Coffin cooling and other lessons I learned while building a keezer
I am seeing a lot more coffin keezer designs on here recently. Thanks to innovative designs from many great HBT contributors more people are opting for the coffin box design versus the more common ‘through-collar’ design. A coffin keezer means more materials and more work time. For some this a small price to pay for a cleaner looking design.
This thread is not about kegerators, this thread is not about towers; this thread is about coffin style keezers.
I do welcome debate in this thread and hope it will serve to educate others. If you have any good ideas about how you solved the problem, please share. But let’s keep it specific to COFFIN COOLING as I feel that quite often, COFFIN COOLING comes up as a topic and people post solutions to TOWER COOLING. To paraphrase Don Rumsfeld; these solutions are ‘notably unhelpful’ to the coffin keezer crowd. I’ve taken all these detours and I want to prevent others from making the same costly mistakes.
The 10 degree differential hypothesis
I have conducted a number of tests with numerous different methods, probes, temperatures, and carbonation levels and found that first pour beer line foaming issues seemed to be resolved when there is no greater than a 10 degree differential between the coffin and the beer temp and also provided that you are already dealing with a balanced system. Though some CO2 will come out of solution with even a 10 degree differential, the impact is much less than if the differential is 20 degrees. If your beer is holding at 38; your beer line should be around 48 degrees; lower temps are even better. This is clearly subject to debate and I welcome input on this.
Following instructions online, I salvaged some PC fans and tried a few things. I even built one of those DIY tupperware container/PC fans setups. When that failed I tried the copper solution. While great ideas for tower cooling---again, these fell short when it came to cooling my coffin. I wish I had never tried them.
The only way I could keep from having foaming issues on the first pour was to back the pressure down to below 7-8. I am now able to run 11-12, fill a glass in a few seconds and the first and second pour are always the same.
My biggest mistake was basing my whole system around a very inefficient recycled PC fan, and a series of design errors based on that one single, underpowered component. When I asked someone for advice I was told ‘you don’t need much power in the fan that only a bit of air movement is needed’. When was ‘more power’ ever not needed in this hobby?!?! More on this later…
The first thing you should consider is the cost/complexity. Do I really want/need a coffin? Am I a good carpenter? Do I have the right tools? Am I able to do some minor wiring?
I am not an expert, but I did learn a lot at my own expense. I just hope this will benefit others going forward and that this will demystify coffin designs a bit.
So, let's get started...
Coffin design-Plan out your coffin design thoroughly and take into account things like the length of the shanks, the air volume you are creating and how you will get air into and out of the coffin. Some guys go through the back for service, some go through the top. What works for you?
Lay out your shanks and connections and measure them, including the thickness of any insulation in your calculations. Longer shanks help if you can get the coffin temp down low enough as they will hold onto the cold for you and create more thermal mass, too long and your design is off; too short and they may not help. I went with 4 inch shank and these seem to work.
The freezer-Most chest freezers cool the walls of the freezer and conduct warm air to the exterior. I’ve seen a few chest freezers that have blowers. A blower freezer design would seem to be ideal in eliminating dead spaces, I just could not find any available.
Size Matters-The overall size of the coffin has a lot do with how you cool it. A larger air volume means that more air is needed to cool it. You can remove air volume by creating a smooth path for air movement and using closed cell foam built up into blocks to help channel air. Whatever route you go, cold air must follow a path, and is then exhausted back into the freezer compartment. Exhaust can be either passive (no fan) or active (fan-optional)
Air movement- There a few different ways of getting good airflow. Generally speaking, smooth, unidirectional flows are easier on the fan and are more efficient. A good design will also eliminate temp stratifications in the keezer and collar itself.
Take a look at the Jester369’s design. The air comes in one direction and then flows out the other end. Very efficient use of the fan and the cold air pathway design.
However Firefly765 also has the right idea. In his case, he pulls the air in through the fan and then exhausts it out through two holes.
My design also works and it stemmed from my original design idea of using a very small coffin and the fan--not only to move air into the tower--but to break up the coffin and keezer stratification. I found that I needed a real powerful fan to make up for the lack of a proper pathway and I had already donated my extra foam to a brewclub member. Even without this filler block I am able to reach my temp differential goal; which I am proud to say stands firmly at 7 or better. If the keezer is closed and the compressor has just been running, my differential is closer to 4-5. My shanks are also within the differential and ALL foaming is solved, seemingly at up to 15 PSI and with 12' lines. After that, I am pushing the beer too much.
(edit: that is the OLD crummy fan in that photo)
Insulation-If your design has a collar, insulate the collar with insulation panels that you can find in the siding section of your local home improvement store. These panels are cheap and can be easily cut and taped with foil furnace tape. Insulation saves energy, use it where you can. Be sure to insulate the walls of your coffin box too.
Collar Height (2x6, 2x8, etc) plays a factor in your overall design as higher collars will have much more dead space above the freezer walls. The taller the collar, the more air you need to move because of the longer distances and large volume of stratified air that tends to settle in the collar dead zone. This is because the walls of your freezer provide the cooling, the wooden collar does not.
Line length and beer balancing
I am not going to include any links to beer line balancing calculators; most have errors. Use them if you wish. I would have been better off just starting with 15’ of 3/16” line per tap. Most people I’ve spoken with have success with 12-15’ feet of line. Some need 20’. I needed 12’. Why? YMMV, nuff said.
Remember that your coffin is higher than a through-collar design by a few feet, more pressure is needed to keep beer flowing at the faucets. Adding a coffin and a collar as I did, makes this even more complicated. Though the calculators had fields for this, they didn’t seem to work for me and they were clearly off on calculating temperature stratification.
Ok, you have a new keezer and you are excited to finish the plumbing. Don’t cut all your beer line lengths at one time! Cut longer lines than you need and then trim them down as needed. (Thanks SweetSounds!) Only run one or two beer lines at first until you are sure the kegs are carbed and you’ve resolved any balancing/foaming issues. If you cut them all too short, you are going to need a new spool of beer line. (PM me if you want some nice 6” runs of beer line, super CHEAP!!)
I tried ‘adding’ 6 feet to a 6 foot line with SS couplers; the ID of the barbs are nowhere near as smooth as the ID of a beer line. This creates nucleation sites and the CO2 will have a tendency to come out of solution at the splice creating bubbles in the line. If you cut your line too short, suck it up and just buy longer lengths. If you have success splicing; let’s hear about it. Why do online brewstores even carry these?!?!?
Use threaded flare fittings and Oetiker clamps not barbs. You don’t need a special tool to be able to clamp Oetikers, just a dull pair of dyke pliers or nail puller pliers. (Thanks SweetSounds!) Oetikers are cheaper than worm clamps, look better, and aren’t going to cut you when you’re reaching into the keezer. I had some barbed fittings and sent them back. Oetikers/flare fitting fittings give you the ability to easily disconnect and reroute lines for cleaning. Barbed fittings will save you a few bucks but are more headache then they are worth over the long run.
Oh, and when you are buying your threaded fittings be sure to include the little nylon washers that go inside of them. (Thanks Dave!) I wasn’t aware that they weren’t included with the fittings—would have been nice to know that. The nylon seats ensure a leak free fitting at every connection and are very cheap. Like $2 for 30 or something silly. Get them.
Perlicks. Need I say more?
As mentioned above, the most efficient design for moving air through the coffin is by designing a smooth path for the air to move through. Simply put: air comes in one side and out the other. This reduces turbulence and allows the fan to completely vent the air in the raceway very quickly. The air must be blown through the path and have a place to exit.
If you have success with any of these methods--please post below and I'll edit the post.
Copper (passive) solution
Great for towers, maybe not for coffins. No power required. This solution works GREAT for towers where the air volume is very small and the copper can be insulated. In my coffin, passive conduction with copper could barely get the temp around the beer lines over 50 degrees without air movement, way beyond my 10 degree differential goal.
The DIY or eBay kegerator cooler
This did not move enough air for me and it created cold spots. Where the line exhausted, that tap was at 40 degrees, the one at the other end approached 50. It also seemed to restrict the airflow and stress the fan. Ultimately, I felt I could get better results by moving the fan to the coffin opening.
I was able to get a variant of this design to get the lines to my desired 10 degrees differential but only if I ran the beer lines inside of the air hose. The design also restricted airflow on the fan further. It was also too fiddly and I was never able to get my shanks cool enough. The fan should cool the shanks and they should also be within the 10 degree differential.
The ideal design-cool air in, air recirculates:
All fans are not created equal. Thinking about saving a few bucks and using that PC fan salvaged from your old Dell? OK, it may work—but just know that most built-in PC fans have a very low CFM and very low ability to create pressure. The bearing design of cheaper fans means that may not be able to create much air pressure when under load –pressure is measured differently than CFM:
· CFM (Cubic Feet per Minute) rates how much air the fan moves in an unrestricted environment.
· Max Air Pressure, usually rated in ‘mm of H20’ indicates the fan’s ability to pressurize a column of water and to work against load.
You also need to consider the power supply in use. Most of us will salvage old phone chargers. Your fan and power supply have voltage ratings and an amperage ratings that you should be concerned with.
Fan Voltage is usually 12v. If you use a 9v charger on a 12v fan the fan will operate at roughly 3/4 speed. If you give it 12v, it will operate at full potential. Some fans vary speed by vary voltage input. DO NOT use a higher rated voltage power supply (e.g. >12v) than your fan is rated for.
Amperage is important, but your fan will draw only the amount of amperage it can use. So, your power supply CAN BE rated over the fan’s amperage rating. But using one that’s underrated is also not good either.
I went with 80 mm PC fans, but if you really want power go with a 120 mm. Just be prepared for some noise in either case.
This one moves 240 CFM and can create 27 mm of pressure:
This one moves up to 84 CFM and can create 26 mm of pressure (and is a bit quieter):
I use one of these, powered at 9v (probably pushing around 60 CFM) and it works for me. I wish I had this kind of info before I started this project. My loss is your gain.
Looking good so far, and this is valuable information.
Why not just use 115 volt fans to move air? You can wire it in directly without having to use an extra power supply. The one I have is 120 mm ball bearing design and pushes 110 cfm. It's main drawback is that it is fairly loud.
I actually looked for high CFM 80mm AC fans as an option, but couldn't seem to find any powerful ones. Most I was looking at needed 1 amp power supplies! I may not have been looking hard enough.
My power supply is DC 9v and 350 mA, and I didn't feel like finding another one (weird where we draw the line sometimes, eh?)
I was resigned to the fact that I was going to have to get a 12v, but when I hooked up my test fans to an adjustable power supply the sound of 12V @ around 120 CFM was...shocking. I still can't believe the amount of centrifugal force generated by the Vantec Tornado!
Are you using the 120mm AC for coffin cooling or is it actually cooling a PC/rack? How do you like it?
Good point though, for people that don't want to wire anything---an AC fan is a great plug and play alternative.
I'm using the fan in my keezer (conventional type with faucets mounted through the collar, no coffin), mounted on standoffs right in the middle of the lid, pointing down. It really moves the air in my keezer. But this is a far less tricky application than a coffin setup, from an airflow perspective. Still, I believe this fan would work really well in a coffin setup, especially if you push from one side and pull from the other. But it would be loud, unfortunately.
I chose the 115 volt fan because of the simplicity of wiring it directly into the existing wiring in the lid of the keezer. I wired it ahead of the light switch so it's on all the time. According to the label on the fan, it pulls .25 amps, so a little less than your 12 v fan. Of course, it's a lower rated CFM than yours too. But if you've got yours dialed down to 9V, it may be in the same ballpark.
This 115 volt fan and this 36 inch fan cord with molded plug to fit the connector on the fan.
I ran the bare 3/4" copper down into the keezer compartment about 6 inches and insulated the the upper foot or so with fiberglass pipe wrap insulation. The lower part of the copper was within acceptable temp range but it did lose temp the further up into the coffin it went. Without a fan at all the temp in my coffin would get up to 58-60 and the upper part of the copper was about 55 degrees. My floor/beer temps are around 40. So if I had to add a fan, then I might as well eliminate the copper.
Remember that in my case I also have a 2x8 collar design; keezers without a collar might have better luck due to better temp gradients.
Following Bradsul's thread, my thought was to modify this for a coffin you'd have to really insulate the heck out of the copper and virtually eliminate air space (foam board, great stuff, etc) so it sounds like you are on the right track. If you look at the successful implementation of this method in towers; it seems to work best with absolutely no air space. While this can be done with a coffin, I felt the fan worked better for me.
Let us know how you do!
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