Chilled-Water VAV Systems - HVAC.Amickracing

Overview of a Chilled-Water VAV SystemIn addition, using chilled water as the cooling medium presents furtheropportunity for energy savings through the use of centralized, higherefficiencycooling equipment and a water distribution system.Flexibility of equipment locationChilled-water VAV systems offer significant flexibility when locating thevarious components of the system. The design team can maximize theamount of usable floor space in the building by using an air-cooled chiller,outdoor air-handling units, and VAV terminal units installed in the ceilingplenum. Or, equipment can be located indoors (water-cooled chillers andindoor air-handling units) to improve access for maintenance and prolongequipment life.Centralizing the cooling and heating equipment minimizes disruption of theoccupants when maintenance or repair is required. Similarly, the VAVterminals can be installed above corridors to minimize disruption of theoccupants.Typically, the only equipment located within the occupied space is thetemperature sensor mounted on the wall. However, as mentioned earlier, incold climates some VAV systems may use baseboard radiant heat locatedalong the perimeter walls within the occupied space.This flexibility also makes chilled-water VAV systems a popular choice fortaller buildings, which are not well-suited for roof-mounted DX equipmentand large areas for vertical air shafts.Finally, using water chillers for cooling centralizes the refrigerant inside a fewpieces of equipment. This minimizes the risks associated with refrigerantleaks compared to having refrigerant-containing equipment spreadthroughout the facility.Flexibility of air-handling equipmentIn general, air-handling units offer greater flexibility than packaged DXequipment. Air-handling units can typically be applied to a wider range ofoperating conditions, making them better suited for systems requiringvariable airflow, lower cfm/ton (L/s/kW) (such as those with high percentagesof outdoor air or colder supply-air temperatures), and tighter space controlrequirements.In addition, air-handling units are typically available with a broader range ofoptions, such as energy recovery devices, dehumidification enhancements,fan choices, air cleaning equipment, sound attenuation choices, and casingperformance (thermal and leakage) options.Able to adapt to changes in building useMost chilled-water VAV systems use an open return-air plenum to allow airfrom all the zones to return back to the VAV air-handling unit. This, combinedwith the use of flexible ductwork to connect the VAV terminal units to supply-8 Chilled-Water VAV Systems SYS-APM008-EN