THE CRITERIA OF OUTDOOR CONDITIONS FOR OPERATING NATURAL VENTILATION OPENINGS

In recent years, natural ventilation system have attracted greater attention as an alternative to reduce building energy consumption. And natural ventilated buildings have been increasingly applied even in large office buildings. In Japan, summer is hot and humid climate, winter is low on both temperature and humidity. And hence, the quality of fresh air in the intermediate seasons varies in both temperature and humidity. Therefore, determining the criteria of outdoor air to introduce natural ventilation is an important factor to achieve energy saving and comfortable indoor thermal environment. In this paper, switching conditions to natural ventilation in 42 buildings with natural ventilation system were investigated and classified in six groups ([t-h type], [t-x type], [t-h-φ type], [t type], [h type], [Lt-h type]). Each type was evaluated with the reference weather data of 2000yr versions from three aspects : 1) total operating hours, 2) continuity, defined as the daily average hours of operating natural ventilation, 3) the quality of supply outdoor air. The total operating hours of the six types in basic setpoints ranged from 972h to 1, 278h. Continuity was between 6.2 and 8.3. Comparison of calculation results based on the reference weather data of 2000yr versions with those based on the Meteorological Agency from 2001 to 2013 showed no significant difference in the operating hours and continuity. For the setpoint, the changing of the lowest outdoor temperature setpoint from 18Co to 15Co in [t-x type] and the changing of the highest dew-point temperature setpoint from 19Co to 15Co in [t-h-φ type] exhibited significant effect. It has been confirmed that the setpoint of relative humidity affected total operating hours at the nights. In order to study the regional difference, futher analysis was conducted with the reference weather data of 20 cities in Japan. And it was founded that operating times of Sapporo and Okinawa in intermediate seasons tend to be shorter than other cities.