Massive Problem with Thermal Stratification in Conical

I just discovered that I have a huge problem with liquid in my fermenter stratifying to level that are totally unacceptable. I have a brewhemoth 22G conical, that I had retrofitted with a thermowell near the bottom of the cylindrical part of the fermenter. I have the immersion chiller that they sell for it, and have been using 5050 glycol/water mix in a chest freezer, 4gal of it total. I just finished installing a 300w heat mat to the outside of the fermenter. Both the power to the glycol pump and the heater are on separate controllers.

I first suspected an issue when I noticed a lot of condensation on the lower part of the fermenter when holding it at 49degF. I've been doing testing with about 17gal in the fermenter. Obviously, the bottom exterior was below dew point, but not the top. I had figured that the bottom was just below, by maybe a degree or so, and the top a bit above. I figured that the top-to-bottom temp. differential couldn't be too large.

Anyway, I just finished installing the heater, and set the temp to 75degF. The water was at about 62degF when I started. I just went out to the shed and checked the progress. I have the heater's RTD taped to the side under some insulation, while the chillers probe is in the themowell. One was reading 72.2, and the other 72.3degF. The cone of the fermenter felt cool to the touch, and the top, including the airspace, noticeably warm. I busted out another RTD and dropped in in through the airlock port.

92degF!!!!!

This is bad news. I'm sure that yeast activity will mix things just fine during active ferm, but am terribly concerned about the temp of the wort before and after this time. I'm not planning on setting the ferm temp to 75F, but the fact that the top was 20degF higher than the bottom is really disconcerting. Prior to active ferment, the bottom temp is probably the more important one, as the yeast should settle. However, if I have the temp set to, say, 66degF, and the ferm finishes, I really don't want the top half of my beer sitting at 86degF!!!

Could I make a stir plate work through the side of the conical perhaps? Anybody else have data or experiences with this issue? I'm totally amazed at the amount of the differential.

Please help!!!

You sound like you are really freaking out. It may be best to get blackout drunk; forget you ever attempted a single step 13F ramp from 62F to 75F with a 300W input; and do a more meaningful and realistic test.

Besides, for any real detailed analysis, some key pieces of info you left out were- your ambient temp, how much time had passed since activating the heater, whether the cooling was still active, where the heating mat was installed, where the probe that read ~90F was located, etc.

A 13F rise is no small increase, and will take time to stabilize. Your temps seem to indicate it was still actively ramping.

A test trying to maintain ferm temps (or a few degrees above/below ambient if ferm temps are much lower/higher than current ambient) is more realistic. Starting with something close to the desired temp is critical, or allowing it to stabilize before evaluating things.

I don't own a conical, but have researched them thoroughly. There is a guy on here who did some temp strat testing on a large (~15g I think) conical. I think he found radial strat, and dual vertical (h/c/h/c like 4 cake layers, so horizontal?) strat zones, or something wacky like that. I think the cone was especially problematic. If I get bored I will search for it.

Other things to consider:

If you installed the heating mat on the upper part of the cylinder, expect stratification. Placing the cooling coil/sensor high, and the heating mat/sensor low should help minimize stratification.

Since it sounds like you are not using a chamber/freezer, insulating the exterior will help with strat, especially if ambient temps will be well above/below desired temp. It will also mitigate the continually very cold area around the chilling coil that might negatively impact the yeast, as they don't like temp swings. Keeping the glycol temps to a reasonable differential will also help with that.

If your glycol chiller is a tub inside a freezer, don't expect anything resembling a cold crash. Only so much heat can be extracted by a freezer, through a tub, through glycol, through a heat exchanger, from the beer. If you want better crashing performance, there are a few AC window unit based chiller builds that have DIY threads.

There are number of DIY coil based jackets threads as well. More surface area for lower temp shock while fermenting, and more rapid cooling for crashing.

Controlling heating and cooling with different controllers can be tricky, and nearly impossible if <2F temp variance is desired. It is best to deactivate one or the other when temps deem they both won't be needed. There are several options for dual stage temp controllers as well, which do a better job of controlling both simultaneously.

My brilliant idea was to add a second glycol pump to recirculate within the chiller. It would make the IC act like a much more thermally conductive piece, but it looks like the bulk of the coils live in pretty much the middle of the beer. For that to be effective you'd want equal chiller area well above and below the stratification.

Ambient T was around 60degF. The 90degF probe was dangled directly into the top inch or two of water. The heat mat is about as low as it can go on the cylinder part of the conical, but does extend up about a foot from there. Above that, there will be airspace inside the fermenter, assuming 16-17gal batches. I did try to insulate when holding the chill to 49degF, using a heavy cotton sleeping bag. This certainly lowered the cycle frequency of the chiller pump, but because the material allowed easy vapor exchange, things got pretty wet inside.

I'm not expecting to be able to cold crash without decent insulation on the outside, unfortunately. Having a chamber around the fermenter was my initial plan to limit condensation. Some desiccant should be able to absorb the moisture initially present, but would be no match for continually introduced air. I can't figure out how to make a chamber and still be able to remove the chiller coils for cleaning etc. I added a couple of gallon jugs of water in the glycol tub to create a thermal buffer.

After writing my initial post, I set the chiller to 67degF and the heater to 65degF, with a 1degF differential. Both on on/off mode. This morning, the two lower probes were reading 64.7degF, and the top reading 69.2degF. I'm going to turn both off now and see how long things will take to stabilize.

Thanks for the input fellas....

It is tough to do variable size batches in a conical, especially with a fixed height internal chiller coil, and still get good perfomance. This is true for almost all brewing equiment.

Deciding what you consider important will nail down the system constraints-
min/max chill coil temp possible/tolerated
ambient condition limits
batch size tradeoffs/compensation
etc.

If you are in the twilight zone of ambient temp almost compensating for heat output, strat will be an issue without circulating, or running both heating and cooling simultaneously. Things are much simpler when only heat, or cooling, is needed at any one time.

An adjustable height internal chiller coil combined with low heat, or the external coil jackets seem to be the best DIY solution to temp control of variable sized batches in conicals. Some have even laid coils on the cone for a second zone, and also switch to a inline heater and reverse the input from top to bottom when heating the glycol.

Adding jugs to the glycol tub will add thermal mass while saving glycol cost, but it is probably a 1:4, or less, mitigation factor. The thermal transfer doesn't happen fast enough through plastic (water in jugs to glycol, or freezer to glycol), especially at low temp diffs. If you aren't trying to cold crash, it is probably enough to stay on top of a fermentation, though. Using a metal tub that contacts the cooling coils in the freezer walls will help with recovery/transfer, if you can't stay on top of a ferm. One guy just uses the freezer itself as a glycol tub.