Performance Analysis of Electronic Expansion Valve in 1 TR Window Air Conditioner using Various Refrigerants CHENNUCHETTY CHINNARAJ * Associate Professor in Mechanical Engineering, Government College of Engineering, Salem-636 011, Tamil Nadu, India PALANISAMY GOVINDARAJAN Department of Mechanical Engineering, Sona College of Technology, Salem, Tamil Nadu, India Abstract: A window air conditioner of 3.5 K.W capacity fitted with expansion devices such as capillary tube, thermostatic expansion valve and Electronic expansion valve was tested for its coefficient of performance, power required and refrigeration effect with respect to the refrigerants R22 and R407C under different operating conditions.initially evaporator temperature was maintained at 279 K and condenser temperature was varied and then the test was conducted again in the same window air conditioner with electronic expansion valve alone as expansion device and by varying the refrigerant super heat temperature at inlet to the compressor from 273K to 293K for the refrigerants R 22, R 407C and R 290 The performance of electronic expansion valve with eco friendly refrigerants shows a positive effect and enable the industry to favorably displace the R22 and other types of expansion devices. Keywords: Window air conditioner; Coefficients of Performance; Thermostatic Expansion Valve; Electronic Expansion Valve; Tonne of Refrigeration 1. Introduction Global concern over Ozone depletion and global warming have resulted Montreal and Kyota protocols. Use and production of Choloro fluro carbon (CFC) and Hydro choloro fluoro carbon (HCFC) have to be ceased in all over the World by the year 2030. The refrigerant R22 used in refrigeration and air conditioning field contains Chlorine and harms the Ozone layer. It must be replaced by eco-friendly refrigerants in future. The Electronic expansion valve(eev), driven by stepping motor controlled pulse signal generator, has widely used in refrigeration systems. The refrigerant flow through the evaporator is controlled by means of monitoring pressure and temperature of it at outlet of the evaporator. Hence it shows better overall performances compared to the capillary tube system and thermostatic expansion valve (TEV). Lazzarian and Noro (2008) proved that the EEV fitted in air conditioner with air cooled condenser enables appreciable energy saving with respect to same installations equipped with traditional thermostatic expansion valve and this is due to the fact that it allows a lower condensation pressure in systems equipped with air cooled condenser, which is adjusted to variations in outside air temperature. Chasis park et al (2007) in their work proved that the applications of electronic expansion valves into multi type heat pumps and inverter heat pumps in building air conditioning systems have increased for comfort environmental control and energy conservation. Ciro Aprea and Rita Mastrullo (2002) stated that, under steady conditions both EEV and TEV are equal in performance but under transit conditions EEV gives better overall performance compared to TEV.
Ma Shanwei et al (2005) have developed a correlation on the basis of the experimental data of electronic expansion valve for R22 and its alternatives R 407 C (R 32/125/134a, 23 /25/52 wt%) and R410A (R 32/125, 50/50 wt % ). Jinghui Liu et al (2008) have developed an one dimensional model in which the evaporation wave theory is employed to investigate the choking flow characteristics in EEV for R22, R407C and R 410A. The refrigerant mass flow characteristics of the EEV are an important issue in heat pumps / refrigeration system operation because the valve regulates the refrigerant flow to match various operating conditions. From the experimental data, Xue Zhifang et al (2008) developed a mass flow correlation for R134a through an EEV. Based on the throttling mechanism and thermodynamic analysis, the mass flow rate is a function of various parameters such as valve s geometric parameter, the inlet refrigerant pressure and temperature, outlet refrigerant pressure and the refrigerant thermo physical properties such as dynamic viscosity and surface tension. 2. Experimental Apparatus The experimental setup shown in Fig.1 is used to test the performance of EEV fitted in a window air conditioner of 3.5 kw capacity under variable operating conditions using the refrigerants R22, R 407C, R 290 as working fluids. Fig.1 Schematic diagram of the test facility The test rig consists of hermetic compressor, environmental chamber constructed as per BIS, 1391, (1992) to simulate the indoor and outdoor conditions with necessary instrumentation, two heat exchangers (condenser and evaporator) and expansion devices such as capillary tube, thermostatic expansion valve and electronic expansion valve. The EEV used in this test rig is a solenoid valve linked to an electronic controller and electronic controller s operation is based on temperature of refrigerant and air at inlet and outlet of evaporator. 2.1. Environmental Chambers The indoor and outdoor simulation chambers are made of double skin PUF insulators walls and the dimensions are chosen as per BIS, 1391 (1992). The heat load is provided by a 3000 Watts heater placed in the indoor chamber which is controlled by a variac. There is a Wattmeter of ± 0.5 % accuracy provided to measure the power supplied to the heater. To ensure uniform temperature distribution within the chambers air circulating fans are provided. A 2 TR split air conditioner is provided in the outdoor chamber to dissipate the heat from condenser. Humidifiers are provided in the both the chambers to maintain the required relative humidity. 2.2. Instrumentation The mass flow rate of refrigerant is measured using a corialis type flow meter of accuracy ± 0.25%. To measure the compressor power, a digital Wattmeter of accuracy ± 0.5% is provided. Pressure transducers with ±0.25 % accuracy and J- type thermocouples with ± 0.1% accuracy are provided to measure the respective refrigerant pressures and
temperatures at salient points. Thermocouples are also placed inside the chambers to measure the average room temperatures. The relative humidity is measured using humidity sensor of accuracy ± 0.1%. All sensors are connected to a computerized data acquisition system (AGILENT 34970 A). 3. Experimentation To have a maximum COP, full charge condition was determined under a standard condition of condenser temperature at 323 K and evaporator temperature 279 K. By keeping the temperature of refrigerant entering the evaporator at 279K and varying its temperature at inlet to condenser as 313K, 318K, 323K and 328K, the tests for the window air conditioner using the refrigerantsr22 and R 407C with various expansion devices such as capillary tube, thermostatic expansion valve and EEV were conducted by setting the same full charge condition for all the three expansion devices and corresponding readings were recorded continuously for 40 minutes using the data acquisition system The refrigerant effect, compressor power and COP were calculated and results for R22and R407C were analyzed. Heat infiltration load into indoor chamber was determined. Again tests were conducted by varying the refrigerant super heat temperature at inlet to the compressor from 273K to 293K in steps of 2K by adjusting the EEV.The indoor and outdoor conditions were maintained by adjusting the power supply to the heaters and controlling the humidifiers. Refrigerant side and airside readings were noted and for better accuracy, the average values were used for computing various performance parameters. For calculating the refrigeration effect and compressor power, the enthalpy values of refrigerant at salient points were obtained from the refrigerant s thermodynamic property value tables using the pressure and temperature readings.all the three refrigerantsr22,r 407C and R290 under study were tested using electronic expansion valve alone and results were analyzed. 4. Results and Discussion By keeping the temperature of refrigerant entering the evaporator at 279K and varying its temperature at inlet to condenser as 313K, 318K, 323K and 328K, the tests for the window air conditioner using the refrigerants R22 and R 407C were conducted and the performance parameters such as refrigeration effect, compressor power and COP were calculated and compared for performance analysis. Figure 2 shows the variation of capacity for R22 capillary, R407C TEV and R407C EEV as a function of different condenser temperature. The capacity of the R407C EEV system is higher by 10.1% than that for the R22 capillary tube system. The capacity of the R407C TEV system is higher by 0.196% than Figure 2 shows the variation of capacity for R22 capillary, R407C TEV and R407C EEV as a function of different condenser temperature. The capacity of the R407C EEV system is higher by 10.1% than that for the R22 capillary tube system. The capacity of the R407C TEV system is higher by 0.196% than that for the R22 capillary tube system Fig 2: Capacity variations for R22 capillary, R407C TEV and R407C EEV at various condensing temperatures. Figure 3 shows the variation of compressor power for R22 capillary, R407C TEV and R407C EEV as a function of different condenser temperature. The compressor power of the R407C EEV system is lower by 14.8% than that for
the R22 capillary tube system. The compressor power of the R407C TEV system is lower by 4.1% than that for the R22 capillary tube system. Fig 3: Compressor power variations for R22 capillary, R407C TEV and R407C EEV at Various condensing temperatures. Figure 4 shows the variation of COP for R22 capillary, R407C TEV and R407C EEV as a function of different condenser temperatures. The COP of the R407C EEV system is higher by 13.08% than that for the R22 capillary tube system. The COP of the R407C TEV system is higher by 1.23% than that for the R22 capillary tube system. By varying the degree of superheat, the experiments were carried out, for the refrigerants R22, R290, and R407C. The performance parameters such as mass flow rate of refrigerant, cooling capacity, compressor exit temperature, compressor power, volumetric efficiency and COP were compared between the refrigerants with the use of electronic expansion valve. Fig 4: COP variations for R22 capillary, R407C TEV and R407C EEV at various condensing temperatures. Figure 5 shows the variation of cooling capacity for R22, R290, and R407C using EEV as a function of different degree of super heat. The cooling capacity of R22 system is higher by 2.42% than that of R407C and 11.7% than that of R290. For R407C and R290 the latent heat is observed to be more in the evaporating temperature ranges and less in the condensing temperature ranges. The reduction of latent heat in the condensing temperature ranges are more predominant compared to the marginal increase in the evaporating temperature ranges. The combined effect of these is to reduce the overall heat carrying capacity of R407C and R290 thereby reducing the cooling capacities.
Cooling Capacity (kw) 4.5 4.3 4.1 3.9 3.7 3.5 3.3 3.1 2.9 2.7 2.5 0 2 4 6 8 10 12 14 16 18 20 R22 R290 R407C Degree of Superheat Fig 5. Cooling Capacity variations of R22, R407C, and R290 at various degrees of super heat. Figure 6 shows the Comparison of the power consumption by R22 and R407C, at lower degrees of superheat there is a marginal increase for R407C whereas it is slightly less at higher degrees of superheat. At all operating conditions R290 shows a reduction in power consumption by 14% compared to R22. 1.6 1.5 Power Input (kw) 1.4 1.3 1.2 1.1 R22 R290 R407C 1.0 0 2 4 6 8 10 12 14 16 18 20 Degree of Superheat Fig 6. Power input variations of R22, R407C, and R290 at various degrees of super heat. Figure 7 shows the variation of COP for R22, R290, R407C using EEV s as a function of different degree of super heat. The Coefficient of performance of R290 system is higher by 3.83%than that of R22 and 7.12% than that of R407C. COP is found to be the maximum with R290. Even though the cooling capacity and mass flow rate are found to be less for R290, a considerable reduction in compressor power, effects in improved COP values for the entire range of superheat.
3.2 3.0 COP 2.8 2.6 2.4 2.2 R22 R290 R407C 2.0 0 2 4 6 8 10 12 14 16 18 20 Degree of Superheat Fig 7 COP variations for R22, R407C, and R290 at various degrees of super heat. 5. Conclusions From the experimental study to evaluate the influence of electronic expansion valve on one TR capacity window air conditioner with refrigerants R22, R407C and R290, the following conclusions are drawn. Experimental results on R22, R407C and R290 produce results in favour of the last two refrigerants and electronic expansion valve as the best expansion device. It is observed that the flow rate of refrigerant and cooling capacity for R407C and R290 are lesser than R22 when electronic expansion valve is used in the system. The system using the refrigerant R290 with electronic expansion valve gives maximum COP due to lesser power consumption than that of R22 and R407C. Considering the Global warming and Ozone depletion, R407C and R290 can be used in place of R22. R290 is a better choice in terms of energy efficiency and ozone friendliness. But higher inflammability is a limitation for it. However detailed experimental study is needed on designing the leak proof system when it is used in the large Air conditioning systems 6. Acknowledgement The authors gratefully acknowledge the financial support provided by the World Bank, Government of India and State Government of Tamil Nadu through the Technical Education Quality Improvement Programme (TEQIP) for the establishment of experimental facility at Government College of Engineering, Salem, Tamil Nadu, India. 7. References [1] Lazzarin.R, Noro.M, (2008): Experimental Comparison of Electronic and Thermostatic Expansion Valves Performances in an Air Conditioning Plant. International Journal of Refrigeration 31, 113-118. [2] Chasik Park, Honghyun Cho, Yontaek Lee, Yongchan Kim (2007): Mass flow Characteristics and Empirical Modeling of R22 and R410A flowing through Electronic Expansion Valves, International journal of Refrigeration 30, 1401-1407. [3] Ciro Aprea, Rita Mastrullo (2002): Experimental Evaluation of Electronic and Thermostatic Expansion Valves Performances using R22 and R407C, Applied Thermal Engineering 22, 205-218. [4] Ma Shanwei, Zhang Chuan, Chen Jiangping, Chen Zhiujiu (2005): Experimental research on Refrigerant Mass flow coefficient of electronic expansion valve, Applied Thermal Engineering 25, 2351-2366 [5] Jinghui Liu, Jiangping Chen, Zhijiu Chen (2008): Investigation of Chocking Flow Characteristics in Electronic Expansion Valves. International Journal of Thermal Sciences 47, 648-658. [6] Xue Zhifang, Shi Lin, Ou Hongfei (2008): Refrigerant Flow Characteristics of Electronic Expansion Valve based on the Thermodynamic Analysis and Experiment, Applied Thermal Engineering 28, 238-243. [7] Bureau of Indian Standards. Room Air conditioners specification, part I: Unitary Air conditioners, BIS 1391, New Delhi, India 1992. [8] Ciro Apera, Rita Mastrullo (2002): An Experimental Evaluation of the Vapour Compression Plant Performances in presence of R407C leaks using an electronic expansion valve, Applied Thermal Engineering 22, pp. 161-171.