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Considerations for two stage heat pumps
Two speed heat pumps are great. Typically they work at 66% of rates capacity and 100% of rated capacity. The stages are controlled by a solenoid valve on the side of the compressor which controls how much refrigerant gas the compressor has to compress (the speed of the compressor does not change). A two stage heat pump will probably have a variable speed blower motor (ECM - electronically commutated motor), this allows to blower to slowly ramp up to speed and slowly run down, it also allows the blower to operate at two different speeds to complement the two stages of the compressor.
- Size the well pump for the mid point demand. For example, our Flordia Heat Pump ES061 has two stages, stage 1 it requires a flow of 7 gallons per minute (7 GPM) and stage 2 a flow of 14 GPM. In this case the well driller should be told to size the pump for the most efficient flow at 10 GPM, but be capable of 14 GPM. Do not assume that contractors will know to do this. The most efficient pump is the smallest pump able to do the job, over sizing the pump makes it run less efficiently.
By using two solenoid valves each in series: with a restrictor valve, and in parallel with each other, it is possible to control the flow of water based on which stage the compressor is running at. The solenoid valves are activated by Y1 and Y2 (compressor stage 1, stage 2) wires from the zone controller.
Schematic for using two valves to control fluid flow
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