[Greenbuilding] Trying to maximize passive solar gain...

[Corwyn]

On Apr 18, 2007, at 20:59, Nick Pine wrote:
>

> Those books (eg Chiras) are often inspired by masonry salesmen who
> gave those recommendations unstintingly and enthusiastically :-) 
> Sunspace
> mass kills solar collection efficiency by making it lukewarm all day 
> instead
> of hot during the day and cold at night and storing solar heat which 
> leaves via
> sunspace windows at night.

How's that?  Start two houses at equal temperatures, heat them with 
solar gain, cool them with normal heat losses, I contend people will 
much prefer to be in the one with high thermal mass.

> Living space mass can limit night setbacks
> which save energy and prolong warmup times after setbacks.

Huh?  Night setbacks save energy by not putting heat into the house 
during the night. It doesn't matter from an energy input standpoint 
whether the house gets cooler or not.  It might matter to the 
inhabitants, one way or the other.  It can't prolong the warmup time if 
it never got cool in the first place, can it?  Yes, a warmer house will 
lose slightly more heat per hour than a colder one, but not waking up 
to frozen toes seems worth it to me.

> Avoid direct gain mass and glass.

I disagree.
>
>> Is there any other advice you might give?

> If your house were (say) 32' square and 16' tall with 80 ft^2 of US R4
> windows upstairs with 50% solar transmission and (say) an R40 ceiling
> and R32 walls, eg 8" SIPs or foamboard and fiberglass, the upstairs
> would have a thermal conductance of 1024ft^2/R40 = 25.6 Btu/h-F
> for the ceiling + 20 for windows + 944/32 = 29.5 for walls. Adding
> 15 cfm for air leaks would make the conductance about 90 Btu/h-F.
>
> With a 60 F average temp (70 day and 50 at night),

70º in the day (say 7:00 - 10:00) and 50º at night (10:00 -7:00) does 
not average to 60º.  Rather 62.5º.  And that requires that you drop 
from 70 to 50 instantly.  Naturally cooling from 70º at 10:00, to 50º 
at 7:00, averages to 66.7º.  (that makes the cost of keeping it at 70º, 
7192 BTUs/day) you can probably make that up in nothing more than a 
smaller furnace (i.e. one that doesn't need to bring the temp from 50 
to 70 in a short time period).

In order to lose 20 degrees over 9 hours at 90 BTU/h-ºF requires having 
less than 1620 BTU/ºF of thermal mass.  The drywall is going to be 
almost that much, to say nothing of the concrete.

>  A frugal 600 kWh/mo of indoor electrical use

600 kWh / month is frugal?  yikes.

Thank You Kindly,

Corwyn

-- 
Corwyn
Kermit didn't know the half of it...
http://www.greenfret.com/
corwyn at greenfret.com