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Re: Spa (Hot tub) Renovation - Gas? Solar?

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Posted by Astro on October 22, 2004, 11:51 am
Sorry Don,

I must be totally daft - what are you talking about?

All I said is that Nick's argument that temperatures in the low 60's with  
high humidity would feel cold is right. Any psychometrics table supports  

As for what you're saying below - of course humidity is tightly controlled  
in many environments! I must have missed the threads where he's arguing  
that it isn't. Can you point to some specifics? I searched already but  
only found the raging debates with Turtle regarding the comfort levels at  
various RH's.

What am I missing here?

Posted by Astro on October 22, 2004, 1:18 pm
okee-dokee. Thanks for the background.
It's good to know more about the players and history in these discussions  
as I get more involved in the field.


Posted by nickspam on October 22, 2004, 10:26 pm

I denied that. Humidification raises fuel bills, even with a lower
thermostat setting, unless you live in an extremely airtight house.


Posted by nicksanspam on October 24, 2004, 12:46 pm

ASHRAE 55 says a 48x48x8' house with R20 walls and ceiling would be equally
comfy at 69.4 F and 20% RH or 68 F and 50% RH. If it's very tight, with 0.5
air changes per hour, would "proper" humidification to 50% save energy?

G = 48'x48'/R20 + 48x4x8/R20 = 192 Btu/h-F, so dropping the room temp
from 69.4 to 68 F saves 1.4x192 = 269 Btu/h. At 69.4 F and 20% RH, Pd
= 0.2e^(17.863-9621/(460+69.4)) = 0.1466, approximately, with wd
= 0.62198/(29.921/0.1466-1) = 0.003063. Air at 68 F and 50% RH has wh
= 0.007347. With 0.5x48x48x8/60 = 154 cfm of air leakage, humidifying
from wd to wh requires evaporating 154x60x0.075(wh-wd) = 2.96 pounds of
water per hour, which requires about 1000x2.96 = 2960 Btu/h of energy,
so the net "savings" is 2960-269 = -2691 Btu/h, or minus 64.6K Btu/day,
costing about $/day more with oil heat or $ per day with electric heat.

I've done these calcs several times now. HVAC people tend to forget that
evaporating water takes heat energy, even if a humidifier belt uses little
energy by itself, and that heat energy has to come from somewhere. And we
often get into discussions about health and furniture, vs energy and forget
that caulking a house (vs humidification) can raise the indoor RH while
SAVING on fuel bills.


Posted by Serendipity on October 24, 2004, 1:36 pm
 nicksanspam@ece.villanova.edu wrote:

But, too dry of indoor air causes all types of health problems such as
mucosal membrane irritation, nose bleeds, increased viral infections,
and more.  Further, improper indoor humidification dries out wood
furniture and the house itself causing wall cracks and worse.  So there
has to be a proper balance of humidity.
Think beyond your assumptions.

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