AT-01-07-2 -- Achieving Dry Outside Air in an Energy-Efficient Manner PDF

The central thrust of this paper is to develop a fundamental engineering understanding of outdoor air (OA) preconditioning equipment that utilizes passive desiccant wheels, sensible heat exchangers, and deep cooling coils to reduce the first and operating costs of cooling, heating, and humidification hardware over competing approaches. The specific equipment analyzed in the paper has an application niche in buildings that employ a separate dedicated outdoor air system. The separate dedicated outdoor air system is designed to meet the ventilation requirements of ANSI/ASHRAE Standard 62-1999, Ventilation for Acceptable Indoor Air Quality and also supply that air dry enough to remove all of the space latent loads efficiently. Application of this type of equipment allows the designer much greater equipment selection freedom with regard to meeting the remaining space sensible cooling/heating requirements. Emphasis will be placed on the physical and thermodynamic performance of each of the individual components of the system, as well as their operation together. Detailed analysis of the component and system performance is presented for all outdoor air thermodynamic conditions that fall into any of the four distinct operating regions of the psychrometric chart. Finally, a detailed analysis of the energy implications of utilizing this type of equipment will be presented and compared to various configurations and a conventional all-air VAV system.

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