In some large systems, a cooling tower is used instead. The tower creates a stream of cold water that runs through a heat exchanger, cooling the hot condenser coils. The tower blows air through a stream of water causing some of it to evaporate, and the evaporation cools the water stream. One of the disadvantages of this type of system is that water has to be added regularly to make up for liquid lost through evaporation. The actual amount of cooling that an air conditioning system gets from a cooling tower depends on the relative humidity of the air and the barometric pressure.
