A method for creating maps of recommended window-to-wall ratios to assign appropriate default values in design performance modeling: A case study of a typical office building in Japan

To support the appropriate default value assignment in design performance modeling (DPM), which is defined as energy/performance simulations in the concept and schematic stages of the design process, a methodology for creating maps of the recommended window-to-wall ratio (WWR) is proposed using integrated simulations and optimizations. A case study is conducted to create maps of recommended WWR in Japan. The distribution of the optimal WWR under varying design conditions exhibits three distinct patterns: (i) As the WWR decreases, the CO2 emissions decrease. (ii) An appropriate WWR value exists (30-50%) at which the CO2 emissions are minimized. (iii) As the WWR increases, the CO2 emissions decrease. Five design conditions of lighting power density, climate, window orientation, internal gains, and building scale are examined in this investigation. The results of the quantitative evaluation indicate that the lighting power density, climate, and window orientation significantly impact the optimal WWR configuration. The optimization results of 10 locations in four main orientations with two lighting power densities (10 W/m2 and 5 W/m2) are processed according to the optimal WWR distribution patterns to generate the recommended WWR maps for Japan. The maps provide architects with the information needed to determine the setting direction of default WWR values for DPM. For example, a larger WWR is recommended for buildings in zones 6-8 of the Japanese climate regions for the current lighting power density (10 W/m2), except for eastern facades. In contrast, a moderate or smaller WWR default value should be carefully assigned according to the window orientation in zones 4-8 when the lighting efficiency improves (i.e., for a lighting power density of 5 W/m2).