Điều khiển tự động trong điều hoà không khí.pdf

iu khin t ng trongiu ho khng kh

Bi:

V Ch Chnhinh Vn Thun

IU KHIN T NG TRONG IU HO KHNG KH

H THNG IU KHIN T NG TRONG IU HO KHNG KH

Nhim v v chc nng ca h thng iu khin

Chc nng quan trng nht ca h thng iu ha khng kh l duy tr cc thng s khhu trong mt phm vi no khng ph thuc vo iu kin mi trng xung quanhv s thay i ca ph ti.

Tuy nhin chng ta vn cha xem xt lm th no m h thng iu ho khng kh cth thc hin c iu khi ph ti v mi trng lun lun thay i.

H thng iu khin c chc nng nhn cc tn hiu thay i ca mi trng v ph ti tc ng ln h thng thit b nhm duy tr v gi n nh cc thng s kh hu trongkhng gian iu ha khng ph thuc vo iu kin kh hu bn ngoi v ph ti bntrong.

Cc thng s c bn cn duy tr l :

Nhit ; m; p sut; Lu lng.

Trong cc thng s trn nhit l thng s quan trng nht.

Ngoi chc nng m bo cc thng s vi kh hu trong phng, h thng iu khin cnc tc dng bo v an ton cho h thng, ngn nga cc s c c th xy ra; m bo hthng hot ng hiu qu v kinh t nht; gim ch ph vn hnh ca cng nhn.

iu khin t ng trong iu ho khng kh

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www.princexml.comPrince - Non-commercial LicenseThis document was created with Prince, a great way of getting web content onto paper.

S iu khin v cc thit b chnh ca h thng iu khin

S iu khin t ng

S h thng iu khin

Cc h thng iu khin t ng trong iu ha khng kh hot ng da trn nhiunguyn tc khc nhau. Tuy nhin mt h thng iu khin u c cc thit b tng tnhau.

Ta nghin cu s iu chnh nhit u ra ca khng kh nu trn hnh 11.1.

y thng s cn duy tr l nhit khng kh u ra dn trao i nhit, c th gin l thng s iu khin. H thng hot ng nh sau: Khi nhit khng kh u radn trao i nhit thay i (chng hn qu cao so vi yu cu , gi tr ny c cit sn b iu khin), s thay i c b cm bin (sensor) ghi nhn c vtruyn tn hiu phn hi ln thit b iu khin. Thit b iu khin tin hnh so snhgi tr o c vi gi tr t trc (set point). Tu thuc vo mi quan h gia cc ilng ny m tnh tn hiu u ra nhm tc ng ln thit b b iu khin (controlleddevice) khc nhau. Tu thuc vo tn hiu t thit b iu khin m thit b iu khins c hnh ng mt cch ph hp nhm tc ng ln nguyn nhn gy thay i thngs iu khin. y nguyn nhn lm thay i thng s iu khin l mi cht trao inhit.

Thng s iu khin:

Thng s iu khin l thng s nhit vt l cn phi duy tr ca h thng iu khin.Trong cc h thng iu ho khng kh cc thng s thng gp l nhit , m, lulng, cng sut vv . ..


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B cm bin (sensor)

L thit b cm nhn s thay i ca thng s iu khin v truyn cc ghi nhn lnthit b iu khin.

Nguyn tc hot ca b cm bin da trn s gin n nhit ca cc cht, da vo lcdng chy ..

Thit b iu khin

Thit b iu khin s so snh gi tr ghi nhn c ca b cm bin vi gi tr t trcca n. Tu theo mi quan h ca 2 gi tr ny m tn hiu iu khin u ra khc nhau.

Phn t iu khin (C cu chp hnh)

Sau khi nhn tn hiu t thit b iu khin c cu chp hnh s tc ng, tc ng ctc dng lm thay i thng s iu khin. Tc ng thng gp nht c dng ON-OFF

Cc ngun nng lng cho h thng iu khin

Ngi ta s dng nhiu ngun nng lng khc nhau cho cc h thng iu khin :

- in nng : i b phn cc h thng iu khin s dng in nng iu khin dotnh gn nh v d dng s dng. Ngun in c in p thng nm trong khong 24 -220 V. Mt s h thng s dng h thng c in p v dng thp : U < 10V, I=4-50mA.

- H thng kh nn : Ngi ta c th s dng h thng kh nn iu khin. H thng c p sut P= 0 - 20 lb/m2

- H thng thy lc : H thng ny thng c p sut ln P = 80 - 100 lb/m2

Cc thit b iu khin

B phn cm bin (sensor)

Trong iu ho khng kh c cc b cm bin nhit , m, p sut v lu lng

B cm bin nhit

Tt c cc b cm bin nhit u hot ng da trn nguyn tc l cc tnh cht nhitvt l ca cc cht thay i theo nhit . C th l s gin b v nhit, s thay i intr theo nhit . Ta thng gp cc b cm bin nh sau:


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Hnh 11.2. Cc kiu b cm bin

Thanh lng kim (bimetal strip)

Trn hnh 11.2a1 l c cu thanh lng kim, c ghp t 2 thanh kim loi mng c hs gin n nhit khc nhau. Mt u ca thanh c gi c nh v u kia t do. Thanh1 lm t vt liu c h s gin n nhit km hn thanh 2. Khi nhit tng thanh 2 ginn nhiu hn thanh 1 v un cong ton b thanh sang tri. Khi nhit gim xung digi tr nh mc, thanh b un cong sang phi.

Mt dng khc ca b cm bin dng ny l thanh lng kim c un cong dng xoctrn c, u ngoi c nh u trong di chuyn. Loi ny thng c s dng lmng h o nhit (hnh 11.2a2.

B cm bin ng v thanh

Cu to gm 01 thanh kim loi c h s gin n nhit ln t bn trong 01 ng tr kimloi gin n nhit t hn. Mt u thanh kim loi hn cht vo y ca ng u kia tdo. Khi nhit tng hoc gim so vi nhit nh mc u t do chuyn ng sangphi hoc sang tri.

B cm bin kiu hp xp

Cu to gm mt hp xp c cc np nhn hoc mt mng mng c kh nng co ginln, bn trong cha y mt cht lng hoc cht kh. Khi nhit thay i mi cht cogin l hp xp hoc mng mng cng phng lm di chuyn 1 thanh gn trn


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B cm bin kiu hp xp c ng mao v bu cm bin

Cm bin in tr

Cm bin in tr c cc loi sau y:

Cun dy in tr in tr bn dn Cp nhit

B cm bin kiu in trB cm bin p sut

B cm bin p sut thng l b cm bin kiu hp xp. Khc vi b cm bin nhit kiu hp xp lun lun i km vi bu cm bin, bn trong c mi cht, th yhp xp c ni trc tip vi tn hiu p sut ghi nhn s thay i p sut ca micht v tc ng ln mng xp.


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B cm bin p sutB cm bin m

B cm bin cng hot ng da trn nguyn l v s thay i cc tnh cht nhit vtl ca mi cht khi m thay i.

C 02 loi cm bin m:

Loi dng cht hu c (organic element) Loi in tr (Resistance element)

B cm bin m

Trn hnh 11.6 l b cm bin m, n c cha mt si hp th m. S thay i mlm thay i chiu di si hp th. Si hp th c th l tc ngi hoc vt liu cht doaxtat.

B cm bin lu lng

Phong k dy nng (hot wire anemometer)


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Trn hnh 11.7 trnh by cu to ca phong k dy nng. Thit b gm mt dy in trv mt cm bin nhit . Mi cht i qua dy in tr v lm lnh n, tc gi t lvi cng sut in cn thit duy tr nhit chun dng i chiu.

Phong k dy nngng pit

ng pit o p sut v lu lng

Trn hnh 11.8 trnh by ng pit o p sut: p sut tnh (11.8a), p sut tng (11.b) vp sut ng (11.8c).

C s o lu lng l s ph thuc gia lu lng vo s thay i p sut khi i quathit b.

v lu lng:


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Tm c l

Lu lng k c vng c l

Trn hnh 11.9 trnh by lu lng k s dng vng c c l nh gia. Ngi ta nhnthy s thay i p sut tnh pha trc v pha sau ca vng ph thuc vo lu lngtheo quan h sau y:

trong :

C- Hng s;

F- Din tch tit din ca ng, m2.

ng Venturi

Lu lng k Venturi

Lu lng k kiu Venturi gm mt ng c c tht gia (hnh 11.10). chnh psut gia u vo ca ng v v tr c tht t l vi lu lng mi cht chuyn ngngang qua ng.


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Lu lng k kiu chn vt xoay

Vng chn vt chuyn ng xoay di tc dng ca dng chy, vng quay cng nhanhnu tc dng chy ln. Thit b c ni vi c cu o ch ch lu lng.

Lu lng k chn vt

Cc thit b c iu khin

Van in t

C 2 loi van in t

* Loi ng m on-off: Van ch c 2 trng thi ng v m. Van thng c 2 loi van 2ng v van 3 ng.

* Loi ng m bng m t (Motorize): Van ng m bng m t cho php ng mnhiu v tr v thng c dng iu chnh lu lng.

- Cn c vo s hng ca dng, van in t c th chia lm loi 2 ng v 3 ng.

* Van 2 ng: Hai ng gm mt ng mi cht vo v 01 ng mi cht ra. Loi van nyc 2 kiu : Loi thng m (NO- Normally Open) v loi thng ng (NC- NormallyClose)


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Van in t 2 ng

a) Loi thng m; bc) Loi thng ng

* Van in t 3 ng: Gm c 3 ng mi cht vo ra. Loi 3 ng cng c chia ra lm 2loi khc nhau:

- Van 3 ng hn hp: C 02 ca vo v 01 ca ra

- Van 3 ng kiu bypass: C 01 ca vo v 02 ca ra.

Van in t 3 ng

a) Van 3 ng hn hp; b) Van in t 3 ng by-pass

Ca gi

Cc ca gi iu khin phi l ca gi m vic ng m thc hin bng m t. Trnhnh 11.14 l ca gi iu chnh, bn hng cc ca gi c gn m t. M t c trcgn vo trc qut ca cc cnh van iu chnh. Khi nhn tn hiu iu khin, m t hotng v thc hin vic ng hay m van theo yu cu.

Lu lng k Venturi


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CC PHNG PHP IU KHIN

iu khin nhit

S iu khin nhit

Trn hnh 11.15 l s iu khin nhit ca mt AHU. AHU c 02 dn trao inhit: mt dn nng v mt dn lnh cc dn hot ng c lp v khng ng thi.Ma h dn lnh lm vic, ma ng dn nng lm vic.

u ra ca khng kh c b tr h thng phun nc b sung b sung m cho khngkh.

Nc nng, nc lnh v nc phun c cp vo nh cc van in t thng ng(NC-Normal Close) v thng m (NO- Normal Open).

iu khin cng sut

Phng php iu khin ON-OFF

Phng php ny thng dc s dng trong cc h thng nh.

Khng ch trng thi ca mt phn t no 2 trng thi : ng v m

V d : iu chnh nhit khng kh trong phng, my iu ha ca s thc hinnh sau :

+ Nhit t trong phng l 22 oC

+ Khi nhit trong phng xung 21oC my s dng chy.

+ Khi nhit ln 23 oC th my bt u chy li.


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Nh vy my s lm vic trong khong nhit t 21 - 23oC .

chnh nhit gia 2 v tr ON v OFF gi l vi sai iu khin.

By gi ta hy biu th trn th s thay i nhit phng v cng sut theo thigian.

Trong iu kin l tng khi nhit ln 23oC th my bt u chy v ngc li khinhit t 21oC th my dng nhng do qu tnh nhit nn n 23oC v 21oC nhngnhit phng vn thay i mt khong no .

Hnh 11.16. iu khin cng sut theo kiu ON-OFF

Trong mt chu k, thi gian khng kh c lm lnh (nhit gim) v t nng (nhit tng) ph thuc vo mi quan h gia cng sut lm lnh Qlnh v tng nhit thaca phng QT.

* c im ca phng php iu khin kiu ON-OFF

- n gin , gi thnh thp nn thng s dng cho h thng nh.

- Cng sut gia cc k dao ng ln. Nn khng thch hp cho h thng ln v iukhin chnh xc.

Phng php iu khin bc.

Thng c s dng cho h thng ln c nhiu my. Phng php ny c u im hnch c s sai lch ln cng sut gia cc k.


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Phng php iu khin bc l thay i cng sut theo tng bc, trnh cng sut thayi qu t ngt. H iu ha c iu khin bc phi c nhiu t my.

Trong h thng ny b iu khin cn c vo tn hiu ca bin iu khin s tc ngln cc r le hay cng tc v lm thay i cng sut thit b ra theo tng bc hay giaion.

Ta nghin cu mt v d: Thit b iu khin cng s mt h thng iu ha gm 3 cmmy chiller.

Bin iu khin l nhit ca nc lnh vo my tnv. Gi tr nh trc l tnv = 8oC

* Khi nhit tng : Khi nc v tnv = 8,5oC ch c t my I lm vic. Nu nhit tip tc tng n 9oC th t my II khi ng v lm vic cng t I. Nu nhit tngn 9,5oC th t my th III khi ng lm vic.

* Khi nhit gim : Khi nhit gim xung 7,5 oC th t my th III ngng hotng. Nu tip tc gim xung 7oC th t my II dng tip. Nu xung 6,5oC th dngthm t I.

iu khin cng sut theo bc

Ta nghin cu th thay i nhit v ph ti:

- Ta c nhn xt l th cng sut thay i tng bc, trnh hin tng xung (thay it ngt).


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- Cc my lm vic nh sau :

+ My I : Lm vic trong khong khi nhit tng ln 8,5oC v dng khi nhit gimxung 6,5oC. Nh vy my I lm vic trong khong thi gian di nht.

+ My II: lm vic trong khong khi nhit tng ln ti 9oC v dng khi nhit gimxung 7oC.

+ My II: Lm vic khi nhit tng ln 9,5oC v dng khi nhit gim xung 7,5oC

Nh vy my I lm vic nhiu nht v my II lm vic t nht. trnh tnh trng trong mch in ngii ta c thit k cng tc chuyn mch i vai tr cc my chonhau, trnh cho mt my nn bt k lm vic qu nhiu trong khi my khc hu nhkhng hot ng.

u, nhc im ca phng php iu khin theo bc :

- Trnh c s thay i cng sut qu t ngt. Thch hp cho h thng ln.

- Cc my lm vic khng u nhau nn phi thng xuyn chuyn i vai tr ca ccmy.

- Bin dao ng (vi sai) ca bin iu khin tng i ln do phi qua tng cp.


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iu khin t ng trong iu ho khng khIU KHIN T NG TRONG IU HO KHNG KHH THNG IU KHIN T NG TRONG IU HO KHNG KHNhim v v chc nng ca h thng iu khinS iu khin v cc thit b chnh ca h thng iu khinS iu khin t ngThng s iu khin:B cm bin (sensor)Thit b iu khinPhn t iu khin (C cu chp hnh)

Cc ngun nng lng cho h thng iu khinCc thit b iu khinB phn cm bin (sensor)B cm bin nhit Cc thit b c iu khin

CC PHNG PHP IU KHINiu khin nhit iu khin cng sutPhng php iu khin ON-OFFPhng php iu khin bc.

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