The amount of evaporator surface required for superheat depends on the temperature difference between the media being cooled and what?

The amount of evaporator surface required for superheat is indeed influenced by the refrigerant temperature. In the context of HVAC systems, superheating occurs when the refrigerant vapor temperature exceeds the saturation temperature corresponding to the evaporator pressure.

The efficiency of heat exchange in the evaporator is contingent upon the temperature difference between the refrigerant and the air or fluid being cooled. A higher refrigerant temperature allows the system to absorb more heat from the cooling medium, promoting better performance and efficiency. Therefore, as the refrigerant temperature rises, more evaporator surface area is necessary to ensure adequate heat transfer and maintain the system's desired superheat level.

In contrast, while sub-cooling, the temperature of the saturated liquid, and head pressure can influence system performance, they do not directly dictate the surface area needed to achieve superheat in the vapor stage. The primary relationship that governs the need for evaporator surface area to reach and maintain superheat focuses on the refrigerant temperature relative to the medium being cooled.