Iranian Association of Chemical Engineering (IAChE) Iranian Journal of Chemical Engineering (IJChE) 1735-5397 Articles in Press 2026 07 06 Thermal Performance Optimization of Double-Glazed Window Systems Using Response Surface Methodology: A Case Study of a High-Rise Office Building 57 76 246798 10.22034/ijche.2026.581564.1593 EN Arian Kavoosi Faculty of Engineering, School of Art and Architecture, Razi University, Kermanshah, Iran Allahbakhsh Kavoosi Faculty of Engineering, School of Art and Architecture, Razi University, Kermanshah, Iran 0000-0001-6840-8983 Journal Article 2026 05 13 This study investigates the thermal performance optimization of double-glazed window systems in Tehran climate conditions with the aim of minimizing building energy consumption. Four key design parameters were considered, including glass thickness (2, 4, 6, and 8 mm), glass type (ordinary, reflective, spectrally-selective, and blue-tinted glass), air-gap thickness between glazing layers (3, 6, 8, and 13 mm), and the type of filling gas (air, argon, krypton, and xenon). The modeling and optimization process was carried out using Response Surface Methodology (RSM) in Design-Expert software. The results demonstrated that increasing the air-gap thickness between the glazing layers significantly reduced the building energy consumption. Similarly, increasing the glass thickness improved the thermal insulation performance and decreased energy usage. Among the investigated gases, xenon exhibited the best thermal performance and resulted in the lowest energy consumption. In addition, reflective glass showed superior performance compared with the other glass types in terms of reducing energy demand. The optimization results indicated that the optimum configuration for achieving minimum energy consumption consists of reflective glass, xenon gas filling, an air-gap thickness of 12.75 mm, and a glass thickness of 2.825 mm. Under these optimal conditions, the minimum building energy consumption was obtained as 161.46 kWh/m². The findings of this study provide useful insights for the design and optimization of energy-efficient double-glazed window systems in a high-rise office building located in climates similar to Tehran.