The evaluation method of HVAC system s operation performance based on exergy flow analysis and DEA method

Transcription

1 The evaluaton method of HVAC system s operaton performance based on exergy flow analyss and DEA method Xng Fang, Xnqao Jn, Yonghua Zhu, Bo Fan Shangha Jao Tong Unversty, Chna

2 Overvew 1. Introducton 2. Descrpton of HVAC system 3. Evaluaton method 4. Ideal operaton level of HVAC system 5. Evaluaton of control strateges for HVAC

3 Introducton In evaluaton of operaton performance of HVAC system, ncreasng attenton s beng gven to thermodynamc analyss of HVAC systems. frst law of thermodynamcs energy cost, COP... Consders conservaton of energy second law of thermodynamcs exergy destructon, exergy effcency... Consders energy s qualty as well as quantty

4 The am of ths study s to establsh the benchmark of HVAC system based on exergy analyss, and propose the evaluaton method of operaton performance of system. HVAC model Exergy flow analyss exergy flow model Ideal operaton level optmzaton technques & DEA method Evaluaton ndex control perfect ndex (CPI) Evaluaton results control strateges

5 Descrpton of HVAC system An arport termnal s HVAC system s chosen as the studyng object, whch s located n Hakou, Chna. The smulaton model of HVAC system s buld n TRNSYS.

6 Confguraton of HVAC system: Buldng locaton Hakou, Chna Gross floor area 99,300m 2 Ar-condtoned area 67,950m 2 Number of floor 4 Operatng schedule 7:00 to 22:00 Coolng system Pump system Chllers Water-cooled The prmary pump, the secondary pump 4 unts rated capacty: T1,T2,T3:2461kW, Y4:4640kW nput power: T1,T2,T3:470kW, Y4:836kW Ar handlng system Desgn ndoor dry bulb temperature and relatve humdty Desgn outdoor dry bulb temperature and relatve humdty (summer) Desgn outdoor dry bulb temperature and relatve humdty (wnter) 40 AHUs, 202 FCUs 25, 55% 34.5, 60% 10, 85%

7 Evaluaton method 3.1 Exergy analyss D F P F Component D P The exergy effcency, exergy destructon rato and exergy cost dstrbuton rato are calculated as: P 1 100% 100% F k E, E ds, n P 1 k P * p, k * p, 100% F P d n n F 1 1 P 100% F : fuel flow of the th component; P : product flow of the th component;

8 3.2 Control perfect ndex (CPI ) CPI s used to measure the gap between actual operaton performance and deal operaton performance. CPI sys, j 1/ 1/ D D c sys, 0 sys, CPI sys,j : the CPI of HVAC system under j th operaton condton; D c sys,j D 0 sys,j : actual exergy destructon of HVAC system under j th operaton condton; : deal exergy destructon of HVAC system (the lowest exergy loss) under j th operaton condton.

9 3.3 DEA method In ths paper, we use DEA method to obtan the benchmark of HVAC system s operaton performance, the deal operaton performance. DEA s a non-parametrc technque used to measure the relatve effcency of decson makng unts (DMU) wth the same general objectves. DMU actual operaton performance v.s. optmal operaton performance under j th operaton condton.

10 Ideal operaton level of HVAC system based on DEA 4.1 Global optmzaton of HVAC for lowest exergy destructon The exergy flow model of the HVAC system: Component I : coolng towers and coolng water pumps; Component II~V : four chllers and chlled water pumps; Component VI : AHUs and secondary pumps.

11 Exergy balance equatons of the HVAC system: Y W E E W E E W E E ' " ' " ' tot I ct I II V II V II V VI VI VI E E E ' '' I II V E ' " II V VI Y W E W W E ' tot I ct II V VI VI Y tot : total exergy destructon of HVAC system; W : nput power of component ; E : outflow exergy of component ; E : nflow exergy of components

12 The objectve of global optmzaton T ct : outlet water temperature set-pont of the coolng tower; T ctwd_mn : mnmum temperature dfference between T chw_out and T chw_out ; Reset set-ponts and optmze PLR of HVAC system under constrants T chw_out : outlet chlled water temperature setpont of the chller; T sa : supply ar temperature set-pont of AHU; PLR : part load rato of chller PSO algorthm : total coolng load of chllers; Q ch_sum MnY f ( T, PLR, T, T ) tot ctw_ out _ set chw_ out _ set _ sa _ set T T T chw_ outmn chw_ out chw_ outmax T T T ctw_ outmn ctw_ out ctw_ outmax T T T ctw_ out mn wb _ out ctwd _mn f T T T ctw_ out mn wb _ out ctwd _ mn T T T sa mn sa sa max PLR mn PLR 1 Q ch_des, chller; : rated refrgeratng capacty of the th Obtan the lowest exergy destructon of the HVAC system under certan operaton condtons N Q PLRQ ch_ sum ch _ des, 1

13 4.2 Ideal operaton level of HVAC system The lowest exergy destructon of the HVAC system under dfferent operaton condtons DEA method The lowest exergy destructon of the HVAC system under all operaton condtons Ideal operaton level CPI sys, 1/ 1/ D D c sys, 0 sys, CPI can evaluate HVAC system s operaton performance under any operaton condton.

14 Evaluaton of control strateges for HVAC

15 5.1 Optmal control strateges for HVAC system Orgnal control strategy: (1) fxed set-ponts: T ct =30, T chw_out =7, T sa =14 (2) turns on chllers n a fxed sequence accordng to total coolng load. Optmal control strateges: (1) optmal supply chlled water temperature reset strategy (CHW strategy) MnJ functon( T ) chw, set chw, set 7 T 12 The objectve functon s used to obtan the mnmum total power consumpton of HVAC system.

16 (2) optmal load allocaton control strategy (Load Allocaton Strategy) The problem of Load Allocaton Strategy for HVAC s a nonlnear programmng problem wth hybrd constrants. Mnmze N CAP PLR P COP 1 X N CAPPLRX 1 1 Q CAPPLRX 0 1 Q PLRmn PLR 1 0 PLR X 1 CAP : refrgeratng capacty of the th chller; X : the on/off state of the th chller, 0 means off and 1 means on; PLR : PLR of the th chller; PLR mn =0.25; CL : the total coolng load of systems.

17 5.2 Results and dscusson Fgure shows the deal operaton level and three fronter lnes of HVAC system under Orgnal strategy, CHW strategy and Load Allocaton Strategy based on annual operatng data. the fronter lne of Load Allocaton Strategy s the hghest; the fronter lne of Orgnal strategy s the lowest ; the fronter lne of CHW strategy s n the mddle.

18 Accordng to the deal operaton level and three fronter lnes of HVAC system, the average value of CPI of each control strategy can be calculated. n stra, stra, CPIave CPI j / n j1 comparng to Orgnal Strategy, CHW Strategy mproves the CPI of the total system from 0.77 to 0.78; Load Allocaton Strategy mproves the CPI of HVAC system from 0.77 to Load Allocaton Strategy > CHW Strategy > Orgnal Strategy

19 Conclusons a) Exergy analyss s appled n the smulaton model of HVAC system; b) Defne the evaluaton ndex of CPI to measure the gap between actual operaton performance and deal operaton performance; c) Global optmzaton s used to obtan the lowest exergy destructon of HVAC under dfferent operaton condtons, DEA method then helps to ascertan the deal operaton level; d) Apply optmal control strateges (CHW strategy and Load Allocaton Strategy) n HVAC system, the average value of CPI of each strategy wll gve reasonable assessments: Load Allocaton Strategy s better than CHW strategy and Orgnal strategy.

20 Thank you!