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T e c h n o l o g y & E v o l u t i o n

Development of an advanced

control system for chillers

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Case Study: Development of an advanced control system for chillers

Prese tazi e di u sistema di c tr ll ava zat per chiller c c mpress re scr ll ad i verter e c mparazi e c u sistema tradizi ale on/off

N ottic d ottimizz zion n g tic d i ci cuiti igo i i, d in p tico di qu i d sp nsiondi tt , Carel d s mp studi so uzioni di cont o o ch s uttino nuov t cno ogi disponibi i sum c to.

lo studio si p opon di c tt izz ununit chi cqu - i p i condizion m nto dot t di

comp sso sc o com nd to t mit inv t v vo di sp nsion tt onic .O t o ni un comp t g mm di d ti di unzion m nto d comp sso in tutt condizioni divo o, si di c ico t mico ch mbi nt i, v p s nt to i sist m di cont o o v nz to ch s utt pot nzi it di go zion continu coo din t d comp sso d v vo tt onic , con

o scopo di vid nzi i isp mio n g tico d iv nt d ottimizz zion d unzion m nto dm cchin n i con onti di un sist m t dizion con comp sso non modu nt sist m di

sp nsion m cc nico.

In tti, possibi it di go i usso di ig nt n ci cuito s d comp ssocont mpo n m nt m indip nd nt m nt uno d t , p m tt di ottimizz i unzion m ntod m cchin di nd o d tt bi d ogni condizion di vo o.P qu sto studio, unit st t o nit di sist mi di misu di po t t ( cqu ig nt ), di unsist m di misu d sso bim nto tt ico (w ttm t o) o t ch di sist mi di cont o o d po t t ,d t mp tu d c ico d t mp tu umidit mbi nt i.

Introduction

This wo k ims to p ovid comp t d fnition o w t - i chi , tu ing n inv t d iv n sc ocomp sso nd n ct onic xp nsion v v .Th f st st p invo v s co ding th op ting d t om th comp sso in possib wo kingconditions.as s cond st p, w wi d sc ib n w dv nc d cont o syst m, b s d on st p ss gu tioncommunic tion b tw n th comp sso cont o go ithm nd th ct onic v v cont o , in o dto obt in signifc nt pow s vings du to th optimis d op ting b h viou o th units. In this w y,th possibi ity to cont o th ig nt ow in th ci cuit nd th comp sso coo ing c p city both

simu t n ous y nd ind p nd nt y ows th unit to wo k with m ximum fci ncy in conditions.This pow b nc wi so b comp d g inst th consumption o st nd d on-o unit

Abstract

V i b sp d comp sso s c n p ovid g t pow s vings in th cont o o i conditioning units.Th duction in coo ing c p city h s g t imp ct on th unit cont o syst m sp ci y g dingcomp sso nd w t imits nd unit st bi ity g n y. To m n g chi unit with v i b coo ingc p city, th cont o d d vic s must b consid d tog th with th cont o syst m its , scommunic tion b tw n d vic s c n c t in y void hunting p ob ms.W h v d v op d chi cont o syst m th t c n t k th dv nt g s o th comp t cont o

o inv t d iv n comp sso , ct onic xp nsion v v nd cond ns ns to m ximiz unitp o m nc in wo king conditions.

Chiller unit descriptionUnit typ : w t - i chi h t pump.r ig nt: r407 CNomin coo ing c p city: 16 kW (Tcond = 40 C, T v p = 4 C, 75 Hz, Sh = 10 C, Sbc = 10 C)Comp sso typ : inv t d iv n sc o comp sso , 5 HpInv t typ : mu ti pu pos 3-ph s inv t , 380 to 460 V 10%, 50/60 Hz 5%Cond ns typ (chi ): fnn d coiev po to typ (chi ): p t

P im y xp nsion d vic : st pp moto ct onic xp nsion v vS cond y xp nsion d vic : th most tic v v

a w t t nk h s b n inst d to cont o th o d pow t th v po to .

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Th w t ow t th v po to is cont o d in simp w t ci cuit with byp ss v v nd md with ow m t , whi th w t t mp tu is cont o d by 4 h t s with so id st t

In this w y w c n simu t w t conditions nd o d pow s o th unit.

Th chi unit h s b n inst d in c im t ch mb th t c n ch mbi nt t mp tu s b15 C nd 35 C. a th oth mbi nt conditions h v b n simu t d using c cu t d cond n-s tion p of . W h v consid d unit wo king with ns t const nt m ximum sp d (m ximum

fci ncy) so th t o ch mbi nt t mp tu th is p cis t g t cond nsing t mp tu

Data acquisitionsystem

Th unit h s b n ftt d with 8 t mp tu p ob s (Pt1000 s nso s) nd 8 p ssu p ob s( tiom t ic p ssu t nsduc s) inst d t ch compon nt in t nd out t in o d to ppboth p ssu d ops nd t mp tu conditions.In this w y w c n d w th comp t ig nt cyc on th P-H di g m.T mp tu p ob s h v so b n inst d to m su w t in t nd out t t mp tu s cond ns i t mp tu s.Fo th m su m nt o th pow b nc w inst d w t ow m t , ig nt m sm t nd w ttm t m su ing comp sso pow consumption (inc uding inv t pow suppev n though w c n si y c cu t th ctu pow consumption o th h t o w t t mpcont o (duty cyc o 2 id ntic p i s o 10kW h t s), w p d to inst vo t g m

nd 3 CT p ob s to m su ctu pow bso ption o th h t .O cou s , this m su m nt n ds to b co ct y int g t d, s th sign h s duty cyc .

Th d t cquisition so tw w s d v op d on PC-windows p t o m, b s d on N tion inst ul bvi w 6i, nd communic t s th cqui d nd c cu t d d t (i. . s tu t d t mp tu s) m in cont o p og m o chi nd w t cont o , b s d on th s m p og mming too .

a d t cqui d with cyc tim o 0.5 s c, nd th histo ic co dings s v d to n ev y 5 s c.

Control system Th chi cont o go ithm is m d up o 4 di nt p ts:comp sso cont o (with o without inv t ) cco ding to th w t t mp tu ;ct onic xp nsion v v cont o cco ding to th sup h t v u ;

cond ns n cont o cco ding to th s tu t d cond nsing t mp tu ;p v ntion nd m p oc du s.

Compressor controlTo p o m comp tiv t sts w d v op d cont o syst m th t c n wo k both with o without thinv t . Both typ s o cont o o ow w t t mp tu s (in t o out t), how v cont o wiinv t qui s n go ithm o th qu ncy.

W so h v th possibi ity to simu t n on-o duty using th inv t t fx d qu ncy.on-off Duty a d parametersTh comp sso cont o h s simp w t t mp tu s t point with di nti th t h s t

ch d to st t th comp sso g in. D u t v u s o ou t sts s t th w t in t t mpt 12 C with 2 C di nti .

InVERTER Duty a d ParametersTh comp sso cont o h s PID go ithm cco ding to th in t (d u t) o out t w tt mp tu . Th inv t qu ncy is inc s d o d c s d to ch nd m int in w ts t point (in C).

W d sign d cont o go ithm with PID p m t s to optimis f st y th w t t mp tu snd th n th st st duty t mp tu chi v m nt.

Wh n th unit is st t d th initi qu ncy is c cu t d p opo tion y, with th di nc bth ctu w t t mp tu nd th s t point.

Th comp sso is stopp d wh n th inv t qu ncy go s b ow th minimum v u (d u t 25 Hz

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Condenser control

Th cond ns cont o h s th s m PID unction s th comp sso . Th n sp d is cont o dcco ding to th cond nsing t mp tu s t point. Th m in di nc b tw n th p m t s is th

co tion b tw n input nd output sign .W t t mp tu d c s s with inc sing comp sso qu ncy ( ny oth p m t shou d o cou s b const nt) with in co tion. Th inc s in th comp sso qu ncy is const nt.Cond nsing t mp tu is co t d with n sp d, which h s cubic co tion with th vo t g

sign om th cont o . Fo this son, th inc s in n vo t g h s qu d tic co tion with thvo t g its . W c n c cu t this using th st v u o th n vo t g .

Electronic valve control

Th ct onic v v is d iv n by st nd d cont o d vic d v op d to mov st pp moto v vcco ding to th sup h t s t point m su d by 2 p ob s inst d t th v po to out t. Th f st

p ob m su s th v po ting p ssu , th s cond on m su s th sup h t d g s t mp -tu . Th cont o d vic is st nd on inst um nt th t communic t s th input p ob v u s, v vposition, cont o p m t s nd st tus with th unit m in cont o (PC).Th m in sup h t cont o h s PID go ithm wo king just with th sup h t nd s t point. How -v , th m ny di nt situ tions in which th unit wo king conditions c itic ( ow sup h t,high cond nsing o v po ting p ssu s, ow v po ting p ssu ).In th s c s s it is impo t nt to h v cont o go ithm th t c n ch ng th st nd d b h viou o th ct onic v v to p v nt th unit om stopping du to high o ow p ssu s o om wo king inc itic conditions o th comp sso .In m ny situ tions th is th possibi ity to ch ng th sup h t s t point o v n b tt to ch ngth v v cont o cco ding to th p ob v u s, to d c s o inc s ig nt ow nd coo ing

fci ncy in o d to k p th unit wo king v n in di fcu t conditions (h vy o d, v y high outsidt mp tu )Th v v cont o go ithm p ovid s p ot ction unctions o th unit w ning situ tions ( ow su-p h t, high cond nsing t mp tu , ow o high v po ting t mp tu ) th t c n b void d by

djusting th v v position.Th 4 di nt imits:

M ximum Cond nsing T mp tu (59 C)M ximum ev po ting T mp tu (18 C)Minimum ev po ting T mp tu (-3 C)Minimum Sup h t V u (3 C)

Prevention and alarm control

Th p v ntion go ithm h s signifc nt in u nc on th b h viou o th unit, s it c n m n g ths m c itic situ tions ist d o th v v cont o , but cont o ing th comp sso qu ncy di ct y.Th 4 di nt p v nt imits nd n tu y th n 4 m imits th t stop th unit.

Cond nsing t mp tu (p v nt 61 C, m 65 C)ev po ting t mp tu (p v nt -5 C, m -8 C)Comp sso disch g t mp tu (p v nt 120 C, m 125 C)

W t out t t mp tu (p v nt 3 C, m 2 C)In th p v nt conditions, th inv t qu ncy is d c s d with d fn d st p s soon s thp v nt imit is ch d, nd th n p opo tion y d p nding on th di nc b tw n th ctut mp tu o p ssu v u s nd th p v nt imits.

W d v oping c cu tion mod th t c s -by-c s c n v u t i th s w ning conditionsh v to b m n g d by ch nging th v v cont o o d c sing th inv t qu ncy ( nd coo ingc p city). W xp ct th wi b th possibi ity to s t th b h viou o th unit in m ximum coo ingc p city o m ximum fci ncy (COP) mod .

Water Control

Th cont o o th o d pow is comp t y s p t om th cont o o th unit, to void ny kind o mutu in u nc . O cou s th y both d nd us th s m t mp tu s om th d t cquisitionp og m.

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Th t mp tu cont o wo ks with PWM (5 s c duty cyc ). W c n both s ct di ct cont o oth o d pow (in kW) with db ck m su m nt o th ctu tot pow consumption o th h t s, o s t w t t mp tu in th t nk (which co sponds to th in t w t t mpo th chi unit) with th s m PID go ithm s th comp sso .Th cont o go ithm ds th w t t mp tu nd modu t s th PWM sign om 0% to 1(0 kW to 20 kW) to ch th s t point.W c n so utom tic y s t th w t t mp tu o pow p of s to simu t di nt oconditions.

Figu 1 shows th cont o syst m ont p n with th cont o p m t s nd s mp o chicont o in th g phs on th ight (co ou d in s input v i b s nd s t points, w t t mpsup h t nd cond nsing t mp tu , whi whit in s output v i b s, inv t qu nposition nd n vo t g ).In th x mp w c n s th cont o ctions du ing v i tion in th o d pow .Th w t t mp tu st ts ising nd th PID inv t cont o cts to m int in th w t s t(13.35 C).Th cont o go ithm inc s s th inv t qu ncy om 45 Hz to 65 Hz nd both th v v cond ns cont o o ow th v i tion in th o d. W c n so s som ch ng s in th w t sup h t s t point.

Fig. 1: Cont o syst m ont p n du inginv t cont o

Inverter controlcharacterisation

On o th f st nd mo impo t nt dv nt g s using n inv t d iv n comp sso g ds thcond nsing p ssu t d to pow consumption: comp ing with ON/OFF duty, th inv tcont o modu t s th comp sso qu ncy t ow v u s. This m ns ow cond ns o d

nd cons qu nt y ow cond nsing t mp tu with const nt mbi nt t mp tu .Figu s 2 nd 3 show th di nt pow consumption t th s m mbi nt (20 C) nd o dconditions (40...100%). as th o d d c s s, th inv t qu ncy so d c s s, nd wc n ow th cond nsing t mp tu nd t d pow consumption.

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Fig. 2: Pow consumption o inv t dutywith m ximum fci ncy cond ns cont o

Fig. :Pow consumption o inv t dutywith const nt cond nsing p ssu cont o

Figu s 4 nd 5 show th p ssu s, sup h t nd ig nt ow in both c s s. W c n so nothow p ssu d op on both sid s d c s s with th inv t qu ncy ( ou p ssu t nsduc s o

ch sid , comp sso out t, cond ns in t nd out t, v v in t o th high p ssu sid , v vout t, v po to in t nd out t, comp sso in t o th ow p ssu sid ).

Fig. 4: P ssu s nd ig nt ow oinv t duty with m ximum cond nsingcont o fci ncy

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Fig. :P ssu s nd ig nt ow oinv t duty with const nt cond nsingp ssu cont o

Th fn su t in t ms o unit COP is shown in Figu 6. as is c , unit p o m nc inc s s

ow ing th o d pow with m ximum COP o 4.55 ( t ound 50% o o d pow ).Th g n in shows th m ximum p o m nc COP cu v comp d with th d k g n on ,which p s nts s xp in d th s m inv t p o m nc without th cont ibution o th owcond nsing p ssu cont o .

as s cond su t w ound th t unit COP h s n vid nt d c s wo king ound both m ximum(75 Hz) nd minimum (25 Hz) qu ncy du to th inv t pow consumption nd comp ssod sign.W think th wi b no p ob ms in tot unit p o m nc g ding duction in o COP t75 Hz s this unning qu ncy is d fnit y not qu nt ( stim t d ound 1...2% o tot unit

unning tim ).On th oth h nd it is possib to s v n gy by cont o ing th minimum inv t qu ncy ino d to void th comp sso wo king with v y ow COP.Fo this son th minimum inv t qu ncy h s b n c cu t d by th cont o go ithm onc s -by-c s b sis. It g n y d p nds on th outsid t mp tu nd h s b n s t b tw n30 nd 35 Hz. W xp i nc d th t wo king with n ON/OFF modu ting qu ncy stopp d t thminimum v u is som tim s mo fci nt th n wo king t const nt ow qu ncy v u s.(s T b 1).

Fig. 6: Unit COP, pow consumption ndcoo ing c p city with m ximum p o m nc

nd with const nt cond nsing p ssu .

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Comparative testswithtraditionalON/OFF duty

Th m in obj ctiv o th comp tiv t sts is to m su th in u nc o on-o duty on thpow consumption o th chi unit. T st sp cifc tions st t with on-o duty t fx d 75 Hz inv t

qu ncy gu ting v i b h t o d with const nt w t s t point (12 C, 2 C di nti ).Pow consumption nd t mp tu s w m su d nd v g v u s w c cu t d in o d toobt in w t s t point v u s o th inv t modu ting qu ncy t st: in this w y w c n m sum n pow consumption with th x ct s m w t t mp tu s nd o d in both unit duti s.Figu 7 shows m n v u s o unit coo ing fci ncy (w t t mp tu with const nt o d pow )

nd pow consumption in both t sts.

Fig. :Comp tiv t st t 20 C mbi ntt mp tu , 10.3 kW o d pow , ound70% o nomin o d pow .

Som o th comp tiv t sts summ iz d in T b 1.

Tab. 1: Comp tiv t st t v ious wo kingconditions.

Both typ s o inv t cont o ist d nd comp d with ON/OFF duty in o d to m su thx ct inc s in pow consumption du to th in fci ncy o on-o cont o nd th b tt

p o m nc o inv t cont o t m ximum fci ncy (with ow st cond nsing t mp tu tch mbi nt t mp tu ).

as dy m ntion d b o (ch p. 5) w xp i nc d high pow consumption t ow inv tqu nci s (b ow 35 Hz) du to th ow COP o th comp sso -inv t syst m wh n unning t

v y ow sp d. T b 1 ( in 4) shows typic condition in which on-o duty is 7% mo fci ntth n inv t duty nd in which th inv t cont o wo ks b tt by stopping th comp sso t25 Hz nd st ting it t ound 50 Hz, with modu tion p iod in b tw n.

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Results and conclusion Ou m in int st conc ns cont o o th unit, f st t ying to chi v th b st w t st bi ity nd thth most ctiv ction to v i tions in o d nd mbi nt conditions. Th m in cont o gwith simp p m t is tion h s th possibi ity to chi v th s su ts with kinds o unit ndinv t d iv n comp sso s, s th di ct communic tion b tw n inv t , v v nd cond nscont o ows p ct t m wo k in conditions.

On th oth h nd, w ound it n c ss y to c t m p o th unit, sp ci y conc ning inv tnd comp sso fci nci s, in o d to k p wo king conditions w ys in good p o m nc

Fo this son, th m y b c s s in which th cont o go ithm p v nts th unit om wo kingow o high inv t qu nci s, o d c s s th unit coo ing c p city to m ximiz unit COP.as s th comp tiv t sts conc n d, w st b ish d t st p otoco to m su th in u nc o th on-o duty on th unit COP, which su ts in n high pow consumption, up to15%, d p nding on o d pow . as s cond st p w consid d th t unit wo king t ow

qu nci s is d fnit y ov siz d comp d to nomin conditions: this ows us to chi v g t bfci nci s by ow ing cond nsing p ssu , with up to 30% ss pow consumption t m diumng inv t qu nci s.

It is c th t pow consumption d t inc ud th consumption o th inv t its : wh ncomp ing with n ON/OFF st nd d comp sso w h v to duc th pow s ving su ts.On th oth h nd, st nd d comp sso (50 Hz, 380 V) is mo xp nsiv th n sm inv td iv n comp sso th t c n wo k t up to 75 Hz with th s m coo ing c p city.

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