1、2008 ASHRAE 209ABSTRACT This paper provides an overview of the Passive Housedesign concept, an approach to building design which has beenused successfully in Germany since the early-1990s to createbuildings which, through increased envelope efficiency, havean annual heating energy consumption of no
2、more than 15 kWhper square meter of floor area (15 kWh/(m2a). It will alsoexamine the design, construction, and operation of the SmithHouse. Built in 2003 in Urbana, IL, it is the first house built inthe US using the specific practices and tools developed by thePassive House Institute in Darmstadt,
3、Germany. INTRODUCTIONSince the discovery of fire, humans have been attemptingto incorporate its heat into their dwellings. Also since that timethey have been dealing with the problems caused by combus-tion, ranging from the simple challenge of how to removecombustion by-products from the dwelling to
4、 more complexchallenges of air pollution and global warming. More recently,mechanical cooling systems have become widespread, creat-ing their own unique set of issues. It is now assumed that aheating and cooling system is a necessity, and its cost is incor-porated into the budget of a building from
5、the beginning. The Passive House approach to building design examinesthe relationship between the mechanical system and buildingenvelope design. Although the answers seem obvious, thefollowing questions should be addressed:Why does a building have a heating or cooling system? Because otherwise its t
6、oo cold in the winter and too hotin the summer.Why is a building hot in the summer and cold in thewinter? Because its poorly insulated and improperlyoriented.Why isnt it better insulated/ properly oriented? Its tooexpensiveWhy is it too expensive, what other aspects of the buildingare affected by ch
7、anging the envelope? The mechanicalsystem!What steps can be taken in the design and construction ofthe envelope to create a building in which the additionalcosts to upgrade the envelope are offset by savings due tominimization of the heating and cooling system? The final question is the essence of P
8、assive House design.The specifics of its answer are unique to each building that isbuilt using the Passive House design process. But in general itresults in a building that has a peak heating and cooling loadthat is small enough to be distributed using only the volume offresh air required for good i
9、ndoor air quality. The correspond-ing operational energy of this system is also extremely low,approximately 80% less than typical homes (Krapmeier,2001).THE PASSIVE HOUSE CONCEPTThe Passive House concept is a design and constructionstrategy for super low energy buildings based on optimizingboth firs
10、t cost and operational costs. It was developed inGermany in the late-1980s by Prof. Bo Adamson and Dr.Wolfgang Feist, (Krapmeier, 2001) It is implemented by deter-mining the factors which normally cause a building to need aDesign and Performance of the Smith House, A Passive HouseDavid Stecher Katri
11、n KlingenbergDavid Stecher is a research associate at IBACOS, Inc., Pittsburgh, PA. Katrin Klingenberg is the executive director of the EcologicalConstruction Laboratory, Urbana, IL.NY-08-0272008, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (www.ashrae.org). Publi
12、shed in ASHRAE Transactions, Volume 114, Part 1. For personal use only. Additional reproduction, distribution, or transmission in either print or digital form is not permitted without ASHRAEs prior written permission.210 ASHRAE Transactionsheating or cooling system, and then systematically reducing
13、oreliminating them from a buildings design.Economic studies performed by the Passive House Insti-tute for new construction homes in Germany showed (Figure1) that as building heating energy cost is reduced (dashed blueline in Figure 1), the upgrade costs increase, due to the neces-sary additional ins
14、ulation, better windows, attention to detailduring the construction process. The existing optimum costbalance appears to be at 45 kWh/(m2a) (14 kbtu/(ft2a) as seenin the low point in the “Total Cost” curve and the upgrade costcurve appears to be exponential. However there is a criticalpoint at which
15、 a step cost reduction occurs, when the tradi-tional heating system, and its associated costs, can be elimi-nated. Elimination of the traditional heating system is possiblebecause the heating load is low enough such that it can bedistributed using only the volume of fresh air that is requiredfor goo
16、d indoor air quality. When the heating energy costs andupgrade costs are combined into total cost, a new economicoptimum occurs at an annual heating energy value of 15kWh/(m2a) (4.8 kbtu/(ft2a).Passive House DesignPaying attention to the following elements is necessary toachieving this goal:Compact
17、Shape. By minimizing the building envelopearea relative to its volume, the area of heat transfer surfacebetween the conditioned (indoor) and unconditioned(outdoor) space is reduced.Super Insulation and Minimization of ThermalBridges. Since the walls, roof and floor of a building consti-tute the bulk
18、 of its surface area, increasing the R-values (ordecreasing the U-values) of these areas is a logical place tobegin. Any insulating material may be used as long as the over-all R-value of the wall assembly is high enough. As overallinsulation levels increase, the influence of elements in theassembly
19、 with low insulating values becomes significant.These elements are referred to as thermal bridges, examplesinclude joints where window frames meet the wall structure,and plumbing, electrical and mechanical penetrations. Airtightness. Air leakage is typically a large source ofheat-loss in a house. Re
20、ducing the number of joints in thebuilding during the design process and taking care to sealevery possible gap or crack during the construction process isnecessary to ensure a building that achieves an air leakage rateof less than 0.6 air changes per hour (ACH) when depressur-ized to 50Pa using a bl
21、ower door. Balanced Ventilation with Heat Recovery and Inte-grated Space Conditioning. Due to the high levels of airtightness, natural ventilation due to drafts in the winter is virtu-ally nil, resulting in the need for the use of a heat recoveryventilator (HRV). Since as much air is being drawn in
22、as isbeing exhausted, there is an opportunity to preheat the incom-ing fresh air by extracting heat from the exhaust air before itleaves the building. The efficiency of the HRV is important, asit affects the timing and size of the peak heating load. Acompact network of small ducts supplies air to th
23、e living andbedrooms and exhausts it from the kitchen and bathrooms,creating the airflow pattern seen in Figure 2. Since thisnetwork already exists, the air flowing through it can be heatedvia a hot water loop, heat-pump, or electric resistance heaterand thus provide both fresh and conditioned air t
24、o the rooms.The building air tightness also contributes to the installedperformance of the HRV by ensuring that no fresh or stale aircan bypass it. (Feist et al 2005)Minimization of Other Loads. Of course after minimiz-ing space conditioning which is the largest energy consumerof the building, the n
25、ext logical step is to minimize the energyconsumed by lighting and appliances, such as the hot waterheater, refrigerator, computers and multimedia devices, etc. IMPLEMENTATION OF PASSIVEHOUSE DESIGN IN THE SMITH HOUSEEnergy CalculationsThe energy performance of the Smith house was calcu-lated using
26、a steady state, spreadsheet based, energy modelingprogram which uses monthly average temperature data todetermine annual heating energy consumption of a building.Peak heat load can also be determined based on two design dayconditions. The software accounts for the following: Climate Factors. Air tem
27、perature, wind conditions (bothtypical area velocity and specific site conditions such as windbreaks), ground temperature, groundwater depth and flowrate, solar radiation, and shading elements of the site andbuildingBuilding Factors. Overall shape and areas, walls (overallU-values accounting for het
28、erogeneous wall composition),roofs, floors, windows (U-values and solar heat gain coeffi-cient (SHGC) of glass, U-value of spacer and frame), doors(U-values), air leakage, ventilation equipment heat exchangeFigure 1 Building costs in Euro vs. annual heating energyconsumption per square meter of usab
29、le floorarea. A step cost reduction occurs whereheating system is eliminated (Krapmeier 2001).ASHRAE Transactions 211efficiency, internal gains (people, appliances, lighting, cook-ing, bathing, etc.), external gains from solar thermal or PVsystems, energy consumption of all devices, specific thermal
30、bridge transmission losses (e.g., for a doorknob or plumbingpenetrations) (Feist et al 2004).The output summary sheet for the analysis performedduring the design phase of the Smith house can be seen inFigure 3. The specific space heat requirement is the amount ofheating energy that a building uses a
31、nnually on a per unit floorarea basis. The sheet also shows the pressurization test results.During the design phase, the expected value is entered, afterthe building is constructed, this value must be verified via ablower door test. The primary energy consumption of theentire house is also included,
32、 to allow the inclusion of alter-native fuels and electricity generation sources in the analysis.The maximum acceptable values of these three elements thata building can have and still be certified as a Passive House areseen in the middle right of Figure 3. The heat load per unit ofusable floor area
33、 can also be seen near the bottom of the figure.Finally, in order to prevent over glazing, the frequency of over-heating is included as a percentage of the entire year. Building CharacteristicsThe Passive House approach dictates minimizing lossesbefore maximizing gains, and as such the shape of the
34、buildingtypically ends up being close to cubical. This is because thecube has the most usable interior volume for its envelope area,with the exception of a sphere. However, the practical require-ments of rectangular beds, dressers, and desks results in muchwasted space in a spherical or geodesic dom
35、e structure.In the process of achieving the 8 kWh/(m2a) (2.5 kbtu/(ft2a) heating energy consumption shown in the energymodeling software output seen in Figure 3, the house is contin-uously re-modeled as design changes are made, resulting inthe specifications seen in Table 1. The completed house can
36、beseen in Figure 8.Foundation. Typical construction for the region is a frostwall with crawlspace. The Smith House uses a slab on gradewith a frost wall. The slab has 357mm (14”) of ExpandedPolystyrene (EPS) Insulation underneath it. The frost wall has152 mm (6”) of EPS on the outside of it.The high
37、 level of insulation against the ground (see Table1 and Figure 4) is due partially to the fact that significant heatloss occurs to the ground, but also that during the designprocess as insulation values are increased and thermal bridgesare eliminated it becomes increasingly difficult to find placest
38、o reduce heat losses. As a result, highly insulating against theground proved to be necessary to meet the energy consump-tion target. Walls. Typical construction is “2x4” stud constructionspaced 406 mm (16”) on center and filled with fiberglassbatting. The Smith house used 305 mm (12”) wooden I-Jois
39、ts asstuds, spaced 610 mm (24”) on center. A fiberglass blown inblanket system (BIBS) was used in the cavity spaces and102mm (4”) of EPS was applied on the outside of the structuralfiberboard sheathing. The installation of the sheathing can beseen in Figure 7. The I-joists were chosen for the follow
40、ingreasons:Only one wall would have to be built instead of two ifdouble stud construction were used, speeding construc-tion. The German division of a multinational I-joist manufac-turer had already developed details for both platformand balloon framing using wooden I-joists.The design of the I-joist
41、 and the manner in which load istransferred when using it as a stud allows for it to over-hang the outer edge of the foundation by 51mm (2”)reducing thermal bridging where the foundation meetsthe wall. (see Figure 5)Roof. Typical construction is to use trusses insulatedusing either blown in cellulos
42、e or fiberglass.The Smith House used 406mm (16”) wooden I-Joistsinsulated with a blown in blanket (BIBS) insulation system.The use of wooden I-joists allowed for the fiberglass to be fullyencapsulated, preventing convective losses. The encapsula-tion was provided on the outside by the roof sheathing
43、 (Struc-tural Fiberboard) and on the inside by the vapor barrier anddrywall. The roof was ventilated by placing furring strips onthe outside of the sheathing and adding a layer of OSB onwhich to lay the roofing felt and metal roof panels. Detail seenin Figure 6.Windows. Typical construction in the r
44、egion uses double-hung or casement type windows with double glazing and vinylor vinyl clad wood frames. Figure 2 Diagram showing airflow movement in a house.Fresh air is supplied into bedrooms and livingand exhausted from kitchen and bathrooms.212 ASHRAE TransactionsThe Smith House used casement typ
45、e windows withtriple-pane glazing with thermally broken (warm-edge) spac-ers and foam insulated fiberglass frames and sashes. The typi-cal U-value of these windows is seen in Table 2. The lowestpossible U-values were selected for the windows. Howeverdepending on the orientation of the window, differ
46、ent SolarHeat Gain Coefficients (SHGC) were chosen. For the Westwindows, a low solar heat coefficient was selected to reducethe potential of overheating in the Summer. The East windowsare shaded from the low angle sun by trees in the Summer, soa low SHGC was unnecessary. The Southern windows used ah
47、igh SHGC to capitalize on solar gains during the winter. Notethat the U-Value for the fixed glass is different than for theCasement Glass, this is due to the increased spacer widthpossible in a fixed window. Table 2 shows both glass andwhole window properties, because properties of the glass,spacer
48、and frame are entered into the modeling software sepa-rately.Airtightness. In order to ensure that the house wascompletely airtight, there are no mechanical, electrical, orplumbing penetrations in any of the walls or roof of the house.All electrical outlets and switches installed on exterior wallsar
49、e surface mounted. For plumbing venting, air admittancevalves are used instead of vent penetrations in the roof. Allservices (electrical, phone, cable) come in through the slab.This may seem extreme, however at the time there wereconcerns over the proper installation of airtight electricalboxes and what elements were necessary in order to achieve aFigure 3 Energy modeling software output summary page for the Smith house.Table 1. Specifications of the Smith HouseLocationUrbana, IL Area105 m2(1,200 square feet), with loft FoundationConcrete-block frost wallFoundation perimeter ins
