50 Electric and Fossil Fuel Variable Air Volume with Natural Gas Boiler and Water-Cooled Chiller This system ranks among the most common HVAC configuration in U.S. commercial buildings. According to a 2022 survey by AMCA International and Applied Marketing Knowledge, variable air volume (VAV) systems could be found in 32% of new, non-single family home construction projects in the United States.1 Its popularity stems from low initial costs and easy of maintenance as a single entry point provides heating, cooling, fresh air and humidity control to the building. As shown in Fig 5.1, an large air handling unit (AHU) delivers conditioned air to this classroom building. The supply air is distributed via a system of shafts and ducts and enters the classrooms through ceiling integrated diffusers(Fig 5.4). Return air is then moved back to the rooftop AHU where a heat recovery unit transmits heat to or from the incoming fresh air during heating or cooling season, respectively. Heating and cooling is provided via two water loops that connect the AHU to a natural gas boiler and watercooled chiller. Boiler and chiller are usually located in a maintenance room in the basement. To reject heat from the chiller, an additional hydronic loop transports warm water to the roof and transmits it via cooling towers to the ambient air (Fig 5.2). In select cooling dominated buildings, cold supply air delivers to all spaces and heating registers in each zone reheat the cold air to maintain a comfortable indoor temperature. This practice is predictably wasteful. References 1 Applied Marketing Knowledge, 2022, HVAC Terminal System Selections: A Real-World Project Data Survey, AMCA International
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