A440.3-98

I1. Purpose of CSA Standard A440.2 I1.1 CSA Standard A440.2 provides methods for evaluating the energy performance characteristics of windows, doorlites, curtain walls, skylights, and sliding glass doors that may be used in buildings of any occupancy. Until CSA Standard A440.2 was developed, it was not possible to compare the energy performance of different windows. If energy performance information was provided by the manufacturer, it was often quoted as the R-value or the U-value for the centre-of-glass area. This did not take into account the effect of the frame and sash, so it usually over-represented the energy performance of the entire window. CSA Standard A440.2 specifies a procedure for evaluating the overall energy performance parameters of the total window including the glass, frame, sash, etc. The properties that affect the energy performance of windows are solar heat gain, heat losses resulting from conduction, radiation and convection, and heat losses resulting from air leakage. CSA Standard A440.2 provides methods for determining solar heat gain coefficient (SHGC) and heat losses resulting from conduction, radiation, and convection (U-value). The procedure for determining air leakage is specified in CSA Standard A440. These energy performance properties are applicable to all windows. CSA Standard A440.2 also provides a method for calculating an overall Energy Rating (ER) for a window to be used in a self-contained low-rise residential building by combining the three properties (a) solar heat gain coefficient (SHGC); (b) overall heat transmission coefficient (U-value); and (c) air leakage into a single overall rating. The ER provides a means to compare the energy performance of one window for use in a low-rise residential building with another. However, because of the manner in which the ER is determined, there are limitations to its applicability. As explained in Clause 6 of this Section, ER is only applicable when comparing windows and sliding glass doors that are to be used in houses under heating conditions.