Chilled-Water VAV Systems - HVAC.Amickracing

Overview of a Chilled-Water VAV SystemBenefits of Chilled-Water VAV SystemsA comprehensive list of system benefits depends on which type of system isthe basis of comparison. The following section discusses some of theprimary benefits of using a chilled-water VAV system.Provides multiple zones of comfort controlChilled-water VAV systems are popular because they are capable ofcontrolling the temperature in many zones with dissimilar cooling andheating requirements, while using a central air-handling unit. This isaccomplished by providing a VAV terminal unit and temperature sensor foreach independently controlled zone.When the sun is shining against the west side of the building in the lateafternoon, a VAV system can provide an increased amount of cool supply airto keep the perimeter zones along the west exposure comfortable, whilethrottling back the airflow to the zones along the east exposure so as not toovercool them.Load diversity results in less supply airflow and a smallersupply fanFor more information on the impact ofload diversity in multiple-zone systems,refer to the Trane Air Conditioning Clinictitled “Cooling and Heating LoadEstimation” (TRG-TRC002-EN).When an air-handling unit is used to deliver air to multiple zones, the methodused to size that supply fan depends on whether the system is designed todeliver a constant or variable quantity of air to each zone. If the system isdesigned to deliver a constant quantity of air to each zone (a constant-volumesystem), the supply fan must be sized by summing the peak (design) airflowrequirements for each of the zones it serves, regardless of when those peakrequirements occur. However, if the system varies the quantity of airdelivered to each zone, as is the case in a VAV system, the supply fan can besized based on the one-time, worst-case overall (“block”) airflow requirementof all the zones it serves, since all zones do not require peak (design) airflowsimultaneously.6 Chilled-Water VAV Systems SYS-APM008-EN