DEVELOPMENT OF A METHOD FOR ESTIMATIING RADIANT TEMPERATURE AND RADIANT EXERGY WITHIN OUTDOOR SPACE

Abstract

 This paper describes a method for estimating radiant temperature and its associated with radiant exergy within outdoor space, which is one of the key factors in micro-climatic design of park space in summer.
 Measurements of outdoor air temperature (T_o) and humidity, wind velocity (V_a), globe temperature (T_g) and surface temperature (T_ei) were carried out for one day during daytime of a hot summer day in August, 2015 at Sapporo Art Park. The radiant exergies emitted from outdoor ground, buildings, trees, grassy plane, water surface of the pond and sky, were evaluated for quantifying the radiant environmental characteristics outdoors. The globe temperatures measured were compared with those obtained theoretically using solar radiation (I), long-wavelength mean radiant temperature (T_mr-photo) taken from infra-red thermal image camera, T_o and V_a. On the basis of the measured results together with the theoretical investigation, we discussed the “coolness” to be available from park space.
 In the open space at Sapporo on 1st day August, which was sunny with patchy clouds, the T_ei of concrete pavement (CP) of plaza at the point S1, and S5, ranged from 43 to 50 °C. At the point S1 and S5, whose form factor (f_i) of CP were larger than 0.3, the rate of warm radiant exergy (WX) were larger than 900 mW/m² during daytime, those were much larger than the rate of cool radiant exergy (CX). This contributes to T_mr-photo being 1 to 3 °C higher than T_o. The WX caused by the absorption of short-wave length radiation at points in shadow at the plaza reached the peak 1.5 to 3 hours later after the peak of the MRT ranged from 50 to 60 °C due to direct I directly incident on the globe. This peak contributes to raising T_mr-photo and T_o by the addition of reflected I from the CP so that MRT remains higher than 40 °C even in shaded space.
 We confirmed the validity of MRT and T_g measured by small gray-colored ball by comparing with that calculated. The CX emitted from the sky can contribute to increase the emergence of “coolness” within the open space. We have confirmed, through this series of measurement and calculation, that the MRT and T_g in outdoor space where we are exposed directly to I and or where even in shaded areas the WX and T_mr-photo are high resulted by the surface of CP whose f_i is higher than 0.3. Provided that a pond is or grassy plane are arranged, and trees are planted so that their canopies cast their shadows over the CP, this would result in decreasing the surface temperature and reflected solar radiation, and thereby the “coolness” may emerge with in the park space.