Energy crisis - Free Essay Example

ntroducton vr nc th nrgy cr, whn dgtl control (thn clld MC for nrgy mngmnt nd control ytm) wr uncrmonouly uhrd nto wdprd u for HVC control, th ndutry h trd to mk thm look nd ct lk th pnumtc control thy hv uprdd. Only occonlly r om of th profoundly xpndd opportunt vlbl wth dgtl control ppld ffctvly. Furthrmor, trm lk rt chdul nd drct ctng, rlvnt only to pnumtc ytm, r tll commonly mployd n wht now th dgtl control r. Whl th proc of trnton to dgtl control tchnolog tolrt th mxd bg, multtud of nw dmnd r rqurng our ndutry to mov hd nd rlz th full potntl of dgtl control tchnolog. Buldng occupnt r dmndng mor comfortbl nd hghr qulty nvronmnt. Buldng ownr contnu to pr for grtr conom n contructon, oprton, nd mntnnc. Fnlly, vrty of prur r upon u to provd mor prc control nd documntton tht tndrd for tmprtur, vntlton, nd ndoor r qulty r bng mt. n th rtcl, wll dcu how DDC tchnolog prmt nw flxblty n th trdtonl rul concrnng th nd for lnr gnl nd rpon wth nput nd output dvc. Whn proprly ppld, th nw flxblty cn rduc th cot of DDC tchnolog. Nxt month, wll how how, by combnng th fundmntl wth mrgng ntr mnufcturr control ntgrton, dgnr cn chv nw horzon n prformnc nd nrgy ffcncy. HVC Control ytm HVC control ytm computrzd ytm for clmt control n buldng. HVC tnd for humdty, vntlton , r-condtonng. Oftn, th ntgrt fr, curty, nd lghtng control nto on ytm. Th ytm typclly u on or mor cntrl controllr to commnd nd montor th rmot trmnl unt controllr, nd thy communct wth on or mor pronl computr tht r ud th oprtor ntrfc. Th control ytm r typclly ud on lrg commrcl nd ndutrl buldng to llow cntrl control of mny HVC unt round th buldng(). Th ltt ytm u th buldng thrnt for communcton btwn cntrl controllr, nd llow oprtor cc from wb browr. Drct Dgtl Control Cntrl controllr nd mot trmnl unt controllr r progrmmbl, mnng th drct dgtl control progrm cod my b cutomzd for th ntndd u. Th progrm ftur nclud tm chdul, tpont, controllr, logc, tmr, trnd log, nd lrm. Th unt controllr typclly hv nlog nd dgtl nput, tht llow murmnt of th vrbl (tmprtur, humdty, or prur) nd nlog nd dgtl output for control of th mdum (hot/cold wtr nd/or tm). Dgtl nput r typclly (dry) contct from control dvc, nd nlog nput r typclly voltg or currnt murmnt from vrbl (tmprtur, humdty, vlocty, or prur) nng dvc. Dgtl output r typclly rly contct ud to trt nd top qupmnt, nd nlog output r typclly voltg or currnt gnl to control th movmnt of th mdum (r/wtr/tm) control dvc.(Vlv/dmpr/motor pd) t w only nturl tht th frt HVC controllr would b pnumtc, th ngnr undrtood flud control. Thu mchncl ngnr could u thr xprnc wth th proprt of tm nd r to control th flow of htd or coold r. To th dy, thr pnumtc HVC qupmnt n oprton, whch cn b cntury old, n om buldng, uch chool nd offc. ftr th control of r flow nd tmprtur w tndrdzd, th u of lctromchncl rly n lddr logc, to wtch dmpr bcm tndrdzd. vntully, th rly bcm lctronc wtch, trntor vntully could hndl grtr currnt lod. By 1985, pnumtc control could no longr compt wth th nw tchnology. By th yr 2000, computrzd controllr wr common. Tody, om of th controllr cn vn b ccd by wb browr, whch nd no longr b n th m buldng th HVC qupmnt. Th llow om conom of cl, ngl oprton cntr cn ly montor thound of buldng. Why Lnr Dvc? Whn pnumtc control domntd our ndutry, buldng ownr pd hgh prc for modult n g l o o p p r f o r m n c n d tblty. On of th prc pd w th rqurmnt tht nput nd output dvc b lnr wth rpct to th ytm vrbl thy nd or controlld. Th nd for lnr rpon w ntl to mtch th lmtd control cpblt of pnumtc controllr. numbr of rul nd convnton wr tblhd wthn our ndutry tht md chvng th lnr rpon rqurmnt r. mong th wr th dvlopmnt of th qul prcntg vlv, whch ncludd th mngly bckwrd rul of thumb tht clld for zng control vlv mllr thn th pp z. mlrly, mchncl nng dvc wr contructd to provd lnr chng n control r prur ovr thr ntr nng rng. Whl th convnton nd rul of thumb rvd th dy of pnumtc, thy now nd to b rthought. Rqurng wht cll xtrnl lnrzton n dgtl control dgn dd cot n two wy. Lnr dvc r oftn mor xpnv thn nonlnr dvc tht my offr mprovd lvl of prformnc n DDC pplcton. Furthr, lnr output convnton, uch dgnng hgh prur drop through vlv or dmpr, crry ubtntl contnuou oprtng nrgy pnlty. By dvlopng nw rul nd convnton, th knowldgbl dgnr cn produc dgn tht hv lowr frt nd oprtng cot nd my oprt mor rlbly wll. Lnr Dvc n th DDC r Th nd for lnr rpon n modultng control loop h not bn lmntd by th ntroducton of dgtl control. Whl dgtl control offr mprovd modultng control cpblt, ncludng proportonl/ntgrl/drvtv (PD) controllr, th control loop contnu to b bd on th prncpl of lnr rpon, t lt ovr crtn rng. Howvr, n mot typcl pplcton, dgtl control cn ly ntrnlly lnrz both nput gnl nd output control functon. ntrnl Lnrzton of nput On wy to rduc th cot of om DDC confgurton to prmt nonlnr nput dvc nd u th DDC ytm for clng to chv th corrct rdng ovr th rng rqurd for th pplcton. contnu to DDC pcfcton tht lmt th lcton of nput dvc to tho tht provd lnr gnl to th DDC ytm ovr wd rng of vlu. xcpt n pcl c, th n unncry rqurmnt tht dd cot nd my cu othr problm. Condr tmprtur nor. Fg. 1 how rtnc curv for n nxpnv thrmtor typ tmprtur nor tht my b mployd for room tmprtur nng. Thrmtor r xcllnt choc for HVC pplcton. Thy r nxpnv, hv xcllnt ccurcy nd vry low hytr, nd rpond quckly to tmprtur chng. Furthrmor, t tmprtur normlly nvolvd n HVC pplcton, thrmtor hv xcllnt long-trm tblty (om cr hould b tkn n choong thrmtor whn tmprtur my r bov 240 F). Fnlly, bcu thrmtor r typclly hgh rtnc (10,000 ohm typcl), thy r not ffctd by vrton n wrng dtnc. Howvr, om dgnr contnu to xclud thrmtor bcu th nput gnl not lnr wth tmprtur ovr wd tmprtur rng. ntd, low mpdnc RTD typ nor r oftn pcfd. Th typ of nor typclly rqur n lctrc crcut t th nor tht lnrz nd trnmt th gnl n wy tht t wll not b ffctd by wrng rtnc (uully currnt loop gnl ud). mployng low rtnc RTD nor wth ddtonl lctronc prnt numbr of potntl problm n DDC pplcton. Frt th mttr of ccurcy. Whl th RTD nor thmlv provd xcllnt ccurcy, t not uncommon to fnd nd-tond ccurc ( u nd-to-nd th compron of th vlu rd by prcon thrmomtr t th dvc comprd wth th ctul rdng t th DDC ytm oprtor trmnl) out of tolrnc. Clbrton of th currnt loop nput my b mor dffcult thn tht of mpl rtnc typ thrmtor. Othr potntl problm wth RTD rng from th ddtonl lctronc (uully loctd t th dvc) tht my complct rlblty u ll th wy to how th nor curv 2 Nonlnr nor rtnc curv. Th nor prformnc curv mooth curv ovr th nor oprtng prur. Th DDC lnrzd curv r of trght ln tht cloly pproxmt th nor prformnc nor nd lctronc r confgurd, whch on occon h bn found to ffct dvrly th nor gnl. Tbl functon tht r now rdly vlbl wth DDC product cn b mployd to cl thrmtor nd othr nonlnr dvc ovr wd rng of vlu. Fg. 2 how how DDC ytm cn lnrz contnuou, nonlnr nor nput curv wth tbl functon. numbr of trght ln curv r tblhd n th tbl functon to pproxmt cloly th nonlnr functon of th dvc. long mpl, nxpnv dvc cn mt th rptblty, hytr, nd tblty rqurmnt for n HVC pplcton, uch dvc hould not b rjctd bcu thr gnl r not lnr. Rqurmnt of Lnr Output Onc t undrtood tht nput dvc nd not b lnr, t not grt lp to rcognz tht th rpon from output dvc controlld by nlog output mlrly nd not b lnr. Howvr, th u hr r mor complx nd mor ngrnd n th rul of thumb tht ngnr frquntly pply utomtclly, o om ndpth dcuon rqurd. Bcu of th pnumtc bckground, vlv dgn mnul commonly tr th nd to lct col/vlv combnton for whch qul ncrmnt n vlv poton wll ffct qul ncrmnt n ht trnfr of typcl htng or coolng col throughout th trok of th vlv ctutor. Fg. 3 how how trdtonl dgn prctc k to lnrz th ovrll prformnc of vlv nd coolng col. Crfully lctng col nd vlv combnton cn provd nrly lnr prformnc ovr th ntr rng of lod poblt. uch lcton don bcu t umd tht th vlv wll b oprtd by controllr wth fxd proportonl gn. Though th dgn prncpl tll wdly mployd, t no longr pplcbl n mny modrn HVC pplcton. n VV coolng col pplcton, th vrton of r flow nd r/chlld wtr tmprtur chrctrtc ct to chng dynmclly th ht trnfr chrctrtc of th vlv/col rrngmnt th prmtr chng. Th mk t vry dffcult to lct vlv/col combnton tht wll b lnr through th vrty of condton tht my ccompny t oprton. Th hghr prformnc of DDC ytm prmt dgnr much grtr flxblty n th dgn of modultng control wthout tblhng ttc (nd thrfor unrltc) dgn crtr. Fg. 4 how vlv nd col combnton tht do not provd lnr rpon of vlv poton to col cpcty. Howvr, modrn DDC ytm prmt clng tbl to b ppld to nlog output wll th nput. Output clng prmt n nhrntly nonlnr dvc combnton to rpond n lnr fhon to gnl from th DDC ytm. n th xmpl, th vlv nd col combnton provd bout 70 prcnt of th dgn coolng cpcty t bout 20 prcnt vlv trvl. Th DDC output to th vlv cn b djutd wth th clng tbl to poton th vlv t 20 prcnt trvl t 70 prcnt output gnl from th DDC ytm. Th clng fctor llow tndrd PD control to oprt th vlv ffctvly bcu of oftwr lnrzton of th vlv/col combnton. Howvr, th chlld wtr flow nd ht trnfr prformnc umd for Fg. 4 vld only for contnt lod-d flow nd nlt tmprtur nd for contnt chlld wtr upply tmprtur. Whthr nhrnt n th ytm dgn or for optmzton ron, rrly n rl HVC pplcton do th othr vrbl rmn contnt control loop oprt. prvouly dcud, th u of lnr output combnton h thrfor bn only wkly rolvd n th pt by ttmptng to lnrz componnt t on t of ytm condton. Obtnng good control ovr wd rng of ytm condton cn b rolvd fr mor compltly nd ffctvly wth th hghr prformnc cpblt of DDC ytm. Th proportonl, ntgrl, nd drvtv gn cn b td to lgorthm tht djut thr vlu th vrbl uch lod-d flow, tmprtur, nd chlld wtr tmprtur chng. vn mor mprv th mrgnc of lf-tunng controllr. Th controllr contnully r-tblh th vrou gn octd wth control loop to provd contnuouly prc control wthout huntng. Th bnft of lf-tunng r pclly mportnt bcu vrbl byond th mmdt control loop cn hv profound nd wdly vryng ffct on ch control loop. lf-tunng ftur r bcomng wdly vlbl wth DDC ytm nd r normouly ffctv n djutng control loop to contnu tbl oprton othr ytm vrbl chng. Controllblty prvouly dcud, lctng qupmnt for lnr rpon hould not b n ovrrdng condrton for dgnr n th r of dgtl control. Howvr, th do not mn dgnr cn b mprc n thr dgn or n th lcton of control loop componnt. Th u of controllblty on tht wll contnu to ply promnnt rol both n th dgn of ytm nd th lcton of ndvdul componnt. Controllblty rmn lrgly zng u. f vlv ovrzd for gvn condton uch tht th mllt ncrmnt pobl from th control loop wll ubtntlly ovrhoot th drd control condton, th loop h bcom uncontrollbl. Th problm tht typclly mrg durng prod of low lod. Fully undrtndng th u of controllblty nd pplyng DDC cpblt corrctly llow dgnr to olv uch problm nd t th m tm vtly mprov th ffcncy nd prformnc of th ytm. lctng control vlv wth lowr prur drop wll rduc th pumpng powr rqurd to mt th lod condton. Trdtonl prctc trongly condmn th d of mployng lrg vlv wth lowr prur drop bcu of th nonlnr rpon nd th lck of controllblty t low lod. Fg. 5 llutrt th dlmm. Th vlv/col combnton wth Vlv my b lctd ccordng to trdtonl dgn prctc bcu t ronbly controllbl t low lod. Th vrtcl x ntrcpt rprnt th mllt ncrmntl coolng trnfr pobl th vlv crckd opn. Not tht t mll-only bout 10 prcnt of th dgn mxmum coolng rt. Th col combnton wth Vlv B h much lowr prur drop bcu Vlv B lrgr z vlv. Whl vlv/col Combnton B would rqur l pumpng powr, th Y-x ntrcpt much hghr thn tht for Combnton . Trdtonl dgn crtr typclly dclr Vlv B unutbl for th pplcton bcu t uncontrollbl t lowr lod nd th vlv poton/ coolng cpcty rltonhp nonlnr. But whn t ntgrtd wth hgh-prformnc control ytm tht cn djut both th chlld wtr tmprtur nd th loop hd prur, wll lnrty nd controllblty of Combnton B rlly b problm? ytm Dynmc To how th quton cn b nwrd, condr th grph n Fg. 6 nd 7. Fg. 6 how th oprton curv for vlv/col Combnton B t numbr of dffrnt pproch (chlld wtr upply l r tmprtur lvng col) tmprtur condton. t clr tht ncrng th chlld wtr tmprtur rltv to th lvng r tmprtur mrkdly mprov th controllblty t low lod. mlrly, Fg. 7 llutrt tht th dcr n prur cro th vlv/col combnton lo mprov th controllblty t low lod. Dgnr cn u th rltonhp to rduc ubtntlly th problm of controllblty. t prod of unform low lod, th DDC ytm cn rduc th hd prur cro vlv nd ncr th chlld wtr tmprtur to mprov controllblty. f ll vlv on common chlld wtr loop xprnc mlr dcr n lod concurrntly, typcl n mny HVC pplcton, th prmtr djutmnt grt hlp n mprovng controllblty t low lod. t pprnt from th two fgur tht lrgr rngblty nd low lod controllblty r chvd by controllng th chlld wtr tmprtur for lod djutmnt. Rng th chlld wtr tmprtur provd bonu of chllr ffcncy ncr, but chlld wtr djutmnt rduc pumpng vng bcu hghr chlld wtr tmprtur ncr th wtr flow ncry to mt lod. ddtonlly, undr crtn crcumtnc dhumdfcton rqurmnt my lmt th prmbl chlld wtr djutmnt. xplotng th ntgrtd control cpblt of DDC ytm nd controllng chlld wtr tmprtur nd hydronc loop prur n coordnton wth th control vlv llow vlv/col Combnton B to prform vry wll n mny HVC pplcton. Nxt month w wll focu on th lvl of ntgrton rqurd to mk vlv/col Confgurton B oprt ffctvly. W wll dcu ntgrtng th oprton of th vrou qupmnt nvolvd n provdng comfort, pobl now through th ndutry mov to provd communcton brdg mong mnufcturr. By concntrtng on lctng th mot cotffctv nput/output dvc nd by utlzng th mrgng communcton pthwy btwn qupmnt from vrou upplr, w wll tht nw horzon of prformnc nd nrgy ffcncy cn b ttnd wth mpl nd conomcl control confgurton. Dgnr mut xplot th bnft of hghr prformng DDC ytm to dvlop n undrtndng of th fundmntl of ntrfcng hrdwr pont to DDC ytm. n o dong, mor n-dpth look nto totl ytm oprton mut b vlutd bfor oluton r lctd. mply followng trdtonl rul of thumb rgrdng lnr nput nd output dvc poor dgn prctc n th dgtl control r. DDC nd mll nd Mdum z Buldng Th control of htng, vntltng nd r-condtonng (HVC) ytm chngng rult of pplyng drct dgtl control (DDC) tchnqu to HVC control. Th rport outln th mn ftur of DDC comprd wth convntonl pnumtc control nd how tht, for mll-to-mdum-z buldng, th DDC ytm cn py for tlf wthn two yr, ftr whch t ffct nt vng ovr pnumtc ytm. Compron btwn Pnumtc Control nd DDC Drct dgtl control of HVC ytm th drct montorng of vry ytm nput (tmprtur, flow, prur) nd drct control of vry ytm output (poton, onlff) from cntrl controllr whch ngl computr or combnton of computr. DDC mpl concpt, but t gnfcnc not obvou untl t comprd wth trdtonl form of HVC control. Trdtonlly, th control of HVC ytm w bd on ndpndnt pnumtc controllr, whch ud comprd r t o oprt th dmpr nd vlv ctutor t o control pc condton uch tmprtur, humdty nd frh-r crculton. On buldng would hv vrl uch ytm, whch wr controlld ndpndntly. For xmpl, n r-hndlng ytm compod of two fn, thr dmpr nd thr vlv (Fgur 1) would b controlld by locl pnumtc controllr whch oprtd ndpndnt unt. ch controllr hd mpl tk: to mntn contnt t pont (for xmpl, upply r tmprtur) by montorng nd controllng vry l m t d numbr of vrbl connctd to t by mn of comprd r ln who prur rprntd th vlu of th vrbl. Th control w djutd mchnclly by tchncn n th fld, nd, clbrton of th pnumtc componnt w rrly crrd out, th ytm oftn dd not control th buldng ffcntly. Bcu th pnumtc controllr wr purly lctromchncl dvc, thr ophtcton nd ccurcy of control wr xtrmly lmtd. ltr vrnt (of pnumtc control) lo mployd pnumtc cntrl, but w t h th ddton of computr ytm. Th comput ytm montord om ddtonl pont (for xmpl, pc tmprtur) nd thr clcultd nw t pont for ch pnumtc controllr or llowd n oprtor t computr trmnl to trnmt mnul t pont to th pnumtc controllr. lthough th nwr vrnt dd th buldng mngr by provdng mor nformton bout buldng condton nd prformnc, ovrll ffctv control of th buldng w tll compromd by th locl pnumtc controllr. ch controlld pont w tll oprtd by pnumtc controllr wth vry lmtd ophtcton nd vrtully no flxblty. Th lmtton bcm mor mportnt wy to mng nrgy bcm mor ophtctd, om WC ytm, uch vrbl r volum (VV) ytm, rqurd n ccurcy of control not ttnbl n mot c by pnumtc controllr. rult, buldng nrgy mngr wr frutrtd by thr nblty to mprov th control trtg wthout rbuldng th pnumtc control ytm for ch chng. DDC h olvd both problm;. ntd of ndpndnt locl pnumtc controllr, DDC u control or montorng pont, ch connctd to computr (or ntrconnctd computr) whch rd th vlu of ch nput nd trnmt commnd to ch output (Fgur 2). Th control trtg r mplmntd by computr progrm, whch cn b chngd by th oprtor t wll. lo, ch trtgy h vlbl to t th vlu of vry ytm nput ntd of vry l m t d locl t. n hort, undr th DDC concpt, th ntr buldng oprt on ntgrtd ytm rthr thn ndpndnt rrrll ytm. Four mn rult ccru: Control cn b mpl or ophtctd drd, nd cn b chngd ly; Th ytm mor rlbl bcu fwr lctromchncl componnt r ndd; Control mor ccurt bcu of th nhrnt grtr ccurcy of DDC lctronc componnt; nd nrgy vd bcu n ovrll trtgy lmnt nrgy wt rultng from multnou htng nd coolng, whch uully occur n pnumtc ytm. Th blty of DDC to ccommodt vrtully ny control trtgy h hd drmtc mpct on mchncl dgn. om nw mchncl ytm cn oprt n mny dffrnt mod, dpndng on xtrnl condton, pc tmprtur, on, condton of torg tnk, nd utlty-prcng tructur. DDC llow uch ytm to b oprtd contnuouly n thr optmum mod, tndrd whch mply cnnot b ttnd by ordnry pnumtc ytm or vn pnumtc ytm wth computr montorng. Conquntly, mchncl dgnr r now fr to d g n th bt nrgy ytm for prtculr buldng wth th urnc tht whtvr control trtg thy pcfy cn b crrd out. ch loop t th rmot procor cn ctvt tlf ndpndnt of th othr; howvr, th mot ffcnt u of nrgy chvd by controllng ll th loop through th cntrl procor. chdulng r-condtonng nd htng lod nd lctvly droppng lctrcl lod f th totl buldng powr pproch th dmnd lmt r two common nrgy optmzton ftur vlbl. Othr ftur, uch optml top/trt, whch clcult th optmum trtng nd toppng tm of htng/coolng unt to prpr pc for occupncy wthout wtng nrgy, r lo ud prt of n ovr-ll trtgy. Mot of th optmzton routn do not rqur ny ddtonl hrdwr nc thy r mplmntd by mply ddng progrm tht n xtng nput nd chng th trtgy for controllng xtng output ctutor. Th buldng ownr or mngr who u DDC ffctvly nd fdbck to vlut h trtg for optmzng buldng prformnc. DDC mplf th proc bcu t contnully montor ch nput drctly nd h torg cpcty to kp fl of th htorcl dt thu obtnd. Th htorcl dt cn b plottd n color on TV crn or ummrzd nd prntd n rport formt for mngmnt rvw. Th mot dvncd DDC ytm (Fgur 3) nclud gnrlzd rport gnrtor whch cn produc n typ of rport t ny tm rthr thn lmt th ur to th rport nggd whn th ytm w procurd* Th ftur of DDC prtculrly mportnt nc th ownr powr to chng h nrgy trtgy gnrlly crt nd for nw rport on nrgy-ntv r dntfd by contnud u of th ytm. n ncllry bnft th blty of th DDG ytm to nclud fclt othr thn WC. Wth lttl ncr n cot, fctor uch control of curty nd lghtng cn b ddd to th ytm, thrby nblng grtr nrgy vng nd lmntng th nd to purch prt ytm for bdg rdng nd door-lock control. Thr no doubt tht DDC offr mor ffctv nrgy mngmnt thn convntonl control but, untl vry rcntly, t pplcton to HVC ntllton h bn lmtd to lrg buldng complx. Mny mll- nd mdum z buldng ntllton do not u DDC mnly bcu of t hgh cot. n th followng cton typcl mll buldng nlyzd nd DDC comprd wth pnumtc control on cot nd pybck b. mll Buldng ytm Th cot of n HVC control ntllton gnrlly rltd to th numbr of pont t o b montord or controlld, whr ch pont dfnd n nlog or dgtl nput (.g., tmprtur nor, fn ttu wtch) or nlog or dgtl output (.g. dmpr poton or pump on/off control. ch buldng ytm, uch r hndlng, domtc hot wtr, or chlld wtr, nclud crtn numbr of pont. rcnt tudy whch ncludd dtld nly of r of buldng HVC ytm, howd tht mll- to mdum-z buldng of bout 37,175 m2 (400,000 q. ft .) would contn bout 180 pont, of whch 35% would b nlog nput, 19% nlog output, 25% dgtl nput nd 21% dgtl output. lthough dffrnt buldng confgurton nd mchncl dgn would ffct th dtrbuton of pont typ, th totl numbr of pont for buldng of th z would uully b clo to 180. Dgnng DDC ytm Gvn th buldng lyout nd th numbr of pont n HVC qupmnt, th ngl grtt dgn trd-off tht btwn cntrlzton nd dtrbuton of computr powr. t th fully cntrlzd xtrm ngl cntrl computr control ll functon drctly nd ll pont r wrd to t. t th othr xtrm (fully dtrbutd), mllr cntrl computr connctd t o myrd of othr mll computr, ch of whch wrd to 10 to 20 nrby pont, n th cond ntnc th cntrl mchn prd vr th whol ytm nd control th pont through th ntrmdry of th rmot procor. ch rmot procor cn control ngl HVC ytm (.g. r-hndlng unt, chllr) ndpndntly. mdn pproch to mploy modrt numbr of rmot unt ch of whch wrd to 50 t o 120 pont. lthough ll th pproch utlz th bnft of DDC, th thr lvl of cntrlzton/dtrbuton nvolv thr fctor tht mut b wghd gnt on nothr. Th frt fctor th cot of computr hrdwr. Th fully-cntrlzd pproch mploy ngl procor, whch th lt xpnv nc t combn ll th computng powr n on plc w t h on nclour nd no duplcton of functon. Th fully-dtrbutd pproch rqur th hvt cptl cot for computr hrdwr. Th cond fctor lctrcl ntllton cot. Th fully dtrbutd rrngmnt yld th lowt ntllton cot bcu ch rmot procor cn b loctd vry clo to t pont nd thu wrng run r hort. Th fully-cntrlzd rrngmnt my b qut xpnv unl ll pont r n on mchncl room. Th mdn rrngmnt (Fgur 4) my b th mot conomcl ovr-ll bcu four rmot procor cn b ud, on n pnthou, on n om othr logcl locton uch bmnt mchncl room, nd othr on vrou floor of th buldng. Th thrd fctor rlblty. Th fully-cntrlzd chm mot ntv to flur nc flur of th ngl computr cu th ntr ytm to fl. lthough th ytm cn b md to fl fly, ytm flur nconvnnt. Th fully-dtrbutd chm lt ntv nc ny componnt computr cn fl whl tll lvng ll th othr runnng, but, prvouly mntond, th cot of th computng qupmnt hght. mdn pproch for mll buldng mk good n; comprom on ll fctor tblhd by dgnng ytm contng of cntrl computr nd four rmot unt. Cot nly: DDC vru Pnumtc Control Th ntlld cot of DDC ytm h trdtonlly bn hghr thn for pnumtc y tn, pclly n mll ntllton, whr th cot of th DDC control procor prd ovr fwr pont. Th cot of pnumtc ytm tnd to r lnrly wth th numbr of pont, lrg ytm rqur mor ndpndnt locl controllr, whr wth DDC cntrl procor rqurd vn f o r ytm wth vry fw pont. Howvr, th rpdly fllng cot of computng hrdwr h rodd th htorcl prc dffrnc btwn DDC nd pnumtc ntllton. For pcfc buldng of 37,175 m2 (400,000 q. ft.), th ntlld cot of pnumtc ytm bout 75% of th cot of DDC ytm lthough th ntl cot of DDC ytm hghr thn for pnumtc ytm, t cn b rcovrd n urprngly hort tm . t rltc to um tht DDC ytm wll yld 10X% nrgy vng ovr nd bov convntonl pnumtc control, du mply to t mor ccurt nd ophtctd control, nd t o t blty to provd th buldng ownr wth nformton bout buldng prformnc nd r whr nrgy hould b bttr controlld. Ftur uch lod hd nd flxbl chdulng lon wll produc lrg nrgy vng, nd th vng wll ncr th ownr bcom mor fmlr wth th oprton of th buldng. f w um yrly mntnnc cot of $12,000 nd $10,000 for th DDC nd pnumtc ytm rpctvly, nd n nrgy ug of 322 quvlnt kWh/m2/yr. (30 kWh/q.ft./yr.) t $0.0275 pr kWh for both ytm, t wll tk 1.4 yr mor for th DDC to py f o r tlf thn t wll for th pnumtc ytm whn ud n th buldng undr condrton. ftr tht tm th DDC ytm wll v mony comprd wth th pnumtc control. nothr mpl clculton how tht for thr-yr pybck th DDC nrgy vng nd b only 5.7%, n ly ttnbl fgur. Concluon Drct dgtl control now cot compttv w t h pnumtc control for WC control n mll- to mdum-z buldng. Gvn th othr dvntg of DDC, prtculrly t blty t o ccommodt chng to control trtgy nd to provd dtld rport of buldng prformnc, DDC hould bcom th domnnt tchnology for buldng n th z rng. ddtonl dvlopmnt ndd to lowr th ct furthr. n th xmpl prntd n th ppr, ntrumntton th hght n g l cot, lrgly bcu ll pcfd ntrumntton ndutrl grd. Th dvlopmnt of commrcl-grd nor nd ctutor, prtculrly ll-lctronc typ, whch would obvt th nd f o r n ntrumnt r upply, wll contrbut grtly to th ccptnc of DDC. cond r of dvlopmnt l n dvng computr progrm for th cntrl nd rmot computr. nrgy mngr dmnd mor ophtcton nd th lbor cot for cutom dvlopmnt r, comprhnv nd flxbl oftwr pckg wll domnt th DDC/HVC mrkt.