if we design solar water heater by two paralel cover glasses. what is the function of the outermost glasses? ?

what is the best range between two glass covers (in mm)? how to calculate the efficiency of this SWH? this swh is length, width, height 137 cm, 126 cm, and 10 cm. thanks for the answers

NachoMahma8 years ago
. Insulation. The air between the panes doesn't conduct heat as well as the glass. . I'll guess that somewhere around 1/8-1/4" (3-6mm) would work well. If the gap is too big, convection currents may become a problem. . Not sure how to calc efficiency. Probably difficult to even get close with a home-brew unit.. From what I've read, "forest green" works slightly better than black. . You should be able to get authoritative answers by searching this site and/or using Google.