Thread: Solar Inverter Sun Screen

Originally Posted by RayG

of course if you used an IR thermometer, then you would have to make sure you correct for emissitivity on the Al..

But, I would argue. I think............correcting for emissitivity of the plate will give you the surface temp of the plate. By not correcting for emissitivity don't you get a relative reading of how much IR is being emitted?(or am I going a step to far?)

The only example I have at hand is some numbers I came up with while looking at ways to insulate the roll-a-doors on my garage.
Inside and outside surface of the door 65C.
Shade cloth a couple of inches in front of door, outside 51C, inside 52.5C.
Foil against the back of door, 77C outside, 36C inside.
Shade cloth and foil, 62C outside, 33.5C inside.
Now even though the foil is touching the door in places so I issue would be near as damn it the same temp as the door, standing inside the garage I can tell you I(or the inverter in this case) feels a lot cooler behind the foil.

Am I drawing the wrong conclusions?


Stuart

Originally Posted by RayG

Hi Bob,

Interesting result, I tried to find a source on-line for absorptivity/emissivity ratios, but the data is very scattered, lots of difference between polished aluminium and oxidized aluminium, and different paints and coatings vary widely. So controlling all the variables is going to be a bit problematic.

One area that might be worth looking at further is the super reflective roof paints that are around...

Ray

Yes a lot of testing is done in the idealised state which changes dramatically one the real world kicks in.

One of my colleagues at work spent decades testing roofing paints and comparing them with Colorbond, galv and ZnAlume. He tested a lot of stuff and even built a weather chamber where he could simulate Summer heat 24/7. About the only thing that he came up with up with over the long term was that white painted surfaces maintained lower temperatures than either Zn and Zn Alum, (I don't think he tested Al), and the that the so called heat insulating paints were not as good as they claimed.