Air Conditioning Cold Water System Frequency Control Pump Control

**Abstract:** In an air conditioning cold water system with variable flow, a primary pump system is commonly used, where one pump is controlled via frequency conversion. However, constant pressure control is not the most energy-efficient method. To achieve maximum energy savings, variable pressure control should be employed alongside variable frequency control. This approach allows the system pressure to adjust according to the pipeline characteristics curve, optimizing energy use. **Keywords:** air conditioning, cold water system, pump, variable frequency control, variable flow, primary pump, energy efficiency, chilled water unit, system pressure, control strategy With the advancement of self-control and automation technologies, variable flow water systems are now widely used in air conditioning projects, especially in large and medium-sized systems, where they are almost universally applied. In variable flow systems, the chiller's performance can adapt to partial loads, maintaining high efficiency. Combining variable flow on both the chiller side and the load side allows for efficient operation. Using a single pump with frequency control can significantly improve energy savings, but the effectiveness depends on the control method used. In a variable flow cold water system, electric two-way valves at the terminal adjust based on room temperature, causing changes in system flow and pressure between the supply and return lines. To accommodate these changes, a bypass valve is often installed as a backup. When the flow drops below the minimum required by the chillers, the pump frequency stops decreasing, and the bypass valve opens to redirect excess flow. With multiple chillers, such as two units, stopping one reduces the flow by 50%, making further reduction less effective. Therefore, the bypass valve usually remains closed. **Principle of Energy Saving with Variable Frequency Control** When the system flow decreases from QA to QB, the operating point shifts from A to B', increasing system pressure. This results in the highest surplus pressure head and the greatest energy-saving potential. If constant pressure control is used, the pressure sensor detects the pressure difference and adjusts the inverter frequency to maintain a set pressure (HA or HB). This reduces dynamic pressure loss compared to fixed-speed pumps, offering clear energy savings. However, when using variable pressure control, the system pressure follows the pipeline characteristic curve, allowing the pump to operate at an optimal point. This method results in even greater energy savings by reducing additional pressure losses. **Energy Saving with Frequency Control** While constant pressure control is simple to implement and widely available, it is not the most efficient approach for air conditioning systems. The most energy-efficient method involves adjusting the system pressure along the pipeline’s characteristic curve. This requires programmable control chips that can dynamically regulate the pump speed based on real-time conditions. During commissioning, the system’s flow, total pressure difference, and pump frequency relationship are measured. These data are used to create an approximate formula for the pipeline’s characteristic curve, which is then stored in the control chip for future reference. The principle of minimum pressure difference is preferred during operation, with the pump starting at low frequencies and gradually adjusting. If a building control system is in place, implementing this advanced control is straightforward. However, without such a system, it becomes more challenging due to the lack of standardized variable pressure control products. Fortunately, with current technological advancements, programmable control devices are easily available. Manufacturers should develop specialized products tailored for variable pressure control in chilled water pump systems, making energy-saving solutions more accessible and effective. **Conclusion** In air conditioning cold water systems with variable flow, using variable frequency control for the chilled water pump is essential for maximizing energy savings. The system pressure should vary according to the pipeline characteristics curve. It is recommended that manufacturers develop appropriate standardized products to support this advanced control method, enhancing energy efficiency and operational performance.

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