Credit: RavenBrick

Credit: RavenBrick

Last week I had a post about Sage Electrochromics and the company’s line of smart windows. But, there is another company, RavenBrick, that says it has a less expensive, film-based approach to smart glass: smart windows (and smart walls) that offer many of the same features without needing any of the wiring required by windows like Sage’s.

RavenBrick says its special film can quickly turn a window opaque – at a preset point – just by using the sun itself. So, let’s say you have a house or building where it would be useful to have sunlight warming the interior when it is colder outside, but where it would also be convenient to block the sunlight on hot days. RavenBrick says it can make a film, preferably used between panes in a single insulating glass unit, that can do that. The film is clear in the IGU at a low temperature but the material in the film goes through a phase change and turns opaque at a higher temperature.

That ability is pretty intriguing by itself. But there are several more important things to note about the company’s film. RavenBrick says the film can be customized and fine-tuned along several important technical and aesthetic parameters. For example, the opacity can come two different ways: by darkening or by whitening. In the former case, the phase changes causes the film to block most of the light and, in the latter case, the phase change instead causes the film to diffuse the light.

One of the film’s creators, Wil McCarthy, wouldn’t reveal what’s in the film, even in general terms (patents pending), other than to say that it was a “nanostructured optical material.” But he told me that the film could be customized along several parameters including what temperature the phase change occurs, what portion of the light spectrum is blocked, what level of diffusivity is desired, etc.

McCarthy, who helped launch RavenBrick, says its technically possible to adjust the temperature change point to a precision of 0.1°C, but for practical purposes he said it makes more sense to develop a commercial product that would be set to change at just one “sweet spot,” such as 80°F, or perhaps offer products customized to a few particular geographic regions.

The company calls an IGU that uses its darkening film a RavenWindow. A RavenWindow would still allow some light transmission – about 5%. McCarthy said the effect is like putting a pair of sunglasses: the change happens quickly, but still allows a useful view from the interior.

An IGU that uses the whitening film is dubbed a RavenLight, and may be more practical in, say, skylight situations where the presence of diffused light is more important than a clear view.

Still another version of the film could turn a window into a mirror with 95% reflectivity.

Of interest to DIYers, the company literature notes that these films could be used in post-construction applications. But McCarthy told me that slapping the film on an existing window would not be as efficient as sealing the film in a double-paned IGU.

RavenBrick has one more major trick up its sleeve: it’s RavenSkin Smart Wall System. Think of it as a thermal battery. McCarthy says its possible to build an entire wall, composed of basically the same reversible phase-change material used in the window film, that would absorb sunlight and other ambient thermal energy during the day, and then gradually release heat in the evening. The wall, for example, could be constructed of material that would gradually reverse a sun-induced phase change and release its heat energy at, say, 72°F.

RavenBrick is a small company still in its start-up phase. Its core technology is this customizable phase-changing material. McCarthy and others at the company often use the term “programmable matter” and say the film is just one example.

Programmable matter is something that McCarthy has been thinking about for some time. Some of his work is conceptual (science fiction stories) and some technical (he has gained several related patents, e.g., one on the use of “programmable dopant inside bulk materials, as a building block for new materials with unique properties”).

Once an aerospace engineer working for a NASA contractor, McCarthy is now focused on making the RavenBrick a success. Besides not needing electrical connections for his company’s products, McCarthy bristles at comparisons to Sage and similar companies. He acknowledges that his smart windows don’t come with the convenience of a light switch, but he notes that two big differences, cost and scalability, favor RavenBrick’s approach. McCarthy says RavenWindow film can be manufactured cheaply, even at the current size limit of 1.3 m2, for what would be an MSRP of $25 per ft2 with a six-year payback period. Standard film-making technology could easily ramp the size up to several meters X infinity and would drive the MSRP to only a few dollars per ft2.

From a business strategy point of view, McCarthy says the biggest difference is that RavenBrick, unlike Sage, “is not interested in making its own windows or competing with the big players in the window industry.” It is only interested in making or licensing the film to the window makers, and providing other R&D services.

Testing of RavenBrick products is underway. McCarthy said ASTM testing has been underway for some time: Three of the four ASTM tests have been successfully completed, the last test is underway and McCarthy is hopeful that a 30-year lifespan will be certified.

He also said the National Renewable Energy Laboratory (NREL) would be installing and testing the windows this summer in some of the lab’s executive offices.

Stay tuned. RavenBrick’s films might fly onto our windows in the next few years.

Here is a short video on RavenBrick: