Score one for sustainability: Workers install PV panels that will help make the home net zero. PHOTO By EMILy BOyD
Passive solar design is a great starting point for a net-zero building, and was used in at least half of the local net-zero homes that we know about. Why not take advantage of solar energy that you are already getting for free? If you are careful about how you orient the house, size the windows and south-facing overhangs (as well as the types of glass you use), and use thermal mass to store this free solar energy, you will be well on your way to achieving a net-zero home. (For more about passive solar technology, see “Here Comes the Sun,” elsewhere in the directory.) It’s also important to keep this conditioned air inside the home. Insulation and air sealing are critical. A net-zero home should have wall, floor and roof insulation that exceed code. Too many windows can create a problem, since walls are much better insulated than glass. Sealing every crack in the building with caulk or foam is an important and cost-effective way to reduce air infiltration and humidity migration that can consume excessive energy. Ducts should be inside conditioned space to eliminate another potential route for unintended air exchange with the outdoors. It’s crucial to have the home designed and inspected to make sure these goals are met. Efficient heating and air-conditioning equipment also matters. Many local
net-zero homes use ultra-efficient geothermal (ground source) heat pumps which provide both heat and air conditioning. Others choose to use solar hot water radiant systems with a gas backup, and may install a very small air conditioning system. Some people choose not to install air conditioning, but it may be necessary for humidity control. Water heaters are another area where efficiency is critical. The most efficient option is solar-water heating. For all electric buildings, heat pump water heaters are more efficient than regular electric tank water heaters. For buildings that use gas, tank-free gas water heaters are an efficient option. Geothermal heat pumps can often provide hot water as a byproduct of heating and cooling when the units are in operation. This preheated water can be used to supplement the primary hot water source. Also, low-flow faucets, showerheads and ENERGY STAR appliances all use less hot water, which saves water and energy. Efficient lighting options are also plentiful. Compact fluorescent light bulbs are inexpensive and easy to find. LED technology can be competitive with CFL lighting when considering lifetime costs. Using occupancy sensors, dimmers and timers can also reduce the energy that lighting consumes. Other electric loads can be re-
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