A direct expansion coil system is a direct method of
refrigeration in which the evaporator is in direct contact with the material or space to be cooled or is located in air circulation passages that communicate with that space. The evaporator of a direct system can include any type of heat exchanger
heat, such as tube coils, tubular coolers, finned coils or any device in which a primary refrigerant, such as ammonia, Freon or carbon dioxide, is circulated and evaporated in order to cool any material in direct contact with the opposite surface of the exchanger of heat.
