I need a physics lesson! - Explain RH

T

tfar

Evolving Lead Gorilla
I was looking for this really nice conversion chart someone posted (should have saved this thing) that indicated the corresponding values for 70%RH at 70F. I think the scale also showed the corresponding absolute humidity.

So I have a couple of things that need clarification and I bet others would be interested, too.

1. Do our usual hygrometers show relative or absolute humidity?

2. If I get it right (and it might be just the other way around), if I want to have 70/70 as a benchmark of how much humidity I want in my cigars but I don't actually have 70 but 66 degrees in my Vinotemp, I need to raise the humidity shown on the hygrometer to higher than 70% in order to get the same effect. Right?

I read somewhere that the conversion is 2.2% for each degree in temperature. It was MoTheMan who said so in a thread here entitled Temp Question.
"To reach the ideal of 70% RH/70 deg. F, For every degree change, you need to adjust the humidity needs to e adjusted 2.2% in the opposite direc., this means that for a temp of 75 F, yor humidity can be as low as 59% to have the same relative WATER CONTENT IN THE AMBIENT AIR."

So in the other direction that would mean 78% at 66 Fahrenheit. Or does that mean that if I have 65% at 66F, this is really the equivalent of around 73% at 70F?

Darn it, I am confused and don't feel to intelligent right now. :hn

I guess it depends on whether the hygrometers are showing simple moisture content in air or whether they already have a relative humidity scale built in.

Can we discuss this to make things idiot proof or Till proof for that matter.

Till

P.S. I want to know this for the sake of knowing it. As long as my sticks feel right and smoke right I don't care how it works. But it would be nice to have the theoretical knowledge nonetheless.
 
You're probably right. Just to give you another hint. This conversion chart I saw was posted by a forum member (I believe it was here) and it was a link to an external web page. The chart itself looked like a jpg of a scanned book. I also think it was on a dealer's site.

I looked through all my bookmarks and documents and googled the heck out of it but I cannot find it.

Till
 
I've seen these charts before.

Heres my take..... KEEP IT SIMPLE, a hygrometer that reads 70/70, is just that.. no more no less. Regardless of weather patterns, room temperature, changes in the moon phase etc...

There may be some scientific evidence to support the conversion charts and the difference between absolute and Relative humidity, but I think most BOTL do as I mentioned above KEEP IT SIMPLE.
 
yeah, K.I.S.S.

And as far as I understand Relative Humidity has more to do with the mixture of water in the air compared to the known pressure of water.
 
Before you get too crazy in looking for what someone elses "ideal" temp/rh, you might want to know that some cigars smoke better according to your palate, and to some degree, I think, where they are from. I believe it is fairly well acknowledged that Cubans seem to smoke better at 55, 60 or 65%, and NCs at a "wetter" content. Temp wise, I think if you stay anywhere between 62 and 72, you will be in a window where you won't have to worry.
The secret is to be in the general range, and no to sweat it. It would be nice to have a large temp and RH controlled cabinet, as some are fortunate to own, but for the general, redneck cooler crowd, we can be pretty safe in the knowledge that if we stay in a general range, our cigars will be very happy in their environs.


You might enjoy them at different RH as well, I think that if you go crazy looking for absolute perfection at such and such a level, you are going to negate the enjoyment. Don't sweat a percentage or two, or a degree or 4.
As far as aging, I bet a few other gorillas will chime in with MUCH more knowledge than myself to help guide you.
 
tfar said:
I was looking for this really nice conversion chart someone posted (should have saved this thing) that indicated the corresponding values for 70%RH at 70F. I think the scale also showed the corresponding absolute humidity.
Click to expand...

It's called a 'psychrometric chart', I've got a few on my PC that I found online, do a google image search and look for the highest resolution results. This chart shows the relationship between RH, 'absolute humidity', temperature, and a few other physical properties depending on the chart.

1. Do our usual hygrometers show relative or absolute humidity?
Click to expand...
They show RH. Relative humidity is a measure of the amount of water held in the air, compared to the maximum amount of water that can be held in the air for the given temperature (saturation concentration). Absolute humidity is a direct measurement of the amount of water in the air, typically grains of moisture per pound of dry air. Divide absolute humidity by the saturation concentration and you get relative humidity.

2. If I get it right (and it might be just the other way around), if I want to have 70/70 as a benchmark of how much humidity I want in my cigars but I don't actually have 70 but 66 degrees in my Vinotemp, I need to raise the humidity shown on the hygrometer to higher than 70% in order to get the same effect. Right?
Click to expand...
Warm air can hold more water than dry air, so if you're above 70 F, you'll want the RH to be lower, if you're below 70 F, you'll need the RH to be higher.

I read somewhere that the conversion is 2.2% for each degree in temperature. It was MoTheMan who said so in a thread here entitled Temp Question.
Click to expand...
It's not quite that easy, but that may be a fair approximation (I haven't checked the math).

So in the other direction that would mean 78% at 66 Fahrenheit. Or does that mean that if I have 65% at 66F, this is really the equivalent of around 73% at 70F?
Click to expand...
This is where the psychrometric chart comes in handy. Use your RH and Temp targets (70/70) and find the absolute humidity. Then take that value and your actual temp and find the RH. The chart takes all the math out and is just a matter of connecting the dots.

I should mention here that I'm a noob when it comes to cigars, I'm not sure what matters most and I'm not well versed in cigar storage conditions, but this is how the science works.

Darn it, I am confused and don't feel to intelligent right now. :hn
Click to expand...
If it helps, I made it most of the way through my freshman ChE class before I figured this stuff out.

P.S. I want to know this for the sake of knowing it. As long as my sticks feel right and smoke right I don't care how it works. But it would be nice to have the theoretical knowledge nonetheless.
Click to expand...

That's the important part. Keep in mind the hygrometers we use are in no way precise instruments, regardless of how many times you calibrate them with those nifty boveda packets. I've got a nice Fluke meter in my lab that cost a few hundred bucks, WITH independent calibration it's only accurate to +/- 1.5%, off the shelf it's only 3%. I certainly wouldn't expect any better from a $10 instrument. Find what works for you and go with it, no sense stressing about the numbers.

Feel free to ask for clarification if I've confused you anywhere.
 
A phychometric table shows RH at a specific temp at sea level.
You need to use a sling psychrometer or a wet bulb thermometer for accurate readings.

What you're talking about is the volume of water in the air around your cigars.
For whatever reason, I think you're suggesting that you want to keep the same volume of water in your cigars at all times?
As air warms it can hold more water.
The chart that musiq posted is a simple relationship between rh and temp that aims to keep the volume of water in the air at a constant level.
http://www.arlinliss.com/__Humidor_Controls/Humistat/temp%20and humidity relationship

Realize that as temperature drops, you don't want the air to have the same volume of water as the dew point will also lower. (Dew point is the temp where the water vapor in the air will turn back to water. The moment that happens, it takes along what's called "the latent heat of vaporization. It takes an inordinate amount of time for the water vapor to condense because it needs about 30 times the energy to change forms. Long story that's not extremely relevant, but you asked for a physics lesson. ;))
What you'll have is cigars with water condensing on or in them, as well as throughout your humidor, creating a nice mold growing environment.

So what you want to do here is abandon this whole line of thinking because all it will do is ruin your cigars.

The change in actual volume of water inside your cigars at 60/60% and 70/70% is negligable. Cigars are hygroscopic, meaning that they will take on and release water very easily.
They will also change very quickly because of the vapor pressure differential between 60/60 and 70/70.
That's to say if you are storing your cigars at 60/60 and move them to your humi at 70/70, they will quickly adsorb water from the air because the vapor pressure inside the cigar is lower than that inside the humidor.
This is exactly what you want to happen. It's what is good for our cigars.


If you want a good understanding of how rh works, the best way to think about it is "how much water is in the air at a given temperature?"
The reason you want to store things long term with less water in them is obvious. Water is going to accelerate the breakdown of organic material by providing oxygen for oxidation, etc.
We want more water when we smoke the cigar to control the cigar's burn rate.
We don't want all that moisture if we're storing cigars because it will facilitate their breakdown.
Hope this helps!!!
Scott

P.S.
I've been writing on RH for about 15 years. Search "shilala humidity" on Google and you'll return about a bazillion results. I've been published in tons of magazines, books, and so forth.
I'm working on a whole bunch of tests right now to find the ultimate humidity control for humidors and incubators. When I'm done there will be a website that wraps around the stuff.
I'd trade everything I ever learned about humidity for one page of "Understanding Women".
I could actually use some info like that. :)
 
Last edited:
shilala said:
P.S.
I've been writing on RH for about 15 years. Search "shilala humidity" on Google and you'll return about a bazillion results. I've been published in tons of magazines, books, and so forth.
:)
Click to expand...

Damm Shilala, and all this time I thought you spent all day making your Cigars look pretty:chk:r
 
shilala said:
What you're talking about is the volume of water in the air around your cigars.
For whatever reason, I think you're suggesting that you want to keep the same volume of water in your cigars at all times?
As air warms it can hold more water.
The chart that musiq posted is a simple relationship between rh and temp that aims to keep the volume of water in the air at a constant level.
http://www.arlinliss.com/__Humidor_Controls/Humistat/temp and humidity relationship

Realize that as temperature drops, you don't want the air to have the same volume of water as the dew point will also lower. (Dew point is the temp where the water vapor in the air will turn back to water. The moment that happens, it takes along what's called "the latent heat of vaporization. It takes an inordinate amount of time for the water vapor to condense because it needs about 30 times the energy to change forms. Long story that's not extremely relevant, but you asked for a physics lesson. ;))
What you'll have is cigars with water condensing on or in them, as well as throughout your humidor, creating a nice mold growing environment.

So what you want to do here is abandon this whole line of thinking because all it will do is ruin your cigars.
Click to expand...

So what I think you are saying is just keep it at 70% RH regardless of temperature, right?
 
i looked into this a lot when i 1st started smoking cigars-the info i found came down to one thing: as cigar smokers, all we're concerned w/is RH which is what the hygros show-nothing wrong w/wanting to understand the theory though
 
shilala said:
What you're talking about is the volume of water in the air around your cigars.
For whatever reason, I think you're suggesting that you want to keep the same volume of water in your cigars at all times?
As air warms it can hold more water.
The chart that musiq posted is a simple relationship between rh and temp that aims to keep the volume of water in the air at a constant level.
http://www.arlinliss.com/__Humidor_Controls/Humistat/temp%20and humidity relationship

So what you want to do here is abandon this whole line of thinking because all it will do is ruin your cigars.
Click to expand...

Yep, Arlin makes some beautiful humidors, but he should really take this info off of his site, as it's very misleading. Store your cigars at 61F/96%RH as his table suggests and you will have a mess on your hands! Here's a link to a pretty easy to understand explanation that has been on the web for a long long time. The Variable Humidity Myth Since this comes up regularly, maybe a sticky with this link, or maybe a detailed explanation from one of our homegrown experts could be made a sticky?
 
If I have to go back to school to learn how to store my cigars, I think it is going to take a lot of the fun out of it. As long as the RH and Temp are in the mid 60's I am happy. If that isn't the perfect condition I don't care because it is good enough for me. I guess the old saying is correct, ignorance is bliss.:ss
 
I honestly hate reading about RH because it makes me so freaking paranoid.

according to this the 65% humidity in my humi will make my cigars crack?

Oi Vey!

I'm not gonna go nuts because I've read, heard and smoked enough cigars at 65% humidity for years to know that's a little absurd.
 
Wow, you guys are amazing. This is such great info; shouldn't we turn this into a sticky for all those who get a littel anxiety attack or are simply curious to know how stuff works?

I want to thank particularly muziq, mark c and shilala for their excellent posts. The chart I was looking for was indeed the chart muziq posted. But had it not been for Mark and Shilala I would now try to get the humidity in my Vinotemp up to around 75 or 78.

This vinotemp thing is new for me. Since Monday it has been holding very constantly at 66/66 and I only have beads in there, no active humidifcation. We shall see how long before I need to remoisten them.

Thanks again. I will smoke a nice stogie in your honor! :)

Till
 
shilala said:
P.S.
I've been writing on RH for about 15 years. Search "shilala humidity" on Google and you'll return about a bazillion results. I've been published in tons of magazines, books, and so forth.
I'm working on a whole bunch of tests right now to find the ultimate humidity control for humidors and incubators. When I'm done there will be a website that wraps around the stuff.
I'd trade everything I ever learned about humidity for one page of "Understanding Women".
I could actually use some info like that. :)
Click to expand...

Wow, shilala, we could have really used you durring this thread: http://www.clubstogie.com/vb/showthread.php?t=69488
Fun starts at the end of page 2.
 
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