Glazing design with variable heat and light transmittance properties, device and method
An energy efficient optical window has different optical properties when irradiated by solar light from front or back side of the window. The window is used to reflect most of the infrared light at summer times, leaving the interior cooler and to absorb most of the infrared light at winter times, making the interior hotter by heat transfer from the hot window pane. Mechanical reversal of the window, inside out, is used to apply the needed version for winter and summer. The window is coated with alternating thin metallic and dielectric layers that transmit most of the visible light while reflecting most of the infrared part of the spectrum when impinged by solar light on one side and transmit most of the visible light while absorbing most of the infrared part of the spectrum when impinged by solar light on the other side.
1. An energy efficient optical window having different optical properties when irradiated by solar light from opposite sides, said window comprising:
a first side and a second side opposite the first side, wherein the window is movable between a winter position wherein the solar light impinges on the first side and a summer position wherein the solar light impinges on the second side; and
an infrared absorbing layer and an infrared reflecting layer adjoining each other and having a high transparency for visible light, said absorbing layer absorbing at least about 40 percent of impinging near infrared light, and said infrared reflecting layer reflecting at least about 80 percent of impinging near infrared light.
2. The energy efficient optical window of claim 1 in which said first and second transparent layers are separated from each other by a separation layer of at least one of air, vacuum and inert gas.
3. A method of providing an energy efficient optical window having different optical properties when irradiated by solar light from opposite sides, said method comprising:
absorbing at least about 40 percent of impinging near infrared light, and
reflecting at least about 80 percent of impinging near infrared light.
4. The method of claim 3 , wherein said absorbing is effected by a transparent dielectric material including embedded nanoparticles of at least one of carbon, vanadium oxide, tin-doped indium oxide, antimony-doped tin oxide, lanthanum hexaboride (LaB 6 ), infrared absorbing dyes having high or very high absorptivity, and any combination thereof.
5. The method of claim 3 , wherein said infrared reflecting layer includes a plurality of metallic layers each of which is separated by dielectric layers, each of which has a thickness between about 50 nanometers and about 100 nanometers to increase visible light transmittance by destructive interference of reflected visible light.
6. The method of claim 5 wherein said metallic layers are nanometric layers of at least one metal selected from the group consisting of silver, copper, aluminum, gold, or any combination thereof.
7. The method of claim 3 , wherein said dielectric layers include at least one material selected from the group consisting of SiO 2 , Al 2 O 3 and MgF 2 , said dielectric layers having thicknesses that cause said metallic layers to reflect near infrared light.
8. The method of claim 2 , wherein said window is pivotably supported and may be positioned to have either said first side or said second side facing incoming solar light.