In air-cooled chillers installed outdoors, after the summer season ends and the chillers are turned off, the water in the evaporator must be drained. In some cases, even by opening the drain cap located under the evaporator, some water may remain in some parts of the evaporator. This amount of water, as the temperature drops during the winter and reaches below zero degrees Celsius, can freeze and put pressure on the copper pipes, ultimately leading to the pipes bursting.
What is the solution?
1- After closing the evaporator return pipes and opening the drain pipe below it, you can help completely drain the water through the pipe located at the top of the evaporator (expansion source pipe), using a flow of nitrogen gas or compressed air. This will direct any remaining water to the drain pipe, ensuring that no water remains inside the evaporator.
Warning:
Never use a pure oxygen cylinder instead of compressed air or nitrogen. Pure oxygen can explode if oil or grease is present inside the evaporator, causing serious hazards including damage to the chiller, people, and surrounding equipment.
2- To prevent burst pipes and fittings, we must ensure that in addition to draining the evaporator water, the water in the chiller’s inlet and outlet pipes that are located outdoors is also drained.
After closing the chiller’s return valves inside the engine room and draining the water, be sure to leave an air vent or drain valve open so that the remaining water does not move toward the chiller if the main shut-off valves are not sealed.
3- Do not close the drain cap under the evaporator after draining the water. This will ensure any water possibly entering the evaporator is drained.
4- It is recommended to equip the lower surface of the evaporator with electrical heating elements and control it through an environmental thermostat. If the ambient temperature reaches below zero, the thermostat will activate the elements and keep the evaporator body warm. This will prevent the possible freezing of the remaining water in the evaporator.
5- In cases where the chiller must also operate during the winter, freezing can be prevented by adding ethanol or ethylene glycol to the system water. To ensure that there is no freezing, it is better to pour a sample of the solution into a plastic container and place it in the freezer. If it freezes after a day, you should increase the amount of ethylene glycol and test again to ensure that the solution does not freeze at sub-zero temperatures.
6- Make sure that a strainer is installed in the return pipe to the chiller. When draining the chiller evaporator, open the drain plug of the strainer and drain the water inside it. Also, clean the stainless-steel mesh inside the strainer, but do not put it back in place to ensure that any remaining water in the pipes will be drained. Even a small amount of remaining water can freeze and cause problems.
Important note:
If for any reason you cannot completely drain the chiller evaporator and as a result, freezing occurs and the pipes crack, water entering the refrigerant cycle can cause serious damage to the compressor, which will be expensive to fix.