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re: a simple solar collector
10 aug 2004
gary   wrote:

>i bought a sample sheet of 0.093 thick acrylic -- it is 30 x 36 inches 
>(about the size of the panels on the eventual door).
>i made a simple wood frame with a rabbet around the inside edge of the 
>frame to mount the acrylic in.  the rabbet allows is 1/8 inch edge 
>clearance all the way around.  i "glued" the acrylic into the frame 
>with silicone caulk (at about 70f).
>the theory is that the 0.093 has somewhat more resistance to buckling 
>than (say) 0.020 polycarbonate, and the silicone caulk would let it 
>expand a bit, while still sealing?

it doesn't need to seal very well, as typical sunspace glazing, if
the main "seal" is plastic film or motorized dampers. it isn't like
a house window. small air leaks just decrease solar collection
efficiency slightly. 

>i put the panel in the sun at noon with the back closed off.
>the inside air temp is running about 135f, ambient is about 80f.
>the deflection is quite small -- perhaps 0.1 cm outward bow at mid 
>panel -- not visible to the eye.

nice. but this acrylic is more expensive than polycarb, no?
and smaller pieces mean more mounting labor and wood and
air leaks and fasteners and shading.
 
>i guess i am wondering if the 0.1 thick acrylic is a better choice for 
>this project than the commonly available 0.02 to 0.03 inch thick 
>polycarbonate?

i'd say no, if we can mount large pieces of pc aesthetically.

>> picture a 4'x8' sheet of flat polycarb in a trampoline frame, always
>> in tension. if we attach it to a light wood frame on a hot day, it might
>> make the wood bow inwards when it gets cold, if the fasteners don't tear.
>> the wood frame might be mounted behind some face boards that let the
>> inner frame move but don't allow much air to leak around the gaps
>> formed by the bowing.

>i may give this a try, but it seems a bit complex.

you might try making it all with 1x3s... an inner 1x3 frame with the pc
attached to the short edges on 1' centers and an outer 1x3 frame with
the inner one screwed loosely to it at the corners and horizontal and
vertical 1x3s screwed to the outer frame as cap strips. two inner
frames could share a vertical outer frame and vertical cap strip,
altho that's still lots of labor and wood...

>> i found the testo in an sbse "agents of change" tool kit...

>sounds like xmas :-)

it was a loan to our "tool day" team. we had to give it back...

our 7/15/04 portland brewery block studies might be on the sbse web site now.

nick




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