Ground source heat pumps (GSHP), someties called geoexchange or geothermal heat pumps, are the most energy efficient, environmentally friendly heating and cooling systems available. Unlike a standard boiler or furnace, which burn fossil fuel to generate heat, a GSHP uses the earth’s energy to heat and cool the home. How does it work? The earth acts as a large solar collector; the sun heats the earth and keeps the temperature several feet below ground constant. About five feet below ground in the northeastern US, the average ground temperature is around 48° Fahrenheit. The standard GSHP capitalizes on the earth’s ability to store heat.

A GSHP consists of a ground loop, a heat exchanger, a refrigerant loop, and a distribution system. The ground loop, using water as a transfer medium, removes heat from the ground in heating mode and dumps excess heat into the ground in cooling mode. The water can be brought directly from a lake, pond, or well and returned to the ground source in an open loop system. In a closed loop system, a water and antifreeze mixture circulates through high density polyethylene (HDPE) pipes in horizontal trenches or vertical boreholes, which can be several hundred feet deep.

The water then passes through a heat exchanger in the unit, which is about the size of a gas furnace, and interacts with a loop containing refrigerant. In the heating mode, heat is then generated through the vapor/compression refrigeration cycle. The heat is then dispersed through forced hot air ductwork or tubing in a radiant floor or floor slab. In cooling mode the vapor/compression refrigeration cycle is reversed, and heat removed from the house is dumped into the earth.

A GSHP does not need fossil fuel to operate. In a conventional heating system, gas or oil is burned to generate heat. A GSHP uses a high efficiency two stage scroll compressor and motor to operate. These units use very little electrical power to operate. A GSHP is rated by its coefficient of performance (COP). State of the art heat pumps operate with a COP of 5. A unit with a COP of 5 will remove four units of energy from the earth for every one unit expended. GSHP have heating efficiencies 50% to 70% higher than conventional heating systems. They also eliminate the need for fossil fuel in heating the home.

In short, GSHPs are highly reliable energy units. The technology has been around for over thirty years. Over one million units have been installed in the United States alone. The Haverhill Public Library is heated and cooled with a ground coupled geothermal heat pump. You may wonder why the technology is not more popular. Why aren’t there more systems installed if they are so energy efficient? Well, the main drawback is the cost. The equipment alone is double that of a high-efficiency gas or oil forced unit. The ground loops are also expensive, wells can cost ten dollars per foor for drilling alone, and most systems need 600 to 1000 feet of pipe. Finally, a GSHP must be a forced hot air or radiant heat unit because temperatures in the distribution system could cost $8000 to $10,000 per ton. Most homes would require a 3 to 5 ton system, based on sqare footage and building envelope energy efficiency. Do the math; to heat and cool your home, a GSHP could cost you $24,000 to $50,000.