Wet-bulb temperature. What a wetted thermometer reads in moving air — the limit of evaporative cooling and the floor under every cooling tower. Plot a state from it.
The wet-bulb temperature is what a thermometer with a wetted wick reads in moving air: evaporation cools the wick until the heat the air gives it balances the heat the water takes, and that balance depends on how dry the air is. It is the lowest temperature evaporation alone can reach, very nearly the adiabatic saturation temperature, and with the dry-bulb temperature it fixes the air's moisture content — a design condition is quoted as the pair, 35 °C dry bulb and 24 °C wet bulb. The gap between them, the wet-bulb depression, is what an evaporative cooler works with: a pad's effectiveness is the fraction of the depression it achieves.
It also bounds every cooling tower: the water leaving a tower can approach the entering wet bulb but never go below it, so a tower's rating is a leaving-water temperature at a stated wet bulb and its approach grows on a humid afternoon. On the psychrometric chart the wet-bulb lines run nearly along the lines of constant enthalpy, which is why an adiabatic process such as a spray or a wetted pad draws as a line of constant wet bulb. The free chart on this site plots any state from its dry and wet bulb.
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 · Dew point · COP and EER · Compressor map · Evaporating and condensing temperature · Range and approach · Heat-recovery (three-pipe) VRF · Typical meteorological year (TMY)