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Development of a high-efficiency domestic refrigerator using CFC substitutes
Development of a high-efficiency domestic refrigerator using CFC substitutes Y. Wu, G. Xie and X. Z. Li Department of Power Machinery Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China Received 17 N o v e m b e r 1991; revised 16 April 1993
Besides the values of the ozone depletion and global warming potentials, energy consumption is another important index to be considered in developing a refrigeration system using CFC substitutes. Many investigators have indicated that unless the original refrigeration system is correspondingly adjusted when using CFC substitutes, the energy efficiencyratio (EER) of the system will decrease. In this paper, the reasons for a decrease in EER are analysed theoretically, and some proposals for increasing EER are put forward. These proposals are used to develop a domestic refrigerator charged with a non-azeotropic mixture of HCFC22/I-IFC 152a as the substitute for the original working fluid, CFC12. The results show that the EER value of the refrigerator charged with this refrigerant mixture is increased by 6.5~ocompared with that of the same refrigerator charged with CFC12. (Keywords:refrigeratingmachine;householdrefrigerator;CFC; substitute;mixture;R12; R22; R152a; efficiency)
Mise au point d'un r6frig6rateur domestique haute performance utilisant des substituts de CFC Dans la conception d'un syst~me frigorifique utilisant des substituts de CFC, il est important de considerer, non seulement les valeurs de Potentiel de destruction de r ozone ( O D P ) et Potentiel d'effet de serre ( G WP ), mais aussi la consommation d'bnergie. Maints chercheurs ont indiqub que, si le syst~me frigorifique original n'est pas correctement adaptb aux substituts des CFC, le rapport d'efficacitk ~nergbtique (EER) diminuera. Dans I'article, on analyse de faqon thborique les raisons d'une diminution du rapport d'efficacitb bnergbtique, et on propose quelques solutions pour l'augmenter. On applique ces solutions propos~es dt la mise au point d'un r~frigbrateur domestique chargb avec un mblange non az~otropique de HCFC22 et de HFC152a, en remplacement du CFC12. Les rbsultats montrent que le rapport d'efficacitb ~nergbtique de ce rbfrigbrateur chargb avec ce mblange augmente de 6,5 %, par rapport & celui de m~me refrigbrateur chargb avec du CFC12.
(Mots d6s: machinefrigorifique;r6frig6rateurdomestique;CFC; substitute; m61ange;R12; R22; R152a; rendement)
When using CFC substitutes, the original CFC refrigeration system becomes unsuitable due to the differences between CFCs and their substitutes in their thermophysical properties. Unless the system is adjusted, its energy efficiency ratio (EER) will be decreased, as has been shown by many investigators in this field 1-4. It is therefore necessary to adjust the original system according to the used substitute: that is, to redesign and/or reselect some key parts of the system. In order to adjust the system properly, it is necessary to analyse the reasons for the decrease in EER and this will help us to find the methods for improvement.
Accordingly, the key parts of the compressor, such as compressor valves, must be redesigned. The compressor valves operate under the effects of both drag and elastic forces of the valve reeds, as shown in Figure 1. When the pressure in the cylinder exceeds the pressure in the discharge chamber, the valve will open and cling onto the valve stop. The valve will close when the drag force becomes smaller than the elastic force of the valve reed. The normal movement of the valves is displayed in Figure 2. In the figure, the ordinate represents the valve displacement while the abscissa stands for the crank shaft angle. The drag force acting upon the valve reed may be determined by the following formulaS:
Reasons for redesigning and/or reselecting some key parts when using CFC substitutes
F = (flS)AP = (flSXkn2M2/8)~k
Compressor
When using CFC substitutes in a refrigeration system, the performance parameters of the compressor, such as suction and discharge pressures, refrigerating capacity per unit of swept volume and so on, will be changed. 0140-7007/94/030205-04 © 1994 Butterworth-Heinemann Ltd and IIR
(1)
where F is the drag force, fl is the drag coefficient, S is the effective force area of the valve reed, P is the pressure, k is the adiabatic exponent, My is the Mach number at valve gap, and ¢ is a function of the crank shaft angle ct. It is clear that for an identical compressor, the drag force will be changed when using different refrigerants because of the different Mach number M v.
Rev. Int. Froid 1994 Volume 17 Num6ro 3
205
A high-efficiency refrigerator using CFC substitutes, Y. Wu et al. discharge chamber alve reed
",k
y
elastic {orce
•drag force
^ piston
dead point
U
dead point
a(deg) Figure 3 Delayed closing of the valve Figure 3 D~lai de fermeture du clapet
Figure 1 Forces acting upon the valve reed Figure 1 Forces agissant sur le clapet flexible
E
a1
dead aoint
dead point a(deg)
Figure 2 Normal movement of the valve: a to b, valve reed opening; b to c, valve reed staying on valve stop; c to d, valve reed closing. Figure 2 Mouvement normal du clapet, ab, ouverture du clapet flexible, bc, clapet flexible h l'arrOt, ed, fermeture du clapet flexible
If the drag force is too large, the valve cannot close in time, resulting in delayed closing as shown in Figure 3. Conversely if the drag force is too small, the valve cannot open fully, bringing about fluttering as shown in Figure 4. The movement of the compressor valve shown in Figures 3 and 4 is abnormal, causing the pressure pulsation in both the suction and discharge chambers of the compressor to increase. As a consequence, its energy consumption will rise. According to the above discussion, compressors should be redesigned or reselected to suit the thermophysical properties of the CFC substitute used.
dead ~oint Figure 4
Fluttering of the valve Figure 4 Battement du clapet
P
3,/
When using CFC substitutes, the 'unit heat loads of both evaporator and condenser will be changed. As shown in Figure 5 6, the unit heat load of the evaporator is qe = hi - h4
(2)
while the unit heat load of the condenser is q¢ = h 2 - h 3
(3)
Correspondingly, the heat loads of the two heat exchangers are as follows: Qe = m(ha - h4)
(4)
Qc=m(h2 - h 3 )
(5)
206
Int. J. Refrig. 1994 Volume 17 Number 3
/ /
A --= --
Evaporator and condenser
dead point
a(deg)
h qe
-qc
Figure 5 Unit heat loads of both evaporator and condenser Figure 5 Charges thermiques de l'dvaporateur et du condenseur
where h 1, h2, h a and h 4 are enthalpy values, and m is the mass flow rate of the refrigerant. When using substitutes, hi, h 2, h3 and h4 as well as m will change, causing heat loads Qo and Qc and the unit heat loads qe and qc to change. When using CFC substitutes, the heat transfer coefficient of the refrigerant will also be changed. Generally, the heat transfer coefficient depends on the flow pattern and thermophysical properties of the refrigerant. Different refrigerants have different thermophysical properties, and therefore have different heat transfer coefficients. Since the heat loads of both the evaporator and condenser and the heat transfer coefficient are changed, it becomes essential to redesign and/or reselect the two heat exchangers.
A high-efficiency refrigerator using CFC substitutes." Y. Wu et al.
1.0
Capillary The pressure drop of a refrigerant flowing through a capillary depends on the dimension of the capillary as well as the thermophysical properties of the refrigerant. When using CFC substitutes, the dimension of the capillary should be redesigned due to the different properties of the various refrigerants in order to meet the desired evaporating temperature for the system.
RMi2ture O.5
Experimental confirmation Based on a domestic refrigerator originally charged with CFC12, a new refrigerator (BC-132) charged with a mixture refrigerant HCFC22/HFC152a was developed. The domestic refrigerator has a storage volume of 132 1. The charged amount of the mixture was determined by trial and error according to the technical specifications for the refrigerator, such as storage temperature, cooling capacity and so on. The composition of the mixture was chosen experimentally so as to keep the compressor refrigerating capacity almost the same as the original one. The same lubricant oil was used for both the original and the substitute refrigerants. As regards the components of the refrigerator, the evaporator was not changed because of the complexity of its shape. The dimension of the capillary was also retained since theoretical calculations v show that with an unchanged diameter only its length has to be adjusted a little when the mixture is applied. Therefore, only the compressor and condenser were reselected and redesigned during development of the refrigerator.
0
,
0
i
l
~
i
. . . .
,
,
,
l
,
,
,
,
100
Figure6
,
200 a (deg)
400
Movements ofboth suction (le~)anddischarge(right)valves
Mouvements du clapet d'aspiration (gauche) et du clapet de refoulement (droite) I. 24
I. 23 ..o v
/
I . 22
i
Mixture R12
........................... 100 200 300
1.21 F
400
u (deg)
Figure 7
Pressure pulsation in the suction chamber
Figure 7
Pulsation de pression dans la chambre d'aspiration
12. 30 12.25 "~ 12. 2q
Mixture
"o
A
R12
12.15 12.10 12.05
100
0
200 = (deg)
300
400
Figure 8
Pressure pulsation in the discharge chamber
Figure 8
Pulsation de pression dans la chamhre de refoulement
2O
Mixture R12
5
0 '
I
1.
2.0
3.0
Redesigning the condenser The substitute HCFC22/HFC152a is a non-azeotropic mixture refrigerant. Its temperature varies during con-
300
Figure6
Reselecting the compressor On the basis of the performance prediction completed by using computer simulation technology8'9, a new compressor was chosen to replace the original one in order to match the requirement of the mixture. Fioures 6-9 are computer-simulated results obtained under the working conditions listed in Chinese standard GB9098-88. The predicted valve movement of the compressor using the mixed refrigerant is shown in Figure 6, indicating that both the suction and discharge valves possess rather good operating performance. The pressure pulsation in both the suction and discharge chambers while using the mixture is plotted in Figures 7 and 8. For comparison, the pressure pulsation is also calculated when refrigerant CFC12 is used. It can be seen from Figures 7 and 8 that the pressure pulsation when using the mixture is smaller than that when using CFC12, thereby resulting in a reduction of energy consumption. Figure 9 shows the predicted P - V diagram of the compressor. Both the diagrams for CFC12 and the substitute used here are computed for comparison. The calculated result shows that the area in the P - V diagram for the substitute refrigerant is 4% smaller than that for CFC12. As the compressor refrigerating capacities charged with CFC12 and HCFC22/HFC152a are almost the same, we can therefore conclude that the energy consumption is reduced by 4%.
'I
Figure 9
P Vdiagram of the compressor
Figure 9
Diagramme P-V du compresseur
I
I
I
I
I
4,0 V ( X lO-SmD
Rev. Int. Froid 1994 Volume 17 Num~ro 3
I
5.
207
A high-efficiency refrigerator using CFC substitutes. Y. Wu et a l. T
/%
Table 1 The tcsl conditions Tableau 1 Conditions d'essai
s Figure 10 Condensation of non-azeotropic refrigerants Figure 10 Condensation des frigorigknes non azrotropiques
d e n s a t i o n u n d e r c o n s t a n t pressure, as s h o w n in Figure 10. In a c c o r d a n c e with this special characteristic, a c o u n t e r flow heat e x c h a n g e r of the w i r e - o n - t u b e type was designed to t a k e the place of the original cross-flow condenser of the p l a t e - o n - t u b e type. The h e a t transfer coefficient for c o n d e n s a t i o n of the freon m i x t u r e was investigated by D a n g et al 1°. It is p o i n t e d o u t in reference 10 t h a t an a d d i t i o n a l t e m p e r a t u r e difference ( A T D ) exists d u r i n g c o n d e n s a t i o n of the m i x t u r e inside a tube. The f o r m u l a for A T D p u b l i s h e d in reference 10 was used here in designing the new condenser. Test results
T h e o p e r a t i n g p e r f o r m a n c e of the refrigerator BC-132 was tested with a M e r l o n i Co. test device (type 1067). The Chinese n a t i o n a l s t a n d a r d GB8059.2-87 was used in the m e a s u r e m e n t . S o m e of the p a r a m e t e r s for the refrigerator are as follows: freezer t e m p e r a t u r e : - 18 °C e n v i r o n m e n t t e m p e r a t u r e : 25 °C freshfood c a b i n e t t e m p e r a t u r e : between 0 ° a n d 7°C T h e o t h e r p a r a m e t e r s are given in Table 1. The test results are given in Table 2. As seen from Table 2, the m e a s u r e d energy c o n s u m p tion for the redesigned refrigerator is 0.704 k W h p e r 24 h period. F o r c o m p a r i s o n , a p e r f o r m a n c e test for the original refrigerator c h a r g e d with C F C 1 2 was carried o u t u n d e r the same test conditions. T h e m e a s u r e d energy c o n s u m p t i o n is 0.753 k W h per 24 h. It can be seen t h a t the value of E E R for the redesigned r e f r i g e r a t o r c h a r g e d with the substitute refrigerant is increased by 6.5~o c o m p a r e d with t h a t for the original refrigerator.
Test device Precision of controlled environment temperature Relative moisture Air speed Power gauge Watt gauge Voltage gauge Current gauge M package and storage load
Merloni Type 1067 + 0.5 C
Prototype machine Climatic type Refrigerant Energy consumption Improvements made
Changfeng BC-132 N HCFC22/HFC152a 0.9 kW h in 24 h period Compressor reselected Condenser redesigned
50% 0.20 ms 1.0 class 0.5 class 1.5 class 1.5 class Chemical substances
fully d e v e l o p e d from a C F C - b a s e d d o m e s t i c refrigerator. F r o m b o t h the theoretical a n d e x p e r i m e n t a l results, it can be c o n c l u d e d t h a t when using C F C s it will be possible to increase the energy efficiency r a t i o ( E E R ) of a refrigeration system if the system is a d j u s t e d p r o p e r l y to suit the substitute refrigerant. F u r t h e r m o r e , c o m p u t e r s i m u l a t i o n is an effective m e t h o d in configuring a refrigeration system a l t h o u g h e x p e r i m e n t a l w o r k is always needed for confirmation. References
1 2 3 4 5 6 7 8 9
Peterson, B. Thorsell, H Comparison of the refrigerants HFC134a and CFC-12 lnt JRefrig (May 1990) 13 (3) Kruse, H. Latest developments and future trends in the field of CFC substitutes News Letter of the lEA Heat Pump Center (June 1989) 7 (2) Fischer, S. CFCs dominate agenda at Chicago ASHRAE meeting News Letter of the IEA Heat Pump Center (June 1989) 7 (2) Xie, G. Zhou, C., Wu, Y., Yang. Z., Zhu. Z. Study of application of mixture refrigerants to small scale refrigeration equipment J Refri9 (1991) (2) (in Chinese) Miao, D. Reciprocating refrigerating compressor Machinery Industry Press, 1983 (in Chinese) Wu, Y., Han, B. Principle and Equipment of Refrigeration Xi'an Jiaotong University Press, 1987 (in Chinese) Xie, G., Wu, Y. Predicting the characteristics on capillary tube in case of using mixture Proc. Chinese Substitution Conference. Guangzhou, China, 1991 (in Chinese) Wu, Y. Mathematical Model of Reciprocating Compressor and its Application Xi'an Jiaotong University Press, 1989 (in Chinese) Dang, Y., Wu, Y. Mathematical simulation and optimizing design for the working process of reciprocating refrigerating compressor Proc 3rd Japan-China Joint Conference on Fluid Machinery
Conclusions
A d o m e s t i c refrigerator using a C F C substitute of a refrigerant m i x t u r e of H C F C 2 2 / H F C 1 5 2 a was success-
10
Osaka, Japan, 23 25 April, 1990 Dang, K., Wu, Y., Jiang, D. Investigation on diffusion resistance of refrigerant mixture during condensation J Eng Thermophys (August 1992) 13 (3) (in Chinese)
Test results Tableau 2 R~sultats des essais Table 2
Type
No.
Refrigerating performance
Safety performance
208
Test item
Test results
1 2
Pull down Storage temperature
3 4
Energy consumption Ice-making ability
1.5 h 16 °C (environment temperature): T= = 2.0 °C 32 °C (environment temperature): T= = 3.5 °C 0.704 kWh per 24 h achieving solid ice in 2 h
5 6 7 8 9 10
Current leakage Starting performance Contact resistance Insulation resistance High voltage Shell temperature
0.22 mA started successfully at 185 V 0.009 £~ 6 Mf~ after moisture test 1250 V 55 °C
Int. J. Refrig. 1 9 9 4 Volume 17 Number 3
Besides the values of the ozone depletion and global warming potentials, energy consumption is another important index to be considered in developing a refrigeration system using CFC substitutes. Many investigators have indicated that unless the original refrigeration system is correspondingly adjusted when using CFC substitutes, the energy efficiencyratio (EER) of the system will decrease. In this paper, the reasons for a decrease in EER are analysed theoretically, and some proposals for increasing EER are put forward. These proposals are used to develop a domestic refrigerator charged with a non-azeotropic mixture of HCFC22/I-IFC 152a as the substitute for the original working fluid, CFC12. The results show that the EER value of the refrigerator charged with this refrigerant mixture is increased by 6.5~ocompared with that of the same refrigerator charged with CFC12. (Keywords:refrigeratingmachine;householdrefrigerator;CFC; substitute;mixture;R12; R22; R152a; efficiency)
Mise au point d'un r6frig6rateur domestique haute performance utilisant des substituts de CFC Dans la conception d'un syst~me frigorifique utilisant des substituts de CFC, il est important de considerer, non seulement les valeurs de Potentiel de destruction de r ozone ( O D P ) et Potentiel d'effet de serre ( G WP ), mais aussi la consommation d'bnergie. Maints chercheurs ont indiqub que, si le syst~me frigorifique original n'est pas correctement adaptb aux substituts des CFC, le rapport d'efficacitk ~nergbtique (EER) diminuera. Dans I'article, on analyse de faqon thborique les raisons d'une diminution du rapport d'efficacitb bnergbtique, et on propose quelques solutions pour l'augmenter. On applique ces solutions propos~es dt la mise au point d'un r~frigbrateur domestique chargb avec un mblange non az~otropique de HCFC22 et de HFC152a, en remplacement du CFC12. Les rbsultats montrent que le rapport d'efficacitb ~nergbtique de ce rbfrigbrateur chargb avec ce mblange augmente de 6,5 %, par rapport & celui de m~me refrigbrateur chargb avec du CFC12.
(Mots d6s: machinefrigorifique;r6frig6rateurdomestique;CFC; substitute; m61ange;R12; R22; R152a; rendement)
When using CFC substitutes, the original CFC refrigeration system becomes unsuitable due to the differences between CFCs and their substitutes in their thermophysical properties. Unless the system is adjusted, its energy efficiency ratio (EER) will be decreased, as has been shown by many investigators in this field 1-4. It is therefore necessary to adjust the original system according to the used substitute: that is, to redesign and/or reselect some key parts of the system. In order to adjust the system properly, it is necessary to analyse the reasons for the decrease in EER and this will help us to find the methods for improvement.
Accordingly, the key parts of the compressor, such as compressor valves, must be redesigned. The compressor valves operate under the effects of both drag and elastic forces of the valve reeds, as shown in Figure 1. When the pressure in the cylinder exceeds the pressure in the discharge chamber, the valve will open and cling onto the valve stop. The valve will close when the drag force becomes smaller than the elastic force of the valve reed. The normal movement of the valves is displayed in Figure 2. In the figure, the ordinate represents the valve displacement while the abscissa stands for the crank shaft angle. The drag force acting upon the valve reed may be determined by the following formulaS:
Reasons for redesigning and/or reselecting some key parts when using CFC substitutes
F = (flS)AP = (flSXkn2M2/8)~k
Compressor
When using CFC substitutes in a refrigeration system, the performance parameters of the compressor, such as suction and discharge pressures, refrigerating capacity per unit of swept volume and so on, will be changed. 0140-7007/94/030205-04 © 1994 Butterworth-Heinemann Ltd and IIR
(1)
where F is the drag force, fl is the drag coefficient, S is the effective force area of the valve reed, P is the pressure, k is the adiabatic exponent, My is the Mach number at valve gap, and ¢ is a function of the crank shaft angle ct. It is clear that for an identical compressor, the drag force will be changed when using different refrigerants because of the different Mach number M v.
Rev. Int. Froid 1994 Volume 17 Num6ro 3
205
A high-efficiency refrigerator using CFC substitutes, Y. Wu et al. discharge chamber alve reed
",k
y
elastic {orce
•drag force
^ piston
dead point
U
dead point
a(deg) Figure 3 Delayed closing of the valve Figure 3 D~lai de fermeture du clapet
Figure 1 Forces acting upon the valve reed Figure 1 Forces agissant sur le clapet flexible
E
a1
dead aoint
dead point a(deg)
Figure 2 Normal movement of the valve: a to b, valve reed opening; b to c, valve reed staying on valve stop; c to d, valve reed closing. Figure 2 Mouvement normal du clapet, ab, ouverture du clapet flexible, bc, clapet flexible h l'arrOt, ed, fermeture du clapet flexible
If the drag force is too large, the valve cannot close in time, resulting in delayed closing as shown in Figure 3. Conversely if the drag force is too small, the valve cannot open fully, bringing about fluttering as shown in Figure 4. The movement of the compressor valve shown in Figures 3 and 4 is abnormal, causing the pressure pulsation in both the suction and discharge chambers of the compressor to increase. As a consequence, its energy consumption will rise. According to the above discussion, compressors should be redesigned or reselected to suit the thermophysical properties of the CFC substitute used.
dead ~oint Figure 4
Fluttering of the valve Figure 4 Battement du clapet
P
3,/
When using CFC substitutes, the 'unit heat loads of both evaporator and condenser will be changed. As shown in Figure 5 6, the unit heat load of the evaporator is qe = hi - h4
(2)
while the unit heat load of the condenser is q¢ = h 2 - h 3
(3)
Correspondingly, the heat loads of the two heat exchangers are as follows: Qe = m(ha - h4)
(4)
Qc=m(h2 - h 3 )
(5)
206
Int. J. Refrig. 1994 Volume 17 Number 3
/ /
A --= --
Evaporator and condenser
dead point
a(deg)
h qe
-qc
Figure 5 Unit heat loads of both evaporator and condenser Figure 5 Charges thermiques de l'dvaporateur et du condenseur
where h 1, h2, h a and h 4 are enthalpy values, and m is the mass flow rate of the refrigerant. When using substitutes, hi, h 2, h3 and h4 as well as m will change, causing heat loads Qo and Qc and the unit heat loads qe and qc to change. When using CFC substitutes, the heat transfer coefficient of the refrigerant will also be changed. Generally, the heat transfer coefficient depends on the flow pattern and thermophysical properties of the refrigerant. Different refrigerants have different thermophysical properties, and therefore have different heat transfer coefficients. Since the heat loads of both the evaporator and condenser and the heat transfer coefficient are changed, it becomes essential to redesign and/or reselect the two heat exchangers.
A high-efficiency refrigerator using CFC substitutes." Y. Wu et al.
1.0
Capillary The pressure drop of a refrigerant flowing through a capillary depends on the dimension of the capillary as well as the thermophysical properties of the refrigerant. When using CFC substitutes, the dimension of the capillary should be redesigned due to the different properties of the various refrigerants in order to meet the desired evaporating temperature for the system.
RMi2ture O.5
Experimental confirmation Based on a domestic refrigerator originally charged with CFC12, a new refrigerator (BC-132) charged with a mixture refrigerant HCFC22/HFC152a was developed. The domestic refrigerator has a storage volume of 132 1. The charged amount of the mixture was determined by trial and error according to the technical specifications for the refrigerator, such as storage temperature, cooling capacity and so on. The composition of the mixture was chosen experimentally so as to keep the compressor refrigerating capacity almost the same as the original one. The same lubricant oil was used for both the original and the substitute refrigerants. As regards the components of the refrigerator, the evaporator was not changed because of the complexity of its shape. The dimension of the capillary was also retained since theoretical calculations v show that with an unchanged diameter only its length has to be adjusted a little when the mixture is applied. Therefore, only the compressor and condenser were reselected and redesigned during development of the refrigerator.
0
,
0
i
l
~
i
. . . .
,
,
,
l
,
,
,
,
100
Figure6
,
200 a (deg)
400
Movements ofboth suction (le~)anddischarge(right)valves
Mouvements du clapet d'aspiration (gauche) et du clapet de refoulement (droite) I. 24
I. 23 ..o v
/
I . 22
i
Mixture R12
........................... 100 200 300
1.21 F
400
u (deg)
Figure 7
Pressure pulsation in the suction chamber
Figure 7
Pulsation de pression dans la chambre d'aspiration
12. 30 12.25 "~ 12. 2q
Mixture
"o
A
R12
12.15 12.10 12.05
100
0
200 = (deg)
300
400
Figure 8
Pressure pulsation in the discharge chamber
Figure 8
Pulsation de pression dans la chamhre de refoulement
2O
Mixture R12
5
0 '
I
1.
2.0
3.0
Redesigning the condenser The substitute HCFC22/HFC152a is a non-azeotropic mixture refrigerant. Its temperature varies during con-
300
Figure6
Reselecting the compressor On the basis of the performance prediction completed by using computer simulation technology8'9, a new compressor was chosen to replace the original one in order to match the requirement of the mixture. Fioures 6-9 are computer-simulated results obtained under the working conditions listed in Chinese standard GB9098-88. The predicted valve movement of the compressor using the mixed refrigerant is shown in Figure 6, indicating that both the suction and discharge valves possess rather good operating performance. The pressure pulsation in both the suction and discharge chambers while using the mixture is plotted in Figures 7 and 8. For comparison, the pressure pulsation is also calculated when refrigerant CFC12 is used. It can be seen from Figures 7 and 8 that the pressure pulsation when using the mixture is smaller than that when using CFC12, thereby resulting in a reduction of energy consumption. Figure 9 shows the predicted P - V diagram of the compressor. Both the diagrams for CFC12 and the substitute used here are computed for comparison. The calculated result shows that the area in the P - V diagram for the substitute refrigerant is 4% smaller than that for CFC12. As the compressor refrigerating capacities charged with CFC12 and HCFC22/HFC152a are almost the same, we can therefore conclude that the energy consumption is reduced by 4%.
'I
Figure 9
P Vdiagram of the compressor
Figure 9
Diagramme P-V du compresseur
I
I
I
I
I
4,0 V ( X lO-SmD
Rev. Int. Froid 1994 Volume 17 Num~ro 3
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5.
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A high-efficiency refrigerator using CFC substitutes. Y. Wu et a l. T
/%
Table 1 The tcsl conditions Tableau 1 Conditions d'essai
s Figure 10 Condensation of non-azeotropic refrigerants Figure 10 Condensation des frigorigknes non azrotropiques
d e n s a t i o n u n d e r c o n s t a n t pressure, as s h o w n in Figure 10. In a c c o r d a n c e with this special characteristic, a c o u n t e r flow heat e x c h a n g e r of the w i r e - o n - t u b e type was designed to t a k e the place of the original cross-flow condenser of the p l a t e - o n - t u b e type. The h e a t transfer coefficient for c o n d e n s a t i o n of the freon m i x t u r e was investigated by D a n g et al 1°. It is p o i n t e d o u t in reference 10 t h a t an a d d i t i o n a l t e m p e r a t u r e difference ( A T D ) exists d u r i n g c o n d e n s a t i o n of the m i x t u r e inside a tube. The f o r m u l a for A T D p u b l i s h e d in reference 10 was used here in designing the new condenser. Test results
T h e o p e r a t i n g p e r f o r m a n c e of the refrigerator BC-132 was tested with a M e r l o n i Co. test device (type 1067). The Chinese n a t i o n a l s t a n d a r d GB8059.2-87 was used in the m e a s u r e m e n t . S o m e of the p a r a m e t e r s for the refrigerator are as follows: freezer t e m p e r a t u r e : - 18 °C e n v i r o n m e n t t e m p e r a t u r e : 25 °C freshfood c a b i n e t t e m p e r a t u r e : between 0 ° a n d 7°C T h e o t h e r p a r a m e t e r s are given in Table 1. The test results are given in Table 2. As seen from Table 2, the m e a s u r e d energy c o n s u m p tion for the redesigned refrigerator is 0.704 k W h p e r 24 h period. F o r c o m p a r i s o n , a p e r f o r m a n c e test for the original refrigerator c h a r g e d with C F C 1 2 was carried o u t u n d e r the same test conditions. T h e m e a s u r e d energy c o n s u m p t i o n is 0.753 k W h per 24 h. It can be seen t h a t the value of E E R for the redesigned r e f r i g e r a t o r c h a r g e d with the substitute refrigerant is increased by 6.5~o c o m p a r e d with t h a t for the original refrigerator.
Test device Precision of controlled environment temperature Relative moisture Air speed Power gauge Watt gauge Voltage gauge Current gauge M package and storage load
Merloni Type 1067 + 0.5 C
Prototype machine Climatic type Refrigerant Energy consumption Improvements made
Changfeng BC-132 N HCFC22/HFC152a 0.9 kW h in 24 h period Compressor reselected Condenser redesigned
50% 0.20 ms 1.0 class 0.5 class 1.5 class 1.5 class Chemical substances
fully d e v e l o p e d from a C F C - b a s e d d o m e s t i c refrigerator. F r o m b o t h the theoretical a n d e x p e r i m e n t a l results, it can be c o n c l u d e d t h a t when using C F C s it will be possible to increase the energy efficiency r a t i o ( E E R ) of a refrigeration system if the system is a d j u s t e d p r o p e r l y to suit the substitute refrigerant. F u r t h e r m o r e , c o m p u t e r s i m u l a t i o n is an effective m e t h o d in configuring a refrigeration system a l t h o u g h e x p e r i m e n t a l w o r k is always needed for confirmation. References
1 2 3 4 5 6 7 8 9
Peterson, B. Thorsell, H Comparison of the refrigerants HFC134a and CFC-12 lnt JRefrig (May 1990) 13 (3) Kruse, H. Latest developments and future trends in the field of CFC substitutes News Letter of the lEA Heat Pump Center (June 1989) 7 (2) Fischer, S. CFCs dominate agenda at Chicago ASHRAE meeting News Letter of the IEA Heat Pump Center (June 1989) 7 (2) Xie, G. Zhou, C., Wu, Y., Yang. Z., Zhu. Z. Study of application of mixture refrigerants to small scale refrigeration equipment J Refri9 (1991) (2) (in Chinese) Miao, D. Reciprocating refrigerating compressor Machinery Industry Press, 1983 (in Chinese) Wu, Y., Han, B. Principle and Equipment of Refrigeration Xi'an Jiaotong University Press, 1987 (in Chinese) Xie, G., Wu, Y. Predicting the characteristics on capillary tube in case of using mixture Proc. Chinese Substitution Conference. Guangzhou, China, 1991 (in Chinese) Wu, Y. Mathematical Model of Reciprocating Compressor and its Application Xi'an Jiaotong University Press, 1989 (in Chinese) Dang, Y., Wu, Y. Mathematical simulation and optimizing design for the working process of reciprocating refrigerating compressor Proc 3rd Japan-China Joint Conference on Fluid Machinery
Conclusions
A d o m e s t i c refrigerator using a C F C substitute of a refrigerant m i x t u r e of H C F C 2 2 / H F C 1 5 2 a was success-
10
Osaka, Japan, 23 25 April, 1990 Dang, K., Wu, Y., Jiang, D. Investigation on diffusion resistance of refrigerant mixture during condensation J Eng Thermophys (August 1992) 13 (3) (in Chinese)
Test results Tableau 2 R~sultats des essais Table 2
Type
No.
Refrigerating performance
Safety performance
208
Test item
Test results
1 2
Pull down Storage temperature
3 4
Energy consumption Ice-making ability
1.5 h 16 °C (environment temperature): T= = 2.0 °C 32 °C (environment temperature): T= = 3.5 °C 0.704 kWh per 24 h achieving solid ice in 2 h
5 6 7 8 9 10
Current leakage Starting performance Contact resistance Insulation resistance High voltage Shell temperature
0.22 mA started successfully at 185 V 0.009 £~ 6 Mf~ after moisture test 1250 V 55 °C
Int. J. Refrig. 1 9 9 4 Volume 17 Number 3