SOLAR TODAY - June 2012

finished basement. The heat pump is rated to provide warm air with outdoor temperatures as low as 17°F (minus 8°C). When temperatures drop below that and the house requires more heat, a heating element in the ductwork automatically turns on, providing a backup system. although the flow of air from the vents is at very low force, the house stays warm throughout.

A Stiebel-Eltron Accelera 300 provides hot water. The 80-gallon heat pump water heater has an energy factor of 2. 51, the best on the market according to the manufacturer. Its maximum power draw is 2. 2 kilowatts. In more than a year and a half, our household of three has never run out of hot water. The mechanical room becomes quite chilly, but so long as we keep the door closed, the cool air the system emits doesn’t affect the rest of the finished basement.

To insulate the original exterior walls, which were now stripped down to the 5/8-inch plywood sheathing, the team spray foamed the entire exterior. Carpenter Tom Cuccaro came up with a way to frame over the sheathing and around the window/door openings so that spray foam could be applied.

To insulate cinder block basement walls, the team installed a wall of 2x3 studs held 2 inches off the block walls. They sprayed behind and between these studs with 4 inches of closed-cell foam. This resulted in an R- 27 wall, with a loss of only 4-½ inches of space.

system production and our energy consumption.

We can turn off a light and watch the numbers change, right on our computer screen.

our insistence on using no fossil fuels for energy creation led us to choose an air-source heat pump HVAC system and a heat pump water heater, both powered by the PV system. Our HVAC contractor recommended the most efficient air-source heat pump he could find: a Mitsubishi Mr.

Slim ducted system (we decided against the Mr.

Slim ductless mini-split for aesthetic reasons). The system is coupled with two Mitsubishi air handlers, one for the main floor and one for the

Creating a Super-Insulated envelope

To supply a constant exchange of fresh air to our airtight house, we installed a lifebreath heat-recovery ventilation (HrV) system. For windows, we wanted to incorporate some passive solar benefits while minimizing heat loss. The south side has a large triple window on the main floor, and a double patio door plus a large window on the walk-in basement level, to let in midday sun. The west side includes an all-glass sliding door and other large window openings. a local window retailer directed us to highly efficient Starmark Triple Heat Shield windows, made by Pennsylvania-based OKNA. We chose white cellular composite triple-pane, krypton-filled casements, each with a U-value of 0.16 (for the whole window assembly). They have the highest insulating qualities I could find and are attractive and well built.

For insulation, we tried to follow Building Science Corp.’s “5-10-20-40-60 rule” for insulation levels in homes in cold climates: R- 5 windows, R- 10 under slab, R- 20 foundation walls, R- 40 house walls and R-60 roofs. In the existing part of the house, the rafters were 2x6s and the walls were 2x4s. To get a lot of insulation in this existing framework, we chose dense-packed cellulose insulation in between the rafters and in wall cavities, 4 inches of polyiso rigid foam on the roof and closed-cell spray foam covering the exterior walls. My Building Performance Insti-tute-certified specialists paid special attention to creating an airtight “shell” with no (or minimal) thermal bridging.

In order to pack 11 inches of cellulose between the rafters, we had to attach another 2x6 to the bot-

A 5.16-kilowatt PV system is mounted on the roof of the addition, designed to face south at the optimal pitch.

this way of building and chose durisol’s cement-bonded, wood fiber ICFs.

Lighthouse Solar designed a 5.16-kilowatt photovoltaic (PV) system, comprising 24 Sanyo HIT 215-watt modules mounted on the roof. A Sunny Boy 6000-US inverter is mounted on the same side of house as the meters. lighthouse Solar included lightgauge, its real-time data-monitoring software, which allows us to track