What antifreeze measures are there for cooling tower operation in winter? How should maintenance be carried out during shutdown periods?
I am an HVAC expert with many years of engineering experience in HVAC system design, construction, and operation and maintenance. The antifreeze issue of cooling towers operating in winter is a key aspect of HVAC system design in cold regions, directly affecting equipment reliability and system safety. Improper antifreeze measures may lead to cooling tower icing, structural damage, or even shutdown accidents; therefore, comprehensive consideration must be given across the three levels of design, operation, and maintenance.
According to Article 8.11.5 of GB 50736-2012 Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings, antifreeze measures shall be taken during winter operation of cooling towers, such as installing electric heat tracing, hot water circulation, or adjusting fan operation strategies. Meanwhile, Article 8.5.4 of GB 50019-2015 Code for Design of Heating Ventilation and Air Conditioning of Industrial Buildings also emphasizes that cooling water systems shall prevent freezing of pipes and equipment in winter. The following, combined with codes and practice, provides a detailed analysis of antifreeze measures and shutdown maintenance key points for cooling tower winter operation.
Antifreeze Measures for Cooling Tower Winter Operation
1. Hot Water Circulation Antifreeze: Install electric heat tracing or a hot water circulation system in the collection basin or pipes at the bottom of the cooling tower. For example, in a cold-region project (such as a commercial center in Harbin), we installed a bypass valve on the cooling tower inlet pipe; during winter operation, part of the hot water is returned to the collection basin to maintain the water temperature above 5℃. This complies with the requirements of Article 8.11.5 of GB 50736 and prevents freezing.
2. Fan Control Strategy: Adjust the fan operation mode, such as using variable-frequency fans or intermittent start-stop. When the outdoor temperature is below 0℃, reduce the fan speed or shut down briefly, using the natural rise of hot air to prevent icing of the fill. In an actual case, the cooling tower of an office building in Beijing adopted a "low-speed intermittent operation" mode in winter, combined with temperature sensors, effectively reducing the icing risk.
3. Insulation and Heat Tracing: Apply insulation treatment to exposed pipes, valves, and the collection basin of the cooling tower, and wrap self-regulating electric heat tracing cables at key locations (such as inlet and outlet pipes). According to Article 9.2.3 of GB 50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Works, the insulation layer thickness shall be calculated based on the local extreme temperature and is generally not less than 50mm.
4. Drainage and Antifreeze Fluid: Before winter shutdown, thoroughly drain the water in the cooling tower and pipes, and inject antifreeze fluid (such as ethylene glycol solution) into the circulation system. However, note that antifreeze fluid may affect heat exchange efficiency, and the concentration ratio shall be determined according to system requirements (generally 30%-50%).
Maintenance Measures During Shutdown
1. Thorough Drainage: Before shutdown, close the cooling tower inlet and outlet valves and open all drain valves (including the collection basin, pipes, and pump body) to prevent accumulated water from freezing. For example, in a data center project in Shenyang, we stipulated that after shutdown, each drain point must be manually inspected to ensure no residual water.
2. Cleaning and Inspection: Clean dirt and algae from the fill, collection basin, and fan blades, and check the lubrication of motors and reducers. According to Article 5.2.4 of GB 50300-2013 Unified Standard for Constructional Quality Acceptance of Building Engineering, equipment maintenance shall be documented.
3. Electrical Protection: After power-off, perform insulation testing on motors and the electric heat tracing system to prevent short circuits caused by moisture. At the same time, cover the electrical control box with a waterproof cover.
4. Structural Protection: Apply anti-rust treatment to the steel structure of the cooling tower and cover it with canvas or plastic sheeting to prevent accumulation of snow and debris. In a project in Xinjiang, we used custom insulation covers, which additionally increased wind resistance.
Actual Engineering Case
Take a five-star hotel in Tianjin as an example; its cooling tower is located on the roof, and the winter extreme temperature can reach -15℃. In our design, electric heat tracing was installed in the collection basin, and a "hot water return" bypass pipe was provided. During operation, the fan start-stop is automatically adjusted through a temperature controller, and when the water temperature is below 4℃, hot water circulation is forcibly started. During shutdown, the property management team drains water, cleans, and covers the insulation cover according to procedures. After two winters of verification, no icing accidents occurred, and the equipment operated well.
Summary
Winter antifreeze for cooling towers requires comprehensive application of measures such as hot water circulation, fan control, insulation and heat tracing, and drainage and antifreeze fluid; during shutdown, thorough drainage, cleaning, electrical protection, and structural protection are required. These measures shall be flexibly adjusted according to local climate conditions and system characteristics to ensure equipment safety and economy. The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific operating conditions, site conditions, and other factors.