Due to the hot and humid climate of the southern coastal cities of Iran, radiation and airflow play a very important role in thermal comfort feeling. If the wind flow is compatible with shade, they cause more evaporation in the perspiration process and cool the body, allowing people to continue working at temperatures above the comfort zone. Therefore, the orientation of buildings in these regions should be determined simultaneously based on the optimum use of solar radiation and wind flow. This research aims to determine the best orientations of buildings, compatible with climate, in Bandar Abbas, Bushehr and Ahvaz cities, by surveying the amount of direct radiation energy received by the vertical surfaces of buildings.
To calculate the amount of direct radiation energy received by the vertical surfaces in different geographic directions, firstly, the parameters related to the solar geometry including solar hour angle, declination angle, side angle, Zenith angle, and sun altitude were extracted using computational relationships and Q-BASIC software, in different hours of the day, in studied cities. Secondly, using the “Law of cosines” computational method and Olgyay chart, the amount of per hour direct radiation energy, received by vertical surfaces in 24 geographic directions was measured through theoretical and real calculation. Thirdly, based on the minimum temperature of thermal comfort, the amount of energy received by the surfaces was calculated for hot and cold periods of the year, separately. Fourthly, the most appropriate orientations for one-sided, two-sided, and four-sided buildings were determined based on the maximum difference between the received energy in the cold and hot periods and the highest percentage of radiation received in the cold period of the year.
The amount of received energy during the hot period compared to the whole year according to the Law of Cosines and Olgyay chart methods, is respectively 80.8% and 82% in Bandar Abbas, 66.1% and 67.9% in Bushehr, and, 67.4% and 65.7%, respectively. The results indicate that the duration of hot period of the year is longer than cold period in studied cities and the highest amount of energy is obtained through the hot period, therefore it is necessary to control the absorption of solar radiation by external surfaces and to prevent the penetration of radiation into the internal spaces during the hot period in these cities. Accordingly, the best orientations for building in studied cities are determined based on the minimum amount of solar energy received during the hot period. The best orientation for one-sided buildings according to the Law of Cosines in Bandar Abbas, Bushehr and Ahwaz is 180º South and the maximum amount of received energy in the hot period is respectively 75.7%, 54.1% and 54.5%. Also, the best orientation for one-sided buildings according to Olgyay chart in Bandar Abbas is the orientations of 165º Southeast and Southwest with the maximum amount of 74.6% and in Bushehr and Ahvaz is 180º South with the maximum amount of 52% and 52.8% received energy, respectively in hot period of the year. Based on the minimum received energy during the hot period, the best orientations for two-sided buildings using the Law of Cosines and Olgyay chart in Bandar Abbas, Bushehr and Ahvaz are the North-South direction. The maximum amount of received energy during the hot period using the mentioned methods is respectively 77.3% and 77.4% in Bandar Abbas, 57% and 56.1% in Bushehr, and 57% and 56% in Ahvaz. Also, the best orientation for four-sided buildings using the Law of Cosines and Olgyay chart in the cities of Bandar Abbas, Bushehr and Ahwaz is respectively (165, -15, 75, 105) and (-165, 15, -75, 105) degrees. The maximum amount of received energy during the hot period using mentioned methods is respectively 79.8% and 81.1% in Bandar Abbas, 66% and 67.6% in Bushehr and 65.4% and 67.3% in Ahvaz.
The results show that the optimum orientations using the Law of Cosines and Olgyay chart methods, for one-sided, two-sided and four-sided buildings are the same in studied cities. In order to obtain the optimum amount of solar energy on vertical surfaces, the best orientation for one-sided buildings in Bandar Abbas, Bushehr and Ahvaz is respectively 180º South and 165º Southeast and Southwest. The best orientation for two-sided buildings in studied cities is North-South and then (165, -15) and (-165, -15) degrees. The best orientations for four-sided buildings in those cities are (165, -15, 75, -105) and (-165, 15, -75, 105) degrees then (180, 0, 90, -90) degrees.
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