Passivhaus construction requires additional investments in the building envelope – triple pane windows and doors, and extra insulation. On this project, the insulation levels are on average two times the r-value required by code. Apart from utility savings achieved later by owners, there are offsetting construction cost savings as well. As a result of the superior insulation, one small ducted mini-split heat pump is enough to heat and cool each house. The footprint is so small it can be installed in ceiling of the first floor modular “box.”
Because of the homes’ air tightness, each house also includes an energy recovery ventilator (ERV) which continuously brings in fresh air. The system includes long flexible ducts which supply fresh air to bedrooms and living spaces, and return ducts which continuously remove air from bathrooms and the kitchen. Situated in the basement, the Zehnder-brand ERV unit is connected to the exterior with graphite polystyrene ducts – one supplying fresh air and the other exhausting indoor air. The ERV unit uses a heat exchanger to transfer 85% of the latent energy from exhausted indoor air to the incoming air. In the winter, warm indoor air is used to pre-heat the cold incoming outdoor air before it enters the house. The same effect operates in reverse in the winter.