Fermenter in a keezer or keezer in a fermenter?

[Munkee915]

I have a 20 cf stand up freezer in my garage i converted to a fermentation chamber with an stc-1000. Now that ive gotten into kegging it occurs to me i may want to chill my kegs to serving temp but still ferment my brew. since buying a 2nd freezer is not an option, I'm thinkin of building a chamber inside the freezer for this. I currently have 2 ideas and im looking for feedback.

1. chill the freezer to serving temp and warm the internal chambers. The chambers would be built out of 1/2" insulation board and lined inside with reflectix. I would also wrap a layer of reflectix around the bucket for added insulation. The buckets would be warmed with 2ft of thermal tape wrapped around the buckets under the reflectix and controlled with another stc-1000

2. build a chamber out of the same insulation board and lined with reflectix. only this time i would place the kegs inside. i would duct the freezer air directly to it and setup ducts with fans to bring air out of the "freezer" chamber and into the rest of the freezer for fermentation temps as needed.

im wondering which would be more efficient? also, would insulation board and reflectix be enough to make up a 40 degree difference in the chambers? The board is rated at R3 + whatever the reflectix inside and around the bucket would add.

 

[Munkee915]

So I've been doing more research and I'm trying to figure out how the R value of the materials works in this. The chamber I'm building should be able to fit a single bucket of about 22" tall and 12.25" in diamater. As such I'm measuring the walls at (rounded to nearest .25 ft, not counting joints, just surface area inside the chamber):

Front/back: 1ft x 2ft = 2sqft each = 4 sqft total
Sides: 1.25ft x 2ft = 3 sqft each = 6 sqft total
Top/bottom = 1ft x 1.25ft = 1.5sqft each = 3sqft total

The R-value of 1/2" polystyrene is listed at 3 (though I've read its more efficient in a cold environment) and R value of reflectix seems to vary from 1 to 4 depending on application. Assuming the lowest value I have an R value of 4 per wall (not counting the reflectix layer wrapped around the bucket in the chamber over the heat tape, or any R value the bucket provides)/ Given that I'm trying to hold a 40* temp difference i believe the formula is:

11.5 (Sqft) * 40 (temp diff) / 4 (r value) = 115 btu's needed to maintain temp = 33.70 watts

Thermal tape is 20 watt/ft so 2 ft is 40 watt so that should be enough to hold the temp difference right? Assuming lowest performance of my materials. Better performance would just cut this number down.

So am I looking at this right? Anyone want to double check my numbers or can think of any other issues that might get in the way?

 

[Munkee915]

A little help here? Anybody?

 

[rekoob]

I would chill to serving temps and warm the smaller chamber to fermentation temps.
I would also insulate the heck out of the "box" for fermentation.
Just cuz that's what we do in DIY projects... over do.
Should be easy enough to just build it and try it without investing all that much. I think you might find you don't need all that much warming if it's insulated well enough. you might have to play around with the box to get it right, maybe a fan that tuns on at some point to allow cooler air into it. I suppose that would mean you would need a dual temp controller for the box and just your single for the freezer for keg temps.
Don't see any reason why this wouldn't work out.

 

[Howhownow]

I would lean to option 2, as you would want the majority of space for fermentation (if there would be room left for 2 fermenters). That would only work of there is a single cooling duct in the freezer.

 

[kpr121]

If you’re looking for electric/power efficiency I would say that the second option is more efficient, since it (ideally*) does not involve having a heat source inside of the cooling chamber ever.

Also, this somewhat depends on which of the spaces will be bigger, but assuming room temp ambient outside the freezer and a bigger fermentation space, option 2 would have the least surface area exposed to the biggest temperature differential (i.e. you only need COLD COLD in the smaller box, and any COLD that escapes ends up in the fermentation space for the most part). Hence more efficient. Lots of variables there though.

*you may still need heaters in the fermentation area depending on ambient conditions as well as whether the insulated box is insulated/sealed enough to keep the COLD COLD in.

 

[kpr121]

FWIW Im considering something like this, but a little more DIY. Want to build an under-brewstand Fermentation Chamber/Kegerator and would like to keep the cooling/heating sources to a minimum. Interested in what others have to say and what you ultimately come up with.

 

[Munkee915]

What would be easier? Keeping heat in from a cold environment outside or keeping cold in from a warmer environment outside? And in which instance does insulation material work best? The freezer is in my garage which can get up to 100* in the summer. Im trying to figure out which is the more efficient solution. I started looking over option 2 and made a few mock ups of what my ideas are. Forgive the crudeness, it's my first try with sketchup:

Since the cool air comes in to the freezer from the top (rectangle on the back wall) my idea was to build the COLD chamber up top:

It's a little tough to see but theres a thin grey layer under the insulation which would be the metal shelf to support the weight. The kegs are pushed over to the side along with my co2 tank (green cylinder, 7lb tank) to make room for a shelf on the side to hold a few bottles and some saved yeast. My concern with this is moving cold air to the bottom for cooling. I thought about installing fans in the bottom but since the cold would naturally fall I'm afraid of it chilling the fermentation chamber even when the fans are off.

Second idea is to move the COLD chamber to the bottom:

Again a little tough to see but there's a thin metal (1/8" thick) shelf in there to support the buckets on top. Also there's a duct in the back that will guide the cold air into the lower chamber. I will probably layer it with insulation material so that it again doesn't inadvertently cool down the upper chamber. I would place some fans in the middle layer to push cold air up into the upper chamber to cool as needed. To me this seems like the better design of the 2 but what do you think?

I'm still working on my mock ups based on my first idea. Hopefully have them done a little later when I have more time.

 

[kpr121]

I think I like second option better. For reasons you've hit on... Cold sinks. The only negative is you lose some space to the ductwork.

I don't think you have to worry too much about efficiency on this, unless your trying to save pennies on energy bill. Since the unit you are using is a freezer and it's designed to freeze the entire chamber, it will be overpowered for it's intended use here.

I would focus on ease of construction, insulation between the two chambers, and flexibility. One thing to think about is how you would ferment two different beers at different temperatures-Having a fermwrap of some sort and a separate temp controller.

 

[Munkee915]

One of the reasons I was thinking of going with a warm chamber inside a freezer is that I could build 2 chambers and control their temps individually. Here are 2 of the mock ups I did with that in mind.

This was my original idea, but it doesnt leave much room for anything else but the kegs (nevermind the 2nd co2 tank, had some trouble trying to remove it from the sketch) so I was trying to find a better way. Although the freezer does have a few shelves on the door that I can use to store bottles and my yeast.

One thing about it was taht I could always remove a chamber if not fermenting 2 batches which would provide more room.

Last night I worked on combining the 2 ideas to provide a cold chamber and 2 fermentation chambers:

In order for this to work I would have to remove the shelving from the door. This would give me about 4 extra inches to extend the chambers outward. It's still a little cramped for space but I can fit 2 buckets in 2 chambers and both kegs and co2 cylinder on the bottom w/ about 7.5" left to build a small shelf. The upper chambers would have to use 1/2" board for space reasons. Hopefully since the cold will be contained to the lower chamber the 1/2" board and a wrap of reflectix is enough to insulate the buckets to keep 60ish temps. This is also the more expensive option as it would require me to buy a sheet of both 2" and 1/2" board.

 

[Howhownow]

One thing to keep in mind as you are envisioning designs is the keg 'plumbing'. Too much maneuvering in cramped space can be a real pain with all of the gas/beer tubing and QD's. Also want to make sure there is room above the height of the keg top for the QD's and tubes.

 

[Munkee915]

I should have plenty of room for the keg plumbing. My CO2 cylinder is about 30" tall to the top of the regulator gauge. That give me at least 8 inches of space above my kegs to run tubing. The drawings are drawn to scale as best I could. The "kegs" are 9" diameter and 22" tall, my "CO2 cylinder" is 30" tall and 4.5" diamater, and my "buckets" are 12.5" diameter and 20" tall. The inside of the fridge measures 57" x 27". Depth varies it's 16.5" at the bottom and goes to 19.5" about halfway up. All the insulation shown is 2" except for the last pic which I use 1/2" for the upper chamber.

 

[Otis1031]

I would first experiment with your first design where your cooling chamber is on top where the cold air enters and totally seal that up to make a mini fridge inside your fridge. Then enclose the lower half of the fridge for your fermenter chamber and chart your temps. If higher temps are needed, creating small opening to the outside with a CPU fan would help remove cold air. Introducing a heat source inside your refrigerator would produce moisture which is not good.

 

[kpr121]

Introducing a heat source inside your refrigerator would produce moisture which is not good.

I liked everything about your post until the last sentence. Not sure I follow that logic.

You could ferment at different temperatures just by using some fermwrap around one of the fermenters. If you wanted to be efficient you could wrap reflectix or other insulation outside the fermwrap, but I dont think that would always be necessary depending on the temperature delta.

 

[Munkee915]

Well im not sure how much heat would actually escape out into the cold chamber fast enough to cause that. I take my ferm temps w/ a probe in the beer itself so I would be measuring the beer temp not the bucket or air temp. Currently I notice my beer can hold close to 67* for some time while the ambient temp in the freezer is in the 70s or even 80s. I would imagine the reverse can be true as well (holding temp while the outside air is 10-15* colder). That and the heat tape would be wrapped around the bucket and insulated w/ a layer of reflectix to maximize heat being directed to the beer instead of the surrounding air. Put all of that inside a 2" thick insulation box, I cant see very much heat escaping out out rapidly enough to cause a lot of condensation. I could be wrong though, its been known to happen.