Vacuum Window Glazings for Energy-Efficient Buildings: Summary Report

    Research output: NRELTechnical Report


    The technical feasibility of a patented, laser-welded, evacuated insulating window was studied. The window has two edge-sealed sheets of glass separated by 0.5-mm glass spheres spaced 30 mm apart in a regular array. A highly insulating frame is required and several designs were analyzed. The vacuum window's combination of high solar transmittance and low thermal conductance makes it superior tomany other windows in cold climates. In the U. S. Pacific Northwest, the vacuum window could save about 6 MJ of heating energy annually per square meter of window in comparison to conventional, double glazed windows. A large, vacuum laser-welding facility was designed and installed to conduct glass welding experiments and to fabricate full sized vacuum windows. Experiments confirmed thefeasibility of laser-sealing glass in vacuum but identified two difficulties. Under some circumstances, bubbles of dissolved gases form during welding and weaken the seal. Glass also vaporizes and contaminates the laser beam steering mirror. A novel moving metal foil mirror was developed to circumvent the contamination problem, but it has not yet been used to complete welding experiments andfabricate full-sized vacuum windows.
    Original languageAmerican English
    Number of pages143
    StatePublished - 1990

    Bibliographical note

    Work performed at Solar Energy Research Institute, Golden, Colorado and at Western Illinois University

    NREL Publication Number

    • NREL/TP-212-3684


    • energy-efficient buildings
    • insulation
    • laser-welding
    • vacuum window glazings


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