Heat exchangers function by allowing a hotter fluid or gas to interact - directly or indirectly - with a fluid or gas at a lower temperature, which allows heat to be transferred and move towards equilibrium. This heat transfer results in a decrease in the temperature of the hotter stream and an increase in the temperature of the colder one. With air / water cooling, heat is transferred from air to water. One example of air / water cooling is cabinet cooling. With water cooling, heat is transferred from water to air. This type of refrigeration is commonly used to cool process fluids.