Causes and analysis of start-up of compressor with liquid in chiller

First let’s define what is called liquid start. When the chiller is in the shutdown state, there is refrigerant liquid in the compressor casing. Causes and analysis of start-up of compressor with liquid in chiller, When the compressor is started next time, the refrigerant liquid will damage the lubrication of the compressor. Starting the compressor with refrigerant liquid Called to start with liquid. The main culprit with liquid start is the large amount of refrigerant mixed in the lubricant!

When the compressor starts, the pressure suddenly drops, and these refrigerants will suddenly boil, causing the oil to foam. This phenomenon is very similar to the phenomenon of foaming cola when people suddenly open the bottle of cola in daily life. The duration of blistering depends on the amount of refrigerant, which usually reaches several minutes or more than ten minutes. A lot of foam floated on the oil surface, even filling the crankcase. Once these bubbles are sucked into the air cavity through the air inlet, the bubbles will be reduced to a liquid. This liquid is a mixture of lubricating oil and refrigerant, which is easy to cause liquid shock.

Ice Rink chiller

Real Ice Rink chiller

How did these refrigerants with liquid start enter the crankcase?

First of all, it is not ruled out that the imperfect design or debugging of the system leads to part of the refrigerant returning to the compressor under the action of gravity when the compressor is stopped. Secondly, it enters the crankcase in the manner of “refrigerant migration”.

The flow of refrigerant under the action of gravity is easy to understand, what about refrigerant migration? To solve the problem, we must first understand what “refrigerant migration” is to eliminate the root cause.

Second, what is refrigerant migration?

When the compressor is stopped, the accumulation of liquid refrigerant in the compressor crankcase is refrigerant migration. As long as the compressor temperature is lower than the temperature in the evaporator, this phenomenon will occur because the temperature difference will cause a pressure difference between the compressor and the evaporator, driving the refrigerant to move to a colder place. This phenomenon is most likely to occur in cold weather, but for air conditioners and heat pump devices, the chiller is far away from the compressor, even if the ambient temperature is high, it may happen.

Refrigerant migration is a slow process. The longer the compressor is stopped, the more refrigerant will migrate into the lubricant. This process will continue as long as there is liquid refrigerant in the evaporator.

The measures to prevent the start of liquid-carrying caused by the migration of refrigerant, there are the following three suggestions:

  1. Install the liquid line solenoid valve. After the chiller is shut down, the solenoid valve is closed at the same time, and most of the refrigerant liquid is trapped on the high pressure side, which greatly reduces the possibility of liquid start.
  2. Install compressor electric heating belt. After the compressor is stopped, the electric heating belt is energized to heat the oil sump, maintain the heat input, maintain the high temperature of the oil sump, evaporate the refrigerant liquid in the oil sump, and avoid the influence of the liquid foam started next time.
  3. The design of the return air pipeline is inverted U-shaped. After the shutdown, due to the high and low drop between the evaporator and the compressor, due to the effect of its own weight, the liquid in the evaporator migrates to the compressor. At the next start, the evaporator operates in advance to evaporate the liquid into gas Safety.
  4. Install gas-liquid separator.

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