Abstract :
This study examines the effect of geometrical indices of a street (Orientation and H/W) on the buildings` direct solar access on an urban scale, which its results can be used by urban planners in designing new neighbourhoods and redeveloping old ones in developing cities. In cold climates, the access of buildings to sunlight due to the street geometry index is necessary to reduce the heating load and affects the thermal performance of buildings. This index (height to width ratio (H/W) and orientation) directly affects the absorption and emission of urban sunlight and changes in them can affect the amount of solar radiation absorption of the building.This study aims to investigate the amount of the buildings` solar has gained in the cold climate of Hamedan. The research method is quantitative and based on numerical data of simulating solar radiation and the geometry of the urban texture of Hamedan. Data analysis was conducted by statistical analysis of box diagram, correlation coefficient, and reference model. First, to examine the effect of street width index, fixed height, and variable street width (6 to 36 meters) and then to examine the height index, fixed street width and variable height (3 to 9 floors) were considered in the modelling. The findings reveal that east-west oriented buildings have the highest solar gain of 17.9% in the winter, and nearly 60% of the streets in the new urban texture of Hamedan are placed in the non-optimal orientation.The average solar gain in northern blocks is more than in southern blocks and streets; with a lower H/W index this gain increases indicating a reverse and intensive correlation. Index H/W compared to orientation has the greatest effect on a solar gain on the building located alongside streets. In shallow geometrical valleys, the temperature from radiation is higher than in deep valleys and as the H/W index rises, i.e., as the street becomes narrower, the direct solar gain decreases. In southern blocks, due to a deep valley in the yard, most of the south façade of a building in the winter is always in the shade of building volumes and absorbs little solar radiation. In this state, the greatest amount of absorption is reflective and scattered. Therefore, increasing the depth of the yard in these blocks to absorb more sunlight was studied in our recommended pattern. From the measured indices in this study, the H/W index has the greatest impact on solar gain for buildings located alongside streets. This index has a 123% higher influence compared to the orientation index on absorbing radiation and is of more importance. In Hamedan, regarding the H/W index, a twelve-meter street has the least absorption, thirty-five-meter, and seventy-five-meter streets have the most absorption in the winter. In our recommended patter, increasing the depth of the yard and using vertical shades for windows leads to a 2.7% and 25.8% rise in solar gain for northern and southern blocks, respectively. This pattern reduces 11.7% and 4.94% of absorption for the mentioned blocks in the summer.
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