Silver foil does work

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Silver foil does work

Postby Sometimewoodworker » Tue Apr 08, 2014 8:10 pm

i've been finding my carport / workshop roof has been getting much too hot. The top of the steel is blue and the underside reaches 60 degrees in full sun.

So I put up one length of the cheapest foil I could find, brown on one side and silver on the other. the temperature on the foil was then only 37 degrees. So I then added foil over the whole width of the roof.

P4010012.JPG
silver foil 0


P4010014.JPG
silver foil 1


P4010015.JPG
silver foil 2


IMG_3802.jpg
Hot!!!
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Re: Silver foil does work

Postby thailazer » Tue Apr 08, 2014 8:46 pm

Does your foil have any foam or is it just foil? Our steel roof has closed cell foam and foil backing and I am amazed how cool it is compared to bare steel. Will measure the temperature differences as soon as my new voltmeter arrives. Looks like it was well worth your time there.
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Re: Silver foil does work

Postby Sometimewoodworker » Tue Apr 08, 2014 9:18 pm

thailazer wrote:Does your foil have any foam or is it just foil? Our steel roof has closed cell foam and foil backing and I am amazed how cool it is compared to bare steel. Will measure the temperature differences as soon as my new voltmeter arrives. Looks like it was well worth your time there.

It's just foil, about ฿1,200 for 70 meters.

I don't quite understand how a voltmeter will help :roll:
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Re: Silver foil does work

Postby thailazer » Wed Apr 09, 2014 6:55 am

It has a thermocouple input so provides temperature measurement capability.
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Re: Silver foil does work

Postby oil » Thu May 29, 2014 2:40 am

nice, thx for sharing
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Re: Silver foil does work

Postby oil » Thu May 29, 2014 2:52 am

Sometimewoodworker wrote:... the temperature on the foil was then only 37 degrees. So I then added foil over the whole width of the roof.

for the fact its just the cheapest foil you could find (1200 TH B for 70 meter) what width did it have and from where to you get it?

it amazed me to see that the temp. was just 37. which is certainly pretty much the surrounding air temperature, So considering that results, its like the thin silver foil is the key, and not some foaming or whatsoever cause cooler then surrounding air temperature it cant get here in TH

just to make sure again, is it Silver Foil (made out of Silver) or is it simple Aluminium Foil,
and the curiosity i dont quite get is why the reflective site is pointing downwards, i read somewhere here already thats how it should be done, i just dont understand from a logic point of view, why? and i really would like to learn that
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Re: Silver foil does work

Postby farmundo » Thu May 29, 2014 5:03 am

Why is the silver foil shiny side down? I think it's because matt black objects absorb and radiate heat the most, shiny silver surfaces absorb and radiate heat the least. So it's not trying to work by reflecting the heat back up to the roof, it's shiny side down because that way the least amount of heat from the roof can be radiated down into the room.
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Re: Silver foil does work

Postby oil » Thu May 29, 2014 5:17 am

farmundo wrote:Why is the silver foil shiny side down? I think it's because matt black objects absorb and radiate heat the most, shiny silver surfaces absorb and radiate heat the least. So it's not trying to work by reflecting the heat back up to the roof, it's shiny side down because that way the least amount of heat from the roof can be radiated down into the room.


with exactly that thought ... because matt black objects absorb and radiate heat the most, i would have assumed that the thin foil which absorbed most of the heat, should be very hot, and not the 37 C ?
so where is my thinking error?
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Re: Silver foil does work

Postby Sometimewoodworker » Thu May 29, 2014 6:09 am

oil wrote:
Sometimewoodworker wrote:... the temperature on the foil was then only 37 degrees. So I then added foil over the whole width of the roof.

for the fact its just the cheapest foil you could find (1200 TH B for 70 meter) what width did it have and from where to you get it?

I think it is about 1 metre but all of them are the same width I got it from DoHome but all the usual big stores have it.

oil wrote:it amazed me to see that the temp. was just 37. which is certainly pretty much the surrounding air temperature, So considering that results, its like the thin silver foil is the key, and not some foaming or whatsoever cause cooler then surrounding air temperature it cant get here in TH
depending on your need and roof it could be. I will use foam for sound, heat and insect/rodent control in our main roof. But in areas where sound control isn't needed I would use foil.

oil wrote:just to make sure again, is it Silver Foil (made out of Silver) or is it simple Aluminium Foil,

For sure none of the foil is Silver. It is all Aluminium with reinforcement and some backing, mine has a brown paper backing as the price goes up the backing and reinforcement changes.

oil wrote: and the curiosity i dont quite get is why the reflective site is pointing downwards, i read somewhere here already thats how it should be done, i just dont understand from a logic point of view, why? and i really would like to learn that


Easy get a frying pan nice and hot then see how close to the hot surface you can put your hand. Then put a large piece (one that covers all the base) of kitchen foil in the pan shiny side up ans try again. The first oneyou will have to keep your hand 5cm or 10cm away 2nd case may be 1cm or 2cm.

This is because shiny silver is a very bad radiator of heat. However gloss white is worse absorber so a high gloss white sheet could work even better.

A white roof gets less hot than a silver one, as do cars.
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Re: Silver foil does work

Postby Roger Ramjet » Thu May 29, 2014 6:20 am

I think everyone should read this first: http://www.newton.dep.anl.gov/askasci/p ... y00246.htm
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Re: Silver foil does work

Postby oil » Thu May 29, 2014 11:54 am

Roger Ramjet wrote:I think everyone should read this first: http://www.newton.dep.anl.gov/askasci/p ... y00246.htm

thx, overall a nice reading, but since i read more of the so called scientific answeres here
i figured that lots of Dr. and Profs. have total opposite opinions on the very same topic LOL
http://www.newton.dep.anl.gov/askasci/phys98.htm

So basially they are saying the silver side inside cause it reflects heat radiation better saying, the body would stay warmer in a sleeping bag, or the house would stay warmer in a house ....
which is basially very good for most houses in the world, just NOT for THAILAND

Home insulation has aluminum foil back for two reasons: to reflect infrared [heat] radiation, and to provide a moisture barrier.


Infrared light is the most common heat transfer radiation in the dark. Some material can easily absorb infrared radiation, and some cannot. Again, it is not based on color.



funny thing there are lots of other interesting articles like
http://www.newton.dep.anl.gov/askasci/p ... y00249.htm

A sleeping bag with a shiny coating (assuming it is reflective in the infrared) should keep you warmer at night and house insulation does have a shiny coating to keep heat from radiating through it (thus keeping heat inside in the winter and outside in the summer). Using this argument the baked potato should cook more quickly with the shiny side in


from another thing there, can t find it anymore to qoute is basially the esential part at the insualtation is the air gap between the roofing and the foil, thats is what blocks the radiation of heat the most.

so .... i am even more confused now LOL.
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Re: Silver foil does work

Postby oil » Thu May 29, 2014 12:01 pm

and btw thanks for the frying pan sample i did understand that one, and again i thinnk its the air bubble between the layers whch block the radiation the most :D
flat out on the pan, the heat raditation might be just the same???
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Re: Silver foil does work

Postby Sometimewoodworker » Thu May 29, 2014 12:03 pm

oil wrote:and btw thanks for the frying pan sample i did understand that one, and again i thinnk its the air bubble between the layers whch block the radiation the most :D
flat out on the pan, the heat raditation might be just the same???

No, air dosen't block radiation at all, and no
It's the poor radiation of the silver surface
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Re: Silver foil does work

Postby Sometimewoodworker » Tue Aug 26, 2014 4:42 pm

4 months on and the experiment was so successful we did the back kitchen.

image.jpg
Before, 61 degrees off the Gray/blue roof


image.jpg
After, 37 degrees off the foil


image.jpg
Everyone is happy


It is now a comfortable room to use now.
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Re: Silver foil does work

Postby Andyfteeze » Sun Sep 07, 2014 9:32 am

The foil works because it reflects the infrared radiation. However it still conducts heat!
The best you can hope for is to ventilate the roof space and foil the ceiling.
A good analogy is. Frypan in shade, frypan in sun! Look at the frypan in the shade as ambient temperature under the foil and frypan in the sun as what the sun is doing to your roof. Because in your situation, you have no ceiling space, the foil reflects the heat very well, lol, but it will still conduct the heat although not as much as the tin roof on its own due to its light mass relative to the roof.
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