Vacuum cooling works by rapid evaporation of water from certain vegetables or other products under very low atmospheric pressures inside a vacuum chamber. Energy in the form of heat is required to change water from a liquid to a vapor state as in the boiling of water. At reduced atmospheric pressure in a vacuum chamber water boils at a lower than normal temperature.

Heat is required to boil or evaporate water. In vacuum pre-cooling this heat comes from the product being cooled. This includes field heat and heat from its respiration. The amount of water removed is roughly 1% of the initial product weight for each 10°C that it is cooled. Generally the moisture comes equally from all parts of the product being cooled and localized wilting is not a problem.

Vacuum chamber is the spaces for fitting pallets of produce and track conveyor system. According to practical application, the space could be manufactured from 1 pallet to 16 pallets or more. Vacuum chamber should sustain the big pressure from outside when decompressed, so it is normally made of steel to ensure enough intension.

Vacuum system take away air from vacuum chamber at desired speed (m3/s) according to actual application. In the vacuum system, vacuum pumps are the main parts. Vacuum pump will affect the water evaporation speed inside chamber. Before vapor in chamber saturated, faster water evaporated, faster produce temperature reduce.

Refrigeration system is composed of compressor, expansion, dry filter, liquid receiver, oil separator, gas separator, pipes, etc. Refrigeration system will condense vapor to liquid water to ensure vapor in chamber will not saturate. If vapor saturated in chamber, the water on produce will not evaporate any more. That means, no water evaporation, no temperature reduce.

All above three systems works well coordinated by control system including temperature control, pressure control, high-low pressure control, compressor control, loading control, remote control, etc. Control system is the central part of whole machine which is always special made according to different applications.