A study on the payback period of building energy consumption optimization in different situations

Buildings are the main pillars of social and economic development of countries and they consume a huge amount of energy and natural resources. This energy consumption is 30 − 50% on average. The present study aims to investigate the effect of the locations of buildings around neighboring buildings and pathways on the payback period of optimization. The research scope includes common residential apartments in Tehran. According to the research method, we consider 6 similar residential blocks in different lighting situations. Using simulation in Design Builder software, we calculate their energy consumption and then optimize their energy consumption. The optimization variables are as follows: the material of the outer wall (clay or LECA) and the fa¸cade (stone or brick), the type of window glass (plain or low-emissivity), the type of gas between the layers of the window glass (air or argon), and the ratio of the window to the surface of various directions the building. The optimization goals include the minimization of energy consumption and construction cost. Design Builder software and genetic algorithm are used to optimize the variables. After optimization, the 6 selected optimized blocks are then calculated in the simulation software and their energy consumption is calculated and compared with the results before optimization. The research results indicate that the mean reduction in energy consumption is 77% in the northern blocks, 65.2% in the southern blocks, and 71% in all blocks, and the optimization results in the northern blocks are about 12% better than the southern blocks. Given the proposed optimization changes, we calculate and compare the increase in the construction cost of each block. The results indicate that the mean increase in the construction cost is 1.6% in the northern blocks, 2.7% in the southern blocks, and 2.2% in all blocks, and the increase in the costs of building northern blocks is about 1.1% less than southern blocks. According to the prices of electricity and gas in Iran, we measure the annual energy cost saving and the results indicate that the payback period of optimization is about 7.7 years in the northern blocks, 13.8 years in the southern blocks, and 10.8 years in average, and the calculations indicate that if the mean global energy prices prevail in Iran, this time reduces to 6 months.