How Geothermal Energy Works

Geothermal heat pump (GHP) technology helps keep buildings warm in winter and cool in summer by using the constant temperature of the ground - in places like Virginia, the ground temperature stays around 53 to 56 degrees.

Here's how it works: In the summer, a fluid (usually water) circulates between the building and a loop of pipes buried in the ground through a Geothermal Pump System, carrying excess heat from the building into the cooler ground.

In winter, the process reverses, with the fluid absorbing heat from the ground and bringing it into the building. Heat pumps in the building facilitate this transfer, making the system highly efficient. Unlike traditional systems that burn fuel on-site, GHP systems simply move heat between the ground and the building, leveraging the stable underground temperature to work efficiently all year round.

Geothermal heat pumps (GHPs)

Geothermal heat pumps (GHPs), sometimes referred to as 'GeoExchange', 'earth-coupled,' 'ground-source', or 'water-source heat pumps', have been in use since the late 1940s. They use the relatively constant temperature of the earth as the exchange medium instead of the outside air temperature. (Energy.gov)

How Do They Work

Although many parts of the country experience seasonal temperature extremes -- from scorching heat in the summer to sub-zero cold in the winter—a few feet below the earth's surface the ground remains at a relatively constant temperature.

Depending on latitude, ground temperatures range from 45°F (7°C) to 75°F (21°C). Like a cave, this ground temperature is warmer than the air above it during the winter and cooler than the air in the summer. The GHP takes advantage of these more favorable temperatures to become high efficient by exchanging heat with the earth through a ground heat exchanger.

Benefits

As with any heat pump, geothermal and water-source heat pumps are able to heat, cool, and, if so equipped, supply the house with hot water. Some geothermal systems have two-speed compressors and variable fans for more comfort and energy savings. Relative to air-source heat pumps, they are quieter, last longer, need little maintenance, and do not depend on the temperature of the outside air.

For more about different types of geothermal pump systems, visit this link. 

Hybrid Systems

A dual-source heat pump combines an air-source heat pump with a geothermal heat pump, combining the best of both systems. Dual-source heat pumps have higher efficiency ratings than air-source units but are not as efficient as geothermal units. The main advantage of dual-source systems is that they cost much less to install than a single geothermal unit and work almost as well.

Lifespan and Costs

Even though the installation price of a geothermal system can be several times that of an air-source system of the same heating and cooling capacity, the additional costs may be returned in energy savings in 5 to 10 years, depending on the cost of energy and available incentives in your area.

System life is estimated at up to 24 years for the inside components and 50+ years for the ground loop. There are approximately 50,000 geothermal heat pumps installed in the United States each year. For more information, visit the International Ground Source Heat Pump Association.