How to eliminate kreezer stratification? (yet another temp/fan question)

[jseyfert3]

My current kreezer is a Magic Chef 5 cubic foot model. A 2x8 makes up the collar. Recently I added a 1.5 gallon Torpedo keg with an endless carbonation lid. This is plumbed into the RO water, and sits on top of a 5 gallon Torpedo keg. Allows endless carbonated water, and still have three 5 gallon kegs for beer and cider (four taps total).

Works great for endless carbonated water. Downside is that now that we aren't pulling water out of a 5 gallon keg, and the 1.5 gallon keg is so high, temp stratification means the water is too warm, and can't carbonate as much as I'd like. Also not as cold as I'd like.

I tried placing a 120 mm computer fan on some legs a few inches off the floor, blowing up between the kegs. The idea/hope was this would push cold air up and cool the 1.5 gallon keg, plus cool the lines for the taps. But it did not. Some quick checks with an IR thermometer showed the inside collar of my kreezer and the 1.5 gallon keg are roughly 50-52 °F after install of fan. IR thermometer showed ~52 °F for water freshly poured into a glass.

Do I need more fans? More powerful fans? This definitely does not seem to be anything close to the world's most powerful computer fan.

I also own a 3D printer, my thought was printing a duct. Have the fan blow into the duct near the floor of the kreezer, and the top of the duct lets air out at the top of the kreezer.

All thoughts and suggestions welcome. I can get pictures later this evening, if desired.

 

[day_trippr]

Put the 1.5 under the 5...

Cheers!

 

[jseyfert3]

Put the 1.5 under the 5...

Cheers!

That was my first thought. Unfortunately, while the Torpedo kegs happily stack in whatever combination, the endless carbonation lid has a water ball lock fitting that sticks up in the middle of the keg and prevents the Torpedo kegs from stacking due to the height of the fitting.

 

[day_trippr]

Well that is just unfortunate

So...in my 14cf keezer holds ten kegs in two rows (2x5) with the rows positioned near the walls leaving an "alley" down the middle. I have a temperature sensor 2" above the floor and another 2" below the lid liner, and I have a 120mm fan running 24/7 resting on the compressor hump blowing horizontally down the "alley" the length of the keezer.

Even with the fan, when the compressor is running the lower temperature drops quicker than the upper, but when the compressor stops the lower quickly catches up to the upper and they track quite tightly.

My take on this is if I positioned the two rows of kegs together in the middle leaving space between the kegs to the two walls and then used two fans on the hump positioned to blow along the walls - where the cold comes from - I could tighten the on-cycle temperature gap. But when I look at the Keg temperature plot I don't see any reason to change anything. My keezer cycles just four times a day this time of year while keeping the beer within +/- 1°F to the desired average temperature.

In your case however it might make sense to add a second fan...

Cheers!

 

[jseyfert3]

Yeah, it sounds like you have way more room between kegs, which helps promote natural convective currents. I don't have much free space.

I decided to try a duct. I quickly made a couple models and my 3D printer is hard at work. There's probably easier and faster ways to try this, like tape and cardboard, but you know, when all you have is a hammer...I mean it's not all I have of course, but it's my newest and shinest toy right now, and I really, really enjoy when I can be like "what if I had X?" sit down with CAD for a bit, and a few hours later there it is in real life.

On the right is an adapter, sits over the fan (which is already standing on four 3D printed legs). Just adapts it down to a 75 mm wide duct. On the left is the duct. Stacks on top of the adapter, and I can add as many as I want.

First thing I'll try is just getting the duct near the top of the freezer and see what that does. If it looks promising, I can make an elbow that blows directly on the 1.5 gallon keg. Or maybe a tee, so it blows on the 1.5 gallon keg but also the other way and helps cool my beer lines and taps too.

I think just bringing the duct near the top of the kreezer will help a lot. I felt with my hand and the fan just doesn't blow air very far up by itself.

If this doesn't work I'll look at buying a more powerful 120 mm fan.

 

[AlexKay]

I use 3 ~150 CFM waterproof 140 mm case fans in my 14 ft3 keezer. They’re on the bottom, and they and the kegs sit on a ~4” raised platform, and the fans blow up between the kegs.

I tried some PVC ducting at one point and it was a complete flop.

 

[jseyfert3]

Here is the kreezer:

3D printed duct:

Installed:

I can feel air moving much higher than I could without the duct, so this is looking very promising. Another section of duct is on the printer now. That’s as high as I can print:

 

[jseyfert3]

Printed off two more duct sections. First one I did single wall as spiral vase print. Too flimsy, that’s why it was wavy. Was trying to save plastic. The two new ones printed with a 1 mm thick wall, and are decently sturdy for the application.

I keep breaking legs off the fan though.

With just the one duct section, this morning I pulled off a glass that was 50, not 52, so seems like a slight amount of progress. Though I also had removed the front middle keg as it was just water (the old carbonated water keg).

Once my fan spacer legs print again with more perimeters and out of PETG instead of PLA I’ll put it back together with two or three duct sections and see what it does.

 

[rawlus]

a blower style fan can usually move more air than an axial or pancake fan. may be worth a try.

may also be worth adding a diffuser at the top of the fan duct to disperse the cooler air horizontally across the area rather than direct it towards the lid?

 

[jseyfert3]

a blower style fan can usually move more air than an axial or pancake fan. may be worth a try.

may also be worth adding a diffuser at the top of the fan duct to disperse the cooler air horizontally across the area rather than direct it towards the lid?

Something like this?

 

[rawlus]

Something like this?
View attachment 827601

sure, could work. if you think about the commercial tower cooler fans available, they are generally a blower style fan, like a 5010 or 5020 DC in a small housing and with a flexible or rigid duct to get to the top of the tap tower…. using the premise that cold air sinks and hot air rises it’s circulating colder bottom air to the top and reducing the temp differential between top and bottom.

adding a unidirectional diffuser to the top of your ducting would in theory disperse the cooler air across the top of the kegs somewhat evenly reducing cold spots and addressing some of the issues youve been having with stratification and uneven temp swings within the keezer airspace.

Most kegerators have an internal fan always circulating air in the airspace but keepers/freezer typically do not unless the builder adds one.

When i had a keezer i had two large DC fans attached to the keezer lid with nylon standoffs and airflow pointing downward to circulate are all the time while also keeping the fans off the keezer floor where it was often wet or potential exposure to moisture.

 

[jseyfert3]

Yeah, part of the issue is that probably have is I had gone cheap when I bought the fan. I bought this one from Amazon, they are rated at 38 CFM, with 58 Pa static pressure.

Sticking with the 120 mm axial form factor, this one from Digikey is 117 CFM and 98 Pa static pressure.

Centrifugal blower could be used, though high pressure is needed only if the air ducting provides significant resistance. If you've got a wide duct, you don't have a lot of pressure drop.

 

[jseyfert3]

Well after about an hour of reviewing my Fluids textbook and with a number of assumptions I got a rough pressure drop of 7.4 Pa across a 0.6 m tall duct that’s 75 mm wide.

In short what it boils down to is I certainly don’t need to worry about a blower style fan at these flow rates. I’ll probably loose about 7 CFM out of the 38 the existing fan has. So roughly 31 is what I’d expect.

This jumps to 9 Pa if I plug in 117 CFM, the axial fan form Digikey. This is because most of the head, and therefore pressure, is actually gravity, not losses from the duct.

In short, it indicates my duct is massively oversized, I don’t need to worry about a blower, axial fan is fine, and what I do need is simply a higher CFM fan, if ducting to specific areas doesn’t work.

 

[jseyfert3]

So I didn't try the diffuser yet. I had printed a third piece of duct which brought the outlet to near the top of the small keg. This didn't seem to help much, still getting 50-52 °F pours. Then I pulled it out and flipped the fan so the fan pulled air down the duct from the top. This seemed to be way more effective, and now the water pours are 48 °F.

Since I have two more of these fans, I'm going to try printing another adapter and duct section and put it in the front left section of the kreezer, as the first fan and duct seems to circulate air well, but it's in a tiny opening. The front left is a bigger area, with more walls of the freezer that get cold, and I'm thinking with that circulating it'll help even more.

 

[day_trippr]

fwiw, I'm on my 3rd full size chest freezer and they all located their evaporator loops fairly high up on the cabinet walls. The bottom foot or more did not have any coils adjacent, which I expect makes collecting and guiding "cold" tricky...

Cheers!

 

[jseyfert3]

fwiw, I'm on my 3rd full size chest freezer and they all located their evaporator loops fairly high up on the cabinet walls. The bottom foot or more did not have any coils adjacent, which I expect makes collecting and guiding "cold" tricky...

Cheers!

Whenever I have the lid open for a while and the freezer is running, I see frost on the lower foot of the freezer, and not on the upper walls. So apparently mine is backwards from your three!

Also would exasperate the temp stratification.

Update: I added a second duct and fan in front left corner, also pulling air down. Temp on water pour didn’t change much, 46-48 on a pour. But this time I noticed the water coming out was getting colder over time.

I poured a second glass and it had a temp of 42. So the keg itself is pretty close, but a first pour is going up from ~42 to ~48, I assume because of the big chunk of stainless it’s going through.

May need to add a fan to cool the shanks specifically. And I really should insulate my collar, that should also help I would think.