Water Sources

The ground water heat pump system is an open-loop system. It requires a reliable supply of good quality water, and a suitable means for disposing of the thermally altered water after the process. It uses well or surface water as the heat source for heating, and as the heat sink for cooling. Typically, a well is required.

Spring water or water from a lake, river, or other source having an appropriate temperature range can also be suitable. If a lake or pond is used, it should be at least one acre (or 40,000 square feet) in surface area for each 50,000 BTUH of heat pump capacity. Also, the average water depth should be at least 5 feet, and there should be an area where the water is at least 6 feet and preferably 10 to 12 feet deep.

Direct use without filtration is not recommended. An alternative is a 15- to 20-foot deep dry well. This can be dug with a backhoe next to the water's edge. Once excavated, a perforated plastic casing should be installed in the well, with gravel backfill placed around it. The gravel bed should provide filtration. Use a submersible pump suspended in the dry well since jet pumps and other types of suction pumps use more energy.

The source must be adequate to provide 1.5 to 3 gallons of water per minute per ton of heat pump capacity. Adequate disposal must also be available.

The quality of water is a major concern. Bad water can corrode the refrigerant-to-water heat exchanger, and reduce the service life of the equipment.

In deciding whether or not to use available good ground water, the pumping cost must be considered. Should analysis indicate that pumping costs will be 25 percent or more of the space heating and cooling energy cost, an alternative closed-loop system should also be investigated.

Water issues, such as reinjection, disposal, and legal restrictions on use, are a major concern, and should be carefully examined.