Suction valve icing

[maxim971]

I have a question similar to QQQ. After starting 4-compressor station I saw an ice on suction valves of compressors. Is it an attribute of liquid flow (insufficient superheat) to the compressor or a normal situation?
Suction temperature -34 deg C.
Condensation temperature +35 deg C.
Is it necessary to adjust TEV?

[Gary]

In order to accurately evaluate the system, we need the following:

Low side:

evap air in temp
evap air out temp
SST (saturated suction temp)
suction line temp near evap coil
suction line temp near compressor

High side:

cond air in temp
cond air out temp
SCT (saturated condensing temp)
liquid line temp at outdoor unit
liquid line temp at metering device inlet

[Dan]

After starting 4-compressor station I saw an ice on suction valves of compressors. Is it an attribute of liquid flow (insufficient superheat) to the compressor or a normal situation?

The observations that Gary requires are important for a thorough understanding, but if you are doing a startup on a parallel compressor rack and see ice on the suction valves, and not previous or upstream of the suction valves, I would think you have a problem that requires immediate addressing. The first thing that comes to mind is turn the machine off, and sit quietly with wonder and fear. Achieving understanding when everything is turned off buys you time to rethink how much you understand and how accurately you recall what you just witnessed.

That only applies if you mean the suction valves of the compressors. If you see ice on Evaporator Pressure regulating valves, then you can relax somewhat.

From your question, I am picturing that you saw ice form only on the suction valves of all the compressors. Perhaps we could improve upon your original question?

[maxim971]

There is an ice on compressors suction valves, suction ball valves (because these are non-insulated), non-insulated areas of suction pipes.

As regards values mentioned by Gary - there are difficult to measure - we don't have thermometrs, measuring temperature on suction line near compressor.

By the way - is it nesessary to have suction line thermometers?

[Andy]

Hi Maxim,
You should be carrying a thermometer as a standard service tools. What you are working on is a refrigeration system, with heat carrying fluids that operate on a temperature pressure relationship.
Ice is normally on low temp suctions. Your refrigerant leaves the evaporator superheated by about 8 deg C,the refrigerant is further heated by ambidnt temperature, but to leave the refrigerant at above 0 deg C the suction would require heating by a further 23 to 25 deg C, unless you have no , or very poor insulation this should not happen.
Determine the temperature at the compressor inlet, if it is close to or matches the refrigerant saturation temperature you have liquid carry-over, if not ice is normal for a low temperature application.
Regards. Andy

[maxim971]

Thanks a lot

[Coolie]

In order to accurately evaluate the system, we need the following:

Low side:

evap air in temp
evap air out temp
SST (saturated suction temp)
suction line temp near evap coil
suction line temp near compressor

High side:

cond air in temp
cond air out temp
SCT (saturated condensing temp)
liquid line temp at outdoor unit
liquid line temp at metering device inlet

Hi Gary

As a matter of interest, how do you go about analyzing the data that you ask for.
I am busy studying an HNC in Refrigeration/Aircon and am quite interested in learning more.
Thanks

[Gary]

In general, TD's indicate load, dT's indicate airflow, subcooling and superheat indicate refrigerant, and approaches indicate heat transfer. You'll be amazed at how much these numbers can tell you. It's like you can see inside the system.

[Coolie]

To put it another way, TD's tell you about the relationship between load and heat flow and then dT's tell you about the relationship between heat flow and mass flow. Subcool and superheat can be used to give a parallax or cross reference with which to qualify the seen balances, the nature of their deviation, between load, heat flow and mass flow.

It all sounds very interesting. I'm sure we'll be covering this within the HNC I am doing now. If we don't then I will seriously consider one of your day courses Marc.
I dont suppose there is a place on the web that covers this subject??