Organisations such as the National Fenestration Rating Council (NFRC) in the United States and the Canadian Standards Association (CSA) in Canada have done a vast amount of work to develop standardised procedures for rating the thermal performance of window systems. These procedures provide an excellent means of comparing one window product to another. One limitation to the use of the information produced in these rating procedures is that the data are produced through measurement or simulation for a fixed window size. To use these data in building energy computer simulations, the U-factor and solar heat gain coefficient (SHGC) data need to be available for the actual window sizes used in a building. The window labelling information provided through the window rating procedures in the US and Canada is not enough to calculate size-specific U-factor or SHGC values. Using minimal information that is provided from the rating procedures and making a few simplifying assumptions will allow for an approximation of the size specific U-factor and SHGC values. The work presented outlines a simplified approach to determining size-specific U-factor and solar heat gain coefficient (SHGC) values.

KEYWORDS: year 1997, Calculating, transmittance, solar heat gain, heat flow, performance, rating, windows, double glazing, triple glazing