Which component primarily allows air-source heat pumps to extract heat from outside air?

Air-source heat pumps operate by transferring heat between the inside and outside environment, even in cold conditions. The outdoor coil is the component specifically designed for this purpose.

As outside air passes over the outdoor coil, it encounters refrigerant that has a low boiling point. This refrigerant absorbs heat from the outside air, even when the air temperature is quite low. As the refrigerant warms up, it evaporates, turning into a gas. This process is crucial for the heat pump's function, as it allows the system to collect heat from outside and transfer it indoors, effectively utilizing what could be considered "waste" heat from the environment.

The compressor, while essential for compressing the refrigerant and increasing its temperature and pressure, does not directly extract heat from the outside air. The reversing valve directs the flow of refrigerant but does not play a role in heat extraction either. The expansion valve is responsible for regulating the flow and pressure of the refrigerant before it enters the evaporator coil. However, it is the outdoor coil that directly engages with the outside air to absorb heat, making it the primary component responsible for heat extraction in an air-source heat pump system.