Temperature regulation while fermenting

[NatiMatt]

I was doing some homework on this and wanted to run something by you guys who have done this a bunch more than me. Basically I am trying to find out if I can remove the need for external heat by properly insulating the mash pot so that the heat generated during fermentation is enough to keep the process warm by itself. So what I found is the following;

1. You can pretty roughly calculate the amount of sugar that is going to be converted associate energy with that in watts since it's all going to end up as heat. In my example this is for 12 gallons of birdwatchers to I'll have about 10 kilos of sugar.

Base values:
10,000 grams sugar
180 grams/mol
235 kj/mol = Gibbs Free Energy of Fermentation

10000/180= 55.555 mol
55.555x235=13042 kj of energy
7-8 days = 605,000 to 691,000 seconds
13,042,000/605,000=21.6 Watts to 18.9 Watts of continuous heat.

In a container that's 1'x1'x2' (or a 15" round diameter pot that 24" tall) you need an R value of between 8 & 12 to maintain a minimum 86 F. I know that's a lot of math, but if it's close to a linear dissipation it should be ok. My guess is in real life it's warmer at first then it cools over time. I may try to set up some trending hardware with an RTD to try to measure what actually happens. Has anyone tried this with any success yet?

*note: this whole deal is based on glucose and doesn't account for any different sugars that may be involved.

[NatiMatt]

Just an update I found out that typical granulated sugar from the super market is overwhelmingly Sucrose not Glucose. This changes the math quite a bit.

10000 grams sugar
342.3 grams/mol
1544 kj/mol

That's 10,000/342.3*1544 = 45,106 kj or 45,106,000 joules

Compared with the just over 13kj from glucose and it abundantly evident that there is a lot more energy available from a complex sugar than a simple sugar if you can break it down.

This follows out to 74.5 watts for 7 day fermentation and 65 watts for 8 days. That puts you down around R2-R4 depending on the room. In a closet it might be ok all by itself if you leave the door closed. Does this fit with experience?

[still_stirrin]

TMTOYH......"too much time on your hands" ....

Good job with the maths...I doubt too many here worry that much about it. If the ferment is below optimum ferment temps for the yeast...add heat. If not...move to a cooler location. Insulating does buffer the peaks and valleys too.

Now, try to figure out how many liters per second of cooling water you need to keep the vapor condensed and cooled to 60*F in your parrot.
ss

[NatiMatt]

Now, try to figure out how many liters per second of cooling water you need to keep the vapor condensed and cooled to 60*F in your parrot.
ss

For this you'll need instrumentation, and you'll need to standardize on Standard or Metric units. I chose standard in the following example because Merica. For starters there are to many different designs to actually math something out based on surface area of the inner and outer jackets, initial cooling water temperature, initial distillate temperature, wind, and ambient temperature. There's just to many variables. With instrumentation it gets a lot simpler though... Basically we are going to assume an initial distillate temperature of 170 F° @ 95% ABV then measure the temperature of the supply water, return water, and the take off rate and use the following to determine the optimal cooling water flow rate. For the purposes of this example I am going to assume 1 gallon per hour distillate rate, but this is easily modified as you'll see below.

Fun Physics Principles

95% ABV has a density of right at 0.8 g/cc we find this by (.95 x .789)+(.05 x 1)=0.8 g/cc
95% ABV has a specific heat (that's the amount of energy in joules required to change the temperature 1 C°) of 2.525 j/gC we find this by (.95 x 2.438)+(.05 x 4.18)=2.525 j/gC
Water has a specific heat of 4.18 j/gC
170F° = 77 C°
60 F° = 15.6 C°
1 Gal = 3785.41 cc

So here we go. I need enough cooling capacity to achieve a 61.4 C° drop in my distillate temperature.

3758.41cc x .8g/cc x 2.525j/gC x 61.4 = 466,148 Joules worth of cooling to get this done.

To calculate flow we are going to need supply (Ts) and return (Tr) temps for the cooling water.

Flow rate in gal/min = 466148/(4.18 x (Ts-Tr) x 60 x 3785.41)

So if you get a temperature change of 5C° you would need about 0.1 gal per minute of LM cooling water to achieve 60 F° in your Parrot.

So intuitively: by volume water takes about twice as much energy to change its temperature 1 degree C as our 95% ABV distillate. So to change 1 gallon of our distillate temp 60 C° we need to change about 6 gallons of water 5 C°.

1 x 60 = 6 x 2 x 5

For the sake of perspective that about enough energy to power a 100 W light bulb for about 1 hour and twenty minutes.

[rad14701]

Got some efficiency issues to deal with, don't you...??? Whether calculating heating or cooling we need to factor in efficiency because almost nothing is 100% efficient... Oh, darn...!!! All those numbers and we still don't know how long a piece of string is...!!!

[shadylane]

Just out of curiousity.
What temp did the ferment start at?
What is the temp of the room the fermenters in?
And did all those calculations take in account the fact yeast doesn't ferment on a linear scale?

[res]

I love the idea of using the excess heat generated at the start of fermentation to keep it cozy all the way through. However I'm not sure it would work just by insulating the fermenter.
I would think you'd end up with a very hot beginning and a less than ideal finish. Maybe you could tap off the extra heat using a heat exchanging coil and store it in a super insulated container to be sent back when the temp starts to decline.

[NatiMatt]

Got some efficiency issues to deal with, don't you...??? Whether calculating heating or cooling we need to factor in efficiency because almost nothing is 100% efficient... Oh, darn...!!! All those numbers and we still don't know how long a piece of string is...!!!

The inability to foresee efficiency is precisely why I said it was to complicated a problem to deal with using only theory. That's why I've suggested the use of instrumentation. With instrumentation all of the inefficiency is built into those measurements and we have a foundation from which to evaluate the problem using known physical attributes. Therefore, it doesn't matter if your LM system is more efficient than mine because we are both going to account for that efficiency in our measurements. The specific heat of water and alcohol is not a matter of efficiency it is a legitimate physical property like mass or compressibility or volume.

Regarding the Free Energy of Fermentation problem, which is somewhat more theoretical, I am not sure about the even distribution of the heat generation I discussed. The amount of energy produced is fairly accurate and well documented. It only matters what kind of sugar you start with (hence my correction from glucose to sucrose). My assumption is that there is more energy release at the beginning and less at the end, but I don't know. That's why I posted this question. That's also why I think it's probably best to set up instrumentation and actually measure what happens. You may disagree, but I think approaching these types of problems with science is the best way to assure quality and safety. Plus I want someone to tell me it's not beneficial to know with confidence they don't need the foam cooler light bulb hassle every time they ferment birdwatchers...I don't know yet, but if I find it out I'm sure others would like to know.

[NatiMatt]

I love the idea of using the excess heat generated at the start of fermentation to keep it cozy all the way through. However I'm not sure it would work just by insulating the fermenter.
I would think you'd end up with a very hot beginning and a less than ideal finish. Maybe you could tap off the extra heat using a heat exchanging coil and store it in a super insulated container to be sent back when the temp starts to decline.

That would be bad ass. I don't know how to do it without comparatively massive energy loss associated with a pump or something, but you're into some cool tech at that point for sure. Bill Gates sponsored a super thermos in the last few years. His intent was to develop a way to reliably get vaccines that require refrigeration to parts of the world where there aren't refrigerators. Basically you put vaccines and ice in the middle of it and it will maintain a temp between 0-8 degrees for up to 60 days in 30C weather. It uses the same tech as the insulation on the space station. Some how there may be a way to do what you're describing, and for all I know its a necessary solution, but I'm not quite as well funded as BG. Do you have any ideas for how regular guys could do this. I'll run a test and post some results in the next couple weeks with some birdwatchers.

I don't have a chart recorder right now so the best I can do is keep a clipboard of my temps during the ferment but I'll make it as lab like as I can in my basement.

Finally I have an anecdotal story about people who actually do exactly this is a slightly larger and different application. Many people know this, but for companies energy is different prices at different times a day. These times are called peak and off peak hours. Energy during peak hours is often times 8-10 times more expensive than during off peak hours. In a large city near where I live there is a pretty big University. They have hundreds of buildings, but almost all of the heating and cooling is central to the main campus, even the remote campuses that are close by (less than a mile) are tied in. Because of this massive difference in energy cost they developed a way to make cooling at night (off-peak) and use it during the day (peak). The way they did it; two gigantic pools of glycol. They cool all night with chillers, then when its peak time the chillers go off and they gradually warm the massive pools throughout the day. Its really smart if you think about it.

[Maritimer]

Hi NatiMatt,

Are you a mathophile? http://homedistiller.org/forum/viewtopi ... 3#p7395033 .

M

[NatiMatt]

Hi NatiMatt,

Are you a mathophile? http://homedistiller.org/forum/viewtopi ... 3#p7395033 .

M

To a point I am I guess. I got in a lot of trouble in college because I didn't see the point in a lot of the exercises. I don't just mean doing the same thing over and over to learn it, I mean I didn't see the value in knowing how to solve math by hand that is designed not to have to do by hand (ie PID control loops for process controls). Basically by the time you've solved it by hand it's useless because the process has moved-that's why we automate things. Secondly I am a huge fan of choosing the right instrumentation to reliably measure the process. You can design around calculations all day long, but in the end you need to take measurements to have any confidence in what's actually happening.

As an example, you can certainly calculate the amount of BTUs a burner is putting off by looking up propane data and spreading the mass of the tank out over the time it takes to go through it. You wouldn't be exactly right, but you'd be close enough for govt work. You could also very reliably calculate how much energy it takes to boil a certain volume of water. You can take this one a long way because water is such a known thing. (ie barrometric pressure compensation, ambient temp, water purity etc...) So you know how much heat you have, and how much water you want to start with, but how long is it going to take to boil half of it away? Now you need more info. What is your pot made out of, what shape is it, how thick is the metal, is there any wind, when I turn the burner on does it create a micro-climate around the pot so that specific ambient temp is different than I thought? Now you're into an awful problem. When you have something very expensive it matters a lot that you get this right. To do that you usually do a couple things: you buy something from someone that has known values for what you want, or if you're really bright, you take something in the direction you generally want and you make a small improvement to existing tech.

In our little home distillation genre almost nothing is expensive really. I mean, I guess you could put up to $1000 in equipment, I'm not sure why you would, but you certainly could, but at that price point you are rigging things anyway. IE if you where to properly set your burner you would do it based on the outlet temp of your cooling water, reflux ratio, & takeoff rate, or some other combination of variable. A still is a control loop where several different things can be the controlling variable. Anyway I don't know anyone who has automated control valves running of PID loops for there gas or cooling water flow rate. Maybe you're out there, but that a more commercial/industrial setup than most hobby guys are going to have. Just one XP Rated Temp Transmitter is 800-1000$ just for the transmitter not including the element, thermowell, or wiring.

All that to say when I think it's useful (ie can I insulate my fermenter and get rid of the light heat source) then I'm interested. If I'm trying to calculate the exact volume of hearts or the exact efficiency of my home made coil, or some other value that really doesn't mean much I'm kinda out.

[Maritimer]

Hi NatiMatt,

The real problem with calculating things is that, although algebra isn't too hard, anything in calculus is just so easy to forget. Mathematica lets you set up your equations, no matter how difficult, and presents you with the solution and visualizations. It's like having one of those genius graduate students working for you--the kind who know everything and can do anything.

If you are even the slightest intrigued, download and install the trial. I can send you some interesting stuff. There is some danger of becoming a convert, though!

M

[NatiMatt]

Hi NatiMatt,

The real problem with calculating things is that, although algebra isn't too hard, anything in calculus is just so easy to forget. Mathematica lets you set up your equations, no matter how difficult, and presents you with the solution and visualizations. It's like having one of those genius graduate students working for you--the kind who know everything and can do anything.

If you are even the slightest intrigued, download and install the trial. I can send you some interesting stuff. There is some danger of becoming a convert, though!

M

Are you selling this thing?

[Maritimer]

Hi NatiMatt,

Not at all. I'm just looking for somebody to share my interests.

M

[NatiMatt]

I use calculus pretty often, but I'm not usually innovating anything. What I mean to say is that I'm not expanding the already established uses for different mathematical tools. I just use things that are already established for that purpose. A simple idea is finding and integral for area under a curve. This is helpful for say determining the volume of a keg laid on its side with a given level. This has been done for generations and, is a reliable method for finding an accurate solution.

Regarding Mathematica I have only used it in school years ago. My memory of the program is that, while powerful, the barrier to use is fairly high. You have to know how to tell it what you want it to do. For me anyway, I can find a strong enough foundation on the google and hack something into excel or work it by hand. Hey though, if it works for you, more power too you.

[NatiMatt]

Baseline Temperature Results:

I started a Birdwatchers last Sunday. I only had enough sugar on hand to get it to about 1.088 but this should be close enough to the actual recipe to derive some temp data. It started at 95 F° in a room with ambient of 62 F°. Up until last night it has been completely insulated except for a carpet square I set it on. I check it every day and it is progressively cooler. 95, 74, 70, 67, 64 last night. As you might expect fermentation is slow at roughly a .004 change per day in Sg. I picked up some heat trace and some foil tape and will bring the whole deal back up to 90F° tonight and will insulate it with 2" foam foil backed insulation. At that point fermentation should pick back up to something more reasonable -.010 Sg per day or more. With the increase fermentation I am going to see how much better the whole thing holds temp.

If all my fancy math was right if I can establish strong fermentation for a day I should able to turn off my heat for the rest of the journey and hold an 85+ temp with just the insulation. Science is fun.

[NatiMatt]

So I heated the whole thing up to 95F° over about 4 hours on Friday the 11th. I put 2" of foam insulation all the way around the fermenter (BOP Stainless Steel) including a lid. I left it in my basement until Sunday night. My Sg had dropped from 1.074 on Friday to 1.052 on Sunday and it was still holding at 91 F°. It had built up about 1" of foam with lots of tomato bits and large bubble. I am curious if I will get down to dry by this weekend so I can run it, but only time will tell I guess.