Fermenterator, how big can I go?

hiya folks, I just picked up a 2.8cuft mini-fridge, and I would like to convert it to a dual chamber/zone fermenter. I'm looking at storage for 2 six gallon carboys per zone.
The long term intention is to have and ale & lager side, Plus, enough room on the lager side for a few corny kegs down the road.

The question is, how large an area do you think I can go with this type of unit (Emerson cr282b)? The space I'm looking to use is 26"w X 48"h X 36"t.

Ive seen people chill some pretty big area with a A/C window unit, so I'm guessing this will work, just figured I'd run it by you fine folks.

The calculation I used to size my fermentation chamber was (Surface Area * Temp-Differential)/(R-Value) = BTUs

Figure out what kinds of temperature's you're going to see where you're going to locate the chamber, and then find out how many BTUs of cooling you're going to need to keep it cool. To simplify, you may want to just assume that the whole chamber will be maintaining lager temps. Throw all of your variables into a spreadsheet with your max needed height, and play with the length and width of the chamber until you think you've found a reasonable BTU output for your minifridge. Keep in mind that you're not going to want to max the little guy out, and that there will be some inefficiencies in your chamber.

Based on no calculations...that seems like a lot to ask out of the little guy. You can probably pull it off with lots of insulation, but you can probably expect a big temperature swing if you throw in a new 'warm' carboy.

DrDarwin - what units do you use for the calculation? in^2 or ft^2?

R vales are (1h*Ft^2*degF)/BTU - so if you're working in inches you'll need to convert one or the other.

Edit: I should say that I left out the /h part of the BTU answer since the BTU rating of a condenser should be time dependent as well (i.e. technically you are looking at XXX BTU/h cooling capacity vs. BTU/h needed).

Thanks for the reply's, glad I asked now!

Is there anyway to figure out the BTU's from wattage or high or low pressure info? I've been over their manual and website, no spec info at all (heck I just called their help line, no dice)

I remember seeing conversions for watts to BTU/h way back when. I think it was something like 1 watt = 3.4 BTU/h. I wouldn't take my word outright on that one though.

It says the power supply is 90watts, not sure if that's the info we need. Assuming that's correct, it's only 306BTU, that doesn't sound like much, the old crusty window shaker in the garage is 5k btu! (well, maybe 2.5k Its pretty beat-up.) I have a call into their tech folks, hopefully they can get back to me with a real number.

In the mean time, lets speculate.

My box looks to be 7824 inches SQ, so with your formula,
7824*40/30=10432

if that's right, I'm not even close on BTU's.

That doesn't seem right, should it be: 7824/12*40/30=869?

newdamage1 said:

It says the power supply is 90watts, not sure if that's the info we need. Assuming that's correct, it's only 306BTU, that doesn't sound like much, the old crusty window shaker in the garage is 5k btu! (well, maybe 2.5k Its pretty beat-up.) I have a call into their tech folks, hopefully they can get back to me with a real number.

In the mean time, lets speculate.

My box looks to be 7824 inches SQ, so with your formula,
7824*40/30=10432

if that's right, I'm not even close on BTU's.

That doesn't seem right, should it be: 7824/12*40/30=869?

Click to expand...

If you are using the /12 to convert to square feet, then you need another 12 in there. There are 144 square inches in a square foot. If this is the case, then 7824/144*40/30=72.44. You should have plenty. Don't forget that if it's well insulated, once it's cold, it will stay cold, so you only need the compressor to come on and give it a little boost every now and again.

The 3.4 ratio is for heating. Cooling is a different story and 6-8 x watts will put you in the ballpark.

Aww...from the topic title I thought someone was going to build a truly epic size fermenter...

Cheers!

david_42 said:

The 3.4 ratio is for heating. Cooling is a different story and 6-8 x watts will put you in the ballpark.

Click to expand...

Good to know. Thanks!

Is that from losses in refrigeration?

So david_42, if I understand you correctly, when calculating for cooling purposes we should actually assume between 6-8 btu per watt. Correct?

I'm no HVAC expert, but I can lend some empirical data.

I use an Emerson minifridge....probably around 2 cu.ft, (it's a small cube). My chamber is ~38" high, 3 carboys wide x 2 carboys deep, (6 carboys fit nicely, with a bit of wiggle room). I used 1.5" white styrofoam on the top, sides, and front. Back is cinderblock with vapor barrier plastic over it, I think, (the wall of my unfinished basement). Floor is concrete, also of the basement. I have 2 fans inside the fridge, one wedged into the freezer, and one taped to the threshold between fridge and chamber. Regular (fabric) duct tape seals the edges on the inside. The door on front (which is also just 1.5" styrofoam) is just wedged on, held on with a couple pieces of tape.

The chamber gets down to about 13*C, or 55*F. I usually run it at 16*C, or around 60*F. It holds 60F even when the door cracks open when the tape lets go, which is often.

Pic:

shortyjacobs said:

I'm no HVAC expert, but I can lend some empirical data.

I use an Emerson minifridge....probably around 2 cu.ft, (it's a small cube). My chamber is ~38" high, 3 carboys wide x 2 carboys deep, (6 carboys fit nicely, with a bit of wiggle room). I used 1.5" white styrofoam on the top, sides, and front. Back is cinderblock with vapor barrier plastic over it, I think, (the wall of my unfinished basement). Floor is concrete, also of the basement. I have 2 fans inside the fridge, one wedged into the freezer, and one taped to the threshold between fridge and chamber. Regular (fabric) duct tape seals the edges on the inside. The door on front (which is also just 1.5" styrofoam) is just wedged on, held on with a couple pieces of tape.

The chamber gets down to about 13*C, or 55*F. I usually run it at 16*C, or around 60*F. It holds 60F even when the door cracks open when the tape lets go, which is often.

Click to expand...

Great info, thank for posting!

I'm going to scale it back size wise, To say around 36" x 36" x 26". Basically just room enough for 4 Carboys and a optional divider. I figure it this way, if I can get the front two to lager (maybe) then bonus. If not, I have room for 20Gal of Ales and whatnots.

Here's my MSpaint mockup that I used to describe this project to a friend. (its awesome, I know. :rockin

I've been working on a chamber pretty similar to what it looks like you're leaning towards. I modeled the whole thing, and have made some improvements to the design after I built most of it. I'll try and upload some pictures tonight.

All in all, my design will hold four 6.5 gallon carboys (assuming a 13" diameter) and one corny simultaneously. Alternatively, it should hold 9 corneys without the carboys. It uses a 2.7 cu ft minifridge to cool the volume, and has a minimum of 3.5 inches of insulation on all sides giving it an approximate R value of 18.5. I calculated total BTUs necessary to cool the space to lager temps using an R val. of 17, and came up with the somewhat conservative BTU need of <150 assuming 90 degree external temperature (which is obnoxious, since my unit will be inside).

Almost forgot to post these.

My phone uploaded them in reverse order so the first one is a bottom up view and the second is more isometric.

The green block shows the usable internal volume of the chamber, and has four 13" diameter cut-outs and one 10" cut-out.

I finished my build yesterday and fired it up last night hooked to my kill-a-watt. It ran pretty much all night to get to 39deg. (from 73 ambient) Time will tell if it can keep those temps once reached. I was late on ordering my diy temp controller parts, they are still 10-12 days out depending on shipping. So it will be a few weeks before I can do a real test.

I'll update with pics and better results once I get all those things in.

oh, and it looks almost exactly like your diagram.