Ground Source Heat Pump Cooling: How It Works and What to Check

How Does Ground Source Heat Pump Cooling Work?

In summer, the system takes heat out of the building, raises or transfers it to a usable temperature, and releases that heat into the ground. The ground is the heat sink: it receives unwanted indoor heat, rather than producing a stream of cold air on its own. The U.S. Department of Energy describes the same summer heat-transfer direction in its geothermal heat pump overview.

1. Room air or indoor water gives up heat. A water-to-air unit draws warm return air across a cold refrigerant coil; a water-to-water unit cools a separate chilled-water circuit for fan coils or other suitable terminals.
2. Refrigerant carries the heat. In a conventional vapor-compression cycle, refrigerant evaporates at the indoor heat exchanger, and the compressor raises its pressure and temperature.
3. The ground-side heat exchanger receives the heat. Hot refrigerant rejects heat to water or water-antifreeze fluid in a separate heat exchanger. The refrigerant then passes through an expansion device before the next cycle.
4. The ground loop rejects the heat into soil, rock or groundwater. A pump circulates fluid through buried pipes. After shedding heat, it returns to the unit to collect more.

The refrigerant and the ground-loop fluid usually run in separate circuits. A typical closed-loop geothermal heat pump does not pump refrigerant through the buried plastic pipes. Direct-exchange systems use a different ground-loop arrangement and require their own design method. For more detail on fluid separation and heat transfer, see our guide to types of heat exchangers.

A reversing valve is common in reversible vapor-compression models: it changes which heat exchanger absorbs heat and which rejects it. A heating-only geothermal unit may not have the necessary cooling configuration. For a general refrigerant-path explanation, see the Airproz heat pump schematic guide.

Active Cooling vs. Passive Cooling: What Changes?

Active cooling uses the refrigerant compressor to produce a controlled cooling effect. Passive cooling transfers heat through cool ground-loop fluid and heat exchangers, with little or no compressor operation for space cooling. These modes do not deliver the same room temperature, humidity control or cooling capacity.

Choose passive cooling when a limited drop in room temperature is acceptable and the expected ground-loop fluid temperature remains low enough for the indoor terminal to absorb heat. For rooms with a firm temperature or humidity target—such as a busy, sunlit office or a humid home—start by checking the rated capacity of an active-cooling design. Ask how much cooling either option can deliver at the warmest expected summer loop condition, not just in early summer.

If summer humidity is high, plan how moisture will leave the building. A chilled floor or uninsulated cold pipe can sweat when its surface falls below the indoor air dew point. Put condensation control, dew-point sensors, pipe insulation and condensate drainage into the design where needed, instead of relying on a thermostat alone.

Which Ground Loop Can Support Geothermal Air Conditioning?

Closed loops exchange heat through sealed underground pipes; open loops move actual groundwater or other approved source water through the system. Both can support geothermal cooling, but the site, water access, soil and approvals determine which design is practical.

A sealed closed-loop geothermal heat pump usually circulates water or a water-antifreeze blend in plastic piping. An open-loop geothermal heat pump uses source water that must meet the equipment’s water-quality and flow limits; local permitting and reinjection or discharge requirements can rule it out. ENERGY STAR defines these two ground-exchange approaches separately in its geothermal product criteria.

Size the ground loop from the building’s heating and cooling loads, ground heat-transfer properties, entering-fluid temperatures, operating hours, pump energy and the annual balance of heat entering and leaving the ground. The ASHRAE ground-source guidance explains why source temperatures and equipment ratings must be checked together.

For buildings that need much more cooling than heating, review more than one summer. Repeated heat rejection can raise loop temperatures and reduce future cooling capacity. Ask for a multi-year loop-temperature estimate. If it shows a continuing rise, the designer may need more ground-exchange capacity or a hybrid heat-rejection system.

How Does Geothermal Cooling Reach Each Room?

A ground loop alone does not cool a room. You also need indoor equipment designed to deliver cooling. This is one of the most important checks when someone already has a ground-source system that was installed primarily for heating.

Water-to-air heat pumps and ducted cooling

A water-to-air geothermal unit uses an indoor coil and fan to cool air that travels through ducts. It can remove moisture when the coil, airflow and drain are designed correctly. Check static pressure, fan energy, filter condition and room-by-room airflow. Ducts sized for a different heating system may not distribute the intended cooling evenly.

For multi-zone buildings, the FCU vs AHU differences guide explains how room temperature control, central ventilation and humidity removal can be divided between indoor equipment types.

Water-to-water heat pumps and chilled-water terminals

A water-to-water unit produces chilled water for compatible fan coils, air-handling units or other cooling emitters. The selected leaving-water temperature and flow rate must match the terminal’s cooling and latent-load needs. Where room humidity is high, a fan coil with safe condensate collection is often easier to manage than a plain radiator or floor circuit. For coil type, airflow and drainage details, see how a fan coil unit works.

Existing radiators or underfloor heating

Existing heating radiators often cannot provide useful cooling at a safe surface temperature. Radiant floors can work only with suitable controls, indoor humidity management and dew-point protection. A heat pump’s cooling setting does not make every heating terminal suitable for cooling.

How Efficient Is a Ground Source Heat Pump for Cooling?

Geothermal cooling can use less electricity than an air-source system because the ground usually offers a more stable heat-rejection temperature than hot outdoor air. The actual result still depends on entering-water temperature, compressor performance, pumps, fans and seasonal load. Evaluate cooling performance across the expected summer range of entering-water temperatures and part-load conditions.

For geothermal cooling, EER is the cooling output in Btu per hour divided by electric input in watts at the stated rating point. COP in many geothermal product specifications refers to heating efficiency, so it is not interchangeable with cooling EER. ENERGY STAR’s published geothermal criteria distinguish closed-loop water-to-air (EER 17.1) from open-loop water-to-air (EER 21.1) for the listed single-stage qualification conditions. These figures describe ENERGY STAR qualification at specified test conditions. Compare project operating cost using model performance, loop or well pumping power, and local water requirements.

Use the manufacturer’s extended cooling-performance table for the exact model. Request output capacity and electrical input at the project’s design entering-loop temperature, indoor cooling condition and fluid flow. Then check which fan and pump loads are already included in the rated watts, and add only the auxiliary loads that are excluded. Compare two systems at equivalent cooling duty and operating conditions. The PNNL Building America guidance recommends design-point manufacturer data instead of choosing solely from a certificate rating.

For a project budget, estimate electricity use across expected operating hours, changing summer loop temperatures and part-load conditions, using the model’s performance data and applicable auxiliary power.

Ground-source vs. air-source cooling: what changes?

For the air-source side of this comparison, read how an air-to-water heat pump works. A reversible air-to-water unit can produce chilled water, while rejecting heat to outdoor air instead of a buried ground loop.

The better-value system depends on total installed cost, local ground-work conditions, design-point efficiency, annual electricity use and the planned ownership period. An efficient air-source system may be the better choice if drilling is difficult or the extra ground work would not be recovered during the planned ownership period.

If an air-source chilled-water system better fits the site, compare Airproz’s R290 monobloc 6/8/12 kW air-to-water series and R290 monobloc 18 kW air-to-water model. These are air-source alternatives, not ground-source heat pumps. Select by the product’s cooling output and electrical input at the required outdoor-air and water temperatures; the series label alone is not the design-point cooling capacity.

What Should You Check Before Choosing Ground-Source Cooling?

Start with the summer cooling load and humidity requirement, then confirm that both the indoor equipment and the ground loop can carry the required heat. Confirm cooling capacity at the project’s design loop temperature, then check the indoor delivery system and ground-loop heat rejection together.

1. Calculate the building cooling load. Include climate, glazing, shade, ventilation, occupancy, equipment gains and both sensible and latent loads. Decide the target indoor temperature and humidity.
2. Choose the delivery method. Confirm whether rooms will use ducts, fan coils or purpose-designed radiant cooling. Identify drainage and dew-point protection.
3. Confirm the heat pump supports cooling. Obtain the exact model’s cooling capacity and electrical input at the project entering-ground-fluid temperature and required chilled-water or supply-air condition.
4. Design the ground-side heat rejection. Use the building’s annual heating and cooling demand, ground properties, summer peak and loop temperatures. Account for heat added by the compressor and applicable pumps.
5. Review the water circuit and permissions. Check actual fluid flow, pressure drop, antifreeze, air separation, pipe insulation, source-water quality and required drilling or water permits.
6. Commission and record results. Measure source entering/leaving temperatures, loop flow, indoor supply/return conditions, electricity use and condensate operation at meaningful loads. Compare those readings with the design and model documentation.

Information to send the design team: building location; peak summer cooling and winter heating loads; annual use; desired room temperature and humidity; land, wells or groundwater information; indoor terminals; and available electrical supply. The designer uses these inputs to check equipment capacity, ground-loop performance and indoor humidity control at the project’s design conditions.

What should the designer return before equipment is ordered?

1. A cooling-mode recommendation: active, passive or a combined approach, with the conditions that could change the choice.
2. Capacity and power at design conditions: the model’s cooling output, input watts and relevant auxiliary loads at the worst expected summer loop temperature.
3. An indoor delivery plan: target supply-air or chilled-water conditions, room distribution, condensate drainage and humidity controls.
4. A ground-exchange design: site assumptions, loop sizing, expected multi-year fluid temperatures, pressure drop and pump electricity.
5. A commissioning checklist: planned readings for loop temperature and flow, indoor conditions, electricity use and condensate performance, for comparison after installation.

For a ground-source project, obtain a geothermal equipment proposal and ground-loop design from qualified providers. Airproz’s published air-to-water heat pumps are air-source systems; compare them separately when an air-source approach fits the building and site. For any shortlisted air-source model, check its cooling mode, output at design conditions and required water temperatures.

Why Might Geothermal Cooling Become Weak or Uneven?

Check what changed in the indoor cooling path and ground loop before assuming the heat pump is undersized. Similar room symptoms can come from very different faults.

Start with the cooling setting, filters, room airflow and condensate drainage. If performance is still weak, a qualified technician can compare ground-loop flow and entering-water temperature with the original design and model performance data. Those measurements help distinguish a flow or control fault from a long-term heat-rejection problem.

Refrigerant and electrical diagnosis, drilling and groundwater work need qualified personnel. After a repair, repeat the same relevant loop-flow, temperature, room-humidity and power checks, where applicable, and compare them with the earlier readings. A fix is complete when the measured cooling performance recovers, not merely when the fault code clears.