Optimizing Electric Humidifier Operation with an Air Side Economizer

Abstract

Air side economizer cycle is a control scheme that is often used in WAC systems to reduce cooling energy consumption by introducing variable quantities of ambient air into a conditioned space to satisfy the space cooling load (free cooling). Humidifiers are used to maintain the pre-set humidity levels in a conditioned space by introducing steam or atomized water into the space. An WAC system containing both electric humidifier and air side economizer cycle can appear to be energy efficient, but has the potential of being inefficient due to lack of proper controls. The economizer, which often operates independently of the humidifier, introduces large quantities of cool and dry ambient air into the space to reduce the mechanical cooling energy, but because of the environmental requirement of the space, the air has to be humidified. The humidification energy could offset the energy savings from the reduction in mechanical cooling energy. The solution for this potential problem is a control scheme that makes the operation of the economizer and electric humidifier interdependent. The control scheme will use ambient conditions and space environmental requirements to calculate the appropriate amount of outside air that the economizer should draw into the space. The control scheme can be implemented through a Direct Digital Control system.