SQLit wrote:

"C & M" wants to:

install a simple solar collector for heating air into my shop...

Good idea.

I was thinking of a flat, baffled collector which would convect air from
inside the shop, to the bottom chamber of the panel while the top chamber
heated up and convected the warm air into the shop...

Sounds overly complex. All you need is some glazing over a dark south wall
with an air gap behind it and a hole at the bottom for shop air to enter
the gap and a hole at the top for solar-warmed air to move back up into
the shop during the day and a lightweight one-way plastic film damper over
the hole at the top (and/or bottom) to prevent reverse airflow at night.

The glazing could be a layer of 4-year greenhouse polyethylene film (5
cents/ft^2) or 20-year polycarbonate (about $1/ft^2) eg corrugated Sun Tuf
from Home Depot. The damper could be a dry cleaner bag, hinged at the top,
opening into the shop, with some hardware cloth over the hole to keep it
from flopping back outside through the hole at night. The glazing might be
6" from the south wall, or it might be a useful sunspace, eg an 8' radius
x 16' long quarter-cylinder with 5 $5 bows on 4' centers made from 2 12'
1x3s bent to an 8' radius with 1x3 spacer blocks on 2' centers screwed
between the 1x3s.

The window is only 20" wide so I guess the width of the collector is
predetermined (or maybe I can make it wider and neck it down to fit
the window...

Sure. The vent opening area might be 2-5% of the sunspace glazing area.

The installation was to angle the collector to match your latitude (+/-)

Vertical glazing works better for winter heating.

A friend of mine sold these in the 70's in Iowa... The reason you do not
still see them is that they did not work all that well.

Nonsense. They work fine. NREL says 480 Btu/ft^2 of sun falls on the ground
and 900 falls on a south wall on an average December day in Boston, with
an average 36 F daytime temp, so a $50 8'x16' sunspace like the one above
with 250 ft^2 of R1 glazing with 90% solar transmission might collect
0.9x8x16x(480+900) = 159K Btu of sun and lose 6h(70-36)250ft^2/R1 = 51K Btu,
for a net gain of 108K Btu, roughly the heat equivalent of a gallon of oil
or a therm of natural gas.

His worked well in the day time and turned into a radiator exhausting
the heat from his house at night.

The solar subsidies of the 70s brought forth a lot of incompetent
vendors. Sounds like he forgot the one-way plastic film dampers,
aka "the 7 cent solution" :-)

Nick