Shortly after moving in almost five months ago, the owner of a newly completed single-story two-bedroom overlooking Echo Lake, in Morris, Minnesota, began monitoring the energy usage of the house. And while it is too soon for a definitive ruling on the building’s four-season performance, the odds are pretty strong it will be exemplary.
Among the factors supporting that expectation are the home’s well-insulated and nearly airtight shell, its simple, rectangular shape, and its extraordinary HERS Index rating: zero.
The 11 7/8-in.-thick double-stud walls are insulated to R-45 with dense-packed cellulose, and the wood truss roof is insulated to R-60 with 18-in. of blown-in cellulose. The slab, with an insulated concrete form (ICF) perimeter stem wall, is insulated to R-40 with 8 in. of extruded polystyrene.
A ground-source heat pump and a photovoltaic array
The slab also is equipped with an in-floor hydronic heat distribution system. Other HVAC needs are met in part by minimally ducted air conditioning from a ground-source heat pump that has three 180-ft. vertical loops. Limited air conditioning is supplied by a fan-coil unit connected to the heat pump, noted Rachel Wagner of Wagner Zaun Architecture, whose team includes Elden Lindamood, the architect who designed the home. There also is a propane fireplace for a “fast bump” in interior temperature.
In all, the house has 1,596 sq. ft. of conditioned interior space, plus an attached two-car garage.
Blower-door testing showed an airtightness of 0.467 air changes per hour at a 50 Pascal pressure difference. Triple-pane Inline Fiberglass windows, with a high solar heat gain coefficient for those installed on the south-facing wall, were used throughout.
Because the home’s 7.74-kW pole-mounted photovoltaic array is expected to generate as much energy on an annual basis as the house uses, the home’s HERS Index is zero.