Relative humidity adjusting/calculations?

[mrthing2000]

I'm getting ready to start curing burley, and we have a lot of humidity swings here in SW Washington. At night it is hitting 90-100% humidity, but in the daytime it drops into the 30-40% range. Right now it is about 50deg at night, hitting around 75-80 most days. Makes trying to control an air cure or sun cure quite unpredictable, especially as colder weather approaches.

Adding humidity seems easy--add a crockpot, a small fountain fogger, something like that. I can measure the humidity and up it as needed.

But taking away humidity, that seems to be more difficult. I've read that upping the temperature changes the relative humidity. So I suppose if it is 60deg at 100% humidity, then upping the temp with a heat source to say, 90deg, the humidity will fall. At least that's what I've understood.

Is there a way to know HOW much--like a formula or something?

I could just measure it frequently, but I wouldn't know 'how much' heat to add to drop it to a certain level. It would change by time of day. That's why I'm probably going to cure in my garage in a homebuilt chamber, which should keep the temps steady.

If it helps, I am using a PID controller to run a heating element, and a humidistat (basically another PID controller) to switch the humidity source on/off. Problem is, I wouldn't know how much to 'up' the temp to get the humidity DOWN, it would be a lot of trial and error. It won't be 'set it and forget it', but since the source takes awhile to get the chamber to full temp, I don't want to overshoot it, and underdoing and adjusting it up manually could take all freaking day, by which the temp outside has changed again.

In my head I realize it is a simple conditional program that needs to be written for my Raspberry Pi, and an Arduino module, but I have no idea how to do that.

 

[Bex]

Just posting here - not because I have an answer for you - but because your thread will be a future question of mine, as well. I live in Northwest Ireland - the weather will be a bit cooler than your conditions, but the maritime climate and humidity problems will be somewhat the same. I have a crop of burley that I hope to get to within the next few weeks, and it's unlikely that I will be able to air cure it without losing it all, so I plan to use my flue curing chamber to do this. While the standard practice may be to cure first (by air curing) and then kilning (in order to age), I've also read here that you can use your curing chamber as it's own 'environment' so that you are using the chamber in an effort to duplicate the needed air curing conditions that you cannot get from your natural environment. Sounds like a win/win to me. So looking forward to some good info on your thread that can help both of us!!

 

[Smokin Harley]

What is your curing containment? small shed, in the house , basement(cellar) ,garage ...Got a picture of where you keep your leaf to cure ?
I don't think there is a formula per se but rather a trial and error and keep adjusting something or another until you reach a point where you find your range of condition to suit your particular area . There could be a formula relating (heat / rH)+ time : cu/ft(mass of tobacco leaf) or something like that but it would have to take place in laboratory perfectly controlled conditions and I'm pretty sure there is quite a few variables that change as the leaf dries or transforms from "raw" leaf to smokeable tobacco as the ammonia dissipates .
I just keep in mind that long ago the tobacco gurus of yore had very basic (natural) conditions and still made tobacco smokeable, it just took them longer depending on where they were located. Once it was picked it was hung ,dried and aged (not much has changed there) ...in my mind it had to be very close to how wine or whiskey is aged and quite possibly it took place in the same basic areas. The natural fluctuation of temperatures and humidity did what we are trying to attempt to recreate by way of kilns and crockpots with digital controllers. But they also had hired hands to basically babysit the barns and either open doors to allow heat out ,fresh air in or build small fires and throw water on the floor to control the heat and humidity. We all know tobacco is a labor intensive crop.

If you've followed my curing or kiln threads I've had quite a time getting to where I am with my leaf. But, I think I'm getting closer to a method that suits my area.
I don't have enough leaf of time to build Pilones to pile ferment but I have a working kiln . I just have to do it in batches. Its a work in progress.

 

[deluxestogie]

A "formula": within the typical habitable temperature ranges, raising the temp 20 degrees F will reduce the relative humidity by about half. So going from 60 degrees F to 80 degrees F will drop the relative humidity to half its starting value.

On the other hand, for shed curing, it's the average relative humidity--measured over two or three days--that is relevant. If the average temp is above 60 degrees F, and the multi-day average relative humidity is in the range of 60 to 75%, then you should get fairly good color-curing, with little risk of mold. Where it becomes problematic for mold is during prolonged stretches of rainy weather, a situation that can be remedied with heat. By contrast, long stretches of low humidity and high temps risks the leaf drying green.

Bob

 

[mrthing2000]

Thanks for the help. It took me a long darned time to find the answer for the 'exact physics formula' but I finally did:


http://physics.stackexchange.com/qu...hange-in-temperature-affect-relative-humidity


In short, it is called the Clausius–Clapeyron equation


For me, it is a bit complex to figure out how to program it into a controller. If I need to add humidity, that's easy.


I can also add heat to drop a 80-100% humidity situation DOWN to a desired 75%.


Luckily it doesn't seem to take much heat to drop it down to 75%. But as the humidity changes, so does the heat need, and vice versa. Its tricky to program a controller for those types of conditions. I might have to hire a programmer to write it for an Arduino or something. Ideally I'd like to set it and forget it, and take the guesswork out of it even if it costs a few dollars. Its very easy to add humidity, or to add heat. The problem is taking away too much humidity. Dehumidifiers aren't cheap.


Perhaps here is an opportunity for a Kickstartr type thing. I'd be game to draw it up and set it out. Just need a humidity source, a heat source, and a couple of temp and humidity probes, and a 'smart controller' programmed to turn these on and off to maintain what we want.


Right now I use a simple drying rack, wrapped in a painters plastic drip cloth, with a small fan going all the time for airflow. I put in a hot plate with bricks above it and some sheet metal to act as a heat shield (to prevent the radiant energy from cooking what is directly above it). It works pretty well. But soon we'll start seeing sustained days of rain. I've got the heat plate running full, and it maintains about 82deg even at night, and around the lower 90s in the daytime. If I see the humidity fall below 60% outside I turn it off.


Its not very exact, and I'd like it to be--but it works for the moment.


I thought about using a hydroponic grow tent as the chamber, piping in air with heat and humidity modified from the outside. If I can figure out the programming of the controller--that's EXACTLY what I'll do, and I'll freely share it. I think it will work well, though I'm not sure how much heat those can take.


I'd like to build a full-on brightleaf capable curing chamber, but minus sheetmetal (super expensive), I'm thinking a grow tent will melt, wood will rot, and plastic might off-gas.