What impact does the cooling water outlet temperature setpoint have on chiller energy consumption? What is the optimal setpoint value?
I am an HVAC expert. The setting of the cooling water supply temperature is one of the core parameters of chiller operating efficiency, directly affecting the unit's condensing temperature, compressor energy consumption and the system's overall energy efficiency ratio (EER). According to Article 8.2.3 of GB 50736-2012 "Design Code for Heating Ventilation and Air Conditioning of Civil Buildings" and Article 8.4.2 of GB 50019-2015 "Design Code for Heating Ventilation and Air Conditioning of Industrial Buildings", the temperature difference between cooling water supply and return should preferably be 5℃, but the specific supply temperature setting must be optimized in combination with equipment performance, climatic conditions and load characteristics. If this parameter is set improperly, it may increase unit energy consumption by 10%-30%, which is particularly important in hotels and other projects operating year-round.
From engineering experience, for every 1℃ reduction in cooling water supply temperature, chiller energy consumption can be reduced by approximately 2%-4% (based on typical performance curves of centrifugal or screw compressors), but the energy consumption of cooling tower fans and the wet-bulb temperature limit must be weighed. The optimal setpoint is usually 30-32℃ (under standard conditions), but dynamic adjustment is required:
- **Summer high-temperature conditions**: When the outdoor wet-bulb temperature is relatively high (e.g., above 28℃), it is recommended to set the cooling water supply temperature to 32-35℃ to balance the heat dissipation capacity of the cooling tower and avoid high-pressure protection of the unit caused by excessively high cooling water temperature.
- **Transition seasons or low-temperature periods**: It can be lowered to 25-28℃, but note that excessively low condensing pressure may cause compressor liquid return or lubrication problems; the unit's minimum condensing pressure limit must be ensured (refer to Article 5.2.2 of GB/T 18430.1-2016 "Vapor Compression Cycle Water Chillers (Heat Pumps)").
**Actual case**: A five-star hotel project (Guangzhou area) originally had its cooling water supply temperature fixed at 32℃. On-site testing showed that in spring (wet-bulb temperature 22℃), lowering the supply temperature to 28℃ increased the chiller COP from 5.0 to 5.8, reducing comprehensive energy consumption by approximately 12%. However, the cooling tower fan variable-frequency control must be adjusted simultaneously to prevent frequent unit start-stop caused by excessively low cooling water temperature. In addition, when variable-frequency cooling water pumps are used, the cooling water temperature difference must be maintained at 5-7℃ to avoid increased pump energy consumption.
**Summary**: The optimal setpoint of the cooling water supply temperature should be within the range of 30-35℃, dynamically adjusted according to the outdoor wet-bulb temperature, while taking into account both the unit's minimum condensing pressure limit and the energy consumption of cooling tower fans. It is recommended to implement adaptive control through the BMS system to balance year-round energy efficiency.
The above are reference opinions. The actual project situation still needs to be further comprehensively evaluated and implemented in combination with specific operating conditions, on-site conditions and other factors.