As part of a liquid desiccant-based A/C system, an inexpensive heat source is needed to regenerate the liquid desiccant (LD). One of the most-common approaches, used by Tech Ingredients for their exerimental systems, is a solar water heater. In turn their design is based on one that Desertsun02 came up with, but they have a nice addition, which is to use low-E glass instead of plain glass. The idea is to increase the efficiency by reflecting the longwave IR that's generated by the hot interior of the water heater back toward the water tubes -- rather than escaping out of the heater.
The problem is that low-e glass isn't all that easy to come by, at least in the searching that I have done. Most vendors are selling complete low-e window units, while the best source for the odd piece of low-e glass is a custom house.
But it turns out that you can get low-e plastic film to put on a standard window, and it's not all that expensive, either. So far, so good: but there are DIFFERENT types of low-e films. The most common is a film with a thin reflective layer of aluminum, which reflects both visible and IR. Not useful for a solar water heater. There is a class of so-called "transparent" low-e films that are available, which might be suitable. Looking at reviews for these films indicates that the biggest challenge is applying the film without wrinkles or bubbles. I suspect that the biggest challenge is that the film is being applied to a window that's already installed. In my case I can lay the "substrate" glass flat, which should make it easier to properly apply the film.
The other potential issue is that the highest-efficiency LD based system requires that the LD be heated to at least 60C to regenerate it. The film will be exposed to this temperature (via convection on the interior of the enclosure). How long will it hold up?? Hard to say, since my application is far different from the intended purpose.
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