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 Post subject: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 5:47 am 
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Cocobolo
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Joined: Wed May 04, 2016 4:17 am
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First name: Gary
Last Name: Leddington
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Hi Folks...

Last week over here in Europe we had a heat wave... it was hot and humid outside (sometimes in the 60-70% range)... but the humidity in my shop was in the 30s... can anyone explain this too me..?

I get how it works in winter... with heating and all. But this one confused me....

Totally screwed up my bracing schedule.

Gary.

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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 5:57 am 
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Joined: Fri Jul 10, 2009 4:44 am
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First name: colin
Last Name: north
Country: Scotland.
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Shop conditions would be a help.
Air conditioning? Dehumidifier? Heating (as if)?

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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 8:27 am 
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Joined: Fri Mar 24, 2006 12:42 pm
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Location: Windsor Ontario Canada
First name: Fred
Last Name: Tellier
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Zip/Postal Code: N8T2C6
Country: Canada
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Read this or similar definitions of RH the actual amount of water in the air varies with temperature. In reality dew point is the most accurate means of measuring humidity in the air
https://en.wikipedia.org/wiki/Relative_humidity

Fred

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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 8:40 am 
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Brazilian Rosewood
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Joined: Tue May 13, 2008 10:44 am
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Location: Western VA, no not West VA
Funny you mention that. I noticed that this year in Virginia too. I try to stay at 40-45% year round. In the winter I run a humidifier and in the summer I run AC and usually a dehumidifier. Even though it's been very humid and hot hear, especially the last couple weeks, I have almost had to run the humidifier in the shop as it has dipped to 35% at times. Really weird. I can only think that my AC is running really dry this year but I have not noticed since I opend this new shop 5 years ago.


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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 9:01 am 
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Old Growth Brazilian Rosewood
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Joined: Fri Nov 02, 2007 9:49 am
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Location: Ann Arbor, Michigan
First name: Hesh
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What hygrometer do you use and how do you know it's accurate?


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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 12:22 pm 
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Cocobolo
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First name: Gary
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No humidifyer or de-humidifyer have been in use... these are ambient readings... no atmospheric modification going on...

I have two hygrometers... i have tested both using the salt trick... one came out at exactly 75% the other at 70% they are both pretty accurate, and agree on the 5% difference however they move.

G.

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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 12:41 pm 
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Joined: Thu Feb 09, 2006 2:35 pm
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First name: Joe
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With no temperature (AC) or humidity (De-humidifier) modifications going on, the number don't quite make sense. Is your shop in a basement area? Does it stay cool in there naturally? Get colder over night?

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 Post subject: Re: Humididty Conundrum
PostPosted: Tue Jul 09, 2019 1:03 pm 
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Cocobolo
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Joined: Thu Nov 21, 2013 2:03 pm
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This has happened to me as well down here in Florida. Just the other day, we had some very humid weather outside and my shop was high 30's, low 40's %RH. Most of the time it aligns with what is going on outside but not always because of interior heating/cooling. Nothing to worry about, just humidify/dehumidify as needed. For the record, my hygrometers are all calibrated to within 1% accuracy.


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 Post subject: Re: Humididty Conundrum
PostPosted: Wed Jul 10, 2019 9:51 am 
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Brazilian Rosewood
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A quote from the Wikipedia page might be a clue, "The same amount of water vapor results in higher relative humidity in cool air than warm air." So the reverse of that would also be true, "The same amount of water vapor results in lower relative humidity in warm air than cool air". So the hot outside temperature warmed up your shop which dropped the relative humidity. This would be based on the fact that your shop walls are not impervious to temperature changes but are relatively impervious to the movement of moisture through them. Sounds good in theory, anyways.


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 Post subject: Re: Humididty Conundrum
PostPosted: Wed Jul 10, 2019 10:37 am 
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Brazilian Rosewood
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Joined: Tue May 13, 2008 10:44 am
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Location: Western VA, no not West VA
You can't argue with math. IT seems counterintuitive but that's the way it works.


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 Post subject: Re: Humididty Conundrum
PostPosted: Wed Jul 10, 2019 11:39 am 
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Cocobolo
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Joined: Wed May 04, 2016 4:17 am
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First name: Gary
Last Name: Leddington
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Status: Amateur
Barry Daniels wrote:
A quote from the Wikipedia page might be a clue, "The same amount of water vapor results in higher relative humidity in cool air than warm air." So the reverse of that would also be true, "The same amount of water vapor results in lower relative humidity in warm air than cool air". So the hot outside temperature warmed up your shop which dropped the relative humidity. This would be based on the fact that your shop walls are not impervious to temperature changes but are relatively impervious to the movement of moisture through them. Sounds good in theory, anyways.


This makes a lot of sense... Thanks so much for getting to the bottom of this!!

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