Architectural uses of plants in a residential area and the effects on the thermal environment

It is well known that plants play an important role in the formation of the environment in a residential area, for instances psychological effects and functions of climate control. However, it seems to be a fact that there are few examples of design plans which are taken those effects into good considerations. The aim of this study is to show the materials for understanding of plants' effects on thermal environment in designing a residential area or house, and to make clear the situation of the space with plants in built environments. I. 29 sites with and without plants were selected as test points for the measurements by using the outdoor thermal environmental meter and other ones. The actual conditions of the thermal environment on clear days in the summer time were investigated. The situation of the surroundings of each test site is understood by computing shape factors of trees, grass, buildings and the sky to the measurement point. II. Based on the measured results, principal component analysis was carried out for the measurement points. Descriptive variables are temperatures at the centers of the three globes, air temperature and wind speed in the day time and at dusk. According to the result of the above analysis, we obtained principal component axes which can be interpreted as “effect of sunshine”, “degree of reradiation feeling” and “wind speed”. The relationship between characteristics of thermal radiation environment and shape situation was examined by plotting principal component scores of every test point on the principal component axes of “effect of sunshine” and “degree of reradiation feeling”. Therefore, the situation of plants in the thermal environment outside buildings was clarified. The findings are as follows: i) The sites with plants are the ones where negative thermal radiation feelings is strong whether they are sunny or not, except for the sites which are surrounded by the materials with high heat capacity and not exposed to the sky like underground passages. This explains the effectiveness of plants on creating a cooler thermal environment in summer. ii) The thermal environment of the space in the shadow of trees dose not influenced by weather, and changes little from the day to the evening. III. Air temperature, total solar radiation, mean radiant temperature and wind speed－the main factors of the thermal environment under the row of trees and in a garden with lawns and on an asphalt parking lot were obtained from the measured values of the outdoor thermal environmental meter. The characteristics of planted space were clarified by explaining the findings of II. with those thermal factors.