Humidity Question

[johnnymk]

I am trying to find some information regarding the amount of moisture(relative humidity) which is contained within a dwelling.

For some reason, my relative humidity is floating between 59-65% during the last month. The temperature within my house averages 73 degrees.

I am using a dehumidifier intermittenly and can get my room down to 54%, but as soon as I turn it off, it goes back up.

I want to find how much water is contained witin a 1000 square foot dwelling at 73 degrees inside, approx. 80 degrees outside or whatever and at sea level. I am trying to calculate how much water I have to remove so that I can get it to around 50% relative humidity without using the dehumidifier a lot.

[Grimm]

Need two more factors there. Need average ceiling height so volume can be calculated and barometric pressure so the mass of the air can be calculated from the volume.

[johnnymk]

Need two more factors there. Need average ceiling height so volume can be calculated and barometric pressure so the mass of the air can be calculated from the volume.

7.5 feet ceiling height and 30 pounds

[zippyjuan]

Pennsylvania can be pretty humid. If you have dried out the air in your house more than the outside air you have to prevent outside air from entering or it will go back up to being as humid as outside.

[tupacboy]

just line ur walls with silica gel... jk.....

[Grimm]

You are looking at about 20 grams of water per cubic meter at 100% humidity at 23 degrees C.
You have about 212 cubic meters (1000 * 7.5 * 0.0283).

So, at 100% humidity you have 4240 grams of water.
At 50% humidity you are looking at 2120 grams of water.

To reduce from 60% to 50% humidity you are taking about 424 grams of water.
1 gram of water = 1 cubic centimeter, so you need to remove 0.424 liters of water.

Don't forgetthat will go up as more water vapor is drawn in from outside and out of other areas of your home... the bathrooms and kitchen for example, the attic as another. You can even pull moisture up from your floor.

Remember that some forms of cooling actualy add water vapor to the air.

[johnnymk]

So you're telling me I have only a litlle over a gallon of water vapor in my house at 60%?

I ran the dehumidifier for over 5 hours today and got 3 pints of water and it reduced it from 62% to 57%.

[Grimm]

So you're telling me I have only a litlle over a gallon of water vapor in my house at 60%?

I ran the dehumidifier for over 5 hours today and got 3 pints of water and it reduced it from 62% to 57%.
I'm just using numbers I pulled off the internet. The graph said 20 grams/cubic meter at that temperature.

Your problem is probably water vapor enting the air from other sources.
Wallboard and floors can hold a lot of water. If you take a shower a lot of vapor enters the air. Any water sitting out can evaporate into the air. A wet towel will evaporate every bit of water into the air, how often do you wash your hands? The water on the counter in your sink or kitchen will evaporate, as will water from the comode. Glasses left out or a tea kettle waiting to be heated next to the stove, coffee machines and even people add to the humidity.

Water vapor will be drawn in from outside, even if there isn't much airflow through an opening. It's ozmosis.

Are you using more than one meter to determine your humidity? If the meter is not accurate you might be making things drier than you like.

[johnnymk]

Well, I will definitely look into getting a new meter, but it was working this winter.

Plus nothing has changed, as far as I know since last summer. Maybe it is the meter.

But by your figures , I should have no water vapor left in my house, unless there is a continuous release from inside or outside. If it were that bad, I would have condensation on all of my windows continuously, and I don't.

But thanks for the help. What did you use as your source?

[Markel]

Water vapor will permeate concrete (which is why basements tend to be damp) and many wall materials (which is why things such as "vapor barriers" are used, but sometimes they are to keep moisture from entering the walls from the living areas). If you wanted to prevent all outside sources of water from your home, you would practically have to seal the house in plastic on all sides. And then there are all the sources inside that Grimm mentioned (so stop exhaling and sweating!).

[Grimm]

Well, I will definitely look into getting a new meter, but it was working this winter.

Plus nothing has changed, as far as I know since last summer. Maybe it is the meter.

But by your figures , I should have no water vapor left in my house, unless there is a continuous release from inside or outside. If it were that bad, I would have condensation on all of my windows continuously, and I don't.

But thanks for the help. What did you use as your source?
I wasn't able to locate the specific sources I used earlier. But I can google many more.
http://www.usatoday.com/weather/resources/askjack/wfaqhumi.htm
http://www.home-inspect.com/itatips/12-03.asp
http://cougar.slvhs.slv.k12.ca.us/~pboomer/grades/demos/atmos.html
http://www.gorhamschaffler.com/understanding_humidity.htm
http://www.csulb.edu/~rodrigue/geog140/lectures/humidity.html (Good chart on this one)

Maybe you should look at controling the vapor entering your house. Verify you have no leaks. Seal your walls, floors, and ceilings. Reduce evaporation by ensuring the lids of your toliets are down. Hang towels outside to dry and such.

[johnnymk]

grimm, that last link is very informative:

Because water vapor is such a small percentage of air (somewhere from 0-4%), there isn't all that much difference, really, between saturation mixing ratio and specific humidity at saturation.

Plus the chart shows 20 grams per cubic centimeter at 23 degrees C.

Thanks

[Grimm]

Plus the chart shows 20 grams per cubic centimeter at 23 degrees C.
If you have 20 grams of water per cubic centimeter in your house you have a real problem!!! :eek3:

[Houdini]

If you have 20 grams of water per cubic centimeter in your house you have a real problem!!! :eek3:

Heh...that would be some heavy water. :)

[johnnymk]

If you have 20 grams of water per cubic centimeter in your house you have a real problem!!! :eek3:

Sorry...I meant meter