Active desiccant integration with packaged rooftop HVAC equipment

Current research indicates a direct correlation between indoor air quality and fresh air ventilation rates which supports requirements for building ventilation standards calling for continuous supply and increased amounts of ventilation to help assure safe and healthy interior air environments [O. Seppänen, W.J. Fisk, M.J. Mendell, Ventilation rates and health, ASHRAE Journal (August) (2002) 56–58; C.C. Downing, C.W. Bayer, Classroom indoor air quality vs. ventilation rate, ASHRAE Trans., 1993, Vol. 99, Part 2, Paper Number DE-93-19-1, pp. 1099–1103. [1,2]]. Off-the-shelf, packaged rooftop equipment used to air condition most facilities is not designed to handle the increased or continuous supply of outdoor air necessary to comply with building ventilation codes written to this new standard [American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. (ASHRAE), Ventilation for acceptable indoor air quality, Standard 62-1989, 1791 Tullie Circle, NE, Atlanta, GA 30329. [3]]. Integration of a rooftop, unitary air conditioner with an active desiccant module (ADM) allows the use of a standard rooftop air conditioner with a thermally regenerated active desiccant component to provide a compact, cost-effective, and simple-to-use packaged system for efficiently pre-treating and supplying ventilation air adequate to ensure healthy indoor environments. By designing a combined vapor-compression/active desiccant system with the desiccant component positioned after a conventional cooling coil, the dehumidification effectiveness of the desiccant is significantly enhanced because it operates on cold, saturated, or nearly saturated, air leaving the evaporator. “Post-coil” rather than the normally used, “pre-coil” desiccant arrangement also minimizes the regeneration temperature required for the active desiccant, allows for partial bypass and post-cooling of the desiccated air after recombination, and dramatic decreases in the overall size for the pre-conditioning unit.