The Effect of Physical Proportions on the Thermal Performance of Porches in the Historical Fabric of Shiraz Based on the Improvement of Thermal Comfort Index

Climate change is one of the most significant environmental reactions that has affected the environment and  along with increasing population, industrial expansion, and urbanization, has led to an increase in urban metabolism and changes in weather patterns. Therefore, thermal comfort, which is a satisfying thermal condition from the surrounding man-made environment, is affected by the surrounding climatic conditions. Historically, the temperature and providing thermal comfort has been one of the most important priority needs of users. In this regard, environmental compatibility, rereading and reproducing concepts in accordance with the environment have been essential. The main objectives of this research in reducing the ambient temperature are to retrieve vernacular strategies and identify the techniques that encompass the natural, cultural, traditional, and social conditions prevailing in an area. The proportions of climatic elements in the façade -the exchange of internal and external boundaries has been one of the main elements in temperature response and balance- including all physical points and vector constituents that form a space with an arch that is closed on three sides, and opened to the courtyard from the front, have shown significant effects on lowering the temperature of their surroundings. In this regard, four porches with four geographical directions (north, south, east and west) in the three houses (with historical antiquity and influential climatic elements like: Sadr Jahromi , Forough–al-Molk and Mohandesi) of Shiraz's historical fabric were selected. In this research, quantitative approaches such as field study and collection of climate data and physical components were used along with computational simulation. The field data and experimental results obtained by devices (portable instruments in the selected buildings) such as thermo-hygrometer to record maximum and minimum ambient temperature and humidity and thermo-pyrometer to measure surface temperature on the targeted points, such as yards and porches were analyzed and validated by Envi-met (climate analysis simulator) software. Lastly, PET thermal comfort index, physiological equivalent temperature and index for determining the comfort temperature in open and semi-open spaces, were calculated using Bio-met software (the impact of all climatic factors can be evaluated by the results of this index). The research results showed that according to the difference between the average PET index of porches and yards, the porch modifier had a greater effect on this index than the yard. Therefore, variables such as the width of the porch, the area of the spatial opening in the facade, and the height of the courtyard have significant impacts according to the geographical direction. By increasing the width of the openings and the height from the surface of the yard, followed by preventing temperature reflections, including long wave infrared radiation emitted based on heat received from surrounding materials and reducing the reception of these rays and their re-emission, the temperature of the PET index decreased, and the PET temperature was in a more appropriate range in terms of thermal perception and degree of physiological pressure. Also, better temperature condition and reduced thermal stress condition were experienced in the porches.