Glycol Temperature Concerns

[Indygunworks]

Hey all. I have recently purchased a two door commercial freezer. Its currently set at -10 degrees F.

I have been kicking around the idea of adding a submersible pump in a approximately two gallon tank inside and running an output and return line through a stainless conical fermentor for temp control. It will be used for fermentation, cold crashing, and lagering.

Is that TOO cold of a temp? I can bump the temp up to 10 degrees for the freezer if needed.

Other thoughts if -10 is to cold is to have a buffer tank on the outside at room temp, a valve to throttle the flow, a coil to allow the liquid to warm a bit before entering the fermentor.

It will be a 7ish gallon conical, and i brew 5 gallon batches on a grainfather.

I am concerned about flash freezing on the chiller coil, and shocking the yeast.

thanks in advance for wherever this discussion goes.

 

[Vale71]

This simply won't work as air will act as insulator between the evaporator coils in the freezer and the glycol in the tank. You will be able to get the glycol chilled initially but as you start cooling your fermentor with it the glycol will get warmer and warmer until you won't get any cooling power at all.

But to answer your original question, if you could really get the glycol to -10°F that would be really way too cold and you would risk ice buildup in the tank coil. Besides that, you'll need a very high percentage of glycol in your mixture to keep it from freezing, which increases cost. 10°F is already a bit on the cold side but could still work unless you want to lager at temperatures that are close to the beer's freezing point. As you near the critical point if the glycol is too cold you will get ice buildup and that ice will act as insulator preventing your chiller from actually holding the beer at the desired temperature.

 

[Indygunworks]

I guess I dont understand why two gallons at ten degrees wouldnt work. Thats a large amount of mass. conicals will be insulated. I will only be maintaining fermentation temp on 5 gallons.

would it change the conversation at all if i added some heat sinks onto the sides of the metal glycol reservoir?

 

[Vale71]

Mass is not relevant. Your tank will absorb a certain amount of heat per unit of time, depending on insulation and temperature differential. As the tank is cooled to a temperature much lower than ambien heat exchange can rise to respectable levels. In order to maintain temperature you'll need to first pump that heat from the tank to the reservoir and than from the reservoir back to the environment through the freezer's cooling circuit. This is a continuous process where every stage needs to be able to transfer the required amount of heat per unit of time to the next stage. Your tank is sittin in a freezer that is probably capable of transferring a lot more than what you'd actually need for such a small tank, but you have insulation (air) between the reservoir and the cooling system and this will prevent your system from delivering the level
of performance needed.

 

[Indygunworks]

Would it help if you saw those two photos and realized this was not a small under powered chest freezer. this thing has to have its own dedicated 20 amp circuit.

 

[Homergah]

Would it help if you saw those two photos and realized this was not a small under powered chest freezer. this thing has to have its own dedicated 20 amp circuit.

No, it doesn't help to see the pictures. They can't change the reality of our physical universe. If you get your glycol down to -10 it will be that temp for only a moment once you start circulating.

Edit: After reading my above post I realize I may have come off like a Dick...Tracey. Sorry. Please don't let anyone discourage you from experimenting. You may have different results than those of us who have already attempted what you are now attempting. If you have lots of heat sinks and move a lot of air around inside the freezer, it probably still will not keep a 5 gallon batch from getting too warm during high fermentation. However, if you place the fermentor itself in the freezer, it will work beautifully with a temp controller on the freezer while receiving data from temp probe inside fermentor.

 

[Vale71]

Showing pictures isn't going to change the fact that you will be trying to transfer heat from the glycol reservoir to the freezer's evaporator coil using one of the best thermal insulators known to man, air. Have you ever wondered why commercial chillers always have the evaporator coil fully immersed in the glycol solution? I assure you that's by design and not by accident.
But of course you're free to try it our for yourself. I'm sure you'll learn a thing or two in the process, but one has to wonder why you would come here asking for advice in the first place??

 

[phreaky]

I'll give it a solid maybe, and throw my anecdotal evidence in. I did nearly the same thing you are thinking, except I used it to run glycol along my trunk line to my tower 10 feet away. I had a junk 5 gallon keg that I cut the top out of, filled with water, and ran a small pond pump in that sent the cooled water down 10 feet of line, through the tower, and back. It definitely kept it cooler than ambient, however it never kept it as cold as the fridge. With the fridge running at 34, the reservoir never got below 48, and the first beer poured at 50-52. The stainless keg just didn't have enough surface area to transfer all the heat gain back into the fridge. I ended up getting a 12x16 transmission cooler, and pumping the return line into it before dumping it back in the keg. That got the reservoir temps down do 38, which made the system almost usable, but still had a bit of foam and warm beer on the first pours.

Being that you are shooting for a much lower temperature, it may be able to work if you include some sort of heat exchanger, and expect the cooling liquid to be much warmer, like 20 degrees warmer than the set point of the freezer. But even with it that warm, that's still colder than needed for a glycol fermenter. I run my chiller at 28 degrees, and it has no problem cold crashing down to 35 degrees.

 

[Vale71]

A keg has ample exchange surface if you could actually wrap the evaporator coil around it. The issue is with the air in between. Just to give you an idea, here is the thermal conductivity of air vs. stainless.

AIR(dry): 0.026 W/m*K
STAINLESS: 17.0 W/m*K

Air is 654 times less conductive than stainless and the larger the freezer the more air you will have in between.