To qualify as a Passivhaus, buildings must have a tight building shell that allows no more than 0.6 air exchanges per hour at 50 pascals of air pressure. The heating load must be less than 4.75 kBtu per square foot per year (1.4 kWh/ft.2/yr.), and primary energy must be less than 38.1 kBtu per square foot per year (11.1 kWh/ft.2/yr.). Primary energy refers to all energy used for space and water heating, appliances, lighting, fans, pumps, etc. Different sources of energy have a different multiplier for their primary energy score. For example, purchased electricity has a high multiplier of 2.7 (each kWh of electricity consumed is multiplied by 2.7) to include generation and transmission losses; natural gas has a multiplier of 1.1; and grid-tied PV systems have a multiplier of 0.7. The last two requirements are verified by reviewing heating, gas, and other utility bills.
While the Seniors’ home is still in the process of becoming certified (a process that takes at least a year, since an entire cycle of heating and cooling, as well as overall energy use, must be analyzed), the house already has met the rigorous building standards. A backlog of applications appears to be slowing the process as PHIUS accommodates growing interest and incorporates the HERS rating system into its standards. These growing pains can only be a good thing as super-efficient building becomes a bona fide movement here in the United States.
Stephen Hren is a builder and writer living in Durham, North Carolina. He is the author of Tales from the Sustainable Underground: A Wild Journey with People Who Care More About the Planet Than the Law (see www.earthonaut.net).
Anchorage Building • anchoragebuildingcorp.com
Passivhaus Institute • passivehouse.com
Passive House Institute U.S. • passivehouse.us