Calculation of Optimum Insulation Thickness Using the Heating Degree-Days Method for the Different Cost Approaches

In this study, the optimum insulation thickness to be applied to external walls was determined by using the heating degree days method for the different cost approaches. Calculations were made for a sample city in Turkey and extruded polystyrene (XPS) was used as an insulation material. By applying the simple payback method and life-cycle cost analysis, optimum insulation thickness, saving amount and payback period were calculated according to increased insulation thickness. As a result, the optimum insulation thickness was determined as 0.0689 m and 0.0558 m for simple payback method and life-cycle cost analysis, respectively. For the determined insulation thicknesses, the payback periods were varied between 7.09 and 9.23 years. Also, at the optimum insulation thickness, the saving amount was obtained between 20.35 USD/m² and 35.58 USD/m² depending on the cost analyses.