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re: thermal mass for multi-story house.
28 jan 2005
 wrote:

>where i  live, southern califonia, near the ocean, the weather is very
>mild and pleasant. except for a few chilly winter nights there are no
>large temperature fluctuations...

sounds like you don't much space heating or cooling at all.

>nonetheless, i woudl like to obtain the benefits of both high
>insulation and thermal mass.

and airtightness, altho i tried to help one californian figure out
how to solar heat a new house with the windows open :-)

>land prices are so high that one cannot afford to build a home with
>the usual "earthship look"...

good.

>herein lies my problem:  an earthship provides large amounts of thermal
>mass, because it has extremely thick earth walls and an earth floor;

and not much insulation.

>...while i can build a concrete slab for thermal mass on the bottom floor,
>i don't think i can do so for upper floors due to the heavy weight involved.

a slab can help cool the house, with ceiling fans. a low-e massy ceiling
can help warm it, with thermosyphoning air heaters. you might look into
"the barra system," which is popular in europe, or put some fin-tube pipe
under a low-e ceiling, with a stratified heat storage tank on the ground.
this can also preheat water for showers.

a whole-house fan with a smart controller may also be useful, letting you
bring in cooler outdoor air when the house needs cooling and warmer dry
outdoor air when the house needs heat.

>...i plan to instead compromise by using eps tridipanels. though i do not
>have any experience with tridipanels, they sound like an ideal way to
>quickly erect a building, while obtaining thermal mass on the inside...

indoor thermal mass is good, but these panels look heavy and expensive. 

>however, i wonder if this is enough thermal mass.

it wants to have lots of surface, with short internal and long external
time constants rci and rce. a thermal capacitance c btu/f with a ft^2 of
surface in slow-moving air has an internal time constant rci = c/(1.5a)
in hours. with a g btu/h-f house conductance, rce = c/g hours. 

for instance, a 30'x40'x8' house with an r40 attic and r30 walls and g=128
btu/h-f and 2400 ft^2 of 1" drywall (2 layers) with 2400 btu/f plus 2400
btu/f of possessions with a = 4800 ft^2 would have rci = 4800/(1.5x4800)
= 0.67 hours (40 minutes) and rce = 4800/128 = 37.5 h.

>for a residential home, i would build a three-story house consisting of
>a finished basement, a ground floor, and a second story.  for the basement,
>i can pour concrete to my heart's content so that i have the house resting
>of a thick thick slab of thermal mass.

concrete also has internal and airfilm thermal resistance...

>i might even be able to build a concrete slab onto the ground floor...

or tuck some 4" pvc water pipes between the basement ceiling joists.

>i don't know. though, if i can provide a concrete floor for the second
>story.  it seems that the expense of reinforcing the house to support
>the extra weight is prohibitively costly...

water stores about 6x more heat per pound than masonry. you might
"pug" the floors with epdm or poly film water ducts between joists.
 
nick




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