In heating mode, the outdoor coil of a heat pump operates as what?

In heating mode, the outdoor coil of a heat pump operates as a condenser. This occurs because the heat pump extracts heat from the outside air and transfers it indoors. During this process, refrigerant in the outdoor coil releases the heat it has absorbed from the outdoor environment, changing from a gas to a liquid state as it condenses. This is the mechanism by which heat is effectively moved from the outdoors to the inside of a building, allowing for indoor heating.

Understanding the function of the outdoor coil in reverse (as it does in cooling mode) is essential. When operating in heating mode, the heat pump's process is essentially reversed; this highlights the dual capability of heat pumps in both heating and cooling applications. The roles of the other components, such as evaporators, heat exchangers, and expansion valves, differ in purpose and function, emphasizing the distinct role of the outdoor coil as a condenser during heating mode.