High Suction Temps

[freezerman11]

Hi,

Could anyone help me out, we have an NH3 system, single stage cooling glycol, (economised)
glycol setpoint is @ -5 degrees,
we run stal 71Es and have a howden 255

On the Howden 255 the suction pressure is 212kPa
and suction temperature of -6.6 at compressor
however on the stal the suction pressure is the same(212) but the suction temperature is @ -3.3 at compressor

Have checked temperature probe and all ok.

any ideas?

[RANGER1]

If the Stal is unloaded suction will be warmer due to internal bypass of gas and lower flow of gas going through comp .
Is this the case ?
Also may depend on location of temp sensor in suction line .

[US Iceman]

Also, some compressor packages have the oil return from the separator dumping back into the suction valve. Under low capacity operation (unloaded) the higher oil temperatures mixing with reduced gas flow can increase the apparent suction temperature indicated. If the suction temperature comes back to what you would call normal when the compressor is fully loaded, I would not worry about it.

[freezerman11]

The compressor is running fully loaded, the PT100 is located on the suction housing, however I am more thinking that there is too much superheat as the VLR does run slighly short, and the gas is superheated before it arrives to the compressor,
They are a Stal71E's and are in poor condition (approx 30 years old),
Lately we have been having discharge temperature problems , hence whilst I think it may be due to excess superheat,

The oil cooling system is thermosiphon controlled with a closed loop circuit with VSD drives on the condensor controling @ 10.5BARg, it seems that if we have all compressor running fully loaded (7 off)and one cycles off on temp that another compressor down the line will start alarming on High oil temp, its as if there is not enough liquid feeding the oil coolers after one or two compressors stop but the thermosiphon vessel is 3/4 full,
I have also ensured that the valves are regulated from No.1 compressor through to No.7 ensuring equal amount of liquid to all oil coolers, there are no oil temperature control valves on the oil cool, just liquid inlet and outlet,

Could anyone shed some light on this?

Regards

[US Iceman]

High suction temperatures at full load can certainly increase the discharge temperature. Especially if you are experiencing oil cooling issues also.

I posted a short reply in the other thread you started.;)