Economic Analysis and Assessing Energy Performance of Simulation-Powered Optimal Window Type and Window to Wall Ratio for Residential Buildings in Tehran

Today, with the rapid depletion of fossil energy sources and increasing of environmental problems, supervision and management of energy consumption becomes more important. Looking at the breakdown of energy consumption by sectors, the buildings sector is seen as one of the priority areas. About 40% of energy consumption of the residential buildings in Iran is fossil fuel-derived. In recent years, housing units increased significantly in Tehran as the largest and most populous city of Iran and targeted subsidies policy is implemented and energy costs have gone up. Therefore providing solutions to reduce energy consumption in this sector is very important. Windows are one of the most important components of building thermal coating that affect the energy efficiency and environmental thermal comfort. It is obvious windows play a critical role in saving energy because about 30% of the total energy loss occurs through them. Therefore the evaluation of the optimal window type and window to wall ratio in the first phase of architectural design, plays an important role in the energy efficiency and improving the quality of indoor environment. The main objective of this paper is to present an approach that provides assistance for designers to select optimal ratio of window to wall for residential buildings concerning economic analysis that affect this assessment. In this research, a building model as a case study (the six-story apartment in the city of Tehran) is considered and then its energy consumption optimized via simulation software. Based on the simulations, two optimization parameters, window to wall ratio and type of windows, are evaluated. In this regard, at the first phase, four types of window glazing with same size in four main orientations and a window to wall ratio of 5 to 55% on residential building was simulated to determine the optimized window to wall ratio through evaluating of energy consumption. At the next step, optimized windows in three directions was considered on building model for simulations of energy consumption and then optimized windows in terms of energy efficiency was identified. Finally, for economic analysis of the use of optimal windows, a newly designed building that uses the optimal window is economically compared to a house that is architecturally and structurally similar to existing buildings and has more energy consumption. The energy costs, payback period and internal rate of return of these two buildings are compared to find the economical differences. The results show that energy consumption of residential buildings in Tehran reduced up to 20/3% only by using high performance windows and optimum wall to window ratio. It can be concluded that the influence and sensitivity of window-wall ratio on the total energy consumption are related to the orientation of outside window, and the glazing types of window. The window orientations could be prioritized in the following order: south, east, west, and north. Also according to the current price of fuel in Iran and the 17/8 years payback period that Obtained from economic analysis, the additional initial cost will be offset by the proposed policies.