What distinguishes a heat pump from an air conditioning unit?

A heat pump is distinguished from an air conditioning unit primarily by its ability to reverse the flow of refrigerant, which is made possible by the inclusion of a four-way reversing valve. This valve allows the system to switch between heating and cooling modes. When the heat pump operates in heating mode, the reversing valve changes the direction in which the refrigerant flows, enabling it to absorb heat from the outside air and release it inside the space being heated. In cooling mode, the refrigerant flow is reversed, functioning similarly to an air conditioning unit to absorb heat from inside and expel it outdoors.

While components like the evaporator, condenser, and compressor are present in both air conditioning systems and heat pumps, it is the four-way reversing valve that is unique to heat pumps and enables their dual functionality. Therefore, this distinguishing feature is what sets heat pumps apart from standard air conditioning units.