Regulating cold tower water

[atsnc]

A customer of ours has twin York Chillers YCWS0140 and BAC towers VT0-132-LD. The System orginally had Trane Chillers until lightning had its way with them. The system was using an economiser system which would use tower water under 45 degrees, through a heat exchanger to provide cooling. The heat exchanger system from what I was told never really worked that well and they abandoned it when the chillers were changed and had a controls upfit.
The problem is now when the water gets below 70 degrees the chillers lock ou on low oil pressure differential due to the pressures running too low. I think the Trane systems used hot gas bypass to eliviate this. The Yorks don't have HGBP.
My question is what is the best way to control the low end tower water temp to control head pressure? HGBP? Condenser water valve with head pressure control? Recirculation loop? Thanks

[hvac_czar]

Modulate tower dampers/ spray pumps/ fans?

[ZeroCool]

I think the best way is a tower bypass, but if you don't have one it's an expensive change. Usually the easiest is to add a HPCV on the leaving side of the chiller. Most have a main valve with a smaller in bypass across the larger for greater control purposes. If you have the plate frame you should still economize, there really is no reason to turn your back on free cooling if its available unless you have some special requirements. The chiller should be off until around 50-55 deg. OAT.

[atsnc]

The problem is the Chiller spec's says it is to have 70-75 degree water for condenser cooling. Anything under that and it makes problems.

[gonefishing]

Maybe a VFD on Tower Fan?


Regards........

[hvac3901]

agree with gonefishing, look for a way to modulate the tower capacity.

[maxster]

how about piping hot water to the heat X and heating up the tower troth to say 70f the other way,or limit the chiller on start-up(slow load up)and let it heat the water with the tower fan off till 75F-85F for the winter.

[pennycuff]

diverting valve, requires repiping and adding the modulating valve, controller, wells,etc installed on a couple of 23xl carriers took care of problems

[jogas]

The tower fan control should be set above 75* so it should be off, A tower bypass is good but pricey. It is only good if you've got a load(enough heat to keep the tower water warm). We've got a 400 ton screw with a condensor water holdback valve on the condensor outlet. If you go that route, don't forget to set it so the valve can only close 75-80%, always keeping a little flow thru the condensor. Ours is controlled off of discharge pressure.
Jogas

[pennycuff]

jogas is correct on all factors, i believe either option is your answer

[Shophound]

We have the whole shootin' match at our facility; towers with sump heaters, VFD drives for the fans, and tower water bypass on a PID loop tied to our Metasys. We were down to 15 degrees outdoor ambient last week and the one 19XR chiller online didn't miss a beat. Chiller has to run 24/7/365 due to nature of facility.

During low ambients the VFD's will ramp down to 20 HZ (minimum) and the bypass takes over from there...have yet to see it go beyond 50% bypass...there's a decent load on the chiller even in winter. Chilly mornings make for cool looking clouds wafting up from the plant's towers.

[atsnc]

Yes the fan is set to come on at 80. The low temp is the one we are having the problem controlling. Looking at the book from the old chillers the only thing I saw that was quite different, was that the Tranes had hot gas bypass. I didn't see any type of water contol valves in the prints or in the unit documentation. Maybe it didn't cause any problems with those chillers. I wouldn't think that HGBP would be a good choice of control for this problem????

[codewriter]

VFD on the open loop pump, and program properly.

or

As jogas mentioned.


Not knowing the price of jogas's idea I dont know which would be easier/cost effective.

[Edited by codewriter on 12-16-2005 at 11:19 PM]

[kwillmech]

what is evap tonnage at your lowest load conditions when you're having problems with the cold cond water?

[RichardL]

Methinks many did not read this post that well..
The chiller in question does not run 24/7..
His problem is occurring when he comes out of economizer and goes to mechanical cooling with 45°f tower water or so and trying to get chiller to run....
Once the chiller has been on for a while and tower water temperature has moderated, he should have no problem..
What good is a VSD or Diverting valve when the Supply water from the tower is 45°f?????
Install a Head-pressure controller and stop the tower water from circulating thru the condenser at all until a livable temperature is reached on the supply condenser water...
Hot gas by-pass won't do much if Ya' ain't got no hot gas to start with...

[atsnc]

RichardL is correct in that the economiser has never worked properly due to the 45 degrees from when the economiser shuts off and the 75 degrees needed to operate the chiller. The fans are not running at this time and the water is just circulating through the tower. What has to be done to get through this period is to regulate the water flow through the condenser manually to keep the pressures up. Once the water temp comes up the valve can be opened fully. Is there a valve made that has a head pressure controller on it. That would work as long as it could regulate automatically. It could be installed in place of the flanged butterfly valves. Any ideas?

[kwillmech]

Trane markets one for the RTHC/RThd chillers. not sure who makes it though.

[gonefishing]

Might check this one. They offer a lot of different styles as well as control optiions.


http://customer.honeywell.com/Techlit/Pdf/63-0000s/63-2557.pdf


Regards........

[RichardL]

JCI makes a fine sensor that will modulate your existing butterfly valves along with the installation of a wonderful JCI pnuematic operator..
Ya'll see how I pushing the new owners of my company...
It's called "Sucking Up" in some circles...
If a promotion is in order...I don't wanna' move to Milwaukee...Them people up there don't live....They just try to Survive.....brrrrrrrrrrrrrrrrr....

[atsnc]

This valve option would be easily installed but I would have to come up with a way to convert the head pressure signal to the valve electrically. You guys are awesome!

[atsnc]

RichardL, I see by your profile you are a York Guy. We shouldn't hold that against you though..... The Commercial Chiller Rep in my area is not doing York any favors. Can't no straight answers at all.

A side note on these York Chillers. I have one compressor that shows the slide valve as unloaded but is loading the compressor until it trips out on high amps. I tried to find info on the slide valve operation, but can't find anyone willing to give me info. Do you know where I can get it?

[gonefishing]

Not being brand specific, just trying to help.

Selection Electronic
http://www.johnsoncontrols.com/cg-valves/selection_guide/publ3449.pdf

Selection Pneumatic
http://www.johnsoncontrols.com/cg-valves/selection_guide/publ3450.pdf

I'm sure Richard can help with the appropriate Pressure tranducer, either electronic or pneumatic.

Regards.............

[RichardL]

I would say that your compressor is running with the slide
I have tried substituting the vane position pot with a more substantial pot(Heavier Duty) but the vibbbbbrrrraaatttiiiooon.....at that point and the sheer weight of anything heavier that that used originally...
You can load and unload the compressors slide valve without running the compressor by connecting the test ports on the slide valve housing with your trusty charging manifold
& hand oil pump...You can select load & unload either from the micro-panel or by pushing the load/unload solenoid valve(s)

[atsnc]

Where can I get info regarding the slide valve. I have heard that getting the pot set properly can be difficult. Any assistance would be truly appreciated. The compressor is a DSX24LASB17 sn VBMX100328.

[jogas]

Originally posted by atsnc
A customer of ours has twin York Chillers YCWS0140 and BAC towers VT0-132-LD. The System orginally had Trane Chillers until lightning had its way with them. The system was using an economiser system which would use tower water under 45 degrees, through a heat exchanger to provide cooling. The heat exchanger system from what I was told never really worked that well and they abandoned it when the chillers were changed and had a controls upfit.
The problem is now when the water gets below 70 degrees the chillers lock ou on low oil pressure differential due to the pressures running too low. I think the Trane systems used hot gas bypass to eliviate this. The Yorks don't have HGBP.
My question is what is the best way to control the low end tower water temp to control head pressure? HGBP? Condenser water valve with head pressure control? Recirculation loop? Thanks

As I understand this post, the tower water used to be used in an economizer function with a heat exchanger (probably plate frame style) under 45* that was abandoned.
This means he has to use the chiller (and the tower water in heat rejection mode) all the time, including below 45* to satisfy the load.
Why can't that load (heat) be enough to keep the tower water warm if the chiller is running from above 45* down below 45*? I'm ASSuming he has an indoor sump. The tower water cannot get below 45* if he's no longer using the water side economizer.
Jogas