Roof simulation a method of detailed thermal survey in visual environment



Considering current population rate and ratio of non renewable energies in countries' annual energy diagram which lead to increase of pollutions reeked from and irreparable effects on living environment, there will be an energy and living environment crisis in close future. So there are two main approaches that should be considered in countries' future program: change of construction status in order to having decrease in energy wastage and replacing fossil fuels with renewable energies. Roof is one of the building's components that most of the time is ignored by designers. The only factor that is considered in roofs design is how to make them waterproof. Whereas building’s roof is one of the most extensive surfaces of buildings external layer which contributes directly in thermal exchanges, study of its thermal function is an important term for making appropriate solutions in decreasing building's total thermal wastage. Because of not having access to constructed models of various roof techniques in our country, computer-based simulation can be an alternative method which creates virtual environment that has specifics of chosen climate. In this way all necessary results can be obtained. Simulation software has no limitation of place or time. For cities that are not considered in software, needed data can be added later by user and then simulation and its results can be obtained in a short time. This article is about a computer-based simulation that is done with Design Builder and RSPT software for various roof selections in Tehran climate. RSPT is software that is designed for a book of Roof Cooling Techniques and Design Builder has a simulation motor as same as Energy Plus but simulation in this software can be done in a visual environment that is more user friendly than Energy plus. Its results are available both in numeric or diagram modes. Weather data for city of Tehran exported from Meteonorm6. After including basic data for building body and city climate in software, complete and detailed results for building temperature were obtained which show detailed changes in hourly data for one year period. Results are in diagrams. Each diagram has two curves, one for outside dry bulb temperature and the other for average internal temperature. Techniques chosen for these simulations are simple roof, double shell roof, air radiator roof, roof pond and green roof (extensive and intensive) that replaced in a detached room which is 5×4 meter. In order to having a model with minimum variables, in all alternatives walls were fixed. There isn’t any air condition in models because these systems need a set point that complicates the results and covers the main effects of changes. Each roof has a specified effect on cooling or heating load. After drawing diagram of Tehran's annual average temperature and then considering it in relation to maximum and minimum boundaries of thermal comfort temperatures, it would be clear that this climate needs thermal solutions for cold months. So we can choose green roof which had a noticeable effect on heating load in Tehran's climate.