Stalking the elusive humidity

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porterdriver
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Stalking the elusive humidity

Post by porterdriver » Thu Aug 04, 2011 17:32

I have a curing chamber that I am building out of a frost-free Kenmore freezer. I thought that way I would have a whole cabinet to work with instead of the traditional split that is found in most refrigerators.

The temperature is controlled by a Johnson Control line-voltage thermostat. It is capable of controlling temperatures via line voltage from 10-120 degrees (F). It is currently set at 45 degrees (F).

The humidity is controlled by a Green Air Products THC-1 line voltage humidistat running a small Crane humidifier. The humidifier is set to its lowest setting and the humidistat is set to 60%.

For monitoring I have two thermometer/hygrometers (for redundancy or confusion, I'm not sure which). One is the Extech Instruments 445715 which has had the hygrometer already calibrated. It has a probe that is inside the freezer with the temp/RH display on the outside. The other monitor is an Acu-Rite 00592W3 that has a remote sensor which cannot be calibrated but is supposed to be +/- 5% on the RH. The remote sensor is sitting on a shelf inside the freezer at the same level as the sensor for the Extech.

I am logging the temp/RH from both monitors throughout the day. Both thermometers seem to be in close agreement with the Acu-Rite reading around 1 degree (F) lower than the Extech.

However, the humidity seems all over the place. The Extech, which I believe is supposed to be more accurate (after all I did calibrate the thing) swings from 43% to 99%. The Acu-Rite (after about 24 hours in the freezer) has been reading very accurately between 59% and 61%. Both devices have been in for the same length of time and the door has not been opened.

I told you all this to ask these simple questions. How critical is the cabinet humidity, especially in terms of the two sets of readings? I get the sense the Extech is giving me instantaneous readings while the Acu-Rite is giving me an average? Is that a safe assumption? Is this setup sufficiently accurate for curing meats, sausages, hams, etc.?

Thanks for listening to the ramble and I look forward to this group's advice.
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Post by ssorllih » Thu Aug 04, 2011 21:35

I can tell you a sad tale about false readings. Just as soon as the frigeration unit comes on line it will suck the humidity down to a near freezing dew point. I learned this by watching jugs of ice flood with condensate when I put them into the chamber. Unless your humidistate in very responsive I believe that you will get rather wide swings in RH.
A fine mist is not humidity until it evaporates. Humidity is moisture VAPOR in the air.
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Post by porterdriver » Fri Aug 05, 2011 15:18

Is there a better system for raising the RH and the humidistat/humidifier system? I am open to suggestions.
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Post by partycook » Fri Aug 05, 2011 21:07

porterdriver,
Welcome ,I also use a green air THC-1 it is connected to a ultrasonic cold air humidifier set at max. I just let the Greeen Air monitor and maintain the humidity level. I have found out that the cold air ultrasonic seems to break up {vaporize}the water a bit better.Humidity levels that I have been using are usually between 70-95 per cent. What type of fan setup are you running? how do you control your fan speed? also to consider is where your incoming air enters and where it exits . could be to close to your temp. and humidity sensors.

Good luck John
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Post by porterdriver » Wed Aug 17, 2011 16:02

partycook,

I have a small 3" fan (don't know airflow) that just runs in there and keeps air circulating 24/7. Should I have the fan tied (so-to-speak) to the humidistat?

I have now included a USB datalogger (Lascar Electronics EL-USB-2+) that records Temp/RH/DewPoint. This should help further confuse me. It is in its first cycle of collecting data.

You have now brought up a point that I'd like to hear more about. Air exchange. At this point, I have made no provision for any kind of air exchange. Can any of you give me some guidance on this point? How much air to exchange, position of inlets and outlets, compensating for heat intrusion through air exchange system, etc.

With that said, what effect does air exchange have on my pursuit of suitable humidity?
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Post by uwanna61 » Wed Aug 17, 2011 22:28

Porterdriver
Is there a heat source in the cabinet, like a heat bulb? How often does the freezer (compressor motor) cycle? Keep in mind every time the compressor cycles, it will remove moisture, if it doesn`t cycle often, then the humidity will hang there. Is the power cord from the freezer, hard wired or plug into the temperature controller? I prefer the hard wired temperature controller, just my preference!
Also, is the humidifier cold air or warm air? Definitely want cold air. Is there a frost free selector on the freezer? If so, turn it off. You may want to do some research on the model of your freezer; it may have a frost free line wired direct into the back of the freezer. This could be the reason the humidity levels jump up and down.

You mentioned that the cabinet temperature is set at 45 deg, try moving the temp up to 58 or 60 degrees and monitor the humidity and temps, and keep an ear out on how often the compressor cycles, let`s say per ½ hour.

As for air speed this can be a bit tricky, it`s a good thing to have, but too much air speed can make your bottom lip quiver a little, according to the finished wrinkly dry product.

On my curing cabinet, if I set the temp up around 60 degrees (inside temp) the humidity will move around +/- 4% when the weather outside is up above 80 degrees. I try to average it out by bumping up humidistat a percent or two. During the cooler months there are no issues for me, seams to hold fine, temp and humidity.

And then, the ideal environment would be a humidifier and dehumidifier working together in the same cabinet. I`m still pondering over the idea and cost and would need a larger stand up freezer for inside space.

Hope this helps, keep in touch
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Post by w1sby » Wed Aug 17, 2011 23:01

I'm not sure if this will be helpful or not, but here goes...

In the cigar world a LOT of guys use "beads" to control humidity in their humidors.
Link to Heartfelt Industries
The page that link pulls up shows cigar sized holders, but if you look around a bit you will find they sell in bulk as well.

The beauty of "beads" is that they wish to remain at a steady humidity level. They will absorb moisture until saturated and give off moisture until barren all the while holding the enclosure at a steady 60% (or 65%, or 70% depending on what you bought).

That being said, I don't know if they would be safe in a smoker, or if the smoke would affect them adversely.

I know they work great in a humidor and I have dealt with the referenced company several times. I am not affiliated with them in any way, just a satisfied customer.
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Post by porterdriver » Wed Aug 17, 2011 23:42

Thanks for the input, folks.

First, to uwanna, no heat source inside box. Sitting in non-climate-controlled shop (did I mention that today was #62 over 100 degrees so far this year?); so inside heat source may not be issue. I will have to wait until my USB datalogger is full and I can plot the compressor cycles; so can't answer that question now. My sense is that it cycles off and on about every hour or so. Power cord is hardwired. Cold air humidifier. No 'frost-free' switch on unit.

Second, to w1sby, the beads sound like an intriguing idea. May have to give that a go. This is strictly a curing chamber...no smoking (takes place elsewhere).

My 'current' question is how wide an RH swing is acceptable for normal types of curing? In other words, does an RH that cycles from 50% up to 90% several times in a day, give the same result as a unit that cycles from 65% up to 75% over that period of time, or even cycles of 69% up to 71% (at the opposite extreme)? How critical is the uniformity over a given time period?
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Post by uwanna61 » Thu Aug 18, 2011 00:41

Porterdrive
My 1st recommendation would be to hold off on fermented salami until the heat your way subsides down to a normal temp. You`re probably saying right about now, yea right!
I feel for you folks down there in the sweltering heat, actually watching it on the news as I type.

As for the temp & humidity naturally consistency would be ideal, as mentioned earlier if there is a slight fluctuation, I believe one can deal with that, but if there was say a 20 - 40 % fluctuation, in my opinion, it would definitely affect the finished product.
Keep working with it, your data should provide some info that could answer a few questions.

Good luck
Chow
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Post by ssorllih » Thu Aug 18, 2011 03:00

I am still working on the RH cycles. You can dry laundry on days when it is very humid and not too humid. If the RH gets low, drying will be quick and going back to a high RH won't compensate for the fast drying. I believe that the flatter we can keep the RH line the better will be the product. I want the ability to record the RH and temperature at five minute intervals for the entire curing and drying period.
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Post by porterdriver » Thu Aug 18, 2011 03:10

ssorllih, take a look at the Lascar Electronics EL-USB-2+. It has many customizations for data collection that you can program.
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Post by ssorllih » Thu Aug 18, 2011 04:07

This appears to be a self contained temperature and humidity recording devise that can down load to my computer. For the price it would be perfect. Thanks
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Post by porterdriver » Thu Aug 18, 2011 16:53

Welcome. It seems to be just what you are looking for but I don't think that the time intervals include exactly five minutes. I think it's more like 10 seconds, 10 minutes, 10 hours, etc.

Nevertheless, it is easy to use and (as you noted) it is self-contained.
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Post by ssorllih » Fri Aug 19, 2011 03:51

The sampling times I mentioned were arbitrary but I have read the data sheets and will probably purchase one with the LCD readout.
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Post by porterdriver » Fri Aug 19, 2011 13:32

I considered getting the unit with the LCD as well. However, I decided against it since the only way to see the LCD was to open the curing chamber to look at the display.

Since I'm nosy by nature and want to know what's going on inside, I got an Extech 445715 with a wired remote probe. I drilled a hole in the door, slid the probe into the chamber, back-filled hole with spray foam insulation, and mounted the display on the door.
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