Geothermal systems, or ground source heat pumps, take advantage of the 45-50 degree ambient temperature of the earth just six feet below ground level. This temperature is brought to the desired temperature through a compressor and circulation system. Geo-thermal systems do not qualify for NYSERDA, but they do qualify for a 30% federal income tax credit. Systems are now available for homes as well as for much larger installations.
HOW IT WORKS
Geothermal heat pumps consist of three basic parts: 1) the ground heat exchcanger; 2) the heat pump unit; and 3) the duct work.
The heat exchanger (simply a system of pipes) is either drilled vertically into the ground, or laid horizontally in a trench or pond. These are closed-loop systems. Open loop systems intake groundwater and discharge the cooled water in another location.
Horizontal loops are installed in trenches normally five foot deep where soil conditions allow for economical excavation. Horizontal loops take up more land area than any other loop type.
Vertical loops are used where land area is limited. A pair of pipes with a special U-Bend assembly at the bottom are inserted into a bore hole that averages between 150 to 250 feet deep pet ton of equipment. The holes are then backfilled with a special grout solution to ensure good contact with the earth.
Pond loops are installed in a pond or lake at least eight feet deep and utilize the water (rather than soil) to transfer heat to and from the pond. A coiled pipe is placed in the water, which should cover about ½ acre. An average home would require approximately 900 feet of pipe.
Open loop installations actually pump water from an underground aquifer through the geothermal unit and then discharge that water to a drainage ditch or pond. Like a closed loop installation, the geothermal unit processes heat energy from the water.
Much like a solar thermal system, a heat transfer liquid (a mixture of antifreeze and water) runs through these systems of pipes and into a heat pump that extracts the heat and transfers it into a blower system in your home. In the summer this process is reversed for cooling.