SciFi + Art = lower electric bill
by TreeHugger on 02.22.05
What crazy TreeHugger equation is this? There already exists house paint that, when applied to interior walls in the normal manner, results in increased interior comfort and a significant reduction in heating and air conditioning bills. It does this using a technology similar to that deployed in “Low-E” windows. The paint is similar, but not identical to Low-E window functionality because, while Low-E paint reduces energy consumption year round, Low-E windows only are helpful during the heating season. The question comes to mind: “Why haven’t I heard of this before”? It’s fairly new and only one brand is currently distributed in the US. Plus it looks like every other water based house paint, and competes in a commodity market. Even Low-E windows took many decades to gain wide acceptance. How to speed it up?
Here’s the creative part of the equation. Imagine muralists and public artists banding together to market their creative services to help curb climate change. Using the Low-E paint palette, they create sanctioned public art on interior walls of shopping centers; offices; airports; etc. When a repainting is scheduled for normal maintenance, building owners are enlisted to have professional interior painters do a Low-E paint base coat for the mural and also on adjacent walls, leaving scaffolding for the mural surface, and supplying the tinted paints for artists to use.
Local, state, and national juried contests are held and cash prizes awarded for artistic winners. The personal financial awards come, however, when the HVAC savings are documented, based on standard methods agreed to, in advance, by participating mall developers, HVAC industries and electrical utilities. Contributing artists get checks for the estimated commercial energy bill savings in year one, paid for by building owners. The PR outcome is obvious. Win for building owner. Win for utilities. Win for art. Win for the climate. It’s a dream equation to which I’d like to awaken.
Greatly simplified technology overview:
The Invisible Heat Mirror: -- Low-E windows modestly cut heating bills because of an invisible, extremely thin coating of tin oxide on the window pane(s). The more windows you have, the more beneficial it is to go Low-E. With a double glazed Low-E window, for example, a type increasingly common in northern US, the tin layer might be on the outside-facing surface of the inner-most of the two panes. Without the Low-E coat, heat radiated from the home’s interior moves easily through the window, toward the out of doors. With the tin coating in place on the pane, however, the coating reduces the rate at which heat energy is “emitted” outward, as electomagetic energy, from the inner pane. This reduced “emissivity” in the outbound direction means that the heat effectively turns around and heads back into your house. Hence, you don’t feel a chill as much when sitting near the coated window and energy is saved.
Several materials, not just tin, can lower emissivity. Radiance brand paint uses powdered aluminum. Low-E additives are finely divided, non-toxic metals or inorganic salts
Remarkably, Low-E paint is beneficial in both the heating and the cooling season. During the "cooling season", heat is conducted into your home's walls from where the sun's rays are incident to exterior walls, eventually reaching the decorative painted surface you see every day. Because of the Low-E paint’s lowered “emissivity”, compared to ordinary decorative paints, less infrared heat is able to radiate inward, cutting the air conditioning load. Where does the heat go? Back out side, by outward conduction, followed by radiative loss to the atmosphere. Because there is less infrared heat radiating in, you feel more comfortable, especially when the AC fan is not blowing actively. This reinforces the energy saving desire to keep the thermostat set conservatively. So there is a secondary phychological feed back loop that's conservation-driving.
Several companies offer Low-E paint for interior attic roof surfaces. Note that this functionality is very different than that of aluminum, glass bead, or light pigmented roof coatings placed on the exterior surface of a roof or wall. These exterior coatings work by reflection only, not by controlling emissivity.
by: John Laumer
How can you have it both ways? In cold weather, less heat is lost through the windows--doesn't that mean that *more* heat will be kept inside during hot weather? Likewise, in hot weather, less infrared heat is able to penetrate into the house--aren't you then loosing a desired warming effect from the sun during cold weather?
Good questions. During winter the furnace puts out very large amounts of heat to keep us comfortable, The Low-E window helps the furnace keep up because the lowered emissivity is directional, letting in the sun's heat but keeping radiant enery inside. In summer, however, the furnace is off, and what makes us uncomfortable is solar gain, not the absence of heat. In most homes/apartments, windows contribute only a small portion of all solar gain. So, yes, the Low-E effect does keep some additional heat in during summer, but in the larger scheme of things it is a trivial effect.
There are window coatings designed to reduce solar gain only. You've no doubt seen their darkening effect on tall office building windows. Efficacy of these older coatings tends to be low and appearance not always very good in either direction.
It is possible to be hihgly selective for IR penetration in both directions and look good. One such hybrid coating selectively reduces IR penetration from outdoors AND AT SAME TIME produces the aforementioned Low-E effect. With such a sun controlling coating,less sun warmth comes into the home during in winter, but this heat loss is balanced by the parallel Low-E effect in that season. I had occasion to be in a room enveloped with windows of this nature on a hot summer afternoon, while the sun was ablaze.
Result? A room formerly unbearable during the summer mid-day, due to wide temperature swings (the AC could hardly keep up), was now quite fine. This particular type of window, as it interrupted incoming IR, became unpleasantly hot to the touch on its in side surface, demonstrating its effectiveness at keeping the heat out of the room.
Which type of window coating is best is going to depend on where you live: Buffalo NY versus Houston TX. Where air conditioning bills exceed heating bills, you are going to want solar gain control first, and vice versa.
FYI, Radiance paint was discontinued several years ago, at least according to the distributor here in Canada. In addition, studies by outside agencies were inconclusive on the benefits of Radiance. I'm still interested in the technology, and I'd like to hear of any interior Low-E paint alternatives.
Thanks for the reply. Informative.
Here is the original maker of heat reflective paints. They supply NASA.
http://www.hytechsales.com/