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HC290 mixture a retrofit for CFC12 systems
International Journal of Refrigeration 28 (2005) 735–743 www.elsevier.com/locate/ijrefrig
HFC134a/HC600a/HC290 mixture a retrofit for CFC12 systems S.J. Sekhar, D.M. Lal* Department of Mechanical Engineering, Anna University, Chennai 600025, India Received 10 May 2004; received in revised form 3 November 2004; accepted 14 December 2004 Available online 16 February 2005
Abstract The environmental concerns with the impact of refrigerant emissions lead to the importance in identifying a long-term alternative to meet all requirements in respect of system performance and service. Even though HFC134a and HC blend (containing 55.2% HC600a and 44.8% HC290 by weight) have been reported to be substitutes for CFC12, they have their own drawbacks in respect of energy efficiency/flammability/serviceability aspects of the system. In this present work, experimental investigation has been carried out on the performance of an ozone friendly refrigerant mixture (containing HFC134a/HC blend) in two low temperature systems (a 165 l domestic refrigerator and a 400 l deep freezer) and two medium temperature systems [a 165 l vending machine (visi cooler) and a 3.5 kW walk-in cooler]. The oil miscibility of the new mixture with mineral oil was also studied and found to be good. The HFC134a/HC blend mixture that contains 9% HC blend (by weight) has better performance resulting in 10–30% and 5–15% less energy consumption (than CFC12) in medium and low temperature system, respectively. q 2004 Elsevier Ltd and IIR. All rights reserved. Keywords: Mixture; Refrigerant; R134a; Hydrocarbon; Experiment; Miscibility; Oil
Me´lange HFC134a/HC600a/HC290 pour remplacer le CFC12 Mots cle´s : Me´lange ; Frigorige`ne ; R134a ; Hydrocarbure ; Expe´rimentation ; Miscibilite´ ; Huile
1. Introduction As per the Montreal protocol, the developed countries have already phased out CFCs and the developing countries are to totally phase out it by 2010. Among the alternatives available HFC134a is not miscible with conventional mineral oil and the substitute POE oil is highly hygroscopic. On the other hand, HC blends have the problem of flammability and limitation in the charge quantity due to safety (fire hazard) regulations. Hence, it would be a * Corresponding author. Fax: C91 44 22203269. E-mail address: [email protected] (D.M. Lal). 0140-7007/$35.00 q 2004 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2004.12.005
significant benefit for the RAC technicians in the service sector if HFC134a can be made to work with mineral oil. It has been reported that the oil miscibility problem for HFC134a in mineral oil could be solved by adding suitable quantity of HC additive [1,2]. Already many research works have been done in the above two refrigerants. The power consumption of a HFC134a system would be 10–15% more than CFC12 system [3]. The performance study on singleevaporator domestic refrigerator indicated that the COP of HFC134a is 3% less than that of CFC12 [4]. Due to the reactive nature of the residual mineral oil with the lubricant polyol ester (POE) oil and HFC134a, a stringent flushing procedure should be adopted so that the mineral oil residue
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comes below 1% while retrofitting CFC12 systems with HFC134a [5]. Experimental studies on the retrofitted HFC134a system indicated 5–8% lesser COP than that of conventional CFC12 system [6]. Further, the COP of the CFC12 heat pumps improve by 3.5%, when they were retrofitted with a mixture of HFC134a/HC600a (80:20) by weight [7]. Experiments were conducted on domestic refrigerators with HC mixtures at various composition, HC290/HC600a mixture with 0.55–0.6 mass percentage of HC600a yielded 3–4% increase in energy efficiency as compared to CFC12 [8]. Thus, it is imperative that HFC134a is less energy efficient than CFC12 while it is also not user friendly because of hygroscopicity of the POE oil. HC refrigerants also suffer from the point of being flammable. With this background of diverse reports on alternative refrigerants the present work was envisaged to study the feasibility of making HFC134a work with mineral oil in CFC12 systems with the addition of HC600a/HC290 mixture to tackle the oil miscibility issues.
2. Refrigerant selection The COP of the domestic and commercial refrigeration systems have been reported to be increased by 10–20% with the use of HC blends that contain HC600a and HC290 [9– 13]. Hence, it has been taken as a viable additive with HFC134a to work with mineral oil compressor. Further, in this paper this HC mixture (55.2% HC600a and 44.8% HC290) is referred as HC blend. Since, the quantity of the HC blend used in the system is less than 10% of the total charge, even if any leakage occurs the full HC quantity does not exceed the lower flammability limit in respect of flammability during normal operating conditions. Janssen and Engels [1] have reported that a minimum of 5% HC is to be added to take care of oil return. From the studies on the properties of HFC134a/HC blend mixture using REFPROP software, it was found that the maximum condensing pressure of the mixture exceeds the design discharge pressure of the compressor when the HC blend mass fraction increases beyond 12% [14,15]. Hence, in the present work experiments were conducted for mixture proportions of 7, 9 and 11% HC blend (by weight) in HFC134a. These mixtures are further referred in this paper as M07, M09 and M11 mixtures. It is to be noted that the mixtures are zeotropic in nature with a temperature glide of 6–12 8C depending upon the operating conditions. However, it is expected that to a certain extent this could be compensated due to the pressure drop in the evaporator.
conventional CFC12 systems operating at low temperature and medium temperature. In the above cases, the deep freezer (with 29 m long evaporator coil) and the walk-in cooler (with 58 m long evaporator coil) were considered to check the oil return characteristics of the refrigerant when it is used in systems with long evaporator coils which is usually prone for oil stagnations. In all the experiments, the reference tests were conducted with CFC12, which was repeated with the refrigerant mixtures considered after recovering the CFC12. The experimental set-up and procedure used for the above study are discussed below. 3.1. Domestic refrigerator The schematic diagram of the experimental facility used in this investigation is shown in Fig. 1. The domestic refrigerator consists of a clinching type evaporator, natural convection air-cooled serpentine type condenser and hermetically sealed reciprocating compressor with mineral oil as lubricant. To optimise the capillary length for M09, five capillary tubes having 0.78 mm diameter and lengths varying from 3 to 4.2 m were provided. Film type RTD sensors (PT100) with G0.25 8C accuracy were used to measure the temperature at various points. Pressure gauges with G0.25% accuracy were also provided suitably. The same type of evaporator coil used in the refrigerator was kept inside a secondary refrigerant (ethylene glycol) calorimeter. To measure the compressor load and heater load a wattmeter with G1 W accuracy and energy meter were provided. The capillary and charge optimisation tests with CFC12 showed that the optimum capillary tube length and charge quantity were 3.35 m and 175 g, respectively. Hence, the above charge quantity was taken as reference to evolve mixture quantities. To measure the per day energy consumption, a test was conducted as per Bureau of Indian Standards (BIS) 1476. The set-up was kept inside a temperature-controlled room where the ambient could be varied from 20 to 43 8C. During pull down the temperature and power consumption were recorded at 15 s intervals. To find out the actual COP, the evaporator inside the refrigerator was disconnected and the system was connected to the calorimeter by suitably operating the ball valves. To determine the actual refrigeration effect and compressor power for a particular calorimeter temperature (temperature of secondary refrigerant), the heater load was adjusted so that the system stabilized at that particular temperature. This test was repeated for K15, K12, K6 and K4 8C secondary refrigerant temperatures and 22, 26, 32, 36 and 43 8C ambient temperatures. The refrigerant mixtures considered are M07, M09 and M11.
3. Experimentation
3.2. Deep freezer
The performance of the considered refrigerant mixtures was experimentally studied as against that of CFC12 in the
The schematic diagram of the experimental facility used in this investigation is shown in Fig. 2. The set-up consists
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Fig. 1. Schematic diagram of the experimental facility used to test a domestic refrigerator.
of a deep freezer modified as a secondary refrigerant calorimeter. The calorimeter consists of a 400 l capacity pressure tight vessel. The inner shell was filled with the secondary refrigerant (HFC134a). At the bottom, there is a rod heater connected to the mains through a suitable dimmerstat and wattmeter for accurate measurement of heater load. The evaporator coil (29 m long, 12 mm diameter copper pipe) was soldered around the shell. To measure the temperature RTD sensors were placed inside the shell and along the length of the coil. The pressures at typical points were also measured. Since, miscibility of the mineral oil with the mixture is a major issue, an oil level indicator (column type) was attached to the hermetic compressor for periodic checking. All the pressure and temperature sensors were connected to a data logging system. To determine the actual refrigeration effect and compressor power for a particular calorimeter temperature (temperature of secondary refrigerant), the heater load was adjusted so that the system stabilised at that particular temperature. The actual refrigeration effect was obtained by
adding the heat infiltration with the heater load. This test was repeated for K18, K15, K10 and K4 8C secondary refrigerant temperatures and 22, 26, 32, 36 and 43 8C ambient temperatures. The refrigerant mixtures considered are M07, M09 and M11. 3.3. Vending machine (visi cooler) The vending machine consists of an air-cooled plate fin condenser, plate fin evaporator, hermetically sealed compressor and capillary expansion device. The experimental set-up used for this study is schematically shown in Fig. 3. Since, capillary tube optimisation is required, four capillaries having 0.86 mm diameter and 2.13, 2.44, 2.74 and 3.05 m long were suitably fixed from a header with ball valves. The compressor was connected with a wattmeter and energy meter to study the energy consumption. To study per day energy consumption and pull down performance, the same procedure used in domestic refrigerator was followed. However, the actual refrigerating power and COP were not estimated. The thermostat inside the
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Fig. 2. Schematic diagram of the experimental facility used to test a deep freezer.
refrigerated space was adjusted to 1 8C cut-off and 4 8C cutin temperatures. Based on the results of the theoretical investigations and earlier experimentation in refrigerator, M09 and M11 mixtures were only considered for vending machine. 3.4. Walk-in cooler The schematic of the experimental facility used in this work is shown in Fig. 4. It consists of a walk-in cooler room of dimension 2300!2300!2800 mm3, a serpentine type evaporator coil having 28 mm diameter and 58 m long aluminium coated M.S. pipe, a 3.5 kW open type compressor with suitable motor, thermostatic expansion valve (TEV), plate-fin type condenser and a receiver of 4 l capacity. RTD temperature sensors, pressure gauges, flow meter and energy meter were suitably fixed to measure the required parameters. An oil level indicator was also provided in the compressor to check the oil return characteristics of the mixture. To conduct no load pull down test, the door was kept open for 48 h till the cooler space reached thermal equilibrium with the ambient. The thermostat cut-off switch was adjusted to maintain 2.5 8C cut-off and 5 8C cut-in temperatures. The system was started and the parameters such as pressure, flow rate and energy consumption were recorded for every 15 s until the first cutoff occurred. Once the system reached the steady state of 2.5 8C cut-off and 5 8C cut-in, the energy consumption test was carried out. During the test all the performance parameters were also recorded. The refrigerating effect
was estimated through an enthalpy balance with the help of mass flow measurements made through suitable flow meter. The detailed procedure has been already reported [14]. After completing the reference tests with CFC12 the refrigerant was recovered and equivalent quantity of the mixture (4.9 kg) was charged. All the tests conducted with CFC12 were repeated.
4. Results and discussion The results obtained from experimental investigations on the performance of HFC134a/HC600a/HC290 mixture and CFC12 in four different types of refrigeration systems are discussed with respect to parameters such as pull down time, Refrigeration effect, actual COP and energy consumption. 4.1. Domestic refrigerator The average energy consumption obtained for CFC12, M07, M09 and M11 at various ambient temperatures is plotted in Fig. 5. From that it has been found that the energy consumption of the mixtures is less than that of CFC12. Among the mixtures M09 is characterised with 4.1–7.6% less energy consumption than that of CFC12. The energy consumption of the compressor with time during the pull down is shown in Fig. 6. It shows that the compressor power of M09 mixture is 2–3% higher than CFC12 during the pull down. But for the same temperature setting in the thermostat, the pull down time for M09 was 11 min shorter
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Fig. 3. Schematic diagram of the experimental facility used to test a vending machine.
than that of CFC12 and, hence, the total energy consumed by M09 during pull down was 0.196 kWh as against 0.216 kWh for CFC12. The measurement of temperature along the length of the coil indicated a temperature glide that was less than 3 K for 80% of the evaporator coil length. However, details of temperature distribution are already published [15]. The refrigeration effect tabulated in Table 1 shows that the mixtures have higher refrigerating effect than CFC12. Among the mixtures M09 is characterised with the maximum refrigeration effect. The improvement is 7–10.5% and 20–26.5% at K15 and K4 8C calorimeter temperature, respectively. The higher latent heat of vaporisation for the mixture as well as higher condensing pressures that causes a higher mass flow rate lead to better refrigeration effect. The improvement in COP of M09 over CFC12 at K15 8C calorimeter temperature for the tested ambient conditions was also found to be 3.8–8.5%. 4.2. Deep freezer As per the procedure discussed, the actual refrigeration effect was calculated and the results are tabulated in Table 2. It is found that the refrigeration effect increases with the
increase in calorimeter shell temperature and decreases with the increase in ambient temperature. Among the mixtures M09 shows 6–8.5% and 14.2–28.4% improvement in refrigeration effect over CFC12 at the calorimeter temperature of K18 and K4 8C, respectively, for the different ambient conditions. The variation of COP with calorimeter temperature at different ambient temperatures is plotted in Fig. 7. In most of the cases, the actual COP is increased by 2–2.5 times while the calorimeter temperature was increased from K18 to K4 8C. This is due to the higher rate of heat transfer as an effect of large temperature difference across the evaporator coil and refrigerated space. It was also observed that the temperature difference between the coil and space increased from 6 to 14 8C as the calorimeter temperature was increased from K18 to K4 8C, respectively. To carryout the oil miscibility study, initially the compressor was filled with 900 ml of mineral oil as per the manufacturer’s guidelines. The level was noted on the column type oil level indicator. The oil level during the operation of the system was recorded. It was found to be 1 mm below the initial level. This can be ascribed to the oil removed along with the refrigerant during recovery. Once
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Fig. 6. Variation of compressor power with time during pull down in a domestic refrigerator and visi cooler.
4.3. Vending machine
Fig. 4. Schematic diagram of the experimental facility used to test a walk-in cooler.
M09 was charged and the system started, again the oil level was noted. After 2 months of continuous operation again oil level was verified with the initial markings. There was hardly any change in the oil level. Further, the sight glass provided in the suction and discharge lines showed no traces of oil in the liquid and suction lines. This proves the oil miscibility of the new refrigerant mixture.
Fig. 5. Variation of per day energy consumption with ambient temperature at K15 8C freezer compartment temperature.
The results obtained from the energy consumption study are tabulated in Table 3. Among the refrigerants M09 shows the lowest energy consumption. Compared to CFC12, M09 has 10.8–17.3% and 13–19.6% less energy consumption for different thermostatic settings at 22 and 43 8C ambient temperature, respectively. The compressor power with respect to time during pull down is plotted in Fig. 6. The total energy consumed during pull down is 0.214 kWh for M09 whereas it is 0.255 kWh for CFC12. This reduction of 16.3% power consumption can be attributed to better COP of the M09 that is experienced in the other tests (Deepfreezer and refrigerator). 4.4. Walk-in cooler At the (experimentally studied and reported [14]) optimum TEV settings and steady state operating conditions the various performance parameters including the COPs and energy consumption per day were studied and are tabulated in Table 4. The actual COP calculated by considering the mass flow rate and actual compressor power is 5.5% higher
Fig. 7. Variation of actual COP with calorimeter temperature at 32 8C ambient temperature in deep freezer.
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Table 1 Refrigeration effect at various ambient and calorimeter temperatures in a domestic refrigerator Refrigerant
Calorimeter temperature (8C)
Refrigeration effect (W) Ambient temperature (8C)
CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11
K15 K15 K15 K15 K12 K12 K12 K12 K6 K6 K6 K6 K4 K4 K4 K4
22
26
32
36
43
73.5 74.5 82.5 79.5 81.5 84.5 93.5 90.0 98.5 103.0 117.0 111.5 108.0 112.0 130.5 123.5
70.0 72.5 76.5 75.0 75.5 80.0 88.5 86.0 93.5 98.5 112.0 107.0 102.0 107.0 125.5 118.0
60.5 62.0 64.5 64.0 66.0 67.0 74.5 71.5 80.5 84.5 98.5 91.5 89.0 93.5 110.5 104.5
59.0 60.0 62.5 61.5 61.5 64.5 70.5 68.5 69.5 72.5 86.5 83.5 76.5 79.0 97.0 92.0
54.0 55.0 57.0 56.0 58.0 60.0 65.5 63.5 70.0 72.5 88.0 80.0 78.0 80.0 98.5 93.0
for M09 mixture. The above improvements are due to the lower density and corresponding lesser mass flow rate of the M09 mixture than that of CFC12, which leads to less compressor work for M09. It has also been observed that the M09 mixture has shorter ON cycle than that of CFC12 for the same space temperature settings. The no load pull down test showed that the first cut-off of the system with M09 mixture is 30 min earlier than that of CFC12. The shorter ON cycle time is due to the higher refrigerating capacity.
The net result of the above is that the M09 mixture shows 30.24% less energy consumption than that of CFC12. In the above systems, temperature distribution was also observed along the length of the evaporator coil to check for temperature glide. The glide was within 3 8C for more than 80% of the coil length which is quite acceptable. It is also worthwhile to mention that the compressor discharge temperature for the M09 is lower than CFC12 in all cases.
Table 2 Refrigeration effect at various calorimeter and ambient temperatures in a deep freezer Refrigerant
Calorimeter temperature (8C)
Refrigeration effect (W) Ambient temperature (8C)
CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11
K18 K18 K18 K18 K15 K15 K15 K15 K10 K10 K10 K10 K4 K4 K4 K4
22
26
32
36
43
260 271 285 277 304 309 342 324 511 545 587 574 873 900 1021 958
222 225 245 240 256 266 294 280 472 508 551 530 810 871 969 922
208 215 234 223 237 245 274 255 431 446 517 500 787 826 940 878
182 191 198 195 210 218 235 227 385 405 475 450 682 720 858 803
160 165 170 169 190 197 214 205 270 285 351 325 580 600 741 684
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Table 3 Per day energy consumption with respect to ambient temperature at different thermostat settings in a visi cooler Thermostat settings
Refrigerant
Energy consumption (kWh/day) Ambient temperature (8C)
Cut-inZ0 8C Cut-offZ3 8C Cut-inZ1 8C Cut-offZ4 8C Cut-inZ2 8C Cut-offZ5 8C Cut-inZ3 8C Cut-offZ6 8C
CFC12 M09 M11 CFC12 M09 M11 CFC12 M09 M11 CFC12 M09 M11
22
26
32
36
43
3.26 2.91 3.03 3.23 2.83 3.04 3.08 2.62 2.9 2.83 2.38 2.56
4.1 3.57 3.76 3.92 3.35 3.54 3.76 3.21 3.58 3.49 2.84 3.12
5.18 4.51 4.72 5.04 4.25 4.54 4.73 3.99 4.29 4.4 3.62 4.07
5.8 5.03 5.22 5.77 4.84 5.18 5.32 4.58 4.78 5.0 4.19 4.69
7.12 6.2 6.52 7.07 6.04 6.46 6.76 5.64 5.97 6.38 5.24 6.0
5. Conclusions The present investigation has resulted in the development of an ozone friendly, energy efficient, user friendly, safe and cost-effective alternative refrigerant for CFC12 in domestic and commercial refrigeration systems. Based on the experimental investigation the following conclusions are drawn. 1. The better refrigerating effect of M09 resulted in 10, 9.8, 20.4 and 10% shorter pull down time in domestic refrigerator, deep freezer, vending machine and walk-in cooler, respectively. 2. The actual COP of the system is improved by 5–17% in low temperature systems. Table 4 Performance comparison of M09 with CFC12 at 32 8C ambient temperature in a walk-in cooler Sl. no.
Description
1
Evaporator inlet temperature (8C) Compressor outlet temperature (8C) Condenser outlet temperature (8C) Refrigerant flow during steady state (kgsK1) Power consumption at steady state (W) Average ON cycle time (minutes) Average OFF cycle time (minutes) COP-theoretical COP-actual Energy consumption per day (kWh/day)
2 3 4 5 6 7 8 9 10
CFC12
M09
K7
K9
77
65
35.6
36
0.116
0.010
1032
1020
12
8
12
13
3.38 1.44 16.5
3.76 1.577 11.51
3. The capillary optimisation tests proved that the standard capillary used in CFC12 systems can be used for the mixture also. But when the thermostatic expansion valves are used suitable super heat adjustment is required. 4. The actual refrigeration effect of M09 is 7–26.5% and 6– 28.4% higher than that of CFC12 in domestic refrigerator and deep freezer, respectively. 5. The M09 mixture reduces the per day consumption by 4.1– 7.6%, 10.8–19.6% and 30.2% in domestic refrigerator, vending machine and walk-in cooler, respectively. 6. The discharge temperature of the compressor is reduced by the M09. Hence, it could improve the compressor life. 7. The continuous running of all the systems discussed above for 18 months, with consistence performance, proves the oil miscibility of the M09 with mineral oil. Maintaining of oil levels in the compressors of deep freezer and walk-in cooler confirms the oil return characteristics of M09. Thus, it can be concluded that the M09 mixture could be an ozone friendly, energy efficient, user friendly, safe and economically viable alternative to CFC12 for domestic and small commercial refrigeration systems. The fact that POE oil can be dispensed with by using HFC134a/HC-blend mixture in the place of HFC134a is a significant finding in this research work. During the tests, none of the existing components was replaced/modified. Hence, in developing countries, for the small-scale service sector, M09 mixture can be used successfully for existing CFC12 appliances in the event of CFC phase out due to Montreal protocol.
Acknowledgements This research work was funded by University Grants Commission (UGC) of India. The authors acknowledge the support of HIDECOR project (funded by Swiss Agency for
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Development and Co-operation Managed by the Consortium; Swisscontact and IT Power India Pvt. Ltd.) by way of providing HC blend (CARE30) for the research.
References [1] M. Janssen, F. Engels, The use of HFC134a with mineral oil in hermetic cooling equipment. Report 95403/NO 07. Presented in the 19th international congress of refrigeration, The Hague; August 1995. [2] M. Sunami, Physical and chemical properties of refrigeration lubricants, ASHRAE Trans 1999; 983–993. [3] E.B. Muir, Commercial refrigeration and CFCs, Int J Refrig 13 (1995) 106–112. [4] D.S. Jung, R. Radermacher, Performance simulation of singleevaporator domestic refrigeration charged with pure and mixed refrigerants, Int J Refrig 14 (1991) 223–232. [5] N.E. Carpenter, Retrofitting HFC134a into existing CFC12 systems, Int J Refrig 15 (1992) 332–339. [6] R. Camporese, G. Bigolaro, S. Bobbo, Experimental evaluation of refrigerant mixtures as substitutes for CFC12 and R502, Int J Refrig 20 (1997) 22–31. [7] M.S. Kim, W.J. Mulroy, D.A. Didion, Performance evaluation of two azeotropic refrigerant mixtures of HFC134a with HC290 and HC600a, Trans ASME 116 (1994) 148–154.
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[8] D. Jung, C.B. Kim, B.H. Lim, H.W. Lee, Testing of a hydrocarbon mixture in domestic refrigerator, ASHRAE Trans Symp 1996; 1077–1084 [AT-96-19-3]. [9] S. Devotta, M. Murthy, N. Sawant, Performance of two door refrigerators retrofitted with a HC blend, IIF–IIR commission B1, B2, E1 and E2. New Delhi, India; 1998, p. 210–20. [10] D. Colbourne, An overview of hydrocarbons as replacement refrigerants in commercial refrigeration and air conditioning. Refrigeration 2000. Northern Ireland Centre for Energy Research and Tech.; November 2000, p. 1–15. [11] I.L. Maclaine-cross, E. Leonardi, Why hydrocarbons save energy, AIRAH J 51 (1997) 33–37. [12] D. Colbourne, K.O. Suen, Assessment of performance of hydrocarbon refrigerant. IIF–IIR Com. B1, B2, E1 and E2, Purdue University, USA, 2000. [13] I.L. Maclaine-cross, E. Leonardi, Performance and safety of LPG refrigerants, Proceedings of the fuel for change conference, Paradise Queensland, Australia, 1995, p. 149–68. [14] S. Joseph Sekhar, K. Senthil Kumar, D. Mohan Lal, Ozone friendly HFC134a/HC mixture compatible with mineral oil in refrigeration system improves energy efficiency of a walk in cooler, Int J Energy Conversion Manage 45 (2004) 1175–1186. [15] S. Joseph Sekhar, R. Russel Premnath, D. Mohan Lal, On the performance of HFC134a/HC600a/HC290 mixture in a CFC12 compressor with mineral oil as lubricant, Ecolibrium, J AIRAH 2 (2003) 24–29.
HFC134a/HC600a/HC290 mixture a retrofit for CFC12 systems S.J. Sekhar, D.M. Lal* Department of Mechanical Engineering, Anna University, Chennai 600025, India Received 10 May 2004; received in revised form 3 November 2004; accepted 14 December 2004 Available online 16 February 2005
Abstract The environmental concerns with the impact of refrigerant emissions lead to the importance in identifying a long-term alternative to meet all requirements in respect of system performance and service. Even though HFC134a and HC blend (containing 55.2% HC600a and 44.8% HC290 by weight) have been reported to be substitutes for CFC12, they have their own drawbacks in respect of energy efficiency/flammability/serviceability aspects of the system. In this present work, experimental investigation has been carried out on the performance of an ozone friendly refrigerant mixture (containing HFC134a/HC blend) in two low temperature systems (a 165 l domestic refrigerator and a 400 l deep freezer) and two medium temperature systems [a 165 l vending machine (visi cooler) and a 3.5 kW walk-in cooler]. The oil miscibility of the new mixture with mineral oil was also studied and found to be good. The HFC134a/HC blend mixture that contains 9% HC blend (by weight) has better performance resulting in 10–30% and 5–15% less energy consumption (than CFC12) in medium and low temperature system, respectively. q 2004 Elsevier Ltd and IIR. All rights reserved. Keywords: Mixture; Refrigerant; R134a; Hydrocarbon; Experiment; Miscibility; Oil
Me´lange HFC134a/HC600a/HC290 pour remplacer le CFC12 Mots cle´s : Me´lange ; Frigorige`ne ; R134a ; Hydrocarbure ; Expe´rimentation ; Miscibilite´ ; Huile
1. Introduction As per the Montreal protocol, the developed countries have already phased out CFCs and the developing countries are to totally phase out it by 2010. Among the alternatives available HFC134a is not miscible with conventional mineral oil and the substitute POE oil is highly hygroscopic. On the other hand, HC blends have the problem of flammability and limitation in the charge quantity due to safety (fire hazard) regulations. Hence, it would be a * Corresponding author. Fax: C91 44 22203269. E-mail address: [email protected] (D.M. Lal). 0140-7007/$35.00 q 2004 Elsevier Ltd and IIR. All rights reserved. doi:10.1016/j.ijrefrig.2004.12.005
significant benefit for the RAC technicians in the service sector if HFC134a can be made to work with mineral oil. It has been reported that the oil miscibility problem for HFC134a in mineral oil could be solved by adding suitable quantity of HC additive [1,2]. Already many research works have been done in the above two refrigerants. The power consumption of a HFC134a system would be 10–15% more than CFC12 system [3]. The performance study on singleevaporator domestic refrigerator indicated that the COP of HFC134a is 3% less than that of CFC12 [4]. Due to the reactive nature of the residual mineral oil with the lubricant polyol ester (POE) oil and HFC134a, a stringent flushing procedure should be adopted so that the mineral oil residue
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comes below 1% while retrofitting CFC12 systems with HFC134a [5]. Experimental studies on the retrofitted HFC134a system indicated 5–8% lesser COP than that of conventional CFC12 system [6]. Further, the COP of the CFC12 heat pumps improve by 3.5%, when they were retrofitted with a mixture of HFC134a/HC600a (80:20) by weight [7]. Experiments were conducted on domestic refrigerators with HC mixtures at various composition, HC290/HC600a mixture with 0.55–0.6 mass percentage of HC600a yielded 3–4% increase in energy efficiency as compared to CFC12 [8]. Thus, it is imperative that HFC134a is less energy efficient than CFC12 while it is also not user friendly because of hygroscopicity of the POE oil. HC refrigerants also suffer from the point of being flammable. With this background of diverse reports on alternative refrigerants the present work was envisaged to study the feasibility of making HFC134a work with mineral oil in CFC12 systems with the addition of HC600a/HC290 mixture to tackle the oil miscibility issues.
2. Refrigerant selection The COP of the domestic and commercial refrigeration systems have been reported to be increased by 10–20% with the use of HC blends that contain HC600a and HC290 [9– 13]. Hence, it has been taken as a viable additive with HFC134a to work with mineral oil compressor. Further, in this paper this HC mixture (55.2% HC600a and 44.8% HC290) is referred as HC blend. Since, the quantity of the HC blend used in the system is less than 10% of the total charge, even if any leakage occurs the full HC quantity does not exceed the lower flammability limit in respect of flammability during normal operating conditions. Janssen and Engels [1] have reported that a minimum of 5% HC is to be added to take care of oil return. From the studies on the properties of HFC134a/HC blend mixture using REFPROP software, it was found that the maximum condensing pressure of the mixture exceeds the design discharge pressure of the compressor when the HC blend mass fraction increases beyond 12% [14,15]. Hence, in the present work experiments were conducted for mixture proportions of 7, 9 and 11% HC blend (by weight) in HFC134a. These mixtures are further referred in this paper as M07, M09 and M11 mixtures. It is to be noted that the mixtures are zeotropic in nature with a temperature glide of 6–12 8C depending upon the operating conditions. However, it is expected that to a certain extent this could be compensated due to the pressure drop in the evaporator.
conventional CFC12 systems operating at low temperature and medium temperature. In the above cases, the deep freezer (with 29 m long evaporator coil) and the walk-in cooler (with 58 m long evaporator coil) were considered to check the oil return characteristics of the refrigerant when it is used in systems with long evaporator coils which is usually prone for oil stagnations. In all the experiments, the reference tests were conducted with CFC12, which was repeated with the refrigerant mixtures considered after recovering the CFC12. The experimental set-up and procedure used for the above study are discussed below. 3.1. Domestic refrigerator The schematic diagram of the experimental facility used in this investigation is shown in Fig. 1. The domestic refrigerator consists of a clinching type evaporator, natural convection air-cooled serpentine type condenser and hermetically sealed reciprocating compressor with mineral oil as lubricant. To optimise the capillary length for M09, five capillary tubes having 0.78 mm diameter and lengths varying from 3 to 4.2 m were provided. Film type RTD sensors (PT100) with G0.25 8C accuracy were used to measure the temperature at various points. Pressure gauges with G0.25% accuracy were also provided suitably. The same type of evaporator coil used in the refrigerator was kept inside a secondary refrigerant (ethylene glycol) calorimeter. To measure the compressor load and heater load a wattmeter with G1 W accuracy and energy meter were provided. The capillary and charge optimisation tests with CFC12 showed that the optimum capillary tube length and charge quantity were 3.35 m and 175 g, respectively. Hence, the above charge quantity was taken as reference to evolve mixture quantities. To measure the per day energy consumption, a test was conducted as per Bureau of Indian Standards (BIS) 1476. The set-up was kept inside a temperature-controlled room where the ambient could be varied from 20 to 43 8C. During pull down the temperature and power consumption were recorded at 15 s intervals. To find out the actual COP, the evaporator inside the refrigerator was disconnected and the system was connected to the calorimeter by suitably operating the ball valves. To determine the actual refrigeration effect and compressor power for a particular calorimeter temperature (temperature of secondary refrigerant), the heater load was adjusted so that the system stabilized at that particular temperature. This test was repeated for K15, K12, K6 and K4 8C secondary refrigerant temperatures and 22, 26, 32, 36 and 43 8C ambient temperatures. The refrigerant mixtures considered are M07, M09 and M11.
3. Experimentation
3.2. Deep freezer
The performance of the considered refrigerant mixtures was experimentally studied as against that of CFC12 in the
The schematic diagram of the experimental facility used in this investigation is shown in Fig. 2. The set-up consists
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Fig. 1. Schematic diagram of the experimental facility used to test a domestic refrigerator.
of a deep freezer modified as a secondary refrigerant calorimeter. The calorimeter consists of a 400 l capacity pressure tight vessel. The inner shell was filled with the secondary refrigerant (HFC134a). At the bottom, there is a rod heater connected to the mains through a suitable dimmerstat and wattmeter for accurate measurement of heater load. The evaporator coil (29 m long, 12 mm diameter copper pipe) was soldered around the shell. To measure the temperature RTD sensors were placed inside the shell and along the length of the coil. The pressures at typical points were also measured. Since, miscibility of the mineral oil with the mixture is a major issue, an oil level indicator (column type) was attached to the hermetic compressor for periodic checking. All the pressure and temperature sensors were connected to a data logging system. To determine the actual refrigeration effect and compressor power for a particular calorimeter temperature (temperature of secondary refrigerant), the heater load was adjusted so that the system stabilised at that particular temperature. The actual refrigeration effect was obtained by
adding the heat infiltration with the heater load. This test was repeated for K18, K15, K10 and K4 8C secondary refrigerant temperatures and 22, 26, 32, 36 and 43 8C ambient temperatures. The refrigerant mixtures considered are M07, M09 and M11. 3.3. Vending machine (visi cooler) The vending machine consists of an air-cooled plate fin condenser, plate fin evaporator, hermetically sealed compressor and capillary expansion device. The experimental set-up used for this study is schematically shown in Fig. 3. Since, capillary tube optimisation is required, four capillaries having 0.86 mm diameter and 2.13, 2.44, 2.74 and 3.05 m long were suitably fixed from a header with ball valves. The compressor was connected with a wattmeter and energy meter to study the energy consumption. To study per day energy consumption and pull down performance, the same procedure used in domestic refrigerator was followed. However, the actual refrigerating power and COP were not estimated. The thermostat inside the
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Fig. 2. Schematic diagram of the experimental facility used to test a deep freezer.
refrigerated space was adjusted to 1 8C cut-off and 4 8C cutin temperatures. Based on the results of the theoretical investigations and earlier experimentation in refrigerator, M09 and M11 mixtures were only considered for vending machine. 3.4. Walk-in cooler The schematic of the experimental facility used in this work is shown in Fig. 4. It consists of a walk-in cooler room of dimension 2300!2300!2800 mm3, a serpentine type evaporator coil having 28 mm diameter and 58 m long aluminium coated M.S. pipe, a 3.5 kW open type compressor with suitable motor, thermostatic expansion valve (TEV), plate-fin type condenser and a receiver of 4 l capacity. RTD temperature sensors, pressure gauges, flow meter and energy meter were suitably fixed to measure the required parameters. An oil level indicator was also provided in the compressor to check the oil return characteristics of the mixture. To conduct no load pull down test, the door was kept open for 48 h till the cooler space reached thermal equilibrium with the ambient. The thermostat cut-off switch was adjusted to maintain 2.5 8C cut-off and 5 8C cut-in temperatures. The system was started and the parameters such as pressure, flow rate and energy consumption were recorded for every 15 s until the first cutoff occurred. Once the system reached the steady state of 2.5 8C cut-off and 5 8C cut-in, the energy consumption test was carried out. During the test all the performance parameters were also recorded. The refrigerating effect
was estimated through an enthalpy balance with the help of mass flow measurements made through suitable flow meter. The detailed procedure has been already reported [14]. After completing the reference tests with CFC12 the refrigerant was recovered and equivalent quantity of the mixture (4.9 kg) was charged. All the tests conducted with CFC12 were repeated.
4. Results and discussion The results obtained from experimental investigations on the performance of HFC134a/HC600a/HC290 mixture and CFC12 in four different types of refrigeration systems are discussed with respect to parameters such as pull down time, Refrigeration effect, actual COP and energy consumption. 4.1. Domestic refrigerator The average energy consumption obtained for CFC12, M07, M09 and M11 at various ambient temperatures is plotted in Fig. 5. From that it has been found that the energy consumption of the mixtures is less than that of CFC12. Among the mixtures M09 is characterised with 4.1–7.6% less energy consumption than that of CFC12. The energy consumption of the compressor with time during the pull down is shown in Fig. 6. It shows that the compressor power of M09 mixture is 2–3% higher than CFC12 during the pull down. But for the same temperature setting in the thermostat, the pull down time for M09 was 11 min shorter
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Fig. 3. Schematic diagram of the experimental facility used to test a vending machine.
than that of CFC12 and, hence, the total energy consumed by M09 during pull down was 0.196 kWh as against 0.216 kWh for CFC12. The measurement of temperature along the length of the coil indicated a temperature glide that was less than 3 K for 80% of the evaporator coil length. However, details of temperature distribution are already published [15]. The refrigeration effect tabulated in Table 1 shows that the mixtures have higher refrigerating effect than CFC12. Among the mixtures M09 is characterised with the maximum refrigeration effect. The improvement is 7–10.5% and 20–26.5% at K15 and K4 8C calorimeter temperature, respectively. The higher latent heat of vaporisation for the mixture as well as higher condensing pressures that causes a higher mass flow rate lead to better refrigeration effect. The improvement in COP of M09 over CFC12 at K15 8C calorimeter temperature for the tested ambient conditions was also found to be 3.8–8.5%. 4.2. Deep freezer As per the procedure discussed, the actual refrigeration effect was calculated and the results are tabulated in Table 2. It is found that the refrigeration effect increases with the
increase in calorimeter shell temperature and decreases with the increase in ambient temperature. Among the mixtures M09 shows 6–8.5% and 14.2–28.4% improvement in refrigeration effect over CFC12 at the calorimeter temperature of K18 and K4 8C, respectively, for the different ambient conditions. The variation of COP with calorimeter temperature at different ambient temperatures is plotted in Fig. 7. In most of the cases, the actual COP is increased by 2–2.5 times while the calorimeter temperature was increased from K18 to K4 8C. This is due to the higher rate of heat transfer as an effect of large temperature difference across the evaporator coil and refrigerated space. It was also observed that the temperature difference between the coil and space increased from 6 to 14 8C as the calorimeter temperature was increased from K18 to K4 8C, respectively. To carryout the oil miscibility study, initially the compressor was filled with 900 ml of mineral oil as per the manufacturer’s guidelines. The level was noted on the column type oil level indicator. The oil level during the operation of the system was recorded. It was found to be 1 mm below the initial level. This can be ascribed to the oil removed along with the refrigerant during recovery. Once
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Fig. 6. Variation of compressor power with time during pull down in a domestic refrigerator and visi cooler.
4.3. Vending machine
Fig. 4. Schematic diagram of the experimental facility used to test a walk-in cooler.
M09 was charged and the system started, again the oil level was noted. After 2 months of continuous operation again oil level was verified with the initial markings. There was hardly any change in the oil level. Further, the sight glass provided in the suction and discharge lines showed no traces of oil in the liquid and suction lines. This proves the oil miscibility of the new refrigerant mixture.
Fig. 5. Variation of per day energy consumption with ambient temperature at K15 8C freezer compartment temperature.
The results obtained from the energy consumption study are tabulated in Table 3. Among the refrigerants M09 shows the lowest energy consumption. Compared to CFC12, M09 has 10.8–17.3% and 13–19.6% less energy consumption for different thermostatic settings at 22 and 43 8C ambient temperature, respectively. The compressor power with respect to time during pull down is plotted in Fig. 6. The total energy consumed during pull down is 0.214 kWh for M09 whereas it is 0.255 kWh for CFC12. This reduction of 16.3% power consumption can be attributed to better COP of the M09 that is experienced in the other tests (Deepfreezer and refrigerator). 4.4. Walk-in cooler At the (experimentally studied and reported [14]) optimum TEV settings and steady state operating conditions the various performance parameters including the COPs and energy consumption per day were studied and are tabulated in Table 4. The actual COP calculated by considering the mass flow rate and actual compressor power is 5.5% higher
Fig. 7. Variation of actual COP with calorimeter temperature at 32 8C ambient temperature in deep freezer.
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Table 1 Refrigeration effect at various ambient and calorimeter temperatures in a domestic refrigerator Refrigerant
Calorimeter temperature (8C)
Refrigeration effect (W) Ambient temperature (8C)
CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11
K15 K15 K15 K15 K12 K12 K12 K12 K6 K6 K6 K6 K4 K4 K4 K4
22
26
32
36
43
73.5 74.5 82.5 79.5 81.5 84.5 93.5 90.0 98.5 103.0 117.0 111.5 108.0 112.0 130.5 123.5
70.0 72.5 76.5 75.0 75.5 80.0 88.5 86.0 93.5 98.5 112.0 107.0 102.0 107.0 125.5 118.0
60.5 62.0 64.5 64.0 66.0 67.0 74.5 71.5 80.5 84.5 98.5 91.5 89.0 93.5 110.5 104.5
59.0 60.0 62.5 61.5 61.5 64.5 70.5 68.5 69.5 72.5 86.5 83.5 76.5 79.0 97.0 92.0
54.0 55.0 57.0 56.0 58.0 60.0 65.5 63.5 70.0 72.5 88.0 80.0 78.0 80.0 98.5 93.0
for M09 mixture. The above improvements are due to the lower density and corresponding lesser mass flow rate of the M09 mixture than that of CFC12, which leads to less compressor work for M09. It has also been observed that the M09 mixture has shorter ON cycle than that of CFC12 for the same space temperature settings. The no load pull down test showed that the first cut-off of the system with M09 mixture is 30 min earlier than that of CFC12. The shorter ON cycle time is due to the higher refrigerating capacity.
The net result of the above is that the M09 mixture shows 30.24% less energy consumption than that of CFC12. In the above systems, temperature distribution was also observed along the length of the evaporator coil to check for temperature glide. The glide was within 3 8C for more than 80% of the coil length which is quite acceptable. It is also worthwhile to mention that the compressor discharge temperature for the M09 is lower than CFC12 in all cases.
Table 2 Refrigeration effect at various calorimeter and ambient temperatures in a deep freezer Refrigerant
Calorimeter temperature (8C)
Refrigeration effect (W) Ambient temperature (8C)
CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11 CFC12 M07 M09 M11
K18 K18 K18 K18 K15 K15 K15 K15 K10 K10 K10 K10 K4 K4 K4 K4
22
26
32
36
43
260 271 285 277 304 309 342 324 511 545 587 574 873 900 1021 958
222 225 245 240 256 266 294 280 472 508 551 530 810 871 969 922
208 215 234 223 237 245 274 255 431 446 517 500 787 826 940 878
182 191 198 195 210 218 235 227 385 405 475 450 682 720 858 803
160 165 170 169 190 197 214 205 270 285 351 325 580 600 741 684
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Table 3 Per day energy consumption with respect to ambient temperature at different thermostat settings in a visi cooler Thermostat settings
Refrigerant
Energy consumption (kWh/day) Ambient temperature (8C)
Cut-inZ0 8C Cut-offZ3 8C Cut-inZ1 8C Cut-offZ4 8C Cut-inZ2 8C Cut-offZ5 8C Cut-inZ3 8C Cut-offZ6 8C
CFC12 M09 M11 CFC12 M09 M11 CFC12 M09 M11 CFC12 M09 M11
22
26
32
36
43
3.26 2.91 3.03 3.23 2.83 3.04 3.08 2.62 2.9 2.83 2.38 2.56
4.1 3.57 3.76 3.92 3.35 3.54 3.76 3.21 3.58 3.49 2.84 3.12
5.18 4.51 4.72 5.04 4.25 4.54 4.73 3.99 4.29 4.4 3.62 4.07
5.8 5.03 5.22 5.77 4.84 5.18 5.32 4.58 4.78 5.0 4.19 4.69
7.12 6.2 6.52 7.07 6.04 6.46 6.76 5.64 5.97 6.38 5.24 6.0
5. Conclusions The present investigation has resulted in the development of an ozone friendly, energy efficient, user friendly, safe and cost-effective alternative refrigerant for CFC12 in domestic and commercial refrigeration systems. Based on the experimental investigation the following conclusions are drawn. 1. The better refrigerating effect of M09 resulted in 10, 9.8, 20.4 and 10% shorter pull down time in domestic refrigerator, deep freezer, vending machine and walk-in cooler, respectively. 2. The actual COP of the system is improved by 5–17% in low temperature systems. Table 4 Performance comparison of M09 with CFC12 at 32 8C ambient temperature in a walk-in cooler Sl. no.
Description
1
Evaporator inlet temperature (8C) Compressor outlet temperature (8C) Condenser outlet temperature (8C) Refrigerant flow during steady state (kgsK1) Power consumption at steady state (W) Average ON cycle time (minutes) Average OFF cycle time (minutes) COP-theoretical COP-actual Energy consumption per day (kWh/day)
2 3 4 5 6 7 8 9 10
CFC12
M09
K7
K9
77
65
35.6
36
0.116
0.010
1032
1020
12
8
12
13
3.38 1.44 16.5
3.76 1.577 11.51
3. The capillary optimisation tests proved that the standard capillary used in CFC12 systems can be used for the mixture also. But when the thermostatic expansion valves are used suitable super heat adjustment is required. 4. The actual refrigeration effect of M09 is 7–26.5% and 6– 28.4% higher than that of CFC12 in domestic refrigerator and deep freezer, respectively. 5. The M09 mixture reduces the per day consumption by 4.1– 7.6%, 10.8–19.6% and 30.2% in domestic refrigerator, vending machine and walk-in cooler, respectively. 6. The discharge temperature of the compressor is reduced by the M09. Hence, it could improve the compressor life. 7. The continuous running of all the systems discussed above for 18 months, with consistence performance, proves the oil miscibility of the M09 with mineral oil. Maintaining of oil levels in the compressors of deep freezer and walk-in cooler confirms the oil return characteristics of M09. Thus, it can be concluded that the M09 mixture could be an ozone friendly, energy efficient, user friendly, safe and economically viable alternative to CFC12 for domestic and small commercial refrigeration systems. The fact that POE oil can be dispensed with by using HFC134a/HC-blend mixture in the place of HFC134a is a significant finding in this research work. During the tests, none of the existing components was replaced/modified. Hence, in developing countries, for the small-scale service sector, M09 mixture can be used successfully for existing CFC12 appliances in the event of CFC phase out due to Montreal protocol.
Acknowledgements This research work was funded by University Grants Commission (UGC) of India. The authors acknowledge the support of HIDECOR project (funded by Swiss Agency for
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Development and Co-operation Managed by the Consortium; Swisscontact and IT Power India Pvt. Ltd.) by way of providing HC blend (CARE30) for the research.
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