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jtnippon 09-01-2007 08:12 AM

Warmer & more humid in morning time than mid day...
Hi all. I live in Raleigh, North Carolina, just to give you an idea of geographical location.

Anyway, my room is half underground. It's not a basement. The house was built on a little hill that is lower on the back end of the house than the front, so to make it look level the builder made the front lower level of the house partially underground. It is NOT basement, it's fully insulated, drywalled, has carpeting, plumbing, wiring, AC venting, etc etc. The builder who made my house did a large number of houses in the same style in my neighborhood back about 30 years ago. Funny thing is they cut a lot of corners and eventually a law suit against him/his company from the original first-buyers of the homes caused him to go bankrupt. Unfortunatly we never knew about this when buying the home in 1993.

Anyway. The question is this. During the day, from about 10 to late at night both the temperature and humidity of the downstairs is lower than the upstairs, about 67 degrees and aymore from 24% to 37% humidity. This is while it's almost 100 degrees outside with 70+ relative humidity outside.

However, during the early morning I notice something very strange. The temperature and humidity is higher. Like now the temperature is 71.1 degrees with a RH of 51%

How should this be possible? I would think that early morning both these factors would be yeilding both better temperature and humidity than in the middle of a summer day...

The only thing I can think of is that because the temperature drops outside, and the upstairs thermostat drops down to where it's set to (75 F) the cold air stops flowing downstairs because the AC shuts off. This in turn raises both the temperature and humdity.

I'm really know nothing about this stuff at all so it's really a shot in the dark for me. I am concerned because I have a lot of electronic equipment that I try to keep both cool AND dry so both heat and humdity are my arch nemesis.

I was considering buying a small 400 sq ft. capable portable AC unit, which would be a bit excessive for my room, but keep getting put off by the thought of dealing with R22 refridgerant leak....or condensation. However I was told that the portable air conditioner by nature of mechanics draws excess moisture from the air, and that the built in 90 pint dehumidifier also would help to remove the moisture.

I could run the AC unit independently of my home's central AC in the morning where it would then switch to using the main AC later in the day.

Unless there is something else I could do.

Thanks for all who look and respond.

rjordan392 09-03-2007 04:06 PM

I believe the clue to your question is a changing dew point.
Overnight, because of dropping temperatures, the dew point will also change. Now if you couple that with an AC system that does not run as much at night as the day hours, then this overnight vapor finds it way into your house when the AC is not running enough to remove it sufficiently. A recent weather reporter on tv explained that it is normal for humidity to be higher in the morning and he brought up the subject of dew point in explaining it. I believe I got it right but I'll leave it to the more knowledgeable to explain it in a better manner.

jtnippon 09-04-2007 02:53 PM

Ah ha...

Thanks for the info.

On another note, I recently found that despite my first thoughts, ANY part of a house somewhat or fully underground, whether it's a dirt floor basement or a fully finished living space, with bathrooms, duct, etc etc, will still have a higher humidity than in the upper portion of the house.

Something about the concrete foundation being porous and allowing ground moisture to come through, though I somewhat doubt this seeing as we're in a severe drought) and other stuff about radon midigation, etc etc....a bunch of stuff I have no clue about.

Anyway, so even though the lower portion of the house isn't a basement at all, the fact that it's still partially undergound is reason enough for the humidity to be higher than the area 10 feet above it.

Again, thanks for the dew point info though, I was going to resort to calling up my local tv station and asking one of the weather men.

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