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ACEE – Volume 02(2), 80-94

Advances in Civil and Environmental Engineering

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ENERGY, EXERGY, ENVIRONMENT AND RISK (EEER)

ANALYSES OF R600A AS A REPLACEMENT OF HFC

REFRIGERANT FOR HOUSEHOLD REFRIGERATOR SYSTEM

Alireza Noorpoor 1*, Mohanna Akhlaghi 1 , Sultan hosein Fattahi 2

1 Graduate Faculty of Environment, University of Tehran (UT), Tehran, Iran

2 Emersun Industrial Groups, Tehran, Iran

* Corresponding author, E-mail: [email protected]

Abstract

Energy-Exergy analysis was applied to investigate environmental impact of R134a in general, and

the effect of change of variables on TEWI in particular. We study on isobutene (R600a) as an

environment-friendly refrigerant with zero ozone depletion potential (ODP) and negligible global

warming potential (GWP), to replace R134a in domestic vapor-compression refrigeration system. Then

FMEA method for risk analysis carried out based on experimental result and presented for predicting

the flammability of pure hydrocarbon of household refrigerator. The result shows average coefficient of

performance (COP) using R600a is higher than from R134a. The system consumed less energy by

using R600a, which shows that it can be used as replacement for R134a in domestic refrigerator.

Furthermore, when the refrigerator is working with R600a type compressor, have a total TEWI about

42% less than HFC refrigerators. This article discusses the relations between environmental impact and

thermodynamics in general, and the thermodynamic property exergy in particular.

Keywords: Exergy analysis, Energy, Domestic refrigerator, Risk analysis, R600a, R134a, TEWI

Nomenclature

Exergy rate (kW)

RC refrigerant charge (kg)

GWP Global warming potential

T Temperature (K)

Work rate (kW)

ISSN 2345-2722

Alireza Noorpoor et al. Journal of Advances in Civil and Environmental Engineering, Volume 02(2), 80-94

18

TEWI Total Equivalent Warming (kg CO2)

ODP Ozone Depletion Potential

accidental refrigerant leaks per year

(% refrigerant charge/year)

refrigerant power (kW)

COP coefficient of performance

Exergetic efficiency

CO2 emission from power conversion ( /kWhe)

1. Introduction

In recent years, the term global warming potential is become a serious environmental problem,

which is hard to be solved without focus on energy consumption (Kayukawa, 2002). All products

include vapor compression systems embodied green-house gas, hence effective solution for climate

change require fundamental transformation of the energy is used (ZhongXiang, 2009). Most modern

refrigeration are based on vapor compression system (Montreal Protocol, 1987). Vapor compression

refrigeration systems have both a direct and an indirect contribution to global warming (Aprea et al.,

2012).

First generation of the refrigerants mostly used ammonia, carbon dioxide, sulphur dioxide and

methyl chloride as a refrigerant which were found to be toxic or hazardous (Bolaji, 2010). However, in

1931 alternative refrigerants were introduced by a shift to chlorofluorocarbons (CFCs) and hydro-

chlorofluorocarbons (HCFCs) for safety issues (Bolaji, 2005). CFCs and HCFCs have many suitable

properties, for example, stability, non-toxicity, non-flammable, good material compatibility and good

thermodynamic properties, make theme a popular refrigerant in large, industrial systems especially for

air-conditioning and refrigerating systems (Radermacher et al., 1996).

Release of CFCs and HCFCs to atmosphere which are large class of ozone-depleting substances,

migrate to the stratosphere. Later, chlorine atoms began to react with ozone and convert theme to

oxygen (Bolaji, 2010). Depletion of the earth’s ozone layer that protect the earth’s surface from UV

radiation, led to phase out of halogenated fluids. Developed countries phased out the CFCs since 1996,

and in 2010, producing and using of CFC refrigerant will be prohibited in all over the world (UNEP,

2003; Sattar et al., 2007). In recent years the European Parliament set a regulation of F-Gases phase out

(Bansal et al., 2011).that prohibits the using of refrigerants having GWPs more than 150. Such

regulation will do so by 2011 (Regulation (EC) n.842/2006 of the European Parliament and of the


18

Council, 2006). So it`s obvious that synthetic refrigerants are no more sustainable from an

environmental perspective due to their ozone depleting potential (ODP) and global warming potential,

therefore Refrigerants such as HFCs have to be replace by alternatives with low global warming

potential (Colbourne et al., 2013). HFCs have high volatility and very low solubility in water and when

releases into the environment, these compounds reside in the atmosphere for years (Wen-Tien, T.,

2005).

Additionally, some problems such as high pressure drop in compressor and evaporator occurs by

using R134a (Smith et al., Energy 2001). The global warming potential for R134a is high so it will be

replaced with a low GWP fluid (Zilio et al., 2011; Bolaji, Energy 2010).

The new generation of refrigerant must offer both high efficiency and low global warming potential

(GWP). Furthermore the atmospheric lifetime should be noted (Calm, Refrigeration 2008). Mohanraj

reported that natural refrigerants (hydrocarbon refrigerants) are the best choice as substitutes for

halogenated refrigerants in domestic refrigerators (Mohanraj et al., 2006). Using hydrocarbon mixture

as a refrigerant, leads to the changes in refrigerator temperature occur faster and the ON time ratio of

the compressor is less than that of using R134a thus reduction in the compressor’s energy consumption

(Mohanraj et al., 2009; Mani et al., 2008). Refrigeration proportion of the worldwide energy

consumption is about 15% (Landymore, 2007; Annual energy review 2010). The latent heat of

hydrocarbons is significantly better than R134a, i.e. the amount of heat absorbed during evaporation is

much higher per kg of refrigerant circulating in the system, and therefore the amount of refrigerant

charge can be reduced (Rasti et al., 2012). Maclaine-cross (1997) measures on various systems and

reported that the use of hydrocarbon refrigerants sometimes reduction the energy consumption about

20% in comparison with R12 and R134a (Maclaine-cross, 1997). In addition R600a has the half price

of R134a which shows the R600a is economically beneficial (Joybari et al., 2013). The results showed

that the R290 could not be used as a refrigerant replacement due to its high operating pressure

compared to R134a (Sattar et al., 2007). Although R600 and R600a offer many desirable characteristics

such as in operating pressure, mass flow rate, discharge temperature and high coefficient of

performance (COP), the compressor should be changed due to its mismatch in volumetric cooling

capacity (VCC) (Mohanraj et al., 2008). Safety guidelines for different refrigerants can be found

elsewhere such as the handbook of GTZ Proklima (Colbourne et al., 2010). R600a is not using in North

America because of the flammability risk and explosion hazards in domestic refrigerators (Calm.,

2008), while in European countries R600a is the most popular refrigerant to use in domestic


18

refrigerators (Bansal et al., 2011).Additionally, among the hydrocarbon refrigerants, R600a is used

more than 95% of market share in many countries (RTOC., 2006).

To optimize refrigeration cycles offer potential energy and cost savings. The refrigeration cycle can

best be evaluated by energy and exergy analyses (Mokhatab et al., 2014).

2. Material and methods

The test ring tabulated to the experiment is a vapor compression refrigeration system developed in

the form a single temperature domestic refrigerator which manufactured to work with 145g of R134a

refrigerant. The schematic diagram and general specifications are summarized in Figs. 1, respectively.

The experimental refrigerator has a capacity of 410L, the main loop of the system under study consist

of four basic components, i.e., a compressor, an evaporator, a condenser, and capillary tubes, as shown

in Figure. 1.

2.1.Testing procedure

Experiments were conducted in a test room with environmental temperature of 25°c.The

refrigerator was instrumented with two pressure gauges and thermocouples at the inlet and outlet of the

compressor, evaporator, capillary tube and condenser for measuring the suction and discharge pressure

and temperature.

Figure 2 shows the present experimental path of the measurements for R134a on a pressure-

enthalpy diagram and a temperature-entropy diagram (T-S diagram), respectively.

Figure. 1 Schematic of the vapor-compression household refrigeration system.


18

Table. 1 Properties of the case study refrigeration system

Property Value Unit

Total volume 410 lit Net volume of freezer 98 lit Net volume of fresh food box 264 lit Ice making capacity 4.5 lit/24h

Climate Temperate

Total net volume 352 lit Voltage 220-240 vol Refrigerant 150 gr Defrost R134a

Capillary tube length (No frost system) 3.55 m

Table. 2 Thermodynamic conditions in different points of the refrigeration cycle

points h P s T v x

1 236.4 114.9 0.9487 -23.3 0.1689

2 290.8 820.5 0.991 54.4 0.02833

3 131 820.5 0.4702 32.2 0.005671

4 131 114.9 0.5269 -23.3 0.0865 0.351

Figure. 2 Pressure-enthalpy diagram of R134a Figure. 3 Temperature-entropy diagram

2.3. Energy, Exergy and Environmental Analyses

In this section we employ energy-exergy analysis for tow gases (R134a and R600a) to minimization

GWP of refrigerator systems.

In real compressor:

(1)

In condenser:

Exergy balance in condenser equation:

-50 0 50 100 150 200 250 300 350 4000x10

02x10

24x10

26x10

28x10

210

310

310

310

310

32x10

32x10

32x10

32x10

32x10

33x10

3

h [kJ/kg]

P [

kP

a]

-23.3°C

32.2°C

54.4°C

0.2 0.4 0.6 0.8

0.3

582

0.3

901

0.9

487

0.9

91 k

J/kg

-K

-0.25 0.00 0.25 0.50 0.75 1.00 1.25

-40

-20

0

20

40

60

80

100

120

140

s [kJ/kg-K]

T [

°C

]

114.9 kPa

820.5 kPa

0.2 0.4 0.6 0.8

0.0

0084

0.0

28

0.0

59

0.1

7 m

3/k

g


18

(2)

Exergy destruction:

[ ( )] ( ) (3)

Exergy efficiency:

(

( )

[ ( )]) (4)

In capillary tube:

(5)

[ ( )]

(6)

In evaporator:

(7)

[ ( )] [ ( )] (8)

(

( )

[ ( )]) (9)

Now we can calculate the exergy destruction of the entire cycle:

(10)

exergy efficiency of the entire cycle:

(11)

The coefficient of performance of the Carnot cycle refrigerator:

(12)


18

The calculated TEWI is sensitive to assumptions of the system lifetime, emission losses, and the

integration time horizon chosen to calculate global warming potential (GWP) values as well as the

source and consumption of energy.

The TEWI is calculated as (Aprea et al., 2012):

TEWI=CO + CO [kg Co2] (13)

CO =RC [ + (

)].V.GWP [kg CO2] (14)

CO =

.H.V [kg CO2] (15)

Table. 3 Parameters of TEWI

Parameter value

H 8760 h 10% year

100%

V 7 years

575 kg co2/kwh

Table. 4 Properties of some common refrigerants.

Global Warming Potential for Given Time Horizon

Industrial Designation

or Common Name Chemical Formula

Lifetime

(years) 20

100

500

HFC-134a 14 38300

1430

435

Isobutene-R600a ( ) 12 <20

<20

<3

3. Result and Discussion

3.1. Inlet temperature of compressor

When T1 is raised, while evaporator pressure is fixed, coefficient of performance and cooling

capacity are increased. Conversely the compressor work and total exergy destruction decreased (see

table 5). Table 4 based on the equations in section 1.

Table. 5 effects of inlet temperature of compressor on different variables using R134a

T1 W

com

Q

evap

Eff

comp COP

Des

com

Des

Evap

Ex

Evap

Ex

Comp

Des

total

Rand

Total

-29 276.9 -117 0.0018 0.42 278.0 -265.6 -8.87 276.9 285.7 3.21

-23 54.18 105.6 0.7558 1.95 12.3 239.7 8.01 54.18 46.17 14.78

-17 49.36 110.5 0.8545 2.24 6.6 250.5 8.38 49.36 40.99 16.97

-11 44.52 115.3 0.9744 2.59 1.0 261.3 8.74 44.52 35.78 19.64

-5 39.65 120.2 1.1240 3.03 -4.4 272 9.11 39.65 30.54 22.98


18

Table. 6 effects of inlet temperature of compressor on different variables using R600a

T1 W

com

Q

evap

Eff

comp COP

Des

com

Des

evap

Ex

Evap

Ex

Comp

Des

total

Rand

Total

-29 504.6 -141.8 0.001188 0.281 506 -322 -10.75 504.6 515.4 2.131

-23 115.6 247.2 0.6176 2.138 41.73 560.8 18.74 115.6 96.9 16.21

-17 106.6 256.2 0.6877 2.402 31.14 581.1 19.42 106.6 87.22 18.21

-11 97.52 265.3 0.7715 2.721 20.65 601.4 20.11 97.52 77.41 20.62

-5 88.26 274.6 0.8736 3.111 10.24 621.8 20.82 88.26 67.45 23.58

Increasing energy efficiency can reduce environmental impact by reducing energy losses. Within

the scope of exergy methods, as discussed, such activities lead to increased exergy efficiency and

reduced exergy losses. Increased efficiency reduces the requirement for new facilities for the

production, transportation, transformation and distribution of the various energy forms, and the

associated environmental impact of these additional facilities. To control pollution, efficiency

improvement actions often need to fuel substitution. Environmental protection project which

undertaken at the regional or national levels, are more effective than individual projects (Dincer et al.,

2007).

Figure. 4 Variability exergy efficiency versus inlet

temperature of compressor (see table 2).

Figure. 5 TEWI of R134a and R600a versus inlet

temperature of the compressor

3.2. Inlet pressure of compressor

As shown in table 7, with reducing the inlet pressure of compressor, the exergy efficiency increase

at a constant temperature. However, it should be noted that there are some limitations on reducing

pressure.

y = 0.4545x + 24.956 R² = 0.9911

y = 0.4087x + 25.376 R² = 0.9924

0.00

5.00

10.00

15.00

20.00

25.00

-25 -20 -15 -10 -5 0

Ex-R

and

(%)

T1(k)

R134a

R600a

Linear (R134a)

Linear (R600a)

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

-40 -30 -20 -10 0

TEW

I

T1

R600a

R134a


11

Table. 7 effects of inlet pressure of compressor on different variables

P1 P4 T4 s1 s4 v1 v4 h1 h4 Wcomp Qevap Effcomp COP

39.9 39.9 -44.66 1.04 0.57 0.50 0.27 238.90 131 51.94 107.9 1.33 2.08

64.9 64.9 -35.39 1.00 0.55 0.31 0.16 238.10 131 52.73 107.1 1.06 2.03

89.9 89.9 -28.67 0.97 0.54 0.22 0.11 237.20 131 53.56 106.3 0.88 1.98

114.9 114.9 -23.3 0.95 0.53 0.17 0.09 236.40 131 54.43 105.4 0.75 1.94

Table. 8 Effect of inlet pressure of compressor on exergy variations in refrigeration cycle

P1 Des

com

Des

con

Des

eva

Des

capi

Rand

comp

Rand

evap

Ex

Evap

Ex

Comp

Des

total

Rand

Total

114.9 12.6 315 239.1 16.9 0.7686 0 0.3935 0 46.44 14.68

89.9 5.849 315 243.8 19.88 0.8908 0 0.3472 0 45.51 15.04

64.9 -2.81 315 249.2 24.07 1.053 0 0.3025 0 44.62 15.4

39.9 -15.33 315 255.9 30.75 1.295 0 0.2565 0 43.76 15.75

Figure. 6 TEWI versus inlet pressure of the

compressor

Figure. 7 TEWI versus total exergy destruction in different

inlet pressure of compressor

3.3. Outlet temperature of condenser

As can be seen in Table 5, the reduction of temperature at point No.2 has led to increase in exergy

efficiency and the coefficient of performance. It stems from the less work required from the

compressor. Nevertheless, the limitations of the design and selection of the compressor and condenser,

prevent the temperature reaching below the desire level.

Table. 9 effects of outlet temperature of condensor on different variables

T2 Wcomp Qcond Effcomp COP Des

com

Des

con

Rand

com

Ex

Com

Ex

Evap

Des

total

Rand

Total

40 39.63 145 1.03 2.66 -1.17 286.5 1.03 39.63 7.99 31.64 20.16 42.4 42.18 147.6 0.97 2.50 1.24 291.4 0.97 42.18 7.99 34.19 18.95 44.9 44.7 150.1 0.91 2.36 3.62 296.3 0.92 44.7 7.99 36.71 17.87 47.3 47.22 152.6 0.87 2.23 5.97 301.2 0.87 47.22 7.99 39.23 16.92 49.8 49.72 155.1 0.82 2.12 8.28 306 0.83 49.72 7.99 41.73 16.07 52.2 52.21 157.6 0.78 2.02 10.58 310.8 0.80 52.21 7.99 44.22 15.3 54.7 54.7 160.1 0.75 1.93 12.85 315.5 0.77 54.7 7.99 46.71 14.61 57.1 57.18 162.6 0.71 1.84 15.09 320.3 0.74 57.18 7.99 49.19 13.97 59.6 59.66 165.1 0.69 1.77 17.32 325 0.71 59.66 7.99 51.67 13.39 62 62.13 167.5 0.66 1.70 19.53 329.7 0.69 62.13 7.99 54.14 12.86

3400

3450

3500

3550

3600

3650

3700

3750

0 50 100 150

TEW

I

P1

114.9

89.9

64.9

39.9,

3400

3450

3500

3550

3600

3650

3700

3750

43 44 45 46 47

TEW

I

DES-total


18

Figure. 8 Exergy efficiency versus outlet

temperature of the condenser

Figure. 9 TEWI versus total exergy efficiency in

different outlet temperature of condenser

3.4. Effect of changing pressure in condenser

Changes in the outlet pressure of the compressor will lead to variations in refrigerant pressure in the

condenser. Care must be taken in compressor limitation when pressure increases, therefore the

refrigerant could not be achieved to saturated state. In general, by given the initial assumptions, rise in

the pressure, at a constant temperature, for condensing procedure in the condenser, is one of the

effective ways to raise the efficiency of the cycle.

Table. 10 effects of outlet temperature of condenser on different variables

T4 P2 Wcomp Qcond Qevap COP Rand

com

Rand

eva

Ex

Com

Ex

Evap

Des

total

Rand

Total

15.7 800 54.79 22.9 -31.89 0.582 0.7542 0.7041 54.79 -2.418 57.21 4.412

-23.3 900 52.99 192.6 139.6 2.635 0.8236 0.3935 52.99 10.58 42.4 19.97

-23.3 1000 51.09 190.7 139.6 2.732 0.8932 0.3935 51.09 10.58 40.51 20.71

-23.3 1100 49.1 188.7 139.6 2.843 0.9649 0.3935 49.1 10.58 38.51 21.56

-23.3 1200 46.98 186.6 139.6 2.972 1.041 0.3935 46.98 10.58 36.4 22.53

-23.3 1300 44.72 184.3 139.6 3.122 1.123 0.3935 44.72 10.58 34.14 23.67

-23.3 1400 42.29 181.9 139.6 3.302 1.215 0.3935 42.29 10.58 31.7 25.03

-23.3 1500 -106 33.62 139.6 1.317 -0.367 0.3935 -106 10.59 -116.6 9.986

3.5. Exergy-Environment

Using exergy as a tool can reduce energy consumption and environmental degradation. The second

law of thermodynamics is discussed to providing insights into environmental impact. Following this,

exergy found to be an effective measure of the potential of a substance to impact the environment.

0

5

10

15

20

25

0 10 20 30 40 50 60 70

Ran

d-t

ota

l

T2

0

1000

2000

3000

4000

5000

0 5 10 15 20 25

TEW

I

Rand-total


89

Figure. 10 TEWI of R134a and R600a versus total exergy

efficiency of cycle Figure. 11 TWEI of assessed years

3.6. Risk analysis

However hydrocarbons pose fire and explosion hazards, so if used in domestic refrigeration

systems, the impact on safety should be negligible. Appropriate equipment and design could reduce the

risk of using R600a in domestic refrigerators. Data has been gathered from industries in Iran, then

FMEA method used to determination of value of risk.

According to results of table11 and table 12, which indicate two major potential failure modes in

household refrigerator show the risk of using R600a is in safe range.

4. Concolution

Using of hydrocarbons with a zero ODP, and a lower GWP in compare with R134a for household

refrigerator systems help to reduce energy consumption. Furthermore, when the refrigerator is working

with R600a type compressor, have a total TEWI about 42% less than HFC refrigerator. In this research,

the relation between exergy efficiency and its impact on environment have been investigated. The

results show that, by increasing in total exergy efficiency, total equivalent warming impact has been

reduced generally. R600a demonstrate better cop and exergy efficiency, which make R600a a suitable

substitution for R134a refrigerant in domestic refrigerator system.

Acknowledgments

We greatly acknowledge Emersun Industry Group for funding and supporting the project.

02000400060008000

1000012000140001600018000

0 10 20 30

TEW

I

Exergy efficiency

R600a

R134a

0

50000

100000

150000

200000

250000

300000

20 100 500

TEW

I

Years

R134a

R600a


88

Table. 11 Identification and Risk Assessment Form1

Identification and evaluation of the risk Reformation activity Evaluation of the risk after

reformation

raw

Fu

nct

ion

haza

rd

con

seq

uen

ce

Ris

k

sou

rce

Cu

rren

t

Con

tro

l

Sev

erit

y

Prob

ab

ilit

y

Det

ect

ion

RP

N

Rec

om

me

nd

ed

act

ion

s

Act

ion

s

For

furt

her

Inves

tigati

on

Sev

erit

y

Prob

ab

ilit

y

Det

ect

ion

RP

N

1

Tra

nsp

ort

atio

n

Hit

the

refr

iger

ator

Dam

age

to t

he

cooli

ng s

yst

em R

efri

ger

ant

leak

age

–

Cre

ate

a fi

re

Lac

k o

f ap

pro

pri

ate

safe

guar

ds

on t

he

syst

em -

lac

k o

f pro

per

trai

nin

g

to t

he

tra

nsp

ort

work

ers

Pac

kin

g w

ith c

arto

n a

nd p

alle

t -

Gas

det

ecto

rs

3

3

4

36

Per

sonal

tra

inin

g t

o h

ow

tra

nsp

ort

the

refr

iger

ator-

pro

vid

e le

ak

det

ecti

on g

uid

elin

es-

supply

a f

ire

exti

nguis

her

in a

ref

riger

ator

box

Educa

tion m

ethods

for

corr

ect

tran

sport

atio

n o

f re

frig

erat

ors

-

Lea

k d

etec

tion

aft

er i

nst

alla

tion

3

2

3

18


88

Table. 12 Identification and Risk Assessment Form2

Identification and evaluation of the risk Reformation

activity

Evaluation of the risk

after reformation

raw

Fu

nct

ion

haza

rd

con

seq

uen

ce

Ris

k

sou

rce

Cu

rren

t

Con

tro

l

Sev

erit

y

Prob

ab

ilit

y

Det

ect

ion

RP

N

Rec

om

men

ded

act

ion

s

Act

ion

s F

or

Fu

rth

er

Inves

tigati

on

Sev

erit

y

Prob

ab

ilit

y

Det

ect

ion

RP

N

2

wel

d

Def

ect

in r

efri

ger

ant

syst

em

Lea

kag

e- i

gnit

ion

Not

know

ing h

ow

to p

roper

ly w

eld -

the

lack

of

stan

dar

d t

ools

- l

ack o

f

pre

cisi

on i

n t

he

wel

din

g

Wel

din

g e

duca

tion

- le

akag

e te

st

3 4 4 48

Per

sonal

tra

inin

g t

o h

ow

wel

d-p

rovid

e le

ak d

etec

tion g

uid

elin

es-

supply

a fi

re e

xti

nguis

her

in a

ref

riger

ator

box

Educa

tion m

ethods

for

corr

ect

wel

din

g-

Lea

k d

etec

tion a

fter

inst

alla

tion

3 3 3

27

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