re: storing heat from warm sunspace air SOLAR.KnowledgePublications.com

re: storing heat from warm sunspace air
19 feb 2003
>> on an average day, we might just store overnight heat in the walls, with
>> cloudy-day heat in a higher temp water store. with r20 walls, g = 12.8.
>> if warm sunspace air keeps the 8' cube with r20 insulation 70 f for
>> 6 hours on an average day and we store about 18h(65-30)g = 8064 btu of
>> overnight heat and the cube air is 70 f during the day and 60 at night,
>> we need 806 btu/f with a short time constant...

>how much depth do we need to do away with the masonry wall and cover the
>ceiling with water with 122 f stratified air underneath for 6 h per day?

we need about 8064/(122-70) = 155 pounds of water, ie 2.4 psf or 0.45".
with rc = 2.4/3 = 0.8 h, it might warm to 122+(70-122)e^(-6/0.8) = 121.97 f
over 6 hours. we might store heat for 5 cloudy days in 5x24(65-30)/(122-70)
= 1034 pounds of water, ie a 3" layer. 

>the floor and people below would get heat from the ceiling by radiation.

bare 122 f water would radiate 0.1714x10^-8)((122+460)^4-70+460)^4) = 61
btu/h-ft^2. excluding the ceiling, the cube only needs (70-30)9.6 = 384,
so we might put aluminized mylar under all but 384/61 = 6.3 ft^2 of duct,
eg the part over the updraft fan, with perimeter holes for return air.

>a slow ceiling fan or reflective louvers could provide fine room temp control.

overhead water allows better room temp control than mass walls, including
setbacks at night or unoccupied times, with the fan off.

nick