[Strawbale] insulation and thermal recovery

[Sherwood Botsford]

Shody Ryon wrote:
> I was wondering if there is any interest in the efficacy of using a space between the skin of a structure for the reflection of radiant heat? Is it worth the extra material and construction costs for the increase in R value, and could that air be captured and used somehow (assisting a thermal recovery ventilation system in winter)? Should the optical space be utilized in the exterior of the sun facing wall and roof and in the interior (between drywall and insulation) in the other walls and roof?
> Shody
>
>
>   
Yes and no.  Salvaging the radiant heat from a SB wall is a losing 
proposition.
The outside wall is very close to ambient temperature.   With reasonable 
detailing, the dominant heat loss in an SB building is air exchange, 
either through the ventilation system or through the process of opening 
and shutting doors for cats, dogs and kids.

Having a system to capture radiant heat from the sun however has merit.
Look on the BuildItSolar.com web site.  Guy there describes a system 
where he built
a false wall on the south side of his shop, back of the wall, next to 
the shop was covered in black plastic.  Front of the wall was covered 
with clear plastic. He openings in the top and bottom of the wall, and a 
couple of fans.  He has a differential thermostat that turns the fans on 
whenever the upper part of the false wall is warmer than the shop.  He 
claims that even when it's -20 outside, the shop is a reasonable working 
temperature by 10 a.m. and will stay that way until about 5 p.m. (He's 
in Montana)

This was with a conventional 2x4 (maybe 2x6) shop.  If I was heating a 
house this way, I think I'd build a floor with two sets of hydronic 
tubes, one above and one below the floor slap insulation.  Then some 
clever programming on bank of valves:
T = current inside temperature.
Tin = desired inside temperature.
Tun = temperature under the slab.
Twa = temperature in the wall space.

T < Tin  Need heat.
   Twa > Tin  Move heat into above slab.
   Twa < Tin AND Tun > Tin  Circulate water between under slab and room 
slab.
   Twa < Tin AND Tun < Tin.  Build fire in fireplace, or divert heat 
from hot-water heater to slab.
T >Tin  Don't need heat
   Twa > Tun  Move heat into slab.

With an edge insulated slab foundation, you could pump heat all summer 
into the under house earth.  If you could get the 10-12 feet under the 
house up to 120 degress F or so, you probably could heat the house all 
winter.
   Twa < Tun  Wait.