# Constant-temperature dehumidification

On Wed, 20 Sep 2006 20:24:53 -0400, "Solar Flare"

The power was from the heat produced by the audience, at rest I think the numbers are somewhere around 400 BTU/hour, maybe more. And 800 times 400 BTU per hour about 320,000 BTU per hour, or 90KW? I don't believe it!
And I think this means that the upward draft caused by that heat is proportional to the size of the audience making it also self controlling.
This system likely worked better in the evening than during the day, but that was ok because the only days the theater was open was Sat and Sun.
If I made a wrong assumption, sorry, I really never thought much about just how little I had to do to manage the heating and cooling system until now.
I also want to mention that the places I lived that had gravity air furnaces seemed much more comfortable. But they had to be in the basement, were not very efficient, and were coal fired. Joe Fischer
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All we need is a difference in bouyancy, ie a column of indoor air that is warmer and/or moister than the column of outdoor air.
Nick
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errs again:

Actually it's more complicated. Partial pressure of water vapor in air and the partial pressure of any standing water determine evaporation/drying rate. Human sinuses have 'water' that stays at the same temperature (unless you're running a fever), so the partial pressure of water vapor in air is pretty much it. And the pp of water vapor is saturation pressure for the dry bulb temperature times the RH. Heating air doesn't change the pp of water vapor (saturation pressure rises as much as RH drops).
Surely you've noticed that running the heat up high in the winter doesn't do anything for your sinuses. Humidification (raising the pp of water vapor) does.
Trouble is, the partial pressure of water vapor is not readily measured. It can be calculated from RH and dry bulb temperature. (find the saturation pressure of water at the dry bulb temperature, then multiply by RH). The next best thing is to track the dew point. When you heat air, the dew point doesn't change. Hot air is better at drying 'things' because the hot air provides more energy to evaporate the liquid.
This winter, rather than track the RH as my house temperature rises/falls (set-back thermostat), I plan on tracking the dew point. I suspect it will give me much more consistent data.
<snip>

It's not just the electric to power the humidifier, it is also the energy to evaporate the water. With many simple humidifiers, that energy comes from the air blowing through it. So the furnace works harder to heat the air back up again.
Yes, it's certainly more comfortable (I have problems with wintertime humidity as well). And the human body 'feels' comfortable when the heat losses through convection and evaporation are matched to our optimum value. Lowering evaporation heat loss (by raising the dew point) can allow for slight increase in convection losses (setting the thermostat down a degree or two). But it's very subjective.
daestrom
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On Tue, 19 Sep 2006 20:08:24 GMT, "daestrom"

I am sure it is, I wondered about it ever since I saw a meteorologist put cotton on a thermometer and swing it round and round in 1946.

Sure, but breathing through the nose moves a lot of air over the same tissue. I won't go into Bernoulli or Venturi.

Please don't say that carpeting doesn't dry out if wet. :-)

It sure does, it makes them bleed, and feel like the tissue is stretched. Then a few hours later they start producing moisture.

And you base this on the next sentence?

Try running a cool air humidifier, and see that it stops evaporating water after a certain humidity. I use a steam humidifier so I can go to higher RH.

Yes, I have read many of the papers by Einstein on specific heat and latent heats.

You are more of a scientist than I want to be to keep a nose dry. :-)

Which is another reason I use a steam vaporizer, I try to put at least 2 gallons of water in the air on a cold night, and I only do this in my room, the rest of the house doesn't matter.
I really need to avoid colds and trips to the doctor.

In order to try to conserve (prompted by the rise in retail natural gas last fall), I am only heating my room, the kitchen and the bath. I wouldn't heat the kitchen but I can feel the convection drafts as the cool air moves into my room.
I really should build a balcony in my room and put the bed and computer and TV on it as I have eleven foot ceilings. I bought some 36 inch balloons that I am going to fill with air (not helium, I talk funny enough now), and put screw-eyes in the wood strips on the ceiling and pull them up with a string, and if the air leaks out I will be able to let them down to fill them.
Every house and every person is different, my house was designed originally as two large rooms with a double fireplace in the common wall, and if it were not for that fireplace, the house would have floated away when the river was up to the peak of the roof in January 1937.
Houses with working fireplaces can't safely be sealed air tight, even if air tight is just a figure of speech.
Actually, the faster the air changes, the higher the relative humidity may be )without a humidifier), I really haven't considered that though, I need it warm, and I want to conserve in a reasonable and rational way.
Joe Fischer
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And what effect did that have, insulating the thermometer by wrapping the bulb with dry cotton? Seems like it would read the temperature much faster if the bulb wasn't insulated.
--

Christopher A. Young
You can\'t shout down a troll.
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On Wed, 20 Sep 2006 21:56:08 GMT, "Stormin Mormon"

Sorry, I didn't say the cotton was dry, it may have been wet with water or even alcohol, I am not a trained weather man. :-) I assume he was checking dew point, but I am not certain. Moist air is lighter than dry air, so dew point was important in several ways for Army Air Force weather forecasting.
Joe Fischer
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Hi Joe;
Joe Fischer wrote:
> > And what effect did that have, insulating the > > thermometer by wrapping the bulb with dry cotton? > > Seems like it would read the temperature much > > faster if the bulb wasn't insulated.
> Sorry, I didn't say the cotton was dry, it may have > been wet with water or even alcohol, I am not a > trained weather man. :-)
In all likelihood it was water. The instrument most use is called a "Sling Psychrometer". http://en.wikipedia.org/wiki/Sling_psychrometer
> I assume he was checking dew point, but I am not > certain.
Actually he was measuring what is called "Wet Bulb Temperature". Along with the "Dry Bulb" or ambient temperature the relative humidity can be calculated.
Dew point temperature is always lower than wet bulb. Wet bulb is basically the cooling effect and is dependent on the relative humidity.
> Moist air is lighter than dry air, so dew point was > important in several ways for Army Air Force weather > forecasting.
Sure, dew point is another method to measure relative humidity.
> Joe Fischer
Duane
--
Home of the \$35 Solar Tracker Receiver
http://www.redrok.com/led3xassm.htm [*]
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Its wrapped in wet cotton, thats what the wet bulb temperature is.

Yes, but its wet cotton, not dry.

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If you need to know how much moisture is in the air then you need to know the (GRAINS PER POUND) of water in the air. You can also use the dew point if you know what you are looking for but the GPP works better. http://www.humiditysource.com/RH_101.html The formula is on the page above. We have special equipment at work that does the math for you. They also make slide rule or disks that you can set to the temperature and the RH that will give you the GPP.
You can also buy (LGR) low grain refrigerant dehumidifyer. They come really close in removeing moisture compared to desicates. Take a look at http://www.dryitup.com There is some links there for dehumidifier manufacturers.
I hope this helps..
Joe IICRC Water Restoration master. Yes I dry out buildings for a living...
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