MT S GII PHP TIT KIM NNG LNG CHO H THNG THNG GI V IU HO KHNG KH TRONG CNG TRNH XY DNG TI VIT

NAM
KS. T XUN HA KS. NGUYN TUN ANH Vin KHCN Xy dng
1. t vn Hi n nay, trong cc to nh c l p t h thng thng gi v iu ho khng kh (HKK), lng tiu th nng lng in thng chim mt t trng rt ln, vo kho ng 60 n 90% tng mc ti u th in ca cng trnh. Kt qu kho st thc t s dng nng lng trong mt s to nh thuc d n nh gi hiu qu s dng nng lng trong cng trnh xy dng thc hin cho cc to nh cao tng xy dng ti Vit Nam trc nm 2000 vi bn i tng chnh l khch sn, to nh hn hp khch sn - vn ph ng, c quan hnh chnh nh nc v siu th cho thy phn nng lng in tiu th cho h thng thng gi v HKK chim t l t 70 n 90% tng mc ti u th nng lng in ca cng trnh (t l 90% i vi khch sn Green park). Nh vy, vic tit kim nng lng hiu qu trong cho cng trnh xy dng ph thuc ch yu v o cc gi i php tit kim nng lng cho h thng thng gi v HKK. Tit kim nng lng trong h thng thng gi v HKK khng n thun l gim bt cng sut my gim ti u th nng lng in m phi i i vi vic m bo cc iu kin tin nghi vi kh hu cn thit cho con ngi v cng trnh. Vit Nam nm trong vng kh h u nhit i nng m nn iu kin kh hu bn ngoi nh nh hng rt ln n ch vi kh hu b n trong cng trnh. tit kim nng lng cho h thng thng gi v HKK cn phi ch t giai on thit k kin trc, cu to lp v bao che cng tr nh ti vic la chn gii php thng gi v HKK ph hp vi chc nng ca tng loi cng trnh. Bn c nh l vic la chn thit b, vt liu v gii php cch nhit hp l. Cui cng l tit kim nng lng trong qu trnh khai thc. 2. Gii php tit kim nng lng trong giai on thit k kin trc Hi n nay, phn ln thit k cng trnh Vit Nam ch cp n vn kin trc, m thut v m bo kh nng chu lc ca cng trnh. Nhng vn c nh hng ln n tiu hao nng lng nh khoa hc v vt l kin trc, vt l xy dng c n t c quan tm. Nh ni trn, nc ta nm trong v ng kh hu nhit i nng m, thi gian nng kh di nn cn tp trung gii quyt vn chng nng. Trong thit k kin trc v k t cu bao che cng tr nh cn c cc gii php khai thc tri t cc yu t c li v hn ch ti a cc yu t bt li ca kh hu tc ng ti cng tr nh. Gi i quyt c vn ny l gi m ti ng k cho h thng thng gi hay HKK ca cng trnh. Cc vn cn quan tm trong giai on thit k kin trc bao gm: thit k kin trc phi gii quyt c y u cu v thng gi t nhin m bo s thng thong cho cc khng gian c ngi hoc l m vic. iu ny r t cn thit cho phn ln thi gian khi nhit khng kh b n ngoi nh m c khng qu 30oC, khi ch cn kt hp thng gi t nhi n v qu t gi l c th to c cm gic d chu cho con ngi. Mun th, c n t c cc yu cu sau: C t l m ca s knh hp l kt hp cc hnh th c ca kt cu che nng va gii quyt c thng thong, chiu sng t nhi n v hn ch nng khi cn. C cc gii php cu to cc lp hp l cho mi, nn v tng bao che va hn ch c nh hng ca bc x m t tri, va chng mt nhit khi c HKK. C n c gii php hn ch tng nhit trong nh do hi u ng nh knh gy ra khi c mng knh ln, hoc kt cu bao che ch yu bng knh. Phn tch k hn v tnh ton thit k HKK v thng gi ta thy c c th can thip v o khu no tit kim nng lng. Trong h thng HKK v thng gi nng lng c tiu th ch yu l m l nh kh phn nhit d trong cng trnh v mt phn dng chy my bm (cho h thng chiller) v qut gi. Vic tm gii php ti t kim nng lng cho h thng HKK v thng gi cng chnh l tm gii php l m gim nng lng tiu hao sn xut lnh ng thi theo hai hng: (i) Gim lng nhit d trong cng trnh v (ii) gi m mc tiu th in sn xut mt n v lnh. Ni dung (ii) l vn ca nh sn xut thit b, khng trnh by y. Di y ch trnh by gii php gim lng nhit d trong nh. Ph ti nhit ca h thng HKK ph thuc v o cc y u t kh hu b n ngoi nh, th i im trong ngy, ma trong nm. Lng nhit d cn thi ra ngo i b ng h thng HKK v thng gi c xc nh bng phng trnh cn b ng nng lng sau: Q = QKCBC + QTB + QCS + QNG + Q KK (kJ/h) (1)

Trong : Q - t ng lung nhit d trong nh. QKCBC - lng nhit truyn v o nh qua k t cu bao che cng trnh; QTB - lng nhit do thit b trong nh sinh ra; QCS - lng nhit do n chi u sng; QNG - lng nhit do ngi sinh ra; QKK - lng nhit sinh ra do trao i khng kh gia trong nh v ngoi nh (lng kh ti cp vo, khng kh thm thu qua khe ca v k t cu ngn che) ph thuc vo iu kin kh hu v lu lng trao i khng kh. Trong bi u thc tr n ch c thnh ph n QKCBC l i lng thay i theo iu kin kh hu v ph thuc v o tnh ch t ca kt cu bao che ca mi cng trnh, cc thnh ph n khc thng t thay i i vi mt cng trnh c th. Trong iu kin kh hu nhit i nng m ca Vit Nam nu kt cu bao che khng hp l th lng nhit truyn t ngo i vo tr ong nh lm tng ng k tng lng nhit d trong cng tr nh. Nh vy, gim ph ti lnh th v n c bn l ph i hn ch c lng nhit ny khi c b c x m t tri. Lng nhit truyn qua kt cu bao che v o nh khi c b c x mt tri c tnh ton theo biu th c: Q = k.F (Ttg - Tt) (W/m 2 k) (2) Trong : K h s truyn nhit ca kt cu bao che; F di n tch b mt kt cu bao che; Ttg nhi t tng bn ngoi nh; Tt nhi t b n trong nh. Gi tr nhit tng Ttg gm hai thnh ph n l nhi t khng kh bn ngoi v nhi t tng ng ca bc x mt tri c xc nh theo biu thc. Ttg = Tn + Tt (3) Trong : Tn nhi t khng kh b n ngoi nh. Tt - nhi t tng ng do nh hng c a bc x mt tri. Tt = J . / n 2 Trong : J cng bc x mt tri W/m . (4)

- H s hp th bc x ca b mt ngo i ca kt cu bao che. n h s to nhit mt ngoi nh c a kt cu b ao che W/m .k Qua cc bi u thc tr n ta th y rng hn ch lng nhit truyn t bn ngoi vo trong nh cn c cc gii php thch hp v kt cu bao che. Gii php th nht l cu to cc lp vt liu thch hp c h s truyn nhit thp hoc c th m m t lp vt liu cch nhit trong cu to cc lp ca kt cu bao che v gi i php th 2 l h n ch nh hng ca bc x mt tri bng cch la ch n lp vt liu ph mt ngo i kt cu bao che c h s hp th bc x thp, cc loi knh c tnh ph n x cao,.. 3. Tit kim nng lng trong thit k h thng HKK 3.1. La chn gii php thit k h thng HKK Phn tch, la chn gii php thit k h thng HKK v thng gi hp l cho tng loi cng trnh c ngha rt quan trng t c hiu qu cao v tit ki m nng lng. Hin nay c hai th loi HKK chnh l lm lnh trc tip v lm lnh gin tip. Lm lnh trc tip l cp lnh trc tip thng qua cc dn trao i nhit lp t trc tip bn trong cng trnh. Cc loi ph bin l iu ho cc b, cc h thng l m l nh thng qua cc dn FCU lp t trong phng m cht ti lnh c th l nc lnh c th l mi ch t lnh. Lm lnh gin tip l cp lnh lm lnh khng kh cc bung trao i nhit m (AHU) ri mi a khng kh c x l v lm l n h vo trong phng. Cc h thng ny thng l trung tm bao gm my sn xut nc lnh (chiller), h thng bm nc lnh v nc tun hon, h thng gii nhit cho my lnh (c th bng nc hoc bng gi), cc bung x l nhit m v h thng ng ng d n khng kh lnh v tun hon. Mi h thng HKK u c cc u im v nhc im ri ng v ch thch hp trong phm vi cng sut, chc nng nht nh. la chn h thng HKK ph hp, tit kim nng lng khi thit k cn phn tch mt cch ton di n v cng su t h thng, chc nng, cng nng ca cng trnh, phi tnh n c im s dng v iu kin vn hnh khi a cng trnh vo s dng.
2

i vi cng trnh c quy m l n, khng gian cc phng ln nh cc trung tm hi ngh, cc hi trng ln, cc rp chi u phim, nh thi u cc cng trnh c ph ti nhit n nh nn thi t k cc h thng iu ho trung tm c my chiller sn xut nc lnh s em li hiu qu cao trong vic tit kim nng lng v m bo iu kin tin nghi vi kh hu. i vi cng trnh c chc nng nh c quan cng s, nh vn phng kt hp nh , nh chung c cao cp N n s dng h thng VRV l h thng HKK mt m nhiu con c s dng cng ngh bin tn iu chnh lng mi cht lnh. H thng ny c u im thay i cng sut d dng t 10 n 130% cng sut lnh ca dn nng (OU) thng qua thay i tc quay ca ng c nh b bin tn. H thng c kh nng t ng ho cao v c th phn chia th nh cc ph n h thng hot ng c lp m khng nh hng ti hiu qu s dng nng lng. Nh b iu khin trung tm m ngi vn hnh hon ton c th ng hoc ngt cho nhng khu vc cn hoc khng c n iu ho khng kh, v vy hiu qu tit kim in trong qu trnh vn hnh t c rt cao. Ngoi ra vic la chn gii php HKK cn ph thuc v o th i gian s dng, y u cu v l m mt hoc si m Qua nghin cu, phn tch c th a ra mt s nh hng c bn cho cc gii php thit k tit ki m nng lng h thng HKK nh sau: - V i h thng HKK c thi gian s dng t 5 15 nm c th lp my HKK gii nhit gi dng c c b hoc h thng VRV c cng sut lnh n 100TR (tn lnh); - V i h thng HKK c thi gian s dng 15 30 nm nn lp t h thng HKK trung tm kiu chiller hoc VRV c cng sut ln. Nn u tin s dng chiller gii nhit bng nc hoc li tm c s dng bin tn; - Khi h thng HKKc ch si m th nn s dng my lnh c bm nhit (heatpump chiller) khng nn s dng in trc tip cho mc ch si m; - Khi h thng HKK c ch kh m nn s dng my lnh thu hi nhit (heatrecovery chiller) c th cung cp nc nng s em li hiu qu tit kim nng lng; - i vi cc khch sn khi c nhu cu HKK v cp nc nng nn s dng t hp my lnh v bm nhi t s cho hiu qu cao v tit kim nng lng; - i vi cc cng trnh c cng su t lnh rt ln tr n 10.000TR nn s dng my lnh hp th trong t hp cp in Nhi t L nh s cho hi u qu cao v tit kim nng lng. 3.2 La chn thit b v cng ngh ph hp Ngoi vi c la chn gii php thi t k h thng HKK ph hp vi tng th loi cng trnh nh nu, vi c la chn thit b v cng ngh ph h p cng mang li hiu qu tit kim nng lng cao. Hi n nay Vit Nam v ang s dng hu ht cc chng loi thit b HKK c tr n th gii. Cc th h my lnh mi ang c nhiu u im v mt s dng nng lng. Cc ch s nh gi v hiu qu nng lng ca thit b lnh khi chy 100% ti iu kin vn h nh tiu chu n ang s dng ph bin hin nay bao gm: - Ch s hiu qu COP ( coefficient of performance). COP = Cng sut lnh/ tng cng sut in ti u th (kW lnh/ kW in); - Ch s hiu qu nng lng EER (energy efficiency ratio); EER = Cng su t lnh/ tng cng sut in ti u th (kW lnh/ kW in); - Ch s ti u th in PIC ( power input capacity; PIC = T ng cng sut in ti u th /Cng sut lnh (kW in/kW lnh). tit kim nng lng cho thit b lnh, u tin la chn cc loi thit b c ch s COP cao ho c ch s ti u th in PIC thp. Di y gii thiu ch s hiu qu nng lng ca mt s loi my lnh ph bin hin nay. Bng 1. Ch s hiu qu nng lng ca mt s loi my lnh TT 1 Lo i my lnh My lm l nh trc tip My nn xon c(Scroll) R22 COP kW l/ kW 3,0 3,3 PIC kW /TR 1,17 1,06 iu kin vn h nh - my nn chy 100% ti o - tn = 35 C - tkh v tt trong nh 27/19 o C Ch 100% ti - Ch 100% ti

2 3

My l nh kiu VRV R22 v R410 Chiller gi i nhit gi my nn

3,2 3,3 2,88 2,95

1,06 1,22 1,19

- tn = 35 o C - Nhi t nc lnh 6,7 o C 4 Chiller gi i nhit gi my nn - Ch 100% ti 3,14 3,22 1,12 1,09 o trc vt R134a - tn = 35 C - Nhi t nc lnh 6,7 o C 5 Chiller gi i nhit nc - Ch 100% ti - My nn tr c vt kp R22 - Nhi t nc l m mt 4,62 4,75 0,76 0,74 o - My nn tr c vt n R134a 29,4 C 5,86 6,27 0,6 0,56 - Nhi t nc lnh 6,7 o C 6 Chiller gi i nhit nc - Ch 100% v 50% t i - My nn li tm chy 100% ti 5,86 0,6 - Nhi t nc v o bnh o o - My nn li tm chy 50% ti ngng 32 C18 C o Mi cht lnh R134a/R123 10,0 0,35 - Nhi t nc lnh 7 C xc nh mc ti u th in ca my lnh c th l lo i my chiller c th dng phng php tnh ton theo tiu chu n ARI ca M xc nh mc ti u th in trung bnh n m. Trong thc t h th ng HKK khng ch c chiller m cn s dng nhiu loi my lnh trc tip khc v trong h th ng HKK s dng chiller cng c n c nhi u thit b b sung khc nh bm nc lnh, bm nc gi i nhit, thp gii nhit, AHU, FCU V vy nh gi ng tiu th in trong h thng HKK c th s dng cng thc tng qut sau: xo n c R22
n n

EC=

i1

Qoi(IPLV) i.hi.k+

i1

Pi.hi.k (kWh/nm) (5)

Trong : EC m c tiu th in ca h thng HKK trong mt nm; Qoi cng sut lnh ca chiller th i (TR); (IPLV)i tr s ti u th in trung bnh nm ca chiller th i (kW/TR); hi thi lng vn h nh c a chiller th i (h); k h s khng ng thi; Pi cng su t in ca thit b ph th i (kW); N s lng thit b c trong h thng. Trong cng thc tr n tr s (IPLV) thng c cc nh s n xut chiller cung cp, cc i lng Q v P cng tng t nh vy. gim mc ti u th in ca h thng HKK trc ht ta phi la chn ch ng lo i thit b ph hp vi cng sut yu c u, chn loi my lnh c ch s IPLV hiu qu v quan tr ng hn cn chn cng ngh bin tn iu khin cng sut lnh, cng sut bm v qut ph h p vi ph ti lnh ca cng trnh. Vic p dng cng ngh bi n t n iu khin v cp cng sut l 10 n 100% ti l r t hu ch trong vic tit kim nng lng. i vi cc cng trnh c quy m l n khuyn khch lp t h thng thit b thng gi thu hi nhit ti s dng nhit tha, tng hiu qu tit kim nng lng. Mt v d c th l vic p dng bin tn iu khin bm nc ti khch sn Daewoo (H Ni) mang li hiu qu tit kim in rt cao. Trong h thng HKK ca cng trnh ny, tng lng tiu th in ca h thng bm bng khong 80% lng tiu th in ca h thng HKK. Nu s dng bin tn (VSD) iu khin bm th c th khc phc c tnh trng chy non ti ca cc bm li tm v c th gim c 2050% tiu th in nng. Theo s liu thng k khch sn Daewoo, sau khi lp bin tn tiu th in vo nhng thng cui nm c th gim c trn 60%. Bng 2. Ti t kim in sau khi lp bin tn cho bm nc trong h thng HKK ti Khch sn Daewoo - H N i Th i gian 9/2000 10/2000 Tiu th in trc khi lp bin tn (KW) 105651 100752 Tiu th in sau khi l p bi n tn (KW) 40997 37350 Lng tit kim in (KW) 64654 63412 T l tit kim in (%) 61,2 62,9

11/2000

105651

31880

73771

69,8

4. Gii php tit kim nng lng trong qu trnh thi cng c im ca tt c cc h t h ng HKK trung tm cho cng tr nh xy dng c quy m ln l cc thi t b lnh, thit b x l khng kh (AHU) h thng bm nc lnh u nm khu vc b n ngoi cc khng gian c n l m mt, v v y cn phi c h thng ng ng dn cht ti lnh n ni c yu c u , c th l ng ng dn khng kh, c th l ng ng dn nc l nh hoc ng ng dn mi cht lnh. trnh mt nhit trong qu trnh vn chuyn cht ti lnh cn thit phi bc cch nhit cho cc lo i ng ng . Cng tc bc cch nhit cc loi ng ng ng v hay khng c nh hng r t nhiu ti hiu qu s dng nng lng khi vn hnh h thng iu ho khng kh. Chnh v v y trong qu trnh thi cng h thng ng ng dn cht ti lnh cn tun th nghi m ng t cc y u c u v bc l p cch nhit cho ng ng. Khi cc lp cch nhit khng c bc kn kht cho c h thng, k c cc van, cc ph kin trn ng ng, cc mi ni hoc bc khng dy, khng loi tr ht cc cu nhit, cu m th ngoi vic tn tht nhit cn gy ra cc hi n tng ng sng lm h hi dn dn ton b lp vt liu cch nhit. Mt v d thc t v tiu tn in nng cho cng tc bc cch nhit khng ng l h thng HKK trung tm ti cng trnh nh lu tr trung ng s 9 Nguyn Cnh Chn. trong qu trnh kho st tm nguyn nhn gy ra ng sng ti mt s khu vc c h thng ng ng dn khng kh lnh, dn nc lnh i qua chng ti thy rng vic bc cch nhit cho h thng ng ng lnh khng m bo v khng ng k thut. Cc mi ni khng c x l kn kht, cc van, ty van v cc ph kin khc khng c bc cch nhit v vy ti cc v tr ny thng xuyn xy ra ng sng thnh nc, sau nc ngm dn vo lp bng thu tinh cch nhit v lm suy gim nghi m trng kh nng cch nhit cho ton b h thng ng ng. Vic ci to, bc li lp cch nhit mt cch ton di n theo phng n do Vin KHCN Xy dng xut loi tr c ton b hin tng ng sng, m bo c cng sut ca thit b duy tr ch nhit m cho cc kho bo qun ng thi gim ng k in nng ti u th so vi trc khi ci to. 5. Gii php tit kim nng lng trong qu trnh vn hnh v s dng Cc gii php nng cao hiu qu s dng, tit kim nng lng cho h thng HKK v thng gi bao gm: T chc qun l, vn hnh h p l theo nhu cu s dng; C ch bo tr cho ton b h thng sau khi a vo s dng; nh k l m v sinh cc dn trao i nhit, c bit cc gi n nng gi i nhit gi khng bm bi bn l m gi m kh nngtrao i nhit ca gin; m bo cht lng nc mm cho cc h thng my lnh gii nhit nc (water chiller); Khng nhit trong phng lnh di mc cn thit v khi nhi t bay hi gim 1o C th in nng tiu tn c tnh tng hn 1%; Duy tu, sa cha cc hng hc kp thi trnh tn tht nng lng cho h thng; C n c i ng nhn vi n chuyn nghi p qun l v v n hnh m t cch ng n, khoa hc h thng HKK v thng gi trong cc cng trnh s mang li hiu qu cao v tit kim nng lng.

6. Kt lun t c hiu qu tit kim nng lng cho h thng HKK v thng gi trong cc cng trnh xy dng cn thc hin tng hp cc gii php t cc khu: thit k kin trc, kt cu cc lp v bao che cng trnh, l a chn h thng HKK v thng gi, l a chn thit b lnh cho tng th loi cng trnh n khu thi cng, v cu i cng l giai on vn hnh, khai thc; Gi i php thit k tit kim nng lng h thng HKK v thng gi c ngha quyt nh n vi c gim tiu hao nng lng cho ton b cng trnh. Ch t lng ca thit k ph thuc rt nhi u vo kinh nghi m v s sng to ca tc gi. Mt thit k hp l v khoa h c c th tit kim c khong 30% ti u th nng lng in trong cng trnh; Cc gi i php la chn thit b v cng ngh hp l cng mang li hiu qu cao v tit kim nng lng, cn khuyn khch p dng cc cng ngh mi nh bin tn, iu khin t ng ton b h thng, thit b thng gi thu hi nhitKinh nghim v thc t cho thy mt s to nh hi n nay Vi t Nam s dng HKK loi VRV c cng ngh bin tn v thi t bthng gi thu hi nhit t

1.

2. 3. 4.

5. 6. 7. 8.

c hiu qu tit kim in t 20 30% trong qu trmh khai thc s dng. Ngo i ra c n gim st, ki m tra cht ch cng tc bc cch nhit cho h thng ng ng, c ch bo tr, duy tu, s a ch a hng hc thng xuyn m bo khng b tht thot nng lng trong sut qu trnh khai thc s dng s em li li ch v tit kim nng lng tng th cho ton b cng trnh./. TI LIU THAM KHO NGUY N C TO N, T XUN H A. V n tit kim nng lng trong thit k s dng h thng iu ha khng kh. Tuyn tp bo co khoa hc hi tho to n Qu c ln I Ngnh l nh v iu ha khng kh Vi t Nam 10 -2006 . L NGUYN MINH. Ti t kim nng lng trong h thng iu ha khng kh trung tm. H i tho khoa hc ton Qu c ln I Ng nh l nh v iu ha khng kh Vi t Nam 10/2006. L NGUYN MINH. Phng php xc nh ti u th in ca chiller trong h thng iu h a khng kh trung tm cng su t ln. T p ch xy dng 7/ 2006. L NGUYN MIN H. Phng php nh gi tiu th in trong h thng iu ha khng kh cng su t ln. Tuy n tp bo co khoa hc, Hi tho khoa hc Quc gia Mi trng s c kh e; hiu qu nng lng trong xy dng; bin i kh hu 01- 2008. NIKOLA KALIANOV v cc c ng tc vin. Hng dn kho st nng lng hiu qu v c p ch ng nhn nng lng. Sphia, Bungari, 2006 (bn dch ting Vit, 2009). NIKOLA KALIANOV v cc c ng tc vi n. Tnh ton nng lng s dng nm trong cng trnh Sphia, Bungari, 2006 (b n dch ti ng Vit, 2009). Hng dn s dng nng lng hiu qu trong ng nh cng nghi p Chu . T i liu ca UNEP. ARI standard 550/590 1998 Arlington Virginia 22203.