Thermo-economic assessment and application of CCHP system with dehumidification and hybrid refrigeration

Accepted Manuscript Thermo-economic assessment and application of CCHP system with dehumidification and hybrid refrigeration Runhua Jiang, Frank G.F. Qin, Huibin Yin, Minlin Yang, Yongjun Xu PII: DOI: Reference:

S1359-4311(17)32631-5 http://dx.doi.org/10.1016/j.applthermaleng.2017.07.048 ATE 10715

To appear in:

Applied Thermal Engineering

Received Date: Revised Date: Accepted Date:

20 April 2017 16 June 2017 5 July 2017

Please cite this article as: R. Jiang, F.G.F. Qin, H. Yin, M. Yang, Y. Xu, Thermo-economic assessment and application of CCHP system with dehumidification and hybrid refrigeration, Applied Thermal Engineering (2017), doi: http://dx.doi.org/10.1016/j.applthermaleng.2017.07.048

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Thermo-economic assessment and application of CCHP system with dehumidification and hybrid refrigeration Runhua Jiang*, Frank G.F. Qin*, Huibin Yin, Minlin Yang, Yongjun Xu Guangdong Provincial Key laboratory of Distributed Energy Systems, School of Chemical Engineering and Energy Technology, Dongguan University of Technology, Dongguan 523808, China Abstract: Combined cooling, heating and power (CCHP) systems have widely theoretical researched and practical applied to solve the energy and environment problems. The schemes of CCHP systems are important to select, which can best satisfy users demand with high thermal economy and low pollutant emission. In this paper, a novel scheme of CCHP system with dehumidification and hybrid refrigeration is proposed, where an internal combustion engine (ICE) is utilized as a prime mover. The absorption dehumidifier is driven by jacket water of ICE to provide dehumidification, and hybrid refrigeration system is consisted of absorption chiller and electric compression refrigerator. A thermo-economic model of the CCHP system is established, and a comprehensive evaluation criteria is proposed as objective function. The analytic hierarchy process and the constrained nonlinear programming solution are employed to optimize design and operation strategy of the ICE-CCHP system. This research discuss its application in a case: the CCHP system apply to following the electric load (FEL), and the optimum equipment capacity of the CCHP system is obtained. Furthermore, the sensitivity analysis is carried out to assess effects on performance of the CCHP system. Keywords: ICE-CCHP system, dehumidification, hybrid refrigeration, thermo-economic model, comprehensive evaluation criteria, sensitivity analysis

Nomenclature Abbreviation CCHP

combined cooling, heating and power

ICE

internal combustion engine

LHV

lower heating value

Symbols APER

annual primary energy rate

APESR

annual primary energy saving ratio

ATC

annual total cost ($/year)

ATCSR

annual total cost saving ratio

C

annual cost ($/year)

CEC

comprehensive evaluation criteria

COP

coefficient of performance

1

F

function

P

power (kW)

Q

heat/cooling/dehumidification load (kW)

V

rate of fuel consumption volume (m3/s)

c

cost per kW($/kW)

j

jth day of a year

t

tth hour of a day

k

interest rate

n

life cycle of device(years)

α

fraction of waste heat recovery from flue gas driven absorption chiller

β

fraction of waste heat recovery from flue gas to meet the heat demand of domestic hot water

η

efficiency

λ

waste heat recovery coefficient

ν

price($)

ω

weighting factor

Subscripts ab

auxiliary burner

ac

absorption chiller

b

burner

c

cooling

d

dehumidification

e

economic

el

electricity

elc

electric compression refrigerator

f

fuel

fg

flue gas

grid

electric grid

h

domestic hot water

he

heat exchanger

i

investment cost

jw

jacket water

m

maintenance cost

obj

objective

2

t

thermodynamic

r

recovery

sg

separate generation system

u

users

1

start day/time

2

end day/time

1. Introduction CCHP (combined cooling, heating and power) systems with advantages such as energy saving, economization and pollutant emission reduction have aroused extensive attention [1-3]. The internal combustion engine (ICE) applied to CCHP system is one of the most widely used technologies, which have the advantages of low capital cost, high reliability and relatively good partial load efficiency. There are amount of research about scheme, design, optimization and evaluation of ICE-CCHP systems

[4-9]

. Hycienth I. Onovwiona presented a parametric model that could be used

in the design and techno-economic evaluation of ICE-CHP system for residential use

[10]

. Mehdi

Farahnak et al. investigated feasibility of employing ICE-CCHP systems to meet the energy demand for various buildings sizes. An optimization algorithm was developed to find the best operation point of the power generation unit at minimum energy cost [11]. Pooya Arbabi et al. offered a general procedure to design and select ICE of CCHP system. It also provide a numerical model to estimate the power and heat economically and technically [12]. Giovanni Angrisani et al. carried out experimental analysis on an integrated scheme combined Micro-CHP system with a desiccant HVAC system. The desiccant wheel was driven by heat from jacket water and flue gas [13]

. Guillermo Rey et al. studied micro ICE-CCHP system with heat recovery based on a Honda

gas engine, and the system incorporated a heat pump to meet the need for air conditioning [14]. Sandeep M.Nayak et al. focused on the design, installation and experimental analysis of ICE-CHP with a liquid desiccant dehumidification system. The research discussed the various aspects involved in heat recovery loop design and electrical interconnection with building load [15]. Though there are so many research focused on ICE-CCHP, little investigation combined actual demand of users and comprehensive thermo-economic mathematical model to optimal design and operation strategy, have been done on performance of the system. In order to further improve schemes of CCHP systems, and more use waste heat generated by flue gas and jacket water of ICE, 3

this paper proposes a novel scheme of an ICE-CCHP system with dehumidification and hybrid refrigeration, which consider actual demand of users. A thermo-economic mathematical model of the CCHP system is established, and a comprehensive evaluation criteria is proposed as objective function to assess the performance of the CCHP system. The analytic hierarchy process and constrained nonlinear programming solution are employed to optimize design and operation strategy. This research will be supplied guide line for ICE-CCHP system, it will have a great influence on the optimization and design of CCHP system. 2

System overview and model

2.1 Flow chart of system Fig.1 shows the flow chart of the ICE-CCHP system with dehumidification and hybrid refrigeration. The prime mover is a gas ICE, which meets the electricity demand of the users. Flue gas of ICE is fed to the absorption chiller to recover the waste heat and provide cooling for the users. Then flue gas discharged by the absorption chiller enters the heat exchanger to produce domestic hot water. The jacket water, as another waste heat source, drives the absorption dehumidifier to produce dehumidified fresh air for the users. When the cooling load of absorption chiller cannot meet the cooling demand, the electric compression refrigerator or the auxiliary burner of the absorption chiller would be launched make up the gap. 2.2 Thermo-economic mathematical model A thermo-economic mathematical model for the ICE-CCHP system with dehumidification and hybrid refrigeration is presented in this section. The following assumptions is used: (1) the capacity of each unit is continuous. (2) The CCHP system connect to electric grid, and is able to obtain/purchase power from electric grid, or is able to output/inject to electric grid if the power production is surplus, but cannot be sold to electric grid. (3) The off-design condition efficiency of units is equal to the efficiency of rated operating condition [16-19]. According to the literatures [20, 21], the relation between the generating efficiency of ICE, ICE , and capacity of ICE, PICE, is given as below: And if

0  PICE  5000 I C E 0 . 2 3 94P

(1)

 0.02092

0.060701 ICE

4

(2)

Therefore the fuel consumption volume of ICE in jth day of a year and tth hour of a day, VICE (j,t), is found as follow:

VI C E( j, t )

PI C E( j, t )  I C E L H V

 0j

3 65t, 0

24

(3)

Where LHV is the low calorific value of fuel. The PICE ( j, t ) is the actual output power of ICE in jth day of a year and tth hour of a day. When the power produced by ICE cannot meet the electricity demand of users, Pu ( j , t ) , and the deficit of electricity demand, Pgrid ,el ( j , t ) , should be imported from electrical grid, so:

Pg r i, d (e jl , t ) P (u j, t )

P I C (E j, t )

(4)

The waste heat recovery of flue gas, Qr , fg ( j, t ) , can be used to drive absorption chiller and supply the domestic hot water. The expression of

Qr , fg ( j, t )  (

Qr , fg ( j, t ) is:

PICE ( j, t )  PICE ( j, t ))  r , fg  ICE

(5)

Where the r , fg is the waste heat recovery coefficient of flue gas. The waste heat recovery coefficient of jacket water is r , jw , and the waste heat recovery of jacket water, Qr , jw ( j, t ) , can be written as follow：

Qr , jw ( j, t )  (

PICE ( j, t )  PICE ( j, t ))  r , jw ICE

(6)

The absorption chiller can be driven by waste heat of flue gas and auxiliary burner, and the cooling load from absorption chiller driven by waste heat of flue gas is Qac , fg ( j, t ) ：

Qr , fg ( j, t )    COPac Qac, fg ( j, t )   0

j1  j  j2 , t1  t  t2 1  j  j1 & j2  j  365, t1  t  t2

(7)

Where  is the fraction of waste heat recovery from flue gas driven absorption chiller, and

COPac is the coefficient of performance of absorption chiller. The j1 and j2 respectively represent the start day and end day of summer mode in a year. The t1 and t2 respectively represent the operation start hour and end hour of the CCHP system in a day. 5

In summer mode, the quantity of dehumidification, Qd ( j , t ) , is related to the waste heat recovery of jacket water and the coefficient of performance of absorption dehumidifier(COPd). We have:

Qr , jw ( j, t )  COPd Qd ( j, t )   0

j1  j  j2 , t1  t  t2

(8)

1  j  j1 & j2  j  365, t1  t  t2

The heat of domestic hot water, Qh ( j, t ) , is only supplied by flue gas in summer mode, and can be supplied by flue gas and jacket water in other times.

Qr , f g( j, t )  Qh ( j, t )  Qr , f g( j, t ) Q,r j w( j, t )

j  j 2 j 1 t t 2 t,

1



1j

1

j

2

j& j

1

36t 5, t2 t

(9)

Where  is the fraction of waste heat recovery from flue gas to meet the heat demand of domestic hot water. The sum of  and  has to be one:

   =1

(10)

The fuel consumption volume of auxiliary burner of absorption chiller, Vab(j,t), can be expressed as:  (Qc (j t, ) Qac, fg j (t , Q) d j t ( , ) ) 1 0 0 0 Qac, fg ( j, t )  Qd ( j, t )  Qc ( j, t )  Qac  Qd ( j, t )  COPac ab  LHV   (Q  Q ( j, t )) 1000 Vab ( j, t )   ac ac, fg Qac  Qd ( j, t )  Qc ( j, t )  COPac ab  LHV 0 Qac ( j, t )  Qd ( j, t )  Qc ( j, t )  

(11)

Where Qc ( j , t ) is the cooling load demand of users,  ab is the efficiency of auxiliary burner, and

Qac is the capacity of absorption chiller. The cooling load of electric compression refrigerator, Qelc ( j , t ) , and the electricity imported from electric grid driven electric compression refrigerator, Pgrid ,elc ( j, t ) ,can be expressed as follow:

( , ) Qc ( j ,t ) Q a c Q d j( t , ) Qac  Q dj t  Q( c , j )t Qelc ( j ,t )  Qac  Qd j( t , )Qc j t( , ) 0 6

(12)

Pg r i, d (e l jc, t ) Q (e l jc, t ) / C O P e l c

(13)

Where COPelc is the coefficient of performance of electric compression refrigerator. The equation of sum electricity imported from electric grid, Pgrid ( j , t ) , is as follow:

Pgrid ( j, t )  Pgrid ,el ( j, t )  Pgrid ,elc ( j, t )

(14)

The annual total cost of the CCHP system, ATCCCHP , mainly include annual electricity cost imported from electric grid, Cgrid , annual fuel cost, C f , annual investment cost, Ci , and annual maintenance cost, Cm .The annual fuel cost equal to the sum of the annual fuel cost of ICE, Cf,ICE, and the annual fuel cost of auxiliary burner, Cf,ab[22,23].

A T CC C H P C f  Cg r  i d i C mC 365

(15)

24

C f  C f , ICE  C f ,ab   f  (VICE ( j, t )  Vab ( j, t ))

(16)

j 1 t 1

365

24

Cg r i d 

 P ( jg ,rt i d)

grid

j 1 t = 1

(17)

Where νf is the fuel price, and νgrid is the electricity price. The cost of ICE, CICE , the cost of absorption chiller, Cac , the cost of electric compression refrigerator, Celc , the cost of absorption dehumidifier, Cd ,and the cost of heat exchanger, Che , constitute the annual investment cost of the CCHP system, which can be effected by interest rate, k , and life cycle of device, n. According to literature [21], the cost of ICE can be summarized in equation (19).

Ci  (CICE  Cac  Celc  Cd  Che )  k /[1  (1  k ) n ] Ci, I C E 1 . 1 3 8 15 0 P

3 ICE

 0 . 1 2P2 2I C E

2 1 4 P.1 6 8I CE

(18)

1 2 6 7 4 . 4 8(19) 5

Cac  cac  Qac

(20)

Celc  celc  Qelc

(21)

Cd  cd  Qd

(22)

Ch e  c he Q 7

he

(23)

Where cac is the cost of absorption chiller per kW, celc is the cost of electric compression refrigerator per kW, cd is the cost of absorption dehumidifier per kW, che is the cost of heat exchanger per kW. The maintenance cost of the CCHP system comprise the maintenance cost of ICE, Cm, ICE , the maintenance cost of absorption chiller, Cm ,ac , the maintenance cost of electric compression refrigerator, Cm,elc , the maintenance cost of absorption dehumidifier, Cm, d , and the maintenance cost of heat exchanger, Cm ,he .

Cm  Cm,ICE  Cm ac,  Cm d,  Cm elc,  Cm he , 365 24

  (cm, ICE  PICE ( j, t )  cm,ac  Qac  cm,elc  Qelc ( j, t )  cm,d  Qd ( j, t )  cm,he  Qh ( j, t ))

(24)

j 1 t =1

Where cm, ICE is the maintenance cost of ICE per kW, cm ,ac is the maintenance cost of absorption chiller per kW, cm,elc is the maintenance cost of electric compression refrigerator per kW, cm , d is the maintenance cost of absorption dehumidifier per kW, cm ,he is the maintenance cost of heat exchanger per kW. In separate generation system, the electric grid supply all electricity demand of users, electric compression refrigerator produce the cooling load to satisfy users demand, and the heat demand of domestic hot water is met by burner. So, the annual total cost of separate generation system, ATCsg, is equal to the sum of annual investment cost, Ci,sg, annual electricity cost from electric grid, Cgrid,sg, annual fuel cost, Cf,sg, and annual maintenance cost, Cm,sg.

A T Cs g  C, i s g C g, r i d s gC, f sCg,

m sg

Ci, s g c e l cQ（ ,jc )t  k/ [1 (1 kn ) ] 365

(25) (26)

24

Cgrid ,sg   grid （Pu ( j, t )  Qc ( j, t ) / COPelc）

(27)

j 1 t 1

365

24

C f ,sg   f  Qh ( j, t ) / LHV / b j 1 t 1

8

(28)

365

24

Cm,sg  （cm h,  Qh ( j, t )  cm elc,  Qc ( j, t )）

(29)

j 1 t 1

Where 3

b is efficiency of burner.

Assessment and optimization algorithm The prime mover of the CCHP system is an ICE using clean natural gas as the fuel. In this paper,

the evaluation criteria for the system don’t cover environment factor but energy and economy [24-29]

.

3.1 Evaluation criteria The energy evaluation criteria of system are annual primary energy rate, APER, and annual primary energy saving ratio, APESR [24, 25]. 365

APER 

 ( P（j, t )  Q ( j, t )  Q ( j, t )) j 1 t 1

365 24

[(V

ICE

j 1 t 1

365 24

APESR  1 

[(V j 1 t 1 365 24

ICE

u

c

h

(30)

( j, t )  Vab ( j , t ))  LHV /1000  Pgrid ( j , t ) /  grid ]

( j, t )  Vab ( j, t ))  LHV /1000  Pgrid ( j, t ) /  grid ]

（P ( j, t ) /  j 1 t 1

Where

24

u

(31) grid

 Qc ( j, t ) / COPelc /  grid  Qh ( j, t ) / b）

 grid is the efficiency of electric grid.

The economic evaluation criteria of system is annual total cost saving ratio, ATCSR [24, 29].

ATCSR 

ATCsg  ATCCCHP ATCsg

(32)

Comprehensive evaluation criteria, CEC, is proposed to assess the performance of CCHP system. As follows:

CEC  t  APESR  e  ATCSR

(33)

t  e =1

(34)

Where ωt is thermodynamic weighting factor, ωe is economic weighting factor. 3.2 Multi-objective function and optimization algorithm The maximum of CEC is used as multi-objective function with two decision variables, APESR 9

and ATCSR, and the constraints are given as expression (36) and (37).

Fobj  Max(CEC )  Max(t  APESR  e  ATCSR)

(35)

APESR  0

(36)

ATCSR  0

(37)

The analytic hierarchy process and the constrained nonlinear programming solution are employed to optimize design and operation strategy of the CCHP system. The assessment and optimization process follow figure 2. 4 Case analysis 4.1 Basic information In this paper, an office building with an area of 41,360m2 in Guangzhou, China, is taken as a case study. Hourly electric load and hourly cooling load of the office building are simulated with DeST software. As shown in Fig.3, the office building has a maximum electric load of 1,021kW and a maximum cooling load of 6,794kW (including the humidification load). See Table 1 and Table 2 for the CCHP system characteristic parameters and the reference price separately [22, 27, 30]. 4.2 Optical design and operation strategy A matrix for comparison between energy and economy is established in this study with the analytic hierarchy process proposed by Santy

[31, 32]

. Solving the comparison matrix, the

thermodynamic weighting factor ωt is 0.75 and economic weighting factor ωe is 0.25. Substituting the weighting factors into the optimization objective function formula (35), constrained nonlinear programming solution are employed to optimize design of equipment capacity and operation strategy of the system. Fig.4 shows relationships among CEC of the CCHP system, capacity of ICE (PICE) and capacity of the absorption chiller (Qac). According to the figure, when PICE is 1,021kW, regardless of the absorption chiller capacity, the CEC has the maximum value. It means that the CCHP system has the best thermal economic performance. Then the ICE generates electricity to satisfy all electricity demand of users, and the CCHP system apply to following the electric load (FEL) [33]. The relationship between CEC and capacity of absorption chiller (Qac) is shown in Fig. 5. With increasing Qac, APESR, ATCSR and CEC all increase and then decrease. If the optimal Qac is 740 10

kW, CEC will reach its maximum, i.e. 0.237, and APESR and ATCSR will reach their maximums, i.e. 0.263 and 0.16, too. Then APER is 0.825. The capacities and other related parameters of equipment of the CCHP system are obtained in Table 3: the electric compression refrigerator has a capacity of 5,843 kW; the absorption dehumidifier has a capacity of 211 kW; the CCHP system has an annual investment cost of 521,911 $/year and a payback period of 4.52 years. 4.3 Sensitivity analysis Sensitivity analysis of the CCHP system is conducted by the influence factors

[34, 35]

. Fig.6 and

Fig.7 separately represents fuel price or electricity price effected on system performance. According to Fig.6 (a) and Fig.7 (a), fuel prices and electricity prices don’t have an impact on thermal dynamic performance but economic performance of the CCHP system. According to Fig.6, ATCSR and ATCCCHP are proportional to fuel prices: With fuel price increase, ATCSR will decrease; CEC will decline; ATCCCHP will increase; payback period will increases slowly and then increases rapidly. In the case of a fuel price of approximately 0.62 $/m3, ATCSR will be zero; with a higher fuel price, the ATCSR will be less than zero, and payback period will be longer. According to Fig.7, a higher the electricity price corresponds to a larger ATCSR and a better CEC. When an electricity price of approximately 0.078 $/kWh, ATCSR will be zero; with a less electricity price, the ATCSR and CEC will be less than zero. The ATCCCHP is directly proportional to electricity price, but payback period is inversely proportional to electricity price. With a higher electricity price, ATCCCHP will increase and payback period will be shorter. The results show that when fuel price is greater than 0.62 $/m3 and the electricity price less than 0.078 $/kWh, the CCHP system will not be economically advantageous compared with a separate generation system. The performance of the CCHP system is also effected by COPac, COPelc and COPd. Fig.8 presents the system performance according to COPac. According to Fig.8, with increasing COPac, the APESR and ATCSR will be increased, and the CEC will be increased. When COPac is higher, the cooling load produced by absorption chiller will be larger, the cooling load produced by electric compression refrigerator will be less, and it lead to ATCCCHP reduced and payback period shorter. Fig.9 describes the system performance according to COPelc. From Fig.9, with increasing 11

COPelc, the APESR and CEC are increasing in corresponding, and the ATCCCHP and ATCsg both decrease, so the ATCSR increases slightly. Because of increasing COPelc, it lead to the cost of cooling load per kW become cheaper, the payback period become longer. Fig.10 illustrates the system performance according to COPd. As shown in the Fig.10, The COPd has more influence on APESR than ATCSR of the CCHP system. When COPd increases from 0.1 to 1, APESR increases from 0.224 to 0.294, but ATCSR has little change. So CEC increases from 0.206 to 0.26 accordingly. ATCCCHP and payback period have slightly changed with COPd. As the results, it can be concluded that COPd has great improvement on thermal dynamic performance of ICE-CCHP system. Seen from the analysis results, the factors have great influence on the thermal-economic performance of the system. Therefore, these factors should be taken into account in optimizing design and operation strategy of ICE-CCHP system. 5

Conclusions In this study, a novel ICE-CCHP system with dehumidification and hybrid refrigeration is

proposed. Thermo-economic model is established to optimize and design the system. Taking an office building as an application, the CCHP system apply to following the electric load (FEL), and the optimum equipment capacity of the CCHP system is determined: the ICE has a capacity of 1,021 kW; the absorption chiller has a capacity of 740 kW; the electric compression refrigerator has a capacity of 5,843 kW; the absorption dehumidifier has a capacity of 211 kW; the CCHP system has an annual investment cost of 521,911 $/year and a payback period of 4.52 years. Then the CEC is 0.237, and APESR and ATCSR will reach their maximums, i.e. 0.263 and 0.16, too; the annual primary rate is 0.825. The decision making and optimal results are proved to be useful in this optimization process. Moreover, sensitivity analysis is conducted by the impacts of factors. When fuel price is greater than 0.62 $/m3 and the electricity price is less than 0.078 $/kWh, the CCHP system will not be economically advantageous compared with separate generation system. The COPac or COPelc is larger, the performance of the CCHP system is better. The COPd has great improvement on thermal dynamic performance, but little on economy of the CCHP system. Acknowledgements 12

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[14] Guillermo Rey, Carlos Ulloa, Antón Cacabelos, Belén Barragáns. Performance analysis, model development and validation with experimental data of an ICE-based micro-CCHP system. Applied Thermal Engineering 2015; 76:233-244. [15] Sandeep M. Nayak, Yunho Hwang, Reinhard Radermache. Performance characterization of gas engine generator integrated with a liquid desiccant dehumidification system. Applied Thermal Engineering 2009; 29:479-490. [16]Fateme Ahmadi Boyaghchi, Parisa Heidarnejad. Thermoeconomic assessment and multi objective optimization of a solar micro CCHP based on Organic Rankine Cycle for domestic application. Energy Conversion and Management 2015; 97:224-234. [17]Yujie Xu, Shijie Zhang, Jinling Chi, Yunhan Xiao. Steady-state off-design off-design thermodynamic performance analysis of a SCCP system. Applied Thermal Engineering 2015; 90:221-231. [18]Pouria Ahmadi, Ibrahim Dincer, Marc A. Rosen. Performance assessment and optimization of a novel integrated multigeneration system for residential buildings. Energy and Building 2013; 67:568-578. [19]Penghui Gao, Wangliang Li, Yongpan Chen, YenWah Tong, Yanjun Dai, Ruzhu Wang. Thermodynamic performance assessment of CCHP system driven by different composition gas. Applied Energy 2014; 136:599-610. [20]Kyung Tae Yun, Heejin Cho, Rogelio Luck, Pedro J. Mago. Modeling of reciprocating internal combustion engines for power generation and heat recovery. Applied Energy 2013; 102:327-335. [21]Xiangqiang Kong.The CCHP systems., China: National Defence Industry Press; 2011. [22]Suat Sevencan, G?ran Lindbergh, Carina Lagergren, Per Alvfors. Economic feasibility study of fuel cell-based combined cooling, heating and power system for a data centre. Energy and Building 2016; 11:218-223. [23]Jiangjiang Wang, Ying Yang, Tianzhi Mao, Jun Sui, Hongguang Jin. Life cycle assessment (LCA) optimization of solar-assisted hybrid CCHP system. Applied Energy 2015; 146:38-52. [24]X.Q.Kong, R.Z.Wang, X.H.Huang. Energy efficiency and economic feasibility of CCHP driven by stirling engine. Energy Conversion and Management 2004; 45:1433-1422. [25]Hui Li, Lin Fu, Kecheng Geng, Yi Jiang. Energy utilization evaluation of CCHP systems. Energy and Building 2006; 38:253-257. [26] Marialaura Di Somma, Bing Yan, Nicola Bianco, Peter B.Luh, Giorgio Graditi, Luigi Mongibello, Vincenzo Naso. Multi-objective operation optimization of a Distributed Energy System for a large-scale utility customer. Applied Thermal Engineering 2016; 101:752-761. [27]Mohammad Ameri, Zahed Besharati. Optimal design and operation of district heating and cooling networks with CCHP systems in a residential complex. Energy and Buildings 2016; 110:135-148. [28]Qiong Wu, Hongbo Ren, Weijun Gao, Jianxing Ren. Multi-criteria assessment of combined cooling, heating and power systems located in different regions in Japan. Applied Thermal Engineering 2014; 73:660-670. 14

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Figure Captions Fig.1 Schematic of the ICE-CCHP system with dehumidification and hybrid refrigeration Fig.2 Flow chart of assessment and optimization process Fig.3 Hourly electric load and hourly cooling load of an office building in Guangzhou Fig 4 Relationships among CEC of the CCHP system Fig.5 System evaluation criteria values according to absorption chiller capacity Fig.6 Effect of fuel price on system performance Fig.7 Effect of electricity price on system performance Fig.8 The system performance according to COPac Fig.9 The system performance according to COPelc Fig.10 The system performance according to COPd

16

Table Captions Table 1 Characteristic parameters of system Table 2 The reference price of system Table 3 System optimization results

17

Electric Grid

Pgrid

+

PICE

Pu

Pgrid,elc

Electric compression refgrigerator Fuel

Internal Combustion Engine(ICE)

Exhaust Gas

Absorption chiller

+

Qc Users

Fuel

Qh

Air Jacket Water

Qd

Absorption Dehumidifier

Fig.1 Schematic of the ICE-CCHP system with dehumidification and hybrid refrigeration. The prime-mover-power-generator is driven by a gas ICE, which meets the electricity demand of the users. High-temperature flue gas of ICE is fed to the absorption chiller to recover the waste heat and provide cooling for the users. Then the low-temperature flue gas discharged by the absorption chiller enters the heat exchanger to produce domestic hot water. The jacket water, as another waste heat, drives the absorption dehumidifier to produce dehumidified fresh air for the users. When the cooling load of absorption chiller cannot meet the cooling demand, the electric compression refrigerator or the auxiliary burner of the absorption chiller would be launched make up the gap.

Users load

Parameters value and units capacity of system

Thermal economic model

Analytic hierarchy process APESR≥0 ATCSR≥0

Target layer Comprehensive consideration of building types, climate conditions, users need and other factors and then optimization

Yes Weight factors

Criterion layer Energy and Economy

Objective function No

Scheme layer System operation scheme Optimum installed capacity

Output

End

18

Fig.2 Flow chart of assessment and optimization process

8000.00 7000.00 6000.00 5000.00 4000.00 3000.00 2000.00 1000.00 0.00 1-1

2-1

3-1

4-1

5-1

6-1

power/kW

7-1

8-1

9-1 10-1 11-1 12-1

cooling/kW

Fig.3 Hourly electric load and hourly cooling load of an office building in Guangzhou

0. 4

CEC

0. 2 0

- 0. 2 - 0. 4 - 0. 6 6000 4000

Qac/kW

2000 0

0

1000

3000 2000 P /kW ICE

Fig 4 Relationships among CEC of the CCHP system

19

4000

5000

0. 3

APESR ATCSR CEC

0. 25

0. 2

0. 15

0. 1

0. 05

0 0

1000

2000

3000 4000 Q /kW

5000

6000

ac

Fig.5 System evaluation criteria values according to absorption chiller capacity

0.5 APESR ATCSR CEC

0.4

0.3

0.2

0.1

0.0 0.0

0.1

0.2

0.3

0.4 0.5 cf/($/m3)

(a)

20

0.6

0.7

0.8

0.9

1.0

25

80

Total cost of CCHP system

70

Payback period/years

20

60 15

50 40 10

30 20

5

10 0 0.0

0.2

0.4

0.6

0.8

0 1.0

3

cf/($/m )

(b) Fig.6 Effect of fuel price on system performance

0.5

0.4

APESR ATCSR CEC

0.3

0.2

0.1

0.0 0.00

0.05

0.10 0.15 cgrid/($/kW.h)

(a)

21

0.20

0.25

0.30

Payback period/years

Total cost of CCHP system/×104 $/year

90

25

80

Total cost of CCHP system

70

Payback period/years

20

60 15

50 40 10

30 20

5

10 0 0.05

0.10

0.15

0.20

0 0.30

0.25

cgrid/($/kW.h)

(b) Fig.7 Effect of electricity price on system performance

0.30

0.25

0.20

0.15

0.10 APESR ATCSR CEC

0.05

0.00 0.6

0.7

0.8

0.9

1.0 COPac

(a)

22

1.1

1.2

1.3

Payback period/years

Total cost of CCHP system/×104 $/year

90

6

50

5

40

4

30

3

20

2

Total cost of CCHP system 10

1

Payback period

0 0.6

0.7

0.8

0.9

COPac

1.0

1.1

1.2

0 1.3

(b) Fig.8 The system performance according to COPac

0.30

0.25

0.20

0.15

0.10 APESR ATCSR CEC

0.05

0.00 1

2

3 COPelc

(a)

23

4

5

Payback period/years

Total cost of CCHP system/×104 $/year

60

6

100

5

80

4

60

3

40

2

Total cost of CCHP system 20

Payback period/years

Total cost of CCHP system/×104 $

120

1

Payback period/years

0

0 1

2

3

4

COPelc

5

(b) Fig.9 The system performance according to COPelc

0.30

0.25

0.20

0.15

0.10

APESR ATCSR CEC

0.05

0.00 0.1

0.2

0.3

0.4

0.5 COPd

(a)

24

0.6

0.7

0.8

0.9

1.0

6

50

5

40

4

30

3

20

2

Total cost of CCHP system 10

Payback period/years

0 0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

COPd

(b) Fig.10 The system performance according to COPd

25

1

0 1.0

Payback period/years

Total cost of CCHP system/×104 $

60

Table 1 Characteristic parameters of system Component

Symbol

Value

Efficiency of auxiliary burner

ηab

0.85

Waste heat recovery coefficient of flue gas

λr,fg

0.51

The fraction of waste heat from flue gas driven absorption chiller

α

0.6

β

0.4

Coefficient of performance of absorption dehumidifier

COPd

0.65

Coefficient of performance of absorption chiller

COPac

1.3

Coefficient of performance of compression refrigerator

COPelc

4.0

Efficiency of boiler

ηb

0.85

Waste heat recovery coefficient of jacket water

λr,jw

0.4

Efficiency of electric grid

ηgrid

0.33

Interest rate

k

0.049

Life cycle of device

n

20 years

Low heating value

LHV

35.88 ×106 J/m3

Fraction of waste heat from flue gas to meet the heat demand of domestic hot water

Table 2 The reference price of system Component

Symbol

Value

The cost of absorption chiller per kW

cab

159.72 $/kW

The cost of electric compression refrigerator per kW

celc

130.68 $/kW

The cost of absorption dehumidifier per kW

cd

290.4 $/kW

The cost of heat exchanger per kW

che

6.534 $/kW

Maintenance cost of ICE per kW

cm,ICE

0.011 $/kW

Maintenance cost of absorption chiller per kW

cm,ac

0.002 $/kW

Maintenance cost of electric compression refrigerator per kW

cm,elc

0.002 $/kW

Maintenance cost of absorption dehumidifier per kW

cm,d

0.007 $/kW

Maintenance cost of heat exchanger per kW

cm,he

0.001 $/kW

Fuel price

νf

0.363 $/m3

Electricity price

νgrid

0.116 $/kW.h

26

Table 3 System optimization results Component

Symbol

Value

Thermodynamic weighting factor

ωt

0.75

Economic weighting factor

ωe

0.25

Capacity of ICE

PICE

1,021 kW

Capacity of absorption chiller

Qac

740 kW

Cooling load of electrical compression refrigerator

Qelc

5843 kW

Quantity of dehumidification

Qd

211 kW

Annual total cost of the CCHP system

ATCCCHP

521,911 $/year

Payback period

4.52 years

Annual primary energy rate

APER

0.825

Annual primary energy saving ratio

APESR

0.263

Annual total cost saving ratio

ATCSR

0.16

Comprehensive evaluation criteria

CEC

0.237

27

Highlights 1.

A novel CCHP system with dehumidification and hybrid refrigeration is proposed.

2.

Thermo-economic mathematical model of the CCHP system is established.

3.

A comprehensive evaluation criteria is proposed as objective function to assess the performance of the system.

4.

The analytic hierarchy process and constrained nonlinear programming solution are employed to optimize

5.

design and operation strategy of the system. The sensitivity analysis is carried out to assess the effects on performance of the CCHP system.

28