The ground-source heat pump that heats and cools our home—and supplements domestic water heating—is our biggest load, consuming almost half of the electricity our RE systems generate. This amount might sound high, but it’s actually quite low because of the high efficiency of the heat pump and its ability to take advantage of ground temperature. If we burned carbon-fuel (like oil or natural gas), the heating load would account for 72% of our home’s total energy consumption.
Since our goal was to reduce our carbon footprint to zero, fossil-fueled appliances were out. Electric resistance heating would have been an option, but ground-source heat pumps deliver heat with less energy input. A ground-source heat pump takes advantage of the relatively constant temperature below frost level in the ground—transferring ground heat to the home in the winter and the home’s heat to the ground in the summer. These systems put out a lot more heat energy than the amount of electric they consume (300% plus), even on the coldest of winter nights. In our system, for every 4.3 KWH of energy sent to the house, the compressor consumes just 1 KWH for an overall efficiency of 330%. (For more on heat pumps, see “Heat from the Earth—A Heat Pump Primer” in HP98.)