How Geothermal Heating Systems Work
Geothermal heating systems are built around the function of a heat pump. Instead of burning fossil fuels to produce warmth, heat pumps capture existing heat and move it from place to place. This allows heat pumps to provide both heating and cooling with one system.
Air-source models pull heat out of outside air and bring it indoors to warm your living spaces. When cooling, they absorb heat from the air inside your home and release it outdoors.
Ground-source geothermal heating systems work on a similar principle of heat capture and release, but instead of the air, they use the ground outside your home as the place where heat is absorbed or dispersed.
A ground-source geothermal heating system consists of a connected set of indoor and outdoor components. The indoor components include the heat pump itself, heat exchangers, and air-handling fans. The outdoor parts consist largely of a series of pipes, called the loop, that’s buried in the ground at a depth of about six to 10 feet. At this depth, the temperature of the soil stays about the same no matter how hot or cold it gets on the surface. This gives the heat pump a consistent and reliable source for heat capture and release.
The loop pipes contain water or a water and antifreeze solution that serves as the heat transfer medium. The liquid in the loop pipes is circulated into your home and back into the outdoor loop. Whether the liquid takes in or gives off heat depends on whether or not you’re heating or cooling the inside of your home.
During heating operations, the liquid in the loop captures heat from the soil surrounding the pipes. The heated liquid flows through the pipes and into your home, where the heat exchanger transfers the heat to the air around the exchanger. The air handler then blows that heated air into the ductwork and out into your home. The liquid is moved back outside and the cycle begins again.
When providing cooling, the flow of liquid in the loop is reversed. Heat is captured from inside your home and released into the soil.
Efficiency of Geothermal Heating Systems
Perhaps the most attractive feature of geothermal heating systems is their exceptionally high level of energy efficiency. This efficiency allows geothermal systems to operate at a very economical level, significantly reducing your monthly cooling and heating expenses.
Geothermal heating systems use electricity to power the equipment that captures heat and moves it back and forth. They typically use 25 to 50 percent less electricity in this operation than more conventional heating and cooling systems. In terms of efficiency, this translates into an efficiency level of 300 to 400 percent, with one unit of electricity being expended to move one unit of heat. This exceptional efficiency is what allows a geothermal system to heat your home at a substantially reduced rate. It also means that energy consumption is reduced, which eases burdens on local utility grids and power suppliers. Emissions are also reduced since utility companies burn less fuel to meet demand.
Economics of Geothermal Heating Systems
Geothermal heating systems can save you significant amounts of money on your monthly heating and cooling expenses. It’s common for geothermal heating systems to slash home heating costs by 50 percent or more. Compared to sources of electric resistance heating, geothermal heating can cut energy consumption and associated costs by more than 70 percent.
For a homeowner, the economics of a geothermal heating system means two very important things:
- Quick recovery of initial investment: Geothermal heating systems do, on average, cost substantially more than traditional gas, oil or electric furnaces. The equipment is more complex and a certain amount of digging and trenching is necessary to bury the outdoor loop pipes. However, the exceptional efficiency of geothermal heating means the initial cost of the equipment and installation can be recovered in monthly savings alone by at least the halfway point of the system’s expected functional life. In some cases, the initial costs have been recouped in as little as two years, but the more common time frame is 10 years.
- Additional savings through tax credits: There are a number of federal, state, and local incentives available that can help reduce the initial cost of a geothermal heating system. The U.S. government offers federal tax credits for geothermal systems installed on or before December 31, 2016. These credits amount to 30 percent of the cost of the system and installation, with no upper limit on the total credit. There may also be relevant state and local incentives available from renewable energy organizations or other sources.
Other Benefits of Geothermal Heating Systems
In addition to the efficiency and cost-saving benefits of geothermal heating systems, they also offer other advantages to homeowners.
- Long functional life: Geothermal systems typically last 20 years or more, and longer if they’re properly maintained and promptly fixed on those rare occasions when a repair is needed. Loop pipes are commonly guaranteed for up to 50 years. This means you can expect a very long-term service from your geothermal system.
- Savings on water heating: Some of the heat from a geothermal system can be diverted to provide hot water for household use. Hot water costs are another major energy expense for homeowners, but a geothermal heating system cut them by 30 percent or more.
- Quiet, safe, and clean operation: Geothermal systems operate quietly and cleanly, generating no greenhouse gases or dangerous combustion by-products on their own. There are very few exposed components that could cause burns or other injuries.
- Flexibility of use: Geothermal heating systems are appropriate for all climates and weather conditions. They can be installed in urban, suburban, or rural settings and are useful for any size home. They support both new installations and HVAC system retrofits. Geothermal systems provide consistent levels of heating and are appropriate for homes that use zoned comfort areas to focus heating and cooling on particular rooms or areas of the house.
Land Evaluation for Geothermal Heating Systems
Since geothermal heating systems require a substantial amount of land for the installation of the loop pipes, it’s important that your installation professional evaluate some characteristics of the land before proceeding with a geothermal installation.
- Land availability: A geothermal installation requires a certain amount of available land for the installation of the outdoor loop. The presence of landscaping features, underground pipes, and drains, or buried sprinkler systems can also affect a geothermal installation.
- Geology: A geological assessment should be performed on the land that will house the ground loop. Characteristics of the soil, such as better heat transfer capability, can reduce or increase the amount of piping needed for the loop. The condition of the land intended for geothermal loop installation can also affect whether you should have a horizontal or vertical installation performed. In most cases, a horizontal installation is used, which places the loop pipes in a horizontal configuration over a larger segment of land. If there’s little topsoil available or if the ground around your home is rocky, a vertical installation can be used. This type of installation installs the loop pipes in a vertical shaft about 400 feet deep drilled into the rock and soil.
- Hydrology: The presence of groundwater below the surface of the earth could have an impact on the installation of a ground loop. In some cases, it may be more practical to use a water-source system that places the loop pipes in a body of water, such as a lake, pond, well or aquifer at a depth where water temperature stays consistent. Pollution and contamination of groundwater or aquifer systems must be avoided and excess depletion of water resources prevented if using an open-loop system. Contact your local geothermal contractor for more information on open-loop systems.
Installation of Geothermal Heating Systems
In all cases, geothermal heating systems should be installed by a licensed and knowledgeable contractor. Using a professional installer ensures that the equipment is installed correctly and in a way that promotes safety and proper function. Check references and licensing on contractors you’re considering. Ask questions about the installation and the equipment until you’re satisfied with the answers you have. Get a signed, itemized contract between you and your installer that indicates in detail what will be done and what is expected of you and him.
Logan Home Energy Services has more than 60 years of experience serving HVAC customers in the surrounding communities. Contact us today for more information on geothermal heating systems and for professional advice on selecting, installing, and maintaining a geothermal system for your North Carolina home.