![]() Cooling capacity may also be stated in tons (where 1 ton equals 12,000 Btu/h), with typical applications ranging from 3 to 10 tons or more. ![]() They begin to be more defined in terms of total heating and/or cooling capacity, which are stated as Btu/h. The HVAC load capabilities of these units generally range from a few thousand cfm to tens of thousands. In addition to the components noted above, these units will typically have control dampers and serve larger areas or multiple zones within a building. Slightly larger AHUs selected for outdoor use, located on grade outside or on the roof, are usually referred to as packaged units or rooftop units (RTUs), respectively. Although not universal, typical load capabilities for FCUs are 200 to 1200 cfm while BCUs might range from 400 to 3,000 cfm. They generally have simple controls and serve a single zone within a building such as a loading dock or maybe a stairwell in a larger building. These small, terminal-type AHUs are referred to as fan coil units (FCUs) or blower coil units (BCUs), based on size and capacity. AHUs can be small, used in local environmental spaces, and include minimal components such as: a fan or blower, a single heat transfer coil, and filter(s). ![]() The control and operation of AHUs is beyond the scope of this article, but these items become increasingly more complicated with the HVAC application and the number of components within the AHU. ![]() Figure 3 is an example of a preliminary AHU elevation selection that illustrates the various physical internal components for a dual duct AHU with multiple plenum fans.īy definition, AHUs are used to condition and/or circulate air as part of an HVAC system. Common appurtenances include, but are not limited to, coils, filters, energy recovery devices, dampers, air-mixers, spray assemblies, eliminators, discharge plenums, and inlet plenums. In addition, AHU appurtenances are equipment or components that may be added to an AHU for purposes, including but not limited to, control, isolation, safety, static pressure regain, and wear. It works closely with ASHRAE in the development of standards for the HVAC industry.įor example, ANSI/AHRI Standard 430-2014 defines a central station AHU (CSAHU) as “a factory-made encased assembly consisting of a supply fan, or fans in parallel, which may also include other necessary equipment to perform one or more of the functions of circulating, cleaning, heating, cooling, humidifying, dehumidifying and mixing of air.” ![]() The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) is a trade association that represents global manufacturers of air conditioning, heating, commercial refrigeration, and water heating equipment. ![]()
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