A great deal of effort is being expended to develop devices and systems which utilize solar energy. While it is critically important that the maximum use of solar radiant energy be achieved, it is equally important to recognize the fact that there are times when it would be more advantageous to simply selectively reject a portion of the solar energy available. For example, in the northern latitudes, the long summer days and the high sun angle provide an abundance of radiant energy that overheats most buildings. In contrast, the winter sun although providing more intense radiation, is visible for a much shorter period of time than the summer sun, due to the low winter sun angle. A good use of solar energy is to maximize the access of winter sunlight into a home, for example, to provide light and warmth while limiting the input of summer sunlight and its occasionally burdensome heat.
It has therefore been a goal of the solar energy industry to provide an apparatus which can selectively reject or admit sunlight automatically, passively, and on a continuous year round basis. Many patents have been directed to apparatus which collect and trap the greatest degree of sunlight possible in order to tap the collected radiant energy. Examples of such apparatus are found in U.S. Pat. Nos. 4,078,603 and 4,076,015 which show collecting means with faces having angularly disposed reflective surfaces. Another example of a collecting means is U.S. Pat. No. 4,137,901 in which a water filled pan with a black bottom is partially enclosed with a reflective housing. U.S. Pat. No. 4,143,492 discloses a saw-tooth-configured member that admits sunlight striking the same at a predetermined angle while blocking sunlight not at that angle.
Glazing material of the subject invention automatically and continually controls the level of radiant solar energy passing therethrough by selectively admitting, rejecting or absorbing radiant solar energy striking the surface thereof.
It is an object of the invention to provide a glazing material which is versatile in its application. It is also an object of this invention to provide a glazing material which will provide a means of preventing overheating of a solar collector that is subject to failure due to a loss of electric power in full sunshine. For example, the collector found in West German Pat. No. 2,552,598 showing alternate reflective and absorbent surfaces uses the reflective areas to boost the solar flux falling upon the absorbing areas thus increasing the likelihood of absorber degradation or failure. The reflective areas of the glazing in this invention, on the other hand, would be used to reflect away radiation to prevent summer overheating that is permitted with the plain glass glazing of the device in West German Pat. No. 2,552,598 or any common flat plate collector. Additionally, the glazing of this invention can be used on east or west facing surfaces or windows to reject low angle summer radiation in the morning or evening thus reducing air-conditioning costs while also permitting low angle winter radiation originating from the south to enter freely and thus reduce heating cost.
The importance of the dual nature of the opaque zones in the subject invention, whereby an absorptive coating followed by a reflective coating is applied to the shaped planar members, is illustrated when considering U.S. Pat. No. 4,076,015 which uses only a reflective principle and attempts to maximize collection with the reflected light. In this case the radiation reflected simply enters an adjacent aperture of the light pyramid and reflects again off the back side of the next reflector thus substituting for the radiation being reflected from the top side of that zone. The result is simply to shift the light from the one reflective zone to the shadow created by the adjacent reflective zone. The reflective zones of U.S. Pat. No. 4,076,015 do nothing to increase collection and more output would result from leaving all zones transparent. The opaque zones of the subject invention, on the other hand, are equivalent to an absorbing "un-mirror" with a reflective backing. Further the energy absorbed by the coating is conducted to the outdoor air as the least path of thermal resistance rather than conducting through the glazing to the area being protected from overheating.
Another device in U.S. Pat. No. 4,257,403 (French, Chevalier) uses only transparent and absorbing surfaces with an ineffective shape as a shade because of the lenticonic aperture. In this case the collection may be improved by the scolloped shape of the opaque zones seriously reduces effectiveness. Furthermore, the opaque zones are insulated so that energy absorbed by the opaque zones is trapped inside the overall device. The device may have stopped the collector absorber from receiving some radiation, but it is unlikely that the amount of shading accomplished would properly protect the overall device from overhearing upon loss of power in full sunshine.
In the subject invention the absorbing surface may be any material such as light green paint known to be a reasonable absorber, a highly absorptive coating such as chrome-oxide on copper or a selective paint with absorptivity in the 0.8 range and emissivity in the 0.3 range. A black tape with a metallized aluminum coating would be equally functional and effective. the glazing. The opaque zone selectively absorbs or reflects radiant solar energy entering this zone depending on the manner in which the glazing is mounted relative to the sun and the angle of incidence of the radiant solar energy relative to the glazing. The planar member defining the opaque zone consists of a first layer of absorptive material applied to one surface of the planar member and a second layer of reflective material applied to the planar member and arranged so that the reflective material is always between the absorptive layer and source of the radiant solar energy.
According to the glazing of the subject invention, the exterior surface of the glazing, that is, the side of the glazing facing toward the source of the radiant energy appears as alternating strips of transparent material and reflective material. The opposite or interior side of the glazing consists of alternating strips of transparent material and absorptive material.