At present, the frequency conversion speed of living water supply in construction water supply more widely, its main reason is: 1. Frequency control water supply water pressure adjustable, you can easily meet the needs of a variety of water pressure. The design stage can reduce the requirement for the accuracy of the calculation of the water pressure because the water pressure can be easily changed at any time. However, the election pump should be noted that the pump lift should be larger, because the maximum frequency of variable frequency speed regulation by the pump. The minimum pressure should not be too small, because the pump does not allow long-term overload in the low lift large flow, or should increase the inverter and pump motor capacity to prevent overload. 2. At present, the inverter technology is very mature, there are many domestic and foreign brands in the market inverter, which provides a full technical and material basis for frequency conversion water supply. Inverter has been widely used in various sectors of the national economy. With any brand of inverter and frequency conversion water supply controller, you can achieve multi-pump parallel constant pressure water supply. Because of the wide range of applications of building water supply, some inverter design and manufacture of the inverter water supply controller directly in the water supply dedicated inverter; This inverter has the advantages of good reliability, easy to use. 3. Frequency Control Constant pressure water supply has excellent energy saving effect. From the pump - the principle of water supply pipe shows that the regulation of water flow, in principle, there are two ways; First, throttling regulation, open large water supply valve, the flow increased; off small water supply valve, the flow decreased. The second method of adjusting the flow rate adjustment, the pump speed increases, the water supply flow rate increases; speed decreases, the flow rate decreases for the water flow often changes in the occasion (such as domestic water), the use of speed regulation flow, with excellent energy saving effect. China's State Science and Technology Commission and the State Economic and Trade Commission in the "China's energy-saving technology policy outline" in the pump and fan speed control technology as a national nine five plan to promote energy-saving technology projects. It should be pointed out that the effect of frequency conversion constant pressure water supply energy saving mainly depends on the changes of water flow and pump reasonable selection, in order to make the frequency conversion constant pressure water supply has excellent energy-saving effect, frequency conversion constant pressure water supply should adopt multi-pump parallel water supply mode. By the pump constant pressure water supply in parallel with the theory that multiple pumps in parallel with constant pressure water supply, as long as one of the pump is a variable frequency pump, the remaining full-frequency pump, can achieve constant pressure variable water supply. Variable frequency variable pressure water supply, variable frequency pump flow is variable, when the variable frequency pump is the largest pump in parallel, you can guarantee constant pressure water supply. Multi-pump constant pressure water supply in the design can be done under the conditions of constant pressure in the constant-frequency pump constant (due to the same conditions), and make it work in the high-efficiency area, variable frequency pump flow is changing , Its work efficiency changes with the flow. Because of the multi-pump parallel constant pressure water supply, inverter pump power is reduced, which can reduce the energy consumption of multi-pump parallel variable frequency constant pressure water supply system to improve energy-saving conditions. When the multi-pump constant pressure water supply system with automatic sleep function of the inverter, when the water flow is close to zero, the pump can automatically sleep to stop the pump, so you can do without water automatically stop the pump without energy loss, with the best Energy saving effect. Multi-pump parallel variable frequency constant pressure variable water supply is usually the following: When the water flow is less than a pump in the constant frequency power flow, by a variable frequency pump speed constant pressure water supply; when the water flow increases, When the speed of the variable frequency pump rises to the working frequency, the water flow will be further increased, controlled by the frequency conversion water supply controller, and a frequency-frequency pump will be automatically put into operation. The flow provided by the common-frequency pump is constant (Power frequency speed flow under constant pressure), the rest of the parallel power frequency pump by the same principle into. In the case of water supply with variable frequency and constant pressure of multiple pumps in parallel, when the flow rate of water drops, the speed of the variable frequency speed control pump drops (the frequency of the power supply of the frequency inverter drops); when the frequency drops to zero flow, the frequency conversion water supply controller sends a command, Automatically shut down a frequency pump to make it beyond the parallel water supply. In order to reduce the frequency of automatic input or when the impact of the pump (hydraulic or current impact). When it is put into, the speed of the frequency conversion pump drops automatically, and then slowly rises to meet the requirement of constant pressure water supply. In the event of an overshoot, the speed of the inverter pump should automatically increase and then slowly decrease to meet the requirements of constant pressure water supply. The above frequency is automatically increased, decreased by the water supply inverter controller. Another frequency conversion water supply mode is usually called constant pressure variable cycle start and first open the first stop working mode. In this water supply mode, when the flow rate of the water supply is less than the flow rate of the variable frequency pump under the constant voltage, the frequency conversion pump will automatically adjust the water supply. When the water flow increases, the speed of the variable frequency pump will increase. When the speed of the inverter pump is increased to the working frequency, the pump of the inverter is switched to the direct power supply by the power frequency grid (not powered by the inverter) under the control of the inverter water supply controller. Inverter is another start a parallel pump into work. As water flow increases, the rest of the parallel pumps are soft-start in the same way as above. This is the cycle of soft-start input. When the flow of water is reduced, the parallel power frequency pump in sequence shut down the pump out of order and the pump out of order by the first input into the first off pump principle by the inverter controller single board computer control. It can be seen from the above that there are usually two working modes for variable frequency and constant pressure water supply. One is the fixed mode of the variable frequency pump, and the other is the soft start mode of the frequency conversion cycle. In variable frequency pump fixed mode, each parallel pump is automatically input or exceeded by frequency mode. Because the variable frequency pump is fixed, when the water flow changes, the variable frequency pump is always in operation, so the inverter pump longest running time. In order to balance the running time of each pump, for the fixed operation mode of the variable frequency pump, it can be designed to operate the timing rotation of the variable frequency pump. That is, when a certain frequency conversion pump runs for a certain period of time, the inverter controller controls the frequency conversion pump to automatically rotate. For example: At the beginning of a pump frequency, 2-3 pump power frequency, when a pump frequency conversion operation T time (T can be set in order) automatically rotate to 2 pump frequency, 3-1 pump frequency; running in this state T time after the automatic rotation for the 3 pump frequency, 1-2 frequency, ....... Timing rotation so repeatedly. Obviously, with a variable frequency pump automatic rotation control variable frequency variable pressure water supply system, variable frequency pump is regularly changing, that is, any one of the parallel pumps are likely to become a variable frequency pump. Variable frequency constant pressure variable water supply theory shows that, in order to ensure constant pressure water supply, variable frequency pump must be the largest of the parallel pump. To this end, for constant pressure water supply and frequency conversion pump automatic timing of the water machine, the size of the parallel pumps should be the same to ensure constant pressure water supply. According to the working principle of the inverter, the inverter in operation is not allowed to switch at its output; otherwise some of the electronic components in the inverter will be subjected to high current impact to reduce the life of the inverter during the switching process. During the automatic rotation of the variable frequency pump, the output of the inverter should be switched; in order to protect the inverter, the inverter should be stopped before automatic switching. The inverter is switched off at the output when it is stopped. After the switchover, restart the inverter to resume normal operation. Therefore, the automatic rotation control of the circuit is more complex, will increase the cost of inverter control cabinet and reduce the reliability of its use. When the variable frequency variable pressure water supply system has a variable frequency pump automatic rotation function, the advantage is that each parallel pump can be rotated to frequency conversion operation, so that the parallel pump wear and tear balanced. However, in any one pump frequency conversion operation, in case of pump failure may make the inverter protection trip and stop working. Each parallel pump is controlled by the inverter operation; when the inverter trips, it is inevitable that all parallel pumps stop and interrupt water supply. Therefore, when the reliability of the pump is constant, the water supply reliability of a variable frequency constant pressure water supply with automatic rotation control function will be lower than that of a variable frequency constant pressure water supply that does not have the automatic rotation control function. The author believes that the reliability of water supply is the main contradiction. Therefore, we do not advocate the use of automatic rotation control frequency conversion constant pressure water supply system. Pumps in parallel, the cycle of soft-start constant pressure water supply system, the same variable frequency automatic rotation of the shortcomings of the work mode. In order to ensure constant pressure water supply, the same requirements for the size of each pump in parallel. To sum up, in order to ensure the reliability of water supply, I do not advocate the use of automatic rotation and frequency cycle soft-start mode of operation. In its User Manual for the ABB Constant Pressure Water Supply System, Tsinghua Unisplendour Automation Group said, "Cyclic soft start! This is a dangerous temptation. Many people who work on constant pressure water supply are keen to develop this technology, but our suggestion Is negative ... ... "We agree with the above academic opinion of the Automation Engineering Department of Tsinghua Unisplendour Corporation and are not keen to engage in frequency conversion soft start water supply. From the pump - the principle of water supply pipe shows that when the throttling loss is equal to zero, then the water supply system has the best energy-saving effect, when the water pump head completely consumed in the water supply and water flow resistance loss. This frequency conversion of water supply known as the state of the variable pressure water supply, the head of this water supply system - flow curve and pipeline system flow resistance - flow curve coincide. In the ideal variable pressure variable water supply system, the point of water, its head is constant, is a constant pressure water supply. In the actual construction, water points are multiple, not one, so it is difficult to determine where is the point of constant pressure water. Transformer variable water supply system is not universal, rarely used in engineering. A practical variable pressure water supply system is called quasi-variable pressure variable water supply system; in the quasi-variable pressure water supply system, the constant pressure value rises with the water flow rate increases. For example, multi-pump parallel constant pressure water supply, when a pump work, the constant pressure value of P1; when put into a pump, the constant pressure value automatically becomes P1 + ΔP1; when two, three, four pumps into the constant pressure value P1 + ΔP1 + ΔP2, P1 + ΔP1 + ΔP2 + ΔP3, P1 + ΔP1 + Δ P2 + ΔP3 + ΔP4,. P1, ΔP1, ΔP2, ΔP3, ΔP4, ... can be set as needed; therefore, the water supply characteristics of quasi-variable pressure variable system (equipment) can be very close to the ideal water supply characteristics of variable pressure variable, which has excellent energy saving effect. Water supply system (equipment) has versatility. For example, internationally renowned ABB water supply inverter has the above-mentioned quasi-transformers variable water supply control functions. In fact, in building water supply, quasi-variable pressure water supply is rarely used, because in actual use, it is difficult to give the specific parameters of ΔP1, ΔP2, ΔP3 ...... and so on. Key References 1 Fu-li Fu, "Frequency Control Pump Principle and Practice", "Inverter World", 1999, N010. 2 Fu Xili, "variable frequency constant pressure water supply equipment, fixed-frequency operation of the pump running mode and the cycle of comparative analysis", "Inverter World", 2000, N012.
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