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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, caused by air conditioning circulating pump capacity is too large failure reasons:
Circulating pump capacity is too large in our country is a common problem, its capacity is 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 cold load is too large:
Design cooling load is the main basis for selecting equipment, so the correct calculation of 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 maximum cooling load of each room often causes different occurrences. 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 cycle resistance, due to lack of experience of designers, making some of the calculation parameters are too conservative, resulting in the calculated value of the circulation resistance is too large, even worse, in the construction design phase estimation method to determine the cycle resistance, resulting in calculation cycle Resistance 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, 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.
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 phenomenon of uneven heating system. 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 the problem, of course, will increase the pump capacity.
Second, the design of the pump operating point along the pump characteristic curve offset to the right reason:
When the working point of the pump is shifted to the right, the lift produced by the circulating pump is reduced, which is extremely unfavorable to the normal operation of the system. In particular, the most unfavorable loop in the system will further reduce the flow of the loop and affect the normal Use function There are two main reasons that cause the work point to shift to the right:
1, First of all, the hydraulic calculation in the design adopts an excessive safety factor and an unrealistic pressure drop calculation method. Second, the designed system does not perform serious hydraulic balance calculation, and no rigorous system commissioning has been carried out 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.