By the Numbers

These are the final results of the PHPP 2004 calculations for the Smith House: 

• Specific space heat demand: 8 kWh per square meter per year (2.5 kBtu/ft.2/yr.). In relationship to the treated floor area (TFA), this calculation describes the total amount of energy that the Smith House consumes for heating on an annual basis per square meter of TFA. (TFA is the discounted interior floor area—stairs are subtracted and storage and secondary spaces are only counted at 60% to determine the actual area that is livable.)
• Whole-house specific primary energy demand: 111 kWh/m2/yr. (35.2 kBtu/ft.2/yr.). The specific primary energy demand describes the total amount of source energy that the Smith House consumes for space conditioning, household electricity, domestic hot water, and miscellaneous mechanical electricity on an annual basis per square meter of TFA.
• Peak heating load: 13.1 W/m2 (4.2 Btu/hr/ft.2). The peak heating load describes the maximum energy input per square foot of TFA needed on the coldest day of the year to keep the house at 68°F. The mechanical system is sized on this value.
• Airtightness: 0.6 ACH₅₀. Air changes per hour at 50 pascal pressure.
• Surface area-to-volume ratio (A/V): 0.74. The A/V describes the compactness of a building. If a building is very compact, then the heat loss relative to the enclosed volume is minimized. For example: A home that has the dimensions of 10 m x 10 m x 10 m has a surface area of 600 square meters. The ratio is calculated by dividing 600 by 1,000 = 0.6. A ratio below 1 is recommended for Passive Houses in cold climates. In warmer climates, it is not as crucial to minimize heat loss by the compactness of the design.

Over the past six years of occupancy, the home’s energy consumption has varied with weather patterns—but the average measured heating energy consumption has been within 10% of the modeled predictions. The overall whole-house specific primary energy demand is shown in the graph. It is significantly lower than predicted due to the owner’s conservation practices. Klingenberg achieves even greater savings than anticipated with her use of high-performance appliances—beyond the assumed energy-efficient appliances specified in the modeling program.