Patent ID: 6907923

Claim:
A heat pump system comprising: a compression device to compress a refrigerant to a high pressure; a heat rejecting heat exchanger for cooling said refrigerant; a tank including a cold reservoir for storing a cold fluid medium that cools said refrigerant in said heat rejecting heat exchanger and a hot reservoir for storing a hot fluid medium that is heated by said refrigerant in said heat rejecting heat exchanger, said tank including a moveable interface plate that separates said cold reservoir from said hot reservoir in said tank, wherein at least one of said cold reservoir and said hot reservoir includes an expandable element that contains one of said cold fluid medium and said hot fluid medium, wherein said cold fluid medium flows from said cold reservoir of said tank to said heat rejecting heat exchanger, exchanges heat with said refrigerant in said heat rejecting heat exchanger to form said hot fluid medium, and said hot fluid medium flows from said heat rejecting heat exchanger to said hot reservoir of said tank during a water heating mode, wherein the tank further includes a first sensor and a second sensor that detect a position of said moveable interface plate, and said water heating mode begins when said first sensor detects that said moveable interface plate moves above said first sensor and said water heater mode ends when said second sensor detects that said moveable interface plate moves below said second sensor; an expansion device for reducing said refrigerant to a low pressure; and a heat accepting heat exchanger for heating said refrigerant.