Throughout North America, homeowners are increasingly turning to geoexchange (geothermal) heating and cooling systems to significantly reduce their energy consumption while increasing their comfort level.
In winter, the ground soaks up solar energy and provides a barrier to cold air. In summer, the ground heats up more slowly than the outside air.
Approximately 70 percent of the energy used in a geoexchange system comes from the ground. The only additional requirement is a small amount of electricity to concentrate the thermal energy and circulate high-quality heat or cool air throughout the structure.
During colder months, the Earth’s natural heat is collected through a series of pipes, called a loop. Installed and buried in the ground, or submersed in a pond or lake, fluid circulating in the loop carries this heat to the home. An indoor geothermal system then uses electrically-driven compressors and heat exchangers in a vapor compression cycle--the same principle employed in a refrigerator--to concentrate the Earth’s energy and release it inside the home at a higher temperature. In typical systems, duct fans distribute the heat to various rooms. In warmer seasons, the process is reversed in order to cool the home. Excess heat is drawn from the house, expelled to the loop, and absorbed by the Earth.
Geothermal systems can also provide some or all of a household’s hot water. An economical way to obtain a portion of domestic hot water is through the addition of a desuperheater to the geoexchange unit. This small auxiliary heat exchanger uses superheated gases from the heat pump’s compressor to heat water, which then circulates through a pipe to the home’s water heater tank.
In summer, when the geothermal system is in the cooling mode, the desuperheater uses excess heat that would otherwise be expelled to the loop. A conventional water heater meets household hot water needs in winter if the desuperheater isn’t producing enough and in spring and fall when the geoexchange system may not be operating at all.
Many manufacturers now offer geothermal systems that use a separate heat exchanger to meet all of a household’s hot water needs.
The loop is typically made of high-density polyethylene, a plastic material that is extraordinarily durable, but which allows heat to pass through efficiently. This is important so it doesn’t retard the exchange of heat between the Earth and the fluid contained in the loop. The liquid used is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system.
Direct Geoexchange (DX) systems utilize copper piping placed underground. As refrigerant is pumped through the loop, heat is transferred directly through the copper to the earth. The length of the loop depends upon a number of factors, including the type of loop configuration used; a home’s heating and air conditioning load; soil conditions; local climate, and landscaping. Bigger homes need larger loops than smaller homes. Those located in climates where temperatures are extreme also generally require larger loops. A heat loss/heat gain analysis should be conducted before the loop is installed.