Carrier 19XR Tower Water Control

[jogas]

We're having surge problems with a 300 ton 19XR. I was told that the tower water needs to be reset according to load. We don't get actual demand as an input to the BAS system, so I'm using evap temp drop.
I've programmed the following reset:
3* (min) Evap Delta T = 65* tower water set point
12* (design) DT = 85* tower water temp set point
Does this sound like I'm on the right track?
TIA,
jogas

[Carrene #2]

That may work for ya. Not ever done it that way before.
How about % motor current, as the basis for reset?

[jogas]

That may work for ya. Not ever done it that way before.
How about % motor current, as the basis for reset?

I don't think we get % amps into the BAS system either.
Is this reset strategy/setpoints correct for this chiller?
jogas

[CaptJackSparrow]

I would also like to see some guidlines to contol tower water temp on Trane VFD chillers with generic BAS as well. I think Tracer Summit has a canned program for this but is there any Trane publised condenser water temps at a given load or is it based on reducing Delta t between chill water and condeser water temp to reduce overall lift at reduced load. What does York base cwt on?

[Randy S.]

I hope your set points are adjustable.

[jogas]

I would also like to see some guidlines to contol tower water temp on Trane VFD chillers with generic BAS as well. I think Tracer Summit has a canned program for this but is there any Trane publised condenser water temps at a given load or is it based on reducing Delta t between chill water and condeser water temp to reduce overall lift at reduced load. What does York base cwt on?

I was wondering the same thing.
Load driven reset verses a CHW (Evap Pressure correlation) / CWT (Condensor Pressure correlation) reset. Yeah, it would have to be constant volume, which this 19XR is.
But.....at least on this 19XR, CHW delta always equals CWT delta.
Lastly, on this 19XR, discharge pressure drives the oil return eductor, so proper head pressure is important.
I'm hoping some Carrier 19XR Guru's will chime in on this.
jogas

[jogas]

I hope your set points are adjustable.

I hope you can give us a complete, insightfull contribution to this discussion
Are you saying the reset set points are wrong?
Or will they have to be changed on a regular basis?
jogas

[slb8101]

I hope you can give us a complete, insightfull contribution to this discussion
Are you saying the reset set points are wrong?
Or will they have to be changed on a regular basis?
jogas

If the machine is a 19XRV set the tower control to maintain 20 degrees above chilled water setpoint. If the machine is a fixed speed machine what I have found that setting the tower control to maintain a condenser water at 68 to 72 degrees entering the machine works well, have you thought about letting the PIC control the tower water through the ISM and settings on the PIC. The ISM control outputs a 4-20ma signal to operate a valve or a VSD on the tower.

[apprentice3yr]

Are you not suppose to keep your 10,10,10 rule so you maintain your 60-70 degree lift ?

[jogas]

If the machine is a 19XRV set the tower control to maintain 20 degrees above chilled water setpoint. If the machine is a fixed speed machine what I have found that setting the tower control to maintain a condenser water at 68 to 72 degrees entering the machine works well, have you thought about letting the PIC control the tower water through the ISM and settings on the PIC. The ISM control outputs a 4-20ma signal to operate a valve or a VSD on the tower.

Thanks for the reply.
It is a fixed speed machine. We've tried fixed set points 72*-78* and still had surge problems. The machine has a fixed 44* CHWS set point. So it should be a constant 64* tower water set point? That seems low, doesn't it?
Also, what is the 10-10-10 rule?
jogas

[slb8101]

Thanks for the reply.
It is a fixed speed machine. We've tried fixed set points 72*-78* and still had surge problems. The machine has a fixed 44* CHWS set point. So it should be a constant 64* tower water set point? That seems low, doesn't it?
Also, what is the 10-10-10 rule?
jogas

The twenty degree rule is for the varable speed machines, normally 72-78 degree tower water with a fixed setpoint you should not have a surging problem. Iwould be looking at the cleanliness of the tubes both cooler and condenser, refrigerant charge,linear float metering device. possibly air in the machine from the factory i saw a few of those machines slip out of the factory with non condensibles still left in the system.

[slb8101]

The twenty degree rule is for the varable speed machines, normally 72-78 degree tower water with a fixed setpoint you should not have a surging problem. Iwould be looking at the cleanliness of the tubes both cooler and condenser, refrigerant charge,linear float metering device. possibly air in the machine from the factory i saw a few of those machines slip out of the factory with non condensibles still left in the system.

Iwould also check water flows across both barrells to see if they are within design criteria and any head pressure control valves or tower bypass valves. I hope this helps as for the 10 -10 -10 rule I do not know.

[apprentice3yr]

Sorry I thought the 10 10 10 rule of thumb was universal in a way. Here's what the 10 10 10 rule is by example:

It's basically your approach

cooler approach is 10* : SST 35* H2O OUT 45* H20 IN 55* = DELTA T OF 10* SO THE 10 10 10 RULE IN AFFECT
condensor approach is 10*: SCT 95* H2O OUT 85* H20 IN 75* = DELTA T OF 10* SO THE 10 10 10 RULE IN AFFECT
lift from the SST - SCT : SST 35* - SCT 95* = 60* DELTA T OF 60*

So a surge is a momentary reversal of flow due to exceeding your lift.
plus whats your cooler, condensor, and tower approach because that will tell you alot about what's going on to right ?