Geothermal cooling works like a conventional air conditioner, but it sends indoor heat into the ground instead of hot outdoor air. Because shallow ground temperatures are steadier than summer air temperatures, a ground-source heat pump can cool efficiently even during very hot weather.
The system still uses electricity for the compressor, pumps and blower. Its performance depends on correct building-load calculations, a properly designed ground loop and careful installation, not simply on burying more pipe.
How Geothermal Cooling Works
A closed-loop system circulates water or a water-antifreeze mixture through buried pipe. In cooling mode, the heat pump absorbs heat from indoor air, transfers it to the loop fluid and releases it into the surrounding ground.
The refrigeration cycle includes a compressor, heat exchangers and an expansion device, much like a standard heat pump. A reversing valve changes the direction of heat transfer for winter heating.
Most residential systems distribute conditioned air through ducts. Water-to-water systems can serve hydronic equipment, but radiant floors alone are generally not used for cooling because surface condensation must be controlled.
Some units include a desuperheater that uses otherwise rejected heat to help heat domestic water during cooling operation.
Ground-Loop Options
- Horizontal closed loop: Pipe is installed in trenches. It is often cost-effective where sufficient land is available.
- Vertical closed loop: U-shaped pipe is grouted into drilled boreholes. It uses less surface area but usually costs more to install.
- Pond or lake loop: Coiled pipe is submerged in a suitable body of water, subject to site conditions and permits.
- Open loop: Groundwater passes through the heat pump and is discharged or reinjected as permitted. Water quality, supply and regulation are critical.
The best option depends on land, geology, groundwater, drilling access, permitting, lifecycle cost and the building’s heating and cooling loads.
Efficiency, Comfort and Operating Cost
Ground-source systems avoid the high outdoor-air temperatures that make air-cooled equipment work harder in summer. They can also provide strong humidity control when equipment and airflow are correctly selected.
Actual cost savings vary with local electricity rates, the system replaced, loop pumping energy, duct condition, thermostat settings and installation quality. Compare modeled annual energy use and total ownership cost, not a generic percentage.
DOE estimates that indoor components may last up to 24 years and ground loops 50 years or more. These are planning estimates, not warranties. Pumps, controls, ductwork and water quality still require attention.
What a Good Design Must Include
- A room-by-room heating and cooling load calculation.
- Ground-loop design using soil or rock conditions, moisture and expected entering-water temperatures.
- Equipment performance data at the proposed loop temperatures and airflow.
- Correct duct sizing, sealing and balancing.
- Condensate drainage and humidity control.
- Loop flushing, pressure testing, purging and commissioning records.
- Required drilling, water, environmental and building permits.
For larger vertical systems, a thermal response test can measure actual subsurface conductivity and help prevent an undersized or unnecessarily large loop field.
Bottom line: Geothermal cooling can be efficient and quiet, but the loop and heat pump must be designed as one system around the building and site.
References: U.S. Department of Energy geothermal heat pumps and DOE heat pump systems guide.
