Well pumps should be sized by a water pumping professional, since pump power consumption can significantly affect the overall economy of the system.
Well pumps are typically the submersible type, selected on:
- Recommended flow rate;
- Well head losses;
- Friction losses including piping;
- Heat exchanger losses; and
- Tank pressure.
The well pump intake must be installed deep enough to remain 15 or more feet below the lowest water level. There should be a filtering screen in the piping to the heat pump. This will limit particles and the subsequent plugging or erosion of the heat exchanger.
ARI Standard 325 assesses a minimum well pump power consumption of 65 watts per gpm. However, values from 65 to more than 200 watts per gpm have been observed. Submersible pumps use less energy than jet or other pump types.
If the well pump is used for both domestic and heat pump requirements, the well pump should be sized to meet the largest requirement. The pump should not be sized for the combined demand, but instead should be used with a storage tank.
The piping should be sized to minimize friction losses. High density plastic polyethylene pipe is typically used, but local codes may require copper piping inside the structure.
A pressure tank is used to store water and supply is to the heat pump. A pressure switch activates the well pump when the tank pressure drops below a preset minimum value. This reduces well pump cycling. The tank also protects the water system from water hammer and harmful surges.
Types of water control valves
Three types of water control valves are recommended for groundwater heat pump installations:
- Pressure regulating valves. These maintain constant pressure and flow rate, and can reduce noise.
- Flow control valves. These are motor- or pressure-operated, and initiated whenever the thermostat calls for heat pump operation.
- Trim valves. These are manually adjusted to set the optimum flow rate.