Groundwater is usually supplied to the heat pump by a drilled well with a submersible pump system. If a recharge well is to be used, it should be drilled at the same time as the primary well. The groundwater should be tested for acidity, dissolved solids and mineral content.
In some large commercial installations, a separate water-to-water heat exchanger is used to keep only pure water in the heat pump.
Advantages & disadvantages
The advantages of using well water include:
- The well drilling and plumbing trades understand the system.
- An open loop system can be installed economically if there are existing wells or a high water table allowing the use of a shallow well.
- An open-loop system is easier to start, since there are no concerns about antifreeze, purging the piping of air and debris, or hidden water leaks.
- In areas with cold well water, intermediate "free cooling" is available by passing the cold well water through a coil in the air handling unit.
Some of the disadvantages include:
- The uncertainty of the well output after drilling.
- The problem of reinjection and disposal.
- Scaling in the heat exchanger can occur if there is a high rate of dissolved solids, minerals, calcium or iron content in the water.
- Water quality can deteriorate over time. Good water this year can become poor water next year.
- Pumping costs are usually higher. For example, a ¾-hp pump might be needed to deliver 10 gpm from a 200 foot well. The same 10 gpm can typically be maintained with a 1/6 hp circulating pump in a closed-loop system.
- Many well water systems use a higher cost cupro-nickel heat exchanger in the heat pump.
- An open loop will require more long-term maintenance to descale the heat exchanger, and redevelop or clean out the return well.
- Consumers are reluctant to pump large quantities of water and discharge the cooled or heated water to waste.
- Local or other restrictions may limit or prohibit use.
When a well is being considered, consult with a reputable well driller who has knowledge of both local conditions and of all the required permits, codes and restrictions. You can also talk with local officials.