by kolm » Fri 28 Nov 2008, 09:31:10
$this->bbcode_second_pass_quote('Tanada', '
')I do beleive in physics so I know that if their claims are true, that the paint resists both conduction and radiation, then it would work. Does it work? I can't afford to test it and I wish UL or CR would and give a full analysis.
Well, I did not test it and have little experience with insulation per se, but the math seems not so well for this one. Recall that the rate of heat flow dQ/dt (i.e., the amount of power you must spend to keep your home warm and cozy), equals the term
k*A*Delta(T)/x,
where k is the thermal conductivity of the material, A is the cross-surface of the wall, Delta(T) is, well, temperature difference between in- and outside, and x - the spoilsport here - is the thickness of the insulation. A and Delta(T) are kinda given, we can play with k and x. We see that 10 cm of an insulation with k=2 is just as well as 5cm of an insulation with k=1. To insulate well, k/x must be small, not just k.
Now, Nansulate claims that some stuff inside their material has a thermal conductivity of 0.017 W/mK. We'll be generous and assume that the whole material has this value. Further, we want to improve an extremely poorly insulated home which, as the sole insulation, has 2cm of plywood (conductivity of 0.13 W/mK), just to make it easier for the paint to shine. We also lay the paint on real thick in- and outside, to get 3mm of paint.
Now, in this absurdly favorable scenario, insulation should rocket off if this stuff is worth anything, right? In other words, k/x should be way smaller for the paint, right? Let's see:
Wood: k/x = 0.13/0.02 = 13/2 = 7.5.
Paint: k/x = 0.017/0.003 = 17/3 = 5.67.
Whoops. Looks like the paint would be slightly less efficient than adding 2.5 more centimeters of plywood. Or less efficient than adding 6mm (not a typo, conductivity is 0.03) of foamed plastics. All that under the caveat that their claims w.r.t. thermal conductivity actually hold water. So if you wanted to insulate your home with adding 2.5cm of plywood, you can calculate if this stuff would come cheaper or not.
It keeps getting worse: If you look at the above numbers, you would at least guess that if you paint a wooden crate thickly with the stuff, the insulation value should double (or better, if the insulation of the crate was worse than that of 2.5cm plywood). Those guys did this, and noted a drop in energy requirement, not of 50%, not of 25%, not of 20%, but only of about 12%. That points to an even worse thermal conductivity than the assumed 0.017.
Keep in mind that there is a law of diminishing returns when insulating your house, too. The better insulated it is, the less you will profit from adding further insulation. A completely uninsulated home might actually have a small benefit from it, a slightly insulated home will barely notice it, a moderately insulated home would get no measurable effect whatsoever.