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.