According to the Japanese government, 90% of the existing housing in Japan is poorly insulated and does not meet the current insulation standards. Poor thermal performance in housing affects the risk of heat-related illness among older adults in summer. In winter, it increases indoor temperature differences, thereby elevating the risk of bath-related acute cardiovascular events. Retrofitting is desirable to reduce thermal health risks in both seasons. However, insulation retrofits have not been widely implemented in Japan because of their high costs. Therefore, this study focuses on combining retrofitting to improve the thermal environment with floor plan modifications, which are generally implemented in response to life stage changes in Japan. In our previous work, we have proposed floor plan retrofit methods to reduce winter thermal health risk. However, summer health risks also need to be considered because elevated indoor temperatures have been associated with heat-related illness among older adults. This study aims to develop new retrofit methods for reducing thermal health risks in summer and winter through floor plan modifications. Numerical simulations using a generic detached-house model showed that, on the hottest day, the toilet room temperature in the proposed model was 4 K lower than in the original model. Furthermore, when additional measures to reduce west-facing solar heat gains were incorporated into the winter-optimised floor plan, thermal health risks in both seasons decreased compared with the original model. These results indicate that the proposed retrofit methods are effective in reducing thermal health risks. • Six floor plan retrofit methods are proposed to improve thermal health in summer. • Adding a west-side closet reduces peak bedroom temperature by 4 K on the hottest day. • Relocating a bathroom from north to south reduces thermal health risks in winter.
KANI et al. (Wed,) studied this question.