Pump combination optimization frequency conversion water supply system

A binary variable flow pump combination of pressure water supply method

Proposed in the literature [1] not using a frequency converter (or pressure tank) automatic regulator feed water method, that is, a combination of binary variable flow pump regulators feed water method, are described below:
Figure 1 is a binary variable flow pump combination of water supply and pressure control system structure diagram.
A total of four pumps M 0 , M 1 , M 2 , M 3 are operated in parallel in this system, and combined with water supply. The rated head of each pump is the same, and the rated flow rate changes twice. If the nominal flow rate of M 0 is q, then the rated flow of the other three pumps M 1 , M 2 and M 3 are 2q, 4q and 8q respectively.
The number 1 indicates that the pump is working, and the number 0 means the pump is stopped. So M 0 , M 1 , M 2 , M 3 four water pump working state each with a binary number a 0 , a 1 , a 2 , a 3 to be expressed. The working states when they are combined together are represented by a four-digit binary number a 3 a 2 a 1 a 0 .

As shown in Table, four binary number shown in FIG. 1 a total of 16 changes, which changes not only represent the situation when the combination of the pump, and represented the pump can provide a combination of the aqueous system outlet flow Q t (calculated for each condition in Of the outlet flow, almost ignored because of the parallel operation of the pump caused by traffic loss). That is, the greater the number, the greater the exit traffic; the smaller this number, the smaller the exit traffic. Thus found according to user size, adjust the system of water flow to ensure that the regulator of water supply, its working principle is: electric contact pressure gauge set the upper limit pressure H 2 , the lower limit pressure H 1 , by H 1 and H 2 The pressure stability range. If the actual water pressure H is low, when H <H 1 , the programmable controller switches the working state of the water pump combination according to the increasing law of the binary number a 3 a 2 a 1 a 0 shown in Table 1, increases the system water flow rate, Rise until H ≥ H 1 , such as high pressure H, H> H 2 , the programmable controller according to a 3 a 2 a 1 a 0 decreasing regularization of the working conditions of the pump combination to reduce system flow, water pressure down until H <H 2 . During normal operation, H 1 <H <H 2 , the actual water pressure H of the water supply system is stabilized within the range specified by H 2 and H 1 to achieve the purpose of stabilizing the water pressure.

The use of this technology, the regulator accuracy is not high, the water load fluctuations are not frequent cases, not using the frequency converter can also be regulated water supply. However, when the voltage regulation accuracy is high, if no frequency converter is used, more water pumps must be provided (of course, the number of water pumps is greatly reduced than the traditional water pump combination method), which is very unfavorable to the optimization of engineering design and convenience of construction. In addition, large changes in user load, do not use the inverter will cause frequent switching pump combination, the system greatly reduced the accuracy of dynamic regulator, the motor start and stop constantly increasing energy consumption. The comprehensive evaluation of the ideal solution is to convert the constant pressure water supply technology and binary variable flow pump combination of water supply technology used in combination.

2 pump combination to optimize frequency control constant pressure water supply program

As shown in Fig. 2, there are three pumps in total (the water pump drawn by dotted line is not included) P 0 , P 1 , P 2 , where the rated flow of P 0 and P 1 is q and the rated flow of P 2 is larger For 2q, three pumps the same rated lift. In addition, only P 0 uses the inverter to continuously control the speed, while P 1 and P 2 are directly controlled by the power frequency power switch.
This pump system is equipped with a typical variable frequency constant pressure water supply system compared to the latter generally the same size with two identical pumps, a frequency control, a power frequency switching control, the use of a small pump. However, due to the inverter control the flow of the pump doubles, so the use of inverter capacity is roughly doubled. To achieve a small capacity inverter instead of large-capacity inverter, reducing the cost-performance of the entire system.

The following describes the working principle of the water supply system of FIG. 2. For switches P 1 and P 2 with switch control, the numeral 1 indicates the operation of the pump, the numeral 0 indicates that the pump is stopped, and the combined operation of P 1 and P 2 is represented by a two-digit binary number a 2 a 1 As shown in Table 2). P 0 By continuously adjusting the motor speed with a frequency converter and combining it with the combination of P 1 P 2 , the flow in the entire feedwater system can continuously vary in the interval 0 ≤ Q t ≤ 4q Water pump caused by the loss of traffic). The difference between Table 2 and Table 1 is that the feed water flow can be continuously adjusted in the entire flow range of 0 ≤ Q t ≤ 4q due to the addition of the variable frequency speed control pump P 0 so that theoretically high precision constant pressure control can be achieved , Rather than within a certain range of voltage regulation described in Table 1. At the same time, compared with the traditional constant pressure frequency conversion water supply system, the design capacity of the inverter can be reduced by half. Therefore, the program combines the advantages of binary variable flow pump combination scheme and typical variable frequency constant pressure water supply scheme.

As shown in Fig. 2, if an additional pump P 3 with a capacity of 4 q (drawn by the dotted line) is added, the outlet flow of the water supply system can be continuously adjusted within the range of 0 <Q t <8q? According to the same working principle, Pressure is basically constant (see Table 3).

Through the above two cases can be concluded that if the design flow of the water supply system is Q, then the capacity of the variable frequency pump can be designed as q = Q / 2 n (n = 1,2,3 ...). At the same time with the n frequency power switch control of the pump, which n the same rated pump head and pump head with the same frequency, but the rated flow design value is twice the change, that is, from small to large: q, 2q , 4q ... 2 n-1 q.
By this (n +1) pump (a frequency control, n frequency switch control) consisting of a combination of water pump frequency control system to optimize water supply, that is, in the entire flow range to achieve high-quality constant pressure water supply, Again the design capacity of the inverter reduced to q = Q / 2 n , reducing the inverter project budget prices and improve the performance of the entire water supply system.

3 Conclusion

This paper presents a combination of water pump frequency control water supply program. It not only retains the advantages of frequency control scheme: the entire flow range can achieve high precision constant pressure water supply, but also use the pump combination technology greatly reduces the capacity of the inverter selection and improve the system's cost performance.

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