Geothermal Heat Pumps
Posted: July 30, 2012
Geothermal energy is simply heat that is extracted from the ground. A classic example of heat from the ground is geysers. With a geyser, heat within the earth heats water enough to force it through small cracks and into the air. The same heat which fuels geysers can be used to create electricity, or to heat dwellings.
Geothermal heat pumps or GHP’s use a geoexchange system to tap into the thermal energy just below the earth's surface. The soil itself keeps the heat in and about 8-10 feet below ground the soil maintains a fairly steady temperature. This stable temperature can be exploited by the geothermal heat pump to heat and cool homes, depending on the season.
In a closed loop system, the heat pump circulates water or antifreeze solution through pipes that are buried in the ground or submerged in water. The relatively consistent temperature in the ground alters the temperature of the liquid in the pipes. A heat exchanger transfers heat between the refrigerant in the heat pump and the liquid in the closed loop in the ground. The geothermal system can condition air to a new temperature and circulate it through a home, thus acting as a heater and air conditioner in one unit.
How Geothermal Heat Pumps Work
For example: on hot days when air conditioning is called for the heat transfer fluid absorbs heat from the interior of the home by means of the heat pump using a vapor compression cycle, the same process that refrigerators use. The heated transfer fluid transfers the heat to the ground as it travels away from and returns to the home to repeat the cycle, ideally 10 degrees cooler. On cold days, when the home is calling for heat, the cycle is reversed and the transfer fluid absorbs heat from the ground and delivers it to the heat pump where the vapor compression cycle is used to warm the home by conventional methods (either forced air or hot water). Whether meeting the cooling, heating or providing Domestic Hot Water (DHW) needs of the home the heat source/sink is infinite and is a renewable energy resource.
Most systems are installed as closed loops running either horizontally, buried at depths between 6 to 10 feet, or vertically in wells drilled just for this purpose. Less conventional systems use a small body of water like a pond or lake to contain a closed loop. Others utilize a robust source of water like artesian wells or a river as a source of water, at a constant temperature in an open loop configuration
Geothermal heat pumps can also provide a home’s Domestic Hot Water (DHW) needs very economically while in either the heating or cooling mode of operation. A systems ability to meet the DHW needs of a home depends on the type of equipment installed.
Before deciding to install a GHP a detailed cost benefit analysis should be performed to determine if the installed cost of the system justifies the investment. Engaging a qualified contractor to conduct the analysis prior to the decision to install a GHP is very important. GHP technology is also a very viable solution to meeting the heating, cooling and hot water needs on Farms, and in many agricultural business settings.
So, if you are looking for heating and cooling system that is environmentally friendly, costs next to nothing to run after installation, are quiet and take up very little above ground space, and can take care of home heating, cooling and hot water all in one system, think geothermal and consider a geothermal heat pump! Tapping this free, endless energy source to heat and cool your home or business and provide hot water needs can result in significant savings when compared to most common fossil fuel technologies like gas, oil, electricity or propane.
For more information, check out Penn State’s Renewable and Alternative Energy web site or Geothermal Heat Energy factsheet or visit the US Department of Energy - Types of Geothermal Heat Systems
Dana Rizzo, Water Quality Educator
Penn State Extension