Deep Well Pumps for Ground-Source Heat Pump Systems

An open-loop ground-source heat pump uses groundwater as its heat source in winter and its heat sink in summer. A deep well pump draws the water, passes it through the heat pump, and the water returns to the ground through a second well.

Sizing the pump

The flow is set by the heat pump units, and often one well pump serves two or more units. The head covers the lift from the dynamic water level, the losses through the heat exchangers and pipes, and any pressure needed at the return well.

Where the energy goes

Heat pump units spend most of their time at part load, but a fixed-speed well pump keeps delivering full flow. The extra pumping shows up in both the power bill and the water bill. A variable frequency drive, controlled from the temperature of the water returning from the heat pump, lets the pump slow down when less water is needed. In heating mode, the controller also keeps the evaporator outlet water from getting too cold by speeding the pump back up.

Points to check

• The minimum speed must still lift the water from the dynamic level
• The water analysis, since groundwater can scale or corrode heat exchangers and pump parts
• A clean, sealed system, to keep air and sand out of the heat exchangers