|
|
re: passive solar home/solar slab
14 apr 1998
steve wrote:
>h. adam steinberg wrote:
>> i want to build a solar heated home and after looking around i found the
>> book by james kachadorian "the passive solar home" from real goods.
kachadorian's book missed the point here and there...
>> ...interesting ideas, like using the cinder blocking channels under
>> the concrete to distibute heat to the solar slab.
i've seen this done with walls as well: stack up hollow blocks aligned
so air can flow vertically through the hollows, and make holes in the
inside face of the wall at the top and bottom (or use perpendicular
u-shaped blocks under a thicker wall, with insulation on both sides)
to let room air flow in and out of the wall. this increases the amount
of wall surface exposed to room air, which makes the wall a better
room-temperature thermal store, by decreasing the internal series
resistance of "the heat battery." also, a wall allows natural airflow,
vs a floor, which needs a fan...
but this can be further improved: if the masonry can somehow be kept
at a higher temperature, it can store more useful space heat, and
provide better room temperature control. a 30 pound cement block that
cools from 75 f to 70 f releases about 25 btu of heat as room air cools
from 75 to 70. the same block cooling from 120 to 80 f might release
about 200 btu (8x more) of heat while keeping a room at exactly 70 f.
"living inside the heat battery" limits the upper storage temp, which
limits how much heat can be stored, and it means the living space air
has to follow heat battery temperature swings.
>> has anyone been in one of these houses, anyone have one? build one?
i've been in richard komp's house in maine, which has a hollow block
floor warmed by solar room air (he calls it a "hypocaust," like an
ancient heated roman bath floor) with less insulation underneath than
kachadorian's later floors. his j.c. whitney 12 v fan and pv panel
force air under the floor, which might be a nice home for mice, were
it not for his pet, ernie the ermine. dr. komp (president of the maine
solar energy association, and author of "practical photovoltaics")
doesn't seem to worry much about mold or dust. i guess there's a vapor
barrier under the floor, and his house air tends to be dry in the winter.
>i'd be careful of any system that uses air ducts in an underground area.
>especially in "moist" areas this would present a large surface for mold,
>etc to grow which may prove troublesome if that air is to be circulated
>thru the living space. the under/in slab passage ways would prove
>impossible to "clean" i'd bet.
how about making the thermal mass water in sealed containers, with about
twice the specific heat by volume of solid masonry, and putting the
containers inside a compact easily-insulated closet/sauna/warm room
that sits on the ground? it could be more easily cleaned, that way.
>i have seen many a house, where by carefully planning, the living space
>is the solar collector(s) and storage (with insulated slabs and other
>thermal mass devices such as masonry walls). while windows and the
>masonry walls inside are not cheap, if they serve a dual purpose, such
>as heating and providing living space, it is most cost effective.
windows between the outdoors and 24-hour heated living space lose heat
at night and on cloudy days, so there's a dilemma: the more windows,
the more solar gain on a sunny day, but the more loss on a cloudy day.
putting most of the windows on a low-thermal-mass sunspace avoids this
dilemma, since we can capture the heat of solar-warmed air in some
thermal mass inside the house on a sunny day, and stop air circulation
and let the sunspace get cooler at night.
nick
|
|
