1990-02-01

Smart Windows for Automobiles 900419

Influenced both by styling considerations and by the aerodynamic benefits possible using flush glazing, car designers are making increasing use of glazing on automobiles. This leads to higher throughput of solar radiation into the car. Solar heat load will thus become a greater problem given that fuel efficiency requirements limit increase in the size of vehicle air-conditioners. Driver discomfort will increase due to the absence of shade, and greenhouse effects will become more serious. This leads to opportunities for energy-efficient glazing in vehicles. Smart windows - windows whose luminous and solar transmission vary dynamically to suit changing climatic conditions - have a potential application as energy-efficient automobile glazing. A variety of chromogenic technologies have been proposed. These include liquid crystal (LC) technology such as encapsulated LC devices consisting of small liquid crystal droplets encapsulated in a polymer matrix. Electrochromic (EC) technology - where transmittance changes under applied electric field or current - is also proposed for energy efficient glazing. A variety of designs are possible including laminate constructions formed from two glass substrates that sandwich an electrochromically active medium, and all solid-state devices fabricated by deposition of electrochromic thin films onto a single glass substrate. This paper reviews how publicly announced chromogenic technologies match automotive window needs and applications. Construction and performance of smart window designs currently under development are described. World-wide activity in this area is reviewed. Various chromogenic and nonchromogenic technologies are compared in terms of how they meet the performance, safety, and environmental resilience required of automotive glazing.

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