Evaporating and condensing temperature. The two saturation temperatures a circuit runs between, found where evaporator, compressor and condenser balance — the solver's two unknowns per circuit. What a solve returns.
A vapour-compression circuit runs between two pressures, and each pressure has a saturation temperature: the evaporating temperature, at which the refrigerant boils in the coil taking heat from the air or water it cools, and the condensing temperature, at which it condenses in the condenser giving that heat plus the compressor's work away. They are the two numbers a circuit is described by. The evaporating temperature sits below the fluid it cools by the coil's approach — 5 to 15 K on a direct-expansion coil — and the condensing temperature above the condenser's entering air by 10 to 15 K; a compressor's map is a function of exactly these two.
Neither is chosen by the designer directly: they are where the three components balance. A hotter day raises the condensing temperature, the compressor pumps less and draws more, and the evaporating temperature follows the reduced capacity upward. This solver treats the pair as the two unknowns of every circuit and finds them by Newton's method, with the head-pressure floor, the frost derate and the map envelope all expressed in the same two temperatures; a refrigerant's pressure–temperature chart converts either to the pressure a gauge on the circuit would read.
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 · Superheat · Subcooling · Sensible heat ratio (SHR) · Bypass factor · Wet-bulb temperature · Dew point · COP and EER · Compressor map · Range and approach · Heat-recovery (three-pipe) VRF · Typical meteorological year (TMY)