Winter Anti-freezing Measures for Air Conditioning Equipment and Fire Protection Systems
2025-03-30
When the ambient temperature is lower than 4°C, the volume of water will start to expand. The lower the temperature, the greater the volume expansion. After it freezes into ice, the density of ice is 0.9g/cm³, while the density of water is 1g/cm³. Therefore, the volume of water in the pipeline network will increase by 1/10 after freezing, generating a huge expansion force, and the expansion force is directly proportional to the volume of the pipeline network. The freezing and cracking of facilities will not only cause economic losses but also pose a great fire safety risk. This article lists some winter anti-freezing measures for air conditioning equipment and fire protection systems for reference.
01 Main Equipment
a. If the equipment is not used for a long time in winter, please drain all the cold (warm) water and cooling water completely. To prevent corrosion, it is recommended to blow dry the equipment and the system with nitrogen and then seal in nitrogen for storage.
b. For outdoor equipment used in winter, please pay attention to the low-load operation of the equipment. When shutting down under light load, please ensure that the circulation pumps of each system run continuously. Please replace the low-temperature type vacuum pump oil to avoid overloading when starting the vacuum pump.
02 Cooling Towers
Generally, the make-up water pipes of cooling towers are exposed outdoors. Most designers use the insulation method to prevent freezing. However, in the actual use process, even with insulation, freezing damage often occurs.
a. If the equipment is not used for a long time in winter, when shutting down, the circulating water and spray water must be drained completely, and the drain valves and drain outlets should be kept open. When the lower water tank is equipped with an anti-freezing heater, please cut off the power supply of the heater to prevent dry burning and fire. After the heat exchanger of the closed cooling tower is naturally drained, compressed air should be further used for drainage, and the drain valve should be kept open.
b. For equipment used in winter, please pay attention to observing the ice formation situation of the cooling tower body. If there is ice, please clean it up in time. 1). When the cooling tower fan runs intermittently, please check the ice layer inside the wind cylinder. If there is ice, the fan can only be started after the ice is completely removed. 2). When the closed cooling tower is in operation in winter, it is recommended to add antifreeze to the circulating water to avoid damage to the heat exchanger caused by the failure to drain the water in time after shutdown.
03 Air Conditioning Terminals
a.
b. For terminal equipment used in winter, especially pay attention that the water pump must run continuously for 24 hours (or other anti-freezing related water pump interlocking measures) during the shutdown period at low temperature at night. All the valves of the water pipeline should be opened, the air valve should be closed, and the doors and windows of the room where the unit is located should be closed.
04 Anti-freezing of Water Pumps
a. For the pipelines of the water system, open the drain valves and exhaust valves of the pump unit, auxiliary equipment and the pipes in the machine room. Drain the cold water and cooling water pipelines completely, and keep the drain valve open. After the water is drained completely, close the gate valves before and after the water pump.
b. To prevent rainwater from entering through the cooling tower, close the main outlet valve of the cooling tower and open the sewage valve of the cooling tower water collection tray to make the rainwater drain out from the sewage valve in time.
05 Adding Antifreeze
When it is inconvenient to drain the water from the unit in winter and there is a possibility of water and power outages, antifreeze must be added for the heating of the equipment, and the local lowest temperature must be taken as an important parameter for selecting the antifreeze.
The main component of the antifreeze is ethylene glycol. The antifreeze is poured into the make-up water tank. After draining the chilled water in the water system, first inject the original antifreeze solution, and then inject the chilled water if it is not enough. Then start the water pump to make the antifreeze and water fully blend, and at the same time, discharge all the air in the water system. There should be no air in the water system. The presence of air will cause the air conditioning equipment to report the protection of the water flow switch and is also likely to cause cavitation.
06 Thermal Insulation of All Chilled Water Pipes
The main purpose of thermal insulation of the chilled water pipes is to prevent condensation on the outer side of the pipes. Another function is to prevent the water in the pipes from freezing. The thickness of the thermal insulation layer is generally more than 20mm.
In addition, an electric tracing tape should be wound around the outer side of the water pipe. As long as the tracing tape is powered, it can continuously heat the pipe to keep the water temperature in the pipe above 10°C. Coupled with the thermal insulation on the outer side of the tracing tape, the water shortage protection of the water heater due to freezing will not occur. The tracing tape should be selected with a thermostat to maintain a certain temperature.
07 Anti-freezing of the Expansion Water Tank
The expansion water tank is generally installed in the equipment room on the roof or the top floor. Although the outer surface of the expansion water tank is insulated and a circulation pipe is provided, in actual use, the circulation pipe rarely really plays the role of circulation. That is, in winter, the water in the expansion water tank is in a low-temperature environment for a long time. Although it is insulated, it will still be frozen. If the expansion water tank is frozen, it will not play the role of expansion, and when the temperature in the system rises, the pressure will increase.
To solve this problem, a DN20 interface can be set on the main air conditioning water supply pipe during construction, and a valve can be installed and opened appropriately to ensure the circulation of the water in the tank. If the air conditioner is not used at night, before the water pump stops, this valve can be fully opened to raise the water temperature in the expansion water tank, which can ensure that the expansion water tank will not freeze for a long time after the pump stops.
08 Fire Protection System Facilities
Take good fire anti-freezing countermeasures (such as heating, adding antifreeze, enabling electric tracing for pipelines, increasing the ambient temperature, etc.) to avoid the freezing and cracking of fire protection equipment.
For projects under construction, please be sure to drain the water in the pipeline network, and do not supply water to the pipeline network that has not been connected to the water inlet yet.
For projects that have been put into use, first, ensure that the ambient temperature of the place where the glass bulb sprinkler heads are used is higher than 4°C. Second, the outdoor pipelines should have thermal insulation measures to prevent the glass bulbs from being burst due to the sharp rise of the water pressure in the pipelines caused by the freezing of the pipelines.
a. Outdoor fire hydrants are divided into above-ground and underground types. In the south, above-ground types are mostly used, and in the north, underground types are selected for anti-freezing. However, in extremely cold weather, the outlet of the underground fire hydrant will also freeze. One solution is to add thermal insulation materials under the manhole cover, and the other is to use underground fire hydrants with anti-freezing valves. The fire hydrants and fire pump adapters exposed on the ground can be protected by the method of "wrapping them with cotton-padded clothes", and the outdoor fire pipelines can be protected by wrapping thermal insulation cotton on the outside.
b. Protection Measures for Fire Protection Facilities in Buildings
Seal the holes, gaps and cracks for air intake in the building. Set up double windproof curtains and air curtains at the entrances and exits. Start the circulating pump of the central air conditioner at night to increase the indoor temperature.
Appendix: Requirements for the Environmental Temperature of System Selection in GB50084-2017 "Code for Design of Automatic Sprinkler Fire Extinguishing Systems"
09 Some Pictures of Freezing Damage of Fire Protection System Facilities
To ensure the safety of fire protection facilities and equipment and avoid unnecessary accidents, we must be vigilant and take protective measures in advance.
01 Main Equipment
a. If the equipment is not used for a long time in winter, please drain all the cold (warm) water and cooling water completely. To prevent corrosion, it is recommended to blow dry the equipment and the system with nitrogen and then seal in nitrogen for storage.
b. For outdoor equipment used in winter, please pay attention to the low-load operation of the equipment. When shutting down under light load, please ensure that the circulation pumps of each system run continuously. Please replace the low-temperature type vacuum pump oil to avoid overloading when starting the vacuum pump.
02 Cooling Towers
Generally, the make-up water pipes of cooling towers are exposed outdoors. Most designers use the insulation method to prevent freezing. However, in the actual use process, even with insulation, freezing damage often occurs.
a. If the equipment is not used for a long time in winter, when shutting down, the circulating water and spray water must be drained completely, and the drain valves and drain outlets should be kept open. When the lower water tank is equipped with an anti-freezing heater, please cut off the power supply of the heater to prevent dry burning and fire. After the heat exchanger of the closed cooling tower is naturally drained, compressed air should be further used for drainage, and the drain valve should be kept open.
b. For equipment used in winter, please pay attention to observing the ice formation situation of the cooling tower body. If there is ice, please clean it up in time. 1). When the cooling tower fan runs intermittently, please check the ice layer inside the wind cylinder. If there is ice, the fan can only be started after the ice is completely removed. 2). When the closed cooling tower is in operation in winter, it is recommended to add antifreeze to the circulating water to avoid damage to the heat exchanger caused by the failure to drain the water in time after shutdown.
03 Air Conditioning Terminals
a.
b. For terminal equipment used in winter, especially pay attention that the water pump must run continuously for 24 hours (or other anti-freezing related water pump interlocking measures) during the shutdown period at low temperature at night. All the valves of the water pipeline should be opened, the air valve should be closed, and the doors and windows of the room where the unit is located should be closed.
04 Anti-freezing of Water Pumps
a. For the pipelines of the water system, open the drain valves and exhaust valves of the pump unit, auxiliary equipment and the pipes in the machine room. Drain the cold water and cooling water pipelines completely, and keep the drain valve open. After the water is drained completely, close the gate valves before and after the water pump.
b. To prevent rainwater from entering through the cooling tower, close the main outlet valve of the cooling tower and open the sewage valve of the cooling tower water collection tray to make the rainwater drain out from the sewage valve in time.
05 Adding Antifreeze
When it is inconvenient to drain the water from the unit in winter and there is a possibility of water and power outages, antifreeze must be added for the heating of the equipment, and the local lowest temperature must be taken as an important parameter for selecting the antifreeze.
The main component of the antifreeze is ethylene glycol. The antifreeze is poured into the make-up water tank. After draining the chilled water in the water system, first inject the original antifreeze solution, and then inject the chilled water if it is not enough. Then start the water pump to make the antifreeze and water fully blend, and at the same time, discharge all the air in the water system. There should be no air in the water system. The presence of air will cause the air conditioning equipment to report the protection of the water flow switch and is also likely to cause cavitation.
06 Thermal Insulation of All Chilled Water Pipes
The main purpose of thermal insulation of the chilled water pipes is to prevent condensation on the outer side of the pipes. Another function is to prevent the water in the pipes from freezing. The thickness of the thermal insulation layer is generally more than 20mm.
In addition, an electric tracing tape should be wound around the outer side of the water pipe. As long as the tracing tape is powered, it can continuously heat the pipe to keep the water temperature in the pipe above 10°C. Coupled with the thermal insulation on the outer side of the tracing tape, the water shortage protection of the water heater due to freezing will not occur. The tracing tape should be selected with a thermostat to maintain a certain temperature.
07 Anti-freezing of the Expansion Water Tank
The expansion water tank is generally installed in the equipment room on the roof or the top floor. Although the outer surface of the expansion water tank is insulated and a circulation pipe is provided, in actual use, the circulation pipe rarely really plays the role of circulation. That is, in winter, the water in the expansion water tank is in a low-temperature environment for a long time. Although it is insulated, it will still be frozen. If the expansion water tank is frozen, it will not play the role of expansion, and when the temperature in the system rises, the pressure will increase.
To solve this problem, a DN20 interface can be set on the main air conditioning water supply pipe during construction, and a valve can be installed and opened appropriately to ensure the circulation of the water in the tank. If the air conditioner is not used at night, before the water pump stops, this valve can be fully opened to raise the water temperature in the expansion water tank, which can ensure that the expansion water tank will not freeze for a long time after the pump stops.
08 Fire Protection System Facilities
Take good fire anti-freezing countermeasures (such as heating, adding antifreeze, enabling electric tracing for pipelines, increasing the ambient temperature, etc.) to avoid the freezing and cracking of fire protection equipment.
For projects under construction, please be sure to drain the water in the pipeline network, and do not supply water to the pipeline network that has not been connected to the water inlet yet.
For projects that have been put into use, first, ensure that the ambient temperature of the place where the glass bulb sprinkler heads are used is higher than 4°C. Second, the outdoor pipelines should have thermal insulation measures to prevent the glass bulbs from being burst due to the sharp rise of the water pressure in the pipelines caused by the freezing of the pipelines.
a. Outdoor fire hydrants are divided into above-ground and underground types. In the south, above-ground types are mostly used, and in the north, underground types are selected for anti-freezing. However, in extremely cold weather, the outlet of the underground fire hydrant will also freeze. One solution is to add thermal insulation materials under the manhole cover, and the other is to use underground fire hydrants with anti-freezing valves. The fire hydrants and fire pump adapters exposed on the ground can be protected by the method of "wrapping them with cotton-padded clothes", and the outdoor fire pipelines can be protected by wrapping thermal insulation cotton on the outside.
b. Protection Measures for Fire Protection Facilities in Buildings
Seal the holes, gaps and cracks for air intake in the building. Set up double windproof curtains and air curtains at the entrances and exits. Start the circulating pump of the central air conditioner at night to increase the indoor temperature.
Appendix: Requirements for the Environmental Temperature of System Selection in GB50084-2017 "Code for Design of Automatic Sprinkler Fire Extinguishing Systems"
09 Some Pictures of Freezing Damage of Fire Protection System Facilities
To ensure the safety of fire protection facilities and equipment and avoid unnecessary accidents, we must be vigilant and take protective measures in advance.
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