I have seen coatings several mm thick, with good effects (hold coated end of metal strip, apply propane torch to other end an inch away).

My guess is that R-1 is possible with a 3.5 mm thick coating. A good way to shelter thermal mass from living space.

Alan

As you know, when thickness gets small, (like paint) the q/time increases substantially. In class we never ever ever ever even consider surface nodes for conduction, only convection.

Is the recent Nobel Prize for "the mysteries of surface chemistry", as Jon Stewart put it, at all relevant here?

I would like the link since Google for Nanotech lead to confusion (I did find that Mercedes Benz started using clear ceramic paint as an overcoat on their higher end models in 2004).

Thanks,

Alan

"new 17 seer from a 10 seer unit"

From what I understand, that's a pretty big jump and it should be 1.7 times as efficient as efficient, more if your old unit had lost efficiency by age. What was the percentage drop in your bill after installation? It's really a shame you did so many things at once and weren't able to measure the effects individually.

"I coated a 6x12 south facing porch roof since it's a clear coat still have the aesthetics but keep the heat out I just need a good hail storm to see how it holds up."

You painted the outside? Would that not let the light in to heat the surface below and then trap the heat beneath?

I'm not trying to hound you or anything, just rather curious. I can think of a good way of testing this stuff though, and that would be to get Kill-a-Watt meter and your fridge, get a good baseline of energy usage (and track room temp), paint your fridge with the stuff and then get an average of after-painted energy usage and see if its statistically significant.

I reviewed the performance of a "nanotech" thermal coating used for an industrial application. While it worked well at reducing radiant heat losses (and would also probably work well at reducing radiant heat gains), it's actual conductive R-value was vastly worse than advertised. Had to resort back to good-old foam. Buyers beware.

Thanks for the information. The one I was looking at was Hy-Tech in Florida. They have lots of claims and say they developed the product together with NASA for use on spacecraft. It seems the roof coatings would be the best way to go, to reflect the radiant energy from the sun. I know out attic gets blazing hot in the summer due to the radiant energy absorbed. Trying to find out more, however.

I have stapled aluminum coated kraft paper (I used paper coated on both sides) to rafters with good, and economic, effects (assuming labor is free or cheap).

Alan

Since a thin film like paint can't stop thermal conduction the only real effect it can have is on radiation. It is convenient to divide that into two wavelength bands, shortwave (visable, and near infrared), which for our application would be sunlight, and longwave, infrared at say 5-25 microns. This later can be considered as radiant heat.
The simplest low tech thing to do would be to use light colored paint (note about half of incoming solar is near infrared, so your eye may not be the best judge). This would reduce the direct heating from the sun. The effect could be significant, as we seem to have a foolish preference for dark colored roofs.

The infrared area is trickier. A non-reflective (in the IR) surface will cool quicker, essentially at a given wavelength reflectivity, and emissivity are inversely related (E=1-A). If some of the infrared wavelengths have a nontrivial mean-free path (how far on average a photon travels before being absorbed). Since radiative barriers, such as aluminum foil have been recommended for years, there must be at least some wavelengths with significant mean-free path in common insultaing materials. In this case I suspect that a layer of foil would do at least as much good, as that paint coating. Depending upon cost that might be a better solution.

If you want a somewhat dark color for say roofing, then some high tech coating that is reflective of the roughly half of the solar input in the infrared might be helpful. I believe that is what has been done in California where tile roofing is the modern norm, and light colored roofing has not yet caught on. Out here away from the coast you can count on summers being 99plus percent cloud free, and any reduction in solar heating would be significant.