Chapter 6 - All-Air HVAC Systems

Abstract

This chapter concerns the idea of a thermal “zone.” A zone is an area of a building that must be provided with separate control if design intent is to be met. From an HVAC system perspective, the design intent that is most commonly of concern when establishing zones is the provision of thermal comfort. Providing for acceptable indoor air quality may also influence zoning decisions. Zoning should be established before system selection. Although costs and budget typically influence system selection and the number of zones that can be reasonably provided, selection of a system that cannot provide the necessary zones means selection of a system that cannot provide desired comfort or indoor air quality. All-air systems provide sensible and latent cooling capacity solely through cold supply air delivered to the conditioned space. No supplemental cooling is provided by refrigeration sources within the zones and no chilled water is supplied to the zones. The same supply air stream may accomplish heating, with the heat source located either in the central system equipment or in a terminal device serving a zone. Further the chapter discusses advantages and disadvantages of all air systems.