DOE-2 Reference Manual Version 2.1 - DOE2.com

m. Variable-Volume Fan System w/Optional Reheat (VAVS)fHc;,r--iIR[(OVERYI _· _ --, PRE HEATICOIL1I EconOMIZER] COIL" ICOOLl NG(OILHEATINGCOIL'--II IHUMIDIFIER:IIIII II IL ___ .-JSUPPL YFANRETURNAI RTO OTHER ZONESMIXEDAIRCO~TROLSEXHAUSTAl R ---F!==[J~hf;fHEAT-iIRECOVERYIICO I L IEXHAUST I IAIR-,----1I RETURN II FAN II~~~' ==~~~~~==~~~~~j1~~~~~~;ti- ITEMS SHOWN IN DASHED BOXESARE OPTIONAL COMPONENTSThe Variable-Volume Fan System is illustrated in the schematic above. Inits most basic configuration, it consists of a central air-handling unit withfilter (not shown), cooling and optional heating coils, and a draw-throughtype supply air fan. Exhaust fan(s) are optional for any or all zones. Aduct system distributes supply air (at a temperature determined by the user)to variable-air volume (VAV) terminal units, located in the zones being served.The VAV boxes (controlled by a room thermostat) vary the amount ofprimary air to the space to control temperature. When the space demands peakcooling, the VAV box allows maximum air flow. As space cooling requirementsdiminish, the primary air flow to the space is reduced proportionately to aspecified minimum flow rate. If less cooling is required than that given atminimum air flow, the reheat coil is activated (if specified). When in theheating mode, the supply air flow rate is held at a constant value equal toMIN-CFM-RATIO. The supply air flow rate will rise above the MIN-CFM-RATIOonly if the user has set THERMOSTAT-TYPE = REVERSE-ACTION. The Btu equivalentof themoisture that is added to the air stream, to maintain a minimumhumidity, 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.B.5 of this chapter. It is highly recommended that the user read that portionof Sec. B.5 that is appl icab Ie to thlS system.I V.62 (Rev ised 5/81)