DOI: 10.3303/CET2188085 
 

 
 

 
 
 
 

 
 
 
 

 
 
 

 
 
 

 
 
 

 
 

 
 

 

 
 
 

 
 
 

 
 
 

 
 

 
 
 

 
 
 

 

Paper Received: 12 June 2021; Revised: 10 July 2021; Accepted: 10 October 2021 
Please cite this article as: Kadam S.T., Khan M.S., Hassan I., Rahman M.A., Papadopoulos A.I., Seferlis P., 2021, Energy, Exergy, 
Environmental and Economic Analysis of Heavy Duty Vapor Compression Chiller with Alternative Fluids in District Cooling, Chemical 
Engineering Transactions, 88, 511-516  DOI:10.3303/CET2188085 

CHEMICAL ENGINEERING TRANSACTIONS

VOL. 88, 2021 

A publication of

The Italian Association
of Chemical Engineering
Online at www.cetjournal.it 

Guest Editors: Petar S. Varbanov, Yee Van Fan, Jiří J. Klemeš

Copyright © 2021, AIDIC Servizi S.r.l. 

ISBN 978-88-95608-86-0; ISSN 2283-9216

Energy, Exergy, Environmental and Economic Analysis of
Heavy Duty Vapor Compression Chiller with Alternative Fluids

in District Cooling
Sambhaji T. Kadama,*, Muhammad Saad Khana, Ibrahim Hassana, Mohammad
Azizur Rahmanc, Athanasios I. Papadopoulosb, Panos Seferlisd
a Mechanical Engineering Department, Texas A&M University at Qatar, PO Box 23874, Doha, Qatar 
b Centre for Research and Technology Hellas (CERTH), 57001 Thermi, Thessaloniki, Greece 
c Petroleum Engineering Department, Texas A&M University at Qatar, PO Box 23874, Doha, Qatar 
d Department of Mechanical Engineering, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece 

sambhaji.kadam@qatar.tamu.edu

A district cooling system (DCS) is superior to conventional air conditioning as it helps to reduce energy
consumption and protect the environment by reducing carbon dioxide emissions. The investigation of the
actual/existing vapour compression refrigeration (VCR) system used in the DCS has not been well documented.
In this context, energy, exergy, environmental and economic (4E) analysis of the VCR chiller, operated with
R134a, used in heavy duty existing DC plant has been systematically performed and compared with the
ecofreindly refrigerant R717. The impact of the evaporation temperature on the total equivalent warming impact
(TEWI), coefficient of performance, exergy efficiency and cost rate is assessed. It is observed that the COP and
exergy efficiency of the VCR with R717 is around 3 % higher compared to a VCR with R134a. This is attributed
to the significantly higher latent heat of evaporation, which ultimately requires a lower mass flow rate of R717.
It is observed that the total global warming impact and Combined cost of R717 are lower by 1.6 % compared to
the R134a. Lower TEWI is attributed to the zero global warming potential, lower compressor power and higher
COP of the VCR system with R717 in comparison to R134a. However, further detailed parametric analysis
considering the capital cost is required to claim the superiority of R717.

1. Introduction

The global cooling demand in diversified sectors has been increased rapidly, roughly consuming 15 % of global
electricity and contributing to around 10 % of global greenhouse gas emissions (She et al., 2018). This
unprecedented cooling demand has been fulfilled majorly using the vapor compression refrigeration (VCR)
system and has a market share of 80 %. In most cases, such units are over-dimensioned compared to the actual
cooling load that they serve and their electric consumption is not controlled or monitored and they often use
environmentally harmful refrigerants (Čož et al., 2017). As a result, such plants are less efficient, less cost
effective, and require large land space (Kadam et al., 2020). District cooling is a sustainable and energy efficient
alternative over the conventional on-site air conditioning units at individual buildings as it offers reduced
environmental impact, more reliable services, and space savings. Remotely operated chiller plants can facilitate
in reducing the anthropogenic heat generation (released by plants installed at individual buildings) that
contribute to reducing the intensity of the urban heat island effect. This is because of the damping heat from the
densely constructed urban area to the nearer remote area where a chiller plant is often erected. A district cooling
system that combines with renewable sources (Hui et al. 2017) or industrial waste heat utilization (Liew et al.
2015) can be a cost-effective option.
Belman-Flores et al. (2017) experimentally assessed and concluded that R1234yf has poor energy performance
and more environmental impact compared to R134a. De Paula et al. (2020) concluded based on environmental,
energy, and exergy analysis that at given operating conditions the overall performance of the R290 is relatively
higher compared to R1234yf, R744, and R134a. Sun et al. (2020) observed that the energy and exergy

511



performance of the economized VCR system using R513a is lower compared to the R134a, however, R513a
exhibits lower irreversibility at high ambient temperature and high space temperatures. Baakeem et al. (2018)
performed a theoretical investigation of energy, exergy, and economic analysis of a multistage VCR system (1
kW) operated with different refrigerants (R717, R22, R134a, R1234yf, R1234ze(E), R410A, R404A, and R407C)
and concluded that the R717 is the best refrigerant among other refrigerants. Wu et al. (2020) concluded that
R290 has superior energy performance and environmental performance among various refrigerants (i.e.,
R134a, R152a, R1234yf, R290, R410a, R32, R744). Roy and Mandal (2019) performed the thermo-economic
analysis of the VCR system of 10 kW cooling capacity and observed that the R152a shows better
thermodynamic and economic performance compared to the R600a, R1234ze. Ande et al. (2018) observed that
the use of copper oxides nanoparticle in R134a can increase the performance of the VCR system by 16.66 %.
The open literature related to district cooling is focused on the energy analysis of a hypothetical plant. To the
best of the authors knowledge no efforts have been made to investigate and document together energy, exergy,
environmental, and economic (4E) aspects of the VCR system used in the DC plant (Eveloy and Ayou, 2019).
4E analysis of a VCR unit has been reported considering different refrigerants, but for small capacities that are
unsuitable for DC systems. However, the cooling requirement of the VCR-driven DC plant is very high, in the
order of thousands of Tons of Refrigeration (TR). For instance, the DC plant at Pearl, Qatar is operated with
VCR chillers to satisfy the cooling capacity of 130,000 TR (Kadam et al., 2020). The type of refrigerants used in
the VCR could have a significant impact on the environment which eventually turn to be an environmental
enemy.  The release of refrigerants, due to slow leakage or during repair and maintenance of plant or accident,
having high GWP could warm the earth by absorbing energy which supposed to escape to space.
Thermophysical properties of the refrigerant can also affect the thermal performance, and hence associated
capital, environmental and operational costs of the DC plant could change. Consequently, it is also important to
conduct the 4E analysis using different refrigerants used in the VCR chiller of the DC plant. On the contrary, few
analyses of hypothetical DC plants are available in the open literature that includes different configurations
(Gang et al., 2016) and exergoeconomic optimization of the distribution network (Čož et al., 2017). In this
context, this paper emphasizes the 4E comparison of the VCR system, operated with existing refrigerant R134a
and alternative refrigerant R717, used for heavy duty district cooling applications. The refrigerant R134a is
classified as a greenhouse gas (it has a high global warming potential) and the control and elimination of these
gasses were proposed in the Kyoto protocol and restrictions were reaffirmed in the Kigali amendment in 2016
(de Paula et al., 2020). The developed economies like the USA, Japan, and EU countries are in the process of
phasing out R134a shortly and are giving preference to alternative refrigerants (Du et al., 2016). Despite some
handling and safety issues with R717, it remains one of the strong choices due to its energy efficiency and
minimal environmental impact. In Jordon, the Abdali district cooling plant of 21,000 TR capacity is effectively
and efficiently functioning using ammonia as a refrigerant (reported in Bara et al., 2021). Recently, Bara et al.
(2021) identified that R717 exhibits better dynamic stability among R134a, R32, R1234yf, R1234ze(E), R600,
R600a, R290, R410a and R22 for large capacity dual chillers. With this motivation, the R717 is considered and
compared with the existing R134a.

2. Material and method

The data for the current study has been collected from the district cooling (DC) plant, situated at the Barwa City,
Qatar, and used for the model development. The model of the VCR system as shown in Figure 1a is
implemented using the ASPEN PlusTM process simulator (V10), which has an inclusive databank of fluids (Al-
Malah, 2016). The primary working fluid (i.e. refrigerant) is the R134a, whereas the secondary fluid is water.
The REFPROP model is selected for the thermodynamic and transport properties, as it is most appropriate for
the fluid under consideration (i.e., R134a and water), it implements three models for the thermodynamic
properties of pure fluids: equations of state explicit in Helmholtz energy, the modified Benedict-Webb-Rubin
equation of state, and an extended corresponding states (ECS) model. The heat exchanger, i.e., the condenser
and the evaporator, are modeled using the HeatX model that has the capacity for rigorous fundamental analysis.
Both heat exchangers are treated with the counter-flow arrangement. The compression and expansion process
is considered as isentropic and isenthalpic.
Figure 1b represents the pressure-enthalpy diagram for the R134a and R717 using the REFPROP property
method for the base case. The measurement accuracy of the flow meter (Siemens MAG 5000) is ± 0.5 %,
pressure transducer (Daikin made) has accuracy of ± 1.5 %, and that for temperature sensors (Daikin made) is
± 0.5 °C. The current simulation approach is validated with the results of Ben Jemaa et al. (2017).  The current
model deviates by 2.69 % and 2.71 % relative to Ben Jemaa et al.’s data in the case of COP and ECOP as 
shown in Figure 2a and b. This indicates that a similar simulation approach can be effectively used for the
analysis of the current heavy-duty VCR chiller.

512



Figure 1: (a) The VCR simulation flowsheet. S1, S2, S3, and S4 are streams of the VCR cycle. CI, CO, CHO, 

and CHI are streams of cooling water inlet and outlet and chilled water inlet and outlet; (b) Pressure-enthalpy 

diagram for R134a and R717 at base case (evaporator temperature (Te) = 6.1 °C, condenser temperature (Tc)
= 42 °C) 

Figure 2: Comparison of the current model with results of Ben Jemaa et al. (2017); (a) COP, (b) ECOP 

3. Performance indicators

The coefficient of the performance (COP) is used as an energy indicator as presented by Eq(1).
Qevap

COP
Wcomp

 (1)

Where Qevap  and Wcomp  are the refrigerating effect and the compressor work in kW. The exergy analysis is

carried out in terms of the exergetic efficiency ( exergy ), as given by Eq(2) (de Paula et al., 2020).

 , , , ,,
1 1

E E E EE des comp des cond des valve des evapdes total
exergy

W Wcomp comp



  

    (2)

where
,

E
des total

is total exergy destruction associated with the VCR system in kW, which is the summation of

exergy destruction of the system components, namely the compressor, the condenser, the expansion valve,
and the evaporator, as presented below Eq(3)-(6) (Morosuk and Tsatsaronis, 2009).

 1 4,E W E Ecomp s sdes comp     (3)

   1 2,E E E E Es s CO CIdes cond     (4)

2 3
E E E

s svalve
   (5)

513



   3 4E E E E Eevap s s CHO CHI    (6)
The environmental impact of the refrigerant usage and the VCR system can be measured using the concept of
total equivalent warming impact (TEWI) (Fischer, 1993). The TEWI accounts for the direct emissions due to
refrigerant leakage and the indirect emissions due to electricity consumption of the compressor, as given by
Eq(7).

 1TEWI GWP m L L GWP m E Lrate ntime timeref ref              (7)

where m
ref

 is the refrigerant charge quantity of the VCR chiller in kg, Lrate  is an annual rate refrigerant

leakage from the VCR chiller in %, Ltime  is the life of the VCR chiller in (y),   is the refrigerant life recovery

rate in %, 
n

E  is the annual electricity consumption of the VCR chiller in kWh/y as given by Eq(8), and   is the

CO2 emission factor for producing electricity (equal to 0.469 kgCO2/kWh for natural gas) (Edenhofer et al.,
2011).

365 /
n

T Q COPoper evapE        (8)

In the cost analysis, combined costs associated with operational and penalty cost rates due to CO2 emissions
are considered as given by Eq(9)

C C Cop env  (9)

The operational and environmental cost is estimated as shown by Eq(10) and Eq(11).

365C W T Cop comp oper ele
   (10)

2
C E Cenv n CO

   (11)

where, C
ele

 is the electricity unit cost for Qatar (1 kWh = 0.03562 USD) and 
2

C
CO  is the unit damage cost of

CO2 emission (equal to 0.09 USD/kgCO2) (Roy and Mandal, 2019).

4. Results and discussion

In this paper, a 4E analysis of the VCR system used in the existing district cooling plant has been carried out.
The performance of the existing VCR system using R134a as a refrigerant is compared with that of the eco-
friendly refrigerant R717. The operating parameters of the VCR with R717 are the same as those of the VCR
with R134a, except for the mass flow rate of the refrigerants. The mass flow rate of the R717 is adjusted to
obtain the same outlet temperature of the chilled water as that of R134a. With an increase in the evaporation
temperature, the refrigerating effect increases, and the compressor work decreases. The COP of the system is
increasing with an increase of the evaporation temperature in the case of both refrigerants. The corresponding
data is presented in Table 1.

Table 1: Thermodynamic, environmental, and economic  comparison R134a and R717 

Te 

(°C) 

Tc 

(°C) 

COP Exergy Efficiency (%) TEWI (Kg CO2) Cost (USD) 

R134a R717 R134a R717 R134a R717 R134a R717 

2.1 42 5.5 5.6 53.4 55.2 5.36E+07 5.16E+07 5.77E+05 5.70E+05
3.1 42 5.7 5.8 55.3 57.1 5.20E+07 4.99E+07 5.59E+05 5.52E+05
4.1 42 5.9 6.0 57.2 59.0 5.05E+07 4.83E+07 5.42E+05 5.35E+05
5.1 42 6.1 6.2 59.2 61.0 4.91E+07 4.67E+07 5.26E+05 5.17E+05
6.1 42 6.3 6.5 61.4 63.2 4.76E+07 4.52E+07 5.10E+05 5.00E+05

From Figures 3a and b, it is observed that the COP and exergy efficiency of the VCR with R717 is around 3 %
higher compared to a VCR with R134a. Although the difference between condenser and evaporator pressures
for the R717 is high in comparison to the R134a at the same condensation and evaporation temperature (see
Figure 1b, the compressor work requirement is slightly lower for R717. This is because of the requirement of
the significantly lower mass flow rate of the R717 compared to R134a. The mass flow rate of the R134a case is
31.5 kg/s. In the case of the R717, it is 4.35 kg/s. The flow rate of the R717 is lower to achieve the same
refrigerating effect; the latent heat of evaporation for R717 is considerably high at the same evaporation
temperature. The COP of the R717 based VCR chiller is slightly higher than that of the R134a-based, VCR

514



chiller. On the contrary, environmental performance and the cost are reduced with an increase in the evaporation
temperature as shown in Figures 4a and b. The corresponding data is also presented in the Table 1.

Figure 3: Comparison of the performance indicators between R134a and R717 at constant condenser 

temperature (Tc = 42 °C), (a) COP, (b) Exergy efficiency 

Figure 4: Comparison of the performance indicators between R134a and R717 at constant condenser 

temperature (Tc = 42 °C), (a) TEWI, (b) Cost 

The TEWI decreases due to a reduction in the refrigerating effect with an increase in the condensation effect.
The reduction in the cost is due to the decreasing trend of the compressor work and the refrigerating effect with
an increase in the evaporation temperature. The environmental impact of the R717 is relatively lower compared
to the R134a. It is observed from Figure 4a that the total global warming impact (TEWI) is lower by 1.6 %
compared to the R134a. The major reason for this lower impact is the zero value of the global warming potential
of the R717, and the higher COP value. Similarly, the summation of the operating and environmental cost of the
R717-based VCR system is 1.6 % lower than the R134a as shown in Figure 4b, due to lower compressor work
and higher COP. Based on the current comparison under the given operating conditions, it is concluded that the
performance of the R717-based VCR chiller is better than that of the R134a-based VCR chiller.

5. Conclusions

The energy, exergy, environmental and economic (4E) analysis of the VCR chiller, operated with R134a, used
in a heavy duty, existing DC plant has been systematically performed and compared with the ecofrendly
refrigerant R717. It is observed that the COP and the exergy efficiency of the VCR with R717 are around 3 %
higher compared to a VCR with R134a. This is attributed to the significantly higher latent heat of evaporation,
which ultimately requires a lower mass flow rate of R717. It is observed that the total global warming impact
(TEWI) and the combined cost of R717 are lower by 1.6 % compared to the R134a. Lower TEWI is attributed to
the zero global warming potential, lower compressor power and higher COP of the VCR system with R717 in
comparison to R134a. However, further detailed parametric analysis considering the capital cost is required to
claim the superiority of the R717. The 4E analysis conducted and results obtained in this study have noteworthy
practical importance. The system designer can adopt a similar approach to quantify the benefits offered by the
other eco-friendly refrigerants as done for R717, before performing experimental testing. This is of great practical
value because a similar analysis could result in a significant reduction in associated capital and operational
costs, at the early stage of planning of the DC plant.

515



Acknowledgments 

This paper was made possible by an NPRP award [##NPRP10-1215-160030] from the Qatar National Research
Fund (a member of The Qatar Foundation).

References 

Al-Malah K. I. M., 2016. Aspen Plus: Chemical engineering applications, John Willey and Sons, Inc., Hoboken,
New Jersey, USA.

Ande R., Koppala R. S. R., Hadi M., 2018. Experimental Investigation on VCR system using Nanorefrigerant for
COP Enhancement. Chemical Engineering Transactions, 71, 967-972.

Bara A., Kadam S., Gkouletsos D., Papadopoulos A.I., Hassan I., Rahman M.A., Kyriakides A.S., Seferlis P.,
2021. Systematic assessment of the dynamic behavior of ecofriendly refrigerants used in dual vapor
compression chiller. Science and Technology for the Built Environment, 27, 917-935.

Baakeem S. S., Jamel O., Alabdulkarem, A., 2018. Optimization of a multistage vapor-compression refrigeration
system for various refrigerants. Applied Thermal Engineering, 136, 84–96.

Ben Jemaa R., Mansouri R., Boukholda I. Bellagi A., 2017. Energy and exergy investigation of R1234ze as
R134a replacement in vapor compression chillers. International Journal of Hydrogen Energy, 42 (17),
12877–12887.

Belman-Flores J.M., Rodríguez-Muñoz A.P., Gutiérrez Pérez-Reguera C., Mota-Babiloni A., 2017. Experimental
study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator. International Journal of
Refrigeration, 81, 1–11.

Čož T.D., Kitanovski A., Poredoš A, 2017. Exergoeconomic optimization of a district cooling network. Energy,
135, 342–351.

de Paula C.H., Duarte W.M., Rocha T.T.M., de Oliveira R.N., Maia A.A.T., 2020. Optimal design and
environmental, energy and exergy analysis of a vapor compression refrigeration system using R290,
R1234yf, and R744 as alternatives to replace R134a. International Journal of Refrigeration, 113, 10–20.

Du L., Meszler D., Minjares R., 2016. HFC-134a phase-out in the chinese light-duty motor vehicle sector.
<www.theicct.org/sites/default/files/publications/ICCT_HFC-134a_China-fleet_201609.pdf>, accessed
23/07/2021.

Edenhofer O, Pichs-Madruga R., Sokona Y., Seyboth K., Matschoss P., Kadner S., Zwickel T., Eickemeier P.,
Hansen G., Schloemer S., von Stechow C., 2011. Special Report on Renewable Energy Sources and
Climate Change Mitigation. Cambridge University Press, Cambridge, United Kingdom and New York, NY,
USA.

Eveloy V., Ayou D.S., 2019. Sustainable district cooling systems: Status, challenges, and future opportunities,
with Emphasis on Cooling-Dominated Regions, Energies, 12(2), doi: 10.3390/en12020235.

Fischer S.K., 1993. Total equivalent warming impact: a measure of the global warming impact of CFC
alternatives in refrigerating equipment. International Journal of Refrigeration, 16, 423–428.

Gang W., Augenbroe G., Wang S., Fan C., Xiao F., 2016. An uncertainty-based design optimization method for
district cooling systems. Energy, 102, 516–27.

Hui L.W., Hashim H., Shiun L.J., Muis Z.A., Yen l.P., Shin H.W., 2017. Technical and economic evaluation of
district cooling system as low carbon alternative in Kuala Lumpur city. Chemical Engineering Transactions,
56, 529-534.

Kadam S.T., Hassan I., Rahman M.A., Papadopoulos A.I., Seferlis P., 2020. Review on modeling of vapor
compression chillers: District cooling perspective. International Journal of Air-Conditioning and Refrigeration
28(02), 2030003.

Liew P.Y., Alwi S.R.W., Manan Z.A., Klemes J.J., Varbanov P.S., 2015. Incorporating district cooling system in
total site heat integration. Chemical Engineering Transactions, 45, 19-24.

Morosuk T. Tsatsaronis G., 2009. Advanced exergetic evaluation of refrigeration machines using different
working fluids. Energy, 34(12), 2248–2258.

Roy R., Mandal B.K., 2019. Thermo-economic assessment and multi-objective optimization of vapour
compression refrigeration system using low GWP refrigerants. 2019 8th International Conference on
Modeling Simulation and Applied Optimization, Apr. 15 – 17, 2019, Bahrain, 1–4.

She X., Cong L., Nie B., Leng G., Peng H., Chen Y., Zhang X., Wen T., Yang H., Luo Y., 2018. Energy-efficient
and -economic technologies for air conditioning with vapor compression refrigeration: A comprehensive
review. Applied Energy, 232, 157–186.

Sun J., Li W., Cui B., 2020. Energy and exergy analyses of R513a as a R134a drop-in replacement in a vapor
compression refrigeration system. International Journal of Refrigeration, 112, 348–356.

Wu J., Zhou G., Wang M., 2020. A comprehensive assessment of refrigerants for cabin heating and cooling on
electric vehicles. Applied Thermal Engineering, 174, 115258.

516