Superheat. How far the vapour leaving an evaporator is above its saturation (dew) temperature; a compressor map is published at one stated superheat and corrected to the operating one. The refrigerant charts carry the dew line it is measured from.
Superheat is how far the refrigerant vapour leaving an evaporator is above its saturation temperature at that pressure — on a blend, above the dew temperature, where the last drop of liquid boils off. It exists because the compressor must never draw liquid: the expansion valve holds a margin of a few kelvin past the point where evaporation is complete, typically 5 to 10 K on an air-conditioning unit. A freezer's suction line runs through a warm store and picks up far more — Copeland rates its refrigeration scrolls at a 65 °F (18 °C) return-gas temperature, which at −30 °C evaporating is nearly 50 K of superheat by the time the gas reaches the compressor.
A compressor map counts every kelvin of that superheat as capacity, because AHRI 540 measures capacity at the compressor inlet: the polynomial is published at one fixed superheat (11.1 K under AHRI 540, 10 K under EN 12900) and the mass flow it implies follows the density of the suction gas. Running the machine at a different superheat needs a correction to both the suction density and the refrigerating effect, which this solver applies to every catalog map and holds against Copeland's own EN 12900 tables within one percent. Only the superheat gained inside the coil is useful cooling; the rest is heat the suction line took from the room, and a freezer declares the split.
Open the builder — the examples in the Design tab's sources list include a machine of this kind, and the Simulate tab runs it against a year of weather.
DOAS — dedicated outside-air system · SZVAV — single-zone variable air volume · VAV terminal box · Economiser · Waterside economiser · Demand-controlled ventilation · Face-and-bypass · Head-pressure control · Humidity ceiling and floor · Cycling and modulation · Coupling · Priority · Category · Nested system · Design point and TMY year · Subcooling · Sensible heat ratio (SHR) · Bypass factor · Wet-bulb temperature · Dew point · COP and EER · Compressor map · Evaporating and condensing temperature · Range and approach · Heat-recovery (three-pipe) VRF · Typical meteorological year (TMY)