Geothermal Heating Systems Explained

By Industry Resource Desk

Commercial operators looking for ways to cut combustion-based heating and manage cooling loads often encounter geothermal heating systems in energy audits or retrofit proposals. The technology is well established in residential construction, but the way it applies to restaurants, grocery stores, and multi-building campuses raises different questions, especially where refrigeration, ventilation, and existing hydronic or ducted systems are already in place.

What Is a Geothermal Heating System?

A geothermal heating system, more precisely called a ground-source heat pump system, uses the relatively constant temperature of the earth a few feet below the surface to help heat and cool a building. This is distinct from direct-use geothermal (tapping naturally hot water or steam at the surface) and from deep or utility-scale geothermal power generation, which draws on much deeper, higher-temperature resources to produce electricity. Ground-source systems used in buildings do not generate power or rely on volcanic activity; they move heat using a buried piping loop and an electrically driven heat pump.

How Geothermal HVAC Moves Heat Year-Round

Below a certain depth, ground temperature stops tracking the swings of outdoor air and settles into a narrow band that stays fairly steady through the seasons. That stability is what makes the ground useful as both a heat source and a heat sink.

In heating mode, fluid circulating through the underground loop absorbs a small amount of heat from the surrounding earth. That fluid returns to the heat pump, where a refrigerant cycle concentrates the heat to a higher, usable temperature before delivering it to the building through a duct or hydronic distribution system. In cooling mode, the cycle reverses: heat is extracted from the building and rejected into the ground loop, which is cooler than the outdoor air on a hot day. The same hardware handles both jobs, switching function with a reversing valve rather than requiring separate heating and cooling equipment.

Core Equipment Inside and Outside the Building

A geothermal installation generally has two halves. Outside, or below grade, is the ground loop: a closed or open network of piping that circulates water or a water-antifreeze blend between the building and the earth (or, in open-loop designs, a water well and discharge point). Inside the building, the heat pump unit contains the compressor, refrigerant coils, and a heat exchanger that transfers energy between the loop fluid and the building's air or water distribution system. Circulating pumps, controls, and sometimes a desuperheater for domestic hot water assistance round out the mechanical room equipment. Because the outdoor unit is essentially buried piping rather than a rooftop condenser, geothermal systems free up roof and yard space that commercial sites often need for other equipment, including refrigeration condensers.

Closed-Loop vs Open-Loop Systems

The piping loop can be configured several ways, and site conditions usually dictate which option is realistic.

Horizontal Loops

Horizontal loops are buried in shallow trenches and suit properties with enough open land area, since they require more surface footprint per ton of capacity than vertical designs. They tend to be less expensive to install where excavation is straightforward, but they need soil conditions that allow even trenching.

Vertical Loops

Vertical loops use boreholes drilled much deeper into the ground, which makes them a common choice where land area is limited, such as tight urban lots or paved commercial sites. Drilling cost and access for drilling rigs become the main constraints.

Pond or Lake Loops

Where a property has access to a sufficiently sized pond or lake, a submerged closed loop can reject and absorb heat without any drilling, often at lower installed cost, but it depends entirely on having a suitable body of water nearby.

Open-Loop (Well) Systems

Open-loop systems draw groundwater from a well, pass it through the heat exchanger, and discharge it back to the aquifer or a surface water body. These depend on adequate water availability and acceptable water quality, and they are subject to permitting and regulatory review in most jurisdictions.

Is Geothermal a Fit for Commercial and Multi-Building Properties?

Geothermal is not limited to single buildings. Networked geothermal, sometimes called a thermal energy network, connects multiple buildings or an entire campus to a shared ground-loop field, allowing loads to be balanced across properties with different heating and cooling needs. Some installations also tie into underground thermal energy storage, banking excess heat or coolness for later use. Beyond space conditioning, a geothermal heat pump can often assist domestic hot water production through a desuperheater or dedicated heat exchanger, reducing the load on conventional water heaters, though it typically supplements rather than fully replaces that equipment.

Feasibility Checklist for Facilities With Heavy HVAC and Refrigeration Loads

Restaurants, grocery stores, and similar facilities carry refrigeration loads that run continuously and reject heat year-round, which changes the feasibility calculation compared to a typical office or home. Before pursuing geothermal, it is worth evaluating:

• Simultaneous heating and cooling loads, including whether waste heat from refrigeration condensers could offset some of the building's heating demand or interact with the geothermal loop sizing.
• Available land or drilling access, since horizontal fields need open ground and vertical boreholes need rig access without disrupting parking, loading docks, or existing utilities.
• Local geology and soil type, which affects drilling difficulty, loop thermal performance, and the number of boreholes required.
• Water availability and water quality if an open-loop design is under consideration, since mineral content and flow rates affect long-term equipment performance.
• Permitting requirements for well drilling, loop installation, and refrigerant handling, which vary by state and locality and should be confirmed early in planning.
• Disruption during retrofit, including how trenching or drilling will affect operating hours, existing ductwork, and site access for a business that cannot easily shut down.
• Contractor experience specifically with commercial-scale ground-source systems, since sizing and controls integration differ meaningfully from residential work.

Maintenance and Operations Considerations

Once installed, geothermal systems shift maintenance attention from combustion equipment to loop and heat pump performance. Routine tasks include checking loop fluid condition and pressure, inspecting circulating pumps for wear, monitoring the heat exchanger for fouling or reduced transfer efficiency, and verifying that controls are correctly staging the system between heating and cooling modes. Troubleshooting a ground-source system often starts with loop flow and temperature readings rather than refrigerant charge alone, since a sluggish loop can mimic other mechanical faults. Facilities with refrigeration equipment sharing mechanical space should also confirm that condensate, electrical, and control wiring for both systems are documented separately to simplify service calls.

Takeaway

A geothermal heating system offers a way to heat and cool a building using the stable temperature of the ground, with the ground loop and heat pump configuration chosen to match land, geology, and water conditions on site. For commercial facilities with significant refrigeration and HVAC loads, the decision depends less on the basic technology, which is well understood, and more on a careful feasibility review covering load profiles, site access, permitting, and long-term maintenance capacity.

This article is general industry information published as an educational resource. It is not advice about any specific project, and it does not reflect a recommendation or opinion of the business hosting this page. Talk to a qualified professional about your own situation.