Relation between Density of Buildings and Absorptivity of the Earth for Solar Radiation in Urban Regions : Part 2-Absorption of Sky Radiation by Spaces composed of Regularly laid out Rectangular Parallelpipeds with Square Horizontal Cross Sections

NAITO Kazuo, MIZUNO Minoru

doi:10.18948/shase.2.5_33

Bibliographic Information

Other Title

都市域における建物密度と日射の吸収率の関係 : 第2報-水平断面が正方形の直方体群からなる凹凸面の拡散性放射に対する吸収率
都市域における建物密度と日射の吸収率の関係-2-水平断面が正方形の直方体群からなる凹凸面の拡散性放射に対する吸収率
トシイキニオケルタテモノミツドトニッシャノキュウシュウリツノ

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Description

It is well known that the rough surfaces absorb more incident radiative energy than the smooth surfaces. In urban regions the surface of the earth is rough due to buildings built on it. Therefore it is expected that in the urban regions the surface of the earth has special absorption properties for solar radiation. It is thought that this speciality of the absorption properties influences on the urban climate. In this paper the absorption properties of the rough surface in the urban regions for solar radiation are discussed. A simple model of the surface of the earth in the urban regions is used to simplify the calculations. The model is the surface on which rectangular parallelpipeds with square horizontal cross sections are laid out regularly at right angles. The absorption properties of the spaces made up of the parallelpipeds decide the properties of the model rough surface. The spaces are called three dimensional cavities for convenience sake. Absorption of sky radiation by the three dimensional cavities is calculated. In the calculation it is assumed that all surface elements of the cavities are gray and have a same absorptivity, a_e, for radiation. The absorptivities of the three dimensional cavities are determined by a_e and the geometries of the cavities, namely, the height of the rectangular parallelpipeds, H, and the transverse and longitudinal intervals between two adjacent parallelpipeds, B and C, when a side of the square cross section is set equal to unity. The calculated absorption properties are compared with those of the two dimensional cavities previously reported by authors. The main conclusions obtained in this paper are as follows: 1) The three dimensional cavities and the two dimensional ones have similar absorption properties. 2) When B=C and H/B remains constant, the absorptivity of the two dimensional cavity is greater than those of the three dimensional ones. 3) When B=C, there is a value of B/C which makes the absorpitivity maximum. The value of B/C is about 0.2. 4) When building to land ratio, namely, 1/(1+B+C+BC), and H are keeped constant, the three dimensional cavities with B=C have the maximum absorptivities and the two dimensional ones (C=0) have the minimum.

Journal

Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan

Transactions of the Society of Heating,Air-conditioning and Sanitary Engineers of Japan 2 (5), 33-42, 1977

The Society of Heating, Air-Conditioning & Sanitary Engineers of Japan