At present, building water supply systems have gradually moved away from traditional technologies such as water towers, high-pressure tanks, and pressure vessels. Instead, they now commonly use computer-controlled variable frequency drives (VFDs) to regulate pump motor speeds for stepless speed control and constant pressure water supply. This modern approach has significantly improved water pressure stability, reduced equipment size, and enhanced energy efficiency. However, the cost-effectiveness of VFDs is often compromised due to their technical complexity, which can lower the overall performance-to-price ratio of the water supply system. To address this issue, one of the most effective strategies is to reduce the inverter capacity without sacrificing the system's performance. Market research shows that larger inverter capacities directly increase project costs. Therefore, when designing large-scale water supply systems, minimizing the VFD capacity becomes a key technical solution to improve engineering cost-performance. A binary variable flow pump combination method for pressure-based water supply was proposed in literature [1]. This method does not rely on a frequency converter or pressure tank for automatic water supply but instead uses a combination of binary variable flow pumps. The system consists of four pumps—M0, M1, M2, and M3—operating in parallel. Each pump has the same rated head, but their rated flow rates double progressively. If the nominal flow rate of M0 is q, then M1, M2, and M3 have flow rates of 2q, 4q, and 8q, respectively. Each pump’s operational status is represented by a binary digit: '1' indicates the pump is running, while '0' means it is off. The combined working states of all four pumps are represented by a four-digit binary number, a3a2a1a0. As shown in Table 1, there are 16 possible combinations, each corresponding to a specific total flow rate at the outlet. The higher the binary number, the greater the flow, and vice versa. The system operates using an electric contact pressure gauge that sets upper (H2) and lower (H1) pressure limits. When the actual pressure H drops below H1, the programmable controller adjusts the pump combination according to the increasing order of the binary number, increasing the flow until H ≥ H1. Conversely, if the pressure exceeds H2, the controller reduces the pump combination in decreasing order, lowering the flow until H < H2. During normal operation, the pressure remains within the stable range between H1 and H2, ensuring consistent water pressure. This binary pump combination method offers a cost-effective alternative to VFDs, especially in scenarios where pressure regulation accuracy is not extremely high. However, for applications requiring high precision, the absence of a VFD may necessitate more pumps, which can be inefficient. Additionally, significant load fluctuations without a VFD can lead to frequent pump switching, reducing system accuracy and increasing energy consumption. To balance these factors, a hybrid approach combining binary variable flow pump technology with VFD-controlled constant pressure systems is ideal. For example, in Figure 2, three pumps (P0, P1, P2) are used, with P0 controlled by a VFD and P1 and P2 operated at power frequency. This setup allows for continuous flow adjustment within a range of 0 ≤ Qt ≤ 4q, achieving high-precision pressure control while reducing the VFD’s required capacity by half. Adding more pumps, such as P3 (with a capacity of 4q), extends the adjustable flow range to 0 < Qt < 8q, maintaining stable pressure throughout. By optimizing the number of pumps and strategically using VFDs, the system achieves both efficiency and cost-effectiveness. In conclusion, combining binary variable flow pump technology with VFD control provides a superior solution for modern water supply systems. It retains the benefits of precise pressure control while significantly reducing inverter size and overall system costs. This approach ensures reliable, energy-efficient, and economically viable water supply solutions for various applications.

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