Low-carbon assessment of building facades using dynamic CO2 intensity of electricity generation in Japan

Abstract

To promote low-carbon power supply in a region, the demand due to building use should be synchronized with the optimal supply patterns. To this end, the usefulness of using the time-varying CO2 intensity of electricity in building design is discussed. Hourly intensities were first estimated and visualized for Tokyo, Japan, and the low-carbon impacts of improved façade performance were compared using case studies with a generic office model. Two cases were compared: one with increased solar shading performance of window glass and the other with combined measures of insulation, natural ventilation, and eaves. CO2 emission savings rate were more significant in the first case (19.4 %) than the second case (18.9 %) when a fixed annual emission intensity was used. In contrast, when hourly intensities were used, the savings rate was 18.1 % and 18.6 %, respectively, reversing the superiority. Consideration of the time-varying CO2 intensity could help evaluate building designs that limit electricity use during high CO2 intensity and shift it to periods of low CO2 intensity. The integration of time-varying factors not only in the mechanical system evaluation but also in building design itself should be integrated to promote the regional transition to a decarbonized society.