Outdoor thermal environment of a traditional settlement with a group of wooden storehouses in summer daytime at Tsushima Island, Japan

Abstract

Traditional settlements have been formed by adapting to local climate and natural features. This study aims to clarify the climatic characteristics of a settlement with a group of wooden storehouses in summer daytime from the viewpoint of environmental design. Waniura settlement in Tsushima Island, Japan was selected as the observation site of this study. The largest group of wooden storehouses in Tsushima Island is in Waniura settlement, and it is in the north of the settlement. About 150 storehouses are located near the port. The microclimate observations in the settlement and heat parameters measurements, including UV intensities at three representative points, were carried out in the summer of 2019. The wind direction in the northern part of the settlement had a different trend than that in the sky. The wind directions in Waniura settlement is affected by the topography when the wind in the sky blows in different directions from the valley line in the settlement. The layout of storehouses affects the wind environment of the group of wooden storehouses and the wind reducing effect appears when the wind blows orthogonally to the parallel storehouses. At the shaded path (point-C) on 1,000 W/m 2 global solar radiation, the MRT reduction was -25.7 °C. The reason the MRT at the shaded path dropped significantly was that the storehouses built close to each other blocked the solar radiation on the shaded path significantly. Furthermore, less solar radiation on the shaded path might contribute to maintaining the low surface temperatures of the pathway and the storehouses. At the shaded path on 1,000 W/m 2 global solar radiation, the UTCI reduction was -4.4 °C. This result emphasizes the importance of providing shade from buildings or other means and directing wind into those spaces to improve the outdoor thermal environment. At the shaded path in the group of wooden storehouses on 1000 W/m 2 global solar radiation, the UV Index reduction was -5.4. This large UV Index reduction at the shaded path can be because the storehouses were built close to each other, thus blocking most direct and diffuse components of UV radiation. It has become clear that a heat island appears in the centre of the settlement with a population of about 200 people in the daytime on a clear summer day. In contrast, the heat island did not appear in the group of wooden storehouses, despite the dense construction of storehouses. This is probably because the storehouse is a low-rise wooden building with low heat capacity and because there is no energy consumption or waste heat there. It is evident that the cooling effect of the group of storehouses on the radiant environment, thermal environment and UV environment appears in the summer daytime. Based on the results of the field observations, it has been empirically shown that it is an effective environmental design method for mitigating the thermal environment in the summer daytime by composing a group of low-rise wooden buildings is concerned with taking into account their ventilation.