a review of design process for low energy solar homes
TRANSCRIPT
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IINNTTRROODDUUCCTTIIOONN
Homes that combine energy efficiency with passiveand active solar technologies can significantlyreduce their overall energy consumption and canbe referred to as low energy solar homes (LESH). Inthe last 25 years, there have been many one-of-a-kind demonstration projects and international ini-tiatives that have promoted the development ofLESH and in some cases, net-zero energy houses(ZESH). An acceleration of their adoption has beenwitnessed in the last few years as countries are start-ing to implement measures to reduce greenhousegas emissions to address global warming. In thecontext of this paper, the difference between a LESHand a ZESH is the first achieves a significant reduc-tion in overall energy consumption compared tostandard construction practices with no actual setenergy consumption target, whereas a ZESHachieves a yearly net-energy consumption of zero.Designing a LESH involves the coupling of manydifferent systems to achieve an energy efficientdesign, which also generates on-site energy usingrenewable energy technologies. The designinvolves the use of various types of systems, whichcan vary depending on the specific design objec-tives, the project location, the knowledge of thedesigner, etc., all of which lead to many different
design configurations. This can be observed byexamining net-zero and low energy buildingdemonstration projects from around the world(Charron, 2005). These projects depended on trial-and-error optimisation using dynamic energy simu-lation tools, coupled with the knowledge of thedesigners. Simulations are normally used in a sce-nario-by-scenario basis, with the designer generat-ing one design and subsequently having a comput-er evaluate it. This can be a slow and tediousprocess and typically only a few scenarios are eval-uated from a large range of possible choices.Although a reduction in the energy use of residen-tial buildings can be achieved by relatively simpleindividual measures, very high levels of perfor-mance require the coherent application of mea-sures, which together optimise the performance ofthe complete building system.
The use of design guidelines is one way thatdesigners try to optimise building performance.There are various books and articles that give spe-cific guidelines on how to design energy efficienthouses following passive solar techniques: (Chiras,2002, CMHC, 1998, Athienitis and Santamouris,2002) to list a few. The difficulty of using designguidelines is that they are generally dependent onthe climate where they were developed and thespecific technologies that were used in their devel-
Rémi CharronAbs t rac t
In recent years, there have been a growing number of projects and initiatives to promote the development and mar-ket introduction of low and net-zero energy solar homes and communities. These projects integrate active solar tech-nologies to highly efficient houses to achieve very low levels of net-energy consumption. Although a reduction in theenergy use of residential buildings can be achieved by relatively simple individual measures, to achieve very high lev-els of energy savings on a cost effective basis requires the coherent application of several measures, which togetheroptimise the performance of the complete building system. This article examines the design process used to achievehigh levels of energy performance in residential buildings. It examines the current design processes for houses used ina number of international initiatives. The research explores how building designs are optimised within the current designprocesses and discusses how the application of computerised optimisation techniques would provide architects, home-builders, and engineers with a powerful design tool for low and net-zero energy solar buildings.
Keywords: Optimisation, Low and net-Zero Energy Homes, Cost Effective Design.
A RREVIEW OOF DDESIGN PPROCESSES FFOR LLOW EENERGYSOLAR HHOMES
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opment. Another drawback of using guidelines isthat they are generally developed assuming idealconditions. There may be situations where a solarhouse is built on a property that is not directly fac-ing south or that is partially shaded, where existingdesign guidelines would perform poorly. Designguidelines that aim to help improve cost effective-ness are also very dependent on the costs of ener-gy and relevant technologies. Projected decreasesin the price of PV technologies in the next couple ofdecades (Hoffmann, 2006) will result in changes tothe configuration of optimal designs. If it becomesless expensive in the future to install larger PV sys-tems as opposed to certain energy efficiency mea-sures, it will likely change the recommendeddesigns.
A design tool that would help address theseissues would integrate optimisation algorithms tohelp designers filter through the countless possibledesign solutions to consider only the most promis-ing options. Coupling optimisation with energy sim-ulation programs would help account for differ-ences in technologies, local climate, economics,and other design constraints to assist the designer.This article presents different international LESH andZESH initiatives, along with a discussion of currentdesign methodologies and how optimisation toolscould help improve the design process. Given thelevel of activity that is currently occurring related tolow and net-zero energy houses around the world,not all programs have been listed. Examples ofprograms that were not mentioned are the LEEDrating program that now covers different buildingtypes from residential to commercial to neighbour-hood development projects, from new constructionto renovations (USGBC, 2007). The LEED neigh-bourhood rating is a pilot program that providesprinciples of smart growth, urbanism, and greenbuilding into the first national US standard forneighbourhood design.
LLOOWW AANNDD NNEETT ZZEERROO EENNEERRGGYY SSOOLLAARRHHOOMMEESS
EEQQuuiilliibbrriiuumm DDeessiiggnn CCoommppeettiittiioonnIn 2006, Canada Mortgage and HousingCorporation (CMHC) in co-operation with NaturalResources Canada (NRCan) initiated the
EQuilibrium demonstration project. The programattracted a lot of attention from architects andhomebuilders from across Canada. A total of 72different teams submitted project proposals toCMHC to be considered for the demonstration pro-gram. A selection committee then reviewed theseproposals and selected 20 projects to continue tothe second phase of the program, the designphase, which followed an integrated design process(IDP) with design charrettes. These 20 teams thensubmitted their final project proposal includingdetailed designs to CMHC. The committee thenevaluated all the projects and selected 12 projectsto be built across Canada, which will be finishedconstruction in late 2007 or early 2008. Oncecomplete, a monitoring phase will demonstrate thefeasibility of building net-zero energy homes in arange of Canadian geographic and climatic condi-tions.
Each submitted design was evaluated basedon five guiding principles: Health, Energy,Resources, Environment, and Affordability (CMHC,2007). To rate the Energy component of thedesigns, the EnerGuide for Houses (EGH) ratingmethodology was used (NRCan, 2007) with somemodifications to reflect to objective of reaching net-zero energy consumption. The main modificationwas to allow participants to justify a modification tothe baseload energy consumption. For the EGHrating, the baseload energy consumption for appli-ances and lighting is assumed to be constant for alldesigns evaluated at 8,760 kWh per year. Thisbaseload consumption is not representative of whatyou would expect in a net-zero energy houses. Ofthe 12 winning designs, the predicted baseloadenergy consumption ranges from assumed valuesof 2,734 kWh to 5,450 kWh per year. These con-sumption values are not modelled and are calcu-lated based on assumptions of what future home-owners would have in terms of appliances andlights. In reality, these values would depend on theenergy consuming behaviours of the future occu-pants. If the houses come with energy efficientlighting with occupancy controls and the most ener-gy efficient appliances, energy consumption will bereduced; however, secondary plug loads such asentertainment systems can result in a wide range ofenergy consumption levels.
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onBBuuiillddiinngg AAmmeerriiccaa PPrrooggrraammThe Building America Program was examined in the2005 review of solar home initiatives (Charron,2005). Building America's systems-engineeringapproach unites segments of the building industrythat have traditionally worked independently of oneanother by forming five Building America teamsthat bring together hundreds of different companiesincluding architects, engineers, builders, equipmentmanufacturers, material suppliers, community plan-ners, mortgage lenders, and contractor trades(Building America, 2007). This industry-led, cost-shared partnership program has the following fivebroad goals: reduce whole-house energy use by40-70% and reduce construction time and waste;improve indoor air quality and comfort; integrateclean onsite power systems; encourage a systems-engineering approach for design and constructionof new homes; and accelerate the developmentand adoption of high-performance residential ener-gy systems.
The fourth goal is to have the industry rethinkhow homes are designed and built. The teamsdesign houses from the ground up, considering theinteraction between the building envelope,mechanical systems, landscaping, neighbouringhouses, orientation, climate, and other factors. Thisapproach enables the teams to incorporate energy-saving strategies at little or no extra cost. In orderto accomplish the systems-engineering approach,players from the building industry that have tradi-tionally worked independently, need to work togeth-er from the start of a project. Their experience hasshown that energy consumption of new houses canbe reduced by as much as 50% with little or noimpact on the cost of construction.
The design process of these integratedBuilding America teams starts with an analysis andselection of cost effective strategies for improvinghome performance. Next, teams evaluate design,business, and construction practices to identify costsavings. Cost savings can then be reinvested toimprove energy performance and product quality.For example, a reduction in the heating and cool-ing load of the building can lead to less expensiveheating and cooling systems, with cost savings thenreinvested in high-performance windows to furtherreduce energy use and costs. The teams then startwith an initial "test" home with the field application
of proposed solutions to test and improve their con-cept from an energy efficiency and cost perspectivewith changes being incorporated into the designbefore additional houses are built. This process ofanalysis, field implementation, re-analysis, anddesign alteration facilitates ultimate home perfor-mance once a design is ready for use in productionor community-scale housing.
CCaalliiffoorrnniiaa SSoollaarr HHoommeess PPaarrttnneerrsshhiippIn California, the New Solar Homes Partnership(NSHP) provides financial incentives and other sup-port for installing eligible solar photovoltaic (PV)systems on new residential buildings with a goal ofcreating a self-sustaining market for solar homeswhere builders incorporate high levels of energyefficiency and high performing solar systems(California Energy Commission, 2007). The NSHPis part of a comprehensive statewide solar programknown as the California Solar Initiative (CSI). TheNSHP, which seeks to achieve 400 MW of installedsolar electric capacity in California by the end of2016, will help meet the three goals of the CSI setout in the Senate Bill 1:
- to install 3,000 megawatts (MW) of distrib-uted solar PV capacity in California by the endof 2016;- to establish a self-sufficient solar industry inwhich solar energy systems are a viable main-stream option in 10 years; and - to place solar energy systems on 50 percentof new homes in 13 years.
The California Energy Commission will provideExpected Performance-Based Incentive (EPBI),based on the reference system receiving$2.60/watt for production homes with solar as astandard feature, or $2.50/watt for other homes.The EPBI pays more for affordable housing with$3.50/watt for individual units and $3.30/watt forcommon areas. Note that the incentive amount willgradually decline as more PV gets installed throughthe NSHP program as outlined in the NSHPHandbook (California Energy Commission, 2007).In addition to the EPBI, additional funding is pro-vided by the utilities for meeting Tier I and Tier IIenergy efficiency requirements.
To qualify, the residential buildings mustachieve energy efficiency levels substantially greater
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than the requirements of the current state mandat-ed energy efficiency standards. As mentioned thereare two tiers of energy efficiency for the program:Tier I - achieves a 15 percent reduction in the resi-dential building's combined space heating, cooling,and water heating energy compared to the currentstandard; and Tier II - calls for a 35 percent reduc-tion in the residential building's combined spaceheating, cooling, and water heating energy and 40percent in the residential building's space cooling.In both the Tier I and II, each appliance provided bythe builder must be Energy Star if an Energy Stardesignation is applicable for that appliance.
PPaassssiivvee HHoouussee SSttaannddaarrddThe 2005 review of solar home initiatives (Charron,2005), presented the Passive House Standard thatstarted in Germany and is being introduced in otherEuropean countries. The Passive House standardwas identified as a good example of low energyconstruction that utilizes passive solar techniques inconjunction with other energy efficiency measures.To meet the requirements, the house needs to havea heating load of less than 15 kWh/m2/yr, and acombined primary energy consumption of 120kWh/m2/yr, including heat, hot water, and house-hold electricity consumption. The Passive Housestandard is continuing to be promoted in Europeand other parts of the world through a number oforganisations and initiatives.
There is an initiative funded by the IntelligentEnergy for Europe SAVE programme, calledPassive-On, that is aiming at developing and intro-ducing a Passive House standard for the warm cli-mates of southern Europe (Passive-on, 2007). Inaddition to the Passive-On project, a second pro-ject, Promotion of Passive European Houses (PEP),is a consortium of European partners, supported bythe European Commission, Directorate General forEnergy and Transport that has a goal to promoteregional economic activities in order to induce asubstitution of expenses for energy use during thelifetime of houses with investment in the buildingenvelope (PEP, 2007). There are various other ini-tiatives that are underway to disseminate the PassiveHouse standard in other parts of the world. GlobalPassive House Technologies Inc. is a Canadiancompany (GPHT Inc., 2007) as part of a joint-ven-ture between companies from Germany, Austria,
USA that are aiming to adapt and introduce thesuccessful German Passive House Standard,renewable energy systems, water management sys-tems, innovative Passive House technologiesthrough technology-transfers and engineering andconstruction of certified Passive Houses into theCanadian and US - Housing market.
PPaassssiivvee HHoouussee CCeerrttiiffiiccaattiioonn To Passive House standard does not dictate whatdesign process needs to be followed, but insteadmandates that strict design guidelines be respected.The Passive House Institute in Germany hasreleased the Passive House Planning Package(PHPP) to assist in the design. The PHPP is essen-tially a series of design tools produced to helpbuilding architects and designers build houses thatachieve the Passive House standard. To ensure thatthe quality is carried through from conception toconstruction, the Passive House Institute (PHI,2007) has a developed a certification processwhere buildings are certified as "Quality ApprovedPassive House" by the Passive House Institute, thePassivhaus Dienstleistung GmbH or other personswho have been authorized by the Passive HouseInstitute. These authorised certification agents getinvolved between preconstruction and final plan-ning, with a preliminary test for certification thatexamines relevant points in the proposed design,construction, building services and energy balancesof the building, and if necessary suggestions forimprovements are worked out. The agents also fol-low up after construction by testing the air tightnessof the building envelope. To date, over 550dwellings, office buildings and public buildingshave obtained the certification.
DDEESS IIGGNN OOPPTT IIMMIISSAATT IIOONN AAPPPPRROOAACCHHEESS
In North America, there are generally very few peo-ple involved in the design of most detached resi-dential house projects. In many cases, the owneror developer, and the house designer/draftspersonare the only individuals involved in the design. Inthe highly competitive detached residential market,very lean production/design teams have evolved.Another factor that has kept the design costs fordetached houses very low is the availability of low
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oncost mass-produced plans and plan books. Forinstance, a quick check on the Internet for residen-tial house plans (eplans, 2007) yielded a full set ofplans for a 222 square metre (2387 square foot)house for $685 US. For this price one would get 5sets of blueprints, which in many jurisdictions inCanada would be sufficient to build a house.
It is difficult to add innovation in the tradi-tional design process of larger commercial or insti-tutional buildings or smaller detached residentialprojects, which often depend on a typical trial-and-error design process. In residential projects this isdue to the automated design process. It is possibleto have an automated process with solar throughthe use of ready-made plans with solar, such as thepassive solar home plans that come with CMHC'sTap the Sun (CMHC, 1998). However, the perfor-mance of active solar technologies can vary fromone location to the next depending on orientation,shading, solar availability, etc., that optimal perfor-mance would be achieved only through site specif-ic designs developed with the use of simulationtools. This section looks at the use of the integrat-ed design process for the design of residentialbuildings, followed by an introduction to using for-mal design optimisation to assist with the designprocess.
IInntteeggrraatteedd DDeessiiggnn PPrroocceessssThe integrated design process (IDP) has evolved asa response to the need to improve the traditionaldesign process of commercial, institutional, or larg-er residential buildings. Although the merit of usingan IDP has been shown in multiple low energybuilding designs, it is seldom used. It is even morerarely used in the design of single detached hous-es. The Canadian EQuilibrium competition man-dated that all teams needed to follow an IDP. TheEQuilibrium design charrettes generally had a sub-stantial number of individuals involved. Forinstance, the Edmonton charrette had approxi-mately 32 individuals involved over the two-dayinterval, plus an earlier charrette where more infor-mation was gathered. The Saskatchewan charrettehad 18 individuals present. Compared to standardhousing design practices, this is a lot of participantsin the design process. However, it is not unusual tohave such high numbers of participants in designcharrettes. NREL's Charrette Handbook (Lindsey, et
al., 2003) recommends 25 to 50 people to partic-ipate in a mini-charrette or full-scale charrette, stat-ing that less than 25 participants reduces the ben-efits of the charrette process.
As can be expected, the costs to conduct acharrette can vary widely. Paying numerous designprofessionals to attend multi-day charrettes can bean expensive proposition. For the case of theEQuilibirum competition, most professionalsattended the charrettes on a pro-bono basis. TheEQuilibrium format allowed for a lot of exposure tothe design professionals and was a great learningopportunity. For a typical homeowner however, theprofessionals would be paid. Using an IDP with alarge charrette can lead to much larger designcosts compared to typical design fees for a house.Given that the charrette process was developedmore for larger commercial or institutional build-ings, it would be very beneficial to define a processthat would be geared towards building individuallow energy houses. Note that builders that aredeveloping whole neighbourhoods would still ben-efit from having large conventional charrettes.
IInntteeggrraattiioonn ooff FFoorrmmaall OOppttiimmiissaattiioonn AAllggoorriitthhmmss ttooDDeessiiggnn PPrroocceessssThe design of low and net-zero energy buildingsinvolves the integration of multiple systems that canvary depending on the specific design objectives,the project location, the knowledge of the design-ers, and other factors. The energy use and energycost of a building depends on the complex interac-tion of many parameters and variables making theproblem far too complex for "rules of thumb" orhand calculations. The application of computerisedoptimisation techniques to the design of low andnet-zero energy buildings would provide architectsand engineers with a powerful design tool (Coleyand Schukat, 2002). This section provides twoexample optimisation tools that have been devel-oped to help design low and net-zero energy build-ings. These types of tools could be a major assetto a designer's toolbox providing assistance in thedevelopment of high performance design alterna-tives.
RReessuullttss uussiinngg GGAA OOppttiimmiissaattiioonn TToooollIn recent years, genetic algorithms (GA) have beenused to optimise different building systems includ-
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ing optimising solar collector and storage tank size(Kalogirou, 2004); a low energy community hallincluding the shape of the perimeter, roof pitch,constructional details of the envelope, windowtypes, locations and shading, and building orienta-tion (Coley and Schukat, 2002); window size andorientation (Caldas and Norford, 2002); conceptu-al design of office buildings (Grierson andKhajehpour, 2002); HVAC sizing, control, androom thermal mass (Wright, et al., 2002) thedesign of an office building in Montreal (Wang, etal., 2005, Wang, et al., 2006); and more. The use
of GA in optimising buildings and other engineer-ing problems is emerging since it has been shownto have high efficacy in solving complex problemsfor which conventional hill-climbing derivative-based algorithms are likely to be trapped in localsolutions (Caldas and Norford, 2002).
This section provides a sampling of theresults that were obtained using a GA OptimisationTool that linked a TRNSYS energy simulation modelwith a GA program based on code written by(Carroll, 2005) in order to find cost-effective lowand net-zero energy solar home designs. The tool
Table 1 . Average HDD, CDD and solar radiation for varying cities
Table 2 . Resulting optimal configurations with cities of varying climates
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onwas first presented in (Charron and Athienitis,2006) and the verification of the models was pre-sented in (Charron and Athientis, 2007). For amore detailed description of the tool and for moreresults, please refer to (Charron, 2007).
CClliimmaattee EEffffeeccttss ooff OOppttiimmaall CCoonnffiigguurraattiioonnThe first element examined is how well the toolcould alter the optimal design of a building chang-ing only the local climate. In order to see theimpacts of climate on the optimal design configu-ration, the optimisation was run with climate datafrom one of Canada's coldest cities, Iqaluit, one ofits milder cities, Nanaimo, a city with an averageclimate, Montreal, and from a hotter US city,Sacramento. The average climate of the cities ispresented in Table 1. The difference in the mostoptimal design between Montreal and Nanaimovaried only by the south window coverage and theexterior wall type; Nanaimo required less insulationin the exterior walls and called for fewer south-fac-ing windows. It is interesting to note that despitetheir very different climates, the overall yearly elec-tricity consumption of Nanaimo and Montreal var-ied by only 12 kWh per year. As expected, the mostcostly design was for Iqaluit, which had an annualelectricity consumption that was 55.3% more thanin Montreal. This was not a surprise since it has107% more heating degree-days per year. Theoptimal design for Sacramento had a monthly costfunction that was 30.8% lower than in Montreal,despite an annual electricity consumption that wasonly 7.3% lower. The cost effectiveness of buildingnet-zero energy homes in Sacramento is better dueto cost savings in other parameters and in the high-er PV generation per installed kW. These resultsstart to explain why more net-zero energy homeshave appeared in California than in Canada, espe-cially if the higher electricity costs and increasedgovernment support for solar technologies are fac-
tored in. The results are summarised in Table 2.
EEffffeeccttss ooff bbuuiillddiinngg aanndd lloott cchhaarraacctteerriissttiiccssOne typical restriction that occurs with new con-struction is a building lot that does not face south.The optimisation tool was used to compare thebase case that faced south in Montreal, versus a lotthat faced 45ºSW and one that faced 45ºSE.Overall window areas, solar thermal collector area,and roof pitch were the only parameters that variedfrom one situation to the other, with the differencessummarised in Table 3. As expected, the south-fac-ing orientation reached the most favourable results.The only difference between the optimal configura-tion for the south and the 45ºSE orientation was theroof slope. For the 45ºSW orientation, the optimalwindow area became smaller on the south façadeand larger on the east façade. The overall electric-ity consumption is not very different between thecases at an increase of only 4.9% and 6.8% for theSE and SW orientations, respectively. Higher costsare attributed to the need for more PV panels, andfor the larger roof slope. An increase in the slopefrom 45.0º to 56.3º is estimated to cost $3,160,and results in a less than optimal PV performance.The higher roof slopes called for in the off-southorientations is a result of requiring more surfacearea to place all the PV and solar thermal collectorsto reach the net-zero energy target. If roof areaconsiderations were not considered, the optimalslope would be 36.9º for south-facing, 26.6º forsouth-west, and 36.9º for south-east facing orien-tations.
IImmppaaccttss ooff DDeecclliinniinngg CCoossttss ooff SSoollaarr EEnneerrggyyAll of the results, unless otherwise stated, used anassumed cost of 13,52 $/W for the PV system,which was based on data for the average cost of acomplete installed PV system in Canada in 2004. Ifthe cost data from 2005 had been used, which had
Table 3 . Variation in optimal results with different lot orientations1 3
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an average cost of 11,25 $/W (IEA PVPS, 2006),the optimal configuration might have been impact-ed for some of the tested scenarios. However, thiswas not the case for the base case that had thesame resulting optimal configuration, the only dif-ference was that the monthly cost functiondecreased by 12.4% to $363.52/mth. One cansee that the monthly costs is highly correlated withthe PV cost as a 16.8% drop in PV cost resulted in12.4% savings in monthly costs for the same opti-mal design configuration.
The reported installed price of a PV systemdropped by 16.8% in a single year from 2004 to2005. At this rate of decline, the price would dropto 7 $/W between 2007 and 2008. At this cost,the optimal configuration and cost function wouldchange. The optimal collector area drops from 12m2 to 9 m2, the tank volume from 681 L to 454 Land the wall changes from the SIPS wall of RSI-8.59, to the 0.05 m x 0.15 m (2"x6") wall of RSI-5.20. These changes increased electricity con-sumption by 9.1%, which increased the required PVcapacity from 4.8 kW to 5.3 kW, and resulted in adecrease in the monthly cost function of almost37% to $258. These results show that as the priceof PV systems decrease that the economic viabilityto achieve the net-zero energy target is improved,and they show the importance of keeping costs up-to-date in order to find the optimal configuration.
TThhee UUssee ooff BBEEoopptt ttoo SSuuppppoorrtt BBuuiillddiinngg AAmmeerriiccaaPPrrooggrraammThe US National Renewable Energy Laboratory(NREL) has developed BEopt that links an optimisa-tion algorithm to building and solar simulation pro-grams to help find cost effective ZESH designs(Christensen, et al., 2005). BEopt uses DOE-2simulation program to calculate energy use func-tions related to the building and TRNSYS for solardomestic hot water and PV generation. For theoptimisation, the tool uses a sequential search tech-nique to automate the process of identifying opti-mal building designs along the path to net-zeroenergy (Christensen, et al., 2004). The sequential-search approach involves searching all categories(wall type, ceiling type, window glass type, HVACtype, etc.) for the most cost-effective combination ateach sequential point along the path to net-zeroenergy (Anderson, et al, 2006). Based on the
results, the most cost-effective combination isselected as an optimal point on the path and putinto a new building description. The process isrepeated based on this new configuration along thepath to net-zero energy.
The BEopt optimisation is looking at the bestways to save energy. Once the cost of energy sav-ings becomes greater than the cost of electricitygenerated with the PV system, the building design isheld constant, and the PV capacity is increased toreach the net-zero energy target. This concept canbe seen in Figure 1, where after point 3, which rep-resents approximately 50% energy savings, thecash flow line is linear until it reaches the net-zerotarget, point 4, since only PV is added whichreduces the utility bills but adds costs to the mort-gage. One interesting result that has been shownwith BEopt is that significant energy savings can beachieved at a lower total monthly cost to the home-owner than a base-case house.
CCOONNCCLLUUSSIIOONN
The growing concern in regards to global warming,the continual development of energy-efficient appli-ances and HVAC systems, the expected drop in PVand solar thermal collector prices, and other drivingfactors should lead to the eventual emergence ofsolar homes that either consume zero net energy orgenerate a surplus of energy. Advances in com-puting power and costs have helped facilitate the
Figure 1. Conceptual plot of the path to net-zeroenergy (Christensen, et al., 2006)
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task to design low and net zero energy solar homes.They have helped improve the accuracy and capa-bilities of building energy performance simulationtools and can soon help in the emergence of a dif-ferent type of tool altogether, the building optimisa-tion tool. In order to help accelerate the uptake oflow and net-zero energy solar homes, new designtools need to emerge that help designers and poli-cymakers determine the most cost-effective mix oftechnologies that needs to be utilised in order toachieve their design objectives.
AACCKKNNOOWWLLEEDDGGEEMMEENNTTSS
Financial support for this collaborative researchproject was provided in part by Natural ResourcesCanada (NRCan) through the Technology andInnovation Program and through scholarship fromthe National Science and Engineering ResearchCouncil of Canada. The author would also like toacknowledge Dr. Lisa Dignard at NRCan for herassistance in reviewing the article.
RREEFFEERREENNCCEESS
ANDERSON, R., CHRISTENSEN, C., and HOROWITZ, S.,2006, Program Design Analysis using BEopt Building EnergyOptimisation Software: Defining a Technology PathwayLeading to New Homes with Zero Peak Cooling Demand,ACEEE 2006 Summer Study Pacific Grove, California,NREL/CP-550-39827.
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Author's AAddressesProf. Dr. Rémi CharronNatural Resources CanadaCANMET Energy Technology Centre - Varennes1615, Lionel-Boulet, Varennes, Quebec, J3X 1S6,CanadaEnergy Systems Engineering Technician (ESET) andTechnologist Program St. Lawrence College 100 Portsmouth Ave.Kingston, ON, K7L 5A6, [email protected]
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