compressor ice build up

[juicetavo]

Hello everybody,

I'm currently working on a cooling system that uses a carrier brand chiller. The chiller is a 30gt model (very old) that uses r22 to cool a 40% glycol solution, and has 60 tons capacity. I've noticed a lot of ice build up on the outside of the compressors (it has 2 of them). I've read the manual and it states that expansion valves are controlled to provide superheated gas exiting evaporator @ 6°C which would suggest that ice build up in the compressors is not likely. Leaving Chilled water temperature is set to -10°C and since it's summer here, chiller is working at full capacity. Also i'm working at high altitude (aprox 2700 m)
So my question is: is this ice build up normal? if it's not so, then what could be the cause?

Thanks in advance for your help :)

[install monkey]

prove the the expansion valve is controlling as recommended or glycol flow problems

[The Viking]

I think there must be a language barrier somewhere in the
manual.
Those 6 degrees will not be the temperature of the gas in the suction line, it is the superheat

If you think about it, for your water to reach -10 the refrigerant needs to be cooler than that.

[install monkey]

30gt chiller freeze protection for low temp operation is -9.5deg!!-raise ur control setpoint

[monkey spanners]

If the system is evaporating at -20c to get the water to -10c then with 6k superheat the gas exiting the evaporator will be -14c and cold enough to frost the suction valve of the compressor if the pipework is insulated and the piperun not too long.

You need to take some temperature and pressure readings at the compressor inlet and evaporator outlet to know whats going on.

[install monkey]

https://rapidshare.com/files/3079996974/30gt-34si.pdf
check the manual

[juicetavo]

I think there must be a language barrier somewhere in the
manual.
Those 6 degrees will not be the temperature of the gas in the suction line, it is the superheat

If you think about it, for your water to reach -10 the refrigerant needs to be cooler than that.

excuse my ignorance, i had the notion that by superheat, it meant the temperature of the gas as it leaves the evaporator (since its the refrigerant leaving at a superheated state). What does this superheat temperature mean then? thanks :)

[mbc]

if ice build up after several running time and comes close to suction valve do not worry about that but if it is passing valve to compressor side you have to check it again
1) it is very important your glycol percentage in system So check it ,is any ice around evaporator pipes
2) circulation of pump is enough .check filters and valves also pump fan.
3) if those items is right then go for suction superheat. you can adjust expansion valve.

[The Viking]

excuse my ignorance, i had the notion that by superheat, it meant the temperature of the gas as it leaves the evaporator (since its the refrigerant leaving at a superheated state). What does this superheat temperature mean then? thanks :)

Ok here goes,
In the thread "Overcharging of refrigerant", HERE (http://www.refrigeration-engineer.com/forums/showthread.php?34089-Overcharging-of-Refrigerant&p=249791#post249791) I recently explained subcooling, superheat is exactly the same but in reverse.

If you imagine the evaporator as a long pipe submerged in hot water, in one end we will inject liquid refrigerant. This liquid refrigerant will then heat up as it travel along the pipe and slowly "boil" or turn in to vapour, at some point there will be no more liquid left, only vapour.

If we at this point let our refrigerant enter a compressor then there is a chance that some liquid droplets will be carried over, sucked along with the vapour, and enter the compressor. As liquid can't be compressed this will damage the compressor.
F
We therefore need a safety buffer. This is created by letting the refrigerant travel further in our pipe, past the point of where all the liquid has evaporated. It will then pick up more heat to ensure that there is no chance of liquid to be carried along.

The difference in temperature between when all the liquid should have boiled off and the refrigerant when it leaves the evaporator is what's commonly referred to as superheat.

(yes, there are other places in a refrigeration circuit where you will find superheated vapour but this is what we were talking about)

[juicetavo]

Ok here goes,
In the thread "Overcharging of refrigerant", HERE (http://www.refrigeration-engineer.com/forums/showthread.php?34089-Overcharging-of-Refrigerant&p=249791#post249791) I recently explained subcooling, superheat is exactly the same but in reverse.

If you imagine the evaporator as a long pipe submerged in hot water, in one end we will inject liquid refrigerant. This liquid refrigerant will then heat up as it travel along the pipe and slowly "boil" or turn in to vapour, at some point there will be no more liquid left, only vapour.

If we at this point let our refrigerant enter a compressor then there is a chance that some liquid droplets will be carried over, sucked along with the vapour, and enter the compressor. As liquid can't be compressed this will damage the compressor.
F
We therefore need a safety buffer. This is created by letting the refrigerant travel further in our pipe, past the point of where all the liquid has evaporated. It will then pick up more heat to ensure that there is no chance of liquid to be carried along.

The difference in temperature between when all the liquid should have boiled off and the refrigerant when it leaves the evaporator is what's commonly referred to as superheat.

(yes, there are other places in a refrigeration circuit where you will find superheated vapour but this is what we were talking about)

Thank you very much! I had studied the refrigeration cycle but there were some technical terms that i wasn't familiar with yet (i just recently started to work in this and i hope to find out a lot more about cooling systems)

thanks again for your help.