More efficient than recirculation for controlling VAV systems are inlet guide vanes or similar devices to reduce the amount of air the fans must move. Manufacturers can outfit custom and semi- custom units with ASD fan controls. Install indirect evaporative cooling modules, which use evaporating water to cool air. The evaporating water is discharged outside rather than being added to the conditioned air . When these modules are installed on single-package equipment, the evaporating water cuts the work the air conditioning unit must do, raising the capacity.
Several manufacturers offer such modules.
The modules consist of a set of tubes with dry interior air passages and an exterior surface coated with a fibrous material to absorb and retain water. Air to be conditioned is moved through the dry air passage, releasing its heat to the cooled surfaces, and cooling the air without adding moisture. To improve the cooling capability of the indirect evaporative module, the system may use building exhaust air as the air source for the wetside air passage. This air has already been conditioned and thus is typically cooler than outside air during the cooling season. This can be especially valuable for buildings that require large amounts of outside air ventilation.