Large Scale Systems can be done by adding multiple heat pumps in parallel. When doing so we recommend the RESOL MX Controller which can pair up to 13 units in series for a very large system size. When adding multiple heat pumps, pipe sizing should be increased after the header to accommodate the added flow of more than one pump. Example if there are three units with 1” piping each. After the header, the piping to the tank should be 1 ¼”-1 ½” (consult a plumber for more technical specifications).
To use multiple cold weather heat pumps we must ensure the units are turned on to “Heat” not “Hot Water” mode. In heating mode the system can be activated by the remote on/off switch SW1 located on terminal Cn35 of the Arctic Heat Pump main board. This switch is closed by factory default. By cutting this connection you open the circuit and the unit will turn off. Closing the circuit will turn the unit on.
In heating mode the controller measures the inlet water temperature not the tank temperature. The parameter setting on the controller for “Heating” is set by adjusting the temperature on the controller. Because the buffer water tank will be measured by the MX controller we want to ensure that the Heat Pump on/off setting is set to the Max temp of 150 F. By doing so the heat pump will always be controlled by the MX controller.
Example: 3 units connected in parallel each using the MX Controller’s R1, R2, R3 as well as S1 attached to the sensor in the thermowell of the buffer tank. The MX controller will be set to control the On/Off temperature based on S1. If we set this to ON=110 and OFF=120 then when the temperature in the tank drops below 110 F the Resol controller will switch on R1, R2, and R3. By doing so we are closing SW1 in each heat pump and turning the heat pump on. The heat pump has been artificially set to 150 F and would run until the unit reached this temperature. However since the MX controller is controlling the SW1 (remote on/off) switch and the temperature now reaches 120 F, all three heat pumps will be turned OFF by opening the SW1 switch regardless of the fact the temperature setting of the Heat Pump controller is set to 150 F.
Flow Valves: It is recommended when running units in parallel that you properly balance the flow so that it is equal in each loop. Remember flow will always take the path of least resistance! You can purchase a Quick Setter flow meter to balance each loop (see below). Alternatively you can use the theory of reverse return to ensure each loop has the same amount of supply and return pipe lengths.