Estimation of Cooling Energy Reduction by Utilizing Cross-Ventilation in Detached Houses, within the Japanese newly introduced Energy Regulation - Evaluating Energy Consumption for Different Uses

The reduction of carbon dioxide emission due to energy consumption in the household sector is an urgent task, worldwide. As a measure to respond to the task, a new regulation has just been enforced since April 2009, in Japan. This regulation evaluates the energy performance of detached houses by estimating the primary energy consumption for different uses, namely, heating, cooling, ventilation, domestic hot water and lighting.

Especially in mild or hot climates, it has been frequently claimed by practitioners that the regulation, which is heavily focused on insulation performance, is not enough and broader aspects should be equally evaluated. The effectiveness of cross ventilation in reducing cooling energy is one of these aspects. However, there have been difficulties to overcome in predicting the effectiveness of cross ventilation on cooling energy reduction. Among such difficulties are the decrease of the discharge coefficient of openings with inclined airflow, variation of the wind pressure coefficient depending on surrounding conditions, etc., occupants' window opening behaviour and actual energy efficiency of air conditioners depending on their output and outdoor conditions. By referring to the results from experiments and observations on cross ventilation and air conditioners, the authors have proposed a solution for the Japanese new energy regulation on how to predict cooling energy consumption, taking the above factors into consideration. Even though there are still problems to be solved, the solution by the authors, shown in this paper, can be a guidepost to a more reasonable evaluation of the energy performance for cooling in buildings, as well as to a more reasonable design practice for windows and openings on the partition walls.