Wednesday, 10 April 2013

Too miraculous to be good - do surface coatings save lots of energy?

Having had my interest tweaked by allegations of falsified insulation values (see "The next insulation fiasco?"), and followed with questions about the certification of green materials (see Muddy green), it was almost fated that another niche market in the green building space would come to my attention.  Actually, this one has been on my radar for a long time.
Quite small differences in the thermal properties of roofs and walls can disproportionately affect star ratings in voluntary schemes such as LEED and Australia's Green Star, and even more so in the mandatory energy efficiency measures for dwellings.  Individual householders are becoming genuinely interested in energy efficiency improvements, as the cost of heating and cooling starts to bite.  So they are excellent targets for advertised claims by manufacturers of paints and other painted-on coatings, promising reductions in energy use, and increased comfort.
The latest such claims came to my notice in on-line advertising by Nansulate®Energy Saving and Asset Protection Coatings of the USA They describe "award-winning products powered by the science of nanotechnology" offering "a highly effective combination of benefits which include thermal insulation, corrosion resistance, mold resistance, moisture resistance, UV resistance, chemical resistance, flame resistance, and lead encapsulation", and claiming to provide "dramatic energy saving and protective solutions for industrial, commercial, government and residential customers around the world." The site provides a link to a supposed test ‘certificate’ here.

A colleague of mine, Associate Professor Alistair Sproul, is a physicist working with the new Cooperative Research Centre for Low Carbon Living, at the University of NSW, Sydney. He is pretty intimate with nano technologies, being a member of the world class photovoltaics team at the university, so he couldn't help himself when I pointed him at the Nansulate web site. He ran a few figures.

I only report here a small part of his first reaction. It starts with the observation that the independent measurements look a little internally inconsistent (the U value and R value changes agree with each other but the rate of heat transfer doesn’t agree with the stated R or U values). Bad start. Alistair is otherwise quite kind to the calculations, until he points out that "the implied thermal conductivity of the (Nansulate coating) layer k = L/R = 0.00085 W/mK – which is about 30 times lower than still air!" He goes on: "The best I have seen people claim for vacuum materials is something like 3 – 6 times lower than still air OR that the value will change with time."

At the risk of getting very technical, there are other factors which could contribute to improved thermal performance in the field. Principal amongst these is changed emissivity (the ability to get rid of heat by radiation) of the original surface, once coated. The scope for improvement is small in summer conditions, as the emissivity of most non-metalic building surfaces is already high. And surface emissivity plays little part in a standardised test for conductive heat transfer, which (to be fair) may be why it isn't mentioned in the test description.
Suffice to say, at the end of the day I cannot satisfy myself that the claims of improved heat insulation, by putting on a thin translucent coating, are supported by the provided evidence.  I have personal reasons to be incredulous. 
Some years ago, I was in charge of a "test-cell" scale field test of the effects of a paint additive. We did find a small but likely real effect on heat transmission that could be attributed to the product. But the point of doing the tests outdoors on test cells was that we were in a position to interpret the results in terms of likely perceptions on thermal comfort, and possible energy savings. We reported to our paint manufacturer client that the effects were too small for them to rely on for marketing. So I wasn't surprised when recently the Australian Competition and Consumer Commission (ACCC) began proceedings against another paint manufacturer, Dulux, for alleged false and misleading paint advertising in relation to the promotion of the temperature reducing capabilities of its InfraCOOL and Weathershield Heat Reflect paints.

The problem, aside from the possibility of deliberate mis-representation, is that nobody I am aware of has yet offered a scientifically robust explanation for why these coatings and additives should work. In the absence of such theoretical explanation, we rely on 'empirical' tests of observed performance. In principle, there is nothing wrong with proceeding in this way, we are obliged to do this in much more critical examples in science (think the unexplained, but real effects of electroconvulsive therapy on clinical depression). It's just that you have to be scrupulous in your experiments, measurements and especially in your analysis.* And the claimed effect has to be worth it.

My clients benefited from an open mind, even if they were so desperate for a market position, that it took them a couple of years, and a court case, to resign themselves to my advice.  Others are not necessarily so scrupulous. A consumer protection agency actually prosecuting for alleged misrepresentation is not exactly common, and will only happen at best after a lapse of some years. Individual consumers or specifiers are unlikely to have someone to turn to for credible expert checking of claims of improved performance. Unfortunately, a healthy cynicism is called for, which, even I am ready to admit, has its downside - I'd hate to miss the next good thing, just because I don't understand it.

  1. For details of the Dulux case, click the ACCC link here.
  2. The Taubmans paints saga culminated in a court case, Freeworld Coatings Pty Ltd ats Worldwide Coatings lP Pty Ltd, which was settled with confidentiality agreements. But readers interested in the way such things happen, can read the original optimistic 'Eco-investment' assessment here.
  3. *BTW. What is the significance of the image at the start of the post? It is from a case study on the Nansulate web site. The text compares the heat loss at positions M1 (uncoated because it is inaccessible behind a radiator) with M2 (coated on the inside of the wall), as evidence of the effectiveness of the coating in reducing heat transfer. The alternative explanation, that the radiator is the source of the heat in the first place, and it is creating a much bigger temperature difference driving heat loss at that part of the wall, either escapes the person providing the analysis - or more likely is meant to escape the attention of the reader.

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