Trane Compressor Switchoff on Stage up

[dje75140]

Hello - There are four TRANE CGAH chllers at this site controlled by a Building Management System. When one Chiller is running at maximum, and,.. the BMS starts the Chilled water pump for the next chiller, .. all four Compressors in the first chiller switch off and then come back on one at a time after anti-recycle timer.
It does not cause any alarms of fault conditions so am unsure what is happening. Have tried adjusting the flow sensor for the affeced chiller but no change. (I thought there may be a quick filck on the flow sensor.) This mainly affects one chiller but I have seen it on others when two two chillers are working and a third pump is turned on. Can you advise what things would cause the compressors to shut down with water pressure / flow fluctuations.
Thanks Douglas

[binti]

Hi Douglas, If this is happening as the 2nd chilled water pump starts i would expect the 1st chiller is seeing a low flow condition. Then the BMS may compensate by opening the by-pass valve.
You mention a flow meter, is this for flow protection? Or is there another flow safety device?
Low flow faults will usually be auto reset (except Mcquay's) It may be happening quickly. I would be holding a meter on the flow switch (or diff press switch) while this 2nd pump is starting to see if the switch opens momentarily.

[Magoo]

Sounds more like a BMS system control problem, that should be stopping the first chillers last compressor, and starting the second chiller first compressor to maintain chilling capacity and the ramping up the second chiller then fully loading again the first chiller.
Probably a program error or input cross over.

[FreezerGeezer]

I'd expect those to have their own controls, with the BMS simply enabling / disabling them. We used to insist that third party BMS systems were only used to enable/disable Trane equipment as a timeclock and for setpoint reset. Trying to control the chillers directly with the BMS always ends up screwing up the chiller in my experience.
I'd expect the same result with any chiller or other plant with it's own built in controller.