Factors affecting the energy-saving rate in the energy-saving renovation of circulating water pumps

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Factors affecting the energy-saving rate in the energy-saving renovation of circulating water pumps. Circulating water pumps are widely used in industries such as petroleum, chemicals, metallurgy, pharmaceuticals, and power generation. These pumps generally have high flow rates and high power levels, and they operate continuously for 24 hours, resulting in high electricity consumption; as a result, companies incur significant electricity costs. Carrying out energy-saving upgrades to the circulating water pump system brings direct economic benefits to enterprises. Therefore, many water pump users now place great emphasis on the energy-saving upgrades of water pumps. Companies specializing in such energy-saving upgrade technologies have emerged as a result, providing necessary services and contributions to businesses and society. When looking at the cases presented by various energy-saving companies, it can be seen that the energy savings rate is usually quite high; 30% is a common figure, and in some cases it even exceeds 50%. Such marketing has led some water pump users to believe that by using the technology provided by energy-saving companies, it is possible to achieve an energy savings rate of around 20–30% in any situation. Therefore, high expectations regarding the energy savings rate are actually a misconception. How large is the potential for energy savings in the energy-efficient renovation of circulating water pumps, and what factors influence the extent of these energy savings? Now let’s discuss this topic: For a water pump system to operate efficiently, it must meet the following three conditions simultaneously: (1) The rated efficiency of the water pump must be high. This depends first on the design level, and second on the manufacturing precision and quality ； (2) The water pump should operate at its efficient point: It should be noted that the efficiency of the same water pump varies at different flow rates; the relationship between pump efficiency and flow rate is a curve that slopes upward. Generally, the highest efficiency is achieved near the rated flow rate, while the efficiency decreases if the flow rate is lower or higher than this value. If the operating conditions deviate too much from the rated conditions, even if the pump has high rated efficiency, its actual operating efficiency will still be low. Going a step further, for high efficiency it is also necessary to consider the load rate of the motor (prime mover) as well as its efficient operating range; in other words, the overall efficiency of the entire water pump system should be at an optimal level. (3) The losses in the piping system (including the equipment) should be kept as low as possible: on the one hand, the design and layout of the piping network and equipment need to be reasonable; on the other hand, the parameters of the water pumps must match the resistance characteristics of the piping network, in order to minimize throttling losses. The extent to which energy can be saved in water pumps depends on the degree of deviation of the above three factors from their optimal values. The lower the rated efficiency of the water pump, the greater the deviation from the rated flow rate, and the larger the losses in the additional piping (including equipment), the lower the overall efficiency of the water pump system. Consequently, there is more room for energy savings, and the energy savings rate is higher. Conversely, if all of the above three conditions are met, there is essentially no room for energy savings in the water pump, and it has no value for modification. Many years ago, when energy conservation was not yet a matter of widespread concern, water pumps had relatively low rated efficiencies. Design agencies also failed to conduct thorough calculations regarding energy conservation in their engineering designs, which led to situations where the actual flow rate deviated significantly from the rated flow rate and there were substantial additional losses in the piping system. As a result, the overall efficiency of the water pump system was low, meaning there was considerable potential for energy savings; it was common for energy savings rates to reach 20–30%. A production load that is much lower than the designed load for various reasons will also increase the deviation and affect the energy-saving rate. In recent years, pump users have placed increasing emphasis on energy conservation; when purchasing pumps, high efficiency and energy savings are considered important criteria. This has driven pump manufacturers to continuously improve quality and innovate in order to enhance their competitiveness, resulting in an overall increase in the rated efficiency of pumps ； Users also explicitly require that energy conservation and reduced consumption be taken into account in engineering design; therefore, design firms must also pay attention to energy efficiency in their designs to achieve more rational designs ； Users should also pay attention to the proper configuration of water pumps and their economical operation. As a result of the combined effect of these factors, the overall efficiency of the newly installed water pump system has improved significantly compared to before; the deviation from the optimal parameters is becoming smaller and smaller. Therefore, there is less room for energy savings in this pump system now, and an energy savings rate of 15% should be considered quite good. Recently, the highest energy-saving rate achieved by our company was 31%, while the lowest was only 5%. So, is there still any value in making improvements when the energy-saving rate is only 5%? Let’s do the math: Assuming a pump with an actual load of 200 KW and an energy-saving rate of 5%, it can save 10 kWh of electricity per hour. At a cost of 0.8 yuan per kWh, this translates to savings of over 70,000 yuan per year. So, how much does it cost to pay the energy-saving company for its services? Different companies may vary; taking our company as an example, our fees generally do not exceed the amount saved in electricity costs over 10 months, with the total fee amounting to less than 60,000 yuan. Compared to the electricity costs before the renovation, customers not only face no additional burden that year, but their total expenses actually decrease as well. The investment is recouped in the same year, and energy savings along with improved efficiency are achieved right away. From now on, we will charge no fees, and users can earn over 70,000 yuan in energy savings each year. It is evident that the economic benefits for users are very high, so it is definitely worth carrying out the modifications; the 5% energy savings rate cannot be ignored. Don’t just focus on an energy savings rate of 20–30%, as that is impossible for many pump systems. As for some energy-saving companies claiming an energy-saving rate of over 50%, I would prefer to believe it to be true, but it is certainly a special case – such as using pumps designed for open-loop systems in a central air conditioning closed-loop system. As for the many claims that an energy-saving rate of 30% can be achieved, they are probably based on selected successful cases; this is considered a normal phenomenon, and I think people can understand it. This article aims to give readers a general understanding of the factors that influence the potential for energy savings in water pumps, so as to enable them to have a reasonable expectation of the degree of energy savings. For water pumps with high power consumption, even a 5% energy savings rate results in significant cost savings on electricity bills, making such upgrades highly worthwhile. It is also pointed out that not all water pumps have room for energy savings; some pumps are not worth modifying. If there are any mistakes, please feel free to offer your criticism and suggestions.