Geothermal Heating and Cooling

If you've been to Iceland (or Boise, Idaho), you've probably heard of geothermal heating, where natural hot springs are tapped into to provide steam and hot water to heat buildings. But did you know that there is a system that can provide low-cost, low-energy heating and cooling by taking advantage of the constant temperature of the ground just a few feet below your home? It's called a geothermal heat pump system, and here's how it works:

In most places, if you drill a few feet down into the ground, the temperature is constant year-round: around 50 to 70 degrees Fahrenheit depending on the location. Geothermal heat pump systems tap into this constant temperature: In the winter, heat energy is extracted from the earth and added to the building. In the summer, the process is reversed - unwanted heat is extracted from the building and added to the earth.

And the benefits are many:

Low Operating Cost
No Required Exposed Outdoor Equipment
Level Seasonal Electric Demand
No On-Site Combustion
Long Life Expectancy
Low-Cost Integrated Water Heating
Simplicity
Low Maintenance
No Supplemental Heat Required
Low Environmental Impact

Several residential buildings in New York City are already reaping the advantages of geothermal heat pump systems. At 360 Court Street in Brooklyn, a residentially converted church, geothermal heat pumps were selected by the developer because it was not possible to install exterior heating and cooling equipment on this historic building. And since geothermal heat pump systems require no external equipment (like roof fans or fuel tanks), the system was a perfect fit. Each apartment in this 34-unit building has its own geothermal heat pump and its own thermostat control.

The Department of Energy has a good pamphlet on geothermal heat pump systems for residential buildings.

Since these systems use heat pumps, it makes sense to get most energy-efficient heat pump available: gas-driven heat pumps. These are basically no different than other kinds of heat pumps: they transfer heat from a "source" to a "sink." However gas-driven heat pumps differ from other kinds of heat pumps in two fundamental ways: instead of an electric motor, a natural-gas engine powers the heat pump compressor; and in winter, heat recovered from the engine exhaust provides supplemental heating to the indoor space. Gas-driven heat pumps also have lower operational costs than other types of heat pumps.