Patent Application
20180274292
This disclosure relates to window blinds, specifically window blinds which reflect solar energy for purposes of cooling.
In certain climates, the energy required to cool a building can comprise a substantial portion of a building's utility bill. A large portion of the cooling required is the result of thermal heating of a building. Windows and glass doors, in particular, allow a substantial amount of radiation into a building. Window coatings or other treatments have been developed to inhibit the transmission of solar radiation into an adjacent room. In addition, some windows are built to be double or triple paned or to have an insulative later to insulate the building from the outside environment. However, these treatments are not easily removable. Since these solutions can only prevent solar heating, they are of less value in environments where it is desirable to prevent solar heating during some seasons and to utilize solar heating during other seasons.
Technology has been developed which allows for daytime passive radiative cooling by use of a metamaterial film. The metamaterial film reflects solar irradiance while simultaneously emitting infrared radiation of the wavelengths of the infrared transparency window of the atmosphere. This material has been proposed for use on roofs and potentially even for walls of buildings, due to the silver backing it is opaque. Consequently, it cannot be used directly on windows.
Infrared reflective optical interference film that is also substantially transparent to visible light has also been developed. Although windows typically absorb or reflect thermal infrared radiation, glass transmits most near infrared radiation. Near infrared radiation can contribute to the warming of an adjacent room through a window. While this material can be used directly on windows because it is transparent to visible light, it is only capable of preventing the transmission of near infrared radiation and is not removable. In addition, it has no ability to cool the adjacent materials.
A window treatment is needed which will allow a synthesis of these multiple technologies to assist in adjustably cooling a home without using any external energy.
We disclose a window blind that may mitigate the effects of solar heating and simultaneously passively cool the blinds through radiation without using any external energy by utilizing multiple materials with different optical properties. The window blind may have slats which may be covered with a metamaterial film. The metamaterial film may be a polymer with silicon dioxide (SiO2) microspheres incorporated into it. It may also include a sheet of silver to which the polymer may be attached. The metamaterial film may induce radiative cooling through a combination of two properties. The metamaterial film may be substantially reflective of solar irradiance while also emitting strongly in the infrared wavelengths that correspond to the infrared transparency window of the atmosphere. Consequently, the metamaterial film may achieve daytime passive radiative cooling, which may allow the window blinds to contribute to cooling the rest of the building.
The metamaterial film may be attached to the top, bottom, or both surfaces of each slat, depending on the embodiment of the invention. This may allow the user to choose whether radiative cooling is desired. In some embodiments of the invention, the slats may be made of or include a thermally non-conductive material.
In addition to the passive radiative cooling described, the disclosed invention may also decrease the amount of solar radiation that may pass through the slats when they are open. The disclosed window blind may also include at least one sheet of infrared reflective optical interference film. The infrared reflective optical interference film may be substantially transparent to wavelengths of light in the visible spectrum but substantially reflective of infrared radiation. Consequently, the infrared radiation that may heat up a room adjacent to a window blind may be substantially blocked while not inhibiting a user's view through the window blind. In some embodiments, the infrared reflective optical interference film may be attached to the front longitudinal edges of each slat. In other embodiments, the infrared reflective optical interference film may be attached to the back longitudinal edges of each slat. In some embodiments, the infrared reflective optical interference film may be a single sheet which is attached to each of the slats. In other embodiments, the infrared reflective optical interference film may be several sheets, each of which may attach on the longitudinal edges of slats which may be adjacent to each other. The infrared reflective optical interference film may be substantially flexible or incorporated onto a material that is substantially flexible.
Window blind, as used herein, means a blind that covers an opening in a building, including a window or door.
While this invention is susceptible of embodiment in many different forms, there are shown in the drawings, which will herein be described in detail, several specific embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principals of the invention and is not intended to limit the invention to the illustrated embodiments.
We disclose a window blind that may mitigate the effects of solar heating and simultaneously passively cool the blinds through radiation without using any external energy.
Radiative cooling occurs as an object emits blackbody radiation through the infrared transparency window of the atmosphere into outer space. This is known to be very effective and has been used in multiple applications to achieve passive cooling at nighttime. However, during the day the effects of solar irradiance negate the cooling gains of radiative cooling. A metamaterial film has been developed that reflects solar irradiance while simultaneously emitting strongly in the infrared wavelengths that correspond to the infrared transparency window. One example of a film with these properties is described in Y. Zhai, et al., Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling. Science 355, 1062-1066 (2017) which is hereby incorporated by reference in its entirety. The current disclosure uses the described metamaterial film to achieve daytime passive radiative cooling, which may allow the window blinds to contribute to cooling the rest of the building. To enhance the effectiveness of the metamaterial film, the window blind may be used outside of the window as well as inside the building.
The window blind may include a plurality of slats, each of which may have a front and back longitudinal edge, two transverse edges, and a top and bottom surface. In some embodiments, the metamaterial film may be attached to a top surface of each of the slats. In some embodiments, the metamaterial film may additionally or alternatively be attached to the bottom surface of each of the slats. In the embodiments in which the film is attached to only one surface, it may be desirable to be able reverse the direction in which the blinds close such that the surface with the metamaterial film may either be substantially exposed to the atmosphere or substantially hidden from the atmosphere. This may be useful in climates in which radiative cooling is not desired year-round. In some embodiments, the slats themselves may be removable such that the position of the metamaterial may be switched to enhance this effect. In another embodiment, the slats may be vertical, which may make it easier to reverse the orientation of the slats.
The metamaterial film may be a polymeric film between 25 and 75 micrometers thick. The metamaterial film may be constructed of one or more of the following: polymethylpentene, poly(methyl methacrylate), and polyethylene. The polymeric film may contain silicon dioxide microspheres (SiO2). The microspheres may be incorporated into the polymeric film at a concentration of between approximately 4% and 8% by volume. The metamaterial may also include a silver coating between the polymer and the adjacent surface of each slat. The silver coating may be between about 100 nm and 300 nm thick. The combination of the polymeric film with the microspheres incorporated therein and the silver coating may allow the metamaterial to reflect solar irradiation and strongly emit infrared radiation corresponding to the infrared transparency window of the atmosphere.
In some embodiments of the invention, the slat may be made of or include a thermally non-conductive material. The thermally-nonconductive material may prevent the slats from transmitting thermal energy from the slat to the window glass, particularly when the blind is used outside the building. The thermally non-conductive material may be one or more of the following: silicone rubber, fiberglass, foam-glass, polyurethane foam, expanded polystyrene, acrylic glass, and Teflon.
When the slats of a window blind are open, the solar radiation that passes through the spaces between the slats may still considerably heat up a room adjacent to the window blind. To further reduce solar heating, the disclosed invention may also include at least one sheet of infrared reflective optical interference film which may be attached to a longitudinal edge of each of the slats. In some embodiments, the infrared reflective optical interference film may be attached to a back longitudinal edge of each of the slats. In other embodiments, the infrared reflective optical interference film may be attached to a front longitudinal edge of each of the slats.
The infrared reflective optical interference film may be substantially transparent to wavelengths of light in the visible spectrum while reflecting infrared radiation. As it may be mostly transparent to visible light, a user's view from the window may not be substantially inhibited by this film on the window blind. The infrared reflective optical interference film may be a multilayer film which may be that disclosed in U.S. Pat. No. RE 34,605 filed Dec. 11, 1992, a reissue of U.S. Pat. No. 5,103,337, which is hereby incorporated by reference in its entirety. The infrared reflective optical interference film may be substantially flexible or incorporated onto a material that is substantially flexible.
In some embodiments of the invention, the infrared reflective optical interference film may be a single sheet. In this embodiment, the sheet may be attached to the back or front longitudinal edge of each of the slats at varying points on the sheet. In other embodiments, the window blind may include a plurality of sheets of infrared reflective optical interference film. In one such embodiment, a first longitudinal edge of a first sheet of the infrared reflective optical interference film may be attached to the back longitudinal edge of a first slat of the disclosed window blind. Then, a second longitudinal edge of the first infrared reflective optical interference sheet may be attached to a back longitudinal edge of a second slat. In some embodiments, the first slat may be adjacent to the second slat.
In some embodiments, the infrared reflective optical interference film may be removable, which may be desirable when cleaning of the window blind is needed. In addition, it may be desirable in climates where thermal heating from the sun is desirable during the day to reduce the cost of heating.
Referring now to the drawings,
As with traditional blinds, the slats of window blind 200 may be opened and closed using tilt strings 230a and 230b. Window blind 200 is shown in
While specific embodiments have been illustrated and described above, it is to be understood that the disclosure provided is not limited to the precise configuration, steps, and components disclosed. Various modifications, changes, and variations apparent to those of skill in the art may be made in the arrangement, operation, and details of the methods and systems disclosed, with the aid of the present disclosure.
Without further elaboration, it is believed that one skilled in the art can use the preceding description to utilize the present disclosure to its fullest extent. The examples and embodiments disclosed herein are to be construed as merely illustrative and exemplary and not a limitation of the scope of the present disclosure in any way. It will be apparent to those having skill in the art that changes may be made to the details of the above-described embodiments without departing from the underlying principles of the disclosure herein.
