McQUAY PFH Watercooled Suction Superheat problem

[wilko123]

Can anyone help please,

We are having suction superheat advisory warnings on a chiller in London, this problem has only become apparent after recent tube replacements and remedial works. We are assuming correct charge and flow rates,

Has anyone come across this before, do they know the correct approaches, superheats for these machines?

Many thanks Wilko

[ptsac]

Can anyone help please,

We are having suction superheat advisory warnings on a chiller in London, this problem has only become apparent after recent tube replacements and remedial works. We are assuming correct charge and flow rates,

Has anyone come across this before, do they know the correct approaches, superheats for these machines?

Many thanks Wilko

Hi Wilko, these are dual centrifs I assume. Flooded evaporator so suction superheat should be as close to 0 degrees C, normally easier to measure discharge superheat at approx 8 C at full load with liquid inj. ( if fitted) shut off. subcool at full load should be say 5 or 6 degrees also at full load.
Approaches are probably 3-4 C at full load.
However, I havent had too much to do with dual machines, but if you quote the full model, serial and style numbers to McQuay they should be able to provide the shop order details which list s/s.heat etc and design flow rates.
Does the alarm say high suction or low suction superheat?
What microtech is fitted?
Some of the sensors fitted to some microtechs are notoriously innacurate.

Phil

[wilko123]

Hi Phil,

Thanks for your input.....McQuay are not always the best bunch to get info out of. Yes these are the dual machines, The alarm is saying high suction superheat. Im pretty sure its the 200 Series Microtech.

Although an advisory alarm the client is getting peeved so need to get to the bottom of the cause.

Thanks

Wilko

[ptsac]

Does this alarm occur when at low load, one compressor or two compressors running? Is the condenser water below 20C, possibly refrigerant reluctant to leave the condenser.
The compressors should match each other for loading or else one will starve the other.
Check the accuracy of the sensors, suction temp and evap pressure transducer.
What temp is the alarm set for?
Sorry more questions than answers.

Phil

[ptsac]

http://www.mcquay.com/mcquaybiz/lite...IMOM/Om125.pdf
Try this link for controller info, you may have this already, hope the link works.

Phil

[ptsac]

http://www.mcquay.com/mcquaybiz/lite...OM200MICRO.pdf
This link is for a later manual

[wilko123]

Hi PTSAC, Sorry not responded been investigating the chiller in question and on various other sites....no rest for wicked... The alarm would appear to occur at low load, do you have a email i could send you some of the alarm history report parameters if interested? thanks Wilko p.s thanks for links to manuals i had the old one but not the new!