Air conditioning temperature difference to explore economic research measures

According to the pump similarity theory, when two pumps deliver the same fluid and the speed is the same, p1p2=W1W22/3, Ns1Ns2=W1W23/5. When the pump flow is adjusted by changing the pump wheel diameter, the temperature difference is doubled and the water volume is reduced to the original. At 50%, according to the formula, the pump power will drop to Ns2=0.55/3Ns1=0.315Ns1, that is, the energy consumption of the cold water pump is reduced by 68.5%. Discuss the energy saving effect of the chilled water large temperature difference system. Similar to the aforementioned fan energy consumption analysis, this method of economic analysis is also problematic. When the air conditioning chilled water large temperature difference system is adopted, the pipe resistance characteristic curve is different from the conventional temperature difference water system due to the change of the water pipe size, so the pump power can no longer be calculated according to the formula. The pump shaft power should be calculated as follows: N=$pW1000@Gtf type N, pump shaft power; W, air conditioning chilled water volume, m3/s; $p, water system total pressure loss, Pa; Gtf, pump full pressure efficiency . The purpose of using large temperature difference technology is to reduce the energy consumption of the pump. The second is to reduce the investment in the pipeline system. However, from the previous analysis, it can be seen that the same pump speed changes, the water volume is reduced by half, and the energy consumption of the cold water pump is reduced by 87.5. When %, the pump head is only 1/4 of the original. At this time, D2=1.021D1, vw2=0.479vw1, that is to say, when the water volume is reduced by half, to obtain this energy saving effect, the pipe diameter is not reduced, but instead increase.

Keep the pump speed unchanged, change the water pump's wheel diameter to adjust the flow. When the chilled water volume is reduced by half and the chilled water pump energy consumption is reduced by 68.5%, the pump lift is only 63% of the original. At this time, D2=0.8448D1, vw2=0.7 Vw1, that is to say, when the water volume is reduced by half, to achieve this energy saving effect, the pipe diameter can only be reduced to 85%. Therefore, when conducting large-scale energy-saving analysis, not only should the operating costs be considered, but also the change in investment should be considered. In order to simplify the analysis, the following considerations for the influence of the head change on a straight pipe section without local resistance, the resistance of the new steel pipe along the equation can be expressed as p=7.D-1.167 where p, the unit resistance of the water pipe, m/m; Vw, average water velocity in the pipe, m/s; D, pipe inner diameter, mp=11.D-4.871 Since the hydraulic calculation of the current water system basically adopts the assumed speed method, the following discussion discusses the energy consumption of the pump when the water velocity in the pipe is constant. Variety. When the total efficiency of the pump is the same and the water velocity in the pipe is equal, according to the formula, it can be deduced: p1p2=W2W10.5835, N1N2=W2W10.4165. For the water system, when the water pipe arrangement, the water distribution and the water velocity in the pipe are equal, the pipe is partially The resistance is basically unchanged, the water temperature rises twice, that is, the water volume is reduced by half. When W2=0.5W1, p2=1.4985p1, D2=0.707D1, that is, the water pipe friction resistance increases by 50%, and the pump motor power is the original 75. %, the diameter of the water pipe is 70.7% of the original. It can be seen from the above analysis that for large temperature difference systems, when the water volume is reduced, it is not possible to calculate how much the pump energy consumption can be reduced by simple calculation, but the detailed analysis and calculation of the entire water system should be performed. At the same time, it must be noted that the air conditioning water system is also subject to many conditions.

When selecting a pump based on system water volume and water resistance, it is limited by the pump model and specifications. Take the 2813kW centrifugal chiller as an example. If the pipeline pump is used, when the chilled water volume is 484m3/h ($tw=5e), the optional head can only be 29 and 36m; when the unit has chilled water of 242m3/h ($tw=10e), the optional head is only 19, 25, 33, 35m. Due to the maximum water speed limit, the domestic HVAC design specification does not stipulate the water flow rate in the pipe. The current value is taken from relevant foreign regulations, such as the recommended value of the early US ASHRAE manual, or the recommended value of the US Carrier; It is the recommended value of National Standard 5 Outdoor Water Supply Design Specification 6 (GBJ13-86). The water velocity in domestic air-conditioning design pipes is generally 12m/s, and the internationally allowed pipe flow rate is much higher than that in China. This is because: due to the development of computing technology, the optimal design can ensure that the pipe is improved under the same water resistance. The flow rate is used to reduce the investment; the most common cause of noise in the closed water system is the air inside the tube. If effective measures are taken to completely remove the air inside the tube, no water flow noise will occur.

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