Chest Freezer -> SSBrewTech Chronical cooling loop

[jhanlon]

I'm seeking input on an improvement to my current temp control (cooling) setup. I've done a lot of searching, but can't find a post with this exact setup.

My setup and environment are pretty standard (pic below):

• 7 gallon Chronical BME
• Aquarium pump inside chest cooler filled with water sends chilled water through fermenter coils.
• Pump cycles regulated by temp controller, temp probe is in the fermenter thermowell.
• Frozen water bottles cycled into cooler water once or twice a day, depending on season and ambient temps.
• Warmest summer temps in garage are 80-85 deg
• Typical ale fermentation temp is 64. No issues pegging it there, or even a bit lower, with current setup.

What I'm trying to solve for is the need to cycle frozen water bottles; If I miss a cycle because I'm away from the house, especially during days 1 - 4 of fermentation, I'm in trouble. (And it's just a pain in the ass.)

In the picture, just to the left of the cooler, is a sparingly-used 5.2 cu. ft. Magic Chef chest freezer. I override the thermostat on it to lager beers, when I'm making those.

My idea is this:

• Place a water reservoir, with the pump, in the freezer, with a glycol/water mix (maybe 35/65 which has a freezing point of about 3F).
• Run insulated cooling lines (~3-4 ft. each) from the reservoir out the top of the freezer to fermenter.
• Override freezer thermostat and keep it around 10F, using temp probe dangling (in the air, not the liquid) at same level as reservoir.
• Use freezer to store other things that you typically keep frozen, so that it's not just to keep water cold.

I've read why this won't work for a wort chiller, due to liquid taking too long to cool back down. I'm not using it for this; I have wort chilling solved for already.

My rationale for this working is this:
Typical pump cycles during fermentation are maybe 5 - 20 seconds, as I use 1 degree differtial, and keep the water in the cooler pretty cold with the ice bottles. This means that not much cooling liquid will be leaving (and thus returning to) the reservoir for each cycle; the freezer should easily be able to keep the solution extremely cold, and even if it rises to 20F after a cycle, the cooling solution being cycled is still probably 20-25 degrees cooler than my current setup. Since the freezer air temp (and not the liquid) is triggering freezer cycles, I see less freezer cycles being needed. Overall, I see the freezer as a version of the chest cooler, except that it can keep itself cold via automation.

What am I not thinking about?

I am not interested in buying or building a DIY glycol chiller at this time, as I can get by with what I'm currently doing.

Thanks in advance for any input.

 

[apache_brew]

I think the general issue with this approach is cooling capacities of freezers and refrigerators (rating of compressor) aren't high enough for the real time cooling requirements of active fermentation and especially cold crashing over brewing durations. How to Size a Brewery Chiller | BV Thermal Systems There's several chiller sizing calculators from commercial chiller manufacturers out there. You'll most likely find that while the glycol in the freezer will do a good job initially to in cooling your wort/beer, once the reservoir heats up, it will take longer to cool it down than you want to produce your beer (you wont be able to maintain chilling and the freezer won't cycle off)

That being said, take a look at the numbers for yourself and try it anyways to see how it turns out. Maybe there's a sweet spot with batch size and or temperature range that could work well for homebrewers.

 

[Gruel]

I like the straightforward calculations in US units at that link, but I think the OPs problem might be not so much the raw cooling power (in BTU/hr) of his freezer, but the heat transfer from the liquid used to cool the fermenter via the air inside the freezer to the freezer evaporator. I.e. the freezer might have enough raw cooling power, but you also have to be able transfer the heat to a liquid storage container inside the freezer at the required rate.

Now, if that freezer can produce the frozen bottles at the required rate, then I think it should be able to cool the circulating fermenter liquid (as long as it is not in an insulated container inside the freezer) since the same effective cooling power (amount of heat energy removed per day from the fermenter) is required, regardless whether the heat is transported by moving bottles or by pumping liquid.

 

[Argyll Gargoyle]

This sounds like an awesome idea. What was the reason for planning to override the freezer tstat? Just to get the glycol colder?