# Centrifugal chillers

• 03-12-2012, 10:57 AM
Bittar
Centrifugal chillers
Dear colleagues.
This is my first contact with the group. I'm not an expert in refrigeration, I'm resorting to this group of professionals in order to clarify some doubts. My question is about centrifugal chillers.
When the compressor capacity is reduced (not by low thermal load but because the compressor is working at its limit with risk of harm), what happens with the process water?
Engineers say the delta T is maintained (the water enters at 17 ° C and exits at 10 ° C) and that the flow rate of process water is kept unchanged in 25m ³ / h.
This is the doubt: If the capacity of the centrifuge is reduced by the action of diffusers and / or vanes, thus reducing the circulating mass of R 134a, how can delta T be maintained without reduction of the water flow.
Someone could, please, help me understand this logic?

Many thanks

Paulo Bittar
• 03-12-2012, 12:28 PM
R123
Their wrong. If your chiller is being limited to protect the chiller, ie. current limit, evaporator limit, or condenser limit, than the capacity will be reduced and your leaving water temp will be running above setpoint. Unless they reduce flow. Either way, the tonnage will be reduced.
• 03-12-2012, 04:37 PM
spinning wheel
correct!
• 03-12-2012, 04:55 PM
HVAC Teacher
It can't.
If I'm interpreting what you're saying
Maintain delta T / reduce flow
Maintain flow / reduce delta T
What's with the reduced capacity?
• 03-12-2012, 05:03 PM
R123
Maintain delta T / reduce flow= reduced capacity
Maintain flow / reduce delta T= reduced capacity
• 03-12-2012, 05:06 PM
spinning wheel
correct as too reduced tonnage. sorry for the misunderstanding.
• 03-12-2012, 05:20 PM
HVAC Teacher
I'm with R123 (just can type faster)!

limiting is just that: reducing the work it's doing.
• 03-12-2012, 06:32 PM
Healey Nut
If its limited (whatever the reason) its not working as hard as it can . tonnage is reduced , leaving water temp will not be maintained . The chiller is limiting itself to try to stay on line , if the limiting condition fails to come under control the chiller will trip then you have zero tons .
• 03-12-2012, 07:22 PM
nique
How could you guys, of all people, engineers are always right!!!
• 03-29-2012, 07:30 AM
Bittar
Thank you all. The information confirms my position on this issue and allow me to solve a big problem. Thanks again for taking the time.

Paulo Bittar
• 03-29-2012, 01:39 PM
Russ57
Given that he states "process water" I wonder if there is a misunderstanding.

Could it be engineers are saying delta T and GPM will be maintained at all times even when running at greatly reduced capacity? Think CAT scan/MRI with a lot of hot gas bypass. Must stay on line regardless of (lack of) load and must maintain delta T and GPM.

We are talking what here?.....roughly 110 GPM @ 12.6 delta T? Not my idea of centrifugal size range.
• 04-21-2012, 11:40 AM
Jimmyhat 597
Just like a 10 ton roof top it can only do so much. Full load amps are reached and you are not making set point you have a load exceeding capacity. customer may say the chiller always handled load before start looking for other issues like Out side air dampers wide open... Had a 19DG doing 60 deg water in 48Deg out at full load amps (420) wanted to know what was wrong. Why could it not make 44? I started the 2nd chiller both went to 70% with 42Deg leaving. Sometimes you got to hook up a second horse or go slower with one