Many parts of the country experience seasonal temperature extremes. A few feet below the earth’s surface the ground remains at a relatively constant temperature. Although the temperatures vary according to the latitude, at six feet underground, temperatures range from 45 degrees to 75 degrees Fahrenheit.
Ever been inside a cave in the summer? The cave is at a cooler temperature than the air outside because the air underground is constant. During the winter, that same constant cave temperature is warmer than the air outside. This is the idea behind geothermal heat pumps. In the winter, they move the heat from the earth into your house. In the summer, they pull the heat from your home and discharge it into the ground.
Studies have shown that approximately 70 percent of the energy used in a geothermal heat pump system is renewable energy from the ground. The earth's constant temperature is what makes geothermal heat pumps one of the most efficient, comfortable, and quiet heating and cooling technologies available today. While they may be more costly to install initially than regular heat pumps, they can produce lower energy bills - 30 percent to 40 percent lower, according to estimates from the U.S. Environmental Protection Agency, who now includes geothermal heat pumps in the types of products rated in the EnergyStar® program. Because they are mechanically simple and outside parts of the system are below ground and protected from the weather, maintenance costs are often lower as well.
As an added benefit, systems can be equipped with a device called a "desuperheater" that can heat household water, which circulates into the regular water heater tank. In the summer, heat that is taken from the house and would be expelled into the loop is used to heat the water for free. In the winter, the desuperheater can reduce water-heating costs by about half, while a conventional water heater meets the rest of the household's needs. In the spring and fall when temperatures are mild the heat pump may not be operating at all, the regular water heater provides hot water.
Remember, a geothermal heat pump doesn't create heat by burning fuel, like a traditional furnace does. Instead, in the winter it collects the Earth's natural heat through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond or lake. Fluid circulates through the loop and carries the heat to the house. There, an electrically driven compressor and a heat exchanger concentrate the Earth's energy and release it inside the home at a higher temperature. Ductwork distributes the heat to different rooms.
In the summer, the process is reversed. The underground loop draws excess heat from the house and allows it to be absorbed by the Earth. The system cools your home in the same way that a refrigerator keeps your food cool - by drawing heat from the interior, not by blowing in cold air.
The geothermal loop that is buried underground is typically made of high-density polyethylene, a tough plastic that is extraordinarily durable but which allows heat to pass through efficiently. When installers connect sections of pipe, they heat fuse the joints, making the connections stronger than the pipe itself. The fluid in the loop is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system. The wells can be vertical when outdoor space is limited or in a horizontal plane when there is more outdoor area.
Another type of geothermal system uses a loop of copper piping placed underground. When refrigerant is pumped through the loop, heat is transferred directly through the copper to the earth. This is not common in Hampton Roads.
Surveys taken by utility companies have found that homeowners using geothermal heat pumps rate them highly when compared to conventional systems. Figures indicate that more than 95 percent of all geothermal heat pump owners would recommend a similar system to their friends and family.
Geothermal heat pumps are durable and require little maintenance. They have fewer mechanical components than other systems, and most of those components are underground, sheltered from the weather. The underground piping used in the system is often guaranteed to last 25 to 50 years and is virtually worry-free. The components inside the house are small and accessible for maintenance. Warm and cool air is distributed through ductwork, just as in a regular forced-air system.
Since geothermal systems have no outside condensing units like air conditioners, they are quieter to operate.
Many people think geothermal is new technology which can make many people reluctant to use it or even consider it. Reality is that geothermal is an idea that is more than 150 years old. (It has been documented in history that during ancient Roman times they used Geothermal for heating and bathing.)
Pros
• Efficient and eco-friendly. Geothermal heat pump systems transfer heat instead of creating it, so they don’t rely on fossil fuels. Geothermal heat pumps get high ratings from the Department of Energy and the Environmental Protection Agency.
• Durable. Underground loops are protected from external elements such as inclement weather and vandalism, and they rank high in safety with no open flame, flammable fuel or fuel storage tanks; no combustion is involved. Pipes are fusion-welded to prevent leaks. The pipes have a life expectancy of 50 years or more.
• Inexpensive to operate. With fewer mechanical operating components, Geothermal heat pumps require less service than conventional heating and cooling systems and have a high reliability rating, keeping maintenance costs low.
• Space-saving. Hardware for Geothermal heat pumps is smaller than conventional heating and cooling systems and requires a smaller mechanical room, which frees up floor space for other uses. This depends on application.
• Comfortable. Geothermal heat pump systems maintain humidity at a constant comfort level.
• Quiet. Geothermal heat pump systems have no outside compressors, which eliminates exterior noise.
Cons
• Expensive initial investment. Installation costs can be several times higher than comparable conventional systems. (There are tax advantages such as a tax credit of 30% of the total cost of a new Geothermal heat pump, includes existing homes and new construction—both principal residences and second homes qualify.)
• Difficult to repair. Repairs to underground pipes, though seldom necessary, can be difficult and expensive.
• Require backup. In extreme climates and rural areas, the systems may require an emergency backup heat system.
• There is a water pump. All Geothermal systems require a water pump to circulate the water throughout the condensing part of the system. Some pumps are larger than others and are noisier. Most are very quiet in closed loop applications. The open loop water pumps applications are noisier, but are usually located in a garage.
Resources:
Department of Energy(www.energy.gov)
Environmental Protection Agency(www.epa.gov)
Energy Star (www.energystar.gov)
Consumer Energy Center (www.consumerenergycenter.org)
Natural Home and Garden (www.naturalhomeandgarden.com)
Geothermal Energy Association (www.geo-energy.org)
