An industrial air conditioning system will usually be a centralised cooling system that has a sophisticated ducting system that enables the cold air to be distributed. It is similar to the ducted system that is able to be used in residential cooling, but on a much bigger and more sophisticated level. Hot, outside air is blown over the refrigerant vapor by the condenser to liquefy it. The expansion valve changes refrigerant into a low-pressure liquid, thus cooling it. Heat is transferred by the evaporator to transform the cool liquid to a warmer gas.