My meat curing chamber build

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redzed
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Post by redzed » Fri Sep 20, 2013 05:26

el Ducko wrote:Creepy. Maybe it's a Halloween problem. (Addams Family theme plays in background.)

...couple of wild guesses:
(1) Is there an air leak or air flow?
(2) There is a possibility that, when the refrigerator is running, moisture condenses out on the coils or freezes. Then, when it shuts, the moisture evaporates. It wouldn't take much to make a noticeable swing.
(3) "It's on account a yo' boogaloo situation." (Wolfman Jack, late '50's.)

I'll go for either #2 or #3.

Ross...? ...got some more insight?
:mrgreen:
I vote for number two. The cooling coils take the moisture out of the air. In my curing chamber the humidity always drops when the fridge kicks in and it does not always recover, especially when it runs often. That's when the humidifier does it's job. Another possible reason is that when the fridge is running there is also a fan that kicks in and it will cause the air to become mixed and, more or less equalize the RH in the chamber. When it is not running, the humid air will rise and if your sensor is on the top, it will reflect that.

Once you get product into your curing chamber, humidity will be even more difficult to control. Swings of several degrees will occur regularly.
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Post by dpeart » Fri Sep 27, 2013 03:48

Well here is another picture. I got the PID for the fridge working quite well. I went with a minimum on time of 1 min and a minimum off time of 1 min. This means that the fridge won't turn on and off quicker than that. Turns out that even with the 1 min on minimum it keeps a decent temperature range.

The humidity still is the killer. I have the humidifier in there, but it doesn't stand a chance when the fridge turns on. Then it will overshoot after the fridge turns off. I need to continue tweaking the PID parameters. Was shooting for 72F at 85% humidity.

Image

Key: tempState and humidState shows when the fridge/humidifier are actually on. The tempOutput and humidOutput is the PID output. The others are fairly self explainatory. (The State ones are the filled squares I still need to get colors)
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Post by ssorllih » Fri Sep 27, 2013 04:03

I am seeing rather short interval variations in to temperature and RH. I suggest that if you consider an average of those excursion on your graphic display you may come out pretty well. The other possibility is to increase the thermal mass in your chamber to help to stabilize the fluctuations. perhaps several gallons of water in jugs.
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Post by el Ducko » Fri Sep 27, 2013 05:44

Let's theorize that the cooling capacity of the refrigerator is plenty over-sized. You're running a mostly empty refrigerator, so that's probably a good assumption. Refrigerators are designed to make things cool, and humidity control is not really an objective. Thus, we may have to do some "tricks" in order to adapt the refrigerator to add that function.

It may be that moisture is condensing out on the cooling coil surfaces, as we were speculating earlier. If that is the case, we could afford to reduce the surface area (actually, block off air circulation past part of the cooling coil), so not as much water is condensed. This may take some hunting around on your part, but I'm thinking that the coils have fins on 'em and putting masking tape to block air flow past, say, two thirds of 'em, might make the condensation problem not quite as bad.

The objective is to reduce condensation surface area. Would it be too much trouble for you to try that? It may not be a practical solution if it is too hard to get at the coils, in which case we might try some other way of doing this. ...and this may be a bogus idea, too. We may have to try a few more tricks. Note, though, that I'm really going after reducing the condensation area, not reducing air flow.

Good luck.
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Post by dpeart » Fri Sep 27, 2013 22:41

I put in a the water pan from my old ECB and that helped a bit, so I figured "more is better!" and added a 5-gallon bucket. That helped a ton. The temperature is rock solid now, it just doesn't move (to within .5F). The fridge cycling still affects the humidity, and always will, but I can now keep it centered at 85%. Not sure how it will work when I change the temp/humidity setpoints, but at least at 72F and 85% humidity it looks good.

I'll post a picture later. The fridge turns on every 5 minutes or so now.

dave
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Post by ssorllih » Sat Sep 28, 2013 00:44

If you broaden your temperature set point to ±1 or 2° it won't harm the cure but it may help to stabilize the RH.
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Post by dpeart » Sat Sep 28, 2013 02:04

Yes I need to figure out how to code that. Now that I have the other stuff working that is next on my list.

Ideas?

dave
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Post by dpeart » Sat Sep 28, 2013 12:22

Here is my first overnighter. Added a +-1F hysteresis to the temp so you can see it change back and forth. This did slow the cycles down to about 1 every 30 mins.

Humidity still is controlled by the cooling cycle, but it looks close enought to 85%?

Image

Yes the picture is really cluttered, I plot a lot of debug stuff so I can figure out what happens if it goes wrong.

Looking for a manual for my fridge so i can see where everything is.

thanks,
dave
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Post by el Ducko » Sun Sep 29, 2013 15:05

Looks like that has tightened up the humidity control quite a bit. (There's nothing like a little load to help equipment perform.) 84% to 86% is pretty doggone good. Good job!
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Post by ssorllih » Sun Sep 29, 2013 17:56

considering that the fermentation and drying periods will be days and weeks and not fractional hours that control line will look very good.
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Post by Diced » Thu Jan 16, 2014 23:46

Hi Dave,

How did the chamber go with meat in it? Did it still maintain the humidity?
I have been working on a similar project with the raspberry Pi and am still struggling with the humidity. I will give the bucket of water trick a go. Mine is set for 13Deg C and 75% RH. It is a challenge at the moment as being summer temps are above 40Deg C and about 20%RH

Image

Did you use a different thread to control the humidity and temp at the same time?
What Sensor did you use?

Cheers
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Post by ssorllih » Fri Jan 17, 2014 03:14

Diced, Open your dead band set points a bit. If you allow a bit wider temperature swings your humidity swings will tighten up.
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Post by Diced » Fri Jan 17, 2014 04:05

Thanks Ross, what sort of band would be acceptable for the temp and humidity? Would something like 10-15C be alright for temp? What about RH?

Cheers
Luke
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