How do geothermal heat pumps work?
Everybody’s talking about them — especially now that we’re offering a $3,000 rebate on them — but what are geothermal heat pumps and how do they work? Let’s dig in! (Get it? No? Read on and you will, we promise!)
What’s a geothermal heat pump?
Even with seasonal temperature extremes — from summer scorchers to winter freezes — the ground remains at a relatively constant temperature year-round just a few feet below the Earth’s surface.1
A geothermal heat pump works by transferring heat to or from the ground surrounding your home and using it to heat and cool the inside of your home. The technology has been around for decades and can cut energy bills up to 50% compared to conventional fossil fuel systems2.
Here’s where the digging comes in: Geothermal heat pumps use a series of pipes or coils buried underground to work their magic. In the winter, the ground absorbs and stores heat from the sun, even if the surface air temperature is cold. (That’s why a gardener can yank a good carrot out of the ground well into the winter.)
During the winter months, a geothermal heat pump circulates a water-based solution through the ground loop, absorbing stored heat. Then, the heated solution is transferred to a heat exchanger, where it warms the air circulated through your home. Dig it?
The anatomy of a geothermal heat pump
A geothermal heat pump has three main components: an indoor unit, ground loop and a distribution system.3
What does the indoor unit do?
Think of this as the command center or the “brain” of your heat pump system. It contains the compressor, heat exchanger and system controls.
What does the ground loop system do?
If the indoor unit is the brains of the operation, then the ground loops are the veins and arteries. There are three different types of ground loop systems, and the geography of your property dictates which system will work best for your home.
In the summer, the process reverses and heat is extracted from your home and transferred to the cooler ground around it, using the same loop system. This not only cools your home but also lowers humidity levels, further enhancing comfort during the heat of the summer.
Horizontal loops are installed in shallow trenches and are often used for residential or small commercial properties.
Drilled deep into the ground, vertical loops are a good option for more heavily populated areas or for urban homes.
If you’re lucky enough to live near a pond or a lake, water loops use nearby bodies of water for heat exchange.
What does the distribution system do?
If you guessed that it’s the “heart” of the operation, then we’re on the right path. Once your indoor unit captures or releases heat, the distribution system pumps it throughout your home through a network or ducts or radiant floor heating. If you’re retrofitting your home, existing ductwork can usually be enlisted to do the job.
How are geothermal heat pumps installed?
Installing a geothermal heat pump is a complex process that requires professional expertise. To help make sure the job’s done right, all TVA EnergyRight rebate-eligible geothermal heat pumps must be installed by a member of the Quality Contractor Network.
Generally speaking, here’s how the process works:
Step 1: Site assessment
Your selected member of the Quality Contractor Network will evaluate your property to determine if it’s suitable for a geothermal system. They’ll consider soil conditions, land area and the proximity of your home to any underground water sources. This initial assessment helps determine which ground loop configuration is best for your system.
Step 2: Estimating and scope of work
Your contractor will provide you with a detailed estimate and a clear scope of work.
Step 3: Excavation and ground loop installation
For horizontal or vertical loops, trenches or wells are dug to install the pipes. This part of the process may take a few days, depending on the type of loop and property size.
Step 4: Indoor unit installation
This part of the process is pretty much like installing a conventional furnace and connecting ductwork.
Step 5: Connecting the system
Once the ground loop and heat pump are connected, the system is filled with a water-based solution that circulates through the loop to transfer heat to and from the ground and into your home.
Step 6: System testing
Your contractor will carefully check for any leaks, verify temperature settings, and explain how to operate and maintain the system.
How long do geothermal heat pumps last?
They’re more costly than a conventional heating or cooling system, but they’re made to last. They’re also up to 65% more efficient than a traditional unit and pay themselves back over time in energy savings — typically within 10 years.
With good routine maintenance, you can expect your geothermal heat pump’s indoor components to last approximately 25 years, rather than the 10- 15-year lifespan of a conventional system. Your ground loops should last for 50-plus years.4
To make geothermal heat pumps more affordable, we’re offering a $3,000 rebate on qualifying systems and federal tax credits of up to 30% of the installed cost may also be available.
Why are geothermal heat pumps such a big deal?
A recent analysis from Oak Ridge National Laboratory (ORNL) and the National Renewable Energy Laboratory (NREL) found that, coupled with building envelope improvements, installing geothermal heat pumps in approximately 70% of U.S. buildings could save as much as 593 terawatt-hours of electricity generation annually. It could help the U.S. avoid seven gigatons of carbon-equivalent emissions by 2050.
“To put that in context, 593 terawatt-hours is about 15% of the current annual electricity demand in the United States,” said Jonathan Ho, lead NREL researcher for the analysis.
The report went on to note that “Widespread geothermal heat pump installations could also save 24,500 miles of new grid transmission lines from needing to be built (36.7 TW-mi) — the equivalent of crossing the United States eight times — because of a reduced need for generation capacity, storage, and transmission compared to other energy pathways. This means geothermal heat pumps could provide benefits to all electricity consumers, even those who cannot install geothermal heat pumps themselves.”5
1Energy.gov, “Geothermal Heat Pumps.”
2Energy.gov “5 Things you Should Know About Geothermal Heat Pumps.”
3The Old House, “Geothermal Heat Pump: How It Works”
4Energy.gov “5 Things you Should Know About Geothermal Heat Pumps.”
5NREL.gov, “New Analysis Highlights Geothermal Heat Pumps as Key Opportunity in Switch to Clean Energy.”
