Performance of sealed evacuated panels as thermal insulation

Abstract

The CFC-blown polyrethane foam currently used as thermal insulation will be banned in the future because of the environmental impact of chlorofluorocarbons. This requires the use of other blowing agents, which often do not possess the same low thermal conductivity as, for example, CFC11. Evaluated panels avoid these environmental problems and can possess lower conductivity than rigid foams. This makes us believe that they are a promising option in spite of the major problem of maintaining the vacuum for a decade or longer. They require: (a) a leak-free sealing and a covering with an extremely low gas permeability; (b) a low and stable inner pressure; (c) an infra-red absorbing filler which withstands outside pressure. The foils used for sealing these panels will influence the overall thermal conductivity, especially if they are, for reason of vacuum tightness, metal coated. Therefore, we have done a parametric study on the influence of materials and dimensions on the performance of evacuated panels.