Tap chi Khoa hoc va Cong nghe 103 (2014) 064-068
Study ofthe Energy Saving Possibility at the Chiller Air Conditioning System ofthe National Assembly House in Hanoi Nghien cuu kha nang tiet kiem nang lirang ciia he thong dieu hoa khong khi Chiller
cua Nha Quoc Hoi tai Ha Npi
Nguyen Due Loi
Hanoi University of Science and Technology - No I, Dai Co Viet Sir., Hai Ba Trung, Ha Noi, Viet Nam Received: March 11, 2014, accepted: October 28, 2014
Abstract
Air Conditioning System (ACS) Is the greatest energy consumer In the buildings in Vietnam In SumrDer it consumes ca. 50-i- 80% the energy bill. The study of energy saving for the ACS Is therefore very necessary and important Not only scientists but also leaders at all levels, particulariy In sectors energy management and environment pays pecial attention to it. The central airconditioning chiller system of National Assembly House (NAH) in Hanoi designed by the German company GMP- IL uses Dry Cooler (DC) to cool the boi water coming out of the condenser According to our calculations, the use of DC by GMP-IL makes the power consumption increased by 53.7 % compared with the use of traditional cooling towers (CT). In other words when using CT, the energy saving can reach 1020 kWh per hour full-load operation,equivaler)t to about 2 million kWh per year and reduce CO2 emissions around 1380 tones into the atmosphere per year Key words' ACS, Chiller, CT, DC, COP. PIC, Energy saving.
Tom tat
He thong di^u hoa (ACS) li ho tieu thu nang Iwgng l&n nhat trong cic tda nhi t$i Vi$t Nam. Trong miia hi no tieu thu tw 50 - 80% hoa dan tiin dien. Do do, viec nghien cOv tiit kl^m ning Iwgng cho h$ thong dieu hoa khdng khi la rit cin thiit va quan trong. Khdng chi cac nhi khoa hgc ma lanh d^o cic cap, d$c bi$t 1^
lanh dao trong ITnh vi/c quan ly nang iwgng va moi trwang die biit quan tam chu y din nd. Hp thong dieu hoa khdng khi trung tam cua Nha Qudc Hdi (NAH) dwac cdng ty Dwc GMP- IL thiit ki, sCe dyng thip giii nhiet kho DC di lim mat nwac nong ra khoi binh ngung. Theo tinh toan cua chCing tdi, viic sii dyng DC cila GI^P-IL da lam cho diin nang tiiu thu tang them 53,7 % so vdi viic sir dung thip gial nhiit truyin thdng (CT). Noi each khac niu sw dung CT truyin thing co the tiet kiim 1020 kWh mdi gid ho^t dgng day til, twang dwang khoang 2 triiu kWh mdi nam vi giam phit thai khoang 1380 tan COz vio khi quyin mdi nim.
TLF khoa: He thdng dieu hoa khong khi. Chiller, Thap giai nhiet, Thap giai nhi^t kh6, Higu qua n^ng lu'gng, PIC, Tilt kiem nang lifo-ng
Nomenclature Governments andthe National Assembly of Viettiam t«,i' condenser inlet water temperature,"C; havea lot of research, policy, guidelines and laws for t . , : condenser outlet water temperat„re,°C; ""'^^ '^'"'"'^ "^ " " ' ' "•"^ ''"'"^ P ' - ' ' ^ ' AHU/FCU: Air Handling Unit/Fan Coil Umt; ,^ J * " ' * = ^ ' = ^ ° ' ' '^^J^ff,}'' ^r"'' ' ' " ' ' ^ ^ f .^J the German company GMP-ILwill consump 53,7%
COP: Coefficient of Performance; more energy than conventional systems. This paper PIC: Power Input per Capacity - 1/COP ™ " T ^ ^ ^ " " ' ' P " ' " ' " " ' * " ""^ 5 " ^ ? * ' • " ' " '
"^ -^ to cool the hot condenser water, is the culpnt causing 1. Introduction the waste of energy, reduced safety, reliability and
r, • . , longevity ofthe equipments.
Saving energy is a topical issue not only
because of the exhaustion of the primary energy 2. Design conditions
source, but also ofthe environmental pollution caused ^ . . .-.. ,, , ,=, , , / L„ „„;„„• * • „ 1, . , ,- Outdoor conditions according to the P ' eve of byemissionsofgreenhousegases, due to the climate v,«t«.™ <it A A ^ ^ c - n n i r t r ^ i V ^--c e „i, c _^L - , ,- . , . Viemam Standard 5687:2010 [61 for ACS for change. Earth warming, natural disasters ragme. Not ^. , " J,"^ „ „ J , , „ . „, nni., V7:»f„-,™ 1, . 1 .u ^ • L , j summer: outdoor temperature 37.8 °C, RH 53.4 % only Vietnam but also other countties m the world „ „ , , ,„. , „ „ „ ^ ^o i or- ., r- • j are taMng a c t o n to protect our . a . i l e Ear... The ^ ^ ^ ^ T ^ ^ ^ ^ , ^ ^ ^ : : : ^ r ^ ' Corresponding Author, Tel (+84) 982.288.995
Email' [email protected]
"C.
Tap chi Khoa h^c v^ Cong nghe 103 (2014) 064-068 3. Calculation the ACS with D C (designed by
GMP-IL-Germany)
Fig. 1 introduces the principles structure and working of ACS with DC and shows temperature variations in the condenser and DC designed hy GMP-IL-Germany. Chilled water temperature entering the evaporator 14 "C, leaving 8 "C. Hot water from condenser will be cooled by DC. The water temperature leaving the condenser 50 "C and the water temperature entering the condenser 45 °C were chosen by air temperature 38 "C. Condensing heat is emitted to tbe open air through the DC by the cooling water circulation with water pump. Due to very high pressure loss in the DC, primary and secondary cooling water pumps are necessary.
The ACS includes the following equipment: 8 water cooled water chillers, screw compressor, refrigerant RI34a, the cooling capacity of each chiller 1060 kW, the total cooling capacity of 8 chillers 8480 kW at about mention operating conditions; total
effective power of 8 chillers: Pi = 8x277.4 = 2219.2 kW, Winter heating capacity is 840 kW. Heating load is equal only ca. 10 % of cooling load. The total input powers ofdifferent equipments are;
- Pnmary secondary chilled water pumps:
P2 = 8 x l l kW + 4x15 k W = 148 kW.
- Fan motors of AHU and FCU: P3 = 367 kW - Primary and secondary cooling water pumps:
P4 = Sxl I kW+8x22 kW = 264 kW.
- Fan motors of 24 Dry Cooler for 8 chiller:
P5= 24 X 6 fans x 0.6 kW = 86.4 kW.
We may see m Fig. I that the cooling process consists of two stages, the first, condensing heat is transfers from refrigerant to the water in the condenser, and then fransfers from water to the air m the DC. Therefore the condensing outlet water temperature should be 50 "C.
Table 1. Parameter and energy efficiency compared between ACS with CT and DC
Category
Outdoor conditions
twi: condenser inlet water temperature, *'C tw2: condenser outlet water teinperature, °C Indoor conditions
COP
Meet the requirements of Construction Regulation QCXDVN 09:2005 with COP„„ - 5,50
PIC (- 1/COP)
% of energy consumption Total coolmg Capacity Qo Effective Power Pe Total effective Power Installed Power Total Installed Power Cooling water pump
Primary Secondary FtU/AHU
Chilled water pump
Primary Secondary DC fans
CTfans
Total input power full load Aimual energy saving Annual reduction of CO2 emission
Unit Cooling Tower (CT)
Dry Cooler (DC)
Energy Saving The P'level of Vietaam Standard TCVN 5687:2010: outdoor temperature 37.8 °C, RH 53.4 % and wet temperature 29.1 °C
°C
•c
chilled wat kW4W
kW/kW
% kW kW kW kW kW kW kW kW kW kW kW kW kW kWh/a kg/a
32 37 er temperature leav
5.93 Yes COP=5.93 0.1686 100%
7x1211.4-8480 204.3 8480/5.93=1430 260 7x260=(1820) 7x11-77 0 367 7x11-77 7x7.5 = 52.5 0 7x5.5 = 38.5 2042 4,250,000 2,760,000
45 50
ng the evaporator 1 3.86 No COP-3.86 0.2591 153.7%
8x1060=8480 277.4 8480/3.86=2197 280 8x280=(2240) 8x11 - 8 8 8x22=176 367 8x11 = 88 4x15 = 60 86 0 3062 6,370,000 4,140,000
°C
767 (420)
11 176 0
11
7.5
47.5
1020
2,120,000
1,380,000
Tap chi Khoa hoc va Cong ngh§ 103 (2014) 064-468
S
Retrig
HE in C l o «
it-p^
Outside rant tk =
condense
H E
«
55-C
-^
n Dry Cooler 1Fig. 1, Chiller's ACS using D C
l-O-t. _B1
Refrigerant \^=i,^'^C•
Open W a t e r Loop '
Fig. 2. Chiller's ACS using CT 4. Calculation the ACS with C T
Fig, 2 introduces the principles structure and working of traditional ACS with CT and shows temperature variations in the condenser. In the CT the cooling water is sprayed directly into the air. The water is cooled effectively by evaporation of a part of water mto the air. Calculation with the same outdoor temperature 37.8 °C, RH 53.4 % and wet temperature 29.1 °C, the condensing inlet and out let water temperature are 32 "C, 37 °C. This result is due to much more effective heat and mass fransfer in the CT. The total effective power Pi = 7 x 204.3 = 1430 kW, The total power of chilled water pumps P2 ^ 129.5 kW, The total power of AHU/FCU is the same P3 = 367 kW. The total fan motor's power Ps = 38.5 kW.The other advantage of this system is due to the small pressure loss through the CT the secondary cooling water pump is not necessary, which could saves 8 secondary pumps x 22 kW = 176 kW and P4 = 88 kW only (see Table 1).
5. Comparative figures Coefficient of Performance COP:
Fig. 3 infroduces the chiller's COP of Trane [13]
and of Daikin [14] The Trane's chillers of type RTHD D2 G2 GI will be installed in NAH.
COP - Qo / Pe, kW/kW, Qo: Cooling capacity ofthe chiller, kW;
Pe; Effective Power (required Power on the axis of compressor), kW.
According to the catalog of Trane, the COP of the chiller = 3.86 at the designed conditions (condensing water outlet temperature t«,2 — 50 "C and chilled water outlet temperature tc2 = 8 "C), The straight line on the right side presents the COP performances of Trane's chiller. The straight line on the left side presents the COP performances of Daikin's chiller [13].
The obtained results are reliable. It totally corresponds to the variation of Daikin's chiller but al a higher level.
O t h e r P a r a m e t e r s : Table I introduces the parameters compared between ACS with CT and DC about the energy consumption and energy savings achieved. The comparative figures are based on the same about presented outdoor conditions 37.8 "C, RH 53.4 % and indoor condition (chilled outlet water temperature 8 °C).
Effective power of chiller: Pe = Qo / COP.
Comparing ACS using CT and DC, effective power difference between two cases is 2197 - 1430 = 767 kW.
Integrated Part Load Value (IPLV) can be calculated according to QCXDVN 09: 2013 [2]:
IPLV = O.OIA + 0.42B + 0.45C + 0.12D
Tap chi Khoa hoc va Cong nghe 103 (2014) 064-068
COP
6
b
3
6,25
r X5;93 "1 "!
\ \ 5 , 4 5 workinarango
^ ^ X , Trane 5,15\ \ , -
' ^ C ^ C ~
- - \ ^ \ 4 , 6 6
_ \ \
3.58'
j ; 35 37 40 45 t ^ 50°C
Condensing water outlet temperature
Fig. 3. COP of Daikin's and Trane's chiller where, A- COP at 100 % load; B- COP at 75 % load;
C- COP at 50 % load and D- COP at 25 % load. The numbers 0.01; 0.42; 0.45 and 0.12 are the annual operating time ratio. A, B, C, D can be taken irom [13] and [14], Assuming that ACS works 5 days/week and 10 hours/ day, the consuming and saving energy should be calculated.
6. Discussion
- Working range: On the nameplate of the Trane's chiller, the maximal motor power Pmaxis 271 kW. But the effective required Power Pe is 277.4 kW.
Normally Pmax must be greater than Pe from 20 to 30
% in case of too great cooling capacity, the evaporation temperature is too high, and even when the power fluctuates. So that we want to confirm that the operation of the chiller at the designed condition with condensing outlet water temperature 50 °C is impossible. It is out of working range of Trane's chillers (see Fig. 3),
Energy savings by the work of the compressors: Fig. 4 presents the effective power (or input power) Pe of compressor depends on the condenser outlet water temperature, by full load capacity 1060 kW (the solid line). At condenser outlet water temperature tw2 = 37 °C, Pe = 180 kW, but at tw2 = 50 "C, Pe - 277,4 kW. To be able to save more energy, we can use centrifugal chillers with COP = 6.6 for example. In this case, with the same cooling capacity 1060 kW, the required compressor's power Pe = 1060/ 6.6 = 161 kW at tw2 = 37 "C (the dashed Ime in Fig. 4). The energy saving is much
300 Pg kW
200
150
ion
;
f71 ^ '
!
\^X 9°/^
.-
^ 2 2 9 2 7 7 4 ,
35 37 40 45 t ^ . t 50 Condenser oull el water temperature
Fig. 4. Effective power of compressor higher than that of screw chiller,
- Energy savings at other appliances: Saving at the condenser water pumps 187 kW, chilled water pump 18.5, at the dry cooler fans: 47.5 kW, Total energy saving is 1020 kW (see Table 1).
We know that the ACS is the largest energy consumer of the buildings. Investment was high (about 500 bilhons VND for ACS, ca. 24 millions USD), but energy to operate it should be many times higher. According to [10], if all lifetime of ACS is considered, the initial investment accounted for 4-10
%, maintenance costs accounted for 1-2 % and operating cost 90-95 %.
Thus, the operating cost is from 10 to 25 times higher than the investment. With the lowest rate 10, the operatmg cost should be about 500 x 10 = 5.000 billion for all of its operatmg life. Energy saving is then about 1670 billions VND, Make the same calculation with installed power; we can determine the saving on investment about 100 billions VND.
- Compared to [13] and [14] also found that the data in this calculation corresponds completelly. The calculation of the energy efficiency results for Trane's chiller is only slightly different because the COPs are different 3.86 by Trane and 3.58 by Daikin.
7. Conclusions
- The operation of chiller is impossible at the designed operation when using of DC,
- The use of DC makes the condensing pressure
Tap chi Khoa h^c va Cong nghe 103 (2014) 064-068 always 1.4 times higher. This means that chiller must
operate in much more severe conditions and the leakage, even bursting abilities constantly exist. The oil temperature is very high too, the oil is quickly ageing, and the lubrication becomes worse. The reliability, the safety and the lifetime of chillers and of the whole system decrease. Nobody knows how it's long-time affection to the ACS.
- The use of DC is contrary to the Construction Regulations in Vietnam issued by the Ministry of Constmction (QCXDVN 09:2009 now 2013) because COP = 3.86 is much smaller than 5.50 required.
- The hybrid schemes presented in [16] may be assured the space heating and cooling effectively for NAH.
- Moreover, the replacement of DCs by TCs is very easy, simple, does not affect other systems and does not slow down the progress ofthe work.
- The NAH is the symbol of the Nation. It should become a symbol of advanced science and technology, green buildings and environmentelly friendly too.
Because of these reasons, we have repeatedly proposed to replace DCs by CTs. It just saves electricity, h will reduce summer stress of electricity, it also helps reduce greenhouse gas emissions and protect our fragile Earth.
[1] NguyenDuc Loi: Dry cooler - Energy Killer of Chiller System in the National Assembly House in Hanoi, Proceeding International Conference Environmental and Spatial Planing in Vietnam, Hanoi December, (2012)16-22.
[2] B9 Xay D\mg, Quy chu&i Xay dung Viet nam QCXDVN 09:2013, Cac cong tiinh xay dung sii dung nang lirong co hieu qua. Nxb Xay dung 2005 (Ministry of Construction, Construction Regulations in Vietnam, the buildings usmg energy efficient.
Publisher of Construction 2013),
[3] TCVN 5687-1992 Thong gio, digu hoa khong khi, suoi am, Nxb Xay dung 1992 (Vietnam Standard:
Ventilation, Air-Conditioning, Heating, Publishers of Construction 1992).
[4] GB 50019-2003 National Standard of the People's Republic of China' Code for Design of Heating Ventilation and Air Conditioning.
[5] TCVN 5687-2010 Thong gio va Digu hoa kh6ng khi, Nxb Xay dung 2010 (Vietnam Standard: Ventilation, Air-conditionmg, Heating, Publisher of Construction 2010).
[6] Nghi dinh so 102/2003/NB-CP: Su dung nSng lirgng tiet kiem va hi$u qua (Decree ofthe Government No.
102/2003/ND-CP: Use energy saving and eOicieiicy), [7] Nghi djnh 56 21/2011/ND-CP' Sii- dung nSng iir^mg tiet kiem va hi?u qua (Decree ofthe Government No, 102/2003/ND-CP: Use energy saving and efficiency).
[8] Luat Sir dyng Nang lugng Tiet kiem va Hi?u qua s6 50/2010/QH12 (National Assembly of Vietnam, Law on Efficiency Use of Energy of Vietnam).
[9] Bo Xay dung; Quy chudn Xay dung Vi?t nam, T^p 1,2, Nha Xu3t ban Xay Dimg, 2007 (Ministry of Construction: Construction Regulations in Vietnam Vol.1 and 2),
[10] Dg tai NCKH, B2008-01-I54 Pham Hoang Luong va cong sir: Nang cao Hi?u qua Su dung Nang lupng.
giam phat thai khi nha kinh trong cac toa nha cao tiiig a Viet nam, DHBK 6/2012 (Research Document, Improving energy efficiency, reducing greenhouse gas emissions in die high-rise buildings in Vietnam) [11] Nghi dinh 75/2011/ND-CP. Xii phat vi pham hanh
chinh ve sii dyng nang luong tiet kiem va hi^u qua (Decree ofthe Government' Administrative sanctions on the use of energy saving and efficiency).
[12] Nguyen Diic Lgi. Dan giai nhiet kho (Dry Cooler) mgt bien tucmg nguy hiem cua dieu boa khong khi T^p chi Xay D\mg BoXay Dung 5/2012 tr. 62-64 (Dry Cooler, a dangerous disguise of air conditioning chiller systems. Joumal of Constmction Engineering, Ministry of Construction, No. 5/2012 p. 62-64).
[13] Trane' Catalog Water Cooled Screw Compressor Senes R(TM)' RTHD D2 G2 Gl.
[14] Daikin' Catalog Water Cooled Chiller Single Screw CUW40-480D5Y(E5Y).
[15] Nguyen Due Loi' Senous Disadvantages ofthe Dry Cooler for Water Cooled Water Chiller. Proceeding of the 5th Asean AUN/SEED-Net Regional Conference on New/Renewable Energy on September 26-27,2012 at HUST Hanoi Vietnam.
[16] Nguyin Due Ltjv. Bi xuit sa d6 lai TKNL dl lam lanh va sudi am voi chiller giai nhiet nude. Tap chi Nang luong Nhiet s6 116, 3/2014 tr 13-17 (Proposed energy saving hybrid scheme of water cooled water chiller for space heating and coolmg).