Mini Fridge as a Head Unit for Fermentation Cabinet

I just had the idea after reading about a few other project so apologize if this had been mentioned. CL is full of too small mini fridge's that can't hold one or two carboys, so what about building a box with a front door and a small mini fridge on top with conduit or PVC pipes going from the bottom of the fridge to the larger box underneath? It seems simple enough, I know i would need temp control to keep it around 65-68 deg F...the best part is that the head unit should remain cold enough to keep a few beers at serving temp!

Sounds like an old "monitor" top fridge from the 1920's.

http://www.antiqueappliances.com/monitor_top_refrigerators.htm

They look cool! Could be a neat idea.

A few points to consider:

Just remember that the cold air in the fridge will sink or settle down into the Fermentation Chamber. You might need to rig up a thermostat controlled door or flap to let the temp in the fridge be beer cold and the chamber be fermentation temps.

My plan is to build mine with the fridge on the bottom. I am thinking route the air into the chamber low and return air high. Then a simple rubber flap over the inlet side in the chamber and fridge. This might help prevent air movement in the duct work caused by cold air from affecting the temp in the chamber. It is kind of like a balance act with the air temps in the duct work, fridge and chamber.

At this point, testing will be needed for sure.

my plan is to have the mini fridge (head unit) on top with a 6pk or so in it, duct work connected allowing the cold air to drop in to the cabinet and a fan wired up to the thermostat to cycle the air only when the fridge is running to pull air up a return and into the head unit (mini fridge);
so cold air falls down into the cabinet, the return pulls air from the bottom of the cabinet up to the top so it gets completely cycled. I have a Johnson temp control i am going to place in a White Labs vial of water placed in the cabinet and it will control the return fan and the mini fridge head unit.

this is a project that i am going to get started on soon...i could also put a heater in there to lager in the cold winters here in ohio.

extra_medium said:

my plan is to have the mini fridge (head unit) on top with a 6pk or so in it, duct work connected allowing the cold air to drop in to the cabinet and a fan wired up to the thermostat to cycle the air only when the fridge is running to pull air up a return and into the head unit (mini fridge);
so cold air falls down into the cabinet, the return pulls air from the bottom of the cabinet up to the top so it gets completely cycled. I have a Johnson temp control i am going to place in a White Labs vial of water placed in the cabinet and it will control the return fan and the mini fridge head unit.

this is a project that i am going to get started on soon...i could also put a heater in there to lager in the cold winters here in ohio.

Click to expand...

I'd keep the probe out of a water filled vial. What seems to work best for me is to tape the probe against the carboy/bucket with a rag over the exposed part. It's not tracking the exact temperature of the fermenting wort, but it's better than just maintaining a static temp in the chamber. It's better because fermenting wort can be several degrees above ambient temperature, so you might need a colder chamber to keep the wort at the proper temp.

I think I got it.

Your Johnson controller is going to control the fridge based on the temp in the chamber.

extra_medium said:

…and a fan wired up to the thermostat to cycle the air only when the fridge is running…

Click to expand...

A fan alone will NOT stop all the colder air from falling or ALL the warmer air from rising.

From your earlier post:

extra_medium said:

...the best part is that the head unit should remain cold enough to keep a few beers at serving temp!

Click to expand...

Sadly, without a way to totally prevent air movement the fridge temp will fluctuate between slightly above and slightly below the chamber temp.

You might try a little change. Get a cheap 120mm PC fan and wire it to a cell phone charger. Then connect it to the duct work from the fridge to the chamber. Have this fan on all the time and it should move plenty of air to keep temps even throughout. You could then extent the cold air duct from the fridge down to the bottom of the chamber and the warmer air return up high.

[While not to scale maybe this drawing will help explain what I am saying.]