7 th International Chemical Engineering Congress & Exihibition Kish, Iran, 21-24 November, 2011 Experimental study of R600a and R436a to replace R134a in a domestic refrigerator and freezer M. Rasti 1, M.S. Hatamipour 1, S.F. Aghamiri 1, M. Tavakoli 2 1-Chem. Eng. Dept., University of Isfahan, Isfahan, I.R. Iran 2-R&D Dept., Entekhab Industrial Group, Isfahan, I.R. Iran mehdi.rasti@eng.ui.ac.ir Abstract After Montreal protocol R134a and hydrocarbons like propane (R290), n-butane (R600) and i- butane (R600a) are using as refrigerant in most of domestic refrigerators and freezers. But in 1996 Kyoto protocol called for phase out of R134a due to its high GWP 1, and replace it with new low ODP 2 and GWP refrigerants. Hydrocarbons have zero ODP and 20 GWP. This paper presents feasibility study of using pure and mixture hydrocarbons as alternative refrigerant of R134a in a domestic refrigerator and freezer. A domestic R134a type refrigerator-freezer tested with three different refrigerants namely R436 3, R600a and 105 g R134a. Temperatures at various locations in the domestic refrigerator-freezer and refrigeration cycle and consumed energy recorded. The results showed that energy consumption of R600a and R436a are the same and about 5% is lower than R134a. The effect of freezer and refrigerator air temperatures on energy consumption considered with R436a as a refrigerant. The results showed that R600a and R436a can be considered as a convenient alternative for R134a. Keywords: R600a; R436a; R134a; Domestic refrigerator-freezer Introduction Recently energy efficiency of household appliances and in particular refrigerators and freezers, is receiving increasing. In terms of energy consumption, a refrigerator is almost the largest single end user of electricity in the residential sector due to its widespread use and continuous operation and therefore, improved energy efficiency is of paramount importance [1]. Energy consumption of domestic refrigerators and freezers in residential sector in Islamic Republic of Iran is about 25%. Many countries have introduced policies to reduce greenhouse gas emissions and therefore encourage a more rationale use of energy. The progression of refrigerants from first generations through four generations is depicted in Fig. 1 [2]. 1 - Global Warming Potential 2 -Ozone Depletion Potential 3 - mixture of Propane and Iso-butane (with 56 % wt of Propane)
first generation 1830-1930s whatever worked CO 2, NH 3, SO 2, HCOOCH 3, HCs,H 2 O, CCL 4, CHCS second generation 1931-1990s safety and durability CFCs, HCFCs, HFCs, NH 3, H 2 O,... third generation 1990-2010s ozone protection HCFCs, HCFs, NH 3, H 2 O, HCs, CO 2,... fourth generation 2010-... global warming zero/low ODP, low GWP, short t atm, high efficiency Fig. 1.Refrigerants progression [2] Table 1 shows the safety and environmental properties of some refrigerants that can be use in domestic refrigerators and freezers. Table 1. Properties of some refrigerants Refrigerant Molecular Explosive limits in air, % Safety Chemical formula Weight by volume Group ODP GWP R12 CCl 2 F 2 120.9 Nonflammable A 1 1 10900 R134a CH 2 FCF 3 102.0 Nonflammable A 1 0 1430 R290 C 3 H 8 44.0 2.3-7.3 A 3 0 < 20 R600a ic 4 H 10 58.1 1.8-8.4 A 3 0 < 20 R436a C 3 H 8 +ic 4 H 10 49.33 3.7-9.5 A 3 0 3 Many researchers have reported that pure hydrocarbon or its mixtures as refrigerant are an environment friendly alternative option in domestic refrigerators and freezers. Sattar et al. [3] used pure butane as refrigerant at 25 C and 28 C ambient temperatures and found that when R134a is used, the energy consumptions are 2.08 kwh/day and 2.25 kwh/day, but when pure butane used it consumes 2.199 kwh/day and 2.197 kwh/day, respectively. Mani and Selladurai [4] reported that the R290/R600a (68/32 by wt %) mixture can be considered as an alternative replacement refrigerant for R134a. Ching-Song et al. [5] reported that based on the
experimental investigation on a 50/50 wt ratio of R290/R600a in a 440 L capacity household refrigerator. They have found a total saving of 4.4% in energy consumption and refrigerant charge is reduced by 40% compared to 150 g for R134a. Mohanraj et al. [6] used a hydrocarbon mixture (composed of R290 and R600a in the ratio of 45.2:54.8 by weight) as an alternative to R134a in a 200 L single evaporator domestic refrigerator under different ambient temperatures (24, 28, 32, 38 and 43 C) and found that 60 g hydrocarbon mixture show a decrease in energy consumption, pull-down time and on-time ratio by about 11.1%, 11.6% and 13.2%, respectively and discharge temperature of hydrocarbon mixture was found to be 8.5 to 13.4 K lower than that of R134a. The literature survey showed that many researchers [7-11] have studied different hydrocarbon refrigerant mixtures as alternative to R12 and R134a in domestic refrigerators under various surrounding temperatures and mass ratio of refrigerant. Many researchers have investigated the process of using hydrocarbons in domestic refrigerators and freezers, even in the decade of 1990s [12-17]. The results support the possibility of using pure hydrocarbons or its mixtures as an alternative to R134a in domestic refrigerators and freezers. Materials and methods The test object was a domestic refrigerator that was originally designed for R134a. The most important specifications of this refrigerator are summarized in Table 2. Table 2. Technical specifications of domestic refrigerator test unit Freezer capacity 60 L Fresh food capacity 178 L Current rating 0.8 A Voltage 220-240 V Frequency 50 Hz No of doors 2 Refrigerant type R134a Defrost system Auto Defrost Charged mass 105 g Capillary tube length 270 cm Capillary tube Inner diameter 0.78 mm Before charging compressor with refrigerant, we evacuate the cycle because air or noncondensable gases in the refrigerant cause a decline in cooling capacity and a rise in input power due to high discharge pressure. In particular, air (oxygen) cause the generation of sludge and shortening of compressor life. Therefore, the non-condensable gas in refrigeration cycle must not exceed 1% (vol.). The recommendable vacuum degree is 0.08 mmhg, and the evacuation time must be 40 minutes or more with the capacity of vacuum pump of 300 L/min or more and it is better to vacuum simultaneously in high and low pressure sides with a pump per system. We evacuated refrigerator simultaneously from suction and discharge points for at least 40 minute. R600a and R436a were purchased from the Parsian Refrigeration Development Co., Iran and the R134a was purchased from the T. S Enterprise Co., China. For achieving good performance and long-life reliability in domestic refrigerator and freezer, purity of R134a,
R600a and R436a was equal to 99.5%, that the purity of refrigerants which used in household refrigeration cycle should be more than 99.5%. Specification of R600a is shown in Table 3. Table 3. Specification of R600a according to DIN 8960-1998 Parameter Specification Unit Refrigerant content 99.5 % by mass Organic impurities 0.5 % by mass 1,3-Butadiene 5 ppm by mass Normal Hexane 50 ppm by mass Benzene 1 ppm per substance Sulfur 2 Ppm by mass Non condensable gases 1.5 % vol. of vapor phase Water 25 ppm by mass Acid content 0.02 Mg KOH/g Neutralization Particles/solids no Visual check Fig. 2 provides a schematic diagram of the top-mounted freezer model and measurement system used in the experimental setup. Fig. 2. Schematic diagram of experimental setup The refrigerator was set in a test room in the manufacturer s site according to Iranian standard 4268 as shown in Fig. 3.
Fig. 3. Schematic of domestic refrigerator and freezer in the test room The ambient conditions (the surrounding temperature and relative humidity) simulated through automated devices such as a heater, cooler and humidifier. Temperatures in the 16 arbitrary points of the refrigerator were monitored and recorded continuously. The temperatures at the inlet and outlet of the evaporator, compressor, condenser, refrigerator cabin, freezer chamber, and dryer were recorded. The consumed voltage and the current, the ambient temperature and the relative humidity were recorded continuously for a cycle through a data acquisition system as well. Analyzing these data, the power consumption, working time, and ON-time ratio of the compressor were calculated. The starting conditions were the same for all experiments. The accuracy of the existing sensors in the test room were as follows: temperature, ; stabilizer voltage, ; relative humidity, and ambient temperature. Results and discussion 1. Hydrocarbon leakage analysis This analysis is based on a major release of hydrocarbon refrigerant with a short exposure time from a R600a charged cabinet. It is based on a 50 g charge of domestic refrigerator in this case study. The following analysis ensures that an explosive situation will not occur. Sudden release of refrigerant would require a rupture in the system. The criterion is such that with a sudden loss of refrigerant, the concentration of R600a in the surrounding space does not exceed 20% of the lower flammability limit. The minimum room volume for safe operational condition of a refrigerator could be calculated by using Eq. 1: V room = m r /(0.2 LFL) Eq. 1
Where m r = actual charge weight (50 g) LFL = Lower Flammability limit (for R600a [Iso-butane] = 0.043 kg/m 3 ) Vroom = Volume of the room in which the appliance is located (with no additional ventilation or airflow) Rearranging, Vroom = 0.050 / (0.2 0.043) = 5.81 m 3 minimum room size Based on a typical room height of 2.4m the minimum floor area is 2.42 m 2. Volume of general rooms that domestic refrigerator and freezer put in it is equal to 3 4 2.4= 28.8 m 3. Assuming the room is sealed and the complete charge is released rapidly, to avoid stratification in the event of a catastrophic leak, the condenser fan of the appliance is required to disperse the refrigerant therefore no explosion will occur. 2. The freezer and refrigerator temperature setting effect Experiments were carry out for four different settings of freezer and refrigerator air temperatures with hydrocarbon mixture (R436a). The starting conditions, both inside the refrigerator and the refrigeration equipment, were the same for all experiments. Suction gas temperature is measured at the distance 15 cm of the insulated surface suction pipe apart from shell surface and discharge gas temperature is measured at the distance 5 cm of the insulated surface discharge pipe from shell surface. The results are summarized in Table 4. Here we observed that higher freezer and refrigerator air temperatures yield a lower energy consumption and ON-time ratio in comparison lower with freezer and refrigerator air temperatures. Therefore, we consider that lower energy consumption is desire with higher settings of freezer and refrigerator. Table 4. Comparison between different refrigerator and freezer temperatures Parameter Test 1 Test 2 Test 3 Test 4 Ambient temperature, o C 32 32 32 32 Ambient relative humidity, % 50 50 50 50 Freezer air temperature, o C 6.4 8 5.8 4.1 Cabinet air temperature, o C -18.5-16.8-16.6-19.6 Discharge temperature, o C 72 70 72 74 Suction temperature, o C 28 30.5 30 30 ON-time, min 44 40 38 50 Off-time, min 66 73 67 56 On-time ratio, % 40% 35% 36.2 47.2 Power consumption in 1 cycle, kwh 0.998 0.0893 0.0962 0.1088 Energy consumption, kwh/day 1.437 1.279 1.361 1.635
Power (kwh) Experimental study of R600a and R436a The effect of freezer and refrigerator temperature setting on power consumption and ON-time ratio is shown in Fig. 4. 200 180 160 140 test 1 test 2 test 3 test 4 120 100 80 60 40 20 0 0 20 40 60 80 100 120 Time (min) Fig. 4. Effect of freezer and refrigerator setting on power consumption 3. Refrigerants with optimal charge For each domestic refrigerator and freezer, the optimal refrigerant charge should be determined in an appropriate test laboratory in order to obtain the best working conditions. If the refrigerant amount exceeds or lacks compared to the proper amount range, it will cause the loss of cooling capacity, lowering efficiency and damage of compressor life. With some experiments on the domestic refrigerator and freezer that was essentially designed for working with 105 g R134a as refrigerant, determined that the optimal charge for R436a is 55 g and the optimal charge for R600a is 50 g. Some important parameters for optimal charge of R600a, R436a and R134a are described in Table 5. The results showed that energy consumption of R600a and R436a is the same and lower than that of 105 g R134a in 24 hours test at 32 C ambient temperature and 50% relative humidity. The results show that the suction temperature and discharge temperature of R600a are lower than R436a and R134a.
Power consumption (W) Experimental study of R600a and R436a Table 5. Comparison between optimal charge of R600a, R436a and R134a Parameter R600a R436a R134a Ambient temperature, o C 32 32 32 Ambient relative humidity, % 50 50 50 Freezer air temperature, o C -18-18 -18 Cabinet air temperature, o C 4.6 4.6 4.6 Discharge temperature, o C 62 69 71 Suction temperature, o C 26 30 34 ON-time, min 69 40 50 Off-time, min 57 57 56 On-time ratio, % 54.8 41.7 46.7 Power consumption in 1 cycle, kwh 0.1302 0.1018 0.1076 Energy consumption, kwh/day 1.543 1.541 1.628 Minimum inlet temperature of evaporator -29.5-30.6-27 ON time ratio is the operating time of the compressor in one cycle divided into the total cycle time. ON time ratio of R436a is lower that of R600a and R134a. The comparison of power consumption in 1 cycle for R600a, R436a and R134a with optimal charge is shown in Fig. 5. Here the results indicate that by using R600a the minimum power is achieved. 200 180 160 140 R600a R436a R134a 120 100 80 60 40 20 0 0 20 40 60 80 100 120 140 Time (min) Fig. 5. Effect of optimal charge of different refrigerants on power consumption
Inlet temperature of evaporator (C) Experimental study of R600a and R436a 4. Evaporator inlet temperature The comparison of evaporator inlet temperature with 50 g R600a, 55 g R436a and 105 g R134a for one On/Off cycle is shown in Fig. 6. Results were obtained at 32 C ambient temperature with 50% relative humidity. The results show that the inlet evaporator temperature of R436a and R600a are 3.5 C and 2 C, respectively colder than that of the R134a; therefore, in order to achieve lower freezer air temperature, it is better to use hydrocarbon as refrigerant. -5-10 -15-20 -25 R600a R436a R134a -30-35 0 20 40 60 80 100 120 140 Time (min) Fig. 6. Comparison of evaporator inlet temperature for 50 g R600a, 55 g R436a, 105 g R134a Conclusion R600a and R436a with a zero ODP, and a GWP lower than R134a injected into the refrigeration cycle of a single evaporator domestic refrigerator-freezer that was originally designed for R134a as over test object, without any mechanical alteration in the refrigerator. The power consumption measured and temperatures sensed at arbitrary points in the test unit and other important parameters measured for R600a, R436a and R134a refrigerants. The results show that in comparison with R134a: - The amount of hydrocarbon mixture charge is reduced by 52% for R600a and 48% for R436a - ON time ratio is reduced by13% for R436a - Energy consumption is reduced by 5.3% in 24 hours for R600a and R436a - Evaporator inlet temperature is colder for both of hydrocarbon refrigerants - Discharge temperature decrease by 12.6% for R600a.
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