re: hair brained solar cistern???
8 jan 2003
>...choosing between a kachadorian solar slab with air ducts under the floor
>to access thermal mass storage and the sand bed, i would be inclined to go
>for the sand bed...
not if you used any numbers or knew shit about physics or cared about cost
and performance and simplicity :-) i just reread k's book. lots of whopping
mistakes. for instance, he thinks a house needs 2/3 ach for health, 27x
more than the 0.025 ach swedish standard.
page 17 says "as you can see, the reduction in solar benefit increases
exponentially as you rotate the home's orientation away from true south."
page 30 says:
if this combination of poured concrete slab over horizontally laid blocks
is ventilated by air holes along the north and south walls, air will
naturally circulate through this concrete radiator when the sun is out...
the south wall will be warmer than the north wall... air that is next to
or alongside the south wall will rise. warmed air will then be pulled out
of the ventilated slab, and the cooler air along the north wall will drop
into the holes along the north wall. this thermosiphoning effect will
naturally continue to pull air through the solar slab.
page 49 says "incorporate an air lock entrance" with miniscule energy
except for a department store, or a house with a huge active family.
page 53 describes foil smack up against plywood:
the interior foil face will reflect heat back into the room, even though
it is sealed inside the thermo-shutter... the outside foil face of the
insulation contained within the wood veneers will reflect the sun's summer
heat back out the window.
page 94 belies the natural air circulation described on page 30:
the duct shown running down the middle of the bgase under the poured slab
is included in all cases. it should always be used as the return-air duct:
do not reverse the air flow pattrern shown on the control diagrams. by
using the solar slab as part of the return-air duct system, the solar slab
will constantly assist the furnace by preheating the return air. even if
the home will be heated with a woodstove and emergency electric furnace,
the return duct should be included and the air mover hooked up per the
appropriate control diagram...
page 101 says:
2. size of electric heating system = 9.25 kilowatt=hours,
with an annual consumption of 7.616 kilowatts,
page 102 says:
the calculation for the electric backup option determined that
we would need 9.25 kilowatts per hour for the saltbox 38...
page 106 says "the theoretical minimum temperature to which a home with
a solar slab will drop is the ground temperature under the solar slab..."
(yes, that will keep the pipes from freezing in most parts of the us,
if a perfectly airtight house with infinite insulation :-)
page 107 says "it also costs more to cool air than to heat air," as if
k. is unaware of evaporation, night sky radiation, or the phrase
"coefficient of performance."
page 137 ignores one-way passive backdraft dampers:
it may seem that a sunspace that is gathering enough heat to become
90 degrees fahrenheit on a cold, 15-degree but sunny winter day would
be beneficial to the home. and yes, it can be beneficial. however,
the same overglazed sunspace that accumulated all that heat during
the cold but sunny day will need lots of added heat when the sun goes
down to prevent it from freezing, which means that the sunspace or
greenhouse will tend to draw heat from the rest of the house as its
flow of solar heat reverses course, back out through the glazing.
but his solar slab is one good way to store overnight heat from inexpensive
passive air heaters or a low-thermal mass sunspace that can add valuable
floorspace to a house. one drawback is dust--it's hard to clean the rough
passages in the hollow concrete blocks. another is fan power. a vertical
thermal mass (eg a chimney with extra flues open at top and bottom) might
store and release heat to a house with no fan power at all...