Separate Heat Pumps
Information about separate heat pumps - where the condenser component is separate from the tank.
Separate HPWHs, also known as stand-alone units, are characterized by the condenser component being distinct from the tank. In these systems, the refrigerant transfers its heat to the water through a separate heat exchanger, typically a plate heat exchanger. Water circulates between the heat exchanger and the tank with the assistance of a pump and water piping.
Refrigerant Loop Process: The refrigerant loop follows a specific process to transfer heat efficiently:
- A fan draws in ambient air over the air heat exchanger, causing the refrigerant to become a warm gas.
- The warm gas passes through the compressor, transforming the refrigerant into a hot gas.
- The hot gas then moves through the water heat exchanger, transferring heat to the water loop. The refrigerant transitions into a cool gas/liquid.
- The refrigerant passes through the expansion valve, becoming a cold liquid.
Water Loop Process: The water loop complements the refrigerant loop, ensuring effective heating of the water:
- Cold water leaves the bottom tank outlet.
- The cold water is pumped through a water pump.
- The cold water is heated in the water heat exchanger by the hot refrigerant.
- The now-hot water enters the top of the tank.
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Schematic of separate HPWH refrigerant and water loops
Pump Flow Rate: Pumps in separate HPWHs operate at either a fixed flow rate or a variable flow rate:
- Fixed Flow: The pump operates at a single speed setting, delivering a constant flow rate. This ensures consistent water circulation.
- Variable Flow: The pump varies the flow rate using a variable speed drive (VSD) motor to achieve a near-constant HP outlet temperature, typically within the range of 60-90 degrees Celsius. The flow rate adjusts based on the inlet water temperature and the HP operating capacity, both of which can vary with time. The VSD motor employs a control algorithm to achieve the desired outlet temperature efficiently.
This dynamic operation of separate HPWHs provides flexibility in adapting to changing water heating requirements, making them suitable for diverse applications.