DOE-2 Reference Manual Version 2.1 - DOE2.com

q. Ceiling Bypass Variable-Volume System (C8VAV)OUTS I DEAIR __IIII['~T-ReCOv(RYI 1 __ -ICUIL--, PRE flEATIIEcoriOMIZERI COILI ~~'=i:' 1=;;=='=' =1, II IL ___ ~TO OTHER ZONESRETURNAIRPLENUMMIXEDAIRCONTROLS, COIL I I RETURN I I I FAt. II " \L __ ~L_riii:AT-iIRECOVERVI 1-- - - IrEXHAUST I ~~' ='(0~~' =~::;~:' .. ==(;;;;;;:;;;~;;:;;;;:!j;~;:;;;;;:;;;lb~~;;;;jj;;:;;;~JJAIR --- ITEMS SHOWN IN DASHED BOXESARE OPTIONAL COMPONENTSThe Ceiling Bypass Variable-Volume system, illustrated above, is exactlythe same as the variable volume fan system (VAVS) with one exception: themethod of reducing the air supply when the zone temperature falls below thethermostat setpoint. Instead of throttling to reduce flow, the zone VAV boxopens a damper that diverts flow to the plenum space above the zone. Thus,total air supply in the duct remains constant, even at part-load. Thisarrangement is most commonly used for systems that are too small for theeconomical use of flow reduction devices, such as inlet vanes or variable-speeddrives. Exhaust fan(s) are optional for any or all zones. The discussion ofsystem design features for VAVS applies as well to this system. The Btuequivalent of the moisture that is added to the air stream, to maintain aminimum humidity, is passed to the PLANT program as a heating load.A number of optional features and control strategies can be specified forthis system. The optional features are discussed in Table IV.2 and thesection entitled, "Explanation of System Options" (immediately following TableIV.2). The possible control strategies for this system are discussed in Sec.8.5 of this chapter. It is highly recommended that the user read that portionof Sec. 8.5 that is applicable to this system.Table IV.19 shows the commands and keywords that must be entered forsimulation of this system, as well as those that are appl icable but optional(i.e., program uses default value if entry is omitted.)IV.78 (Revised 5/81)