Wednesday, January 7, 2009

Research into Existing Solutions, by Evan

Research about Some Ways to Reflect the Heat off of a Roof:

Mirrored Shingles, Liquid Crystal Windows, and Electrochromic Windows
by Evan

Our team thought about different things that could reflect the solar heat off of a roof instead of it absorbing into the dark roof. One way was using mirrored shingles. A mirror is a perfect reflector and would make all of the sun’s heat reflect back into the air. One big problem with this is that the reflected light would bother pilots.
We also thought about using liquid crystal windows on the roof of a building to reflect the heat. We researched it and found out that it really does not do it. Then we found out about Electrochromic windows and thought about using them on the roof. They would reflect the heat, but they are too expensive. Here is information we found about both of these types of windows.

Liquid Crystal Windows
The first commercially available "smart window," liquid crystal windows are used for privacy control. They do not provide energy savings.
In this window's normal "off" condition, the glazing is a translucent milky white. When an electric current is applied, however, it turns slightly hazy clear. The switch between the two states is nearly instantaneous.
The technology works this way: two layers of film enclose a layer of tiny liquid crystals. This assembly is laminated between two pieces of heat-treated glass. Both faces of the film are covered with a transparent, electrically conductive metal coating. These conductive coatings are wired to a power supply.
When the power is off, the liquid crystals are randomly scattered. Light entering the glazing does not have a clear path out, and the window is a translucent milky white. When an electric current is applied between the two conductive coatings, the liquid crystals align neatly and you can see through the window.
Other than the diffusion of light, the optical properties of the two states are nearly identical -- the window lets in nearly the same amount of light and solar heat whether it's on or off. Because there is little change in performance properties and because it requires constant energy to maintain its clear state, this liquid crystal window provides no energy saving benefits.

Electrochromic Windows
Flip a switch and an electrochromic window can change from clear to fully darkened or any level of tint in-between.
The technology has been suggested for cars, where with a touch of a switch the driver can tint the mirror or sunroof. In buildings, the changeable windows allow for privacy, to cut down glare, and to ward off increases in solar heat.
The action of an electric field signals the change in the window's optical and thermal properties. Once the field is reversed, the process is also reversed. The windows operate on a very low voltage -- one to three volts -- and only use energy to change their condition, not to maintain any particular state.
To make an electrochromic window, a thin, multi-layer assembly is sandwiched between traditional pieces of glass. The two outside layers of the assembly are transparent electronic conductors. Next is a counter-electrode layer and an electrochromic layer, with an ion conductor layer in-between. When a low voltage is applied across the conductors, moving ions from the counter-electrode to the electrochromic layer cause the assembly to change color. Reversing the voltage moves ions from the electrochromic layer back to the counter-electrode layer, restoring the device to its previous clear state. The glass may be programmed to absorb only part of the light spectrum, such as solar infrared.
Early research indicates that the technology can save substantial amounts of energy in buildings, and electrochromic glazings may eventually replace traditional solar control technology such as tints, reflective films and shading devices.
The website is:

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