I'm wanting to install a simple solar collector for heating air into my
shop, just as an assist - not full-out heating. Apologies in advance if
this isn't the right forum but couldn't find a NG that seems to fit. I know
that I saw a slew of these back in the 70's but I'll be hanged if I can come
up with one now. 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. It
would seem logical that the baffle plate should be sheetmetal for quicker
heat-up. 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 - other funtional issues come to mind with that). The installation
was to angle the collector to match your latitude (+/-) and fit the top with
an extension appropriately angle to bring it into the shop, with diverters
to prevent the heated air from re-entering the collector. So, what's the
consensus of opinion? No fair asking the wife.
A friend of mine sold these in the 70's in Iowa. Took one winter for him to
bail on the idea.
The reason you do not still see them is that they did not work all that
well. His worked well in the day time and turned into a radiator exhausting
the heat from his house at night.
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.
Sure. The vent opening area might be 2-5% of the sunspace glazing area.
Vertical glazing works better for winter heating.
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.
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" :-)
Pick up the last issue of Home Power magazine. It has *exactly* what you
need: an article on building auxiliary assist solar air heater for a
barn/shop. With bill of materials and improvements list. I think you'll
get some ideas from it.
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