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re: what would be the most energy efficient, safe, low maintenance house available today?
21 dec 1999
 wrote of:
 
>...kachadorian's solar slab design.

i reviewed his book in manuscript form.

>...this is a design that isn't hugely limiting to the architecture... 
>but may provide 40-50% of a northern home's heating needs.

i doubt it, but even so, one might do a lot better. 

>basic plan is a concrete slab floor poured over a concrete building
>block "radiator". manifolds are formed in-place.  relies primarily on
>passive convective airflow (room air)...

warm air rises. why would it want to flow under the floor? lots of warm
air needs to touch lots of thermal mass surface to raise the slab temp
on a sunny day without overheating the house and ensure a low day/night
temperature swing. during a cloudy week, such a house gets exponentially 
colder and colder, without woodstoves and so on.

removing most of the solar glazing to a low-thermal-mass sunspace (one
that gets cool overnight and stays cool during a cloudy week) with an
insulated wall between the living space and the sunspace allows the same
or more solar gain when warm air flows between the sunspace and the house
during the day, but reduces the nighttime and cloudy-day heat loss from
the living space... 

dr. rich komp (author of practical photovoltaics and president of the
maine solar energy association) says warm hollow floors like his
(which predates kachadorian's) aren't new. romans built hypocausts,
hollow floors heated with warm air from hot water or fires. so did
chinese peasants. warm hollow floors make good homes for dust and
varmints. rich's friend ernie the ermine takes care of that problem.

>and a thermal mass with a temperature swing less than 10f degrees.

living inside the heat battery, we are subject to its temperature swings,
and if there are no temperature swings, there is no solar heat storage.

we can't charge the slab up to a high temperature because we have to
live with it in the room. the same amount of thermal mass at a higher
temperature stores more useful heat than lower temp mass, and it allows
keeping a constant room temp until the mass cools to something close to
that room temperature.

floor slabs don't usually have much insulation between themselves and
the room air, and they are difficult to insulate because of their shape.
the same amount of insulation applied to a cube with equivalent mass
lowers the rate of heatflow a lot more. 

and water stores about 3x more heat than masonry by volume. it can
also be cheaper and more useful, even in sealed containers.

so, we can do a lot better.

nick (now plumbing a $420 1500 gallon 275 pound rainwater tank)




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