197

J. of Advanced Engineering and Technology

Vol. 1, No. 1 (2008) pp. 197-201

The Comparison of Performance Characteristics in Refrigeration System using R717 and R22

Sung Bae Kim† and Suk Joo Hong*

Graduate School, Dept. of Mechanical Engineering, of Chosun University, Gwangju, 501-759, Korea

*Dept. of Mechanical Engineering, Chosun University, Gwangju, 501-759, Korea

(Received : Jul. 17, 2008, Revised : Aug. 29, 2008, Accepted : Sep. 23, 2008)

Abstract : The production and use of freon substances are recently restrained due to the destruction of ozone

layer and global warming. In this aspect of environmental problems, the best solution is to use natural

refrigerant such as ammonia. This study is to apply R717 and R22, to study performance characteristics from

the superheat control and to compare the energy efficiency of two refrigerants from the high performance.

The condensing pressure of refrigeration system is increased from 1,500 kPa to 1,600 kPa, and the degree

of superheat is increased from 0 to 10 at each condensing pressure. The result of the experiment proved that

R717 is suitable as an alternative refrigerant of R22 compared with each COP.

Keywords : HCFC(hydro chloro fluor carbon), degree of superheat, condensing pressure

1. Introduction

Refrigeration system is being applied widely in industries

such as small refrigerators, cars, ships, skyscrapers and large-

scale chemical plants. It has been used especially in chemical

processing industry for gas separation and liquefaction, solidification

of core material in synthesis to separate, maintenance process

to prevent liquid stored in low temperature from excessive

pressure, and drying and clearing reaction heat, etc[1].

Worldwide pending questions forward are to improve

energy efficiency and to develop alternative refrigerants to Freon.

Consuming those alternatives is very severely controlled. To

study on establishing design technology of mutual assistance

equipment is being progressed actively in the world to cope

with this control. The study on the alternative to R22 is

inevitable of all things[2-4].

Refrigerants like R12, R22 and R717 have not only made

human lives comfortable but also been a motive to generate

all sorts of machinery industries. Ammonia has been used as

a refrigerant in almost all systems except quite small-sized

systems. It had dominated over refrigeration field from 1890

to 1940 due to the good thermodynamic characteristics and

low cost. However, it has not been recognized as a good

refrigerant because of its toxicity and inflammability, even

though its thermodynamic characteristics are excellent as a

refrigerant. After that, R12 and R22 which are called Freon

are recognized as the best refrigerants as mankind has ever

discovered and they have been used broadly. But R22 is a sort

of chemicals like Hydro Chloro Fluor Carbon(HCFC) which

has phased out according to Montreal Protocol, an international

agreement on the materials destructing ozone layer. So it must

be very reasonable that studying on natural refrigerants gets

accomplished very actively.

R717, an organic compound, and propane and propylene,

sorts of hydrocarbon, are natural refrigerants which are easy

to get and purchase cheaply. Especially they are environment-

friendly refrigerants which are not collided with the environment

of the earth. Among them R717 has excellent characteristics

in wide range of temperature and so it is used a lot in chemical

process, and is expected to be preferred as a good refrigerant[5].

R717 generally is considered to be reasonable in efficiency

and price, and is a refrigerant widely used the most in the

process of foods and drinks and in the facilities of refrigerated

warehouses. It is suitable as an alternative refrigerant to R22

for an industrial refrigeration system, although its market share

is small. But its usage in the system for pleasant facilities

goes slowly worrying about its toxicity. Nevertheless R717 is

environment-friendly as a natural refrigerant and known to have

a good efficiency[6]. The existing study on the refrigerant of

R717 has been deficient and restrictive so far. So much more

study on the refrigerant of R717 is required to be carried out.

R717 is a suitable refrigerant for low temperature refrigeration

and R22 for middle temperature air-conditioning. However, a

noticeable result is expected in case of using R717 and R22 in

the same refrigeration system. So we will compare performance

characteristics of each refrigerant through the experiments

whose system shows the degree of superheat changes depending

on condensing pressure. We also try to make clear the superiority

of R717 as an alternative refrigerant to R22.

†Corresponding AuthorTel : 061-689-4951E-mail : ksbkim@hanmail.net

공학기술논문지 제1권 제1호 (2008)

198 Sungbae Kim and Sukjoo Hong

2. Experimental Equipments& Procedure

2.1. Experimental Equipments

Figure 1 is the schematic of experimental equipments to

study the performance characteristics in refrigeration system

which shows the degree of superheat changes depending on

condensing pressure.

R22 and R717 were used as operating fluids in this system.

The experimental equipments were composed of a compressor,

a condenser, a receiver, a constant temperature bath, an expansion

valve and other accessory equipments. They were made very

carefully to minimize the loss of pressure in the system. The

part of low pressure in the system was insulated in order not

to be affected from the outside temperature which meets KS

standard. Pressure sensors, temperature sensors, mass flow meters,

a superheat controller, pressure control valves and a power

meter were equipped in the system to measure the phase

change in those operating fluids within the system. And they

were controlled within the range of errors of measuring machines

(± 0.1oC of temperature, ± 0.1bar of pressure, ± 0.1% of mass

flow and ± 0.1% of power consumption). A screw-open type

compressor was used to do the experiment under constant load,

and the side of slide was fixed to maintain the load constantly.

A heat exchanger of shell & tube type was used for a

condenser and an evaporator and water was used as fluid for

phase change(cooling water and chilled water). A heater of

1kW and a 3-way control valve were installed to keep up

constantly the temperature of fluid for phase change. A constant

temperature bath was installed to be controlled automatically

by a thermometer controller.

An inverter circulation pump and a flow control valve were

installed to keep up constantly mass flow of chilled water for

an evaporator.

To control degree of superheat, an electronic expansion valve

was used [7]. It calculates the degree of superheat according

to the suction temperature and the suction pressure of each

sensor attached to a manual expansion valve and an outlet of

an evaporator, and then opens the valve automatically by PID

control to make the set up value. A pressure control valve was

installed to control condensing pressure. It reads a pressure

sensor on the top of a condenser and controls cooling water

flow of a condenser automatically by the set up pressure. A mass

flow meter was installed to measure mass flow of cooling

water of the condenser. Mass flow meters were installed each in

a receiver and an outlet of an evaporator to measure mass

flow of a refrigerant.

2.2. Experimental Procedure

Before operating the experiment of refrigeration system,

the values of each measuring machine attached to equipments

with ones of the transmitted were compared, errors were checked,

and then the operation condition was monitored by monitoring

program. A circulation pump was operated to examine whether

the flow of an evaporator is controlled constantly, then the mass

flow was checked.

In order to keep the same condition of each refrigerant equal,

enough amount of a refrigerant was charged and the load of

R22 was decided about a half of R717 within the system

permitted. If the operation condition became stable, experiments

were conducted by steps of 500kPa of condensing pressure

from 1,500 kPa to 1,600 kPa, and by steps of 1oC of degree of

superheat from 0 to 10oC according to the condition of condensing

pressure. At the beginning of the operation, an electronic expansion

valve was used to make degree of superheat close to the set

up value and then a manual expansion valve was used to keep

up the correct set up value constantly. the experiment was

conducted repeatedly to make accuracy of the experiment data

high. The result data of the experiment were measured by 2

seconds by data acquisition system, and then analyzed by PC.

3. The result & Considerationof The experiment

The result of the experiment was considered, which compared

COP of power consumption of compressor and refrigeration

capacity. It depends on the change of heat capacity of condenser,

heat capacity of evaporator, mass flow of refrigerant, suction

pressure, mass flow of cooling water in a condenser and the

temperature of chilled water in the outlet of an evaporator,

when changing degree of superheat by condensing pressure.

3.1. Refrigerant Mass Flow

Figure 2 shows mass flow of suction vapor in compressor.Figure 1. The schematic of refrigeration system.

J. of Adv. Eng. and Tech., Vol. 1, No. 1 (2008)

The Comparison of Performance Characteristics in Refrigeration System using R717 and R22 199

Mass flow generally decreased as condensing pressure and

degree of superheat increased. The compression rate of a compressor

increased and the volume efficiency decreased as condensing

pressure went high, and then its mass flow decreased.

Being compared refrigerants, the mass flow of R22 increases

the highest under 1,500 kPa of condensing pressure and 0 of

degree of superheat. For R717, however, the highest mass

flow is under 1oC of degree of superheat. Using R717 as a

refrigerant in a heat exchanger of shell & tube type, refrigerant

fluid is vaporized in about 0 of degree of superheat, bubbles

come on the surface of the tube and they rise up getting lost

heat by cold refrigerant fluid around them. At this time the

refrigerant gas becomes liquid again, and this subcooled

boiling [8] is concluded as a cause. Thus, less amount of refrigerant

gas than expected comes into the compressor in around 0

degree. R22, however, didn't show this phenomenon. There may

be delicate differences caused by the type of a heat exchanger

and the value of properties of the refrigerant.

Taken all together, R717 has a pretty gentle slope compared

with R22, and this shows its stability under the change of

condensing pressure and degree of superheat.

3.2. Compressor Suction Pressure

Figure 3 is the result of the experiment on suction pressure

of compressor. As condensing pressure changed, suction

pressure of compressor resulted differently each other from

refrigerants. Generally the higher degree of superheat, the

lower suction pressure.

Suction pressure of compressor depending on condensing

pressure had seldom changed in case of R717. But in case of

R22 it went up as condensing pressure became high. As

shown in Figure 2, mass flow of suction vapor in compressor

decreased as condensing pressure went higher. All together,

pressure should be decreased, but the increase of condensing

pressure made high pressure go up and had constant degree of

super-cooling. This made low pressure go up, and thus the

rising of low pressure was concluded to work more than the

decrease of mass flow. In case of R717, the decline of mass

flow of practical refrigerant depending on the rising of

compression rate was concluded to work more than the rising

of low pressure because its load was twice of R22.

Suction pressure of a compressor declined as the degree of

superheat went up because mass flow of suction vapor in

compressor decreased as shown in Figure 2. For R717 mass

flow decreased little, on the other hand suction pressure decreased

much. It resulted from the value of heat properties of R717 as

a refrigerant. Its ratio volume depending on the phase change

of the refrigerant increased more being compared with R22,

and it meant suction pressure was more sensitive than the

change of mass flow.

3.3. The Mass Flow and the Temperature of

Condenser Cooling Water

Figure 4 and Figure 5 show the mass flow and the outlet

temperature of condenser cooling water. The outlet temperature

of cooling water declines as the flow of cooling water increases.

On the contrary, the temperature goes high in inverse proportion

to the flow of cooling water decreased.

For R717, the mass flow and the outlet of cooling water in

1,500 kPa and 1,600 kPa of condensing pressure had no

difference even if changed the degree of superheat. The mass

flow of condenser cooling water decreased much as condensing

pressure was high under 1,500 kPa and 1,550 kPa of condensing

pressure and 0~4oC of degree of superheat. But under 4

oC~

10oC, the mass flow of condenser cooling water decreased little

even if condensing pressure went high. The enthalpy of refrigerant

vapor discharged from compressor increased as the degree of

superheat went high under the equal condensing pressure.

The mass flow of cooling water generally should increase

much, but increased less than under 0~4oC. It is concluded that

the large refrigeration area of condenser achieved refrigeration

enough to the increase of enthalpy.

3.4. Condenser Heat Capacity

Figure 6 shows the value of heat capacity measured by the

flow of condenser cooling water and the outlet temperature.

Figure 3. The relations of suction pressure and degree of superheat

at each condensing pressure.

Figure 2. The relations of suction mass flow rate and degree

of superheat at each condensing pressure.

공학기술논문지 제1권 제1호 (2008)

200 Sungbae Kim and Sukjoo Hong

Heat capacity decreased as condensing pressure and degree of

superheat went high. Condenser heat capacity increased in

proportion to mass flow of a refrigerant and suction pressure

high. It shows mass flow of a refrigerant and suction pressure

are the factors which have an effect on the change of condenser

heat capacity.

The aspect of heat capacity of two refrigerants were equal

except the increase of heat capacity resulted from sub-cooled

boiling of R717. The difference of heat capacity due to the

difference of load showed same to other figure.

3.5. Outlet Temperature of Evaporator Chilled

Water and Evaporator Heat Capacity

Figure 7 and Figure 8 show the outlet temperature of

evaporator chilled water and evaporator heat capacity. For both

refrigerants, the chilled water outlet temperature went high and

evaporator heat capacity went low as condensing pressure and

degree of superheat were high. High outlet temperature of

chilled water and low heat capacity of evaporator means that

refrigeration effect gets less that much. High condensing

pressure makes saturation pressure of evaporator refrigerant

high and it makes refrigeration effect decreased. For degree of

superheat, the cause can be the decline of refrigerant mass

flow as shown in Figure 2. Compared condenser heat

capacity with evaporator heat capacity, heat capacity was almost

similar. Generally condenser heat capacity should be as big as the

power consumption of compressor, being compared with

evaporator heat capacity. The reason why the result came out

like this could be explained as the circulation refrigerator oil

was radiated from an oil separator in the system.

3.6. Power Consumption and COP

Figure 9 and Figure 10 show power consumption and COP.

Figure 4. The relations of cooling water mass flow rate and

degree of superheat at each condensing pressure.

Figure 5. The relations of cooling water outlet temperature and

degree of superheat at each condensing pressure.

Figure 6. The relations of condenser heat capacity and superheat

temperature at each condensing pressure.

Figure 7. The relations of chilled water outlet temperature

and degree of superheat at each condensing pressure.

Figure 8. The relations of evaporator heat capacity and degree

of superheat at each condensing pressure.

J. of Adv. Eng. and Tech., Vol. 1, No. 1 (2008)

The Comparison of Performance Characteristics in Refrigeration System using R717 and R22 201

For both refrigerants, power consumption increased as

condensing pressure and degree of superheat went high. Keeping

up condensing pressure constantly and making the degree of

superheat high decreases the refrigerant mass flow vaporized

from evaporator and evaporation pressure. It makes compression

ratio go up and power consumption increase.

Figure 10 is the result of the experiment on COP. COP is

the relation of evaporator heat capacity and power consumption.

As condensing pressure and degree of superheat went high,

evaporator heat capacity decreased and power consumption

increased. R22 showed higher because of subcooled boiling

at 0~2oC of degree of superheat. But R717 showed higher at

more than 2oC of degree of superheat.

Being compared the leading slope of each refrigerant, R717

showed more stable COP than R22 did depending on the

degree of superheat. R717 also showed almost equal COP to

R22 even though it had twice of load. It means that R717 will

show higher COP in case it is measured under the equal load.

4. Conclusion

This study compared the performance characteristics in

refrigeration system using R22 and R717, and concluded as

follows;

1. For circulation amount of refrigerant, R717 was more

stable than R22 at the change of condensing pressure

and degree of superheat. Its circulation amount of refrigerant

was about 1/4 of R22 and the suction pressure was much

lower even if operated with double load of R22. This

confirmed that R717 is superior to R22 in miniaturizing

refrigeration system.

2. As degree of superheat went up, refrigerant mass flow come

into evaporator decreased, compression ratio became big,

the power increased and then the loss of energy got bigger.

3. COP showed R717 became higher than R22 at more

than 2oC of degree of superheat. If operated with the

equal load, R717 must show the higher than R22 on the

whole. R717 was proved to have the most suitable condition

to save operating cost with energy-saving at 1oC of

degree of superheat.

4. R717 is a natural refrigerant. Considering not only its

efficiency depending on developing attached systems

hereafter and its stability being complemented but also

economical and environmental aspects, it seems to be

suitable as an alternative refrigerant to R22 which is

currently one of restricted items.

Nomenclature

r : Mass flow of refrigerant, [/h]

cw : Mass flow of condenser cooling water, [/h]

Tch : Outlet temperature of evaporator chilled water, [oC]

Tcw : Outlet temperature of condenser cooling water, [oC]

Ps : Suction pressure of compressor, [kPa]

Qe : Evaporator heat capacity, [kW]

Qc : Condenser heat capacity, [kW]

References

(1) Stoecker, W. F., Refrigeration and Air conditioning, 2nd ed.,

McGraw-Hill, New York, 1-12, 296-307 (1982).

(2) Nonaka, M., et al., The Int. Symp. on HCFC Alternative

Refrigerants., 111-116 (1998).

(3) Nakayama, M., et al., Room A/C, Ref., 72(835) 60-64(1997).

(4) Akutsu, M., et al., Sanyo Technical Review., 30(1) 20-26

(1998).

(5) Effect of Ammonia, Refrig., Res. Found. Inform. Bull.,

Washington, D.C., 4 (1979).

(6) James, M., and Piotr, A. Domanski, Magazine of the SAREK.,

34, (1), 60-69 (2005).

(7) Higuchi, K., Refrigeration., 61, 45-52 (1986).

(8) Cengel, Y. A., Heat Transfer., McGraw-Hill, New York, 461-505

(2002).

m·

m·

Figure 9. The relations of power and degree of superheat at each

condensing pressure.

Figure 10. The relations of COP and degree of superheat at each

condensing pressure.