DOE-2 Reference Manual Version 2.1 - DOE2.com

d. Dual-Duct Fan System (DDS)iHEAT-)I~~~~VERY I r~ - - --J! 1 I ECONOMIZER IOUTSIDE I HR I I IAIR --- 1 ---c II 11\L __ -.l L_RETURNAIRHEATINGCOILHOT AIR DUCTIHEAT- -IIRECOVERYI,COIL IEXHAUST I HR IAIR -- ,...-! c 1I IL __ ~r-----'I~~~URN:ZONENO. 2 I: ~:==~F=~~~~-~J~I :L _____ ..JI--IT~~S SHOWN IN DASHED BOXESARE OPTIONAL COMPONENTSThe dual-duct type fan system, illustrated in the schematic above, can beeither the cons tant vol ume or var i ab le volume type.The constant-volume type is identical to the multizone type of system(see MZS for description), except that the hot and cold air streams (from thewarm air duct and cold air duct) are extended to individual mixing boxes,located in the zone being served, where the two air streams are mixed.The variable volume type dual duct system is as described above, exceptthat the type of mixing box used in this system is capable of reducing flow inresponse to a decrease in cool ing demand. Mixing of the cold and hot airstreams occurs only after flow has been reduced to a prescribed minimum; thus,total energy usage is reduced.Exhaust fan(s) are optional for any or all zones. The program assumes theexistence of a preheat coil and calculates the preheat load, if and when themixed air temperature falls below the required PREHEAT-T. The Btu equivalentof the moisture 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 the sectionentitled, "Explanation of System Options" (immediately following Table IV.2).The possible control strategies for this system are discussed in Sec. B.5 ofthis chapter. It is highly recommended that the user read that portion ofSec. B.5 that is applicable to thlS system.I V. 28 (Revised 5/81)