When calculating super-heat with R-407C, what value must be used?

To accurately calculate superheat with R-407C, the dew point value is essential. The dew point represents the temperature at which a substance transitions from a vapor phase to a liquid phase. In the context of refrigerants like R-407C, this value is crucial because superheat is the difference between the actual temperature of the refrigerant vapor at the evaporator outlet and the temperature of the refrigerant at the dew point.

Using the dew point ensures that the calculation starts from a point where the refrigerant is fully vaporized, providing a clear reference for determining how much additional heat has been added to the vapor above this saturation point. This is vital for ensuring the refrigerant is adequately superheated before it enters the compressor, which helps prevent liquid slugging and potential damage to the compressor.

Other values, such as the bubble point or mixed phase value, do not serve the same purpose in determining superheat, as they might refer to temperatures under different conditions where liquid and vapor coexist or where more complex interactions are involved. By using the dew point value, you can effectively assess the heat content of the refrigerant and monitor the system's performance accurately.