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Old 01-11-2011, 02:05 PM   #16
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condensation on double pane windows


Thank you all for your input, I had an Air Specialist come and and fix the problem, I no longer get the condensation on the windows but I don't understand what he did even though he explained it to me, I taught I would share the information and see if some one can make head or tales of it.

He described my situation as a stack effect, negative pressure in the basement and positive pressure on the upstairs which is causing ex-filtration. Since I do not get condensation in my basement windows only in the upstairs. He solved the problem by:

-sealing up some areas in my basement and attic region.
-disconnect the cold air return vent in my basement so now my basement has no return vent he said that my return is leaky anyways so I will always have some return vent by putting more would make my situation worst.
-disconnect the 3" dia duct that goes into my cold air return vent and sealed up the hole on the outside
-brought in a 4" dia duct fresh air duct and brought it right next to my water heater which is attached to my chimney and dropped it into a sheet metal box with holes all around the top of it.

And for whatever reason the condensation disappeared on my upstairs windows, it's just a little weird I just don't understand how that worked

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Old 01-11-2011, 02:52 PM   #17
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condensation on double pane windows


Quote:
Originally Posted by oberon View Post
Warm air does not “hold” more moisture than cold air – that is a myth.
I agreed with everything you stated except the above.

Example:

The maximum humidity ratio for say 40*F air would be .005#moisture/#dry air but the maximum humidity ratio for 85*F air would be .028#moisture/#dryair.

More than 3x the amount of moisture can be held at 85*F as opposed to 40*F before reaching dew point at each respective temperature.

Thanks for the great explanation and I am sure you will have an answer for this, at least I hope you do.
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Old 01-15-2011, 08:06 PM   #18
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condensation on double pane windows


Quote:
Originally Posted by Jackofall1 View Post
I agreed with everything you stated except the above.

Example:

The maximum humidity ratio for say 40*F air would be .005#moisture/#dry air but the maximum humidity ratio for 85*F air would be .028#moisture/#dryair.

More than 3x the amount of moisture can be held at 85*F as opposed to 40*F before reaching dew point at each respective temperature.

Thanks for the great explanation and I am sure you will have an answer for this, at least I hope you do.
Thanks back!

Although the idea that warm air holds more moisture than cold air is very common, and it is even taught in school science classes from elementary to college, it still isn't technically correct.


Here are a couple of links that do a great job of explaining the concept.

http://www.ems.psu.edu/~fraser/Bad/BadClouds.html

http://www.kidsnewsroom.org/elmer/in...CloudsFAQ.html
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Old 01-06-2013, 08:18 PM   #19
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condensation on double pane windows


Quote:
Originally Posted by oberon View Post
Thanks back!

Although the idea that warm air holds more moisture than cold air is very common, and it is even taught in school science classes from elementary to college, it still isn't technically correct.


Here are a couple of links that do a great job of explaining the concept.

http://www.ems.psu.edu/~fraser/Bad/BadClouds.html

http://www.kidsnewsroom.org/elmer/in...CloudsFAQ.html
I know you posted quite a while ago and you had a great write up. Thanks for the general information which was great. But I too must take issue with your statement hot air does not have more "holding" capacity than cold air. That unfortunately statement is not accurate, it's simply misleading.

Yes technically air does not have a hold water in the air. Water has a partial pressure that is a function of temperature. This means if you place water in a vacuum of specific space and temperature, when the system equilibrates a specific mass of water will fill the space. As temperature increases partial pressure increases so more water vapor can fill the void. A sample graph can be found here: http://upload.wikimedia.org/wikipedi...sure_Chart.png

So conclusion, as temperature increases so does mass of water in the same volume. A great description on this phenomena can be found here: http://www.atmos.umd.edu/~stevenb/vapor/ (My Alma Mater, sorry...shameless plug)

Now we live on planet earth so we have a very set atmosphere which is mostly made up of Oxygen and Nitrogen, we call air. As temperature increases the air will have more water vapor in the same amount of air either by KG or Volume. Excellent graphs can be found at the engineering toolbox http://www.engineeringtoolbox.com/mo...air-d_281.html

You can clearly see in the graphs, a volume of air or mass will have more water vapor as temperature increases, regardlessif its by mass or volume of air. Furthermore, Air is not an ideal gas and assume space, this space will compete with the water vapor and influence the amount of water vapor that can assume a space. Thereby there is a relationship between water vapor, air and space most easily understood as air's capacity to hold water.

The websites you link, I'm not a fan. The author is simply trying to say a localized phase change is occurring due to temperature change. This is a very simplistic view. Clouds form under many different conditions/phenomena which are best described by statistical thermodynamics and nucleation. Been a long time since I've had to solve phenomena so I can no longer do it justice. If you interested though, go speak with a thermodynamics professor in the Chem E department of a local university.

Anyway, thanks for the great write up earlier, I really appreciated it.


PS: The Hopkins PhD I site refers to 300% relative humidity which is called a meta-stable state. The easiest but HIGHLY UNSAFE way to observe a Meta-stable state is put water in a glass and microwave it. The water can super heat to above 100 C without boiling, then when you move it, it can boil instantly often injuring the person moving the water. So don't try this unless you have proper PPE (Gloves, lab coat, face shield, etc....)

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