Could a European Super Energy Efficient Standard Be Suitable for the U.S.? John Broniek, IBACOS BEST1 CONFERENCE June 12, 2008
Agenda European Passive House Program Creating Passive House Designs in U.S. Locations Modeling Results and Observations TRNSYS Modeling Conclusions and Recommendations
European Passive House Program
Passivhaus Institute A passive house is a building in which a comfortable interior climate can be maintained without active heating and cooling systems (Adamson 1987 and Feist 1988). The house heats and cools itself, hence, passive. The European Parliament called in January 2008 for an introduction of this efficiency level for all new buildings all through Europe - as early as 2011.
Passive House Performance Targets An annual heating consumption target of 15 kwh per m 2 of floor area An annual sensible cooling consumption target of 15 kwh per m 2 of floor area A source energy consumption maximum value of 120 kwh per m 2 of floor area for the sum of all energy consumptions within the house The frequency of temperatures that exceed 25 C needs to be 10 percent or less for the year (frequency of overheating) or mechanical measures to reduce the cooling load must be used
Passive House Main Recommendations Building enclosure components have a maximum U-value under 0.15 W/m 2 K (R-38) The building enclosure achieves a value of 0.6 ACH at 50 Pa depressurization when tested with a blower door Windows have center of glass U-value less than 0.8 W/m 2 K (R-7.1) and a solar heat gain coefficient of 0.50 or greater Windows have a total U-value less than 0.8 W/m 2 K Heat recovery ventilators are high-efficiency (sensible efficiency greater than 75 percent) with minimal electrical consumption
Creating Passive House Designs in U.S. Locations
Passive House Designs in U.S. Climate Zones Location IECC Climate Zone Heating Degree Days (HDD) 18 C Base Cooling Degree Days (CDD) 18 C Base Minneapolis, Minnesota Zone 6 4376 388 Fort Wayne, Indiana Zone 5 3447 461 St. Louis, Missouri Zone 4 2643 867 Atlanta, Georgia Zone 3 1571 574 Dallas, Texas Zone 3 1317 1427 Miami, Florida Zone 1 83 4361
Modeling Based on Typical House 203 m² floor area Four bedrooms Front east Glazing: west (53%), east (42%) Garage underneath Use Passive House Planning Package
Energy Calculation Differences Heating Set Point Temp Cooling Set Point Temp Passive House Building America 20 C (68 F) 21.7 C (71 F) 25 C (77 F) 24.4 C (76 F) Occupants 5.8 3.5 Source Multipliers 2.7 for electricity and 1.1 for natural gas 3.16 for electricity and 1.02 for natural gas
Key Modeling Assumptions Natural air ventilation through open windows provides nighttime cooling during favorable summertime conditions Interior shading of windows during daylight hours when cooling was likely. Shading reflects an indoor blind that reduces solar heat gain by 63 percent Heating only designs: 92 percent AFUE natural gas condensing boiler with an air handler Other designs: Heat pump system, 18.4 SEER and 7.65 HSPF, a 7 kw (nominal) capacity outdoor unit
Modeling Results and Observations
Cold Climate Heating target drives specs; heating needed, no cooling House design very challenging (Minn), hard (FtWyn) Floor Slab Foundation Walls (Minn) Exterior Walls Attic/Roof Windows 204 or 356 mm (Minn) extruded polystyrene (XPS) Precast concrete wall with 64mm XPS exterior, batt insulation within cavity, interior insulated wood stud wall; total effective U-value: 0.128 W/m 2 K (R-44) Double stud walls with cellulose insulation within cavity (total depth 432 or 341mm), 51 mm layer of polyisocyanurate sheathing on exterior face; total effective U-value: 0.078 0.097 W/m 2 K (R-73,R-59) 560 or 432 mm blown-in cellulose insulation; Total effective U-value: 0.065 0.087 W/m 2 K (R-87,R-65) Triple-glazed; total window average U-value: 0.970 W/m 2 K; g-value: 0.59
Mixed-Humid Climate Mechanical cooling needed Heating energy target drives compliance measures House design are largely feasible Floor Slab Exterior Walls Attic/Roof 102 mm XPS insulation 190 mm wood stud wall with damp spray cellulose insulation within cavity and 13 mm (St. Louis) or 25 mm XPS foam sheathing on exterior face; effective U-value: 0.190-0.206 W/m 2 K (R-30,R-28) 305 mm blown-in cellulose insulation; total effective U-value: 0.130 W/m 2 K (R-44) Windows St.Louis: Triple-glazed; total window average U-value: 0.970 W/m 2 K; g-value: 0.59 Atlanta: Double-glazed; total window average U-value: 1.714 W/m 2 K; g-value: 0.44
Hot-Humid Humid Climate Cooling target drives compliance; mech cooling needed House designs extremely challenging Floor Slab Exterior Walls Attic/Roof Windows Airtightness 102 mm or 204 mm (Miami) XPS insulation Dallas:190 mm wood stud wall and 51 mm polyisocyanurate; U value: 0.149 W/m 2 K (R-38) Miami: 341 mm (total depth) double wood stud wall,190 mm block, 51 mm polyisocyanurate; U-value: 0.096 (R-59) 458 mm or 508 mm (Miami) blown-in cellulose; U-value: 0.078 0.087 W/m 2 K (R-73,R-65) Triple-glazed. Total window average U-value: 1.290 W/m 2 K; g-value: 0.36 Glazing reduced by 29% Dallas, 79% Miami 0.4 ACH at 50 Pa depressurization (Miami)
Building America and HERS Index Results Applying Passive House standard results in very energy-efficient house designs; 66% Building America source energy savings and HERS Index of 41
Primary Energy Target Results US electrical consumption twice level suggested
TRNSYS Modeling
TRNSYS Modeling Conditioning System Performance Loads, temperatures & RH values for each zone Nine zones plus attic, garage and basement (if applicable) Room-by-room hourly schedules for major appliances, miscellaneous loads, lighting, and occupancy Six minute time step
Peak Hourly Heating and Sensible Cooling Load Values Low-capacity heat pump system, heating (6.6 kw) and cooling (6 kw) system have adequate capacity 10.0 9.0 Peak Hourly Load Kilowatts 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 Heating Cooling 0.0 Fort Wayne Minneapolis Atlanta St Louis Dallas Miami
Daily Temperatures for Ft. Wayne High interior temperatures during cooling season, natural ventilation not providing enough cooling
Daily Temperature Values in Dallas during the Cooling Season Rooms usually comfortable, over-cooling happening If airflow balancing based on median load calcs over peak hourly (Manual J), improved comfort displayed 25 Temperature C 24.5 24 23.5 Kitchen/Living Dining/Entry Cooling Setpoint 23 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct Month
Daily Relative Humidity Values in Dallas during the Cooling Season Humidity levels high in Hot-Humid locations; more dehumidification needed Relative Humidity% 85 80 75 70 65 60 55 50 45 40 35 30 1-May 1-Jun 1-Jul 1-Aug 1-Sep 1-Oct Month Kitchen/Living Dining/Entry
Conclusions and Recommendations
Conclusions and Recommendations Applying Passive House standard results in very energy-efficient house designs, average 66% Building America whole house source energy savings and HERS Index of 41 No designs are truly passive ; Heating needed; Mixed-Humid and Hot-Humid designs require mechanical cooling Passive House designs less onerous in Mixed-Humid & IECC Zone 5 (Fort Wayne) locations More stringent energy-efficiency measures for Hot- Humid designs and IECC Zone 6 (Minneapolis) making them very challenging
Conclusions and Recommendations TRNSYS says mechanical cooling needed in Ft Wayne Air-source heat pump maintains set point temperatures but some overcooling occurs; airflow balancing critical High humidity levels in Hot-Humid Passive Houses; dehumidification capability very important for comfort
Thank You US DOE Building America Program Questions? jbroniek@ibacos.com