View Full Version : How low can you go?(cond temp)
07-02-2006, 10:27 AM
How low can the entering condenser water temp be on a Carrier 19xl-R134A. It seems like 65 deg is the most efficient- .56 Kw/ton( above 70%). My boss thinks thats too cold. He likes 72 deg. The startup manual said the leaving cond water temp should be 20 deg above the leaving chilled water temp. Is that correct? Our leaving chilled water temp is 45 deg, so 65 deg leaving cond water temp? That would put our entering temp at 56-57 deg. Thanks
07-04-2006, 06:16 PM
Take another look at the manual & you will see its the "entering condenser water" that can be within 20* of the leaving chilled water temperature.
So if your leaving chilled water is 45 then 65 condenser water is ideal.
Lowering the condenser water temp is no joke, its serious energy savings.
The pressure difference between the cooler & the condenser is the amount of lift, in some cases you can reduce the lift by as much as 50%!
Thats cutting the compressors work in half.
And in case anyone wants to inform you that running the towers hard like that burns up alot of energy so it isn't worth the trouble, believe me when I tell you that one or two tower fans wound out is small potatos compared to the motor on a chiller.
If you were to put a drive on that machine you could run the condenser water down even further.
One more thing, IOM's are full of information & usually you can find out anything you need to about the operation of a given machine.
Alot of statements are very "matter of fact" & often there is no deep explanation or example to go with certain specifications but, if its in there, you can bank on it.
07-04-2006, 07:12 PM
You go there chiller mekanik!!!!!!!!! Maybe if enough of us preach "cooling tower relief" enough, everyboby will start believing it!!!!!!!!
07-04-2006, 10:14 PM
You said 70%, that must be motor amps and not speed? ( 19xl )
It make a diff if it's got a vfd 19xrv. just asking?
At 70% motor and you can keep your water at 65*-cool and your boss should'nt be your boss.
07-05-2006, 01:14 AM
Yes, it is motor amps. I trended the kw/ton at 70 deg condenser water entering and at 65 deg(above 70% amps). The chiller runs at .56 kw/ton at 65 and .62 kw/ton at 70. I measure the difference it took to get cond water down to 65 deg, which was 90% tower speed, up from 70%. It uses 10 more amps for that 20% speed increase. I figured 50 amps saved at the more efficient cond temp. So we could save roughly 40 amps by operating at 65 deg entering. I took this to my boss and he said I'm nuts. 65 is too cold or at least thats what the Carrier tech said. I told him there was some pretty smart guys on here that say its ok, but he wants to go with what our tech is telling him. Oh well, his bonus is tied to our utilities consumption, not mine!
07-05-2006, 09:50 PM
One must be careful when lowering condenser temps to acheive savings, you may wind up with a load of nuisence trips and oil problems. The 19 should not be a problem, but not all chillers like the colder tower water.
I always go as far as the machine will let me without the trips.
07-05-2006, 10:25 PM
See if you can get your hands on the original design specs for that chiller. All manufacturers have computer print outs for all large tonnage machines for full and several part load conditions. All of them I've seen from Carrier have 65 dgree tower water at 65 % load. This is true for both fixed and variable speed machines. Note, " %load isn't neccessarily the same as % amp draw, as you've already found, when you have cooling tower relief. If you can get the specs. you can show your boss and the service tech what the Carrier engineers say.
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