I need a physics lesson! - Explain RH

[tfar]

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.

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.

[Soprano3695]

Dude its too late for any answers to these questions.

[tfar]

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

[Dgar]

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.

[Shaun Raney]

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.

[dustingaunder]

Try here. It is a little dry and sciencey, but it should help. Hygrometers show relative humidity.

DG

[muziq]

Till, here's a link provided to me by Arlin Liss, a custom humidor maker, regarding a problem I was having with getting my RH down in my aristocrat:

http://www.arlinliss.com/__Humidor_C...20relationship

I think this is what you're looking for.

[replicant_argent]

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.

[Mark C]

Originally Posted by tfar

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.

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?

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?

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.

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?

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.

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.

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.

[dwhitacre]

Originally Posted by muziq

Till, here's a link provided to me by Arlin Liss, a custom humidor maker, regarding a problem I was having with getting my RH down in my aristocrat:

http://www.arlinliss.com/__Humidor_C...20relationship

I think this is what you're looking for.

This is very helpful information!!! I will print this out and paste it to the side of my Coolidor.

Thanks Muziq!!!

RG for you!!!

[shilala]

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_C...20relationship

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.

[jaharr]

Very helpful, thank you. My office humidor is in an environment with alternating temperatures.

[yazzie]

Originally Posted by shilala

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.

Damm Shilala, and all this time I thought you spent all day making your Cigars look pretty

[fizguy]

Originally Posted by shilala

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_C...20relationship

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.

So what I think you are saying is just keep it at 70% RH regardless of temperature, right?

[wharfrathoss]

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