A440.3-M1991

Note: Clause numbers in this part of the User Guide correspond to those in the body of CSA Standard A440.2. Commentary is not provided for all Clauses in the Standard. 1.1 The angle from horizontal at which windows are installed has some effect on thermal properties. The Standard specifies the determination of reference values for vertical installation, as most windows are installed at this angle. These values of F and U are generally appropriate for comparing the performance of windows installed at other angles. The ER value, however, is based on solar radiation incident on vertical surfaces and therefore does not apply directly to windows installed at other angles. 1.3 The energy rating in the Standard is not currently relevant for energy use required for mechanical cooling of residences. The effect of windows on energy requirements for cooling of a residence can be calculated, but a simple comparative rating procedure has not yet been standardized. Similarly, the energy rating is not directly applicable to heating or cooling applications in multistory apartments or commercial building applications, where the relationship of heating and cooling loads to weather conditions is more complex. In developing the energy rating, each of the weather factors in 13 Canadian cities with more than 4000 heating degree-days were averaged, including solar radiation incident on windows facing the four cardinal compass directions, to produce a single set of average weather conditions. Rating values based on these average conditions therefore do not apply to any specific location. The ranking of the windows, however, is the same, for the most part, as that which would be obtained using local weather conditions. The ranking of windows would, however, likely be affected if an ER value were computed for a specific orientation. A method for obtaining ERS values for a specific location and orientation is provided in Part 2 of this User Guide, for those who may wish to select or market windows on this basis. The ERS values so obtained can be used to make a comparative estimate of the effect on annual heating energy requirements of alternate window installations, and the User Guide provides a method for making such estimates. See Clause 8 of this User Guide regarding the effect of window size on Er values. 1.5 Thermal properties of windows may change with time. For example, there may be some uncertainty about the long-term service life of some sealed glazing systems. Similarly, air leakage rates for some air-sealing systems change more rapidly than others. Standard methods for establishing the ability of windows to retain certain thermal properties have not been established.