Inexspensive all-season passive thin metal film for energy savings in cities.

Active thin film electrochromic or thermochromic coatings have been used in smart windows. However, the current cost of active thin film windows is approximately 10 times that of passive film windows. This paper proposes an inexpensive passive thin metal film for all-season energy savings. The proposed passive thin metal film allows heat to flow preferentially in one direction. Thin metal films attached to glass indoor can absorb solar heat and the solar can radiate the heat to a room and to the glass respectively until thermal equilibrium. Because of the heated metal film against the room, as long as the temperature of the film is higher than that of the room, there is no heat flux from the room to the thin metal film which is called perfect thermal insulation. The 960m² film was installed in an actual hotel in Japan over 10 years and contributed to reducing the energy cost of air conditioning from 54 million yen to 43 million yen, demonstrating an annual energy savings of 11 million yen (US$0.1 million). This paper briefly describes how the proposed economical passive thin metal film will provide all-season energy savings. [ABSTRACT FROM AUTHOR]