Re: Solar-Heated Workshop (more)

Robatoy wrote:

| Now, one concern I have, is dust. I think the passive aspect of your
| product is the cat's meow (pyjamas), but would it be possible to
| gently force-feed the panels with, say, some muffin fans, and then
| push the air through some filtration? Or do you think that there's
| enough convection to pull through some basic filtration?

Those panels were the first of a new design, and the convective air
flow wasn't particularly "gentle" - we (the customer, the construction
crew, and I) were all surprised. In full sun a couple of weeks past
the vernal equinox it was more like what you might expect from a
furnace blower.

The speed at which the panels move air is dependent on the
differential between the temperature of the intake air and the
temperature of the air passing through the heat exchanger. Raising the
temperature of the air is less of a design challenge than producing
designing an absorber/heat exchanger that maximizes the convective
flow.

| In my line of work, dust is a bitch. The stuff is like talcum powder
| in consistency, but heavier so it does fall down to floor level
| pretty quickly.
| What if one made a box to hold a furnace filter, and then reduced to
| the inlet of your panel? Kinda like a funnel shape?
|
| I'm sure all that has crossed your mind already...would you like to
| share?

Of course! (Not /everything/, but enough to provide some "handles" for
grasping the essentials. <g>)

The short answer is that it works best to control dust right at the
point of creation. There just isn't any other effective solution -
because once it's loose, you're "herding cats".

Next best is to provide a totally closed path for collector air (no
flow of room air through the panel). This would keep the collector
clean in the dirtiest of environments and would be "spendy", but could
still be done with a passive system. If we end up with "Carbon Taxes",
this might begin to look like a more affordable zero-carbon solution
for messy operations.

What can't be seen in the photos is that the absorber/heat exchanger
are highly reflective - with smooth, shiny surfaces. The front of the
box itself is painted flat black, but that's only to satisfy
expectations of what everyone "knows" a solar collector should _look_
like. But "look" has only to do with the human eye and the limited
range of _visible_ frequencies.

I'm much greedier than to settle for that limited range. The challenge
here is to effectively trap as wide a range of radiation frequencies
as I can - all the way from RF through IR - most of which isn't
visible to the human eye - and use it to heat air.

The physics says that I could use mirror-bright absorber elements and
the panel would still appear black - and I'd get a bit more heat. I'm
positively itching to build that experimental panel!

Anyway (back to the subject) the biggest problem with dust isn't that
it's the wrong color, and it isn't even that it interferes with
absorbtion (although it does that to a minor degree) - it's that the
dust interferes with the airflow and heat exchange process.

Probably more than you wanted to know...

--
Morris Dovey
DeSoto Solar
DeSoto, Iowa USA
http://www.iedu.com/DeSoto/interest.html


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