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Old 03-06-2013, 01:46 AM   #11
kartracer
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Subscribed. Santa brought me a 20g Stout conical (with thermowell) and I'm thinking about a fermentation chamber for temp control. I had been fermenting in glass carboys just sitting in my basement which is about 66* in the winter and about 72* at most in the summer. Lots of air ducts in the unfinished part throw off heat in winter and radiant cooling (is there such a term?) in the summer. By opening air registers, I can get it warmer in winter and cooler in summer.

So I'm looking for a used upright freezer and am wondering what a good method for controlling the wort temperature is. I'm not going to use any advanced automation (like BCS or Brewtroller) and have been thinking about the STC-1000. I'll keep reading and learning. Maybe just controlling the basement temperature based on visually looking at the analog thermometer in the TW will suffice...

Mike

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Old 03-07-2013, 07:48 PM   #12
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Quote:
Originally Posted by cupido76 View Post
Follow up:

Check out this post: http://www.homebrewtalk.com/f11/imme...2/#post4971588

I asked that poster to tell me if his controller is connected to air or liquid probes and I don't have an answer yet, but this person is monitoring temperatures inside their fermenter and inside the fridge.

The thing to note here is that only a 5 or 6 degree swing in air temperature is maintaining a liquid temperature within about 0.3 degrees, so I'd be willing to bet that the OP's air temperature swing of 35 degrees is drastically over-shooting how much cooling is needed to get the liquid where it should be, and that the cause of this over-shoot is how slow the liquid reacts to changes in air temperature.

That could just be because of how much liquid you're fermenting... I'm not sure, and I'm still keen to find out where the poster of the graph controls their temps from.
That was me. I posted a graph trying to show something about thermodynamics in a fridge as related to a chiller. The graph cupido76 is referencing is attached below. The blue is the wort thermowell temp which is partially controlling the fridge. This is a five gallon batch so the dynamics are a little different. The red is the freezer air. As we all know the freezer temp will vary dramatically vs the wort. I had an all out war recently debating the accuracy of controlling the freezer with the freezer air or wort temp. I know for a fact that if you can babysit the controller, controlling with the freezer air would theoretically be more consistent. The wort temp swings will be smaller because the freezer will swing less more often. I tested controlling the freezer with the wort temp and I was right but I don't really want to babysit anymore so I came to the conclusion that a hybrid of both would work best and that is what you see in that graph. I use an arduino sort of board to control things so I have a little more freedom in my algorithm. What it will do is turn on when it reaches 0.1 higher than the target temp. It will then stay on until the wort reaches 0.1 cooler than the target temp OORRR the freezer air drops more than 5 degrees below the target temp. This prevents the freezer from swinging down into freezing temps while still getting a handful of degrees cooler than the wort. The goal is to slowly coerce the temp of the wort, not jerk it around all over the place. I would guess in a 10gal batch you'd see the freezer air swing down to 5 below the target temp and hover around there for a few cycles until the wort chills down below the target. I'd be curious to try it when my freezer is empty again. My mash tun is >10gal. I can test in that with water.
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Old 03-07-2013, 10:41 PM   #13
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Spintab: can you clarify what kind of babysitting you have to do with the sensor in air?

I would think there would be an initial delay in getting your wort to match the air temp, but after that I would have thought you'd have no issues maintaining that temp... No?

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Old 03-07-2013, 11:09 PM   #14
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You're right, finding that initial sweet spot in the first 12 hours or so takes a little doing, changing your target by a degree or two and watching how the wort reacts. Once fermentation starts you have to drop your target temp to compensate for the added heat. Can't drop it too far or the yeast will get sleepy but it has to go down far enough to avoid a big gain in temp. As the fermentation slows down you have to raise your target back up. All that while compensating for ambient temp changes around the freezer. It's not a lot of huge temp changes, just a lot of small ones. I have a web app connected to my controller so I can watch it while at work and what not. Once you reach about 5 days in and fermentation is done or drastically slowed, you can pretty much set it and forget it.

If you can get things going using the wort to control the freezer, you don't really have to worry about all that. The controller and freezer will cycle as much as they need to to keep the wort in the ballpark of your target. The key is preventing the freezer from going through the huge 20-30 degree temp swings the op was talking about.

Without the limiting algorithm that I'm using I'd probably suggest sticking the probe in a small container of water, like a mason jar maybe. Whatever you do, your target temp should always be a reference. Keep the thermowell in the wort and do what you need with the target temp to keep the wort temp where you need it. I've heard way too many people talk about their fermentation happening at specific temps based on ambient temp alone. Have to watch the wort.

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