Jalil Shaeri; Roza Vakilinezhad; Mahmood Yaghoubi
Abstract
In the last decades, increasing world population and carbon dioxide emission, have led to the increasing importance of energy conservation, especially in the building industry. In Iran, ...
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In the last decades, increasing world population and carbon dioxide emission, have led to the increasing importance of energy conservation, especially in the building industry. In Iran, almost 40 percent of energy is used in the buildings, where the main part of it is wasted through windows. Hence, reducing the amount of heat transfer and insulating the windows is essential. In recent years, glass technology has offered various alternatives for building energy conservation, including window insulation, transparent covering films and integrated dynamic shadings. Multi- pane windows with various glass layers are one of the solutions to control solar heat, sunlight transmission and noise through windows. They are used in combination with shading devices, especially in office buildings. Studies have shown that using multi-pane windows, heat transfer and building energy consumption decrease depending on the different climates and building thermal properties. However, the impact of different types of filling gases and the optimal window type on building energy consumption in different climates has not been studied. In the present study, the effect of double- and triple-glazed windows containing different gases on the cooling and heating loads of a sample office building are investigated. Altering window layers, its thermal properties will change, including heat transfer coefficient, visible transfer rate, the amount of direct sunlight transmission and solar heat transfer coefficient. The Air, Argon, Krypton, Xenon gases and the mixture of them are used for the gap filling between two or three layers of clear glass. The case studies are Bushehr and Bandar Abbas cities with hot-humid climate, Mashhad and Tabriz cities with cold climate and Shiraz, Yazd, Isfahan and Tehran cities with hot-dry climate. In each city, eleven alternatives have been simulated for a typical office building by changing window type and the intermediate gas. The simulations were performed using Design Builder software version 5.02.003 to calculate annual cooling and heating loads for the sample building. Windows in the base model are simple windows with clear glass of three millimeters thickness. According to ASHRIE standard, the heating and cooling set points of 22 °C and 24 °C are considered in the simulations. Comparing total building energy consumption with different types of windows and gases, the proper alternatives are defined. In order to validate the results, DOE-2 simulation software has been used. The building energy consumption in Bushehr City has been examined for the eleven alternatives. Since the difference between two groups of the results is 4 percent, all the results are valid. Based on the results, applying double- and triple-pane windows leads to reduced cooling and heating loads of the sample office building in all studied cities. In Bushehr City, using triple pane windows will result in 12.7 percent reduction in the building cooling load while it would be 10.8 percent by applying double-pane windows. The reduction in building cooling load would be 27.5, 25.6 and 17.3 percent in Tabriz, Mashhad and Shiraz cities if triple-pane windows were used. Using double-pane windows, the cooling load reduction would be 14.6 to 17.3 percent in cities with hot-dry climates and 11.9 percent in Bandar Abbas City. According to the total building energy consumption, the triple-pane window filled with air and Xenon gas is the most appropriate window type in all cases. Using such a type of windows will lead to 14.5, 13.5, 34.2 and 38.2 percent reduction in building energy consumption in Bushehr, Bandar Abbas, Tabriz and Mashhad, respectively. So in cities with hot-dry climate, the application of triple-pane windows filled with air and Xenon gas would reduce the building energy consumption by the average of 22.8 percent. Unlike triple-pane windows, the appropriate alternative among double-pane windows is different in each city. In Bushehr City, double-pane window filled with air and argon gas has the most building load reduction. It is also one of the best choices in Mashhad, Shiraz, Yazd, Isfahan and Tehran cities, however the building energy consumption is best reduced using other alternatives filled with argon or krypton gases. By applying such double-pane windows, the amounts of energy reduction in each city equal to 24.7, 15, 15, 17.8 and 16.3 percent for Mashhad, Shiraz, Yazd, Isfahan and Tehran cities, respectively. In Bandar Abbas and Tabriz cities, the most proper windows are those filled with krypton and xenon with 10.8 and 23.3 percent energy reduction. The results of the present study help designers to select the best double- and triple-glazed windows for office buildings in each city.
