Heat Pump Water Heater (HPWH) is a promising technology that uses the same mechanical
principles as refrigerators and air conditioners to generate hot water.Unlike conventional ele-
ctricity and fossil-fuel-fired water heaters, HPWHs take heatfrom the surrounding air and tra-
nsfer it to the water in the tank.
    The heat pump works by taking heat from the surrounding air and using it to heat low pres-
sure liquid refrigerant in the heat pump’s evaporator, vaporizing the liquid.The refrigerant then
passes through the compressor, which raises the refrigerant pressure and thus the temperat-
ure as well. The heated refrigerant gas passes through the heat pump condenser, where it g-
ives off its heat to the water and condenses back into the liquid state. The liquid refrigerant
now passed through an expansion valve where the pressure is reduced and the cycle starts over.