44 Fan Coil Unit with Natural Gas Boiler and Water-Cooled Chiller In the United States, this is currently the most common dedicated outdoor air system. According to a 2022 survey by AMCA International and Applied Marketing Knowledge, Fan Coil Units are installed in 23% of new, nonsingle family home construction projects in the United States.1 For this system, fresh air requirements are met through the rooftop air handling units (AHU) in Fig 4.6. Fresh air enters the building through the AHU, is distributed via vertical shafts and horizontal ducts and enters individual spaces through supply grilles (Fig 4.8.) The outside air is conditioned through electric resistance heating and direct expansion (DX) cooling coils. The AHU system can accommodate heat recovery. Heating and cooling loads are met through a natural gas boiler and watercooled chiller that are both located in the basement (Fig 4.7). Heat from the chiller is transported by water pipes to the rooftop and rejected via cooling towers to the ambient air. Hot and chilled water loops connect the boiler and chiller to fan coil units (FCU) in each room. A thermostat-controlled fan recirculates indoor air through the FCU to adjust local temperature conditions. References 1 Applied Marketing Knowledge, 2022, HVAC Terminal System Selections: A Real-World Project Data Survey, AMCA International
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