A chiller evaporator barrel exchanges heat between one refrigerant and another. This refridgerant circulates throughout the facility and passes through piping and coils. Is most cases a forced air coil is used; heat is removed from the air by a heat exchange process with the water and the coil. The cooler air then passes through ductwork and into the facility.

Many chillers are designed to make more than one pass to ensure heat transfer. Each pass is separated to ensure flow through the chiller barrel.