Smart windows

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Abstract:
Smart windows are based on innovative composite glasses and allow to automatically adapt the characteristics of light and heat transmission to different external circumstances. For energy efficiency Smart window are a promising technology since they may shield direct sunlight through the windows and thus save energy for air-conditioning. Cleaning window treatments can be a hassle. In this regard Smart windows are an easy alternative. When summer sun is bathing our house in rays things can really heat up inside room. Smart window can be used to block that extra heat. By blocking UV radiations, Smart windows can protect paintings and furnishings in our home or office. Although thermo tropic and photo chromic technology can be used in Smart windows, both applications are ultimately impractical as energy saving devices because they cannot be manually controlled. Photo chromic technology is most commonly used in sunglasses. Photo chromic material darkens with respect to sunlight. Thermo tropic material responds to heat. Currently liquid crystals suspended particle devices & electrochromics are being touted as the latest and greatest technologies with reflective hybrids closely at their heels.
Index terms
Smart window, photo chromic technology, thermo tropic, reflective hybrids.
I. INTRODUCTION
magine turning a knob and controlling the amount of light passing through a window. Several technologies for such switchable glazing are available or under development. One such technology is called Smart window where the user can actually control the amount of light passing through the glass. They can also regulate the amount of solar energy transmitted thorough them. There are presently three types of smart window technologies (SPD), liquid crystal and electro chromic.
They are characterized by their ability to vary the throughput of radiant energy by electrical low voltage pulses. Apart from energy saving aspects the possibility to vary the transmittance also results in increased comforts. With the glass it will be a lot easier to keep offices cool in summer. They can also save money.
II. TECHNOLOGIES USED
Smart windows are based on innovative composite glasses and allow to automatically adapt the characteristics of light and heat transmission to different external circumstances. For energy efficiency Smart window are a promising technology since they may shield direct sunlight through the windows and thus save energy for air-conditioning. There are several technologies used in Smart windows. They are
Thermotropics
Photochromics
Liquid crystals
Suspended particle Displays
Electrochromics
Cleaning window treatments can be a hassle. In this regard Smart windows are an easy alternative. When summer sun is bathing our house in rays things can really heat up inside room. Smart window can be used to block that extra heat. By blocking UV radiations, Smart windows can protect paintings and furnishings in our home or office. Although thermo tropic and photochromic technology can be used in Smart windows, both applications are ultimately impractical as energy saving devices because they cannot be manually controlled. Photochromic technology is most commonly used in sunglasses. Photochromic material darkens with respect to sunlight. Thermotropic material responds to heat. Currently liquid crystals suspended particle devices & electrochromics are being touted as the latest and greatest technologies.
II. TYPES OF WINDOWS
1. ELECTROCHROMIC WINDOWS
Electrochromic window system consists of 7 layers of materials. They are
Glass or plastic panel
Conducting oxide
Electro chromic layer such as tungsten oxide
Ion conductor / electrolyte
Ion storage
A second layer of conducting oxide
A second glass or plastic panel
Electro chromic window consists of up to seven layers of materials. The essentials function of the device results from the transport of hydrogen or lithium ions from an ion storage layer and through an ion conducting layer.
The electrochemical layer is typically tungsten oxide(WO). The presence of the ions in the electro chromic layer changes its optical properties causing it to absorb visible light. The large scale result is that the window darkens. The central three layers are sandwiched between two layers of a transparent conducting oxide material. To protect the five layers of materials, they are further sandwiched between two layers of glass. All of the layers, of course, are transparent to visible light.
The electro chromic (EC) window consists of a series of thin conducting layers that change optical properties when an electrical voltage is applied. Each layer is thinner than a sheet of paper, and together the layers support the transport of electrons and ions. One layer of the film- colorless lithium metal oxide acts as the positive electrode, another layer- tungsten oxide acts as the negative electrode. When voltage is applied, lithium ions begin to traverse from the positive electrode to the negative electrode, a process that turns the tungsten oxide to lithium tungstate (a light absorbing, blue gray substance), formed by the chemical addition of ions. The longer the voltage is applied, the more ions are transferred, and the darker the window becomes. During the production process, ceramic thin-film layers containing the electrodes are deposited with great precision on to a transparent substrate primarily by a vacuum coating technique. The multilayered electro chromic device is then mounted inside a conventional glass frame. The conducting layers are connected to a power supply, controlled by a switch. The switch allows the number of the ions and thus the amount of light transmitted in the electro chromic film, to be varied incrementally by a simple on- off switch, a user adjustable rheostat to meet individual user performance of heat and sunlight, or an automatic system driven by sensors or timing devices.
2. 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, 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 galss. Both face 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 nearly identical the window lets in nearly the same amount of light 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 to maintain its clear state, this liquid crystal window provides no energy saving benefits.