Acta Geographica Sinica ›› 1999, Vol. 66 ›› Issue (1): 83-89.doi: 10.11821/xb199901010

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EQUIVALENT SOLAR RADIATION AZIMUTH AND THE SELECTION OF THE DIRECTIONOF BUILDING EXPOSURE

Sun Hanqun, Fu Baopu   

  1. 1. Department Geographic Education, Jiangsu Institute of Education, Nanjing 210013;
    2. Department of Atmospheric Science, Nanjing University, Naning 210008
  • Received:1997-10-11 Revised:1998-08-26 Online:1999-01-15 Published:1999-01-15

Abstract: The sunrise and sunset hour angles on a slope are determined by considering the sun’s horizontal hour angles and the non horizontal hour angles of the slope. Such coordinated relationship varies with latitude φ, slope angle α, slope azimuth β, and solar declination δ . When latitude φ and slope azimuth β meet the condition of |sin β |cos φ >sin23 45°, the coordination of sunrise and sunset hour angles has only one form for any solar declination δ . But when |sin β |cosφ≤sin 23 45°, the coordination will vary with slope azimuth β . For any given solar declination δ and latitude φ, there are two slope azimuths β1 and β2 (where | β1 |=arcsin(sin δ /cos φ ), | β2 |=π-| β1 |). Between β1 and β2 and beyond β1 and β2, the coordination relationships are different. This detailed study provides a way to determine the concrete form of coordination for any slope azimuth. Based on the coordination of sunrise and sunset hour angles on a slope, we deduce a series of formulas that are used to calculate the daily duration of sunshine and the daily extraterrestrial solar radiation on the wall surface. From the results of calculation, we obtain the distribution of daily duration of sunshine and daily extraterrestrial solar radiation with slope azimuth. We find that there is a pair of slope azimuths, where the daily duration of sunshine in summer half of the year is equal to that in the winter half when the absolute values of solar declination are equal. These slope azimuths are called “equivalent duration of sunshine azimuth (EDSA)”. There is also a pair of slope azimuths where the daily extraterrestrial solar radiation in the summer half is equal to that in the winter half at the same time. These slope azimuths are called “equivalent insulation azimuth (EIA)”. Together, EDSA and EIA are called “equivalent solar radiation azimuth (ESRA)”. ESRA is a function of latitude (only. The value of EDSA can be expressed as | β |=arccos(tg φ ). The value of EIA can be expressed as | β |=arctg(cos2φ /sin φ · Yφ ), where Yφ is a solution of the equation y +tg2 φ ·tg y =0.

Key words: wall surface, equivalent solar radiation azimuths, building exposure

CLC Number: 

  • TU113.3