TEC Zoning Control System for Stand-Alone and BACnet® MS/TP ...

In colder climates, VAV system heating operation without terminal reheat typicallyresults in colder walls on the outer perimeter of the zone. Although the dry bulbtemperature of the zone is well maintained, occupants may be uncomfortablesimply because of the lower outer wall temperature. In addition, heating deliveryfrom the ceiling in outside zones is not as efficient as heating delivery directlywhere the losses occur, such as when a perimeter electric baseboard or a perimeterhydronic baseboard is used.In regions where the heating load is low and only required for a short period of theyear, a properly sized VAV system can deliver the required heating comfortwithout the use of terminal reheat. Ideally, the design of the ductwork and areadiffusers should be the most efficient arrangement possible, with the heatingdelivery concentrated close to the outer walls of the zone.In problematic situations where efficient heating delivery is an issue, fan poweredVAV systems can reduce occupancy discomfort by providing a constant flow to thezones, to maximize heating delivery.Exception AreasAn office installation typically requires that a single VAV system service multipleareas or zones. These areas are likely a mix of internal and external zones. Verifythe requirements of each zone to determine a true total peak load beforecommitting to a final VAV system design and size.It may be necessary to intentionally oversize or undersize the VAV system to meetthe daily load demands. The following are examples where oversizing may berequired:• areas with large windows that are exposed to the sun for long periods of time• conference rooms• cafeterias• areas with vending machines• areas with extra lighting• areas with computers, photocopiers, and other electronic office equipmentAreas such as computer rooms, kitchens, or large meeting rooms may require anindependent VAV system, and should not be included with other zones that arenetworked to the rooftop controller. Certain critical areas may call for cooling allyear long and, based on the VAV system settings, could provide proper occupancycomfort for only a portion of the year. Knowing in advance the critical areas of thebuilding, and designing for these zones appropriately, results in a morecomfortable environment for all building occupants.10TEC Zoning Control System for Stand-Alone and BACnet® MS/TP Networked ApplicationsTechnical Bulletin