A new energy standard for evaluating window thermal performance has been established in Canada. To allow for simple comparison of windows, a single energy rating number is calculated based on specific house and weather conditions that are intended to be an appropriate average for population centres across Canada. However, this method does not allow for a selective choice of windows based on window-specific applications or location and orientation. As a result, a simple method for evaluating window energy performance for different locations and orientations has been developed, and is presented. Energy rating numbers, ERS, can be calculated based on the orientation of the window, the local environmental conditions, and the building characteristics (including building total heat losses and window area). This ERS is for residences only, and is intended primarily as a uniform basis for comparing windows in relation to their effect on seasonal energy requirements for heating. Negative ERS values indicate that the window arrangement considered will result in a net increase of the heating load in the house. ERS values that are positive indicate that over the heating season there will be a net gain in energy (therefore, a net reduction in heating requirements) attributed to the window. Tables of climate-dependent factors used in the calculation of ERS have been established for 13 Canadian cities, 8 different orientations, and 2 house types (including a typical post-1975 Canadian house and a high-insulation house). However, similar tables can be established for virtually any location for which specific weather conditions are known. As a result, this ERS calculation procedure may serve as a basis for a universal method for comparing window performance.

KEYWORDS: windows, calculating, energy consumption, performance, orientation, housing, low energy housing, heat load, standards, Canada, heat flow, comparing, energy, rating, weather, climate, location, buildings, properties, heat loss