Silver foil does work

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Re: Silver foil does work

Postby splitlid » Sun Sep 14, 2014 7:47 am

I don't make the stuff, just pointing out that it's shiny on both sides.
There seems to 2 issues here. 1 is insulation the other is just silver foil.
Silver foil reflects heat
Insulation prevents heat (cold)from passing from one area to another. Silver foil on the insulation which ever way it faces reflects heat.
Is that correct?
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 8:07 am

Roger Ramjet wrote:
Sometimewoodworker wrote:Thank you for a reference that makes my point for me. It looks as if it is you that can't read
from your own reference material

The amount of radiation emitted is a function of the EMISSIVITY factor of the source’s surface. EMISSIVITY is the rate at which radiation (EMISSION) is given off. Absorption of radiation by an object is proportional to the absorptivity factor of its surface which is reciprocal of its emissivity.
Although two objects may be identical, if the surface of one were covered with a material of 90% emissivity, and the surface of the other with a material of 5% emissivity, the result would be a drastic difference in the rate of radiation flow from these two objects. This is demonstrated by comparison of four identical, equally heated iron radiators covered with different materials. Paint one with aluminum paint and another with ordinary enamel. Cover the third with asbestos and the fourth with aluminum foil. Although all have the same temperature, the one covered with aluminum foil would radiate the least (lowest [5%] emissivity). The radiators covered with ordinary paint or asbestos would radiate most because they have the highest emissivity (even higher thn the original iron). Painting over the aluminum paint or foil with ordinary paint changes the surface to 90% emissivity.

Which means you have your foil facing the wrong way.
I notice you never correct yourself when you make mistakes. Tell me about what space blankets do again. The Telaban and IS love them, it hides their heat signature from the FLiR in choppers. I wish you'd instruct them to turn the shiny side out..... just like your kitchen.... no that's wrong the heat is from the floor there.


Which mistake??

I'm talking about radiant barriers
you don't seam to be able to read your own linked documents. Or understand the difference between a reflective barrier (which should face the heat source) and a radiant barrier (which should face away from the heat source)

As far as foil rescue blankets are concerned the physics are the same the most efficient use is shiny side out. If they work at all with the shiny side in they are significantly less efficient as your material I quoted above proves.

Do please learn to understand a subject properly and read your own material carefully.

Reflective barrier reflects heat
Radiant barrier does not radiate much heat (5%)

Reflective, reflects
Radiant, does not radiate
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 8:27 am

splitlid wrote:I don't make the stuff, just pointing out that it's shiny on both sides.
There seems to 2 issues here. 1 is insulation the other is just silver foil.
Silver foil reflects heat
Insulation prevents heat (cold)from passing from one area to another. Silver foil on the insulation which ever way it faces reflects heat.
Is that correct?


Not completely and this is where the confusion comes in

"Insulation prevents heat (cold)from passing from one area to another." Yes
"Silver foil on the insulation which ever way it faces reflects heat." Not very well one way, the foil may reflect heat back to the insulation but most heat transfer from poor insulation is conducted not radiated.
The underside will reflect heat but most people do not have a heat source under their insulated roof in Thailand.

However it is another property of silver foil that makes it useful that you have missed, that is that as well as being a good reflector it is a very poor radiator.

If you watch the second part of the YouTube video I posted you will see that foil on the frying pan will get very hot, put your hand on the foil and you will burn your hand (conduction) put your hand a few cm above the foil and their is very little heat (poor radiation)
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Re: Silver foil does work

Postby splitlid » Sun Sep 14, 2014 8:36 am

Sorry. I meant if the foil faces up or down. Not what side it is glued to the insulation
So your foil is reflecting heat and the brown paper is just trapping the heat. Causing the air between the paper and roof sheet to be hot
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 8:42 am

Roger Ramjet wrote:
Sometimewoodworker wrote:Thank you for a reference that makes my point for me. It looks as if it is you that can't read
from your own reference material

The amount of radiation emitted is a function of the EMISSIVITY factor of the source’s surface. EMISSIVITY is the rate at which radiation (EMISSION) is given off. Absorption of radiation by an object is proportional to the absorptivity factor of its surface which is reciprocal of its emissivity.
Although two objects may be identical, if the surface of one were covered with a material of 90% emissivity, and the surface of the other with a material of 5% emissivity, the result would be a drastic difference in the rate of radiation flow from these two objects. This is demonstrated by comparison of four identical, equally heated iron radiators covered with different materials. Paint one with aluminum paint and another with ordinary enamel. Cover the third with asbestos and the fourth with aluminum foil. Although all have the same temperature, the one covered with aluminum foil would radiate the least (lowest [5%] emissivity). The radiators covered with ordinary paint or asbestos would radiate most because they have the highest emissivity (even higher thn the original iron). Painting over the aluminum paint or foil with ordinary paint changes the surface to 90% emissivity.

Which means you have your foil facing the wrong way.
No it means that you can't or won't understand the difference in the meaning of EMISSION from reflection and why a single sided radiant barrier works by having low (5%) EMISSION

It does not work by reflection. It works by having low EMISSION

Hint
EMISSION, low good
reflection high good
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 9:04 am

splitlid wrote:Sorry. I meant if the foil faces up or down. Not what side it is glued to the insulation
So your foil is reflecting heat and the brown paper is just trapping the heat. Causing the air between the paper and roof sheet to be hot


Again here is the confusion about single sided foil between reflection and emission

The roof radiates heat this will heat the back of the foil because it isn't reflective that will heat air by conduction
However the front of the foil will only radiate/emit (thanks RR for the reference) 5% in ideal conditions

So single sided foil works by being a poor emitter not a good reflector.

If I were to face the silverside up it would be much less effective. It would reflect, yes not perfectly but yes, however dust would collect over time so reducing its reflective quality and much more importantly the brown side is a much better emitter so it would radiate much more heat.

In short and simplified; brown down hot, silver down not hot.

If you have an enclosed roof then the much more expensive double sided foil will probably be better. But because it reflects heat back to the roof efficiently and so makes the roof itself hotter it is not good for some kinds of roofing material.
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Re: Silver foil does work

Postby fredlk » Sun Sep 14, 2014 9:13 am

Sometimewoodworker wrote:The roof radiates heat this will heat the back of the foil because it isn't reflective that will heat air by conduction
However the front of the foil will only radiate/emit (thanks RR for the reference) 5% in ideal conditions

So single sided foil works by being a poor emitter not a good reflector.

If I were to face the silverside up it would be much less effective. It would reflect, yes not perfectly but yes, however dust would collect over time so reducing its reflective quality and much more importantly the brown side is a much better emitter so it would radiate much more heat.

If you have an enclosed roof then the much more expensive double sided foil will probably be better. But because it reflects heat back to the roof efficiently and so makes the roof itself hotter it is not good for some kinds of roofing material.

Well done. Now even I understand the principles behind your successful installation.
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Re: Silver foil does work

Postby Roger Ramjet » Sun Sep 14, 2014 9:46 am

Sometimewoodworker wrote:So single sided foil works by being a poor emitter not a good reflector.

If I were to face the silverside up it would be much less effective. It would reflect, yes not perfectly but yes, however dust would collect over time so reducing its reflective quality and much more importantly the brown side is a much better emitter so it would radiate much more heat.

In short and simplified; brown down hot, silver down not hot.

If you have an enclosed roof then the much more expensive double sided foil will probably be better. But because it reflects heat back to the roof efficiently and so makes the roof itself hotter it is not good for some kinds of roofing material.

Finally you've nearly got it right. The one thing you missed was the air gap between your brown paper and the silver foil. You don't have one, the air gap is between the roof that radiatess the heat and the brown paper that absorbs the heat. You should have the silver foil facing upwards so it reflects the radiated heat. I notice that now dust has come into play whereas before it was just a tangent to you and not important. The fact that you have air circulating between the upside down foil takes away the reflected heat, except in your case where you have the brown paper absorbing the radiated heat.
But at least you're getting close.
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 10:55 am

Roger Ramjet wrote:
Sometimewoodworker wrote:So single sided foil works by being a poor emitter not a good reflector.

If I were to face the silverside up it would be much less effective. It would reflect, yes not perfectly but yes, however dust would collect over time so reducing its reflective quality and much more importantly the brown side is a much better emitter so it would radiate much more heat.

In short and simplified; brown down hot, silver down not hot.

If you have an enclosed roof then the much more expensive double sided foil will probably be better. But because it reflects heat back to the roof efficiently and so makes the roof itself hotter it is not good for some kinds of roofing material.

Finally you've nearly got it right. The one thing you missed was the air gap between your brown paper and the silver foil. You don't have one, the air gap is between the roof that radiatess the heat and the brown paper that absorbs the heat. You should have the silver foil facing upwards so it reflects the radiated heat. I notice that now dust has come into play whereas before it was just a tangent to you and not important. The fact that you have air circulating between the upside down foil takes away the reflected heat, except in your case where you have the brown paper absorbing the radiated heat.
But at least you're getting close.


You are still not getting close at all yet.

Some time you might understand the physics involved and the difference between emission/radiation and reflection and how and why it is important.

If you want to understand, which I'm not sure you do, you need to understand the difference between a radiant (emissive) barrier and a reflective barrier. The articles you posted explain the difference between emission/radiation and reflection.

Single sided foil is sold to be used as a radiant barrier an works because it is a poor radiator/emitter 2%~5% (the backing is a good emitter 96%)

Air doesn't take away reflected heat. Air has little effect on radiated heat. Air moves heat by conduction then convection.

Single sided foil is an efficient radiant barrier, if installed correctly.
Single sided foil is not a good reflective barrier and over time gets worse because of dust.

When installed correctly, as mine is, dust is an insignificant factor.

Your idea of having a sheet of brown paper only as any part of an insulation system gave me the best laugh I've had for a long time.

Your idea of using a product designed to be used as a radiant barrier as a reflective barrier shows you still don't, can't, or won't understand how and why it works.

Here is a part of your link with the important parts circled, NB it is the emission that is important
image.jpg
Emission for foil and paper
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Re: Silver foil does work

Postby pipoz » Sun Sep 14, 2014 1:00 pm

This is how the roofer is installing my roof foil membrane

SCG shiny face with lettering facing down, although external upside face (with no letters) looks a bit shinny as well.

"I really don't care, as I plan on sitting outside during the day under a palm tree, drinking a bottle of red and swimming in the pool.

At night I plan on sleeping with with the A/C on and throwing my leg over the TG.

Either way I wont raise a sweat."


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11 September 2014 Laying the Reflective Foil Membrane Day 112.jpg
Installing Roof Foil Membrane
Last edited by pipoz on Sun Sep 14, 2014 1:28 pm, edited 1 time in total.
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Re: Silver foil does work

Postby Ians » Sun Sep 14, 2014 1:19 pm

Correct - shiny down - leg over, that's the way to go.
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 1:23 pm

pipoz wrote:This is how the roofer is installing my roof foil membrane

SCG shiny face with lettering facing down, although external upside face (with no letters) looks a bit shinny as well.

"I really don't care, as I plan on sitting outside during the day under a palm tree, drinking a bottle of red and swimming in the pool.

At night I plan on sleeping with with the A/C on and throwing my leg over the TG.

Either way I wont raise a sweat."

pipoz


It's a common way and works well, is quick to install and leaves little time for damage.

It is also possible to install under the purlins and could be a little more effective that way. The problem if it's fitted under the purlins is unless the roof cover is fitted quickly there is a bigger chance of damage.

The upper slightly shiny face will work as a reflector though not a very good one in your case as there is almost no air gap on the top. That isn't so important as it is the poor emission of the shiny face that is most important. The trade name on the foil will reduce its effectiveness a little bit too.

But all in all it is a very good inexpensive way to help reduce heat gain from any roof.
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Re: Silver foil does work

Postby pipoz » Sun Sep 14, 2014 1:57 pm

Sometimewoodworker wrote:
pipoz wrote:This is how the roofer is installing my roof foil membrane

SCG shiny face with lettering facing down, although external upside face (with no letters) looks a bit shinny as well.

"I really don't care, as I plan on sitting outside during the day under a palm tree, drinking a bottle of red and swimming in the pool.

At night I plan on sleeping with with the A/C on and throwing my leg over the TG.

Either way I wont raise a sweat."

pipoz


It's a common way and works well, is quick to install and leaves little time for damage.

It is also possible to install under the purlins and could be a little more effective that way. The problem if it's fitted under the purlins is unless the roof cover is fitted quickly there is a bigger chance of damage.

The upper slightly shiny face will work as a reflector though not a very good one in your case as there is almost no air gap on the top. That isn't so important as it is the poor emission of the shiny face that is most important. The trade name on the foil will reduce its effectiveness a little bit too.

But all in all it is a very good inexpensive way to help reduce heat gain from any roof.


Thanks Sometimewoodworker

I also plan on running a wire mesh along the bottom cord of the roof truss, just on top of my concrete ring beam, then laying my thermal insulation on the mesh, over the bed room areas.

I am not worried about insulating the main living area, as I have large doors front and back and will have several ceiling fans to move the air around and through the living room area, plus none of the living room walls are exposed to the outside sun (they are shaded). Plus Thai's seem to spend most of their life outside under Sala's and then just come inside to go to sleep

If I lay the roof insulation on a wire mesh (at the top of the concrete beam level), then it will sit about 150 mm above the top of my plasterboard ceiling, leaving a small air gap between the two surfaces

I have looked a the Insulation available in Thaiwatsadu and Home Mart, as follows,
CRB 24 Density x 50mm
CRB 32 Density x 50mm
CRB 48 Density x 50mm
Super Cool 24 Density x 50mm
FSO 48 Density x 50mm

The rate per m2 seems to vary from TB 265 per m2 for the CRB 24 Density x 50mm up to TB 843 for the CRB 48 Density x 50mm.

My question to you is, which would you consider most appropriate for me, given I will just insulate the ceiling area above the bedrooms. Any ideas

pipoz
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12 Sept 2014 Loading Roof Tiles Day 113-01.jpg
Roof Truss Installation
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Re: Silver foil does work

Postby Andyfteeze » Sun Sep 14, 2014 2:18 pm

just had a thought!!! lol
remember E=MC^C
e= energy ( heat if you Like)
M= Mass
anything to do with movement of mass or energy or even movement itself follows the above equation
high energy = high MASS
I keep telling you guys, its to do with the mass of the foil.
reflection, convection and conduction are all measures of how the MASS is performing.
remember you have a 60^c furnace 2-6 inches above the foil. NOTHING will stop it from heating up. no amount of reflection will stop it. so what else is in play, may I ask?
now I will say a small mass for the last time this year. lol

the better form of Material has foil on two sides with an insulating barrier sandwiched in the middle. A hybrid if you like. but its still has the limitation that it still heats up over time.( that's where pink batts came into play in Australia. but you cant really use glass batts here because of the humidity. polyester batts on the other hand are almost ideal. but its horses for courses, not the most cost effective method to use in this situation. foil under the roof is ideal, all things considered, in this situation.)
stop it, your making me come out of retirement and think too much!
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Re: Silver foil does work

Postby Sometimewoodworker » Sun Sep 14, 2014 2:22 pm

pipoz wrote:
Sometimewoodworker wrote:
pipoz wrote:This is how the roofer is installing my roof foil membrane

SCG shiny face with lettering facing down, although external upside face (with no letters) looks a bit shinny as well.

"I really don't care, as I plan on sitting outside during the day under a palm tree, drinking a bottle of red and swimming in the pool.

At night I plan on sleeping with with the A/C on and throwing my leg over the TG.

Either way I wont raise a sweat."

pipoz


It's a common way and works well, is quick to install and leaves little time for damage.

It is also possible to install under the purlins and could be a little more effective that way. The problem if it's fitted under the purlins is unless the roof cover is fitted quickly there is a bigger chance of damage.

The upper slightly shiny face will work as a reflector though not a very good one in your case as there is almost no air gap on the top. That isn't so important as it is the poor emission of the shiny face that is most important. The trade name on the foil will reduce its effectiveness a little bit too.

But all in all it is a very good inexpensive way to help reduce heat gain from any roof.


Thanks Sometimewoodworker

I also plan on running a wire mesh along the bottom cord of the roof truss, just on top of my concrete ring beam, then laying my thermal insulation on the mesh, over the bed room areas.

I am not worried about insulating the main living area, as I have large doors front and back and will have several ceiling fans to move the air around and through the living room area, plus none of the living room walls are exposed to the outside sun (they are shaded). Plus Thai's seem to spend most of their life outside under Sala's and then just come inside to go to sleep

If I lay the roof insulation on a wire mesh (at the top of the concrete beam level), then it will sit about 150 mm above the top of my plasterboard ceiling, leaving a small air gap between the two surfaces

I have looked a the Insulation available in Thaiwatsadu and Home Mart, as follows,
CRB 24 Density x 50mm
CRB 32 Density x 50mm
CRB 48 Density x 50mm
Super Cool 24 Density x 50mm
FSO 48 Density x 50mm

The rate per m2 seems to vary from TB 265 per m2 for the CRB 24 Density x 50mm up to TB 843 for the CRB 48 Density x 50mm.

My question to you is, which would you consider most appropriate for me, given I will just insulate the ceiling area above the bedrooms. Any ideas

pipoz

I'm no expert on other kinds of insulation,however an educated guess would say that if the insulation is not in contact with the ceiling I makes almost no difference what you put down, in fact a sheet of 3mm plywood would probably be just as useful, more so if it had a foil top (but that would deteriorate over time). The air gap will allow convection and normal air movement in the roof space to warm the ceiling.

One point about ceilings of air conditioned rooms in Thailand is you will probably have warm moist air above so you need to be careful about condensation. This applies to insulation as well. If the insulation is in a bag then no problem, I haven't looked but think a lot of Thai insulation is. However the US and UK use of glass fibre and rock wool batts isn't suitable in Thailand as when they get wet, and they would here, the insulation value drops a lot.

Why don't you want to lay the insulation directly on the ceiling?
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