Geothermal Energy
What is Geothermal Energy?
Geothermal energy, simply stated, is heat that is extracted from the ground. A classic example of heat from the ground is geysers, such as the one pictured. Here, 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 utilized to create electricity, or to heat dwellings.
source: nps.gov/yerll/naturescience/geysers
The use of geothermal energy dates back to primitive humans, who bathed in hot springs which were heated by the Earth's inert heat (often underground magma chambers). Modern uses of geothermal energy are much more high-tech and useful. They include heat exchange systems, "heat pumps", and even large scale power plants.
source: Geo-Heat Centre Quarterly Bulletin
Geothermal Heat Pumps
Geothermal heat pumps (GHPs) use a geoexchange system to tap into the thermal energy just below the earth's surface. Most of this energy is actually solar energy which is stored in the first few meters of soil. 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.
source:blog.mapawatt.com
How Geothermal Heat Pumps Work
The GHP (as pictured above) circulates a liquid through pipes which run underground. The ground they are surrounded by maintains a relatively consistent temperature which will alter the temperature of the liquid in the pipes. The liquid (at air temperature) therefore travels from the home, underground and through the pipes, and back into the home but at the ground temperature. Then through compression or expansion of the liquid (via a compressor or refrigeration unit, respectively) at ground temperature 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.
For example: on an 80 degree day in Pennsylvania, the soil 10 feet beneath the ground will maintain a temperature of about 50 degrees. The liquid from the home will begin its circulation through the underground pipe system at the air temperature (80 degrees) and will return to the house at the underground temperature (50 degrees). Once in the house, the system uses compressors and a vapor-exchange system which superheat the liquid to a gas and the exchanges heat from the gas to another pipe of liquid that stays inside the house. The pipe of liquid in the house then conditions air to the desired, cooler temperature. The conditioned air is then sent throughout the house via a duct system. The liquid in the pipe loop stays in circulation and the process repeats.
source: Dr. Jonathan Matthews, Penn State University
Components of a Geothermal Heat Pump (Closed Loop)
- Pipe loop which travels below ground
- Pump to circulate fluid through the pipe loop
- Compressor to alter the temperature of the liquid
- A Heat exchanger which moves the thermal energy from the ground loop liquid to another liquid in the home
- Duct work to send the conditioned air throughout the home
source: www.geoexchange.org
Other Forms of Geothermal Energy
However, the above mentioned method describes just one way of obtaining geothermal energy: the closed loop system. It's known as a closed loop because the liquid travels between the house and the ground through one continuous pipe and doesn't leave the pipe. There are other methods of utilizing the earth's thermal energy without using an underground closed loop system.
One such method is the open loop system, where rather than recirculating the same liquid, ground water is drawn from below the earth's surface and put through the system then discharged at a new point.
Another method is pond system. It is very similar to the underground closed loop system, but rather than having a pipe loop buried underground, the pipe loop is submerged in a body of water, such as a pond.
Geothermal energy can also be used to heat water for domestic uses. By using the already superheated liquids and gases created through normal use of the GHP, the system can heat enough water to support a domestic household.
source: www.geoexchange.org
Is a GHP Right For Me?
The main drawback of GHPs is the high capital cost since they are more expensive to install than other systems. But once installed they require a very small amount of electricity to run and no fuel. A careful analysis is required to determine if your facility would be suitable. Depending on the cost of electricity and other fuels, geothermal heat pumps can be an economical option for many farm applications, including space heating, milk cooling, and hot water generation.
source: Dr. Jonathan Matthews, Penn State University
Advantages to GHPs vs. Other Heating/Cooling Options
- GHPs are environmentally friendly
- GHPs cost next to nothing to run after installation
- GHPs are quiet and take up very little above ground space
- One system can take care of home heating, cooling and hot water
sources: Dr. Jonathan Matthews, Penn State University & www.geoexchange.org
