Research on the Application of Variable Frequency Water Pump in Energy Conservation of Aquarium Life Support System

The maintenance system of the aquarium is the most energy-efficient part of the aquarium, and using variable frequency water pumps to save energy is a reliable and efficient way. By combining with specific examples, the performance of variable frequency water pumps in energy conservation of life sustaining systems was calculated. A special case was selected to analyze the energy consumption of variable frequency water pumps, and the relationship curve between the flow ratio and energy consumption ratio of variable frequency water pumps during operation was given. After economic analysis, the economic benefits of using variable frequency water pumps in the maintenance pipeline system have been determined. The analysis results indicate that the frequency conversion water pump has a significant energy-saving effect on the use of the livelihood pipeline system, and the initial investment can be recovered. Can provide reference for energy-saving solutions for the operation and maintenance of the aquarium

The earliest aquarium in the world was built by France in 1789, and later established by Britain in London in 1853. Under the leadership of Britain and France, countries such as the United States, Germany, and Italy have also established aquariums. China began establishing aquariums in 1932, and the first aquarium established in China was the Qingdao Aquarium. In the 21st century, China's economy has developed rapidly, and tourism has become one of the pillar industries of the national economy. As an important component of the tourism industry, the impact of ocean museums on the national economy is also increasing. At the same time, the construction scale and quantity of ocean museums are also increasing. Our country's aquariums are mainly divided into freshwater aquariums, seawater aquariums, and marine and freshwater aquariums, with seawater aquariums and marine and freshwater aquariums being the majority. For example, Dalian Shengya Ocean World, Beijing Ocean Museum, Qingdao Ocean Museum, etc. At present, with the improvement of China's comprehensive national strength, the construction of oceanariums in China is becoming increasingly strong. In 2005, there were only 43 ocean museums in China, mainly located in coastal areas. Utilizing their geographical location can effectively reduce costs. As of 2017, after more than a decade of development, there are now more than 160 aquariums across the country. The construction of ocean pavilions is becoming increasingly popular, which has led to an increasing emphasis on energy consumption in ocean pavilions. The aquarium is a very energy-efficient building, and compared to ordinary buildings, the energy consumption of the system that maintains a suitable environment for humans and animals in the aquarium is enormous. Especially the air conditioning system and life support system. The life support system of the aquarium is the most energy consuming in its operation and maintenance. A sound and complete life support system is crucial to the survival of the entire aquarium. The life support system of the aquarium is a water circulation system composed of various water treatment systems, and the water pump, as the equipment driving the entire system, consumes a huge amount of energy. Nowadays, the power device of the life support system in the aquarium generally uses a power frequency water pump, and the flow regulation of the power frequency water pump is achieved through the opening of the valve. Therefore, a large amount of water head is consumed on the valve, which undoubtedly increases the energy consumption of the entire life support system. But with the development of variable frequency technology, such problems can be solved through variable frequency water pumps. Variable frequency water pumps can control their own speed and provide flow according to demand, thereby avoiding the problem of excess head needing to be consumed by valves. Although initial investment may increase, the resulting price difference will be recovered in a short period of time. The principle of a variable frequency water pump is that a frequency converter is installed in the variable frequency water pump, which controls the speed of the water pump through the frequency converter, thereby achieving the goal of controlling flow and head. Figure 1 shows the pump characteristic curve and pipeline characteristic curve of the variable frequency water pump. When the speed of the water pump decreases, the pipeline characteristic curve does not change, but the water pump characteristic curve changes from curve 1 to curve 2. The intersection point between the water pump characteristic curve and the pipeline characteristic curve (the working point of the water pump) changes from point A to point B, the head decreases from HA to HB, and the flow rate decreases from QA to QB [4]. In theory, there is a relationship between flow rate Q, head H, power N and pump speed: QA QB=N1 N2, HA HB=(N1 N2) 2, NA NB=(N1 N2) 3 (1). Therefore, it can be seen that when the pump speed decreases, both the head and flow rate of the pump decrease. From equation (1), it can be seen that the change in flow rate is directly proportional to the first power of speed, the change in head is directly proportional to the second power of speed, and the change in power is directly proportional to the third power of speed [5,6]. Therefore, when using a variable frequency water pump, reducing the speed of the water pump will result in a decrease in the head, flow rate, and energy consumption of the water pump, and the proportion of the decrease in energy consumption of the water pump will be greater [7]. In addition, although the characteristic curve of the water pump has changed, the head change caused by frequency conversion is the square ratio of the speed, and the required head H=SQ2 for the pipeline is directly proportional to the quadratic power of the flow rate, that is, directly proportional to the quadratic power of the speed. Therefore, when the water pump is subjected to variable frequency speed regulation, the variation amplitude of the head of the water pump and the required head of the pipeline is consistent [8]. Therefore, in the subsequent selection of variable frequency water pumps, the selection of variable frequency water pumps can be based on the power frequency water pump selection scheme. Figure 1 Head characteristic curve and pipeline characteristic curve of variable frequency water pump 2 Energy consumption analysis of marine life support system The marine life support system is a multidisciplinary integrated technology that includes multiple disciplines such as marine biology, chemistry, physics, materials science, etc. It is the foundation of the daily operation of the marine life support system. Its main function is to provide the living environment needed by marine organisms based on their living habits. The life support system of the aquarium mainly includes six parts: gravity filter, cold and heat exchanger, pressure filter, drip filter, ozone treatment system, and protein separation system. The various systems are connected by pipelines to form a complete life support system. In terms of power device selection, except for the protein separation system which uses a Venturi water pump, the other systems generally use a power frequency water pump, and the life support system of the aquarium is generally in uninterrupted operation. Therefore, the life support system is one of the main energy consumption systems of the aquarium, and the annual energy consumption of the life support system generally accounts for about 67% of the total energy consumption of the aquarium. In the actual operation of life support systems, not every system needs to operate continuously at full load. For example, the water pump on the seawater sand tank can use a variable frequency water pump, while the general aquarium will use a power frequency water pump. After feeding marine organisms, the water pump needs to run at full load to filter and remove them. But during other time periods, it is only necessary to maintain the normal demand of marine organisms, which will significantly reduce the energy consumption of water pumps. 2.1 Energy saving performance of variable frequency water pumps in the maintenance system of the aquarium. Taking Sanya Underwater World as an example, the entire maintenance system of the aquarium is equipped with 32 water pumps, among which B1-B20 is a circulating pump, QB1-QB2 is a submersible pump, and SLB1-SLB10 is a Venturi water pump. The total annual energy consumption of all water pumps is 201 978 3 × 104 KW • H, with an annual energy consumption of 201 for the circulating water pump 968 × 104 KW • H. More than 99% of the energy consumption of all water pumps. In order to ensure the normal operation of the entire life support system, submersible pumps and Venturi pumps must use power frequency pumps. However, the energy consumption of submersible pumps and Venturi pumps is very low, less than 1% of the total energy consumption of pumps. Most of the remaining circulating pumps can be replaced by variable frequency water pumps. Using B1-B13 for energy conservation analysis, Figure 2 is a schematic diagram of the maintenance system at the location of B1-B13. These 13 water pumps can be divided into 5 major areas: Zone ① (B1, B2), Zone ② (B3, B4), Zone ③ (B5, B6, B7), Zone ④ (B8, B9, B10, B11), and Zone ⑤ (B12, B13). Replace the power frequency water pumps in 5 areas with variable frequency water pumps and conduct energy consumption analysis

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Taking the third area as an example, there are three water pumps installed in this area. Currently, three power frequency water pumps are used, with a flow rate of 150 T/H and a rated power of 1.16 million cubic meters. Data Zhang Dianguang et al.: Research on the application of variable frequency water pumps in energy-saving of the life support system of the aquarium, 11 KW. It can be estimated that the annual power consumption of these three water pumps is: number of pumps x rated power x operating time x annual operating days=3 x 11 x 24 x 365=289 08 MWH. Replace these three water pumps with variable frequency water pumps of the same flow rate and rated power. Below is the theoretical calculation of energy consumption for variable frequency water pumps. The energy consumption of the variable frequency water pump is calculated using formula (2): N= Γ SQ3 Η (2) In the formula: N is the input power, KW; Γ Is the weight of seawater, KN/M3; S is the total impedance, (KG • M) -1; Q is the flow rate of the water pump, M3/S; Η To improve the overall efficiency of variable frequency water pumps. Η The overall efficiency of a variable frequency water pump depends on the relative speed percentage of the pump motor or the relative flow rate change ratio (load ratio of the variable frequency water pump) [9]. According to Table 1, it can be obtained that Η The value of. When the variable frequency water pump is running at full load Η＝ 707 9, the current power should be the rated power of 11 KW, and the current flow rate is 150 T/H. Therefore, it is sought that Γ• S=107 613 3. This value is a constant and depends on the characteristics of the pipeline, and does not change with changes in rotational speed. Therefore, it can be concluded that the power consumption of the variable frequency water pump in the third region under different flow loads is N=107 613 3 x Q3 Η (3) Table 1 Variable frequency water pump under partial load Η Value [9] Q/Q0 10 20 30 40 50 60 70 80 90 100 Η 0. 275 0 442 0 542 0 601 0 638 0 660 0 676 0 687 0 Based on formula (3) and the data provided in Table 1, the relationship between the energy consumption and flow rate of the variable frequency water pump in Region ③ is calculated as shown in Table 2 and Figure 3. Table 2 Relationship between Flow Load and Energy Consumption of Variable Frequency Water Pump Μ Q/(T/H) (Q/Q0)/% N/KW 0 275 215 10 0 028 287 0 442 4 30 20 0 140 769 0 541 5 45 30 0 388 148 0 601 0 60 40 0 828 968 0 637 5 75 50 1 526 378 0 660 4 90 60 2 546 12 0 675 5 105 70 3 952 765 0 686 6 120 80 5 804 949 0 697 1135 90 8 140 755 0 707 9 150 100 10 The relationship between the load flow rate and energy consumption of the variable frequency water pump in the third area of Figure 3 of 996 65 can be concluded from Figure 3 that under full load operation, the energy consumption per unit time (H) of each variable frequency water pump is 11 KW. When working with frequency conversion, when the flow rate is 90%, the energy consumption is 8 14 KW, energy-saving by 26%; When the flow rate is 80%, the energy consumption is 5 804 KW, energy-saving by 47%. In actual operation, when the frequency converter is installed on the water pump, the current of the motor will increase by about 10%, and the heating energy consumption of the motor will increase by 21% [10,11]. So in actual operation of variable frequency regulation water pumps, when the load flow rate is adjusted to 80%, the energy-saving effect is 26%. The relationship between energy consumption and load flow rate during actual operation is shown in Figure 3, and the relationship between load flow rate and energy-saving ratio is shown in Figure 4. In the third area, there are a total of three water pumps. During the day, the metabolism of animals is intense, and the variable frequency water pump operates at full load. At night, the animals enter a sleep state, and the metabolism is slow. At this time, the waste generated by metabolism is less, and the water quality is better than during the day. The life support system does not need to operate at full load. When the animals enter a sleep state, the load of the water pump is automatically adjusted to 80% of the full load (running for 8 hours). According to this adjustment plan, it can be estimated that the annual energy savings of the water pump in the third region are 3 x 11 KW x 8 x 365 x 26%=25 053 6 MWH. Estimate energy consumption for the remaining four regions and plot the energy consumption curve on the same chart for observation, as shown in Figure 5.

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2.2 Economic Analysis Based on the comprehensive energy consumption data of the water pump in the livelihood system, the energy-saving effect of using variable frequency water pumps in each region is significant. Taking the variable frequency regulation set to 80% for 8 hours of operation as an example, the total annual energy savings in the first and second regions are about 56% 180 8 MWH; The third region can save about 25% of energy annually 053 6 MWH; Data of 1.17 million cubic meters, Zhang Dianguang, et al.: Research on the Application of Variable Frequency Water Pumps in Energy Conservation of Aquarium Life Support Systems. Region 4 can save about 45% of energy annually 552 MWH; The fifth region can save 11% energy throughout the year 388 MWH. If frequency converters are installed on the water pumps in all 5 areas, the total energy savings under this scheme will be 138174 4 KW • H, according to the Hainan Province's Qiong Price List, the industrial electricity price per kilowatt hour is 0 61 yuan, a total of 84286 yuan can be saved 38 yuan. According to the market price of frequency converters: 7 A 5 KW frequency converter is priced at around 4000 yuan, an 11 KW frequency converter is priced at around 7000 yuan, a 15 KW frequency converter is priced at around 12000 yuan, and 18 The price of a 5 KW frequency converter is around 14000 yuan. It will cost approximately 133000 yuan to equip the water pumps in all 5 areas with frequency converters. Therefore, using this energy-saving method to operate the livelihood system only requires 1 The investment in purchasing frequency converters can be recovered in 57 years. The above only analyzed the energy consumption and economic performance when the load flow is 80%. When the load flow rate decreases to 60%, the energy-saving effect will further increase. Figure 5 shows the relationship between load flow rate and energy consumption of variable frequency water pumps in different regions. Conclusion 3: Although using variable frequency water pumps will increase initial investment, from the perspective of energy-saving effects, one and a half years can completely fill the price difference. At the same time, the use of variable frequency water pumps also makes energy conservation more flexible, and the organisms inside the aquarium are not unchanged. Usually, aquariums introduce new animals for breeding and performances. The food intake, activity level, and metabolism of each animal are different. By using a variable frequency water pump to drive, the flow rate of the variable frequency water pump can be adjusted according to the living habits of different organisms. It is a targeted energy-saving method. This article only studied the relationship between energy-saving effect and load flow rate. When using variable frequency water pumps in livelihood pipelines, the load flow rate of the variable frequency water pump must be adjusted according to the water quality. The energy-saving effect is directly related to the water quality, and the relevant conclusions need further research.