The U.S. Department of Energy is strengthening its Energy Star window performance standards in 2009 and 2013 to acknowledge energy-saving technologies superior to generic low-e glass (see climate maps below).
In terms of insulating performance, low-e glass tops out at about R-4 compared to an insulated wall of R-19. Triple-pane units improve generic low-e insulating glass performance from R-4 to R-9 but add weight and require stronger frames, according to Bruce Lang, VP of Marketing & Business Development at Southwall Technologies Inc., Palo Alto, Calif. Lang says Southwall’s Heat Mirror insulating glass (left) insulates from R-6 to R-20 in a standard insulating glass unit.
In commercial applications glass can no longer just address over-heating from too much solar energy. Heat Mirror and coated triple pane not only can reflect solar heat but also improve insulation and reduce carbon emissions from heat loss.
One consequence of improving the insulating performance of glass is more glass will be used in commercial applications increasing the possibilities for daylighting as well as limiting in some cases the need to expand/upgrade heating and air conditioning systems.