[Greenbuilding] Quick Question re Thermal Mass!

[Corwyn]

On Oct 15, 2007, at 16:05, Mary Bull - Greenwood Earth Alliance wrote:

> Greetings, Greenbuilders!
>
> I hope this email finds you well!
>
> We are having to make a decision about flooring for the "great room" 
> (420 SF--not so great, really ;-) where all the south light hits in 
> winter. I have assumed for a while now that it must be of some sort of 
> masonry (we are thinking slate tiles now). However, my new natural 
> builder says that these will not provide the mass needed for adequate 
> thermal absorption because they will not be thick enough (about an 
> inch or so including the mortar they are set in). However, he says 
> that the interior walls themselves coated with a thick layer (2 inches 
> or so) of earth-clay will provide enough thermal mass. I am not 
> convinced, because not as much wall will be receiving direct sunlight 
> as floor.

Slate:
	using a specific heat value of .2 (for general stone) and a density of 
167 lb/ft^3 for a 1 inch thick over an area of 420 ft^2 we get: 33.4 
BTU/ft^3 and 35ft^3 of material = 1169 BTU / ºF.

Clay:
	using a specific heat value of .22 (presumably wet clay) and a density 
of 63 lb/ft^3, for a 2 inch thick layer over 656 ft^ (sqrt(420) 
(assuming a square room) * 4 walls * 8 feet high) we get: 13.86 
BTU/ft^3 and 109 ft^3 of material = 1515 BTU / ºF.

So you would get 30% more thermal mass from the walls as from the floor 
(All Else Being Equal).  However, the general rule of thumb is that 
thermal mass in direct sunlight performs about as well as 6 times as 
much out of direct sunlight (since it can reach a temperature above 
room temperature).

So what percentages of floor and wall are getting direct sun, for how 
long?

Thank You Kindly,

Corwyn

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