Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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~.
393
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 $~ the guide
. ~ne ~ctua~or-14.:.~The t~iac switches on the sys~em interf~ce
boa~d 16 a~ contr~lled in~resp~nse to ~Gntrol ~i~nals
:- rer~i~ed ~y~the-.t~iac s~itche~-~ro~^~he-pr~ces~r ~ard 17.
In *his manner, elec~rical power iS ~u~lied th~ough the
eleetrical lines 21.~o the ~uide vane.~ctuator 14 under
c~n~rol of t~e processor:~ard 17 to ~perat~ t~e-g~de vane
30 actllator ~ e ma~rnGr.-aco~rding.t o ~h~prin~ipl~s of t~e
pT~B~nt i~vention ~hich i~ descri~ed i~ tail below. Of
- c~n~.~e7 - aB~ eadily.-~p~ar~D~-to-~ne- D ~rdinaTy skill
in ~he art to whi~h ~he~res~nt-inven~ion ~e~ains,~witchi~g
- devi~s other ~h~n tri~ s~itc~e~ ~ay ~e-~ d in-.. r~ntro~lin~ I
3~ poweT~flow ~rom ~he pOW~T ~uppl~.(not sh~wn) thr~ugh ~h~
!
3~33
electrical lines 21 to the guide vane actuator 14 in response.
to output con~Tol signals from the proc~ssor board 17.
Ihe ~uide vane actuator 14 may ~e any device sui*able for
~riving the guid~ v~nes 12 ~ow~rd either their open or closed
position in response to el~trical power signals rec~ived via
- electrical lines ? 1 . For example, ~he guide vane actuator 14
- ~ay be an electric motor, such as a model~.MC-351 mDtor
-~vailzble.f~m the-~ar~ Colm2m C~mpany ha~ing a pla~ç of
~usin~ss in ~ockfard, Illinois" for driv~ng. the ~uide vanes
12. t~ward ~ithe~ their open Dr ~l~sed posi~ion de~Fnding on
whic-h one.of two-~riac switches ~n the fiyfitem int~Tf~ce board
l& is actua~ed.in TespOnse to. CDntrOl signals received ~y the
triac switches fr~m the proce~s~r~board.17. .The guide:vane
~15 actuatQr 14 drives.the.:gui~e van~ 12 t~ward ~ither their
fully open or fully closed position at a con~tant~ fixed rate
only.during that portion of a ~el~cted ~ase.time i~terv~l
during which:the ~ppropriate.traic s~-itch o~..~he.system
int~rface board 1~ is ac~uated.
2D
Re$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::~
11
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.
