Geothermal Heatpumps
Geothermal heatpumps are one part of three main components to a ground source heating and cooling system. This page details how closed loop residential geothermal systems work.
© California Energy Commission
Geothermal Heat Pump System Components
The components of a geothermal heat pump system are:
- A ground loop system of pipes.
- A geothermal heat pump.
- The in-home air distribution system.
How Does Geothermal Work?
The beauty of a residential geothermal heatpump system is that the same equipment that keeps your home warm in the winter keeps your home cool in the summer.
But many ask, "how does geothermal work?" since it seems like you are getting something for nothing. The ground outside in the winter is cooler than the temperature you would like in your home so how can the ground warm the house?
First of all, even in the winter below the frost line (anywhere from a couple to several feet down) the ground temperature ranges from about 50 to 55 degrees Fahrenheit (10-13 degrees Celsius). (In some regions you may have to go a bit deeper to obtain this temperature range.) But most people would like their homes warmer than 50-55 degrees Fahrenheit. So where does this extra heat come from?
The magic lies in the refrigerant which circulates in either the closed loop system and the heat pump or just in the heat pump. Read on for a simplified explanation.
How Heat Pumps Work — A Simplified Explanation
In winter, geothermal heatpumps systems collect heat from the earth using a loop of pipes installed below the surface of the ground (or submersed in a pond or lake). A fluid flows through the pipes and brings the ground heat to the house.
This fluid in the ground pipes can be either an antifreeze mixture (a solution of water and alcohol) or a refrigerant (like that in the coils of your refrigerator). The fluid could also be water but this is not recommended for regions where the temperature drops below freezing since if the pipes travel underground anywhere above the frost line (for instance where they enter the home), they could freeze in the winter.
After passing through the closed loop pipe system, the now ground-warmed antifreeze or refrigerant enters the geothermal equipment in the home. Assuming the closed ground loop system contains a refrigerant, this refrigerant will now have changed from a liquid to a low temperature vapor (it has a very low boiling temperature). Pipes containing the vapor enter the home and the geothermal heatpump. There, the vapor is compressed.
This compression reduces the volume of the refrigerant vapor and increases its temperature. The now hot refrigerant gas transfers its heat to the surrounding air within the heat exchanger component of the heat pump. A fan blows this warm air into the duct work of the in-home heat distribution system.
Geothermal heatpump systems with antifreeze in their ground loop pipes work in the same way except that there are two heat exchangers inside the geothermal heat pump. The first heat exchanger transfers the warmth from the antifreeze solution to a separate set of piping containing refrigerant. This warmed refrigerant then follows the same path as in the above description to a second heat exchanger.
The Cooling Cycle of Geothermal Heatpumps
In summer, geothermal heating and cooling systems work in reverse. Warm air from the home is dispersed into the ground. The refrigerant is cooled by the earth and the cool refrigerant returns to the geothermal heatpump which then transfers this cool energy to the air distribution system in the home.
Advantages and Disadvantages of Geothermal
The table below shows the pros and cons of geothermal energy.
| Pros of Geothermal Energy | Geothermal Energy Disadvantages |
|---|---|
|
Most homeowners will find the monthly cost of geothermal is about $50-$100 less as compared to conventional heating equipment. Geothermal heatpumps provide a comfortable even heat inside the home. The refrigerant used in most geothermal systems, R-410A is non-toxic and does not contribute to ozone depletion. Since there is no combustion in geothermal systems, there is no carbon dioxide output. This lack of reliance on combustion and the burning of fossil fuels makes for a healthier home environment since the heating system is not contributing to indoor air pollution nor can it produce carbon monoxide gas. |
The initial cost of geothermal heating and cooling is higher than conventional systems. If a refrigerant other than R-410A is being used, it could potentially be harmful to the environment. Some antifreeze solutions produce CFCs and HCFCs. Although rare, a break in the ground loop system can be extremely difficult and costly to find. Ductwork must be installed separately in order to provide outside air to spaces within the home. (Although geothermal systems can be connected to existing ductwork in the home.) |
Advantages of Closed Loop Refrigerant Geothermal Systems
There are several advantages of closed loop geothermal heatpump systems over open loop systems. There are also advantages to the systems that use refrigerant in these loops over the systems that use antifreeze or water in the loops.
Advantages of Refrigerant Ground Loop Systems
- Refrigerant ground loop geothermal systems are usually more efficient than water-based loop systems.
- They require a smaller length of buried pipes.
- They do not have problems with the exposed parts of the pipes freezing
- They have a higher degree of heat transfer.
Disadvantages of Open Ground Loop Geothermal Systems
In a closed-loop system, the same refrigerant or water circulates through the pipes repeatedly. In an open-loop system, water is pumped out of the water source, such as a well or a man-made lake, and when the heat has been extracted from the water, that water returns to the well or surface lake.
Open loop systems are generally not recommended for the following reasons.
- Higher maintenance costs.
- Open loop systems continually bring water in from outside the system. This can lead to mineral build up and corrosion throughout the geothermal system as well as a potential for clogging.
