To minimize heat gain during the summer, reflective shades are installed over the south and west windows. Brigham keeps the shades drawn from noon to sunset, if not longer, between May and September.
Only electric appliances were installed, including an induction cooktop, convection oven, and two on-demand tankless water heaters (see sidebar.) Brigham opted for passive alternatives to dishwashing and clothes drying. After being hand-washed, dishes air-dry in kitchen cabinet racks, where they are also stored. In the laundry room, a large floor-to-ceiling cabinet hides drying racks for clothing. A high-efficiency lighting scheme utilizes a combination of LED and fluorescents to help minimize energy consumption and meet LEED requirements.
Domestic hot water loads were modeled at 25 gallons per day per person, within the range of typical residential loads suggested by ASHRAE. This load represented cooking, cleaning, bathing, and waste water usage, but did not include the additional water required for a large soaking tub originally designed into the master bathroom. “It was one of the few things the homeowner really wanted,” Sofield says. “But she opted not to build it after she saw the numbers.” Each bath would have used 11.75 kWh and at least 100 gallons of water—more resources than Brigham felt comfortable consuming for what she considered to be a luxury item.
Throughout the home, fixtures and fittings satisfy the LEED requirements for water-use efficiency, meeting the set limits for average flow rates—less than 1.5 gallons per minute for the faucets and outdoor spigots, less than 1.75 gpm for the showerhead, and less than 1.1 gallons per flush for each of the two toilets. A small-capacity Energy Star clothes washer handles Brigham’s weekly washing needs. Additionally, the home claimed the maximum LEED credits allowable for managing roof runoff. In Colorado, where water laws dating to the 19th century still grant usage rights to roof runoff to downstream users, rain retention is prohibited. Sofield enlisted a civil engineer to size the infiltration ponds appropriately to return water to the aquifer.
The home’s heating, ventilation, and air-conditioning system relies on a high-efficiency Carrier electric air handler capable of delivering 1,050 cfm in cooling mode and 945 cfm in heating mode. Modeling showed that the cost of the additional PV needed to operate the air handler was less than the cost of an air-source heat pump, the primary alternative considered.
The floor between the first and second levels houses the supply-air ductwork that provides conditioned air to all spaces. Return-air circulation occurs naturally through gaps beneath the doors into the bath and laundry rooms, and louvered doors into the first-floor office. With slotted-sheet steel risers, the staircase acts as a giant vertical return, feeding the return air grille on the ground level.
Cooling is accomplished with an earth tube (or ground-loop heat exchanger)—a 12-inch-diameter PVC pipe buried 3.5 feet deep beneath the home that runs along the perimeter of the foundation. Return air from the home circulated in the tubes is cooled by the ground temperature and delivered back to the house via the air-handler. Based on average earth temperature data from the National Renewable Energy Laboratory, the earth tube can provide air cooled to 78°F—even during the hottest months of July and August. Ideally, the earth tube, Corbin says, would have been trenched deeper into the ground to provide even cooler air, but digging deeper was cost-prohibitive.