CA1281393C - Automatic chilled water setpoint temperature control using return chilled water temperature - Google Patents
Automatic chilled water setpoint temperature control using return chilled water temperatureInfo
- Publication number
- CA1281393C CA1281393C CA000528239A CA528239A CA1281393C CA 1281393 C CA1281393 C CA 1281393C CA 000528239 A CA000528239 A CA 000528239A CA 528239 A CA528239 A CA 528239A CA 1281393 C CA1281393 C CA 1281393C
- Authority
- CA
- Canada
- Prior art keywords
- temperature
- leaving
- setpoint
- evaporator
- heat exchanger
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
- F25B49/00—Arrangement or mounting of control or safety devices
- F25B49/02—Arrangement or mounting of control or safety devices for compression type machines, plants or systems
- F25B49/022—Compressor control arrangements
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/1917—Control of temperature characterised by the use of electric means using digital means
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
- G05D23/24—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature the sensing element having a resistance varying with temperature, e.g. a thermistor
Abstract
AUTOMATIC CHILLED WATER SETPOINT TEMPERATURE
CONTROL USING RETURN CHILLED WATER TEMPERATURE
ABSTRACT OF THE DISCLOSURE
A control system for controlling the entering chilled water temperature of a refrigeration system at a selected setpoint.
A microcomputer system receives electrical input signals indicating of an operator selected entering chilled water temperature setpoint and refrigeration system operating parameters indicative of an operator selected entering chilled water The microcomputer processes these input signals to generate a leaving chilled water temperature control point which is a function of the entering chilled water temperature setpoint and the temperature drop across the chiller.
CONTROL USING RETURN CHILLED WATER TEMPERATURE
ABSTRACT OF THE DISCLOSURE
A control system for controlling the entering chilled water temperature of a refrigeration system at a selected setpoint.
A microcomputer system receives electrical input signals indicating of an operator selected entering chilled water temperature setpoint and refrigeration system operating parameters indicative of an operator selected entering chilled water The microcomputer processes these input signals to generate a leaving chilled water temperature control point which is a function of the entering chilled water temperature setpoint and the temperature drop across the chiller.
Description
J
~ ERATIJRE
CO~TROL USING 3~ETURN CHILLED WATEP~ TEMPERATU:RE
.
Baok~uund o~ the Invention The ~res~nt inven~i~n r~lates to ~ethod~ of.~perating and conkrDl rystEm~.for refrigeratiDn ~yst~ms and, more particu-larly, to ~ethod~ of op~rati~g and con*rol systems for pacity :control devices, such as com~ressor ~nlet ~uide vanes,:in centrifugal vapoI.cDmpr~ssion ~efr.igeration ~ystem~
where~y a predeteImin~d e~tP~ingise~poi~ ~0mperature is -~i~tained at ~he.chiller.
-~enerally9 r~rigeratIGn-systems include an evaporat~r Dr .~ooler/chiller, a compr~ssor, and a condenser.. Usually, a heat transfer fl~id is circulated through tubing in the evaporator thereby ~orming a heat transfer coil in the evapDrator to ~ransfer h~at fr~ the h~at transfer fluid flowing~.throu~jh :~he ~u~ing to:re~ri~rant.in ~he ~vaporator.
The heat ~ransfer~ fluid -chilled in-~the tubirlg in the evapora-~r is-~ormally ~at~r ~r glycol ~hich is.circulated ~o a r~mote location t~ satisfy a ref~igeration load. The re.rig-er~n~ in thc ev~porato~v~porates as it absorbs he~t.fxom the heat traTIsfer.:fluid flowing ~roug~i-the ~ing in the evapo~ator, and. *h comp:ressor o~erates to extrac~ ~his 25 refrig~2nt vap~r from~.~e evapor~tor, ~to comp:~es~ .this r~fri~seTan~ va~r9. and to discha~ge the. ~ompl~ssed- vapor *o : ~he c~ndenser. .In th~- con~enser, the ~l~friger~Lnt va~or is ; conden~ed ~nd deliYered ~c~c to ~he evaporator where the -1 ref~ig~la~ion cycl~ ~Pgi~s agai~.
T ~ maximiz~ o~ r~ting e:Eficiency1 it .i~ d~sir~3~1~ tc~ ~atc~
am~mt ~ w~sk-~dDne ~ e.~resa~I *o ~hE~ wo~k.-ne~d -- *o sati~:~y.-the r~ atiDn 1l~2rd- placæd ~m t~e: Terig~tion syst~m. .C~nly, thl~ s .~one ~y capa~i:ty c~n~rol ~ans 3~ which~ adjust the :~mount t3:~ refri~erant vapor fl~wing thrnugh - t~e compre~sQr. ~Ehe capacity cQ~trol ~nea~ may be a ~evice 1.3~3 - such as guide var.es which are positioned between the compres- !
.60r and the evaporator which m~.between ~ fully.open and a :Eully closed posi~ion in riesponse to the t~mperature of the . chilled heat trans~er fluid leaving t~e coil-in the eva~ora-:tor Wh~n the-.-evapDrator chilled heat trans~er.fl~id temper-atuTe~falls, indicating a-reduction in ~efri~eraticn load on the.refrigeration syste~, the guide vanes move *oward their losed position, decreasing t~le amount of refrigerant vapor fl~wi~g thro~gh the compT~ssor. This decreases the amount of wor~ that ~t be done by.the c~mpresso~ there~y decreasing the ~mount.o~.~nergy ne~:ded to operateithe refrige~ation system.: At ~e samei tim~i, thi~s hai~ t.~e ieffect o~:.increasing the tempera*ure of the chilled heat.transfer ~luid leaving the.evaporator. I7~ contrast, when the tempe~atur~ of the 1~ leavin~ chilled he~t transfer ~l~id.ri-ses, i~dicating an increase in load on the refrigeration system, ~he guide vanes move toward ~iir:ully open pos~ion.~.~his-increases the amount of vapor fl~ing-through the c~mpreS~oT and.~he compressor does more work theTeby decreasing the-t~mperature 2~ Df.the ehilled hez~ transfer ~luid leavin~ the ~vaporator ~nd - allowin~ th~ refrigeration system to respond to the increased :re~igeration load. In-~his manner~.the c~mpressor operates to maintain the temperature of ~he chilled heat transfer fluid leaving the-evapo~ r at,~r.wit~in a certain. range .2~ of, a se~ p~in~ tempera~ure.
~ny di~feTent.c~pacity rDntrol.systems~are known ~Dr run-...trolling a.refrigeratiDn syst~m in the manner described `ahove. For e~ample,.one ~uch control system,. a mod~l ~P-8142-024`Electronic Chiller ContTol ~vaila~le from ~he ~r~er-Colma~ C~mpany ~v~n~ a plac~ ~f;~usin~ss in Ro~kford, IIlinois, ad~sts a-capac~ d~vi~e in~a refriger~L-n syst~ Ps.a functi-on ~ d vi ~iDn .~ l~avin~ eY~po-sa*or chille~l- water .tem~erat~ ~rom a` ~desi~e~ set point 3~ t~mperature. ~hen the evapo~ator chi~led wate~ tempe~ature~
de~i~tes fT~m~thP~selected set point ~emperature ~y a 3~33 ~redetermined ~mount the capacity control device is cuntinu-ously adiu~ted by an actuator whi~h is cuntinuously energized by a stream of electrical p~l6es s~pplied to the actuator.
5 Cercain energy ~nanag~men~ sy~tems ~ake it desirable to maintain a constant enteTi~ chilled water tempeTature and -.let the leavin~ ~hilled water t~mperature "float" Qr seek its ,own eq~ili~rium tempera~ure a~ the load varies. ~his is the ~ ~ reveT~e Df conv~tional ~rior art chilled wat~r temperature '.eont~ y~t~ms. ~oweves,. co~trolling chiller caparity based solely on a deviation of e~ter.i~g.chilled wa ~r t~m~erature .from.a fi~ed e~t~ring chilled1w~ter ~e~peTatu~e setpoint, in .a manner analo~ous to ~ha~ used in .priox.l~aving chilled '.water te~.perature control systems causes exagge~ated vane movements:~ith little:s~bility in the!~ys~2m, ~eca~6e a substantial time delay e~ists ~etween capacity ~hanges made al.~he ~chiller.and the res~lting.temperat~re chan~es sensed .in the wat~r ~nt~ring the chiller. ~.hi~ .ti~e lag.in.the WateT 1ODP cause-s the-c~ntrol-~o ~v~rcvmpensa~e and the ~Q ~esult is cantrol instability and exces~ive te~pera~ur~
oscill~tion.
Thus, th~e ~xist~ a ne~d to develop cap-acity.~ontrol tech-.niques f~r chillers whi~h maint~in a cDn~tan~ ~ntering :~hilled ~a~..te~pera~ur~ and-w~l~h minInize ~he ~isadvan~ag-~s.of controlling'~hill~ cap~city in-r~spons~ to.leaving chilled.water.temp~rature-o~ devia~ion~f entering chille~
- water tFmp~a~ure.from^~ fiæe~ setpoint..
-30 Summary of the Invention - T~r~fore, i~ n o~i~ct..... ~f ~he pre~ent inv~nti~m~to ^ ~ovid~-a..~im~ .f~i~i~n~-2nd ~ffe~ti~e.~ic~c~m~te~
- sys.~m-fDr :cv~trQlling ~he:cap~ity ~f ~ refrig~ra~ion ~ystem ;in ~on~ ~D.~en~er~ng wat~r.~pQin~:tem~ ux~.
It i~ ~nother object of the present invention ~o p~ovide an easily programmable microcom~u~er system for controlling the capacity of a ~efrigera~i~n sys~em by gene~ating a leaving ::chilled water control point so ~s to ~rovide a desired . entering chilled wat~ 3etpoint ~mpera~uT~.
It is still an~t~er o~j~ct of the present-inven~i~n to proYide a control sche~e for controlling the capacity of a -refrige~ation system ~at is ~er~ious to changes in chiller 10 i. water flow rate~
~hese and o~her ~jects.of the present invEn~i~n are A~tained by a capacity control ~ystem for a refrigeration system co~prising means::for generating a setpoint signal corre~pond-ing to a selected setpoint temperature~for the hat transfermedium entering the evaporator ~the setpo-int tFmperatU~e is a ~alue selected by an -~perator ~D~ inpu~d lnto the mirr~p~o ~SB or);^~earls ~r generating~a first co~t~ ignal..~hich is a functior~ of the temreraturP-o~ the hea~ transfe~ ~nedium en~eTing th~ evaporato~,- means for generating a.~econd control si~nal which is a func~ion of the ~emperature of the ~e2t t~anæfer me~tium l~a~ving ~the ev~poTator, and processor - means for' Teceiving said setpoint ~ignal, and said firl;t and æecond c~m~rol signals :for p~:~cessing th~- received si~nals 25 according --to ~prog~ammed ~locedllr~s ~D det2~1ine ! a .control - :point t~perature fDr the hea~ tr~ilsfe~medium .1~ vi~g the e~7~porator (the ~:ont~ol poi~t temperatu~e is -a; value generat-ed ~y the mi~op~oc~ssor al~d i~ used to cont~ol the lo~d, - e.g. -~y~ positioning.~he gllide vanes), and for gene~ating an 30 o~ control -si~;nal I'or cont~ollin~ the capacity ~f.~he rhille~ i~ ~esponse to ~ ollt~ C ontrDI signal.
Ih~:p~o~so~means, a micro~mputer,~ t~Imine~st~ leavi~g ~hilled-w~r~t~mp~satllre ~on~o~ i~t using A`~he e~t~in~
3~ c~illed wat~r se~point and the t~mperature drop acT~ss.~he 3~3 .~vaporator. This c~ntrol feature is stated mathematieally as follows:
LWCP = ~P - ~T ) Wh~re;
. ~ Ti ~o . and wher~;
I,WCP ifi the.leavrng.e~illed wa~eT ~mp~rature eontrol poi~t, `. EWSP i~:the ente~ng c~illed ~ater t~mperature setpoin~, Ti is the water..t~mperature enteri.ng the:e~p~rat~T, and To is t~e water t~mperatUre l~aviDg ~he ~vaporator.
. :
By selecting a desired BetpOint or the enteri~s chilled water, .o~erA~:io~ of tl~e capacity co~:rol dev~ce may be easily, efficiently, and ~Eec~lv~ily .tailored l:~.mee~ i sp~`~ific job requirements~ af a par~icular jo~ -appli~ati~n far 20 ~he.ref~igeration syst~m ~y ~stah~i~hi~ .~he leaving chillec J
~a~er te~perature control point.
;Brief Descri~ion of t~;ie Drawin~s i St:ill oi~her ob3ect~: an~iadvar~tages o- ~hæ pr~?sent inven~tion 25 will be c.pp~:r~t ~from t~e ~ foll~ing .de~ailed des~riptir~n of -the pre~ t ~reIltion i~ cDnjLm~ i~n ~i~h the. accompanying dsawings, in whieh th~ ~eferenc~eTals designate li~ce or . correspondin~-part~ thT~ Lou~ :the ~ame, In ~ish:
.
3 u . Figure ~: is a` schema~ismillustra~i~ .of a ce~ rifugal -va~or - - - .. c~mpre~;sion :r~frigera~ y~t~m ~i~:h. a .~on1:rol sys~m. for ~ . v~r~ng ~ apacity~ ~ r~fri~ ~Lt3~n 3~st~m acrl~di~s t:o h~ prin~ip1~ of . ~:h~ .. ;~s4nt i~x5~II~ icm7';' ~nd - I
, ~ ,", . . : i . .; .
~8~ 3 ~igure ~ is a graph of entering and lea~ing chilled water tempera~re as a function of load for a typical chiller system.
Referring to Figure 1, a~,~apor.compressi~n re~ig~ration 0.` 6~'StEm 1 iS shown having a cen~i~gal ccmpress~r 2 with a corltrol systFm 3 for varying the c~pacity of the refrigera~
. tio~-~ystem 1 accoTding^~o the principles of the present 10 ,.invention. ~s shown i~ ~igur~ 1, the ref~igera~ion system 1 .includes a c~nden~er 4, an evaporator 5 and ~ poppet valve 6.
.In operatiDn, c~mpress~d~gaseous -refrigeT~nt,,is.discharged from t~e cDnrp~essor 2 ,~through c~ressor~ discharge lin~ 7 to the condenser 4 wherein the gas~us reriger~nt.is condGnsed 15 : by r~la~ivPly cool cDndensing wa~er flowlng through tubing 8 in the condenser 4. .'The condensed liquid refrigerant rom the condenser 4 pad~es ~hrough ~he poppet valve 6, which forms,~,liquid,s~al.-..t~,keep cQ~de~r vapo~ from ~nte~ing.~he --- evaporator and ~o ~intain ~he pre~sur-P.difference between ~0 the condens, r,and the evaporator, in rEfrig2~ant line 9 *o evapora~or:5. Th~ uid refrigerant in the evaporator 5 is ~f -`evaporated to cool ~ hea~.tran~fer.~luid, such,as water or ~. glycoI-, flowing through tubing 10 in the evapora~or 5. This ~.chilled h~a~ transfer ~fluid is: use~ ~o cool a bui:L~ling or is 25 used fo- :o~:~er .sLlch purposes. ~e gas~ous refri~e~ant fro ^ the evapo~tor ~ flaw6 ~rough :com~essr~ suc~ion: :lins~
- back i~ com~Te~sor ~ under the control Df compr~ssDr .inlet - . guide^ sranes 12. ~ gaseous refrig ra~ enterin~- the com-pressor . 2 through the .guid~ .vanes 12- is compressed ~y ~he 3D. compressor 2 .and dis~har~;ed fram:*h~-c~mpT~ssor 2 ~rough ~he co~ps~ssor ~isch~r~se line 7 .~:o com~lete the - re:~rigeration '~; CyC~ i8 ~.~frig~ativn~ ycle i~:ro~im~ y r~ted .; dlIrin~; nDrmal Dper~ion of the rPfrig~ra:tion ~;y~;tem 1.
: 3~i The compresso~- inl~e~ guide :~anes 1~ are~ op~ened and clos{~d ~y ~ I
a gilide vane ac~u~tor 14 c~ntroll d :~ the capa~:i~y c~m~Tol system 3 which comprises a syste~ inter~ace board 16l a - -proc~s~or board 17, a set point and dis~lay b~a~d 18, and an analog/digi~al c~nverter 19.. Also, te~eratur~ sensor l3 ~or s~nsing the tem~era~ure of ~h~ ~eat transfer fluid leaving the ~v~poTatQ~ -~ thr~ugh the.t~L~g 10 an~ t~mperature ~ens~r 15 for ~ensing~he ~emperature of the heat transfer fluid enteTi2ng the evaporatar 5 ~hrough the ~ubi~g lO, are con-: nected by electrical lines 20 and 2~ directly to the A/D
:~ conve~ter 19.
10Pre~erablv9 the ~æmperature ~,e~lsors 13 and l~are t~mperature respon~ive r~sistane~ devices ~uch as a ~hermlstor6 having their sensing portions located in` the heat transfer fl~id in the ~u~ing lO in the evaporator ~ with their.resistances 1~ monito~ed by the.AlD,conver*er, ~s shown in.~i~ure 1. Of cours4 ~ as will be r~adily apparent to one o~ oTdinary skill - in t~e art to ~hich the~present in~ntion peItainsl--the tempesat~re sen~ors. 13 and 1~ ~ay be any of a vari~ty of temperature sensors sui~able.for ~ererating a~signal-indic2-20~ ~ive o~ the temperature o~ t~e heat transfe~ ~luid in the tubing 10 in th~ e~apora~or ~ and for supplying these gener- i ated- signals tc~th~ AID con~erter.l9.
,: Th~rocessoT 'Doald 17 may ~e any slevic~ or. combin tion of ,5 . de~ es,. c~pa~le o-E rec~iving ~ ~lurality o~.: input signal~, ~roc~ssing t~ :rg~ceiv~d :inpllt -s ignalB aoc o~ding to prep~Dgrammed prDcedllres, ~d prod~cing. d~ired o~l~Ut . contTol signals- ill:. r~pons~` to ~he- Tec~eived and p~ocessed input signals, i~^a ~anner ~accord~ng~ to the principles of- the 30 pTes~nt iIl~entioIl. Ft)r e:Eample, ~-processor b~ld l7 m~
co~pri~e ~ microcsm~ut~r, su~ a~ ~L ~odel .8D31 micIoeomputer svail~bl~-- f~Dm Inl~ ion ~ch ha~ la~ Qf bu~
. nes~ at S~nt2~ Cla~
` 3 ~ Also, pref~ra~ly, the AID -ronv~ter 19 i~3 -~ duaI :s~ope A/D
co~v~rter~whi~h ~;~all ~roces~ n~ g-illputs and ~sich is L3~
suitable fo~ u~e with the processor board 17. Also, it should be no~ed tha~, although the A/D ~onverter 19 i~ shown as a sepaT~te module in Figure l, thi~ A/D converter 19 may ~e physically pa~ of ~he ~rocessor board 17~in an actu~l 5 - cap~ity c~ol sys~2m 3.
F~rtheT, ~r~ferably, the set point and di~play ~ard 1~
-cDrprises a ~isual display, includingt ~or example, light emit~ing diodes (LED'~) or :liqui.d ~ys~al disp~ay (LCD'~) 1~ :devices forming a ~Llt~-digit display which is under the cun~rol of the processor board.l7.. Al~o, th~ ~et p~int -and . display board 18 .includes a device, such as- a key pad which se~es a~s a da~a entry ~ort as well as a programming tool~
- for en~ering the te~pe~a~ure setpoint of the,rhllled water 1~ entering-~he Evapor tor ~ through the ~aporator chilled -~
wa~er tu~ing.lG.
~till-furth~r, p~efera~ly, the sy~tem in~r~ace ~oar.d 16 includes at least Dr.e s~itching device~ ~uch--as a ~del S~-140 ~riac availa~le from G~neTal El~ctric, ~rp. which has .. a plac~ of business at Auburn, New York~ which is used as a -~witching element ~or~.c~ntrolli~g:~a su~ply o~ elect~ical pow2r (not shown) thrcugh electrical lines ~-1 $~ the guide . ~ne ~ctua~or-14.:.~The t~iac switches on the sys~em interf~ce boa~d 16 a~ contr~lled in~resp~nse to ~Gntrol ~i~nals :- rer~i~ed ~y~the-.t~iac s~itche~-~ro~^~he-pr~ces~r ~ard 17.
In *his manner, elec~rical power iS ~u~lied th~ough the eleetrical lines 21.~o the ~uide vane.~ctuator 14 under c~n~rol of t~e processor:~ard 17 to ~perat~ t~e-g~de vane 30 actllator ~ e ma~rnGr.-aco~rding.t o ~h~prin~ipl~s of t~e pT~B~nt i~vention ~hich i~ descri~ed i~ tail below. Of - c~n~.~e7 - aB~ eadily.-~p~ar~D~-to-~ne- D ~rdinaTy skill in ~he art to whi~h ~he~res~nt-inven~ion ~e~ains,~witchi~g - devi~s other ~h~n tri~ s~itc~e~ ~ay ~e-~ d in-.. r~ntro~lin~ I
3~ poweT~flow ~rom ~he pOW~T ~uppl~.(not sh~wn) thr~ugh ~h~
!
3~33 electrical lines 21 to the guide vane actuator 14 in response.
to output con~Tol signals from the proc~ssor board 17.
Ihe ~uide vane actuator 14 may ~e any device sui*able for ~riving the guid~ v~nes 12 ~ow~rd either their open or closed position in response to el~trical power signals rec~ived via - electrical lines ? 1 . For example, ~he guide vane actuator 14 - ~ay be an electric motor, such as a model~.MC-351 mDtor -~vailzble.f~m the-~ar~ Colm2m C~mpany ha~ing a pla~ç of ~usin~ss in ~ockfard, Illinois" for driv~ng. the ~uide vanes 12. t~ward ~ithe~ their open Dr ~l~sed posi~ion de~Fnding on whic-h one.of two-~riac switches ~n the fiyfitem int~Tf~ce board l& is actua~ed.in TespOnse to. CDntrOl signals received ~y the triac switches fr~m the proce~s~r~board.17. .The guide:vane ~15 actuatQr 14 drives.the.:gui~e van~ 12 t~ward ~ither their fully open or fully closed position at a con~tant~ fixed rate only.during that portion of a ~el~cted ~ase.time i~terv~l during which:the ~ppropriate.traic s~-itch o~..~he.system int~rface board 1~ is ac~uated.
Re$erring now to ~igure 2, a sDlid straight-line hori~on~al - -curve~A is sh~wn whic~ represents the entering.chilled w~ex - temperature se~p~int that i~ de~iTed tG ~e ~aint~ined by ~he ~ ~efrig~x~ion syatem of the pres~nt inv~ntion. .This setpoint 25 -iis arbi~rary a~d~. is-.en~red .in~o -the setp~int and displaY.
oa~d by the operatQre~y-way D~ the ~y pad. d~y ~aintainir.
a:fixe~ enterIng chllled wa~e~ tempeTature the ~p~rat~r may redu~e-~nergy.c~nsumptiGn d~rlng cer.~in load condi~ions, . partic~larly ~ low loads.; ~hæ leaving chill~d-water con~rol 30~. point ~f the ~esent:inven~iDn, 2S shown by .~he sDli~ sloped - :. li~e curv~ B7-~pres~nt~ the.. contrDl pDin~ a~ ~hich the le~vi~g ~hiIl~d w~t~r;is ~e~at~d~ur~ng.~ny.l~ d~nditiDn :. w~ e setp~t of;c~rve A. '~2 v~r~ic l axi~.~f Figur~ 2 -~s the~ temper~ture o~ ~he Ghilled ~a~er.-;-enterin~ or leaving 3~ the e~pora~r~ The horizontal a~is of Figure 2.is.~he.loa~ !
. .
3~3 on the refrigeration sys~em. An arbitrary val~e of 10F was chosen as evapor~tor ~T at full load and coIles~nding~Yalu~s of ~T at various loads a~e shown.
In Figure 2, the curve labeled ~ ~llustrates an arbitrary fi~d setpDi~t for the ~ntering chill~d.~ater temperature.
! Thus, in this example, ~he opel-a*or desiTes the refTigeratiol-~yst~m to~control the te~p~ratllre of the ent ring chilled water at ~F.
The dashed s ~ ight-line ho~izontal ~ur~ C reprYsents ~he : fi~ed leaving chilled wat~r ten~er~ture setpoint Df the pTior art, while the dashed sloped line Curve.D represents the `1~ floatin~ en*~ring chilled water te~per~ure of the prior art.
Once ~ predetermined enteri~ chilled ~a~er.set~o~nt is selected, the l~aving ~hill~d water temp~x~t~re .control p~int i5 calculated by the ~icroprocessor, and is-perio~ically .,0 updated e.~. once ev~xy ~ive- ~econds, to e~sure that:the leaving chilled water.temper~ture is t~ correct value for - ~he ~resen~.load. If hDweuer, t~ a* changest. for example a load would, over a period of time, decrease ~r~m 50% to 10~, *~e l~aving chill-ed wat~r ~mpera~ure con*rDl point 2~ would incr~àse fr~ 50~-.to:54~ hi6-incr~ase ~ill b~ d~ne - at a`gradual Ia~e s~ch a~ ~.12~-d~gre~.e-~er minute. ~Thus, : the~ac~ual leaving.chill~d ~ater temperatur~ sensed~ he - sEn-sor 13 w~uld, instantaneousIy, still indicate '~D~ while - the leaving chilled wat~r temperature ~Dnt~ol-~oin~.w~uld be calling for A leaving chill d water slightlY abDv~Q~.
Th~,.~ d~ia~ion would-2xifit.~ h~ ac~al leaving ;chi~ d wa~er ~mperatur~nd-th~ Ying `~ ~at~r tgm~ature. c~ntrol ~ and :th~ devi~tiD~ is i~pu~ted .to ~he sy~em intf~rf ce-~ad:which ~ he ~aid~-vane ~35 - actuatDr 14 ~ ~o~-e~the gu}de ~ane~ 12:toward th~ir.closed po~ition untit-~he actuàl temper~ur~ ~ the leaving chilled ~8~.3~3::~
water is equal to the l~aving chilled wa~er temperature cont~ol point.
In this manner th~ chill~eT will make a ~mooth t~ansition ~rom a ~iven load lev~l to a~D~r ~e~au~e ~he. leaving chilled water temperature sensursImmed-iately det~cts the water t~mperature change caused by the altera~ion in guide vane p~sition. Thus throu~h the use of the g~nerated control ~oint, ~he desired enterlng chiilled wate~ t~pe~ature is ~ain~ain~d during~he tran~ition.
~rther, it shDuld be n~te~ that the ~hilled w~t~ flow rate ~ay vary without changir.~ *he control scheme, sin~e the leaving.chilled water tempe~ture contTol point is only a function of t~ entering chilled.water ~mperat~re setpoin~
and the water ~emperature enterin~ and leaving the evaporator.
While this invention has been des~ ed ~nth ~efe~ence to a particular em~odiment discl~sed h~reinl it-is not confined to the d~tails s~t.forth h~rein.and this.application is i~tended to cov~r anv mDdifica~ions or c~ es ~s may come wit~in the scope of the i~ention.
~ ERATIJRE
CO~TROL USING 3~ETURN CHILLED WATEP~ TEMPERATU:RE
.
Baok~uund o~ the Invention The ~res~nt inven~i~n r~lates to ~ethod~ of.~perating and conkrDl rystEm~.for refrigeratiDn ~yst~ms and, more particu-larly, to ~ethod~ of op~rati~g and con*rol systems for pacity :control devices, such as com~ressor ~nlet ~uide vanes,:in centrifugal vapoI.cDmpr~ssion ~efr.igeration ~ystem~
where~y a predeteImin~d e~tP~ingise~poi~ ~0mperature is -~i~tained at ~he.chiller.
-~enerally9 r~rigeratIGn-systems include an evaporat~r Dr .~ooler/chiller, a compr~ssor, and a condenser.. Usually, a heat transfer fl~id is circulated through tubing in the evaporator thereby ~orming a heat transfer coil in the evapDrator to ~ransfer h~at fr~ the h~at transfer fluid flowing~.throu~jh :~he ~u~ing to:re~ri~rant.in ~he ~vaporator.
The heat ~ransfer~ fluid -chilled in-~the tubirlg in the evapora-~r is-~ormally ~at~r ~r glycol ~hich is.circulated ~o a r~mote location t~ satisfy a ref~igeration load. The re.rig-er~n~ in thc ev~porato~v~porates as it absorbs he~t.fxom the heat traTIsfer.:fluid flowing ~roug~i-the ~ing in the evapo~ator, and. *h comp:ressor o~erates to extrac~ ~his 25 refrig~2nt vap~r from~.~e evapor~tor, ~to comp:~es~ .this r~fri~seTan~ va~r9. and to discha~ge the. ~ompl~ssed- vapor *o : ~he c~ndenser. .In th~- con~enser, the ~l~friger~Lnt va~or is ; conden~ed ~nd deliYered ~c~c to ~he evaporator where the -1 ref~ig~la~ion cycl~ ~Pgi~s agai~.
T ~ maximiz~ o~ r~ting e:Eficiency1 it .i~ d~sir~3~1~ tc~ ~atc~
am~mt ~ w~sk-~dDne ~ e.~resa~I *o ~hE~ wo~k.-ne~d -- *o sati~:~y.-the r~ atiDn 1l~2rd- placæd ~m t~e: Terig~tion syst~m. .C~nly, thl~ s .~one ~y capa~i:ty c~n~rol ~ans 3~ which~ adjust the :~mount t3:~ refri~erant vapor fl~wing thrnugh - t~e compre~sQr. ~Ehe capacity cQ~trol ~nea~ may be a ~evice 1.3~3 - such as guide var.es which are positioned between the compres- !
.60r and the evaporator which m~.between ~ fully.open and a :Eully closed posi~ion in riesponse to the t~mperature of the . chilled heat trans~er fluid leaving t~e coil-in the eva~ora-:tor Wh~n the-.-evapDrator chilled heat trans~er.fl~id temper-atuTe~falls, indicating a-reduction in ~efri~eraticn load on the.refrigeration syste~, the guide vanes move *oward their losed position, decreasing t~le amount of refrigerant vapor fl~wi~g thro~gh the compT~ssor. This decreases the amount of wor~ that ~t be done by.the c~mpresso~ there~y decreasing the ~mount.o~.~nergy ne~:ded to operateithe refrige~ation system.: At ~e samei tim~i, thi~s hai~ t.~e ieffect o~:.increasing the tempera*ure of the chilled heat.transfer ~luid leaving the.evaporator. I7~ contrast, when the tempe~atur~ of the 1~ leavin~ chilled he~t transfer ~l~id.ri-ses, i~dicating an increase in load on the refrigeration system, ~he guide vanes move toward ~iir:ully open pos~ion.~.~his-increases the amount of vapor fl~ing-through the c~mpreS~oT and.~he compressor does more work theTeby decreasing the-t~mperature 2~ Df.the ehilled hez~ transfer ~luid leavin~ the ~vaporator ~nd - allowin~ th~ refrigeration system to respond to the increased :re~igeration load. In-~his manner~.the c~mpressor operates to maintain the temperature of ~he chilled heat transfer fluid leaving the-evapo~ r at,~r.wit~in a certain. range .2~ of, a se~ p~in~ tempera~ure.
~ny di~feTent.c~pacity rDntrol.systems~are known ~Dr run-...trolling a.refrigeratiDn syst~m in the manner described `ahove. For e~ample,.one ~uch control system,. a mod~l ~P-8142-024`Electronic Chiller ContTol ~vaila~le from ~he ~r~er-Colma~ C~mpany ~v~n~ a plac~ ~f;~usin~ss in Ro~kford, IIlinois, ad~sts a-capac~ d~vi~e in~a refriger~L-n syst~ Ps.a functi-on ~ d vi ~iDn .~ l~avin~ eY~po-sa*or chille~l- water .tem~erat~ ~rom a` ~desi~e~ set point 3~ t~mperature. ~hen the evapo~ator chi~led wate~ tempe~ature~
de~i~tes fT~m~thP~selected set point ~emperature ~y a 3~33 ~redetermined ~mount the capacity control device is cuntinu-ously adiu~ted by an actuator whi~h is cuntinuously energized by a stream of electrical p~l6es s~pplied to the actuator.
5 Cercain energy ~nanag~men~ sy~tems ~ake it desirable to maintain a constant enteTi~ chilled water tempeTature and -.let the leavin~ ~hilled water t~mperature "float" Qr seek its ,own eq~ili~rium tempera~ure a~ the load varies. ~his is the ~ ~ reveT~e Df conv~tional ~rior art chilled wat~r temperature '.eont~ y~t~ms. ~oweves,. co~trolling chiller caparity based solely on a deviation of e~ter.i~g.chilled wa ~r t~m~erature .from.a fi~ed e~t~ring chilled1w~ter ~e~peTatu~e setpoint, in .a manner analo~ous to ~ha~ used in .priox.l~aving chilled '.water te~.perature control systems causes exagge~ated vane movements:~ith little:s~bility in the!~ys~2m, ~eca~6e a substantial time delay e~ists ~etween capacity ~hanges made al.~he ~chiller.and the res~lting.temperat~re chan~es sensed .in the wat~r ~nt~ring the chiller. ~.hi~ .ti~e lag.in.the WateT 1ODP cause-s the-c~ntrol-~o ~v~rcvmpensa~e and the ~Q ~esult is cantrol instability and exces~ive te~pera~ur~
oscill~tion.
Thus, th~e ~xist~ a ne~d to develop cap-acity.~ontrol tech-.niques f~r chillers whi~h maint~in a cDn~tan~ ~ntering :~hilled ~a~..te~pera~ur~ and-w~l~h minInize ~he ~isadvan~ag-~s.of controlling'~hill~ cap~city in-r~spons~ to.leaving chilled.water.temp~rature-o~ devia~ion~f entering chille~
- water tFmp~a~ure.from^~ fiæe~ setpoint..
-30 Summary of the Invention - T~r~fore, i~ n o~i~ct..... ~f ~he pre~ent inv~nti~m~to ^ ~ovid~-a..~im~ .f~i~i~n~-2nd ~ffe~ti~e.~ic~c~m~te~
- sys.~m-fDr :cv~trQlling ~he:cap~ity ~f ~ refrig~ra~ion ~ystem ;in ~on~ ~D.~en~er~ng wat~r.~pQin~:tem~ ux~.
It i~ ~nother object of the present invention ~o p~ovide an easily programmable microcom~u~er system for controlling the capacity of a ~efrigera~i~n sys~em by gene~ating a leaving ::chilled water control point so ~s to ~rovide a desired . entering chilled wat~ 3etpoint ~mpera~uT~.
It is still an~t~er o~j~ct of the present-inven~i~n to proYide a control sche~e for controlling the capacity of a -refrige~ation system ~at is ~er~ious to changes in chiller 10 i. water flow rate~
~hese and o~her ~jects.of the present invEn~i~n are A~tained by a capacity control ~ystem for a refrigeration system co~prising means::for generating a setpoint signal corre~pond-ing to a selected setpoint temperature~for the hat transfermedium entering the evaporator ~the setpo-int tFmperatU~e is a ~alue selected by an -~perator ~D~ inpu~d lnto the mirr~p~o ~SB or);^~earls ~r generating~a first co~t~ ignal..~hich is a functior~ of the temreraturP-o~ the hea~ transfe~ ~nedium en~eTing th~ evaporato~,- means for generating a.~econd control si~nal which is a func~ion of the ~emperature of the ~e2t t~anæfer me~tium l~a~ving ~the ev~poTator, and processor - means for' Teceiving said setpoint ~ignal, and said firl;t and æecond c~m~rol signals :for p~:~cessing th~- received si~nals 25 according --to ~prog~ammed ~locedllr~s ~D det2~1ine ! a .control - :point t~perature fDr the hea~ tr~ilsfe~medium .1~ vi~g the e~7~porator (the ~:ont~ol poi~t temperatu~e is -a; value generat-ed ~y the mi~op~oc~ssor al~d i~ used to cont~ol the lo~d, - e.g. -~y~ positioning.~he gllide vanes), and for gene~ating an 30 o~ control -si~;nal I'or cont~ollin~ the capacity ~f.~he rhille~ i~ ~esponse to ~ ollt~ C ontrDI signal.
Ih~:p~o~so~means, a micro~mputer,~ t~Imine~st~ leavi~g ~hilled-w~r~t~mp~satllre ~on~o~ i~t using A`~he e~t~in~
3~ c~illed wat~r se~point and the t~mperature drop acT~ss.~he 3~3 .~vaporator. This c~ntrol feature is stated mathematieally as follows:
LWCP = ~P - ~T ) Wh~re;
. ~ Ti ~o . and wher~;
I,WCP ifi the.leavrng.e~illed wa~eT ~mp~rature eontrol poi~t, `. EWSP i~:the ente~ng c~illed ~ater t~mperature setpoin~, Ti is the water..t~mperature enteri.ng the:e~p~rat~T, and To is t~e water t~mperatUre l~aviDg ~he ~vaporator.
. :
By selecting a desired BetpOint or the enteri~s chilled water, .o~erA~:io~ of tl~e capacity co~:rol dev~ce may be easily, efficiently, and ~Eec~lv~ily .tailored l:~.mee~ i sp~`~ific job requirements~ af a par~icular jo~ -appli~ati~n far 20 ~he.ref~igeration syst~m ~y ~stah~i~hi~ .~he leaving chillec J
~a~er te~perature control point.
;Brief Descri~ion of t~;ie Drawin~s i St:ill oi~her ob3ect~: an~iadvar~tages o- ~hæ pr~?sent inven~tion 25 will be c.pp~:r~t ~from t~e ~ foll~ing .de~ailed des~riptir~n of -the pre~ t ~reIltion i~ cDnjLm~ i~n ~i~h the. accompanying dsawings, in whieh th~ ~eferenc~eTals designate li~ce or . correspondin~-part~ thT~ Lou~ :the ~ame, In ~ish:
.
3 u . Figure ~: is a` schema~ismillustra~i~ .of a ce~ rifugal -va~or - - - .. c~mpre~;sion :r~frigera~ y~t~m ~i~:h. a .~on1:rol sys~m. for ~ . v~r~ng ~ apacity~ ~ r~fri~ ~Lt3~n 3~st~m acrl~di~s t:o h~ prin~ip1~ of . ~:h~ .. ;~s4nt i~x5~II~ icm7';' ~nd - I
, ~ ,", . . : i . .; .
~8~ 3 ~igure ~ is a graph of entering and lea~ing chilled water tempera~re as a function of load for a typical chiller system.
Referring to Figure 1, a~,~apor.compressi~n re~ig~ration 0.` 6~'StEm 1 iS shown having a cen~i~gal ccmpress~r 2 with a corltrol systFm 3 for varying the c~pacity of the refrigera~
. tio~-~ystem 1 accoTding^~o the principles of the present 10 ,.invention. ~s shown i~ ~igur~ 1, the ref~igera~ion system 1 .includes a c~nden~er 4, an evaporator 5 and ~ poppet valve 6.
.In operatiDn, c~mpress~d~gaseous -refrigeT~nt,,is.discharged from t~e cDnrp~essor 2 ,~through c~ressor~ discharge lin~ 7 to the condenser 4 wherein the gas~us reriger~nt.is condGnsed 15 : by r~la~ivPly cool cDndensing wa~er flowlng through tubing 8 in the condenser 4. .'The condensed liquid refrigerant rom the condenser 4 pad~es ~hrough ~he poppet valve 6, which forms,~,liquid,s~al.-..t~,keep cQ~de~r vapo~ from ~nte~ing.~he --- evaporator and ~o ~intain ~he pre~sur-P.difference between ~0 the condens, r,and the evaporator, in rEfrig2~ant line 9 *o evapora~or:5. Th~ uid refrigerant in the evaporator 5 is ~f -`evaporated to cool ~ hea~.tran~fer.~luid, such,as water or ~. glycoI-, flowing through tubing 10 in the evapora~or 5. This ~.chilled h~a~ transfer ~fluid is: use~ ~o cool a bui:L~ling or is 25 used fo- :o~:~er .sLlch purposes. ~e gas~ous refri~e~ant fro ^ the evapo~tor ~ flaw6 ~rough :com~essr~ suc~ion: :lins~
- back i~ com~Te~sor ~ under the control Df compr~ssDr .inlet - . guide^ sranes 12. ~ gaseous refrig ra~ enterin~- the com-pressor . 2 through the .guid~ .vanes 12- is compressed ~y ~he 3D. compressor 2 .and dis~har~;ed fram:*h~-c~mpT~ssor 2 ~rough ~he co~ps~ssor ~isch~r~se line 7 .~:o com~lete the - re:~rigeration '~; CyC~ i8 ~.~frig~ativn~ ycle i~:ro~im~ y r~ted .; dlIrin~; nDrmal Dper~ion of the rPfrig~ra:tion ~;y~;tem 1.
: 3~i The compresso~- inl~e~ guide :~anes 1~ are~ op~ened and clos{~d ~y ~ I
a gilide vane ac~u~tor 14 c~ntroll d :~ the capa~:i~y c~m~Tol system 3 which comprises a syste~ inter~ace board 16l a - -proc~s~or board 17, a set point and dis~lay b~a~d 18, and an analog/digi~al c~nverter 19.. Also, te~eratur~ sensor l3 ~or s~nsing the tem~era~ure of ~h~ ~eat transfer fluid leaving the ~v~poTatQ~ -~ thr~ugh the.t~L~g 10 an~ t~mperature ~ens~r 15 for ~ensing~he ~emperature of the heat transfer fluid enteTi2ng the evaporatar 5 ~hrough the ~ubi~g lO, are con-: nected by electrical lines 20 and 2~ directly to the A/D
:~ conve~ter 19.
10Pre~erablv9 the ~æmperature ~,e~lsors 13 and l~are t~mperature respon~ive r~sistane~ devices ~uch as a ~hermlstor6 having their sensing portions located in` the heat transfer fl~id in the ~u~ing lO in the evaporator ~ with their.resistances 1~ monito~ed by the.AlD,conver*er, ~s shown in.~i~ure 1. Of cours4 ~ as will be r~adily apparent to one o~ oTdinary skill - in t~e art to ~hich the~present in~ntion peItainsl--the tempesat~re sen~ors. 13 and 1~ ~ay be any of a vari~ty of temperature sensors sui~able.for ~ererating a~signal-indic2-20~ ~ive o~ the temperature o~ t~e heat transfe~ ~luid in the tubing 10 in th~ e~apora~or ~ and for supplying these gener- i ated- signals tc~th~ AID con~erter.l9.
,: Th~rocessoT 'Doald 17 may ~e any slevic~ or. combin tion of ,5 . de~ es,. c~pa~le o-E rec~iving ~ ~lurality o~.: input signal~, ~roc~ssing t~ :rg~ceiv~d :inpllt -s ignalB aoc o~ding to prep~Dgrammed prDcedllres, ~d prod~cing. d~ired o~l~Ut . contTol signals- ill:. r~pons~` to ~he- Tec~eived and p~ocessed input signals, i~^a ~anner ~accord~ng~ to the principles of- the 30 pTes~nt iIl~entioIl. Ft)r e:Eample, ~-processor b~ld l7 m~
co~pri~e ~ microcsm~ut~r, su~ a~ ~L ~odel .8D31 micIoeomputer svail~bl~-- f~Dm Inl~ ion ~ch ha~ la~ Qf bu~
. nes~ at S~nt2~ Cla~
` 3 ~ Also, pref~ra~ly, the AID -ronv~ter 19 i~3 -~ duaI :s~ope A/D
co~v~rter~whi~h ~;~all ~roces~ n~ g-illputs and ~sich is L3~
suitable fo~ u~e with the processor board 17. Also, it should be no~ed tha~, although the A/D ~onverter 19 i~ shown as a sepaT~te module in Figure l, thi~ A/D converter 19 may ~e physically pa~ of ~he ~rocessor board 17~in an actu~l 5 - cap~ity c~ol sys~2m 3.
F~rtheT, ~r~ferably, the set point and di~play ~ard 1~
-cDrprises a ~isual display, includingt ~or example, light emit~ing diodes (LED'~) or :liqui.d ~ys~al disp~ay (LCD'~) 1~ :devices forming a ~Llt~-digit display which is under the cun~rol of the processor board.l7.. Al~o, th~ ~et p~int -and . display board 18 .includes a device, such as- a key pad which se~es a~s a da~a entry ~ort as well as a programming tool~
- for en~ering the te~pe~a~ure setpoint of the,rhllled water 1~ entering-~he Evapor tor ~ through the ~aporator chilled -~
wa~er tu~ing.lG.
~till-furth~r, p~efera~ly, the sy~tem in~r~ace ~oar.d 16 includes at least Dr.e s~itching device~ ~uch--as a ~del S~-140 ~riac availa~le from G~neTal El~ctric, ~rp. which has .. a plac~ of business at Auburn, New York~ which is used as a -~witching element ~or~.c~ntrolli~g:~a su~ply o~ elect~ical pow2r (not shown) thrcugh electrical lines ~-1 $~ the guide . ~ne ~ctua~or-14.:.~The t~iac switches on the sys~em interf~ce boa~d 16 a~ contr~lled in~resp~nse to ~Gntrol ~i~nals :- rer~i~ed ~y~the-.t~iac s~itche~-~ro~^~he-pr~ces~r ~ard 17.
In *his manner, elec~rical power iS ~u~lied th~ough the eleetrical lines 21.~o the ~uide vane.~ctuator 14 under c~n~rol of t~e processor:~ard 17 to ~perat~ t~e-g~de vane 30 actllator ~ e ma~rnGr.-aco~rding.t o ~h~prin~ipl~s of t~e pT~B~nt i~vention ~hich i~ descri~ed i~ tail below. Of - c~n~.~e7 - aB~ eadily.-~p~ar~D~-to-~ne- D ~rdinaTy skill in ~he art to whi~h ~he~res~nt-inven~ion ~e~ains,~witchi~g - devi~s other ~h~n tri~ s~itc~e~ ~ay ~e-~ d in-.. r~ntro~lin~ I
3~ poweT~flow ~rom ~he pOW~T ~uppl~.(not sh~wn) thr~ugh ~h~
!
3~33 electrical lines 21 to the guide vane actuator 14 in response.
to output con~Tol signals from the proc~ssor board 17.
Ihe ~uide vane actuator 14 may ~e any device sui*able for ~riving the guid~ v~nes 12 ~ow~rd either their open or closed position in response to el~trical power signals rec~ived via - electrical lines ? 1 . For example, ~he guide vane actuator 14 - ~ay be an electric motor, such as a model~.MC-351 mDtor -~vailzble.f~m the-~ar~ Colm2m C~mpany ha~ing a pla~ç of ~usin~ss in ~ockfard, Illinois" for driv~ng. the ~uide vanes 12. t~ward ~ithe~ their open Dr ~l~sed posi~ion de~Fnding on whic-h one.of two-~riac switches ~n the fiyfitem int~Tf~ce board l& is actua~ed.in TespOnse to. CDntrOl signals received ~y the triac switches fr~m the proce~s~r~board.17. .The guide:vane ~15 actuatQr 14 drives.the.:gui~e van~ 12 t~ward ~ither their fully open or fully closed position at a con~tant~ fixed rate only.during that portion of a ~el~cted ~ase.time i~terv~l during which:the ~ppropriate.traic s~-itch o~..~he.system int~rface board 1~ is ac~uated.
Re$erring now to ~igure 2, a sDlid straight-line hori~on~al - -curve~A is sh~wn whic~ represents the entering.chilled w~ex - temperature se~p~int that i~ de~iTed tG ~e ~aint~ined by ~he ~ ~efrig~x~ion syatem of the pres~nt inv~ntion. .This setpoint 25 -iis arbi~rary a~d~. is-.en~red .in~o -the setp~int and displaY.
oa~d by the operatQre~y-way D~ the ~y pad. d~y ~aintainir.
a:fixe~ enterIng chllled wa~e~ tempeTature the ~p~rat~r may redu~e-~nergy.c~nsumptiGn d~rlng cer.~in load condi~ions, . partic~larly ~ low loads.; ~hæ leaving chill~d-water con~rol 30~. point ~f the ~esent:inven~iDn, 2S shown by .~he sDli~ sloped - :. li~e curv~ B7-~pres~nt~ the.. contrDl pDin~ a~ ~hich the le~vi~g ~hiIl~d w~t~r;is ~e~at~d~ur~ng.~ny.l~ d~nditiDn :. w~ e setp~t of;c~rve A. '~2 v~r~ic l axi~.~f Figur~ 2 -~s the~ temper~ture o~ ~he Ghilled ~a~er.-;-enterin~ or leaving 3~ the e~pora~r~ The horizontal a~is of Figure 2.is.~he.loa~ !
. .
3~3 on the refrigeration sys~em. An arbitrary val~e of 10F was chosen as evapor~tor ~T at full load and coIles~nding~Yalu~s of ~T at various loads a~e shown.
In Figure 2, the curve labeled ~ ~llustrates an arbitrary fi~d setpDi~t for the ~ntering chill~d.~ater temperature.
! Thus, in this example, ~he opel-a*or desiTes the refTigeratiol-~yst~m to~control the te~p~ratllre of the ent ring chilled water at ~F.
The dashed s ~ ight-line ho~izontal ~ur~ C reprYsents ~he : fi~ed leaving chilled wat~r ten~er~ture setpoint Df the pTior art, while the dashed sloped line Curve.D represents the `1~ floatin~ en*~ring chilled water te~per~ure of the prior art.
Once ~ predetermined enteri~ chilled ~a~er.set~o~nt is selected, the l~aving ~hill~d water temp~x~t~re .control p~int i5 calculated by the ~icroprocessor, and is-perio~ically .,0 updated e.~. once ev~xy ~ive- ~econds, to e~sure that:the leaving chilled water.temper~ture is t~ correct value for - ~he ~resen~.load. If hDweuer, t~ a* changest. for example a load would, over a period of time, decrease ~r~m 50% to 10~, *~e l~aving chill-ed wat~r ~mpera~ure con*rDl point 2~ would incr~àse fr~ 50~-.to:54~ hi6-incr~ase ~ill b~ d~ne - at a`gradual Ia~e s~ch a~ ~.12~-d~gre~.e-~er minute. ~Thus, : the~ac~ual leaving.chill~d ~ater temperatur~ sensed~ he - sEn-sor 13 w~uld, instantaneousIy, still indicate '~D~ while - the leaving chilled wat~r temperature ~Dnt~ol-~oin~.w~uld be calling for A leaving chill d water slightlY abDv~Q~.
Th~,.~ d~ia~ion would-2xifit.~ h~ ac~al leaving ;chi~ d wa~er ~mperatur~nd-th~ Ying `~ ~at~r tgm~ature. c~ntrol ~ and :th~ devi~tiD~ is i~pu~ted .to ~he sy~em intf~rf ce-~ad:which ~ he ~aid~-vane ~35 - actuatDr 14 ~ ~o~-e~the gu}de ~ane~ 12:toward th~ir.closed po~ition untit-~he actuàl temper~ur~ ~ the leaving chilled ~8~.3~3::~
water is equal to the l~aving chilled wa~er temperature cont~ol point.
In this manner th~ chill~eT will make a ~mooth t~ansition ~rom a ~iven load lev~l to a~D~r ~e~au~e ~he. leaving chilled water temperature sensursImmed-iately det~cts the water t~mperature change caused by the altera~ion in guide vane p~sition. Thus throu~h the use of the g~nerated control ~oint, ~he desired enterlng chiilled wate~ t~pe~ature is ~ain~ain~d during~he tran~ition.
~rther, it shDuld be n~te~ that the ~hilled w~t~ flow rate ~ay vary without changir.~ *he control scheme, sin~e the leaving.chilled water tempe~ture contTol point is only a function of t~ entering chilled.water ~mperat~re setpoin~
and the water ~emperature enterin~ and leaving the evaporator.
While this invention has been des~ ed ~nth ~efe~ence to a particular em~odiment discl~sed h~reinl it-is not confined to the d~tails s~t.forth h~rein.and this.application is i~tended to cov~r anv mDdifica~ions or c~ es ~s may come wit~in the scope of the i~ention.
Claims (6)
1. A capacity control system for a refrigeration system of the type which includes an evaporator wherein a refrigerant absorbs heat from a heat transfer medium passing therethrough, comprising:
means for generating a setpoint signal correspond-ing to a selected fixed setpoint temperature for the heat transfer medium entering the evaporator;
means for generating a first control signal which is a function of the temperature of the heat transfer medium entering the evaporator;
means for generating a second control signal which is a function of the temperature of the heat transfer medium leaving the evaporator; and processor means for receiving said setpoint signal, and said first and second control signals for processing the received signals according to preprogrammed procedures to determine a control point temperature for the heat transfer medium leaving the evaporator, and for generating a control point temperature signal for controlling the load on the evaporator.
means for generating a setpoint signal correspond-ing to a selected fixed setpoint temperature for the heat transfer medium entering the evaporator;
means for generating a first control signal which is a function of the temperature of the heat transfer medium entering the evaporator;
means for generating a second control signal which is a function of the temperature of the heat transfer medium leaving the evaporator; and processor means for receiving said setpoint signal, and said first and second control signals for processing the received signals according to preprogrammed procedures to determine a control point temperature for the heat transfer medium leaving the evaporator, and for generating a control point temperature signal for controlling the load on the evaporator.
2. A capacity control system as set forth in claim 1 wherein said processor means determines said control point temperature in proportion to the difference between said selected fixed setpoint temperature and a difference in temperature of the heat transfer medium across the evaporator.
3. A method of generating a leaving chilled fluid temperature control point for a refrigeration system having an evaporator wherein a refrigerant absorbs heat from the chilled fluid passing therethrough, which comprises:
generating a temperature setpoint signal corre-sponding to a desired entering chilled fluid temperature;
generating a first temperature signal corresponding to actual entering chilled fluid temperature;
generating a second temperature signal correspond-ing to actual leaving chilled fluid temperature; and generating a leaving chilled fluid temperature control point as a function of said setpoint, said first temperature, and said second temperature signals.
generating a temperature setpoint signal corre-sponding to a desired entering chilled fluid temperature;
generating a first temperature signal corresponding to actual entering chilled fluid temperature;
generating a second temperature signal correspond-ing to actual leaving chilled fluid temperature; and generating a leaving chilled fluid temperature control point as a function of said setpoint, said first temperature, and said second temperature signals.
4. A method as set forth in claim 3 wherein said generated leaving chilled fluid temperature control point is in proportion to the difference of said temperature setpoint signal and, the difference between said first and said second temperature signals.
5. In a refrigeration system having a centrifugal compressor, an evaporator, a liquid heat exchanger in the evaporator, and a condenser, a method of controlling the liquid entering the heat exchanger at a predetermined setpoint temperature comprising the steps of:
sensing the temperature of the liquid entering the heat exchanger;
sensing the temperature of the liquid leaving the heat exchanger;
producing a control point temperature signal for the liquid leaving the heat exchanger that is a function of the predetermined setpoint temperature and said temperatures of the liquid entering and leaving the heat exchanger; and varying the capacity of the liquid heat exchanger in response to the deviation between the temperature of the liquid leaving the heat exchanger and the produced control point temperature.
sensing the temperature of the liquid entering the heat exchanger;
sensing the temperature of the liquid leaving the heat exchanger;
producing a control point temperature signal for the liquid leaving the heat exchanger that is a function of the predetermined setpoint temperature and said temperatures of the liquid entering and leaving the heat exchanger; and varying the capacity of the liquid heat exchanger in response to the deviation between the temperature of the liquid leaving the heat exchanger and the produced control point temperature.
6. A method controlling the liquid entering the heat exchanger at a predetermined setpoint temperature as set forth in claim 5 wherein the step of producing a control point temperature signal includes the step of producing said control point temperature signal in proportion to the differ-ence between (a) the predetermined setpoint temperature of the liquid entering the heat exchanger, and (b) the differ-ence between the sensed temperature of the entering the heat exchanger and the sensed temperature of the liquid leaving the heat exchanger.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US82540486A | 1986-02-03 | 1986-02-03 | |
| US825,404 | 1986-02-03 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1281393C true CA1281393C (en) | 1991-03-12 |
Family
ID=25243939
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000528239A Expired - Lifetime CA1281393C (en) | 1986-02-03 | 1987-01-27 | Automatic chilled water setpoint temperature control using return chilled water temperature |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS62182556A (en) |
| KR (1) | KR910004007B1 (en) |
| CA (1) | CA1281393C (en) |
| FR (1) | FR2593898B1 (en) |
| GB (1) | GB2186399B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT394911B (en) * | 1990-09-12 | 1992-07-27 | Vaillant Gmbh | ELECTRONIC ROOM TEMPERATURE CONTROL |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR1414102A (en) * | 1964-09-24 | 1965-10-15 | Carrier Corp | Improvements to control systems |
| US4282718A (en) * | 1979-09-12 | 1981-08-11 | Borg-Warner Corporation | Evaporator inlet water temperature control system |
| US4539020A (en) * | 1983-07-10 | 1985-09-03 | Kawasaki Steel Corporation | Methods for obtaining high-purity carbon monoxide |
| US4506516A (en) * | 1984-04-06 | 1985-03-26 | Carrier Corporation | Refrigeration unit compressor control |
| US4589060A (en) * | 1984-05-14 | 1986-05-13 | Carrier Corporation | Microcomputer system for controlling the capacity of a refrigeration system |
| US4538422A (en) * | 1984-05-14 | 1985-09-03 | Carrier Corporation | Method and control system for limiting compressor capacity in a refrigeration system upon a recycle start |
| US4546618A (en) * | 1984-09-20 | 1985-10-15 | Borg-Warner Corporation | Capacity control systems for inverter-driven centrifugal compressor based water chillers |
-
1987
- 1987-01-27 CA CA000528239A patent/CA1281393C/en not_active Expired - Lifetime
- 1987-02-02 GB GB8702264A patent/GB2186399B/en not_active Expired - Lifetime
- 1987-02-03 KR KR1019870000841A patent/KR910004007B1/en not_active IP Right Cessation
- 1987-02-03 JP JP62024412A patent/JPS62182556A/en active Pending
- 1987-02-03 FR FR8701280A patent/FR2593898B1/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB8702264D0 (en) | 1987-03-11 |
| JPS62182556A (en) | 1987-08-10 |
| FR2593898A1 (en) | 1987-08-07 |
| KR910004007B1 (en) | 1991-06-20 |
| KR870008161A (en) | 1987-09-24 |
| GB2186399A (en) | 1987-08-12 |
| GB2186399B (en) | 1990-03-28 |
| FR2593898B1 (en) | 1989-07-28 |
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