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Old 03-26-17, 10:31 PM   #7
DEnd
Apprentice EcoRenovator
 
Join Date: Nov 2011
Location: NC
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Quote:
Originally Posted by buffalobillpatrick View Post
My windows & doors U=.25 = R-4

My walls 6" Polyiso foam is R-2 / inch @ 0*F and R-6 / inch @ 70*F
My wall average @ 0*F outside is about R-4 / inch = R-24

So my windows & doors loose heat about 6X faster per square foot, than my walls.

Conduction Heat Loss: Q = Area x U-value x Delta-T

Comes close for walls, windows, & doors, but ignores some BIG factors such as infiltration, wind washing, and Clear Cold Night Radiation.

Underslab insulation

Calculating heat loss

Radiant slab heat loss down & horizontal is very complex.
Depends on under slab & perimeter R-values, soil type, water content, soil temperature, outdoor temperature, slab temperature, room temperature, slab size, etc, etc.
Yeah, I started to get into all of that, then realized to actually give you all the math and reasoning I'd be writing a book. and it likely wouldn't be done as well as the other books out there.

As far as windows and doors they do have an effect on comfort, but the biggest issues is the percentage of wall area they take up, and their U-factor.

The decreased tubing spacing is just decreasing system response times, allowing a greater percentage of BTUs to reach the walls and windows faster. And remember at design conditions your system should be running flat out anyway. So if it's designed correctly it will still be comfortable when it is most likely to be uncomfortable. That just leaves the shoulder times. During those times the wall will only be receiving a small portion of its BTUs from the point closest to the wall. For relatively high loss walls that extra tubing is a good thing, for lower loss walls and homes it really isn't needed. There are also other ways to get the same effect, such as increasing thermal conductivity, decreasing thermal mass, modulating water flow and temperature, etc...
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