 In heating, ventilation, and air conditioning (HVAC) applications, a heat pump is typically a vapor-compression refrigeration device that includes a reversing valve and optimized heat exchangers so that the direction of "heat flow" (thermal energy movement) may be reversed.The reversing valve switches the direction of refrigerant through the cycle and therefore the heat pump may deliver either heating or cooling to a building.In cooler climates, the default setting of the reversing valve is heating.