VA-89-21-1 -- Integrated Desiccant Cold Air Distribution System ✓ Most Recent

Strong design trends toward the use of cold air distribution systems, which generally operate with lower supply air temperatures (i.e., 40°F to 45°F), provide unique opportunities to enhance the cost effectiveness of physically integrated desiccant and evaporative cooling and air-handling components of variable-air-volume (VAV) systems. With higher outdoor ventilation rates required by the proposed ASHRAE Standard 62-1981R, a higher premium cost is incurred for refrigerating this air to a 40°F or 45°F supply air temperature if cooled by conventional air-conditioning methods. The newly developed integrated desiccant cold air distribution (IDCAD) system can work with a variety of conventional or advanced direct gas-fired desiccant regeneration developments expected to be commercially available in.the near future.

The IDCAD air-handling unit employs three supply fans: one for the hot deck and two for each cold deck, thereby allowing for separation of ventilation rates for both exterior and interior occupied zones. This design feature allows for significant reductions in the amount of building return air in ductwork while permitting lower containment space levels than conventionally designed VAV systems within separately served interior and exterior occupied building spaces.

This latter air distribution feature allows one to take full advantage of weft-known VAV energy savings while maintaining maximum design "ventilation efficiency" at aft other varying part-load conditions, as will be demonstrated in a design study involving a representative multiuse commercial building. Use of desiccant pretreatment of outdoor (i.e., ventilation) air can minimize the need for excessively diluted air rates for indoor air quality controlm now a major problem with most conventionally designed VAV systems suffering from sick building syndrome (SBS) or building-related illness (BRI).