ambient temp effect on chillers operation

[fridgeilliterat]

I dont understand the fundamentals and would appreciate some explanation. We have a chiller system that maintains the temperature of a process chemical in the range -2/+2oC.The system works well until the ambient temperature exceeds 35oC. At this point the compressors trip out on head pressure I am told. When the ambient temp drops the system starts up fine.

Why does this happen?
Can this be improved?

[US Iceman]

Since you are describing this as an ambient temperature problem is it safe to assume the condenser(s) is air-cooled?

Welcome to the RE forums.

[fridgeilliterat]

Since you are describing this as an ambient temperature problem is it safe to assume the condenser(s) is air-cooled?

Welcome to the RE forums.

We have 2 Carrier compressors running in parallel with air cooled condenser.

[nike123]

We have 2 Carrier compressors running in parallel with air cooled condenser.

If unit works OK and High pressure switch is set as it should be, than you have unit which is not designed to work in high ambient conditions.

That mean that condenser is dimensioned at such way that cannot reject much heat at higher ambient temperature (design TD of condenser is high), and used compressor is not designed to work safely with elevated condensation pressures/temperatures and therefore protected with such low high pressure switch settings.

Cheapest solution is to install some automatic water spraying assembly with nozzles to spray water at condenser fins to help that high pressure stays low in these few hot days.

Water could be released and closed with solenoid valve which could be switched ON/OFF by thermostat on liquid pipe or pressure switch at (which is better solution) high pressure side.

[Argus]

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I’ve worked on chillers using R22 in the North African desert in the past where we often exceeded 45 degrees – it knocks your performance, but a properly designed chiller will work.


It’s not clear what refrigerant you are using, in any case I would have thought that 35 degrees is not excessive for air cooled chillers using conventional refrigerants. Plenty of places get hotter than that.


Discounting any defects with the machine that we don’t know about, two things spring to mind; first are the coils clean? Second is condenser air allowed to re-circulate due to overhangs or obstructions?



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[Sridhar1312]

Normally the condensing pressure is directly related to ambient temperature if it is air cooled chiller.
naturally when the ambient goes to 35 degree C the condensing pressure goes up and restarts when the pressure is at set point.Alternatively condensing pressure can be set at pressure equivalent to 36 degree C then tripping problem can be solved.
If tripping takes place even after setting the condenser mcoil may be dirty then cleaning of condenser will certainly avoid tripping.

[US Iceman]

... two things spring to mind; first are the coils clean? Second is condenser air allowed to re-circulate due to overhangs or obstructions?

If the condenser was properly selected for the actual heat rejection of the system and the intended ambient operating conditions, then the answer to your problems would one of those mentioned by Argus above.

A third possibility may non-condensable gases in the condenser also. This is however a remote possibility if proper service procedures have been used during maintenance.

[Scramjetman]

Also check that someone hasn't overcharged the machine with refrigerant at some stage. Check the subcooling level of the condenser when it is running hard on a hot day. Sometimes fridgies get a little excited about charging until the sightglass is clear and ignore the subcooling level. The net effect is that the system can be overcharged which drives up the head pressure.