Geothermal heat pump

Geothermal heat pumps are an extremely efficient heating and cooling choice for any building, in just about any climate. They differ from conventional heat pumps in the method they use to extract heating and cooling energy from the outdoors.

A typical air-source heat pump has an outdoor unit with a coil and fan in it. Refrigerant (a special chemical that can change from a liquid to a vapor at low temperatures) passes through the coil and extracts heat from the surrounding air. Even on a day when heating needs are constant, there is enough heat in the outdoor air to cause the refrigerant to extract heat. The hot vapor refrigerant passes through another coil in the house where a furnace fan distributes the warm air.

The efficiency of the heat pump is about 200 to 300 percent. In comparison, a typical electric furnace is 100 percent efficient, and a high-efficiency gas furnace is about 91 to 95 percent efficient, not including duct losses.

A geothermal heat pump, sometimes called a ground-source heat pump, has an indoor unit that looks much like a conventional heating system. Buried outdoors is the secret to efficiencies that can exceed 500 percent. Instead of an outdoor coil that is exposed to the extreme variations of weather and temperature, a ground-source heat pump has its outdoor coil in the ground, where the temperature is a moderate 50 to 70 degrees, year-round.

There are several methods of installing geothermal coils. Some systems are long tubes installed in an existing or new well, while others are manifold or coiled systems of buried pipe in a long trench on the property. A water and antifreeze mixture circulates in the pipes, quietly moving heat to and from your home. The heat from the outdoor pipes is passed to a refrigerant circuit, like an air-source heat pump.

Installing a well or burying a coil in a trench is not an inexpensive proposition. We've seen bids for geothermal systems where the trenching and outdoor coil added $10,000 to the cost of the installation.

Effective January 1, 2009, the utility is offering a $2,000 rebate on an installed geothermal heat pump system. We also have financing available for these installations. Contact Energy Services at 992-3355 to learn more.

Is it worth the extra cost to upgrade to geothermal? It's a matter of house size, desired comfort and heating and cooling bills. If your home is large enough, a doubling of the efficiency of the heat pump might be cost effective. In smaller homes, you'll gain comfort from a new geothermal system, but the savings may not offset the costs for many, many years.