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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8140
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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centrifugal chiller freeze up

Customer Question

centrifugal chiller freeze up
Submitted: 5 years ago.
Category: HVAC
Expert:  Phil replied 5 years ago.

Phil :

All work to be done by licensed professional. WE KEEP GOING UNTIL YOU HAVE THE INFORMATION YOU NEED, I come and go. This is step ONE.

Phil :

Hello

Phil :

Have the tubes ruptured? Has chilled water gotten into the refrigerant side of the chiller heat exchanger?

Phil :

Tell me about the freeze thermostat settings. Those will be thermostats with red reset buttons on them. depending on the age of the chiller they will look something like this.

Phil :

but with a red reset button on front that the one in the picture does not have

Phil :

The probe inserts into a thermometer well in the side of the chiller barrel, there are usually two or three of these on larger chillers.

Customer :

OAT 31 degrees. Two tower fans on high speed.

Phil :

Thanks, those are seriously non functional controls of course that will freeze the cooling tower in spots depending on the load, but not the chilled water side of the system....

Phil :

The problem is caused by s defective cooling tower sump water temperature controller...

Customer :

Tower water temp 50 degrees. Too much sub cooling. Chiller at 29%, concern about possible freeze up. Please give an explain the seriousness of a possible freeze up in the chiller. Turning off one tower would increase the heat load to prevent a possible freeze up.

Phil :

Tell me if the cooling tower fans are VFD controlled

Phil :

The chiller barrel will have freeze lock out thermostats mounted at two places or more..with red reset buttons on them. Those must not be set below 36F.. thats because water freezes at 32F if there is no glycol in the system.. and the thermostats can easily go out of calibration by a few degrees.

Phil :

see the picture I posted, virtually all of them are of that type.

Phil :

If the chiller barrel tubes freeze *once.. they will not generally break... but they can.. if the chiller barrel tubes freeze repeatedly they rupture and fill the refrigrant side of the system with water.

Phil :

On larger chillers with direct drive compressors, (motors external to the refrigerant circuit) its a problem but does not ruin the compressors, the fix is to plug or replace the ruptured tubes... tapered brass plugs are made for that purpose.

Phil :

In your situation it is unlikely that freezing the cooling tower will have that effect... that is not an entirely damaging situation at this point

Phil :

but does need to be corrected.

Phil :

You can run with the cooling tower fans off until the sump comes back up to 50F

Phil :

as long as the pumps still circulate condenser water through the tower .. they should be ok at this point.

Phil :

*** there are two types of cooling tower fan control... fan cycling, and variable frequency drive.

Phil :

various types of controllers are used depending on which... its not much of a job for a good controls man to sort out what the problem is in either case.

Phil :

Its bad temperature sensor in either case as a rule.... only the type and wiring strategy change.

Phil :

You may click the accept button for answers to date if you like, that way you can follow up on the same dime, days or months later as needed.

Phil :

Thanks!

Customer :

If the chiller would freeze up on a 1300 ton, how high could the repairs go in the event of this? I am aware a chiller should shut down prior to freeze up but there is a possibility that the safety does not work. At what point would you increase the heat load prior to the safety in the event you are not around to monitor closely the chiller.

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