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zolimer
03-04-2008, 04:33 AM
We have a 1400 ton falling film chiller(Turbo) that we want to run @ 28 degrees. Our tank normally holds 44 k gallons(54,000 max). We are using 40% glycol. What would the ratio be to run with minimal icing? Water is the secondary refrigerant. Please include the math. Thanks Tim,

gwapa
06-04-2008, 01:46 AM
Hello Tim
Could you be a little more precise ? I would like to know:

Do you want to run the chiller at 28°F outlet temperature
Do you want to have ice but not to much or you donīt want to have ice at all?
are you usin 40% glycol and 60% water plus inhibitors?
With the glycol are you cooling water as second refrigerant?Regards
Gwapa

zolimer
08-04-2008, 12:28 AM
Hello gwapa, Thank you for taking the time to respond! The answer to questions one is yes., Two, ice is ok, as long flow stays in the chiller and out of the drain. Excessive is ice build up on the coil is causing water to flow out of the unit and into the drain. As far as inhibitors in the glycol mix, not that i know of. We are using Dowfrost 40 type glycol. I guess the mix of glycol and water would be the secondary refrigerant. Thanks Tim,

zolimer
08-04-2008, 03:27 AM
To clear things up, I am adding 40% glycol(Dowfrost 40) to 44,000 gallons of pure water! Thanks Tim,

US Iceman
08-04-2008, 05:05 AM
HI Tim,

I wanted to follow this thread for awhile before commenting and asking questions.


Is the 28°F temperature you want the evaporating temperature or the chilled fluid (water or glycol mix) temperature? I'm assuming chilled fluid temp. from your reply to gwapa.
Does the return chilled fluid flow directly over the plates in the cabinets or is the return fluid drawn from another tank and then pumped over the plates?
If you want a 28°F chilled fluid temperature, what evaporating temperature are you running? Probably a lot lower to get the total cooling capacity you need since it appears this was originally designed by Turbo to cool water only. Please correct me if I guessed wrong.
Have you talked to Turbo about this?
And if so, what recommendations did they provide to you?

zolimer
08-04-2008, 11:05 PM
Hello US Iceman, Yes we are going for a 28 degree fluid temp. The fluid is recirculated between the chiller and storage tank until the chilled fluid is called for from the process tanks. At that point the circuit works like this. Process tank to chiller to storage tank.

On a side note the turbo chiller does a good job of keeping up with the demand as we had this shut down over easter weekend for three days and it took one hour to pull the storage tank water from 60 degrees to 33 degrees, i was impressed!

Our evaporating psig has been 42 we are running at around 31.8 degrees. So far we have added 1040 gallons of 40% glycol with about the same amount of freezing on the coil.

I have not talked to Turbo, Although that may not be a bad idea! We are trying to increase capacity in this experiment. And the reason i ask this question is that if it is going to take 5000 gallons of glycol to 44,000 gallons of water it may not be worth the effort!

Is there a chart that i could use to determine the ratio to lower the freezing point of water by 4 degrees?

frank
09-04-2008, 01:16 PM
Is there a chart that i could use to determine the ratio to lower the freezing point of water by 4 degrees?

http://www.chemistrystore.com/ChemicalMSDS/Dowfrost.pdf

US Iceman
09-04-2008, 03:13 PM
Hi zolimer,

Adding glycol has some negative effects besides the initial cost of the glycol. People tend to add a lot more glycol than what they need, so it is important to define whether the glycol requirements is for freeze protection or burst protection.

Secondly, the glycol percentage will change the mixed fluid properties (specific heat, specific gravity, viscosity, etc). This can affect the heat transfer (usually lower with more pump horsepower). This also affects the heat exchangers where the glycol is pumped to.

Before you purchase a lot of expensive glycol my recommendation would to ask Turbo for help in re-rating the plate sections to see if you can actually get what you hope to achieve.

zolimer
14-04-2008, 03:30 PM
Frank, Thanks for the link! US Iceman, I think we are going to scrap the glycol approach. These chillers are not needed 24-7, If we can effectively communicate with the
people inside the plant, when they are done with the tanks we can raise the back pressure for a few hours a day. Its a little more work, but the best approach. Thanks for the help! Tim,

US Iceman
14-04-2008, 03:40 PM
If you have a back-pressure regulator on the suction line, you might also change the module to a dual pressure regulator. Then you can run the lower pressure during plant operation and by flipping a switch go to the higher pressure setting.

zolimer
21-04-2008, 05:49 AM
Hello, i would like to clear something up and it may not be a big deal, but i was looking at the paper work that came with the Chillers and found out that they are 496 ton. (1400 gpm)

US Iceman, We do have dual pilot regulators, with moa switches., when we increase suction pressure, we are in a no load state! In my experience, We would have to defrost for 24 hours with no intervention at all to remove all of the ice!

I checked the calibration of the temp sensors and they were dead on! I wish that there was a hot gas coil built into the feed header to put a load on these things during the few hours that we can shut them down! Thanks,

US Iceman
21-04-2008, 03:18 PM
Well, if they have dual pressure regulators why not make them automatic instead of using the manual/off/on/automatic switch?

When the process load shuts off, turn off the liquid feed (liquid solenoid valve) and let the pressure rise to the higher setting. If the higher setting is above the freezing point of water, the ice should not form at all (unless the normal operating suction pressure is so low that ice forms on the plates anyway).

Once the pressure rises to above freezing the boiling should stop and no ice should form. Yeah, hot gas would make it happen sooner.

Jim Denkmann
16-05-2008, 01:55 AM
What type of glycol are you using? Ethylene or propylene? Glad to help - if 40 F and propylene, your % is ~30 which will take you to 9 F evaporating temperature before crystallization.

zolimer
21-05-2008, 04:20 AM
Iceman, I dont want to seem like a fair weather friend. I have been working crazy hours( we had a guy quit) while preparing for the refrig. 1 course at Lanier Tech in the the first week in june. I will also be taking the RETA CARO exam on the last day, so my plate is very full! We do have a dual pilot setup with MOA switches. Here is the problem, The piping is oversized and we have had some low pressure pilot failure's i.e.... broken springs. We have been running off of the high pressure pilots and what we have been doing lately is turning off the liquid feed to the surge drum until the secondary refrigerant(water) reaches a temperature that will put a load on it. Then turn on the liquid feed and raise the pressure to quickly defrost the plates and the feed header! Not an ideal situation, but we have to make it work until we find a solution. The surge drums do have safety relief valves on them that feed back into the suction header, so no environmental concerns, but i would like to see this setup work as it was designed!
instead of baby sitting this small component of a very large system.

Jim, Thank you for responding! We are starting to get away from the idea of using glycol at this point in time! The reason being the once every two month's all of the water in the storage tank gets dumped to clean the tanks. We are getting to a point where we can manage this, although not ideally!

US Iceman
21-05-2008, 04:41 AM
Not a problem... I know it's getting to be that time of year again where the schedules go crazy. Having someone quite just compounds everything else.

It sounds like you just need to get a few days where you can think straight. My first impression is that you are pushing these plates very hard to do an increased capacity (by running at a lower suction pressure). As a result you have some ice formation.

I really think there is a little more to this solution, but at least you have some ideas for consideration until you can get some time to spend on this.

Let me know when, and we'll try to help.

zolimer
25-05-2008, 05:39 PM
Ok, Here it is, We are pushing this equipment too hard. I have been under the impression that when you set suction pressure, that you have to compensate for superheat which is true with an direct expansion evaporator! I have learned since that this compensation is not necessary in a flooded evaporator? Correct me if i am wrong here, please, I may be wrong for all i know! We are running at 42 psig, which is 28 degrees F. I adjusted the suction regulator to 44 psig, which raises the temperature 1 degree F. I have found my ice build problem to be considerably more manageable. I will just have too find the magic number and tweak accordingly! If any body sees a flaw in my line of thought, let me know! I am here to learn!

US Iceman
25-05-2008, 09:48 PM
Gravity flooded or liquid overfeed should have zero degrees of suction superheat. Otherwise you are loosing capacity on the plates.

44 psig should be OK as long as you don't experience any low water flow situations. Otherwise the low flow will allow the ice to begin freezing on the plates. At a higher flow closer to whatever the design flow rate is you might see some ice on the tubing or headers, but the plates should be clear of ice.

If you raise the evaporator pressure you change the temperature differential between water and the plates so the total plate cooling capacity will go down slightly.

At the same time by raising the evaporator pressure the compressor suction pressure should be able to rise just a bit. All of this depends on how your system is set up though.

zolimer
30-05-2008, 05:00 AM
At a higher flow closer to whatever the design flow rate is you might see some ice on the tubing or headers, but the plates should be clear of ice.

Iceman, You Know your stuff! This is exactly what we have been experiencing lately, and somewhat easy to manage now! This has been one heck of a learning experience, and your help is greatly appreciated! This site and its members are a great blessing to our trade!

US Iceman
06-06-2008, 03:20 PM
Just think how much fun this used to be before the internet. Then you were limited to only yourself and the installing contractor (and maybe the manufacturer).:D

Glad to be able to help.