Issues Chilling Brites - Glycol Mixture?

[freysbrewing]

We built our own glycol chilling system and wrapped two, non-jacketed, 800L (6.5BBL) Brite tanks with tubing around two years ago. We measured our glycol solution with a borrowed glycol reader at the time of building (it was a very expensive reader borrowed from a local airport a friend worked at). We had never had much issue with cooling. If anything, we had the opposite problem. The chiller was an 8000btu A/C, the glycol was mixed adequately (although we added more glycol over time). It seemed to be a very efficient system and within the first few months we accidentally froze the beer on both of the Brites (at separate times) when the pump sending the glycol into the tank had a probe issue. But it would cool 65º beer down into the 30ºs in less than 24 hours.

But a few months ago, we suddenly had a lot of cooling issues. Thinking it was related to when a line ruptured we pulled the two wrapped tanks apart and rewrapped them. When that didn't help, we looked at the cooling unit and decided to replace the 8000btu A/C with a 10k and 8k dual A/C setup. That didn't do anything either. At this point, we started thinking our glycol was the cause, and after looking at this chart http://www.probrewer.com/library/ref...-about-glycol/ we replaced all the glycol in the system. We cut 100% pure glycol with water. We used two of our brix refractometers to measure and it's reading 23º Brix. The thing is, I am pretty sure the ratio of glycol to water is off compared to what the chart is telling us. I believe it's closer to a 45/55 or 40/60 solution (I lost my notes from when we added the glycol & water, so I'm going off of memory).

We're still not able to get either of the tanks below 38ºF, and that takes several days, while the glycol gets down around 18º and stops. If we turn off the recirculation to the tanks, the glycol gets colder (although it warms back up to the same temp after we put it back on Brites). The glycol solution is *not* freezing in there though. I would add more water, but I don't want to introduce more issues at this point. Can someone give me some advice?

Note: With recirculation on, I pulled the glycol from about 6" deep with a turkey baster.

Thanks!

[mmussen]

A couple thoughts I had from just reading your post.

1 - 18oF is way colder than I've ever seen a glycol system run. I'm used to seeing glycol temps at around 26 or 27 F.
Based on what you're guessing your glycol concentration is you may well be freezing glycol in the AC units and not getting much as much heat transfer. That may also explain why the glycol temp goes down when you turn off the cooling. - Based on that chart your glycol freezes around 16o and your AC units are probably colder than that.

I'd suggest taking a sample of the beer in the tank and checking that temp, as well as trying to mix the tank some (say by bubbling CO2 into it) there's a fair chance you've got some stratification going on in the beer of the tank and its making the temp probe read incorrectly.
Also with your glycol temp that low you may well be freezing beer on the inside of the tank where the glycol lines are. That will massively slow down heat transfer and could explain why your tanks are taking longer to cool.

Also - check that you don't have any moisture around the coils and in the inslulation - you may well be loosing a lot of cooling power to creating ice or cooling water in the insulation.

Cheers and good luck

[dick murton]

Agree with the previous comments, but perhaps to add to them -

The chiller system should have a primary evaporator operating temperature, let us say minus 8 C (ca 18 F). You glycol needs to be strong enough to stop it freezing around the evaporator coils, but then you should have a thermostat somewhere in the glycol recirc system that tells the compressor to stop operating when the glycol temperature is say minus 2 deg C (ca 28 F), which is still plenty cold enough to cool the beer, with minimal risk of freezing the beer adjacent to the beer tank cooling coils.