Air conditioning circulating pump capacity, number of units, the choice of the best pump operating point and technical and economic analysis to discuss how to choose the pump to ensure that the air-conditioning system is running well and reduce power consumption. First, the cause of air conditioning circulating pump capacity is too large Fault reason: circulating pump capacity is too large in our country is a common problem, its capacity often 2-4 times the actual needs, resulting in a serious waste of project investment and operating costs. The main reasons are as follows: 1, the design of the cold load is too large: the design of the cold load is the main basis for the selection of equipment, so the correct calculation of the building cooling load on the entire air conditioning system design is very important. At present, the calculation method of air conditioning load provided in textbooks and design manuals is not only calculating the wall load of the envelope, but also the load of windows and doors, and the calculation result is for a specific room. However, the capacity of air conditioning system equipment is determined by the cooling load of the entire building. Due to the different orientation, location, use function and heat source of each room in the building, the time that the maximum cooling load in each room often appears is not the same. Therefore, the maximum building cooling load should be the maximum value of the hourly load stack per room. According to the survey, some designers in our country simply calculate the maximum cooling load of each room when calculating the cooling load of the building, resulting in the calculation result far exceeding the actual required load. Therefore, we must pay enough attention to this to make the design load more reasonable and correct. 2, the system cycle resistance is too large: In the calculation of system resistance to circulation, the lack of experience due to the designer, making some of the calculation parameters are too conservative, resulting in the calculated value of the circulation resistance is too large, what is more, in the construction design phase estimation The method determines the circulation resistance so that the calculated cycle resistance is more than double the actual value. Air conditioning system is full of water to run, pump inlet and outlet to withstand the same hydrostatic pressure. Therefore, the head of the selected pump can only overcome the pipeline system resistance. However, some designers consider the hydrostatic pressure within this circulation resistance, which of course increases the capacity of the circulating water pump. 3, the system static pressure problem: air conditioning system is full of water to run, pump inlet and outlet to withstand the same hydrostatic pressure. Therefore, the head of the selected pump can only overcome the pipeline system resistance. However, some designers consider the hydrostatic pressure within this circulation resistance, which of course increases the capacity of the circulating water pump. 4, the system of hydraulic balance problem: As the design does not seriously carry out the system of hydraulic balance calculation, after the completion of the project did not complete the required commissioning, often resulting in system hydraulic imbalance, the system appears uneven hot and cold phenomenon. Some technicians mistakenly believe that the cause of this phenomenon is that the circulating pump capacity is too small, the result is simply to increase the pump to solve it, naturally, the pump capacity increases. Flange ball valve Second, the design of the pump operating point along the pump characteristic curve to the right offset reason: the pump operating point to the right offset, the pump produced by the lower lift, which is the normal operation of the system is extremely unfavorable, especially Is the most unfavorable loop in the system, will further reduce the flow of the loop, affecting the normal use of the function. There are mainly two reasons for the shift to the right of the work point: 1. The first is to calculate the excessive safety factor and the unrealistic pressure drop calculation method in hydraulic calculation. 2. The second is to design the system without serious hydraulic balance calculation , But did not carry out rigorous system debugging after construction. Therefore, in order to make the system run according to the design conditions, in addition to the relevant calculations should be carefully and carefully, but also in the selection of the pump when the pump operating point at the left side of the optimal choice of the appropriate location to prevent the pump actual working point Beyond a certain range in uneconomical operating conditions, affecting the normal operation of the system.