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Anti-freezing measures for central air conditioning in clean workshops during winter
2026/6/22
01. Prevention of water system freezing (core focus)
The air conditioning water system of the cleanroom includes the chilled water, cooling water, hot water and humidification water systems. During winter shutdown or low-load operation, these systems are prone to freezing, and targeted protection measures are required:
Continuous operation of system anti-freezing
Maintain water flow rate and water temperature: In the hot water system, the supply water temperature should not be lower than 45℃, and the return water temperature should not be lower than 35℃. For the chilled water system, if it needs to maintain a processally low temperature (such as in a semiconductor clean room), the water pump must operate continuously, with the water flow rate being ≥ 0.6m/s, to prevent localized stagnant water from freezing.
Pipe insulation and heating: All water pipes exposed to outdoor or non-air-conditioned areas (such as connection pipes of roof cooling towers, humidification water pipes inside exterior wall fresh air ducts) should be protected with both flame-retardant rubber insulation and electric heating. The power of the electric heating should be selected based on the ambient temperature (-10℃ or below suggests 20-30W/m), and a temperature controller should be set (start temperature 5℃, stop temperature 15℃).
Parallel valve linkage control: During low-load conditions, open the pump bypass valve to ensure the minimum flow in the main heat exchanger, preventing local water temperature from being too low and causing freezing; for air-cooled heat pump units, a winter anti-freezing bypass circuit needs to be set up, and the water in the circulating pipeline will automatically circulate when the unit is shut down.
2. Anti-freezing system for intermittent operation/shutdown systems
Emptying and draining water: In case of short-term shutdown (more than 24 hours) and when the ambient temperature is below 0℃, it is necessary to completely drain the accumulated water from the cooling tower, outdoor pipelines, and end equipment, including low-point drain valves and high-point exhaust valves, to ensure there is no residual water.
Filling antifreeze: For systems that have been shut down for a long time or are unable to be emptied (such as underground pipelines, precision heat exchangers), ethylene glycol antifreeze can be filled. The concentration should be determined based on the lowest ambient temperature (30% concentration at -10℃, 45% concentration at -20℃). It is important to note the compatibility of the antifreeze with seals and metal pipes.
System inspection: During the downtime, conduct daily inspections. Check whether the sewage valve is leaking, whether the insulation layer is damaged, and whether the electric heating is operating normally.
02. Anti-freezing Measures for Fresh Air Treatment System
The fresh air ratio in the clean workshop is high (usually 10% to 100%). In winter, when the temperature is low, the fresh air can easily cause frost formation and cracking on the heat exchanger, so special protection is required:
Preheater preheating: Before the fresh air enters the unit, it first passes through a hot water preheater or an electric preheater to raise the temperature of the fresh air to above 5℃, and then enters the dehumidifier or humidifier to prevent the fresh air at low temperature from directly contacting the cold surface and forming frost.
Heat exchanger anti-freezing control: If the air cooler is not in use in winter, the inlet valve should be closed and the internal water should be drained. If it needs to be operated (such as for dehumidification), the chilled water temperature should be ≥ 5℃, and an anti-freezing alarm should be set (when the surface temperature of the air cooler is lower than 2℃, the hot water bypass should be automatically opened or the fresh air valve should be closed). For the outdoor heat exchanger of the air-cooled heat pump unit, an automatic defrosting function should be set. Through timed reversing and electric heating for defrosting, thick frost layers can be avoided, which may affect heat exchange and block the air ducts.
Ventilation valve linkage protection: When the machine stops, the ventilation valve automatically closes to prevent cold air from entering the machine room; when the machine starts, the preheater is activated first, and then the ventilation valve is gradually opened to avoid cold shock.
03. Anti-freezing Measures for Air Ducts and Terminal Equipment
Pipe insulation and sealing: The air ducts in the clean room (especially the return air ducts) need to be insulated to prevent cold air from penetrating and causing condensation on the outer wall of the ducts, resulting in the formation of condensate water that flows along the ducts and freezes at the end equipment. The connection points of the duct flanges need to be sealed tightly to avoid air leakage.
Fan coil unit anti-freezing: For intermittent operation fan coil units, when stopping for the winter, the water supply valve should be closed and the accumulated water should be drained; for long-term operation, the hot water circulation should be maintained and a temperature controller should be set (the system will automatically start when the room temperature drops below 18℃).
Humidification system protection: For steam humidification or electrode humidification systems, during winter, the water in the humidification tank needs to be drained to prevent the tank from freezing and cracking; for the high-pressure mist humidification system, electric heating should be installed on the pipelines to avoid nozzle blockage.
04. Intelligent Monitoring and Emergency Measures
Temperature monitoring alarm: Temperature sensors are installed on outdoor pipelines, heat exchanger surfaces, and the environment of the machine room. When the temperature drops below 0℃, an audible and visual alarm will be triggered automatically, and the electric heating and hot water bypass measures for anti-freezing will be activated simultaneously.
Emergency backup power supply: For critical anti-freezing equipment (such as circulation pumps, electric heating, and temperature controllers), a UPS backup power supply is provided to prevent the failure of anti-freezing measures in case of power outage.
Formulate anti-freezing plans: Clearly define the system operation modes, shutdown operation procedures, and emergency handling plans under different environmental temperatures in winter. Regularly provide training for maintenance personnel.
05. Special Requirements for Cleanroom Processes
Clean workshops for semiconductor and biomedicine production are highly sensitive to temperature fluctuations. Anti-freezing measures must not compromise the accuracy of constant temperature and humidity. For instance, electric heating should be controlled precisely to avoid local overheating; the adjustment of bypass valves should be smooth to prevent sudden changes in water temperature.
For the ducts and valve insulation layers in high cleanliness areas (Class 1 to 100), materials that do not produce dust and are easy to clean (such as stainless steel shell with rubber insulation) should be used to prevent the insulation layers from falling off and contaminating the clean room.
