Optimum Form, Aspect Ratio and Orientation of Building Based on Solar Energy Receiving in Hot-Dry Climate; Case Studies of Isfahan, Semnan, Kashan and Kerman Cities, Iran

The form, size and orientation of the building are the most important effective parameters on internal climate and have direct effect on thermal performance of the building. The aim of this research is to investigate the amount of received radiation energy of vertical surfaces in buildings and to determine the appropriate form, aspect ratio and orientation of building in accordance with the hot-dry climate in the cities of Isfahan, Semnan, Kashan and Kerman. In this research, six polygonal forms, including square, rectangle with North-South and East-West orientation, hexagonal, octagonal, hexadecagon, and triacontadigon (circle) were studied. All the investigated forms had the same floor area and height, oriented to the South. The aspect ratios of the rectangular form were 1:1.2, 1:1.4, 1:1.6, 1:1.8, 1:2, and the orientation of the optimum aspect ratios were 180º, 165º, 150º, 135º, 120º, 105º SE and SW. Using the “Law of Cosines” computational method, the amount of received radiation energy on vertical surfaces was calculated, for different months and in 32 geographic directions, in terms of the cold and hot periods of the year. The results show that the best forms of the buildings in Isfahan, Semnan, Kashan and Kerman cities is the rectangle with East-West orientation. The most suitable aspect ratio for the EW rectangular form in studied cities is 1:1.6 and the best orientation for the determined aspect ratio is 180º south.