We left off with a
minor passive solar project outlined, a 1000 square foot bungalow winterized
and solarised in Columbus, Ohio. Calculations for a clear day in January
suggested that about two/thirds of the heating load for the day would be provided by passive solar. The additional investment to achieve this result would be
minimal. A contrary example, with the same footprint, but wrongly oriented glass
of equal area, performed poorly in comparison.
We did make a few
assumptions; firstly, the house has good solar exposure in winter. This is
non-negotiable, clearly. The second assumption is that the house has a long
wall facing south, i.e. the long axis of the house is more or less on an
east-west line. This is much more negotiable. Even an orientation 30 degrees
away from the ideal or a different plan shape is still workable.
We made a third assumption of a ground floor
slab-on-grade with 3 inches of under-slab foam insulation. This is unlikely to
be the case. More often, the average house in a cool climate will have a
basement with an uninsulated slab that gets almost no sun, and with a joist and
strand-board and carpeted main floor over. The foundation walls are masonry or concrete, but probably insulated on the inside. All this
mass in the basement is useless for heat storage.
The available thermal
mass of the house will be much smaller, roughly 60 cubic feet of the gypsum
core of the drywall on the ground floor being the only significant component with
a heat capacity per cubic foot close to that of concrete, but somewhat
insulated by the thick paper facing. We'll use this more typical bungalow with
basement as our example as we proceed with our investigation.
We hinted in the first part
of this article that an economical and elegant means could be found to achieve the effect of thermal mass without
attempting to retrofit the house with an impractically bulky and massive
thirty-six ton Trombe wall.
John Michael Greer, in
his post Alternatives to Absurdity characterized
the passive solar techniques of the 70's - including thermosiphon air panels,
Trombe walls, and attached greenhouses, as baby steps towards learning to live
comfortably on nature's diffuse energy flows. I'd like to suggest an order of magnitude
improvement to the design problem of heat storage in a passive solar house, an
idea of tremendous potential that was indeed researched, patented, but with the
subsequent cheap oil and good times starting in the 80's, was never commercialized,
and remains largely overlooked. A curious fact, that such an energy-saving
invention was buried.
