In an evaporator coil, which components are referred to as the primary surface?

In an evaporator coil, the primary surface is defined as the components that facilitate the heat exchange process between the refrigerant and the air or fluid surrounding the coil. In this context, the tubes play a crucial role as they carry the refrigerant through the evaporator. The refrigerant absorbs heat from the environment, causing it to evaporate in these tubes.

The tubes form an essential part of the heat exchange process because they allow the refrigerant’s change of state to occur, effectively cooling the air passing over the evaporator. While fins do enhance the surface area for heat transfer, they primarily support the function of the tubes by increasing the efficiency of heat exchange rather than being the primary surface themselves. Insulation does not participate in the heat transfer process; instead, it is designed to minimize heat loss or gain during the refrigerant's movement through the coil. Therefore, identifying the tubes as the primary surface is consistent with their role in the evaporator coil's function.