In most cooling applications, the air leaving the cooling coil is not entirely saturated since some air does not come in contact with the cooling coil. The fraction of air that misses the coil is called the bypass factor, BF. The bypass factor can be determined from the temperature of water supplied to the cooling coil and from the states of incoming and exiting air. The process is shown on the psychrometric chart below.

The air that does not come in contact with the cooling coil is the “bypass factor” (BF) of a cooling coil may be found from;