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Solar Air collectors? Do they work? Buy or make? - Page 2

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Posted by Bill Kreamer on October 27, 2004, 5:29 pm
Hi Gary, Hi Stuart.

You should email me for a .pdf of illustrated instructions for a high
efficiency solar air heater using the following features - Bill Kreamer

The two most important characteristics for air-cooled solar absorbers are
_very_ high surface area, and single-pass flow-through mounting. To get the
surface area, I used furnace filter for many many years, until I eliminated
painting with black spray paint, and got even more surface area, by using a
thin, black polyester blanket. Performance improved (the collector ran
cooler, and the room got hotter), and I've never gone back.

So here are some design tips which, along with foil-faced foam insulation,
will have a positive effect on your solar heater project:

1. Use a very high surface area, black absorber material, and use a
through-the-absorber flow pattern. Flat plate materials (dimpled,
corrugated, etc.), or even screen, etc. are not the best for an air-cooled
solar absorber. You can use any blanket-like black material, as long as you
can see only glints of sunlight through it. I prefer black polyester
dressmaker's felt. Simultaneously, use a single-step, parallel flow path.
Arrange for cooler input air to flood the entire face of the collector
(don't use a serpentine, or serial, flow path). Take heated output air from
the entire rear area at once. That is, supply room temperature air to the
front of the absorber, and collect hot air from the rear.

2. Silicone glue the felt absorber to aluminum rails (1x1 flashing "ells").
Orient the rails and absorber on the diagonal to the general air flow. This
will produce a "front to rear" flow through the absorber.

3. Make the inside walls of foil-faced insulation; keep the interior
collector walls reflective. Don't make anything inside the collector black
but the absorber; let the absorber do all the solar absorbing and heat
transferring functions.

4. Get a fan (70-115 cfm for each 24 to 40 sq. ft. of face area) from

5. Use the "2E245" snap disc thermostat from Grainger.com.

6. Place your inlet and outlet at nearly, but not exactly, the same height.


Again, just email me for a .pdf of illustrated instructions using these
- Bill Kreamer (kreamer@adelphia.net)

If you'll be using the space in the evening, or at night, or on cold grey
mornings, afternoons, etc., pencil in modest window area for viewing
purposes. Then add collectors (and a "primary/backup" heater of your choice)
for heat. Size per Nick's advice.

- Bill K.

Posted by prepusa on October 26, 2004, 12:52 am
Hi there:

Check out www.hotboxsolar.com

They sell a reasonably priced air heater that uses concentrated sunlight.

Posted by nicksanspam on October 26, 2004, 2:57 pm

Say it's 16'x24'x8' tall, with a long south wall.

How much? G = 1024/R Btu/h-F.

An easy climate. NREL says Santa Maria has 1390 Btu/ft^2 of sun on
a south wall on an average 51.1 F January day, when your studio might
need 8h(65-51.1)G = 114K/R Btu of heat.

No shading... :-)

How about thermosyphoning air panels on the south wall warming low-e
ceiling mass and a slow ceiling fan controlled by an occupancy sensor
and a room temp thermostat?

Sure, if designed to do that. You need about 570K/R Btu for 5 cloudy days...

Gary spent $/ft^2. Cleardome charges $95/(2'x8') = $5.94/ft^2.

Then again, they are still selling indoor solar collectors :-)

help@prepusa.net wrote:

Wow, only $99/(2'x4') = $9.88/ft^2 :-)

Looks like "they" is "you" :-)

I'd use a single layer of "Dynaglas" corrugated polycarbonate.
This greenhouse roofing material comes in 4' wide sheets.
Flat polycarbonate comes in 4'-wide rolls.

Your brown shingles behind a single layer of black window screen.

Grainger sells them, but I'd thermosyphon.

Then again, you want 100% solar heating. You might have room for 4
4x8s among the windows. If 1 ft^2 collects 0.9x1390 = 1251 Btu and
loses 6h(130-51.1)1ft^2/R1 = 473, the net gain is 778. There's a
tradeoff between polycarb ($/ft^2), insulation ($.34/ft^2 for "R7.2"
1" double-foil polyiso board) and ceiling mass ($/4"x10' 55 Btu/F
thinwall PVC pipe.)

If each of N $0 4x8 collectors can make 24.9K Btu/day, the studio needs
R = 114K/(24.9KN) insulation and P = 570K/((130-80)55) ceiling heat store
pipes for cloudy days. If pipes cost $ each and covering 1024 ft^2 of walls
and ceiling with R-value R insulation costs $.34x1024R/7.2...

N   Cc    R     Cr    P    Cp    total cost

1   50    4.58  221   45   225   $96
2  100    2.29  111   91   455    666
3  150    1.53   74  135   675    899
4  200    1.14   55  182   910   1165.

If the ceiling is 16'x24' of poly film ducts ($0) containing up to
5" of water over mylar film ($0) over welded wire fence ($0)...

N   Cc    R     Cr    Cp    total cost

1   50    4.58  221   120   $91
2  100    2.29  111   120    331
3  150    1.53   74   120    344
4  200    1.14   55   120    375.


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