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日本語

Currently, countermeasures for UHI mitigation have been implemented widely. It has also been reported that the solar reflectivities of a building’s exterior wall surface and pavement act as important indexes affecting the air-conditioning requirements for buildings in terms of energy use. Rooftops covered with diffuse highly reflective (DHR) materials (i.e., highly reflective paints) can reflect solar radiation to the sky so long as there are no higher buildings around. However, if there are taller buildings nearby, much of this radiation ends up being reflected onto neighboring buildings and roads. This heat is absorbed by the neighboring buildings and roads, thus aggravating the UHI phenomenon. To solve this problem in applying DHR materials to building facades, RR materials have been recommended to replace DHR materials to mitigate the UHI phenomenon and reduce the energy consumption of buildings.

However, RR materials are still in the research stage and have not yet been used in practice. Before RR materials can be applied to building envelopes in practice, more theoretical work urgently needs to be done to predict the reflection directional characteristics of RR materials. Up to now, optical experiments have been the main method adopted to evaluate the reflection directional characteristics of RR materials, but it has proved difficult to achieve accurate model predictions.

Thus, a joint research team led by Assistant Professor Jihui Yuan at the Dept. of Architecture and Civil Engineering of Toyohashi University of Technology, in collaboration with Osaka City University, has proposed two analytical models to potentially evaluate the reflection directional characteristics of three RR samples determined by their research team, then comparing the prediction results of the two analytical models to that of the optical experiment in the research. The results of this research were published in the Elsevier journal "Energy & Buildings" on September 15, 2020.

This research mainly consists of three parts; the first is the production of RR samples, the second is the optical measurement of RR samples, and the third is the proposal of analytical models based on optical measurement data.

In this study, two analytical models were introduced to evaluate the reflection directional characteristics of RR materials. To propose an appropriate model to evaluate the reflection directional characteristics of RR materials, the angular distribution of reflection intensity evaluated by two analytical models for three types of RR plates were compared. It was shown that applying the AND model to evaluate the angular distribution of reflection intensity for RR materials achieved more favorable results than in the original analytical model.

Future work should endeavor to improve the evaluation accuracy of analytical models, focusing on proposing other models to possibly evaluate the reflection directional characteristics of RR materials, such as using the artificial neural network (ANN) methodology. Moreover, forthcoming work will also aim to develop three-dimensional optical systems to continue this research, by proposing a three-dimensional model for evaluating the three-dimensional reflective directional performance of RR materials.

This study was supported by Osaka City University and the UNITIKA Corporation of Japan. The author is sincerely grateful to the UNITIKA Corporation of Japan for providing the glass beads used to create the RR samples, and Osaka City University for providing the optical apparatus.