With temperatures plummeting, how can air conditioning equipment be protected from freezing?

In winter, we need to protect ourselves from the cold, and as refrigeration professionals, we also need to "care for and maintain" our refrigeration equipment. Especially in the cold north, we need to take precautions against the cold for central air conditioners, particularly large commercial central air conditioners in shopping malls, manufacturing plants, and hotels. So how do we prevent freezing, and what measures are there to prevent it?

I. Preventing Host Freezing

　　Close the inlet and outlet valves of the host condenser or evaporator, open the drain valve and vent valve, and then use compressed air to blow out the remaining water.

II. Preventing Water Pump Freezing

　　Close the inlet and outlet valves of the refrigerant water pump, open the water pump drain valve and vent valve, and drain the water. Open the valve at the lowest point of the cooling water system to drain the cooling water, and open the water pump drain valve. After the system water is drained, to prevent rainwater from entering through the cooling tower, close the cooling tower outlet main valve and open the cooling tower sump drain valve to allow rainwater to drain out in time.

III. Preventing Cooling Tower Makeup Pipe Freezing

　　Generally, the cooling tower makeup pipe is exposed outdoors. Most designers use insulation to prevent freezing, but in actual use, even with insulation, freezing often occurs. To solve this problem, add a valve where the cooling tower makeup pipe exits from indoors, and add a drain valve at the lowest point of the makeup pipe. In winter, close the indoor valve and open the drain valve at the lowest point to drain the water in the outdoor pipe. In this way, the pipe does not need insulation and will not freeze.

IV. Preventing Expansion Tank Freezing

　　Expansion tanks are generally located on the roof or in equipment rooms on the top floor. Although the expansion tank has insulation and a circulation pipe, in actual use, the circulation pipe rarely plays a real circulation role. That is, in winter, the water in the expansion tank is often at a low temperature. Although it is insulated, it will still freeze. If the expansion tank freezes, it will not be able to expand, and the temperature in the system will increase, increasing the pressure.

　　To solve this problem, during construction, a DN20 interface can be set on the air conditioning water supply main pipe, and a valve can be installed and opened appropriately to ensure that the water in the tank circulates. If the air conditioner is not used at night, before the water pump stops, this valve can be fully opened to raise the temperature of the water in the expansion tank, ensuring that the expansion tank does not freeze for a long time after the pump stops.

V. Preventing Fresh Air System Freezing

　　The function of the fresh air unit is to process the outdoor fresh air and send it to various rooms. In winter, the fresh air unit heats the cold outdoor air. That is, the fresh air unit's evaporator is in direct contact with the outside cold air. To prevent the evaporator from freezing when heating is stopped, an electric multi-leaf regulating valve should be added at the fresh air inlet and linked with the fresh air unit. When the fresh air unit is running, the air valve is open; when the fresh air unit is closed, the air valve is closed. This can prevent the outdoor cold air from directly cooling the water in the evaporator after the fresh air unit and refrigerant water pump stop running, causing the water to freeze and damage the evaporator.

VI. Adding Antifreeze

　　In winter, if it is inconvenient to drain the water from the unit and there is a possibility of water and power outages, antifreeze must be added for equipment heating, and the lowest local temperature must be used as an important parameter for selecting antifreeze. The main component of antifreeze is ethylene glycol. The antifreeze is poured into the makeup tank, the chilled water in the water system is drained, the antifreeze concentrate is injected first, and then chilled water is added if necessary. Then, the water pump is turned on to allow the antifreeze and water to fully mix, and the air in the water system is discharged. The water system cannot contain air; the presence of air will cause the air conditioning equipment to trip the water flow switch protection and easily cause cavitation.

VII. Insulating All Cold Pipes

　　The main purpose of insulating chilled water pipes is to prevent condensation on the outside of the pipe, and another purpose is to prevent the water in the pipe from freezing. The insulation layer thickness is generally more than 20 mm.

　　In addition, electric heating tape should be wrapped around the outside of the water pipe. As long as the heating tape is powered, it can continuously heat the pipe, keeping the water temperature in the pipe above 10℃. Together with the insulation on the outside of the heating tape, freezing that causes the hot water machine to lack water protection will not occur. The heating tape should be selected with a temperature limiter to maintain a certain temperature.

　　Source: Refrigeration Encyclopedia

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