In December 2013, an ice storm caused an extended power outage in Maine, leaving many residents scrambling to keep their pipes from freezing. But even with no utility electricity for five days, below-freezing temperatures, primarily overcast conditions, and no supplemental heat, the homes at Belfast Cohousing & Ecovillage (BC&E) lost only 2°F a day, on average, for a total drop of 8°F to 10°F. Nearby homes, by contrast, were below freezing after 24 hours.
How did they do it? Passive House design, passive solar orientation, and a small building footprint.Small, Smart Design
The super-efficient ecovillage homes are heated largely by passive solar gain. Despite Maine’s cold winters and relying on electric space and water heating, a 900-square-foot BC&E home can approach net-zero energy with a 3.5-kilowatt PV system, and a 1,500-square-foot home can zero out with a 4.5 kW system.
Although the homes aren’t certified, the Passive House Institute US standards guided the design process. A southerly orientation; generous south-facing glazing; triple-pane windows and doors; lots of insulation; airtight construction; and a compact footprint resulted in a 90% reduction in the energy used for space heating compared to the average house. The homes share walls, reducing the exterior surface area and heat loss to the outside.
When designing the ecovillage homes, architect Matthew O’Malia of GO Logic used the Passive House Planning Package (PHPP), a spreadsheet-based design tool for architects and designers. “The Passive House standard is revolutionary in that it has spawned a new way of thinking around high-performance buildings,” says Gibson. The PHPP energy model spreadsheet is used to determine a building’s energy gains and losses. “You have a section of wall with certain properties, and the program can calculate how much heat is going to move through that wall over time. If you determine every way a building can gain or lose energy, you come up with a comprehensive model for how a building is going to perform.”
However, Gibson points out, PHPP has its limitations. The software was designed in Europe and has been very accurate in predicting how the building will perform, but doesn’t accurately model household electricity use in U.S. homes. “We use a lot more electricity than Germans do,” he says. “And you can’t predict occupant behavior, such as how someone might set their thermostat.”