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View Full Version : Chilled Water A/C System.. antifreeze or no?







WangFu
25-07-2007, 10:38 AM
I am working with a chiller system that had antifreeze in it until I asked the boss what was in the system. He didn't know and had me drain the system and refill it with water and a corrosion preventative. The reason I asked was because I was told many years ago that antifreeze will ruin the system unless the chiller is coated. I have noticed a difference in the temperatures with plain water. Can anyone set me straight here? Does antifreeze retard heat transfer? Will it damage the copper in the system? I know its kinda late now, but for future reference Id like to know more. Thanks

The MG Pony
25-07-2007, 06:03 PM
Antifreeze will not appreciably effect the waters thermal transport ability and never have I heard that it damages copper? I may be wrong so hold off.

Lowrider
25-07-2007, 09:13 PM
Glycol will not damage the copper (not the one used in cars!!!) but will reduce the transfer of heat a little and will put a higher demand on the pomps since it increases the viscocity.

Where did you leave the antifreeze?

What temperature is the unit running on?

What's the frost protection set at?

Heater tape around the evaporator if the unit is outside? And setpoint at which outside temp to go on?

US Iceman
25-07-2007, 09:38 PM
The reason I asked was because I was told many years ago that antifreeze will ruin the system unless the Chiller (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=36) is coated.


I have personally seen this happen on a chiller, but the anti-freeze used at that time was an automotive brand, not a heat transfer fluid. No burst pipes or coils, just the coating problem on the chiller tubes which caused a flooding problem with the TXV's!

My first question is: why did the system have a glycol mix in it in the first place? Obviously, someone thought it necessary for some reason.

If that system has anything exposed to cold temperatures below freezing at any time, you find yourself in a precarious situation. If anything freezes and bursts I would not want to be the one to try to explain why the glycol mix was removed. Heat transfer improvement or not!

NH3LVR
25-07-2007, 09:52 PM
Another possibility for the use of Antifreeze in circulated water systems is to prevent biological growth.
IF memory serves. 20% Ethylene Glycol or 30% Propylene will keep the system from growth.
I may be a bit off on the numbers-it has been awhile.

WangFu
26-07-2007, 03:22 AM
I am just guessing here, but the antifreeze was most likley for two reasons. Corrosion protection and freeze protection. From time to time I hear stories of a chiller freezing and breaking tubes, ruining the refrigeration plant and contaminating the chilled water system. Being an AC system the outlet is generally about 45F and the low cutoff being at 42F. The system is aboard a containership so the possibility of the ambient dropping below freezing could be an issue depending on the location in question (say winter time in China during a drydock period where the system is left idle). Interestingly I believe I do have a terrible flooding problem that I cant seem to remedy. The charge is R-22 and the oil foams constantly. Id love to know how to rectify that, I have tried setting the superheat the way I would on a direct expansion system but it didn't solve the flooding. Thanks for the input so far! Just for more info the heat exchanger is remote, about 500' of horizontal and another 50-60' vertical via 6" pipe. There are 2 chillers each with their own 5H60 and circ pump, but the remote is a common line splitting into 2 heat exchangers for cold duct. Hot duct is steam heat exchanger reheating the chilled air. As for where the antifreeze went... the boss can explain that one. I have no comment.

US Iceman
26-07-2007, 03:53 AM
Interestingly I believe I do have a terrible flooding problem that I cant seem to remedy. The charge is R-22 and the oil foams constantly.


That sounds awful familiar to me. That's the same problem I encountered. Now that the glycol has been drained and the system is simply circulating water, has the flooding problem decreased?

Are the compressors above the chiller, or below?

And, do they operate at partial load for long periods of time and then suddenly load up for short periods?




Id love to know how to rectify that, I have tried setting the superheat the way I would on a direct expansion system but it didn't solve the Flooding (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=179).


If this unit is direct expansion, then there is only one way to set the evaporator superheat.

WangFu
26-07-2007, 08:50 PM
That sounds awful familiar to me. That's the same problem I encountered. Now that the glycol has been drained and the system is simply circulating water, has the flooding problem decreased?

Are the compressors above the chiller, or below?

And, do they operate at partial load for long periods of time and then suddenly load up for short periods?




If this unit is direct expansion, then there is only one way to set the evaporator superheat.


I cant say the flooding has decreased any, the oil foaming is of course the worrisome aspect and the more disturbing signal. It may be a bit less but its hard to say absolutely yes.

The compressors are located directly beneath the chillers, with the condensers located above both (shell and tube water cooled).

The system load doesn't fluctuate back and forth radically. On a typical voyage the load increases and stays heavy throughout the tropics and then drops off gradually as we return to the cooler waters.
Having said that there are times when the unloaders work back and forth a bit trying to maintain the suction pressure, but the foaming exists all times that the compressor is running.

As far as the superheat goes, maybe I need to focus myself better on what is going on. On smaller systems without capacity control I just look at the pressure and temp to get my superheat. With this one I am looking at the suction which varies with the unloader and the temp which varies much, much slower in response to it.

US Iceman
26-07-2007, 09:25 PM
The reason I asked about the unloading is I have seen some DX chillers running for long periods at part load. Then when the compressors load up, there has been some tendency for some liquid refrigerant (that seems to lay in the bottom of the chiller) suddenly start to boil violently then jump out of the chiller, back to the compressor.

From your description it sounds like the problem is almost continuous instead of intermittent.

To confirm you actually have flooding, check you discharge superheat. If the actual discharge temperature is close to the actual condensing temperature, then you probably have some liquid carryover.

If the discharge temperature is relatively higher than the condensing temperature, the likelihood of liquid carryover is much smaller.

WangFu
27-07-2007, 02:58 AM
The compressors are located directly beneath the chillers, with the condensers located above both (shell and tube water cooled).


I mis-spoke here the chiller is side by side with the compressor but the suction line is elevated a good 36". Not impossible for very large carryover but I wouldn't rule it out. I didn't mention that there are external oil coolers which use system liquid and dump right back to the suction just before the service valve, they are operated on a thermostat/solenoid valve. I can see when they are energized because the thermostat has an LED. The only subjective difference is the suction valve gets colder, suction pressure rises and the chiller outlet temp rises. The oil foaming issue doesn't change. Maybe Im making too much of the oil foaming, but Carrier made a strong impression on me about the do's and don'ts. I have replaced several broken suction discs on one unit already and I have to say it is an awfully hot spot to work (140F+) and Id prefer to avoid that job again.

I don't know the nature of the antifreeze mixture that was in the system (automotive or otherwise) I can only say it looked and smelled like what I use in a car. In the situation you are familiar with, were the chillers permanently damaged or did everthing work out after replacing with water?

Thanks for all your input so far... Ill be out of touch while we make our next crossing, but I'll check back in about a week

US Iceman
27-07-2007, 03:46 AM
I didn't mention that there are external oil coolers which use system liquid and dump right back to the suction just before the Service Valve (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=94), they are operated on a thermostat/Solenoid Valve (http://www.refrigeration-engineer.com/forums/glossary.php?do=viewglossary&term=96).


Now that's very interesting. That might be source of the liquid causing the oil foaming! Refrigerant cooled oil coolers could cause some overfeeding if the TXV's act up, or are not set right, or if the liquid solenoids energize to early.

If suction valves have been breaking that's almost always due to liquid refrigerant.



In the situation you are familiar with, were the chillers permanently damaged or did everything work out after replacing with water?


The chillers were not damaged, because they did not freeze up. However, they were an absolute mess because we found the automotive antifreeze had coated the outside of the tubes. We used a mild detergent and warm water circulated through the system piping (water side!) to clean this up. And a repeated rinse with clean water.

After all that, we pre-mixed the proper glycol (we used Dow SR-1) and then pumped that into the water piping until the system was full. Then let the pumps run for a day or so to ensure the mixture was well mixed. (you need to monitor the glycol temperature when running like this to make sure it does not get to hot!)

After this, we then re-started the refrigeration system.

The whole system had to be re-commissioned, but afterwards, it worked just like it was supposed to.

I learned more about water chillers on this and one other project job that made me appreciate all of the little details and the things that can and do go wrong!

TXiceman
27-07-2007, 04:01 AM
The glycol systems are very much effected by the glycol/brine concentration. I have been on several systems designed to run on 25 to 30% by weight glycol. Over a period of time, the customer added glycol which happened to be 50% by weight. At temperatures below about 25 dF, it may take as much as 30% more heat transfer surface to achieve the same temperature drop across the chiller. As the concentration goes heavier and the temperature goes down, the heat transfer coefficient drop like a rock on propylene and ethylene glycol.

Ethylene glycol is a poison and much not be spilled or put down a sewer. This is like normal auto antifreeze. Propylene glycol is not so toxic and is pretty safe.

A lot of times a owner will run a 10 to 15% propylene glycol mixture for the corrosion inhibitors. PG and EG can be run is normal copper tube and steel exchangers.

Some trade names for these glycols are Dow Therm and Dow Frost in the Dow Chemical products.

Yes if you are running above freezing and switch to plain water, you will see an improvement in heat transfer. All low temperature heat transfer fluids do decrease the heat transfer in an exchanger. So MGpony, you need to review your statement and look at the heat transfer data on glycols.

Ken

NH3LVR
27-07-2007, 04:44 AM
The glycol systems are very much effected by the glycol/brine concentration. I have been on several systems designed to run on 25 to 30% by weight glycol. Over a period of time, the customer added glycol which happened to be 50% by weight. At temperatures below about 25 dF, it may take as much as 30% more heat transfer surface to achieve the same temperature drop across the chiller. As the concentration goes heavier and the temperature goes down, the heat transfer coefficient drop like a rock on propylene and ethylene glycol.
I saw this illustrated once in a plant blowing plastic bottles. The Glycol was automotive antifreeze.
When I arrived the suction pressure was down as well as production.
My clue was that the glycol solution was very green.
When I quizzed the operator he admitted that he had added antifreeze just before the problem occurred. We put a hose in the tank and added 20 gallons of water. The system started operating normally almost immediately.

mohamed khamis
27-07-2007, 11:57 AM
I mis-spoke here the chiller is side by side with the compressor but the suction line is elevated a good 36". Not impossible for very large carryover but I wouldn't rule it out. I didn't mention that there are external oil coolers which use system liquid and dump right back to the suction just before the service valve, they are operated on a thermostat/solenoid valve. I can see when they are energized because the thermostat has an LED. The only subjective difference is the suction valve gets colder, suction pressure rises and the chiller outlet temp rises. The oil foaming issue doesn't change. Maybe Im making too much of the oil foaming, but Carrier made a strong impression on me about the do's and don'ts. I have replaced several broken suction discs on one unit already and I have to say it is an awfully hot spot to work (140F+) and Id prefer to avoid that job again.

Hi Wangfu

As i understand you are asking about two things oil foaming and using or not using of anti-freezing agents:

Regarding to oil Foam:

As u mentioned "the suction valve gets colder, suction pressure rises and the chiller outlet temp rises and u replaced several broken suction discs on one unit" all of that indicates flooding problem and this due to the external oil cooler as US iceman mentioned.

It may be the amount of refrigerant liquid is larger than required to cool the oil and hence there still amount of liquid have been not boiled off and enters the suction pipe in a liquid form. So it is better to install throttle valve before the solenoid valve to decrease the amount of refrigerant liquid.

Otherwise install accumulator in the suction side before the compressor to protect it from the flooding. This problem is typically as the starting-up of refrigeration unit after defrost cycling.

regarding to anti-freezing agents

As our fellows said the adding of glycols deteriorates the water heat transfer coefficient as a result of lowering the thermal conductivity and specific heat capacity of the water. However, as my knowledge the propylene glycol is non -corrosive and no-electrolytic solution.

Cheers:)

brian_chapin
27-07-2007, 02:56 PM
Yes if you are running above freezing and switch to plain water, you will see an improvement in heat transfer. All low temperature heat transfer fluids do decrease the heat transfer in an exchanger.

Very true - one other thing to worry about though when switching to plain water...

I had an experience where a plant running for 8 years on a dowfrost system decided it was too expensive and moved to plain water.

I think we went through about a dozen heat exchangers before they switched back. Some sort of buildup in the pipes broke free when they switched to water - it looked a lot like rusted coal chips kept filling up the heat exchangers. Within a week of converting back to dowfrost they problem went away.

Of course, all this piping was sch40 black pipe which might be the whole problem.

wkd
01-08-2007, 09:40 PM
You will see thermal performance changes from GLycol to water ,Glycol density is higher that water and the specific heat changes from 4.19 for water to approx 3.7 for 30% solution.Correct glycol type should not affect the components.
Have you tried seeing what happens when you turn the oil coolers off does the superheat control regain operation.How are the oil coolers regulated TEV etc it may be these are flooding the oil cooler and dumping liquid into the suction as you described giving you a red herring.If the superheat is correct and the discharge superheat indicates no flooding ,as one member suggest,and the oil coolers are not causing the problem have a look at the oil is it the correct type? has it been contaminated?Lastly for this post check the refrigerant has this been contaminated I have had serious problems with superheat control when someone filled a small mix of R22 with R407C.You could leave the unit to stand and chek pressure and temp to see if they match the refrig tables this will tell you if the frig is contaminated with non-condesables or a mix.Happy hunting sounds like an interesting problem.

WangFu
09-08-2007, 07:46 AM
Thank you for all the great feedback! I am now clear on the antifreeze issue. We are not using plain water, but a mix of water and a product called Nalcool2000 which is a corrosion inhibitor. Probably not as good as the products suggested.

My problem with oil foam does not seem to be a superheat issue, and my oil coolers are regulated by a TEV. I am pretty sure I have it nailed down to oil problems. I drained one compressor and popped off the sump to have a look inside. I found some valve plate bits holding the oil return reeds open and blocking oil return. I managed to get 8 gallons of lubricant out of a system that should have had no more than 3 gallons in it. I now have both of the units running a bit low on oil so I can see if any more oil returns to the crankcase. BTW the bits were not in the compressor I worked on before :D

The oil we have been using is a mineral based WF-68. I don't think there is a compatibility problem with the oil and R-22.

As for the broken valve discs I am not sure if the problem was too much oil, flooding, slugging or a combination. I have corrected the oil problem and the flooding is no longer an issue. The only thing that could be an issue is if the units cycle off on low temp protection or high pressure cut out, since both conditions will stop the compressor without first pumping down and causing it to slug on restart.


Thanks!

mohamed khamis
09-08-2007, 10:36 AM
The only thing that could be an issue is if the units cycle off on low temp protection or high pressure cut out, since both conditions will stop the compressor without first pumping down and causing it to slug on restart.

Thanks!

This is Occasional condition but if it is pretty frequent it is better to install a accumulator in suction line to mitigate the surge of the liquid flooding into compressor.

Cheers