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Old 08-15-2013, 05:42 PM   #1
CKing
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Default Thermodynamic Help?

Been thinking more about fermentation temperature control. And was wondering if the following scenario is worth any merit along with how to accurately plan for a specific temperature range:

Chill Wort to 70 degrees (about the best I can do in Summer)
Basement is a constant 65 degrees
Plastic bucket primary placed in larger plastic bin with 10 gallons of water chilled to 60 degrees added (not a full blown swamp cooler set up)
Chilled water maintained with ice a couple times a day, but rising 1-2 degrees per day for the first few days

Without taking samples or using thermometers in the primary, is there a basic way to calculate how effective the heat transfer could be between the chilled water around the primary and it's effect to the temperature of the wort during the first few days of fermentation?

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Old 08-15-2013, 05:53 PM   #2
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CKing,
This is my technique. I have asked the same Q previously (although not in a dedicated thread) but not gotten a definitive scientifically based answer. Best consensus seems to be that the thermal mass will help moderate temps., but there still will probably be a temp. rise in the center mass of the fermenter. I have a fermenator strip on my bucket, and a floating aquarium thermometer in the swamp cooler. Granted neither are terribly accurate, but I can keep fermenting temps about 6-10 degrees below environmental temp, depending on how many ice bottles I use and how often I change them out.
I'm going to keep my eye on your thread to see if anyone answers with a better answer.

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Old 08-15-2013, 08:59 PM   #3
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Yeah, I'm looking more for numbers, factors, equations, etc. that would apply to this method.
9 months out of the year I don't really worry since the tap water is colder and my wort chiller can get the wort down to low-mid 60's
It's the summer months that I want to adjust for.

Cheers!

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Old 08-16-2013, 03:13 AM   #4
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There is obviously some way to calculate this, but I see it being freakin complicated for nothing.

To do it properly, you'll be looking at the water temp and wort/beer temp, the room temp (as that will effect how fast your water warms up, and humidity might even play a role), the material of your fermenter (glass or plastic, and how thick?), the water level etc... There are so many factors to take into account that you'll probably never really be accurate.

Instead, just use the method you want and keep track of the temps in the fermenter. Two or three tries down the road, you'll probably have it dialled in. Sure, the first one won't be perfect, but it'll work.

I did that for my most recent batch. Got wort down to 75 with my immersion chiller, then rotated my frozen bottles regularly. I kept my wort between 62-64 (based on fermometer on my FV) for 5 days without any trouble at all, and after that I slowed down and let it rise to 68. And I kept it there with very, very little effort afterwards.

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Old 08-16-2013, 03:56 AM   #5
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I agree with the previous poster that it's a lot of complication for nothing.

Get a thermowell and a thermometer. Measure and adjust the cooling water by adding ice as necessary.

My intuition (I am an engineer) is that you'll probably be 2-4 degrees higher in the center of the fermenter than your cooling water during days 1-4 of fermentation. Both plastic and glass are good insulators so don't expect a homogeneous temperature.

Since you're dealing with a lot of thermal mass your temp changes will also be relatively slow so record what you do and use it to establish a better base line for next time. You'll probably need a few pounds of ice on each of the first few days, then quickly won't need any as fermentation finishes and you'll be able to remove the fermenter from the water.

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Old 08-16-2013, 02:22 PM   #6
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For the time and effort it takes to reliably calculate this and design a system that achieves your desired results consistently, would it not be simpler (and maybe even cheaper ofer the long haul) to pick up a used refrigerator and buy or build a temp controller?

For $50 total investment, I have been brewing in the same fermentation chamber for 5 years (free used refrigerator and a $50 analog Johnson controller). My results with that are consistently more stable and more repeatable than any of my previous efforts with swamp cooling.

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Old 08-16-2013, 02:43 PM   #7
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The problem with calculating this is the lack of important data. Here are factors you'd need to take into account:
= the exothermic reaction of fermentation. You'd need to know how much energy that produces... which is no doubt variable over time.
= the conductive properties of the materials of the containers and their thicknesses. You can get close answers online.
= an accurate way to measure out cold water or ice to match heat absorption in the ice bath.
= the conductive properties of the concrete or carpet or whatever of your basement floor (assuming that's where it's sitting).
= accurate data for the room temps throughout the day and night.

The math isn't that tricky... it's data collection and constant monitoring that is the hard part. The heat produced by fermentation would be so variable based on so many contributing factors that it would make prediction almost impossible. Not to mention you'd have to constantly be metering out coolant.

My solution was an ice bath that pumps cold water into an insulated bucket holding my fermenter. I use a thermal controller to monitor and regulate the temperature by turning the pump off.

Good luck, man. I tried doing the same calculations.

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Old 08-16-2013, 02:54 PM   #8
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Though if you want to know how the thermal properties of the water around your fermenter work the basic principles of equilibrium will give you a rough idea of what to expect.

The fermenter produces heat from fermentation and your ambient air temps are both getting rid of heat into your water tub. That means eventually that water will become at least 65 degrees given your ambient in your basement. Which means your fermenter (fermentation heat aside) will also eventually reach 65. Your thermal mass of ten gallons means that it will take longer for everything to reach 65. Now add in the energy produced by fermentation and it will get an unknown quantity higher.

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Old 08-16-2013, 04:22 PM   #9
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Cking, if your basement is 65F you don’t need much cooling.

If you have 5 gallons of beer at 70F going into 10 gallons of water at 60F, The system will equalize fairly quickly at about 63 1/3. Then it will drift slowly up to 65. In a ten pound batch there’s enough fermentation heat to melt about 2 ¼ pounds of ice, but that takes place over about three days.

If you’re fermenting at 65, we’re done. If you want it cooler, then obviously you need more ice. How much is hard to figure, too many variables. If you want to ferment at 60-62, I’d guess you need another two pounds of ice per day.

YMMV, but there’s your ballpark.

I have to quibble with schematix a little bit. I ferment with a carboy in a water bath and the beer is always less than 1F warmer than the water. That’s with the water level with the beer.

The thermal conductivity for glass is close to 1, water is .6, plastic .4-.5. In this application that’s pretty much no insulation at all.

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Old 08-16-2013, 04:42 PM   #10
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Quote:
Originally Posted by CKing View Post
Been thinking more about fermentation temperature control.
I took the title literally and though you had a real nasty thermodynamics question (something about the change in Gibbs energy during fermentation or something equally unpleasant). Application of the first law will do here.

Quote:
Originally Posted by CKing View Post
Without taking samples or using thermometers in the primary, is there a basic way to calculate how effective the heat transfer could be between the chilled water around the primary and it's effect to the temperature of the wort during the first few days of fermentation?
No and some of the reasons for this have been pointed out by other posters. To put the first law to work you want intimate thermal contact between the fermenting beer and the cooling water. This could be done by using a metal fermenter (keg - corny or otherwise) inside a larger container through which cool water is circulated/maintained or you could use a plastic or glass fermenter with an attemperating coil of copper or aluminum. As the metal is a good conductor you can assume the temperature of the beer is close to the temperature of the cooling water. As cool beer is denser than warm the beer close to the walls of a metal fermenter or close to the coils in an coil system will sink and this causes circulation so the fermenting beer temperature, while not strictly uniform, won't range over a wide set of values either.
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