Abstract: A reversible mode heating and cooling system comprises a conventional reversible heat pump unit having a compressor, a reversible valve, an indoor heat exchanger in heat exchange relationship with indoor ambient air, refrigerant expansion means and an outdoor heat exchanger in heat exchange relationship with outdoor ambient air, and operatively associated therewith, an auxiliary heat exchanger in heat exchange relationship with a heat exchange fluid for enhancing the capacity and efficiency of the system to evaporate refrigerant during the heating mode and to condense refrigerant during the cooling mode. The auxiliary heat exchanger is arranged for selective parallel or simultaneous parallel and series flow of refrigerant through the auxiliary heat exchanger and the outdoor heat exchanger to enhance the heating efficiency of the system at very low outdoor ambient temperatures.

Abstract: A reversible mode heating and cooling system comprises a conventional reversible heat pump unit having a compressor, a reversible valve, an indoor heat exchanger in heat exchange relationship with indoor ambient air, refrigerant expansion means and an outdoor heat exchanger in heat exchange relationship with outdoor ambient air, and operatively associated therewith, an auxiliary heat exchanger in heat exchange relationship with a heat exchange fluid for enhancing the capacity and efficiency of the system to evaporate refrigerant during the heating mode and to condense refrigerant during the cooling mode. The auxiliary heat exchanger is arranged for selective parallel or simultaneous parallel and series flow of refrigerant through the auxiliary heat exchanger and the outdoor heat exchanger to enhance the heating efficiency of the system at very low outdoor ambient temperatures and the cooling efficiency of the system at very high outdoor ambient temperatures.