The circulating loop pump in a geothermal system should provide a flow of fluid through the loop adequate enough to maintain good heat transfer during both cooling and heating modes.
The circulating pump must have sufficient power to overcome the resistance encountered while flowing through the:
- Ground heat exchanger and headers
- Heat pump water to refrigerant heat exchanger
- Equipment room piping, including all fittings and hoses.
For residential and small commercial projects, many heat pump manufacturers offer standardized pump modules that include the circulator and the necessary valves for system charging, maintenance and operation.
Some include a reservoir for air trapping. Others include a self-flushing feature and an air-purging system.
For commercial installations, the circulating pump must be selected to meet the requirements determined by the designer.
A flow rate of two to three gpm per nominal ton of cooling capacity, and water pressure drops in the 25 to 30 foot range, are typical. Keep in mind that the pressure drop with antifreeze solutions runs 25 to 36 percent more than with water.
Where multiple heat pumps are used, multiple circulating pumps, or a single pump with a standby pump, can be used. Plotting the curves of the loop and loop plus heat pump, with the circulating pump performance, help in understanding the relationships. The flow rate must be kept out of the laminar flow region and within the manufacturer's data range.