(personal

commun

ication

2006

)

32–4

2kW

h/m

2/yeartotal

energy

use

76–8

2%

DebisBuilding,

Potsdam

erPlatz,Berlin

75kW

m/m

2/yeartotal

80%

Dou

ble-skin

façade

andpassiveventilatio

nGrut(200

3)

Ionica

Building,

UK

64kW

m/m

2/yeartotal

46%

Goo

d-practiceair

cond

ition

edbu

ilding

Hyb

ridventilatio

nHyb

vent

website

(hyb

vent.civil.auc.

dk)

Solar

Bau

prog

ram,10

build

ings

inGermany

25–1

40kW

h/m

2/yearprim

ary

energy

exclud

ingoffice

equipm

ent

50–9

0%Typ

ical

office

build

ings,30

0–60

0kW

h/m

2/year

prim

aryenergy

Mechanicalnigh

tventilatio

nwith

expo

sedthermal

mass

orhy

dron

iccoolingintegrated

with

grou

ndwater,

external

shading,

redu

cedglazingarea,minim

alinternal

heat

gains,efficientlig

hting.

Wagneret

al.

(200

4)

Solar

Office,

Dox

ford

InternationalB

usinessPark,

UK

85kW

h/m

2/year

80%

Typical

new

air-

cond

ition

edbu

ildings

intheUK

(400

kWh/m

2/year)

Passive

ventilatio

nandcooling;

BiPV

functio

ning

aspartialshadingdevices.

PrasadandSno

w(200

5)


Tab

le1

(con

tinued)

Buildingandlocatio

nEnergyuse

Energy

saving

sReference

for

comparisonof

energy

use

Key

features

Reference

ElizabethFry

Buildingand

Zuckerm

anBuilding,

University

ofEastAng

lia

30–3

7kW

h/m

2/yearheating

93–1

00kW

h/m

2/yeartotal

High-performance

envelope,concrete

hollo

w-coreceiling

slab

with

nigh

t-tim

eventilatio

n,high

airtig

htness

Coh

enetal.(20

07),

TurnerandTov

ey(200

6)Asian

exam

ples

KierBuilding,

Sou

thKorea

68kW

m/m

2/yearelectricity,

18kW

m/m

2/yearheat

Dou

ble-skin

façade,g

roun

dcoup

ledheatexchanger,solar

thermal

andPV.

PrasadandSno

w(200

5)Liberty

Tow

er,Meiji

University,Japan

48%

Japanese

build

ing

code

Hyb

ridventilatio

nHyb

vent

website

(hyb

vent.civil.auc.

dk)

Tok

yoEarth

Port

380kW

m/m

2/yearprim

ary

energy

45%

Typ

ical

office

build

ingin

Japan

Hyb

ridventilatio

nBaird

(200

1)

Torrent

Pharm

aceutical

ResearchCentrein

Ahm

edabad,India

64%

for

electricity

Con

ventionalmod

ern

build

ing

Evapo

rativ

ecoolingandhy

brid

ventilatio

n(passive

downd

raug

htcooling)

Fordet

al.(199

8)

Dem

onstratio

noffice

inBeijin

g65

kWm/m

2/yearelectricity

78kW

m/m

2/yeartotal

60%

Sim

ilarlyequipp

edoffice

inBeijin

gwith

centralair

cond

ition

ing

Optim

ized

build

ingform

andorientation,

improv

edwindo

wsandchillers,redu

cedwindo

warea,simple

daylightingscheme

Xuet

al.(200

7)

Ministryof

Energy,Water

&Com

mun

ications

Building,

Putrajaya,Malaysia

100kW

h/m

2/yeartotalon

-site

energy

usebasedon

compu

tersimulation

64%

Con

ventionaldesign

(275

kWh/m

2/year)

Daylig

hting,

insulatio

nin

wallsandroof,energy

efficient

equipm

ent,energy

managem

ent,room

temperature

24°C

insteadof

23°,tig

htbu

ilding

Roy

etal.(200

5)

Shang

aiEco-Building,

NationalCon

struction

Departm

ent

48kW

h/m

2/yearheating+

coolingon

-site

energy

use

basedon

compu

ter

simulations

69%

Con

ventionaldesign

(155

kWh/m

2/year)

Windo

wshadingdevices,advanced

glazing,

high

lyinsulatedenvelope,naturalventilatio

nZhenet

al.(200

5)

aAvailablefrom

Steph

enPop

e,Natural

Resou

rces

Canada

bGross

energy

use,

exclud

ingcontribu

tionfrom

PV

COPcoefficientof

performance,DCVdemand-controlledventilatio

n,DG

doub

le-glazed,

DOASdedicatedou

tdoo

rairsupp

ly,GSH

Pgrou

nd-sou

rceheat

pump,

TB

thermally-

brok

en,TG

triple-glazed,

UFA

Dun

derfloor

airdistribu

tion,

VAVvariable

airvo

lume,

VSD

variable-speed

drive


of the overall cost in the case of commercial buildings.For both commercial and residential buildings, the costof achieving a given energy performance will be lowerin new buildings than in existing buildings, and theachievable energy performance is much better for newbuildings (as certain design decisions cannot bereversed). Thus, failure to rapidly implement vastlybetter building performance requirements in buildingcodes represents a significant lost opportunity.

Cost of deep savings in residential buildings

Increasing the amount of insulation entails greaterinsulation costs and hence greater annual mortgagecosts but reduced heating costs. Figure 2 shows thetradeoff between these two for residential buildings inCanada. There is a very broad minimum in the totalcost, and total costs at insulation levels substantially

greater than currently required are substantially lessthat at required insulation levels. Absolute costs aredifferent in other countries, but the broad features ofthe cost curves highlighted here are still applicable.

Window performance can be chosen so as topermit elimination of perimeter heating on the coldestwinter days, down to temperatures of −40°C whileserving as a net heat source over the course of theheating season (due to passive solar gains exceedingheat losses). The elimination of perimeter heating inturn reduces costs and amplifies the savings in heatingenergy use by shifting the warmest temperatures awayfrom the window area (Harvey and Siddall 2008).Figure 3 shows the window heat loss-coefficient (Uvalue) below which perimeter heating units can beeliminated, as a function of the coldest anticipatedoutdoor temperature.

Figure 4 shows the progressive decline in the costof the additional investment required to meet thePassive House standard (which requires 4–8 timesless heating energy use than in conventional newhousing) in central Europe. Through learning, costshave fallen to the point where the incremental costcan be justified based on 2005 energy prices andinterest rates. Schnieders and Hermelink (2006) reportthat the additional cost averaged over 13 PassiveHouse projects in Germany, Sweden, Austria, andSwitzerland is 8% of the cost of a standard house butthat when amortized over 25 years at 4% interest anddivided by the saved energy, the cost of saved energyaverages 6.2 eurocents/kWh (the range is 1.1–11 eurocents/kWh). This is somewhat more thanthe present cost of natural gas to residentialconsumers in most European countries, which rangesfrom 2–8 cents/kWh (IEA 2004). Audenaert et al.(2008) estimate extra costs of 4% for low-energyhouses and 16% for Passive Houses in Belgium(having energy savings of 35% and 72% relative tocurrent standard houses in Belgium).

An analysis of the cost of reducing energy use insingle-family houses in the US indicates that totalfinancial costs (annual mortgage costs plus energycosts) are minimized at an energy savings of only40% (Anderson et al. 2006), but this analysis did notconsider the savings arising from elimination ofperimeter heating units when high-performance win-dows are specified nor did it consider simplemeasures such as overhangs for shading to reducecooling loads.

0

10

20

30

40

50

60

70

0.476 0.370 0.323 0.286 0.256 0.233 0.213 0.196 0.182 0.149

U-value (W/m2/K)

Life

-cyc

leco

st($

/m2 )

Extra incremental heating cost, $20/GJ vs $15/GJ

Extra incremental heating cost, $15/GJ vs $10/GJ

Incremental heating cost at $10/GJ

Incremental construction cost

R20 walls R40 walls

Fig. 2 Comparison of incremental lifecycle costs of walls inCanada with increasing amounts of insulation (successivelysmaller U values). The lowest part of each bar is theincremental construction cost relative to the least-insulatedwall, the second part of each bar is the incremental heatingcost relative to the best-insulated wall for a heating fuel costof $10/GJ, the third part of each bar is the additionalincremental heating cost if the heating fuel costs $15/GJinstead of $10/GJ, and the top part of each bar is theadditional incremental heating cost if the heating fuel costs$20/GJ instead of $15/GJ. Incremental heating costs and/orconstruction financing costs were computed assuming HDD=5000 K-day, 6%/year interest, 3%/year energy-cost inflation,and financing over a 30-year period. Not included in this costcomparison are the reduction in cooling energy use and thedownsizing of heating and cooling equipment that occurs withhigher-performance thermal envelopes. Source: Harvey(2006)


Cost of deep savings in commercial buildings

As an example of the savings in first-cost that is possiblefor commercial buildings with advanced, energy-efficient designs, Table 2 gives a breakdown of capitalcosts for commercial buildings in Vancouver, Canada,having conventional windows (double-glazed, air-filled, low-e) and a conventional heating/coolingsystem, and for buildings with moderately high-performance windows (triple-glazed, low-e, argon-filled) and radiant-slab heating and cooling. The

high-performance building is 9% less expensive tobuild than a comparable conventional building,while using about half the energy.

Another example of a building with large energysavings costing less than if built according to code isprovided by one of the first buildings built on the newOregon Health and Science University, River Campusin 2006. This 16-storey building is expected toachieve an energy savings of 60% relative toASHRAE 90.1-1999 through such measures as hybridventilation using the stack effect in stairwells, solarpreheating of office ventilation air, heat recovery onlaboratory ventilation, radiant heating or cooling,demand-controlled displacement ventilation, PV mod-ules as exterior shading, accurate equipment sizing,and commissioning. Incremental costs or upfrontsavings are given in Table 3. Cost savings due todownsizing of the mechanical systems permitted bythe efficiency measures exceeded the cost of theefficiency measures. A further credit arises from thespace saved due to more efficient and downsizedmechanical systems. The net result is a constructioncost savings of about $3.5 million out of an originalbudget of $145.4 million (a 2.4% savings) andoperating cost savings of $600,000/year.

In other cases, highly efficient buildings have costmore, but the time required to pay back the additionalcost with energy-cost savings has been short. As anexample, the recently completed science building at

0

50

100

150

200

250

300

350

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00

20

01

20

02

20

03

20

04

20

05

20

06

20

07

20

08

20

09

20

10

Ad

ditio

na

lIn

ve

stm

en

t(E

/m2)

of

Pa

ssiv

eR

ow

Ho

use

s

1991 Prototype: experimental house,

4 dwellings in Kranichstein using

handicraft batch production

PH in Gro -Umstadt:

Reduced costs by

simplification

Settlement in Wiesbaden:

Serially produced windows

& structural elements

Settlements in Wuppertal,

Stuttgart, Hanover

Row houses in Darmstadt,

802

Profitability with

contemporary

interest rates & energy prices

ß

C /m

Fig. 4 Learning curveshowing the progressive de-crease in the incrementalcost of meeting the PassiveHouse standard for the cen-tral unit of row houses.Source, Feist (2005)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

-40 -30 -20 -10 0 10

Outdoor Design Temperature (oC)

Ma

xim

um

Pe

rmitte

dU

-Va

lue

(W/m

2/K

)

Inner glazing T = 16oC


Indoor Air Temperature = 20oC


Fig. 3 Window U value below which perimeter heating is notneeded as a function of the minimum expected winter outdoortemperature and of the minimum permitted temperature of theinnermost glazing surface. Source, Harvey and Siddall (2008)


Concordia University, Montreal, with offices, class-rooms, and 250 fume hoods, achieved a 45%reduction in energy use relative to ASHRAE 90.1-1999 at an incremental cost of 2.3% ($1,356,000 outof $59,500,000) while yielding an annual energy costsavings of $854,000, for a payback time of 19 months(Lemire and Charneux 2005).

Table 4 provides information on the incrementalcost and energy savings for 32 buildings in the USAthat met various levels of the Leadership in Energy andEnvironmental Design (LEED) standard. The energysavings are broken into reductions in gross energydemand, and reductions in net energy demand includ-ing on-site generation (by, for example, PV modules),which tends to be expensive. The cost premium is thetotal cost premium required to meet the various LEEDstandards and so includes the cost of non-energyfeatures as well. Nevertheless, average costs are less

than 2% of the cost of the reference building and aresmaller on average for buildings with 50% savings innet energy use than for buildings with 30% savings.

Measured performance information on ten buildingsin the German SolarBau program where at least 1 yearof data were available by 2003 is given in Wagner etal. (2004). Five of the ten buildings achieved the100 kWh/m2/year primary energy target (compared to300–600 kWh/m2/year for conventional designs), butno building used more than 140 kWh/m2/year ofprimary energy.1 Additional costs are reported to becomparable to the difference in cost between alterna-tive standards for interior finishing.

In addition to energy-cost savings, high performancebuildings—especially buildings with daylighting, tasklighting, and natural ventilation that can be controlled bythe occupants—have difficult-to-quantify but importantadditional savings. These include improved workerproductivity, improved retention of workers, and im-proved competitiveness in hiring skilled workers.

Energy savings through retrofits of existingcommercial and residential buildingsand associated costs

To achieve significant reductions in overall energyuse by buildings, considerable effort will need to bedirected at existing buildings due to the fact that most

Table 3 Economics of the new Oregon Health and ScienceUniversity building

Item Cost

Total project cost $145.4 millionEnergy efficiency features $975,000PV system $500,000Solar thermal system $386,000Commissioning $150,000Total $2,011,000Savings in mechanical systems $3,500,000Value of saved space $2,000,000Net cost −$3,489,000Estimated annual operating cost savings $600,000

Source, Interface Engineering (2005)

Table 2 Comparison of component costs for a building with aconventional VAV mechanical system and conventional (dou-ble-glazed, low-e) windows with those for a building with

radiant slab heating and cooling and high-performance (triple-glazed, low-e, argon-filled) windows, assuming a 50% glazingarea/wall area ratio

Building component Conventional building High-performance building

Glazing $140/m2 $190/m2

Mechanical System $220/m2 $140/m2

Electrical System $160/m2 $150/m2

Tenant finishings $100/m2 $70/m2

Floor-to-floor height 4.0 m 3.5 mTotal $620/m2 $550/m2

Energy use 180 kWh/m2/year 100 kWh/m2/year

Costs are in 2001 Canadian dollars for the Vancouver market in 2001, are given per m2 of floor area, and are based on fully costedand built examples over a 3-year period. Source, Geoff McDonell (Omicron Consulting, Vancouver), personal communication,December 2004, and McDonell (2003).

1 Primary energy in the case of electricity is the energy used bythe power plant and is about three times the energy content ofthe electricity used by the building.


of the buildings that will exist in 2030 and even in2050 in some countries already exist today. However,even long-lived buildings require periodic majorrenovations (and certainly at least once between nowand 2050), which provide opportunities for achievingdeep (50–75%) reductions in energy use.

Commercial buildings

Measures that can be taken to reduce energy use inexisting commercial buildings include upgrades to thethermal envelope (such as reduction in air leakage, orcomplete replacement of curtain walls), replacementof heating and cooling equipment, reconfiguration ofHVAC systems, implementation of better controlsystems, lighting improvements, and implementationof measures to reduce the use of hot water. Thequantitative savings from specific measures dependson the preexisting characteristics, climate, internalheat loads, and occupancy pattern for the particularbuilding in question. However, large (50–70% ormore) savings in energy use have been achievedthrough retrofits of commercial buildings throughoutthe world.

Some examples from the literature of savingsachieved through relatively simple measures are:

& A projected savings of 30% of total energy use in80 office buildings in Toronto through lightingupgrades alone (Larsson 2001);

& A realized savings of 40% in heating + cooling +ventilation energy use in a Texas office buildingthrough conversion of the ventilation system fromone with constant airflow to one with variable airflow (Liu and Claridge 1999);

& A realized savings of 40% of heating energy usethrough the retrofit of an 1865 two-storey officebuilding in Athens, where low energy was

achieved through some passive technologies thatrequired the cooperation of the occupants (Balaras(2001)

& A projected savings of more than 50% of heatingand cooling energy for restaurants in citiesthroughout the USA by simply optimizing theventilation system (Fisher et al. 1999)

& A projected 51% savings in cooling + ventilationenergy use in an institutional building complex inSingapore through simple upgrades to the existingsystem (Sekhar and Phua 2003)

& A realized savings of 74% in cooling energy usein a one-storey commercial building in Floridathrough duct sealing, chiller upgrade, and fancontrols (Withers and Cummings 1998)

& Realized savings of 50–70% in heating energy usethrough retrofits of schools in Europe and Aus-tralia (described in the March 1997 issue of theCADDET Energy Efficiency Newsletter, publishedby the International Energy Agency)

& Realized fan, cooling, and heating energy savingsof 59%, 63%, and 90%, respectively, in buildingsat a university in Texas, roughly half due to astandard retrofit and half due to adjustment of thecontrol-system settings (which were typical forNorth America) to optimal settings (Claridge et al.2001)

& Average realized savings of 68% in natural gasuse after conversion of ten US schools from non-condensing boilers producing low-pressure steamto condensing boilers producing low-temperaturehot water, and an average savings of 49% afterconversion of ten other US schools from high- tolow-temperature hot water and from non-condens-ing to condensing boilers (Durkin 2006)

& Projected savings of 30–60% in cooling loads inan existing Los Angeles office building simply byoperating the existing HVAC system in a manner

Table 4 Energy savings relative to ASHRAE 90.1-1999 and cost premium for buildings meeting various levels of the LEED standardin the USA

LEED level Sample size % Energy savings, based on Cost premium (%)

Gross energy use Net energy use

Certified 8 18 28 0.66Silver 18 30 30 2.11Gold 6 37 48 1.82

Source, Kats et al. (2003)


so as to make maximum use of night coolingopportunities (Armstrong et al. 2006)

& Projected savings of 48% from a typical 1980soffice building in Turkey through simple upgradesto mechanical systems and replacing existingwindows with low-e windows having shadingdevices, with an overall economic payback timeof about 6 years (Çakmanus 2007)

& Projected savings of 36–77% through retrofits of avariety of office types in a variety of Europeanclimates, with payback times generally in the 1–30-year range (Hestnes and Kofoed 1997, 2002;Dascalaki and Santamouris 2002)

It should be emphasized that comprehensive retro-fits of buildings are generally done for many reasonsin addition to reducing energy costs. Thus, measuresthat are extensive enough to significantly reduceenergy use may not pay for themselves in terms ofenergy cost savings alone, but this does not mean thatthey should not be carried out.

A significant potential area for reduced energyuse in existing buildings is through replacement ofexisting curtain walls or upgrades of existinginsulation and windows. Given the current frenzyconstructing nearly all-glass buildings but not evenusing high-performance glazing, replacing existingglazing systems and curtain walls will be anessential future activity if deep reductions inheating and cooling energy use are to be achieved.Recently, the curtain walls were replaced on the24-storey 1952 Unilever building (Lever House) inManhattan (see http://www.som.com/content.cfm/lever_house_curtain_wall_replacement), so thereseems to be no major technical problems in under-taking complete curtain wall replacements on high-rise office buildings.

In the case of brick or cement façades, one optionis to construct a second glazed façade over the first—creating a double-skin façade—which opens upopportunities for passive ventilation and reducedcooling loads through the provision of adjustableexternal shading devices. This has often been done inEurope. A North American example of the construc-tion of a second façade over the original façade isprovided by the Telus headquarters building inVancouver. In this case, the second façade wasconstructed as part of measures to increase theearthquake resistance of the building. Construction

of a second façade can also be undertaken as ameasure to preserve original facades that are deteri-orating due to moisture problems related to defects inthe original construction.

Residential buildings

Energy use of residential buildings can be reducedthrough upgrading of windows, adding internalinsulation to walls during renovations, adding exter-nal insulation to walls, adding insulation to roofs atthe time that roofs need to be replaced, and throughmeasures to reduce uncontrolled exchange of insideand outside air. Some documented examples ofcomprehensive retrofit measures and the energysavings are:

& sealing of ductwork alone in US houses saving anaverage of 15–20% of annual heating and airconditioning energy use (Francisco et al. 1998)

& a retrofit of 4,003 homes in Louisiana, includingthe switch from natural gas to a ground sourceheat pump for space and water heating, therebyeliminating natural gas use and still decreasingelectricity use by one third (Hughes and Shonder1998)

& upgrade of multiunit housing in Germany using,among other measures, External Insulation andFinishing Systems to achieve a factor of 8 reduc-tion in heating energy use (see www.3lh.de)

& an envelope upgrade of an apartment block inSwitzerland reduce the heating requirement byalmost factor of 3 (Humm 2000)

& reduction of heating energy use in retrofits ofhouses in the York region (UK) by 35% throughair sealing and modest insulation upgrades and aprojected 70% savings with more extensivemeasures (Bell and Lowe 2000)

& comprehensive retrofit of old apartment block inZurich, including replacement of roof, achievingan 88% savings in heating energy use measuredover a 2-year period (Viridén et al. 2003)

In apartment buildings with balconies, the bal-cony slabs are a conduit for heat loss. Glazing thebalconies so that they serve to preheat ventilationair, and integrating the balcony with the ventilationsystem of the apartments, can turn a thermalliability into an asset. Transpired solar air collectorsover vertically extensive equatorward-facing walls


http://www.som.com/content.cfm/lever_house_curtain_wall_replacement

http://www.som.com/content.cfm/lever_house_curtain_wall_replacement

http://www.3lh.de

are another solar option, as well as transparent solarinsulation, construction of a second (glass) façadeover the original façade, and installation of con-ventional solar-air thermal collectors. Savings of60–70% in old (per-1950) buildings and 30–40% innew (1970 or later) buildings in Europe have beenobtained in these ways (Boonstra et al. 1997; Halleret al. 1997; Voss 2000).

Studies for the European Mineral Wool Manufac-turers Association by the Dutch consulting firmEcofys indicate that the energy consumption in oldbuildings in western Europe (EU-15) can be reducedby more than 50% with no additional cost over a 30-year lifetime, and by up to 75% in new countries ofthe EU-27 (Petersdorff et al. 2005a, b).

A number of single-family and multiunit residen-tial buildings have been upgraded to the PassiveStandard in Europe. In the case of an old detachedhouse (documented at www.hausderzukunft.at/results.html/id3955), the renovation reduced theheating energy use from 280 to 14.6 kWh/m2/yearat 16% greater cost than a conventional renovation,but the impact of the extra cost on mortgagepayments is less than the energy cost savings. Inthe case of a 50-unit residential building (docu-mented at www.hausderzukunft.at/results.html/id3951), heating energy use was reduced from 179to 13.3 kWh/m2/year at 27% greater renovation cost.

Construction of a generic scenario for futureenergy use and energy intensity

The energy use for a given building sector with agiven fuel in a given region at a given time in thefuture will depend on:

& the fraction of the existing floor space that hasbeen renovated by the given time

& the difference between the energy intensity beforeand after renovation

& the fraction of the existing floor space that hasbeen replaced by the given time

& the difference between the energy intensity of theold and replacement floor space

& the net addition of new floor space each yearbetween the present and the year in question

& the energy intensity of the new floor space addedeach year

Older buildings on average are more energyintensive than more recent buildings. In Canada,for example, new commercial buildings on averagehave an energy intensity about 16% less than thestock average, while the most energy-intensivebuildings (those built in the 1960s) have an energyintensity about 16% greater than the stock average. LetΔE be the deviation in the energy intensity of newbuildings from the stock average. ΔE=0.16 for totalaverage energy use applied to all buildings acrossCanada but would be different in other countries andfor different building types within any given countryor region.

To illustrate the challenges in achieving largeabsolute reductions in the total energy use by buildingstock, even as far in the future as 2050, the followingaccounting procedure was used to calculate thevariation in total building use and in the averageenergy intensity from 2005 to 2050 relative to thevalues in 2005,

& the entire building stock is divided into 45 equalcohorts of size fstart (fstart is given as a fraction ofthe floor area in 2005, so fstart=1/45);

& the initial energy intensity Estart of each cohortrelative to the average initial energy intensity isassumed to vary across the cohorts from 1+ΔEto 1−ΔE, with an equal fraction of the buildingstock in energy-intensity intervals of equal width

& the cohorts are replaced or renovated in order ofdecreasing energy intensity (so in 2006, someportion of the most energy-intensive cohort isrenovated and some portion is replaced, while in2007 the second most energy-intensive cohort isrenovated or replaced, and so on)

& the portions of the total building stock that arerenovated and replaced by 2050 are Freno andFreplaced, respectively, so the floor areas renovatedor replaced in a given year (as a fraction of thetotal floor area in 2005) are freno=Freno/45 andfreplaced=Freplace/45, respectively (if Freno+Freplaced

=1.0, then freno+ freplaced= fstart)& in addition, the building floor area, as a fraction of

the initial floor area, is assumed to grow by somespecified amount between 2005 and 2050

& the energy intensity of a new building, or of arenovated building after the renovation, dependson the year in which it is built or renovated, anddoes not change once built or renovated


http://www.hausderzukunft.at/results.html/id3955




& the energy intensity of successive cohorts of newbuildings decreases over time from Enew-0 to Enew-f,and the energy intensity of renovated buildingsdecreases over time from Ereno-0 to Ereno-f (all theseenergy intensities are relative to the initial stockaverage)

& the initial energy intensities Enew-0 and Ereno-0

persist until year I1, then decrease linearly to theirfinal values by year I2, and are held constantthereafter.

Thus, the total energy use of the building stock inyear n, E(n), relative to energy use in 2005, is givenby

E nð Þ¼Xn

i¼1

frepl ið Þ þ fnew ið Þ� �

Enew ið Þ þ freno ið ÞEreno ið Þþfremain ið ÞEstart ið Þ

8>><

>>:

9>>=

>>;

þX45

i¼nþ1

fstart ið ÞEstart ið Þ

ð1Þwhere n is the number of years since 2005 (and so runsfrom 1 to 45), Enew(i) is the energy intensity of newbuildings built in year i (Enew(i) runs from Enew-0 toEnew-f, as explained above), Estart(i) is the energyintensity prior to renovation of buildings renovated inyear i (Estart(1)=1.0+ΔE and Estart(45)=1.0−ΔE),Ereno(i) is the energy intensity after renovation ofbuildings that are renovated in year i (Ereno(i) runs fromEreno-0 to Ereno-f), and fremain(i)=1.0−frepl(i)−freno(i). Itis assumed that the most recently built existingbuildings (those built in 2005) have an energy intensityequal to 1.0−ΔE, and it is also assumed that newbuildings in 2006 (and up to year I1) have the sameenergy intensity. Thus, we set Enew-0=1.0−ΔE.

Figure 5 shows the variation in the average energyintensity and in total energy use by the building stock,relative to the average and total in 2005, for low (25%growth) and high (100% growth) scenarios of floor area,for ΔE=0.16, and for the following technology cases:

& ModerateThe energy intensity of new and renovatedbuildings decreases from 84% of the 2005 stockaverage in 2010 to 42% in 2050 (i.e., a factor of 2reduction compared to average current practicefor new buildings).

& Deep

& The energy intensity of new buildings decreasesfrom 84% of the 2005 stock average in 2010 to21% in 2050 (i.e., a factor of four reductioncompared to average current practice for newbuildings), while the energy intensity of renovatedbuildings decreases from 84% of the 2005 stockaverage in 2010 to 33% in 2050.

& Deep and fastSame as Deep, except that the intensity levelsachieved by 2005 in Deep are achieved by 2020instead

As can be seen from Fig. 5a, the combination of adoubling in floor area and even a factor of fourreduction in the energy intensity of new buildings anda factor of three reduction in the energy intensity ofrenovated buildings, gradually achieved by 2050, isnot sufficient to prevent absolute energy use fromincreasing (albeit by only 22% before decliningslightly). This is because many existing buildingshave been renovated and many new buildingsconstructed before most of the eventual reductionsin energy intensity are achieved. Conversely, if theassumed final energy intensities are reached by 2020,then a 25% reduction in absolute energy use by 2050occurs. For countries where only a 25% furtherincrease in total floor area occurs, absolute energyuse by buildings can be reduced by almost a factor oftwo with deep and fast reductions in the energyintensities of new and renovated buildings.

Figure 5b shows the variation in average energyintensity (relative to 2005) for the above scenarios.Average energy intensity is smaller for the scenariowith high growth in floor area because a larger fractionof the future building floor area is relatively new (and,therefore, has lower than average energy intensity)when there is greater growth in the total floor area.

The results presented here are merely illustrativebut serve to underline the importance of rapidlyreducing the energy intensity of new and renovatedbuildings in order to achieve modest (25%) tosubstantial (50%) reductions in absolute energy usefrom the buildings sector.

Implications for CO2 emissions

We have not explicitly considered the impacts ofenergy efficiency measures on CO2 emissions. The


reduction in relative CO2 emissions depends on (1)the relative importance of fuels and electricity as end-use energy in the buildings sector; (2) the relativechanges in demand for electricity and for fuels(including any shift between fuels and electricity asoverall end use demand decreases); and (3) the mix ofenergy sources used to supply electricity on themargin (that is, supplying the next increment ofincreased or decreased electricity use). The sourcesof electricity on the margin (and the efficiency ofmarginal fossil fuel sources) often vary with time ofday and season, so the timing of electricity savings as

well as the magnitude will affect the resulting changein CO2 emissions. Conversely, any measures thatincrease flexibility in electricity demand (such ashigher performance envelopes or thermal energystorage) may permit shifting electricity demand totimes when only non-fossil energy sources supply thegrid, thereby permitting CO2 emission reductions, ormore permit greater use of variable non-fossilelectricity sources (such as wind energy). Thus,relative CO2 emission could, with well-designedpackages of efficiency measures, be larger than therelative savings in electricity demand.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Rel

ativ

eE

nerg

yU

se

High Growth, ModerateHigh Growth, DeepHigh Growth, Deep & FastLow Growth, ModerateLow Growth, DeepLow Growth, Deep & Fast

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2000 2010 2020 2030 2040 2050

Year

Rel

ativ

eE

nerg

yIn

tens

ity

High Growth, ModerateHigh Growth, DeepHigh Growth, Deep & FastLow Growth, ModerateLow Growth, DeepLow Growth, Deep & Fast

a

b

Fig. 5 Variation in the av-erage energy intensity andin total energy use by thebuilding stock, relative tothe average and total in2005, for scenarios of low(25%) and high (100%)growth in the total buildingfloor area by 2050, and formoderate or deep and slowor fast reductions in theenergy intensity of new andrenovated buildings, ascomputed using Eq. 1. Seetext for details


Concluding comments

Significant savings in energy use in new buildings ofall types and in all climate zones, compared to currentpractice, are possible using existing technologies. Forcommercial buildings, a 25% reduction should beeasily achievable by most design firms; a 50%reduction requires a higher degree of skill during thedesign process but normally does not require uncon-ventional systems; a 75% reduction normally requiresunconventional systems (such as displacement venti-lation and chilled-ceiling cooling in commercialbuildings) and an enlightening occupant behaviorbut, has been achieved in many buildings around theworld. In residential buildings, heating loads can belargely eliminated with high levels of insulation, high-performance windows, and construction of a close toairtight envelope with mechanical ventilation and heatrecovery. Passive techniques can greatly reduce cool-ing requirements in both commercial and residentialbuildings. The main obstacles to achieving these highenergy savings in new buildings is the lack ofknowledge and motivation within the design profes-sion. Extensive training programs in the integrateddesign process and in the techniques for reducinghearting, cooling, ventilation, and lighting loads inbuildings as well as training of all the trades involvedin building construction are urgently required, evenwith a significant strengthening of building codes.Given the long lifetimes of the building stock and theurgency of the global warming problem (see Risbey2008), an appropriate target would be to achieve afactor of 3–4 reduction in the energy intensity of newbuildings by 2020 and programs to achieve (onaverage) a factor of 2–3 reduction in the energyintensity of existing buildings whenever significantrenovations are carried out.

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