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

[CV_Geardrive]

Hi Douglas,
First of all you should check the water pressure drop in evaporator when the unit is running alone and after an other chiller starts.
Also check for fluctuation in water pressure drop at the moment that an other pump starts.
If the piping design is OK you should have always the same measurement. If not check your piping.
If your system is primary-secondary check if the bypass is fully open, and in general check all external components like water check valves, secondary pumps etc.
These chillers has only a differential water pressure drop sensor (B56) and the cut out set point is about 20Kpa. Any external flow switch are connected to X21-X22.
If needed place a jumper to X21-X22 just for test.
I suggest you to place a jumper between X1-X6 and a jumper between X1-X12 (if the unit has two circuits)
With this you should always have operation command to chiller. Also set the pump of affected chiller in manual on.
If the BMS is controlling the units via serial link set manually chiller and pump on.
If you solve the problem with these jumpers then you have problem with the sequence of operation of BMS.
In reference to water flow, the compressors can shut down only if you have a cut out by differential water flow switch or external water flow switch or cut out by low pressure pressostat or low saturated refrigerant temperature.
In any case you should have an alarm, resettable or not. Check the “C” menu for historic alarms.
If you need the programming guide of SMM please let me know in order to mail to you.
Hope I help.
Regards,
CV

[install monkey]

put all the pumps in hand to prevent the flow switches fluctuating on pump start up-the chillers can the cycle on return water as normal and you'll have better control of water temp and save on running costs.also are the water strainers clean

[Lowrider]

put all the pumps in hand to prevent the flow switches fluctuating on pump start up-the chillers can the cycle on return water as normal and you'll have better control of water temp and save on running costs.also are the water strainers clean

putting all pumps on will not safe u money nor will it keep the temperature in check.plus the chiller will allways run in part load

Can u provide a drawing of the system layout complete with pumps etc. ?

[dje75140]

Hello all - Thank you for the information and circuit diagram. The problematic Chiller is fitted with a Control Monitor VS 0200. Using the information you provided I concluded the problem is related to poor adjustment of this Control monitor. The system uses the output of this to determine if the Chiller pump is running. It appears when the second Chilled water pump switched on it resulted in a flick on the output of this flow sensor monitor. It was not enough to shut down the pump control but it was enough to cause the chiller compressors to shut down. After adjustment it is now staging up without shutting down the compressors however the adjustment appears very sensitive. I will need to monitor it for a while to be sure it is resolved.
Thanks again for your help.
Douglas

[dje75140]

Hello all - Thank you for the information and circuit diagram. The problematic Chiller is fitted with a Control Monitor VS 0200. Using the information you provided I concluded the problem is related to poor adjustment of this Control monitor. The system uses the output of this to determine if the Chiller pump is running. It appears when the second Chilled water pump switched on it resulted in a flick on the output of this flow sensor monitor. It was not enough to shut down the pump control but it was enough to cause the chiller compressors to shut down. After adjustment it is now staging up without shutting down the compressors however the adjustment appears very sensitive. I will need to monitor it for a while to be sure it is resolved.
Thanks again for your help.
Douglas