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Old 07-05-2012, 02:43 PM   #1
Boodlemania
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Hey all

After picking up a used chest freezer for next to nothing on CL, I used the 4th to build out my keezer. It went off like a charm. I want to expressly thank the folks on this site who have posted their pics and ideas regarding keezers as it made the process of building mine MUCH easier as well as giving me a final product that I think I'll be happy with.

Plus, my wife gets her fridge back, so it's a win all around.

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Old 07-05-2012, 03:00 PM   #2
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Hi

Now spend some quality time fine tuning your temperature controller. A thermometer you can read from outside the keezer is a very handy thing for this task...

More or less:

The controller is only just so accurate. The location you have your probe at may or may not be perfect. Your beer wants to be at 36 to 38F sitting in the keezer. You probably will need to bump the controller up or down a few degrees to get it to run right at 37F. Let it run for at least 12 hours before you try to get it perfect, 24 hours would be better still.

You only want the compressor to cut in every so often. If it's not off for at least 15 minutes something is probably wrong. A cycle (on to off to back on again) time of 45 minutes or more is a reasonable thing on a partially loaded freezer on a hot summer day. If your controller has a setting for it, you can adjust the cut in and cut out to get the cycling down to a reasonable level. Again, not all setups are the same, so it will take some fiddling.

Fortunately all of this is a "load it up and set it once" sort of thing. There's not a lot of need to revisit the process in six months. All that assumes you already have fans in the freezer and don't add or take any away. If you don't have fans yet - get some...

Bob

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Old 07-05-2012, 04:15 PM   #3
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Bob,

Thanks for the tips.

- I plan on "fine tuning" my temperature, but as of right now the keezer has been operational for ~20 hours with 4 kegs that were already cold. I'm going to wait until this weekend to tune once I'm comfortable that everything has settled out.
- I am using a 2.5' long, 8" diameter pine log (house construction leftover) with a hole drilled to precisely fit the temperature probe as a constant thermal mass to prevent short-cycling the compressor.
- The controller I'm using (THIS ONE) has a compressor cycle timer, so I'm good there.
- I have one fan inside, mounted to the collar in the center of the long axis of the keezer, which is wired to run when the compressor runs.

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Old 07-05-2012, 04:39 PM   #4
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Hi

Pine is a fair insulator and not a real good thermal storage medium. Water stores heat very well as do things like copper or steel. I'd suggest the probe may not be very well coupled to the freezer. Poor coupling normally means poor control.

You want to control the temperature of many things in the freezer. Each of the kegs need to be at a constant temperature. The lines also need to be fairly constant. If possible it would be nice to keep the shanks and faucets constant, but that rarely is practical. The kegs move pretty slowly, so in a lot of ways they are the easiest thing to control.

Your compressor can indeed be damaged by short cycling. It can also be damaged by running to long (it gets hot ...). There's a tradeoff between the two, since long cycles mean more run time. If you spend some quality time with normal fridges and freezers, you'll find they cycle a lot more often than you might think. They also don't get anywhere near as hot as a long cycle setup does....

Bob

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Old 07-05-2012, 05:04 PM   #5
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Thanks again!

You've got me curious. I've got a DMM with a temperature probe and data logging abilities. I'll set that up tonight and attach the probe to a keg to see how well the control is working.

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Old 07-05-2012, 05:19 PM   #6
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Hi

I'm sitting here watching a 10 channel thermocouple thermometer on my keezer so here's a few pointers .... (no built in data logging, but $125 and it and all it's thermocouples made it through the cal lab)

1) The top edge of a commercial keg will pretty much follow the average air temperature of the freezer *if* it's in the air flow from the fan.

2) A room temperature glass of water takes a *long* time to get to freezer temperature (think hours) if it's out of the direct air flow. It'll take an hour or more even if it's right in front of the fan.

3) A probe taped to the wall of the freezer about half way down, in the vicinity of the edge of the hump is an interesting thing to watch.

4) To really get the temperature of the keg, you need a light weight thermocouple and tape or putty. Best to put it about half way down the body of the keg and on the side away from the fan.

5) No big surprise - the third (or sixth or what ever) keg that's furthest from the fan takes a bit longer than the one thats right next to it.

6) Useful data points are on the floor of the freezer, about half way up in the back, and right up near the top of the keg. If you use the glass of water approach, plan on taking a good long while with a single channel gizmo.

7) Data every minute is plenty fast enough.

8) Towels are a handy accessory if you are using glasses or bottles of water...

9) The really cool way to observe a decoupled control loop is to watch it overshoot when it first fires up.

Have fun.

Bob

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Old 07-05-2012, 10:47 PM   #7
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Hooked up my DMM once I got home and started data logging. I taped the probe halfway down one keg on the opposite side from the fan. Setpoint on the temperature controller is 40F. The readout on my DMM, attached to the keg, was 40.2F (after stabilizing out from the heat from my hand). I'm logging for 24 hours at 2.5 minute intervals. I'm mainly interested in how stable the reading is. Once I know that, I'll do the same with the AC power on the cooling circuit to gauge how often and how long the compressor runs.

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Old 07-05-2012, 10:53 PM   #8
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Hi

Once the control loop settles in, it gets pretty boring. You really need to watch it under dynamic conditions to see what's going on. You also very much want to see what the line temperatures are doing. Warm lines mean foamy beer.

Bob

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Old 07-05-2012, 11:02 PM   #9
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That's true, but I'm mostly concerned about two things:

- The accuracy of the temperature setpoint vs. the actual temperature of the kegs.
- The duty cycle of the compressor

The comment about line temperatures is true, but I haven't finalized my line/faucet installation yet. I'm trying to take this in steps. Right now I'm still using the party taps that I used in my wife's (confiscated) fridge.

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Old 07-06-2012, 12:05 AM   #10
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Hi

Once it all settles out, the keg will likely be at the controller set point, almost regardless of sensor placement. Yes, you can get stupid with a sensor, but most people don't.

The real fun is when you unplug the thing to clean the lines. It warms up while you are doing the job. You fire it up and some parts of the system get really cold (overshoot). If one of those is near a line. Frozen beer slushies...

Bob

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