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Research paper−262−Synthesiology - English edition Vol.5 No.4 pp.262-269 (Mar. 2013) already available on market overseas.In Japan, the electrochromic switchable glass research was conducted by major glass manufacturers until the 1990s. One of the authors (Yoshimura) was involved in the research of switchable material from the days of the National Industrial Research Institute of Nagoya that was the precursor of AIST Chubu. The switchable material was investigated as one of the passive energy-saving techniques in the national project of ‘Sunshine Project’ and ‘New Sunshine Project’. Although a product with excellent performance was fabricated, the research was terminated at around 2000 because the prospect for practical use could not be conceived due to cost issues. The research entered the so-called “valley of death” or the “period of nightmare.”At that time, the author (Yoshimura) started to look at the “switchable mirror” that might reignite the research of this switchable glass. The switchable glass was a new switchable material discovered in the Netherlands in 1996.[4] While the conventional switchable material changed from transparent to deep blue color, the new material changed from transparent to a mirror state. In the mirror state, it reflected and cut off the sunlight. Because the mirror state reflected and cut off more sunlight compared to conventional switchable glass, this allowed a window with higher shading performance. In conducting the switchable mirror thin film research, we had in mind the achievement of the practical use of the energy-saving windowpane from the beginning, not just doing research for materials. In this paper, we present how the research was conducted to achieve practical use of the switchable mirror glass.1 IntroductionThe Materials Research Institute for Sustainable Development is engaging in research for “energy-saving building components” that are materials useful in reducing the CO2 emission in the civilian sector. The Energy Control Thin Film Group is in charge of the research of windowpane glass. The percentage of energy consumed in cooling and heating reaches about 30 % of the energy consumption in the civilian sector, and the window is a component that greatly affects cooling and heating efficiency. While the objective of a window is to let in light, ordinary windowpane allows the permeation of heat as well as visible light, and it is a factor that leads to the loss of insulation of the building. Increasing the insulation property of the window has great energy saving effect, and recently, the uses of highly insulating pair glass and low-e glass are becoming common. In Japan where the summers are very hot, the energy-saving effect can be further increased by effectively blocking the sunlight (shading) in addition to increasing insulation. The switchable glass is a windowpane that can automatically control the inflow and outflow of light and heat.The switchable glass is fabricated by coating the glass with thin film material that can reversibly vary the optical property (chromogenic material). There are several types of switchable glasses. For example, an electrochromic glass accomplishes the switching electrically,[1] a thermochromic glass changes according to temperature,[2] and a gaschromic glass changes by surrounding atmosphere (gas).[3] Among these switchable glasses, there is a long history of research of the electrochromic glass, and some types of glasses are - R&D strategy toward its practical use-“Switchable mirror” is a new thin film material that can be switched between transparent and mirror states. Using this material on window glass saves energy by effectively shading rooms from sunshine, thereby decreasing cooling load in summer. In this paper, we introduce our R&D strategy for further development and practical deployment of this material. In addition to R&D of the material itself we also measured the amount of energy saved when the material was used in the windows of buildings. The results we obtained from such field tests will enable us to develop a window glazing with better energy-saving performance.Development of switchable mirror glassKeywords : Smart window, energy efficiency, cooling load, chromogenic material, durability[Translation from Synthesiology, Vol.5, No.4, p.253-260 (2012)]Kazuki Yoshimura*, Kazuki Tajima and Yasusei YamadaMaterials Research Institute for Sustainable Development, AIST 2266-98 Anagahora, Shimo-Shidami, Moriyama-ku, Nagoya 463-8560, Japan *E-mail: Original manuscript received April 6, 2012, Revisions received May 16, 2012, Accepted May 18, 2012

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