A heat pump system includes a compressor, a heat rejecting heat exchanger, an
expansion
device, and a heat accepting heat exchanger. A storage tank stores the water that
cools the refrigerant in the heat rejecting heat exchanger. A mechanical interface
plate positioned between a hot water reservoir and a cold water reservoir in the
storage tank reduces heat transfer between the hot water and the cold water. During
a water heating mode, cold water from the cold reservoir flows into the heat sink
to cool the refrigerant in the heat rejecting heat exchanger. As the water exchanges
heat with the refrigerant, the water is heated in the heat sink, exits the heat
sink, and flows into the hot reservoir of the storage tank. During a water discharge
mode, the hot water in the hot reservoir is removed from the storage tank and flows
into a hot water discharge. Cold water from a water source flows into the cold
reservoir of the storage tank to refill the storage tank.
