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Figure 1 Statistics of condenser types in 62 systems in the United States and Canada. Selection and energy saving of evaporative condensers for refrigeration* Zhang Jianyi1, Mi Wentao1,2 (1. School of Mechanical Engineering, Jimei University, Xiamen 361021； 2. School of Food, Shanghai Fisheries University, Shanghai 200090) Abstract: This article explains the common methods and general steps for selecting evaporative condensers. Based on the empirical data recommended at home and abroad, it is calculated that the power consumption per unit heat discharge of the evaporative condenser is approximately 21.86 W/kW and 11.12 W/kW respectively. The energy consumption of the former is approximately twice that of the latter. At the same time, this article proposes an energy consumption accounting formula for evaporative condenser selection, and analyzes the application of this formula through examples. The study found that the operating energy consumption of different brands of evaporative condensers varies greatly. The energy consumption calculation formula proposed in this article can easily compare the operating energy consumption of evaporative condensers of different brands. The one with the smallest power consumption Φ value per unit of heat discharge is the one with the smallest operating energy consumption. Keywords: evaporative condenser ； Selection ； Energy consumption ； FormulaSelection of Evaporative Condensers in Refrigerating Plants Zhang Jianyi1, Mi Wentao1,2 (1.College of Mechanical Engineering, Jimei University, Xiamen 361021, China; 2.College of Food Science, Shanghai Fisheries University, Shanghai 200090, China) Abstract: Traditional methods and steps used in the selection of evaporative condensers are introduced. Calculation results based on experimental data from Chinese and US Standards show a great difference in energy consumption. The theoretical energy consumption of evaporative condensers is approx. * mately 21.86 W/kW for the former, but 11.12 W/kW for the latter. A formula to audit the energy consumption of evaporative condensers is proposed, and the application of the formula is tested to practical products. The results indicate that the energy consumptions of different brands of evaporative condensers are quite different. The proposed formula allows operating energy consumption of evaporative condensers to be compared, with the minimum energy indicated when the value of Φ in the formula is a minimum. Keywords: Evaporative condenser; selection; energy consumption; formula 1 Introduction The evaporative condenser is a highly efficient and energy-saving heat exchange equipment. Due to the advantages of high heat transfer efficiency, compact structure and easy installation, it has been used in the United States and other countries. * * Be widely used. According to the author's survey of 62 public cold storage refrigeration devices in the United States and Canada, the application of evaporative condensers accounts for about 81%, see Figure 1. Generally, the temperature difference between the inlet and outlet water of a vertical water-cooled condenser is 2 to 3°C, and that of a horizontal water-cooled condenser is 4 to 6°C. Theoretically, in a water-cooled condenser, 1kg of cooling water can take away 8.37~25.12kJ of heat, and the latent heat of vaporization of 1kg of water under normal pressure of 35°C is 2418kJ/kg. Therefore, the theoretical water consumption required by the evaporative condenser is only 0.3% to 1% of that of the water-cooled condenser. At the same time, it eliminates the sensible heat transfer stage of the cooling water in the condenser, making the condensation temperature closer to the wet bulb temperature of the air. Its condensation temperature can be 3 to 5°C lower than the cooling tower water-cooled condenser system, and 8 to 11°C lower than the air-cooled condenser. This * * This greatly reduces compressor power consumption. At the same time, due to the reduction in circulating water volume, the power consumption of the water pump is also significantly reduced. The literature points out that the fan power consumption of evaporative condensers is similar to that of water-cooled cooling towers. Due to the reduction of the head and flow of the water pump, the power of the pump * Funded by the Key Science and Technology Project of Fujian Provincial Department of Science and Technology (2006I0022) ； Funded by Jimei University Scientific Research Fund 1 2 3 8 58 0 10 20 30 40 50 60 Plate vertical horizontal air-cooled evaporative power consumption is about one-quarter of the system combining a cooling tower and a shell-and-tube condenser. The literature points out that evaporative condensers can save more than 80% of electricity compared to vertical water-cooled condensers, and about 10% compared to horizontal water-cooled condensers. Therefore, evaporative condensers are generally favored by industrial refrigeration users at home and abroad. The author found that different brands of evaporative condensers at home and abroad are designed based on different standards, and the energy consumption of the condenser system varies greatly. This article first explains the selection method of evaporative condenser, and then calculates the theoretical energy consumption of evaporative condenser based on different domestic and foreign empirical data. Finally, through the motor configuration of typical evaporative condenser products, the energy consumption calculation formula of the evaporative condenser is summarized. 2. Methods for selecting evaporative condensers. Currently, there are two main methods for selecting evaporative condensers.: One is to select based on the heat load of the condenser. ； The second is to choose based on the cooling capacity of the refrigeration system. The currently commonly used method is mainly based on the heat load selection of the condenser. The steps are as follows:: a) Determine the total heat dissipation required by the system. The total heat dissipation is the sum of the compressor cooling capacity and the motor power consumption. ； b) Determine design conditions, condensing temperature and wet bulb temperature ； c) Find the load correction coefficient based on the heat rejection coefficient chart (determined by condensing temperature and wet bulb temperature) ； d) Multiply the total heat rejection of the system by the heat rejection coefficient to determine the corrected heat rejection load and select the appropriate model. ； This selection method is only applicable to refrigeration systems composed of piston or screw refrigeration compressors. If the cooling water of the oil cooler of the screw refrigeration compressor is independent, the total heat rejection above should be subtracted from the heat of the oil cooler before selecting the type. For example, it is known that the refrigerant is R717, the condensation temperature is 35°C, the wet bulb temperature is 25°C, and the heat rejection is 586kW. Select the condenser model according to Table 1 and Figure 2. From Figure 2, it can be seen that the heat removal coefficient is 1.3 when the condensation temperature is 35°C and the wet bulb temperature is 20°C. Therefore, the corrected heat exhaust load is 586×1.3=761.8 kW. According to Table 1, the heat dissipation of model C is too small. Therefore, the evaporative condenser model D is selected. Table 1 A certain brand of evaporative condenser model and heat rejection model ABCDEFG Heat rejection (kW) 603 646 711 797 883 991 1077 Heat rejection coefficient Wet bulb temperature (℃) 10 0 3.0 2.0 1.0 15 20 25 30 30 35 38 Condensation temperature Figure 2 The heat dissipation coefficient of a certain brand of evaporative condenser (R717) 3 Theoretical energy consumption calculation of evaporative condenser The energy consumption of the evaporative condenser system is mainly composed of a fan and a circulating water pump. The fan power can be calculated by the following formula: Nf＝Pf·LD (1) where: Nf Fan power per unit condensing load (W/kW) Pf Fan air pressure (Pa) LD Air volume corresponding to unit condensing load m3/(s ·kW) Water pump power can be calculated by the following formula: Ns＝9.8 Gw·Hz (2) where: Ns Water pump power per unit condensing load (W/kW) Gw Water flow rate corresponding to unit condensing load (kg/s·kW) Hz Water pump head (m) The literature recommends the empirical data of evaporative condensers in the United States, and the domestic machinery industry standard JB/T7658.5-95 Evaporative condensers for ammonia refrigeration devices also recommends empirical data. A comparison between the two is shown in Table 2. Table 2 Source of empirical data for domestic and foreign evaporative condensers Heat load q (kW/㎡) Circulating water volume Gw Air volume LD American Industrial Refrigeration Handbook 4 0.018 108 JB/T7658.5-95 ≥1.74 0.032 220 In the calculation, Pf is selected as the middle value of 312 Pa. Considering the actual installation situation, the head of the water pump is set to 10m. According to formulas (1) and (2), the domestic evaporative condenser Nf=18.72 W/kW, Ns=3.14W/kW ； American evaporative condenser Nf = 9.36 W/kW, Ns = 1.76W/kW. Therefore, calculated based on domestic and foreign recommended empirical data, the energy consumption of the evaporative condenser is approximately 21.86 W/kW and 11.12 W/kW respectively, with the latter energy consumption approximately 51% of the former. It can be seen from the above analysis: (1)． When choosing an evaporative condenser, users should pay attention to comparing the standards on which it is designed. According to the standard, the greater the heat load per unit area, the better the heat transfer performance of the condenser. ； The smaller the circulating water volume and air volume, the lower the energy consumption. (2)． The domestic standards for evaporative condensers have low thresholds, poor product performance, and high energy consumption. However, it should be pointed out that in recent years, many domestic manufacturers of evaporative condensers have formulated higher corporate standards in order to improve the competitiveness of their products. For example, the corporate standard of Shanghai Shangfeng Refrigeration Equipment Co., Ltd. stipulates that the heat load of the condenser is 4 kW/㎡, but the actual product is as high as 5.41 kW/㎡. 4 Energy consumption accounting formula and application of evaporative condenser 4.1 Proposal of energy consumption accounting formula After comparative analysis of the technical parameters of typical products, the author found that different evaporative condensers have obvious differences in their energy consumption per unit of heat rejection. Obviously, the energy consumption of the evaporative condenser consists of water pumps and fans. The technical manual of the product contains the rated power of the water pump and fan and the heat rejection of the condenser. Based on this, the calculation formula of the power consumption Φ per unit of heat rejection can be summarized. PPQ Φ = Σ Σ Σ water pump fan + (3) where: ΣP Total rated power of water pump condenser water pump (kW) ΣP Total rated power of fan condenser fan (kW) ΣQ Discharge heat of condenser (kW) According to formula (3), the user can use the Φ value to compare the power consumption per unit of heat dissipation of different brands based on the required condensation load, that is, the brand with the smallest Φ value has the smallest operating energy consumption. In the following, evaporative condenser products are selected for example calculation based on the heat rejection of 345 kW, 1200 kW and 2010 kW respectively. 4.2 Application of energy consumption accounting formula At present, the typical domestic evaporative condenser products mainly include the Sino-US joint venture Shanghai EVAPCO ATC series, the Sino-US joint venture Dalian Bingshan Baltimore CXV series, the domestic Yantai Binglun ZNX series and Shanghai Baofeng SPL type, etc. When users choose evaporative condensers of different brands, they must not only clarify the standards on which the product is designed, but also conduct detailed energy consumption calculations. The following selects three typical brands of evaporative condensers A, B, and C from the above manufacturers, and uses formula (3) to calculate energy consumption. According to their respective technical manuals, the equipment configurations of three different brands of evaporative condensers with different heat rejection capacities are known, as shown in Table 3. Table 3 Three different brands of evaporative condensers with different heat dissipation equipment configurations, fan circulating water pump, heat dissipation size, brand rated power (kW) air volume (m3/s) rated power (kW) flow (L/s) heat dissipation (kW) Evaporative type A 4.0 5.7 0.55 8.5 345 Small evaporative type B 5.5 14.3 1.1 12 345 Evaporative type C 1.3 5.5 1.2 12.5 350 Evaporative type A 7.5 20.3 2.2 31.6 1198 Medium evaporative type B 18.5 36.5 4.0 38.0 1202 Evaporative type C 3.4×2 18.3 5.8 40.0 1200 Evaporative type A 5.5×2 33.3 4.0 50.5 2012 Large evaporative condenser B 22-11 66.7 4.0 38.0 2016 Evaporative condenser C 6.0×2 30.6 7.9 65.0 2000 From formula (3), it can be seen that the total power consumption of the fan, water pump and condenser system per unit of heat rejection of three brands of evaporative condensers with different heat rejections is shown in Table 4. Table 4. Power consumption per unit of discharge heat of evaporative condensers of three different brands with different discharge heat amounts. Small, medium and large brands ABCABCABC Fan power consumption Φ 1 (W/kW) 11.60 15.94 3.71 6.26 15.39 5.67 5.47 16.37 6.00 Water pump power consumption Φ 2 (W/kW) 1.59 3.19 3.43 1.84 3.33 4.83 1.99 1.98 3.95 Total power consumption Φ (W/kW) 13.19 19.13 7.14 8.10 18.72 10.50 7.46 18.35 9.95 Φ A,B,C/ ( Φ A,B,C)min 1.85 2.68 1 1 2.31 1.30 1 2.46 1.33 Assume that under the same heat rejection, the product prices of evaporative condensers of different brands are basically the same. It can be seen from Table 4 that if you want to choose a small evaporative condenser with a heat rejection of about 345 kW, you should choose evaporative type C ； The power consumption per unit heat discharge of evaporative types A and B is approximately 1.85 times and 2.68 times that of evaporative type C. If you want to choose a medium-sized evaporative condenser with a heat rejection of about 1200 kW, you should choose evaporative type A ； The power consumption per unit heat discharge of evaporative types B and C is approximately 2.31 times and 1.30 times that of evaporative type A. If you want to choose a large evaporative condenser with a heat rejection capacity of about 2010 kW, you should choose evaporative type A ； The power consumption per unit heat discharge of evaporative types B and C is approximately 2.46 times and 1.33 times that of evaporative type A. The above calculation analysis shows that the operating energy consumption of evaporative condensers of different brands varies greatly, up to 2.68 times. According to formula (3), the energy consumption of evaporative condensers of different brands can be easily calculated to ensure that the selected evaporative condenser is the most energy-saving. In actual products, there is a certain gap in the prices of evaporative condensers of different brands at home and abroad, and users often pay more attention to one-time investment. Therefore, special attention must be paid when selecting models. You cannot only consider one investment. You should attach great importance to the difference in operating energy consumption and conduct a comprehensive analysis and comparison based on operating energy consumption costs. 4.3 Discussion on the energy consumption of fans and water pumps of evaporative condensers of different brands. From Table 4, it can be concluded that the average power consumption of fans and water pumps of different brands of evaporative condensers with different heat dissipations is about 9.60 W/kW and 2.68 W/kW respectively. The average power consumption of water pumps is about 28% of the fans. It can be seen from the literature that the relationship between the heat transfer coefficient K of the condenser and the spray water volume and air flow rate is as follows: K=cG0.48L0.22 (4) In the formula, K is the heat transfer coefficient of the condenser ； c is a constant ； L is the amount of spray water ； G is air flow. It can be seen from formula (4) that since the index of air flow rate G is approximately twice the index of spray water amount L, in order to improve the heat transfer coefficient of the evaporative condenser, it is generally necessary to increase the air volume of the fan instead of increasing the flow rate of the water pump. Therefore, the energy consumption of the fan in the evaporative condenser dominates. It should be pointed out that one of the main reasons why the energy consumption of water pumps and fans of evaporative condensers of different brands is different is that the energy consumption of evaporative condensers is closely related to the form of spray water, the arrangement form of the serpentine coil and its cross-sectional form. Different product designs will result in different energy consumption of water pumps and fans. 5 Conclusion (1). When choosing an evaporative condenser, users should pay attention to comparing the standards on which it is designed. According to the standard, the greater the heat load per unit area, the better the heat transfer performance of the condenser. ； The smaller the circulating water volume and air volume, the lower the energy consumption. (2)． In product selection, different brands of evaporative condensers are used, and the operating energy consumption varies greatly. For example, for a small evaporative condenser with a heat rejection of approximately 345 kW, the energy consumption per unit heat rejection of brand B is approximately 2.68 times that of brand C. ； For a large evaporative condenser with a heat rejection of approximately 2010 kW, the energy consumption per unit heat rejection of Brand B is approximately 2.46 times that of Brand A. Therefore, when selecting, you should conduct energy consumption calculations on evaporative condensers of different brands in order to find the most energy-saving product. (3)． The energy consumption accounting formula (3) proposed in this article can easily compare the operating energy consumption of evaporative condensers of different brands. The brand with the smallest power consumption per unit of heat dissipation is the brand with the smallest operating energy consumption. References J. Zhang, EA Groll. Survey of the Design of Refrigeration Plants for Public Refrigerated Warehouses. ASHRAE Transactions, 2005, 111:327-332. Zhang Jianyi, Li Li. Energy-saving principles and technologies for refrigeration and air-conditioning equipment. Machinery Industry Press, 2007. Zhuang Youming. Energy consumption comparison and economic analysis of evaporative condensers and water-cooled condensers. Refrigeration, 2001, 20(1): 65-69． Wilbert F. Stoecker. Industrial Refrigeration Handbook. New York: McGraw-Hill, 1998. Refrigeration Equipment Standardization Technical Committee of the Ministry of Machinery Industry. Refrigeration and air conditioning technical standards application manual. .Machinery Industry Press, 1997. About the author: Zhang Jianyi, male, born in 1953, professor/dean of Jimei University. Correspondence address: No. 9, Shigu Road, Jimei District, Xiamen, Fujian Province, School of Mechanical Engineering, Jimei University, Postal Code: 361021 Contact number/Fax: 0592-6183503, 13600932479 Email: jyzhang@jmu.edu.cn