A mini-split air-conditioning system has an outside air compressor like a central air conditioning system, but the evaporator system is located in the room it cools, eliminating the pumping of cooled air into the room through ducts. With more than one evaporator unit, the system is considered multi-split.
In a mini-split system, the compressor converts the refrigerant from a gas to a liquid. As with the central cooling system, the liquid travels through a copper pipe to the evaporator unit. As the liquid converts to a gas in the evaporator, it gets cooler, chills the cooling coils and returns to the condenser as a warm gas. A blower circulates air in the room over the coils for cooling. Any water that condenses as the air passes through the cooling coils drains away through a plastic tube.
While mini-split systems only cool one room, they offer advantages over a window air conditioner. Placing the compressor away from the area the unit cools reduces noise, allowing the unit to operate at about the same noise level as a central cooling system. The evaporator is located high on the wall, out of the way and does not prevent using the window for natural ventilation. Mini-split systems are available as heat pumps that provide heating and air conditioning.