How Does Geothermal Heating Heat a Home Warmer Than 55 Degrees?
Air temperatures fluctuate with the seasons, but only a few feet beneath your feet the temperature of the earth remains consistent. No matter what the thermometer on the surface may read, temperatures less than 10 feet underground remain an average of 55 degrees Fahrenheit year-round. This is the basis for an unvarying source of energy that can heat your home. Geothermal heating exploits the latent heat energy in the earth to provide warmth without natural gas combustion or electrical heating. Don't worry that you'll be stuck with a brisk 55 F in your home when you install geothermal heat, the system converts geothermal heat to make your home reliably toasty even in the coldest weather.
How Geothermal Works
A typical ground-source geothermal system consists of long, hair pin-shaped loops of plastic tubing buried in the ground on your property. This arrangement, known as a ground heat exchanger, may be installed in a horizontal configuration at an average depth of 5 feet or buried vertically in deep bore holes. A heat-absorbing fluid similar to anti-freeze is pumped through the network of tubing. As the liquid circulates, it absorbs the latent heat energy present in the ground year-round. The warmed fluid is conveyed from the loop field to a heat pump located in a sealed compartment inside the home.
Raising The Temperature
A heat pump in heating mode is basically an air conditioner running in reverse. At the primary heat exchanger, the system accepts heat energy extracted from an external source, in this case the 55-degree fluid circulated from the GHEX, and transfers it to frigid refrigerant vapor that absorbs heat very efficiently. The warmed vapor is then conveyed to a compressor that concentrates the molecules of heat energy in a vapor compression cycle, raising the temperature of the vapor to approximately 120 F. This hot vapor passes through tubing in the secondary heat exchanger installed in the ductwork, which functions as a condenser that sheds heat as the vapor condenses back into liquid. Air pulled over the heat exchanger is heated by this shed heat, then dispersed into the ducts to warm the home.
Cooling For More Heat
After leaving the primary heat exchanger, the cooled heat-exchanging fluid circulates back through the buried loop field to absorb more heat energy from the ground. The refrigerant in the heat pump passes through an expansion valve that causes it to rapidly cool back to a frigid state, then returns to the primary heat exchanger to accept more heat energy delivered by the heat-exchanging fluid.
Pros And Cons Of Geothermal
Because the only energy consumed by a geothermal heat pump is electricity to run the circulating pump, compressor and blower fan, geothermal heating is highly efficient. For every one unit of electrical energy consumed, the system produces four units of heat without combustion or its byproducts. This 400-percent energy efficiency is unmatched by other conventional sources. A high-efficiency natural gas furnace, for example, offers an efficiency no higher than 95 percent. Drawbacks of converting to a geothermal heating system include the high upfront costs of excavation to install the GHEX and the fact that certain soil types native to your property may transfer heat from the ground less efficiently than others.
Gus Stephens has written about aviation, automotive and home technology for 15 years. His articles have appeared in major print outlets such as "Popular Mechanics" and "Invention & Technology." Along the way, Gus earned a Bachelor of Arts in communications. If it flies, drives or just sits on your desk and blinks, he's probably fixed it.