Heat pump system with hot water defrost

An integrated heat pump and hot water system that includes,

• a heat pump having an indoor heat exchanger unit and an outdoor heat exchanger unit that are selectively connected to a compressor inlet and a compressor outlet by a flow reversing means and to each other by a refrigerant liquid line containing a bi-flow expansion valve for metering refrigerant moving in either direction through the liquid line, said bi-flow expansion valve having a positive shut off means to prevent refrigerant from flowing therethrough,
• a refrigerant to water heat exchanger having a water flow circuit that is in heat transfer relation with a first refrigerant condensing circuit and a second refrigerant evaporating circuit,
• said refrigerant condensing circuit being connected into a discharge line connecting the outlet of the compressor to the reversing means whereby all refrigerant discharged by the compressor passes through said condensing circuit,
• said refrigerant evaporating circuit being connected at one end to the inlet of the compressor and at the other end to an evaporator line that is operatively joined to the liquid line at a point between the bi-flow expansion valve and the outdoor heat exchanger,
• a metering valve in the evaporator line that is selectively movable between a first closed position whereby refrigerant is prevented from moving through the evaporator line and an open position whereby refrigerant is throttled from the liquid line into the evaporator circuit, and
• control means for cycling the metering valve and the bi-flow expansion valve.