Relative humidity
Also known as: RH
Short definitionShows what percentage of the maximum water vapour it could hold at that temperature the air is carrying. In a cold room this value decides whether produce wilts, loses weight or rots.
Warm air holds more water vapour. Relative humidity is how full the air is; at 100% the air is saturated and starts to release water. As air cools, the ratio rises even though the water in it stays the same. That is why cold room air saturates quickly and the moisture collects on the evaporator surface as water or ice.
When a room is designed, the humidity the product wants is asked at the start. Leafy vegetables and carrots want 95–100%, most fruit 90–95%, meat 85–90%, onions and garlic 65–70%. The evaporator selection is what really sets the humidity: with a small temperature difference between room and evaporator and a large surface the air stays moist, with a large difference it dries. If that is not enough, a humidifier is added.