Abstract: This paper examines failure cases of circulating pumps in central air-conditioning systems, highlighting the critical importance of selecting an appropriate pump head. Through case studies, it emphasizes the need for accurate hydraulic calculations and provides practical methods for proper pump selection. The findings offer valuable insights for HVAC system designers aiming to enhance efficiency and reduce operational costs. Bimetallic Screw And Barrel,Ni-Based Alloy Barrel,Bimetallic Barrel,Alloy Screw And Barrel Zhejiang Guangming Plastics Machinery Co.,Ltd. , https://www.gmscrews.com
Keywords: Central air conditioning, Pump head, Proper selection, Hydraulic calculation, System efficiency
Abstract: This article investigates engineering failures caused by improper selection of circulating water pump heads in central air-conditioning systems. It underscores the significance of rational pump head selection and outlines effective strategies for achieving optimal performance. These insights are particularly useful for HVAC professionals seeking to improve system reliability and energy efficiency.
Keywords: Central air conditioning; Water pump head; Proper selection; Hydraulic design; Energy efficiency
1. Introduction
In a central air-conditioning system, the circulating pump is responsible for delivering chilled water in summer and hot water in winter to terminal devices. Proper pump selection should be based on both the system’s flow rate and resistance, as outlined in HVAC design manuals. However, in real-world projects, some engineers rely too heavily on experience rather than following established calculation methods. Additionally, with the rapid development of new air-conditioning equipment and accessories, many designers fail to thoroughly understand their impact on system performance. This can lead to pump selection that does not meet the actual requirements, increasing operating costs or even causing system failure. Such issues have drawn significant attention from air-conditioning engineers.
2. Theoretical Analysis
The water flow in an air-conditioning system depends on the temperature difference between the supply and return water, while the system resistance is determined through hydraulic calculations. A properly selected pump should operate within its high-efficiency range, with the working point defined by the intersection of the pump curve and the pipeline characteristic curve (as shown in Figure 1). In practice, two common problems arise:
1) Overestimation of system resistance leads to excessive pump head selection. This results in unnecessary valve throttling, increased energy consumption, and potential instability, especially during winter when flow rates are lower.
2) Underestimating system resistance causes the selected pump to have insufficient head, leading to inadequate flow and poor system performance. In such cases, replacing the pump is often the only solution.
3. Case Studies
Case 1: Project A involves a single-story high-rise building with a height of 29 meters. The system includes one imported Carrier centrifugal chiller with a cooling capacity of 1163 kW and two circulating pumps. During commissioning, the pump motor current was excessively high, and abnormal vibrations and noises were observed. Further analysis revealed that the pump head was too large, resulting in severe cavitation and inefficient operation. Replacing the pump with a low-head model significantly improved performance and reduced energy consumption.
Case 2: In Project B, a regional air-conditioning system serving multiple buildings faced circulation issues. Despite fully open valves and clean filters, the pump could not provide sufficient flow. Investigation showed that the pump had an insufficient head due to excessive inlet resistance caused by a fine mesh filter. After replacing the filter and recalculating the system, the pump was replaced, resolving the problem but at a considerable cost.
4. Conclusion
1) Selecting the right circulating pump for an air-conditioning system is not just about experience; it requires a solid understanding of theoretical calculations and system requirements.
2) The pump head should not be chosen solely based on the assumption that higher is always better. Instead, the focus should be on achieving economic and efficient operation.
3) With the fast-paced development of air-conditioning technology, careful evaluation of product performance is essential to ensure compatibility and long-term reliability.
5. Recommendations
To avoid similar issues in future projects, engineers should follow standardized hydraulic calculation procedures and stay updated on new technologies. Regular maintenance and monitoring of system performance can also help detect early signs of pump inefficiency or failure. By combining theory with practical experience, HVAC designers can ensure that their systems are both reliable and energy-efficient.