Y is hot dry air impossible/impractical?

Posted by Zyp on October 1, 2008, 3:07 am

Green Xenon [Radium] wrote:

> On Sep 30, 11:09 am, "Stormin Mormon"

>> Relative humidity depends to some extent on temperature. The same air
>> outdoors cold, moved indoors still has the same water per some
>> volume of air. Grams per meter, is it measured? However, at the
>> warmer temp, the RH is lower. And this is uncomfortable. During the
>> winter, many home heating systems add water to the air. The moist
>> air feels warmer, because there is less evaporation from your skin.
>> Hot dry air is not practical because it feels cooler.

> Well, cold dry air also feels less cold than cold wet air at the same
> temp.
> I remember visiting a cave in Grand Canyon. The air was only 50
> Fahrenheit but did not feel uncomfortably cold because the humidity
> was only 5%. Now if the humidity was what it was outside the cave,
> then I would be shivering.

Are you sure the humidity was only 5%?

Here's the problem, cool air can only hold so much water. When you take
cool air, heat it, then it can [in a warmer state] hold more water. So, the
result is the relative humidity [as compared to what it COULD hold] is lower
than when it was cool. With lower humidity, our body tends to feel dry.
Higher humidity makes us feel clammy.

--
Zyp

Posted by Green Xenon [Radium] on October 1, 2008, 1:16 pm

> Are you sure the humidity was only 5%?

Yes. That's what our guide said and what the cave's humidity indicator
displayed.

> Here's the problem, cool air can only hold so much water. =A0When you tak=

> cool air, heat it, then it can [in a warmer state] hold more water. =A0So=

, the

> result is the relative humidity [as compared to what it COULD hold] is lo=

wer

> than when it was cool. =A0With lower humidity, our body tends to feel dry=

> Higher humidity makes us feel clammy.

Humid air tends to conduct heat better than dry air. So it is easier
to perceive extreme temperatures -- hot or cold -- in humid air as
opposed to dry air. It's like metal vs. wood. Wood can be of more
extreme temperatures than metal but not as uncomfortable to the touch
as the metal would be at the same temperature.

Posted by old and grunpy on September 29, 2008, 8:40 pm

> On Aug 9, 8:02 pm, .p.jm@see_my_sig_for_address.com wrote in
> http://groups.google.com/group/alt.hvac/msg/9646d0d0d4cfa110?hl=en :

>> And when you heat a house, you do NOT want 'dry air'.

> Why not? What's wrong with dry convective heating?

>> Even
>> if you could have it, which you can't.

> What makes hot dry air impossible?

NUMBER ONE DRY AIR IS NOT HEALTHY BELOW APX. 35%
NUMBER TWO WHEN YOU HAVE DRY AIR FOR HEATING
IT YOU WILL WANT TWO TO THREE HIGHER BECAUSE
SKIN EFFECTS AND OR SENSITIVE HEAT

Posted by Green Xenon [Radium] on September 29, 2008, 8:49 pm

> > On Aug 9, 8:02 pm, .p.jm@see_my_sig_for_address.com wrote in
> >http://groups.google.com/group/alt.hvac/msg/9646d0d0d4cfa110?hl=en:

> >> And when you heat a house, you do NOT want 'dry air'.

> > Why not? What's wrong with dry convective heating?

> >> Even
> >> if you could have it, which you can't.

> > What makes hot dry air impossible?

> NUMBER ONE DRY AIR IS NOT HEALTHY BELOW APX. 35%

So humidity below ~35% is unhealthy. I never knew that. I thought less
humidity usually means more comfort.

> NUMBER TWO WHEN YOU HAVE DRY AIR FOR HEATING
> IT YOU WILL WANT TWO TO THREE HIGHER BECAUSE
> SKIN EFFECTS AND OR SENSITIVE HEAT

What do you mean by "sensitive heat" and "skin effects"?

BTW, thanks for a sensible response. Some other posters are getting
sick pleasure out of being total jerks.

Posted by Noon-Air on September 30, 2008, 12:12 am

>> > On Aug 9, 8:02 pm, .p.jm@see_my_sig_for_address.com wrote in
>> >http://groups.google.com/group/alt.hvac/msg/9646d0d0d4cfa110?hl=en:
>> >> And when you heat a house, you do NOT want 'dry air'.
>> > Why not? What's wrong with dry convective heating?
>> >> Even
>> >> if you could have it, which you can't.
>> > What makes hot dry air impossible?

>> NUMBER ONE DRY AIR IS NOT HEALTHY BELOW APX. 35%

> So humidity below ~35% is unhealthy. I never knew that. I thought less
> humidity usually means more comfort.

>> NUMBER TWO WHEN YOU HAVE DRY AIR FOR HEATING
>> IT YOU WILL WANT TWO TO THREE HIGHER BECAUSE
>> SKIN EFFECTS AND OR SENSITIVE HEAT

> What do you mean by "sensitive heat" and "skin effects"?
> BTW, thanks for a sensible response. Some other posters are getting
> sick pleasure out of being total jerks.

Maybe you should do your own homework there sport.

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