Well Pumps



 

Well pumps are typically of the submersible type. They are selected based on the recommended flow rate; well head losses; friction losses including the piping, valving, heat exchanger losses; and tank pressure. Submersible pumps use less energy than jet or other pump types.

The well pump should be sized by a water pumping professional, since pump power consumption can significantly effect the overall economy of the heat pump system. 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 refrigerant-to-water heat exchanger.

ARI Standard 325 assesses a penalty for the water pump effect. This penalty ranges from 5 watts per gpm per unit psi pressure drop through the unit water coil for 1 to 4 gpm water flow rates, down to 2 watts/gpm-psi for 20 gpm and above, plus 60 watts/gpm based on 50 feet external head.

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 it 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.

Three types of water control valves are recommended for groundwater heat pump installations. They are:

  1. Pressure regulating valves. These maintain constant pressure and flow rate, and can reduce noise.
  2. Flow control valves. These are motor- or pressure-operated, and initiate from whenever the thermostat calls for heat pump operation. And...
  3. Trim valves. These are manually adjusted to set the optimum flow rate.