Metzen's Mini Fridge Glycol Chiller Conversion

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Metzen

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I'm transitioning from a fermentation chamber to a glycol cooling system using a converted mini fridge with a freezer compartment as a chill source. I had read a few comments on this approach on these forums but nothing that provided much detail on build or examples. I'll keep this thread updated as I test my first brew and make observations.

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My ferm chamber worked perfectly fine, but let's start with a few key reasons for the transition to glycol:

1) Wanting to ferment more than one batch at different temps at the same time (i.e. Ferment, cold crash, or lager different batches at the same time)
2) Lack of space in my "brewery" (term used very loosely) and unwillingness to buy multiple fridges to handle more than one vessel

So a glycol based solution was appealing. However, I only brew small batches (usually 5 gal, rarely 10 gal) and spending $1k or more for a chiller would never get approved by the Mrs.

I considered a few DIY options:

(i) AC unit conversion - documented in depth across this forum - seemed a bit clunky and wouldn't fit well in the closet (see photo above) in which I planned to keep my fermenters. I also planned to stack Brew Buckets and this wouldn't have been an a very sturdy base for this
(ii) Chest freezer with glycol reservoir - never liked the idea of relying on air or surface contact between a freezer and the reservoir as a heat transfer medium
(iii) Water chiller or aquarium chiller - concerned that they wouldn't provide enough cooling to lager or crash chill
(iv) Mini fridge, immersing the freezer compartment in the glycol/water solution - decided to go this route (more info on how it works below)

The benefits of the mini fridge are:
(a) self-contained chiller that I could store in a living space if needed (with a decent mini fridge and blingy vessel to sit on top, you can turn this into a conversation piece IMHO)
(b) can stack my ss brewtech buckets on top of fridge
(c) super cheap as the mini fridge cost me $60 with incremental cost of an ink bird temp controller, barb fittings, a container to hold the glycol, etc. All in was about $120 excluding the BrewBucket cost and accessories given these items are required regardless of the type of chiller

Basic components/concept of this system (for those less familiar with glycol chilling):
- The freezer compartment of the mini fridge cools the glycol by being immersed directly in the glycol reservoir and solution
- Ink bird or other temp controller reads the temperature of the glycol and turns the fridge on and off to keep the glycol at a set temp (this is independent of the fermentation controller that will control your fermentation temperature, see below)
- Your fermenter will need an immersion coil, a glycol or cooling jacket, or some other way of getting the chilled glycol running through or around the wort to cool it down. I use the ss brewtech FTSs for my brew bucket that has an immersion coil dropped from the fermenter lid into the wort.
- You will need a fermentation controller (I am using the SS brewtech FTSs that goes with my brew bucket, but any is fine) that reads the temp of your fermenting beer and toggles a pump on and off that sends the chilled glycol to the immersion coil, cooling jacket, etc. when the fermenting wort needs to be cooled. The pump sits in the glycol reservoir in the mini fridge and sends the glycol through tubing running out of the fridge to to the fermenter.

Parts for my build:
- Haier 2.7cf fridge (HC27SG42RB) (bought an open box with minor external damage during a sale - $60)
- Polycarbonate container (to be used as glycol reservoir) rated for freezing temps with a minimum 9.5" width, max 12" height, max 12" length
- Ink bird or other temp controller
- 2 x 1.5" 1/4 MIP nipple fitting
- 3 x 3/8" barb to 1/4 MIP fitting
- 3 x 1/4 FIP to 1/4 FIP elbow fitting
- 1 x 1/4 FIP to 3/8 MIP fitting
- 1 x 3/8 barb to 3/8 FIP fitting
- 3/8 ID 1/2 OD vinyl tubing
- 4+ clamps to secure tubing to barbs
- optional but recommended: quick disconnects for tubing (on order for my setup)
- 4 x 7/16" ID neoprene washer
- 4 x 5/8" ID metal washer

DISCLAIMER: FOLLOWING THE BELOW WILL VOID ANY WARRANTY ON YOUR FRIDGE. I ALSO HAVE ONLY TRIED THIS AND AM STILL TESTING ON MY OWN FRIDGE. I'M NO PRO AND HOLD NO RESPONSIBILITY IF YOU BREAK THE FRIDGE, SPRAY GLYCOL EVERYWHERE, DAMAGE SOMETHING ELSE IN THE PROCESS, OR THIS JUST DOESN'T WORK FOR YOUR SETUP.

Build steps:
1. Unscrew and remove the plastic freezer compartment door.
2. Unscrew from the roof of the fridge one side of the freezer compartment farthest away from the coolant line (middle of the fridge in my unit, coolant line is back right corner).
3. Once freezer compartment is connected by only one side, SLOWLY and CAREFULLY bend and straighten the freezer compartment down against the side wall of the fridge. DO NOT CRIMP OR KINK ANY COOLANT LINES INCLUDING THE LINE FEEDING THE FREEZER COMPARTMENT. You can bend the compartment easily by sticking a few fingers or a cylindrical object between the bottom corner of the freezer compartment and the side wall of the fridge to use as leverage/support. Just go slow.
4. Remove the thermo probe of the fridge's thermostat from the freezer compartment (usually connected with a metal clip to the bottom of the freezer compartment)
5. Position your flattened freezer compartment into your glycol reservoir. Secure your reservoir in the fridge.
6. Drill two holes into the fridge where there are no coolant lines or other obstructions (I used the door as there is usually no obstruction there in most if not all mini fridges). I drilled 5/8" holes that fit my 1/4 MIP nipple fitting. My door was 1.25" deep (at its shallowest point in the top shelf on the door - avoid the plastic structures of the door that jut out to form shelves and can dispensers) so a 1.5" length nipple worked well.
7. Feed a 1/4 MIP 1.5" long nipple through each hole and add a neoprene and metal washer to each side (neoprene closest to the fridge to provide insulation) before attaching your barbed fittings.
8. Attach and cut vinyl tubing to length both inside the fridge to reach bottom of glycol reservoir and outside fridge to connect to fermenter.
9. Drop the pump connected to your fermentation controller (whichever you use) into the reservoir and ensure it is connected to the outlet tubing/fitting leaving through the fridge wall.
10. Fill your glycol reservoir with 33% glycol (~1 gallon) and 66% distilled water (~2 gallons) assuming your reservoir can hold 12 quarts or more. There are other posts on proper concentration of glycol you can reference.
11. Drop your ink bird or other temp controller temp probe into the bottom of the reservoir.
12. Plug the fridge into your ink bird or temp controller. I feed the ink bird wires through the top of the fridge door near the hinge.
13. Ensure the fridge's thermostat is set to a moderately cold setting (try not to overwork the compressor during the initial cooling of the glycol) and reposition the fridge's thermostat probe back into the flattened freezer compartment.
14. Set the ink bird or your temp controller to a level 15-20 degrees F below your target temp so that the glycol is chilled to 15-20 degrees below target.
15. Let the ink bird or temp controller maintain glycol temps while your fermentation controller toggled the pump on and off when cooling is needed.

My main concern with the mini fridge was whether it would provide enough cooling for lagering and crash chilling.

As a first test, I brought the glycol down to 10-15 degrees without much of an issue. The fridge was warm to the touch on both sides as expected but not overly hot. The key is not to overwork the compressor when the 3 gallons of glycol/water are first added. Ramp temps up slowly. Once you are in range, I found that the temp is maintained quite well. I was pleasantly surprised with how efficiently the mini fridge cooled. I ran an external loop of tubing between the inlet and outlet ports without insulation just to test the effect of heat loss while running the pump. The fridge and ink bird seemed to keep up just fine.

The next test is to chill 5 gallons of wort/water running through my SS Brewtech Brew Bucket. I also have a batch completing primary in my ferm chamber now. I plan to attempt a crash chill in the next couple weeks. Will report back soon.

Pending additions/changes to the system:
- Quick disconnects with valve shutoff to enable easy detachment and reattachment of glycol lines to the fermenter
- Insulation for the fittings and other areas of potential heat transfer (this is super critical when using a system not designed for glycol chilling as any heat transfer not from the wort will significantly impact efficiency)
- Door clamp/lock to ensure the fridge door doesn't pop open while in use. I have found that the vinyl tubing I use slightly straightens when cooled and puts outward pressure on the door given the lines feed through the door. I don't want it popping open unintentionally.

Would appreciate feedback or suggestions if anyone has them!!

Cheers
M
 

narddawg314

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I recently bought a cool zone wrap but was having the same dilemma about how to cool the damn thing. I have a mini fridge that I currently use for single 5 gallon batches as well and this could be the next evolution....great build in my opinion.
 
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Metzen

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The common option of an ice bath in a cooler is too much of a hassle - replacing frozen bottles several times a day wasn't going to work for me. Plus I travel for work and wouldn't be around enough to be able to manage it. Hoping this will do the trick and enable varied temp ranges down to cold crashing. We shall see...
 

narddawg314

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any chance to test this yet? I'm wondering what size reservoir you'd need to hold two 5 gallon fermenters in the mid 60's where the ambient temp is 70-75.

I'm considering modifying a cube mini fridge so that I can lay it on it's back...re-orient the compressor so that it's sitting upright of course, and then seal the inside so I can fill it with glycol instead using a container like you have in there.
 
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Metzen

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Haven't had a chance to test yet as I'm on a business trip running long. I've got a batch that I'll be dry hopping tomorrow and then cold crashing Sunday. I should have some initial results that I'll post here on Sunday.
 

Sadu

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Do you still get to use the rest of the fridge for something else? Its a good idea immersing the freezer unit, Im sure this will work great. I have a glycol reservoir in the back of my kegerator and it keeps ales at low 60s very nicely.
 
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Metzen

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There is some shelf space left but I don't plan to use it. The fridge I'm using is small at only 2.65 cf so you wouldn't be able to fit much more in it. If you had a larger unit i'm sure you could. I'm searching for a larger container to use as a reservoir to fill the full width of the shelf it sits on.
 

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I'm searching for a larger container to use as a reservoir to fill the full width of the shelf it sits on.
I've been considering fabricating one...I can weld but not sure that metal would be an ideal container. DIY is frustrating and fun all at the same time.
 
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Metzen

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I decided on a commercial food bin slightly bigger than the one I showed in the photos. Thought about fabricating but I'll wait till I get a few runs in. If not needed I'm fine not spending the time on a $12 part
 
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Metzen

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Quick update. Switched on the FTSs for the first time to start the crash chill today. She got down to 50F in the fermenter no problem (6gal batch inside with ambient temp at 72F). So I'm comfortable this will be viable for lagering 1 vessel. However, she definitely started to stabilize (you'll see the inkbird sitting at 47F with a target of 29F; fermenter is at 49.5F near the bottom and at 50.3F near the lid).

I reconfigured the position of the pump intake and the return tube in the reservoir to ensure max exposure of the glycol to the freezer coils. Will report back on progress later.

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Metzen

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After over 24 hours - it looks like we stabilized at 42-43F in the fermenter. I'm a few degrees away from where I'd like to be.

First area of focus was insulation on all the tubing and fittings. This all seems to be working well with no major, noticeable temperature leakage to the touch. You'll notice I used two different insulators for the tubing. The thicker foam (on the return) gives no indication of inside temp while the slimmer black foam (glycol out) is slightly cool to touch. Not sure if this is due to insulation efficiency or just the fact that the outlet should be cooler than the return. I may replace with the thicker foam everywhere and see if it has any impact.

The biggest area of heat transfer seems to be the bucket itself. Even with the neoprene jacket, it is sweating (the jacket is damp with beads of water forming on the ss brewtech logo) and quite cool to the touch. The exposed steel portions of the bucket are also obviously sweating as expected.

As noted above, I continued to play with the position of the pump and glycol return in the reservoir to ensure highest utilization of cooling by the freezer coils. I will slide some risers under the reservoir to immerse a bit more of it in the glycol.

As ambient is around 70, almost 30 degrees of cooling isn't disappointing, but my goal was high 30s (i.e. 38ish).

Any other suggestions?
 

narddawg314

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I wonder if you put some frozen 2 liter bottles in the fridge to take up some space and help keep the temp down, if it would get cooler?
 
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Metzen

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Any updates? Likes, dislikes, anything you would do differently?

Haven't been able to brew since the last batch.

Pros: Easily get down to lagering temps and good enough for cold crash. Cleaner look than most DIY glycol chilling setups (keep it next to the bar in my basement). Cheap.

Cons: Won't be able to manage significant temp differentials for larger batches (>10 gals). Might be able to lager 2 5 gal batches at once but not more.

Next time I will raise the reservoir to get more of the freezer coils in the glycol to further lower the minimum temp.

Overall, definitely happy with it for my general use.
 

Mordhaus

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Haven't been able to brew since the last batch.

Pros: Easily get down to lagering temps and good enough for cold crash. Cleaner look than most DIY glycol chilling setups (keep it next to the bar in my basement). Cheap.

Cons: Won't be able to manage significant temp differentials for larger batches (>10 gals). Might be able to lager 2 5 gal batches at once but not more.

Next time I will raise the reservoir to get more of the freezer coils in the glycol to further lower the minimum temp.

Overall, definitely happy with it for my general use.
Thanks for the info. This is one of the routes I was considering, but ended up buying a 5k btu ac unit to build a chiller.
 

tjpfeister

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Any more follow ups? I was considering this option, but looking to control two fermenters at 10gal each.
 
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Metzen

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Any more follow ups? I was considering this option, but looking to control two fermenters at 10gal each.
I’ve been using it and no issues to report. I have since been stepping down the temps when crashing to reach lower temps (at 44 F, then 42, then 40, then 38). Pausing at each step seems to allow the glycol in the fridge to stabilize given that it is not warming while moving through the lines. It then can maintain the sightly lower temp of the next step. 38 F is the lowest I’ve gone.

Also, I’ve noticed in the graphs that the beer temp stalls when the glycol is below freezing (glycol will be 28 and below but the beer temp won’t drop lower than 38ish). I suspect it has to do with ice forming around the coil and insulating the even cooler glycol that’s in the line. Therefore, I have been keeping the glycol at no less than 33/34 as it allows me to get beer temp to 37/38 no problem without risking ice forming in the bucket.

I am crashing 5.5 gallons of an ale now 35 degrees F below ambient.

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Based on what I’ve seen, I think 35 degrees F below ambient is the limit for a 5 gallon batch (5.5 gallons in the fermenter). I’ve never tried a 10 gallon.

Here’s how I would estimate its capacity (I don’t know if the math holds - please someone chime in if you know better - I don’t have time to do the research unfortunately):

Observed:
5gal * 35F below ambient = 175 cooling units

Estimates:

Three 10 gal batches at Ale temps
3 batches * 10gal * 5F below ambient (ale fermentation) = 150 cooling units (Works!)

One 10 gal batch at Lager temps
1 batch * 10gal * 20F below ambient (lager fermentation) = 200 cooling units (Maybe but probably not?!)

To answer your specific question, I definitely think you could control two 10gal ales with it (probably up to 3), but I’m not sure if you could lager even one 10 gal batch (would depend on your ambient temps). Crashing is also probably out of the question.

Cheers
M
 
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ganrique

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What pump are you using inside the fridge?

A regular submersible aquarium pump?
 

tjpfeister

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Cheers to Metzen for laying the ground work. Encouraged by his findings I took my own approach.

My thoughts are- by increasing surface contact of the evap coil I can enhance the cooling ability of the unit, and by using the entire fridge as a tank, I can increase the thermal mass.

So the old dorm fridge I picked up is charged with R12 (and older, colder refrigerant from the 80s and prior). My initial testing found that, when set to max, the evap coil would get down to -14F, the air inside the fridge down to 20F, and the test jars (two one quart jars) were freezing... This made me optimistic that my $16 investment had potential.

So the RTV is curing again (silicone WILL NOT bond to acrylic plexiglass) on my new beefed up polycarbonate (lexan) front cover. If it holds 12gallons of glycol solution successfully this time, I'll post my own thread on it... If it doesnt, to the curb it goes!

Fingers crossed
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Metzen

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Cheers to Metzen for laying the ground work. Encouraged by his findings I took my own approach.

My thoughts are- by increasing surface contact of the evap coil I can enhance the cooling ability of the unit, and by using the entire fridge as a tank, I can increase the thermal mass.

So the old dorm fridge I picked up is charged with R12 (and older, colder refrigerant from the 80s and prior). My initial testing found that, when set to max, the evap coil would get down to -14F, the air inside the fridge down to 20F, and the test jars (two one quart jars) were freezing... This made me optimistic that my $16 investment had potential.

So the RTV is curing again (silicone WILL NOT bond to acrylic plexiglass) on my new beefed up polycarbonate (lexan) front cover. If it holds 12gallons of glycol solution successfully this time, I'll post my own thread on it... If it doesnt, to the curb it goes!

Fingers crossed
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Cheers. Looks super cool. Looking forward to seeing how it turns out.
 

Transamguy77

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I don't know how I missed this thread! I had a similar idea but not use glycol and to pump it through a heater core with a fan behind it to cool my fem chamber that I added to the small fridge.

Super cool idea thanks for sharing.
 

Gadjobrinus

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Agree with transamguy, really happy to be coming to the thread, if only today. Big thanks Metzen, and everyone else, for this. I always just did lagers in a controlled fridge, but I am a bit stuck in working out environmental control for my English ales, which are my love and my focus. I will be starting them in an open fermentor, and though I have a coolbot that uses a monster AC (when I was making cheese, worked great), I'm no longer comfortable blowing cool, unfiltered air over the beer. So was looking for a solution and the idea of an IC or "attemperator" seemed a good one, just couldn't figure out how to do it. This gets me going.

Many thanks again for sharing your ideas.
 

TANSTAAFB

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Cheers to Metzen for laying the ground work. Encouraged by his findings I took my own approach.

My thoughts are- by increasing surface contact of the evap coil I can enhance the cooling ability of the unit, and by using the entire fridge as a tank, I can increase the thermal mass.

So the old dorm fridge I picked up is charged with R12 (and older, colder refrigerant from the 80s and prior). My initial testing found that, when set to max, the evap coil would get down to -14F, the air inside the fridge down to 20F, and the test jars (two one quart jars) were freezing... This made me optimistic that my $16 investment had potential.

So the RTV is curing again (silicone WILL NOT bond to acrylic plexiglass) on my new beefed up polycarbonate (lexan) front cover. If it holds 12gallons of glycol solution successfully this time, I'll post my own thread on it... If it doesnt, to the curb it goes!

Fingers crossed
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Any updates?
 

tjpfeister

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Yes-ish, I'm currently wet testing the "vessel." That is to say that at this point it does indeed hold 10gal of 50/50 propylene glycol and it does not leak. I am opting to stop at 10 for now and hold my other 2 gallons in reserve as the tank is quite full and the front bulkhead, despite being made of 1/4" lexan, is still deflecting slightly under the weight (calculated static force against that surface is about 40lbs). I'll throw some pictures up to show the innards and the frame I welded to secure the bulkhead without cracking it (like also happened to the acrylic I tried previously).

I currently have a batch in my conical and the cooling cool needs light modification... when thats all done I'll post the results in a new thread so as to end any thread-jacking
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tjpfeister

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Oh yeah, and I need to modify the hinges to accept the extra 3/8" of material now under the door
 

tjpfeister

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In case anyone is following- the first two hours of run time demonstrated a problem. The condenser simply wasnt built to dissipate THAT much thermal energy. The fridge smelled hot and the compressor kept tripping the thermal breaker. After 2 hours it had stalled at 54F when starting at 62F. Air movement is needed.

Tonight I purchased a small fan and positioned it to blow over the condenser and compressor... The results are much better, the first hour dropped 62F down to 47F and the unit is not getting hot. By my math 15Fx10galx8lbs= 1200btu

Thats not massive, but it is a respectable number. Ill keep it running and post back the results as I feel significance warrants.

Suffice it to say, without a condenser fan this project will not work.
 

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Metzen,
Have you added a 2nd fermenter? If so, I assume you you ran a separate set of lines. Is the 3 gal of glycol water mix sufficient or did you increase the size of the reservoir? Did immersing more of the coil help. I am using 7 gal chronicals and want the ability to control 2 different brews. I am trying to decide to go the ac route or yours. This is cleaner look.
 

tjpfeister

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Sorry to butt-in, but I can add some insight. I used Metzon's notion and set up the fridge as a 10gal tank, with two circuits (planning on adding a second vessel, likely 7gal). The 10 gal bath, set to 20*F, is capable of getting my uninsulated fermenter down to 42*F. This does tend to tax the glycol fridge, and it runs continuously even with a fan blowing on thr condenser. (You need to add a condensor fan if you plan on chilling a larger volume of glycol, there's too much thermal mass for the light duty condenser to dissipate). With this in mind, temp controlling several vessels is not an issue, but cold crashing may be, depending on ambient conditions. Hopefully insulation remedies this, but my personal rig has only be used to test water and is currently working on its first batch of beer.

I would love to hear more back on what the OP has found with his; cheers!

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Bkenyon61

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I got the SS Brewtech FTSs2 conversion kits and it includes the insulating jacket so it should be more efficient. With my set up I would typically have 5.5 gal in the fermenter and I could see these Being at diffferent temps. Based on other posts a 5000 btu ac unit with 6 gal glycol mix is more than sufficient. Do you think a mini fridge would achieve the same return
 

narddawg314

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Sorry to butt-in, but I can add some insight. I used Metzon's notion and set up the fridge as a 10gal tank, with two circuits (planning on adding a second vessel, likely 7gal). The 10 gal bath, set to 20*F, is capable of getting my uninsulated fermenter down to 42*F. This does tend to tax the glycol fridge, and it runs continuously even with a fan blowing on thr condenser. (You need to add a condensor fan if you plan on chilling a larger volume of glycol, there's too much thermal mass for the light duty condenser to dissipate). With this in mind, temp controlling several vessels is not an issue, but cold crashing may be, depending on ambient conditions. Hopefully insulation remedies this, but my personal rig has only be used to test water and is currently working on its first batch of beer.

I would love to hear more back on what the OP has found with his; cheers!

Do you have any in progress photos of how you sealed that fridge? Or what materials you used?
 

tjpfeister

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Do you have any in progress photos of how you sealed that fridge? Or what materials you used?
I intend, at some point, to start a thread with all the details. Short version on the story is to use 1/4" thick polycarbonate (not plexiglass), seal it all with silicone (I recommend Permatex The Right Stuff- found online or at automotive stores), and I built the steel frame with 1/8" x 1" stock cut and welded to fit. Screw holes were all countersunk so the surface is flat and the door seal sits flush.
 

jaymosbeershack

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Looks really nice. Way cleaner than my set up. I dealt with my cold crash by adding a condenser/evaporator with an extra copper coil in a block of ice. Keeps the glycol cold for the long running.
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tjpfeister

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Not pretty, but I insulated the lines and fridge. You get (predictably) diminishing returns as delta-temp between glycol and beer gets smaller, but by stepping the temp down in increments, it allows the glycol bath to recover and successfully hammer the temp down each time. Pardon the clutter, but here it is at 38*F. I could likely push to 35 if I wanted to listen to the pump run more.
So at this point I have to call mini-fridge-large-glycol-volume-chiller a success.
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tjpfeister

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Follow up- sucessfully hit 35*F and hit the beer with gelatin. Set the differential to 3*F so the pump kicks on at 38*F. This is pushing the limits of the system as the pump kicks on every 110 minutes or so and runs for about 12 minutes to get back to 35F, the fridge doesn't get much down time. To Rehash the numbers- thats roughly 12 gallons of beer being chilled by 10gallons of glycol at 20F.
I also suspect that the diaphragm pump is warming the glycol as I have seen less and less return below 42F. I wonder if the pump could draw through the coil rather than pushing, if that might help. Obviously better insulation and more glycol volume would also improve my results.
 
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