The energy shortage has triggered many uncertainties in the present practices of system design and control within the building industry. One of these uncertainties is the effect of humidification on energy conservation. In the near past, it was accepted that there are benefits to maintain certain humidity levels. To assess whether humidification does conserve energy, it is necessary to consider simultaneously the following: heat transfer through the structure, infiltration, condition of outside air, moisture addition, and moisture sources in the controlled space. The results should be compared with the energy consumption of the same configuration but without humidification. Such an analysis should be dynamic and throughout the season.

A great deal of material was published on the effect of humidification on people comfort, and recently ASHRAE has adopted a new comfort standard (see Fig. 1). It is obvious that it is desirable to maintain in winter low humidity and low temperature in order to minimize energy consumption for heating and humidification. In summer, it is obvious that it is desirable to maintain the highest possible dry-bulb temperature and humidity in order to conserve energy that is required for cooling and dehumidification.

This paper is directed towards commercial and industrial buildings where the humidification and dehumidification are done in the air handling unit, rather than moisture addition in space itself. This paper will consider the many aspects of humidification and dehumidification and their effect on energy input into the system.

As is well known, a commercial building can be subdivided into an interior zone and an exterior zone. The exterior zone is equipped with systems to compensate the heat gain or loss through the envelope of the building including the internal loads. The interior zone is invariant to outdoor conditions and has to handle only the internal heat sources. In the commercial building, the air handling systems, in general, are divided into interior air handling systems and exterior air handling systems. The discussion from here on will, relate to such configuration.