PDA

View Full Version : Very Low Discharge Temperature on Ciat water chiller



sputnique
05-09-2012, 08:53 PM
Hi guys

first time post so bear with me. I'm currently working fpr a French company on an Aquaciat Chiller with twin Copeland compressers. I found and repaired a leak on the low side so decided to empty all the system and recharge with the correct amount of R410. Everything went well, I got a good subcooling and superheat readings when the system was at full charge. When I reached operating temperatures, the system runs by alternating from one compresser to the other without ever having the two at the same time.

The whole circuit seems to be way too big for just the one compresser. The TXV has no way of downsizing to compensate nor can the evaporater although the condenser fan has a low speed and high speed cut-in.

The problem is, I've get a very low discharge temperature which is dangerously close to High side temperature readings. Am I running the risk of liquid slugging with such low discharge temperatures? Is there anyway I can raise the discharge temperature? The only thing I can think of is to increase the superheat but I'm reluctant to do this with just the one compresser ticking over.

Teuria
05-09-2012, 09:16 PM
Hi

You're talking about discharge temp and high side temp, if i'm getting it right you're talking about same thing , just with different names. Discharge = Highpressure side of compressor.

What are exact temperatures and pressures while running with one comp and what those are when running with two comps?

sputnique
05-09-2012, 09:49 PM
Sorry I meant the Hot gas discharge temperature. With one compresser running, I'm getting LP readings of around 43F / 125 psig and HP of about 95 to 105F / 295 to 340 psig. The hot gas temperature is only slighltly hotter at around 105 to 115F. The water Setpoint is 52.7F on the return pipe.

The trouble is that to get the 2 compressers running together I'd have to open the doors of the room that I am cooling. And I can't do that because it's in a very polluted part of a papermill with lots of corrosive and poisonous gases floating around. Which in turn eat their way through all types of electronic and mechanical equipment. I get to change evaporaters every 2 years if I'm lucky, every 6 months if I'm not.

Teuria
06-09-2012, 02:57 AM
Hi

What is suction superheat in that point?
Is your water side ok?
Have you measured leavingwater temp and returnwater temp?
How long compressor runs?

goshen
06-09-2012, 05:33 PM
Hi
you can try and change your hp setting ,is this an air cooled unit or water?
in both cases you can change the desierd hp setpoint and raise your pressure ,
good luck

Magoo
07-09-2012, 05:03 AM
Hi
agree with goshen, lift the SDT control setting, would seem the system is over designed with 11'C CHW control .

sputnique
09-09-2012, 07:54 PM
Thanks guys for taking the time to reply.

I have duly increased the HP setpoint by 14.5 psi and the fan kicks in a little later which has given me about 40 to 50F more hot gas temperature. I'll keep an eye on this as summer slowly turns to autumn.

Thanks once again for going to so much trouble for me.