Geothermal HVAC heats and cools a building by trading heat with the ground instead of the outdoor air. A few hundred feet down, the ground in the St. Louis area stays in the mid-50s °F all year. That's warmer than the air in January and cooler than the air in August, so a geothermal system does less work than a rooftop unit or a gas boiler to keep the same building comfortable.
You'll also hear it called a ground-source heat pump or geoexchange system. It isn't the same as the geothermal power plants in places like Iceland or California, which tap volcanic heat to make electricity. Commercial geothermal HVAC works almost anywhere, including here.
How geothermal HVAC works
Every system has three parts:
- The ground loop. Sealed plastic pipe runs down into vertical bores, usually 300 to 500 feet deep and 15 to 20 feet apart. Water, or water with a food-grade antifreeze, circulates through it. Nothing is pumped out of the ground or into it.
- The heat pumps. Inside the building, heat pumps use the loop's water as their heat source in winter and their heat sink in summer. They sit in mechanical rooms or closets, not on the roof.
- Distribution. The heat pumps deliver heating and cooling through ductwork or a building's existing air handlers. Many buildings reuse their ducts.
In winter, the loop carries heat up from the ground and the heat pumps move it into the building. In summer, it runs the other way: heat from the building goes down into the ground.
Why the ground beats the air
A conventional air-source system has to pull heat out of 10°F January air or dump it into 98°F August air. A geothermal system works against 55°F water instead. That's why Oak Ridge National Laboratory found that geothermal schools it studied used about 26% less energy. Lincoln, Nebraska, which has run geothermal schools for decades, pays roughly 70 cents a square foot a year to heat and cool them, compared with about $1.50 for its conventional schools.
The types of ground loops
- Vertical closed loop. The standard for commercial buildings. The bores go down, not out, so the well field fits under a parking lot, an athletic field or a lawn.
- Hybrid. A smaller well field paired with a small boiler or cooling tower that handles the peaks. Useful when ground space is tight, and it cuts drilling cost.
- Horizontal loop. Pipe laid in long trenches a few feet down. It needs a lot of open land, so it's more common for homes and small buildings.
What geothermal costs, and why
Geothermal costs more to install than conventional HVAC, mostly because of drilling. For planning, we figure a geothermal system at about 44% more than a conventional one. The real number depends on the building's size and use and on the rock underneath, which a test bore measures.
The federal investment tax credit closes most or all of that gap. It's 30% of the geothermal system's cost, plus 10% more if the equipment is U.S.-made and another 10% in qualifying "energy communities." Schools, churches, nonprofits and local governments get it as a cash payment. Businesses take it off their federal taxes. At 40%, a system that was 44% more expensive ends up about 14% cheaper than conventional up front.
Try it with your own number. The geothermal calculator takes a conventional HVAC price and shows the geothermal price, the credit and what the credit could pay for.
How long geothermal lasts
| Equipment | Typical life |
|---|---|
| Rooftop units | About 15 years |
| Indoor geothermal heat pumps | 20 to 25 years |
| Underground loop | About 50 years |
Over 50 years, a conventional system typically replaces its rooftop units three times. Geothermal replaces its heat pumps about twice and keeps the same loop. With indoor equipment and no boilers or cooling towers, maintenance is mostly filters and routine checkups.
Is geothermal right for your building?
It's worth pricing if any of these are true:
- Your rooftop units, boilers or chillers are near the end of their life.
- You're building new, adding on, or rebuilding a parking lot or field, so the ground is already being dug up.
- You're a school, church, nonprofit or public agency, and the credit comes back as cash.
- You plan to own the building for a long time.
The first step is a feasibility review: the building's heating and cooling load, the available ground, a cost comparison against conventional replacement, and the credit percentage your site qualifies for. Ask us for one, or call 636-327-4238.