Author Topic: How much refrigeration do I need for my homebrew keg cabinet  (Read 2344 times)

Offline rb30022

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How much refrigeration do I need for my homebrew keg cabinet
« on: January 04, 2012, 07:17:31 PM »
I have constructed a keg cabinet as part of my bar in my basement and am trying to figure out how much refrigeration I need to keep my kegs cool. The cabinet measures 27" H x 40" W x 24" D and has 1.5" of pink Styrofoam insulation board on all sides. I read Chris Bible's article in this month's BYO and calculated that I need about 400 BTU/Hr to keep the interior at about 35 deg F with an exterior temperature of about 75 deg F but this seems like a low number. Can anyone tell me if this value is in the right ball park? Also, I am trying to decide whether to use conventional refrigeration or thermoelectric. For conventional, I am looking at a remote condenser unit off to the side with an evaporator inside the cabinet. A thermoelectric unit could be mounted directly to the side of the cabinet. Any thoughts on pros and cons of each type of system?  Can anyone suggest a unit that can provide the level of cooling that I need at the above temperatures.

Thanks.

Offline euge

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #1 on: January 04, 2012, 07:28:31 PM »
I'm all for using a TEC system, but my experiences with them have been mixed. Cools well but keeping a stable temp was problematic. Zymurgy has the article about the Ghettochill 9000 with two TECS and a power supply.

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Offline rb30022

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #2 on: January 04, 2012, 07:44:58 PM »
Yes, I read the article in Zymurgy as well and went back and read the article on the Gettochill 5000 in last year's gadgets issue but I didn't see any info on how to choose a unit of the correct size.  I did a little research on thermoelectric units and it looks like they become less and less efficient the larger the temperature differential you are trying to achieve.  If I was interpreting the information correctly, I looked like I would need a 1500 BTU unit to pump 400 BTU/Hr at a 40 deg F differential.

Offline oscarvan

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #3 on: January 05, 2012, 01:42:11 PM »
Not much help with your engineering issue, but I did notice you said 35º.....IMHO waaaayyyy too cold. 45 is the highest I can set my keggerator, and it would be on 50º if I could. Cold kills flavor.
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Offline a10t2

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #4 on: January 05, 2012, 01:46:10 PM »
If you want someone to check your math, you have to give the r-value for the insulation.
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Offline rb30022

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #5 on: January 05, 2012, 06:01:58 PM »
I looked online and found that the R value for the foam ranges between 4 and 8 per inch of insulation so I used a value of 4.

I know that 35 is colder than I really want to keep my beer but I want some factor of safety so the unit wont have to run all the time.  The cabinet is actually devided into two compartments and I want to be able to keep my lagers and lighter ales at about 40 deg in one compartment and my heavier ales at about 50 deg in the other.  I plan to use thermostaticaly controlled fans to draw cold air from the colder compartment to the warmer.  I just want to make sure that, if anything, I have more refrigeration than I need rather than less.

Offline a10t2

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #6 on: January 05, 2012, 08:07:24 PM »
OK, so the area is 27*40*24 = 25920 in^2 = 180 ft^2. Going with an r-value of 4.0 ft^2-°F-hr/BTU-in:

(180 ft^2)(40°F)/(1.5 in)(4.0 ft^2-°F-hr/BTU-in) = 1200 BTU/hr.
« Last Edit: January 06, 2012, 09:36:45 AM by a10t2 »
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Offline euge

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #7 on: January 06, 2012, 01:22:37 AM »
The cold sinks shed a lot of condensation so you might consider this in you decision.
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Offline morticaixavier

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #8 on: January 06, 2012, 08:51:42 AM »
OK, so the area is 27*40*24 = 25920 in^2 = 180 ft^2. Going with an r-value of 4.0 ft^2-°F-hr/BTU-in:

(180 ft^2)(40°F)/(1.5 in)(4.0 ft^2-°F-hr/BTU-in) = 1200 BTU/hr.

I am confused, 27" = 2.25 ', 40" = 3.33...' and 24" = 2'

so volume is 2.25*3.33*2 = ~15 cubic feet rather than 180. am I missing something?
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Offline a10t2

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #9 on: January 06, 2012, 09:36:23 AM »
am I missing something?

No, but I am because we want surface area, which is (2*27*40)+(2*40*24)+(2*24*27) = 5376 in^2 = 37.33 ft^2. And the power required is 249 BTU/hr.

Apparently I shouldn't have done that late at night.
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Offline morticaixavier

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #10 on: January 06, 2012, 10:50:47 AM »
am I missing something?

No, but I am because we want surface area, which is (2*27*40)+(2*40*24)+(2*24*27) = 5376 in^2 = 37.33 ft^2. And the power required is 249 BTU/hr.

Apparently I shouldn't have done that late at night.

ahh cool, well as long as we are wrong. ;)
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Offline rb30022

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #11 on: January 06, 2012, 06:47:48 PM »
Sorry.  I'm new to this forum stuff so I don't know how to quote who I'm responding to but 249 BTU/hr is the same number I got.  I just thought I might me plugging in a number in with the wrong units somewhere.  I bumped it up to 400 to account for leakage and so the unit wouldn't have to run all the time.  Since we're all coming up with the same number, what I need to know now is what kind of refrigeration unit I need to provide that rate of cooling.  I've looked at a unit designed for boats manufactured by Mermaid, the MM2 remote refrigeration unit with their 425M evaporator, but I didn't see a BTU rating on their web page.  I've also looked at a 1/4 HP Embraco condensing unit which is rated at 3650 BTU http://www.globalindustrial.com/p/hvac/compressors-line-filter-dryers/compressors/embraco-condensing-unit but that seems like way more than I need.  I also found a Dayton unit (CU102 Commercial Temperature Air Condensing Unit) http://www.daytonrefrigeration.com/servlet/the-163/dayton-refrigeration%2C-refrigeration-parts%2C/Detail but again the BTU rating seems way more than I need.  What I'm not sure of is how the rated capacity applies at the temperature differential that I am looking for, especially after discovering how much the TEC units drop off with temperature differential.  I'm hoping someone with some refrigeration experience and/or knowledge can give me some guidance on how large a unit I need to pump 400 BTU per hour at a 40 deg F differential.  I would prefer a TEC unit because of he simplicity of installation but the efficiency issue may make that unfiesable.  Any guidance would be greatly appreciated.

Offline a10t2

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Re: How much refrigeration do I need for my homebrew keg cabinet
« Reply #12 on: January 07, 2012, 02:09:06 PM »
What I'm not sure of is how the rated capacity applies at the temperature differential that I am looking for

I know people have done something similar to what you want, although on a larger scale, using a window air conditioner. That might be the cheapest and/or easiest option. Any commercial unit should be overkill for what you need.
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