Chiller Oil Heaters on UPS Power

[TECMSC]

The operating condition is: chiller is at full load, utility outage and chillers shut down, generators quickly start and power is restored to restart the chillers.

If the generators start quickly and power is restored would you really need to have the crankcase heaters and associated controller on UPS power?

 

[MintJulep]

It depends.

The point of crankcase heaters is to prevent oil dilution by refrigerant. So, in the time between loss of power and the generators coming on-line, how much refrigerant can accumulate in the crankcase?

A you just going to slam the chillers back on when you have generator power, or will there be some sort of staging/sequence for restart?

 

[TECMSC]

we would have a restart sequence to avoid overloading the electrical busses. I think it would take at least 4-5 minutes for the chillers to get back to 100% load.

 

[MintJulep]

Well, maybe not much refrigerant will migrate to the crankcase in 4 or 5 minutes, but if it did, 4 or 5 minutes is probably not going to be enough time for the heater to boil it off.

Do you have a suction accumulator?

 

[imok2]

As far as i can see this is a moot problem because if the oil temp drops the heaters must come on(UPS) other wise if the temp is ok the heaters will( should) be off, I'm assuming they have a stat control

 

[TECMSC]

mintjulep
I'd have to verify the accumulator-I think it would be integral to the chiller. also, if the heater came on as soon as the generators kicked in (15seconds?) then we shouldn't have a problem with oil migration to the crankcase (although we would still have a longer reboot time for the controller)

imok2
heater and controller are designed to be on UPS power. If the controller (not on UPS) needed to reboot after a power outage it adds time to the chiller restart sequence.

I appreciate your resopones and after thinking through this it seems to boil down to three isuses: 1. keeping refrigerant out of the oil(lesser problem due to short off time) and 2. chiller restart time which is more critical to operations and heater controller should be on UPS power, and 3. just to add one more: if the heater shorted to ground - the current could find its way to a breaker and shut down equipment.

considering #3, however unlikely, in order to ensure no ground fault effect to the UPS system it makes sense to design the heater on house power and controller on UPS power.