An air handler is a large unmixed heat exchanger used for comfort control in large buildings. In one such application, chilled water (Cp = 4.2 kJ/kg⋅K) enters an air handler at 5ºC and leaves at 12ºC with a flow rate of 1000 kg/hr. This cold water cools air (Cp = 1.0 kJ/kg⋅K) from 25ºC to 15ºC. The rate of heat transfer between the two streams is