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Old 08-16-2012, 04:40 PM   #1
Kmcogar
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Just received a free mini fridge. It's one of those really small ones. I believe it's 2.1 cubic feet.

Can I use this to make my fermentation chamber? Will it be able to keep my carboy cold enough? I plan on only having 1 carboy in the chamber.
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Old 08-16-2012, 04:43 PM   #2
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If it is anything like my dorm fridge, you won't fit a carboy in there.

 
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Old 08-16-2012, 04:59 PM   #3
scoppi
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From what I've gathered on here, most mini fridges put out 100-150 BTU's. Use this equation to figure out how large you can make the chamber, and what R value your insulation will have to be:

Q= (1/R-value) x A x ΔT

Where Q is the maximum possible flow of heat in BTU/hr for the enclosure
(1/R-value#) is conductance expressed in BTU/Hour*sqft*░F
A is the surface area of the enclosure in square feet
and ΔT is the change in temperature across the wall in ░F

This is taken from Post #10 in this thread:

http://www.homebrewtalk.com/f51/what...hamber-190459/

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Old 08-16-2012, 08:45 PM   #4
Kmcogar
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Quote:
Originally Posted by mredge73
If it is anything like my dorm fridge, you won't fit a carboy in there.
No, I'm not trying to fit it inside. Just build around it.
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Old 08-16-2012, 08:46 PM   #5
Kmcogar
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Quote:
Originally Posted by scoppi
From what I've gathered on here, most mini fridges put out 100-150 BTU's. Use this equation to figure out how large you can make the chamber, and what R value your insulation will have to be:

Q= (1/R-value) x A x ΔT

Where Q is the maximum possible flow of heat in BTU/hr for the enclosure
(1/R-value#) is conductance expressed in BTU/Hour*sqft*░F
A is the surface area of the enclosure in square feet
and ΔT is the change in temperature across the wall in ░F

This is taken from Post #10 in this thread:

http://www.homebrewtalk.com/f51/what...hamber-190459/
Looks like I am gonna have to brush up on my math skills
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Old 08-17-2012, 01:52 AM   #6
scoppi
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Quote:
Originally Posted by Kmcogar View Post
Looks like I am gonna have to brush up on my math skills
We can run through the equation, just need to know how big you want to make it.

 
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Old 08-17-2012, 01:58 PM   #7
Kmcogar
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Well, I want it for only one carboy(6.5 gallon). I usually only have one going at once due to time constraints. The carboy with the airlock is about 28 inches tall and 13 inches in diameter. I would like the chamber to be just big enough to fit the one.

I guess I'll keep a little space for maneuverability. Let's say 32 inches tall and 16 inches wide on the inside.

Thoughts?



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Here's the specs of the fridge that are printed on the inside
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Old 08-17-2012, 05:14 PM   #8
Kmcogar
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By the way, I've been trying to gather information from other threads.

List of things I have: (free)
-computer fan
-2.1 cubic feet mini fridge
-insulation (not sure the R rating but I think it will work)
-plywood
-screws

What else do I need to make this thing look pretty? The wife hates ugly. Also I'm in the military so I need it to be easy to take apart for moving
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Old 08-17-2012, 06:07 PM   #9
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Are you using some sort of air vent between the chamber and the fridge?

optional:
split 2x4 for framing
power source for the computer fan; it is probably 12vdc
Casters to roll it around without scratching the floor and to make moving easier.
Sandpaper and paint in your wife's favorite color.
You may also want to think about so sort of moisture barrier, I have trouble with condensation with my stand up freezer and it is sealed pretty well.
Ranco temperature controller; about $40 on ebay. I know there are ways to modify the factory thermostat to make this work but the ranco (or similar) can do this much easier and more precise.
Permanently installed handles for lifting it; this thing sounds like it can get heavy.

 
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Old 08-18-2012, 02:09 AM   #10
scoppi
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Quote:
Originally Posted by Kmcogar View Post
I guess I'll keep a little space for maneuverability. Let's say 32 inches tall and 16 inches wide on the inside.
Ok, so let's say it's a 16"x16"x32" chamber.

I'd suggest insulating it at least 2" thick, giving about an R value of 9. This will depend on the type of insulation you use.

The other thing we need to know is what temps you plan on running it at, and the ambient temp around the chamber. I'll do two different cases, one where the difference in temperature won't exceed 15 degrees (which should be the case most of the time if you're fermenting ales) and a case where the temperature difference will be about 45 degrees (in case you want to brew lagers or cold crash). With these values we can figure out the amount of BTU's necessary, which will hopefully be less than 150.

Case 1 ; Temp difference = 15 degrees:

Q = (1/R value) (A) (Change in T)

A = Inner surface Area
16 in = 1.33 ft
32 in = 2.66 ft
A = (1.33ft * 2.66ft * 4) + (1.33ft * 1.33ft * 2)
A = 17.7 sqft + 3.5 sqft
A = 21.2

Q = (1/9) (21.2) (15)
Q = 35.3

So your fridge should be plenty powerful enough to handle a chamber of that size for ales.

Case 2 ; Temp difference = 45 degrees:

Q = (1/R) (A) (Temp difference)
Q = (1/9) (21.2) (45)
Q = 106

So your fridge should be able to handle lager fermentation.

You can also solve for the largest you can make the fridge if you make A your unknown variable, and set Q between 100 and 150. I'd do it, but I really need to know what your temperature differences will be.

Hopefully this was helpful.

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