Geothermal, Storage

What is the Lifespan of Geothermal Heat Pumps?

A reader writes: I was talking with a friend the other day and he said that he heard that closed-loop systems only last about 10 years because the ground temperature equalizes after several years as a result of so much heat being removed. He said that after 10 years the ground no longer maintains its average ground temperature of 55 degrees F. I have never heard of that before and scientifically that doesn’t make any sense to me. I’m guessing you’ve come across this argument before?

Here is my response to this question: Even in this shaky economy, ground-coupled or geothermal heat pump sales are steadily increasing in the United States. Over 1,000,000 geothermal (or ground-source) heat pumps are used in U.S. residential, commercial and government buildings. And each year, U.S. homeowners install approximately 50,000+ geothermal heat pumps.  WaterFurnace, based in Indianna was founded in 1983, Earthlinked, based in Florida was founded in 1980 and Oklahoma-based ClimateMaster is over 50 years old. None of the residential systems that these companies have installed have this kind of saturation problem.

Dan Ellis, ClimateMaster, CEO and one of the early leaders in the industry says that this issue is confronted “only in larger commercial systems with a dense ground heat exchanger array and with unbalanced seasonal loads, (ie more heat rejection than extraction or vice versa).”

He continues, “In these situations the center of the ground-coupled heat exchanger (GHX) array begins to act as thermal storage. This is a well-known design aspect that good GHX design software considers. The software looks out over long time periods to allow for any impact. The size of the GHX is adjusted to keep within design parameters over the long time period. Alternatively, the load can be balanced with supplemental heat rejection or in many others ways.”

Last summer, I had a geothermal heat pump ductless HVAC system installed at my Arlington, Virginia home. And I specify ground-coupled (geothermal) heat pumps systems for my clients striving for net-zero or zero energy buildings. I want to emphasize that even for larger commercial systems, geothermal heat pump systems and hybrids with solar thermal, are the most energy efficient systems for heating and cooling buildings.

Overall, I am a big fan.

Scott Sklar, founder and president of The Stella Group Ltd., in Washington, DC, is the Chair of the Steering Committee of the Sustainable Energy Coalition and serves on the Boards of Directors of the Sustainable Buildings Industry Council, the Business Council for Sustainable Energy, and the Renewable Energy Policy Project. The Stella Group, Ltd., a strategic marketing and policy firm for clean distributed energy users and companies using renewable energy.