Optimum insulation thickness design of exterior walls and overhauling cost to enhance the energy efficiency of Albanian's buildings stock

Abstract

In the present climate, thermal insulation is crucial for reducing energy consumption for heating or cooling in buildings, increasing the lifespan of structures, and building elements, and improving human comfort. The wall's composition layer has advanced regularly since the building regulations and established norms. However, calculation methods have remained quite the same, governed by Fourier's law. Therefore, to address this gap, a linearization process, and a correction factor of the optimized insulation thickness for four different insulation materials (i.e., EPS Graphite, EPS, GW, and RW) and five energy carriers (i.e., electricity, diesel, natural gas, liquefied petroleum gas, and biomass) by removing the boundaries of heating degree days by using Mathcad software is proposed. Other financial parameters (i.e., inflation rate, interest rate, lifespan, and present worth factor) and heating system features that lead to the optimized insulation thickness are considered. The RETScreen Expert model was coupled with a Mathcad script to compute a standardized corrected optimized insulation thickness (COIT) value by applying sensitivity analyses at ±35% of the most influencing parameters to calculate the total overhauling cost for different building types in Albania. A correction of the existing window's heat transfer coefficient for a different glass-to-wall ratio is proposed. Our findings suggest that the overall heat transfer value (U) should be equal to or less than 0.30 (W/m2•K), leading to a range of corrected optimized insulation thickness (COIT) from 0.03 m up to 0.11 m. Moreover, results exhibited encouraging economic and environmental values concerning the unrenovated buildings leading to annual net savings of 23.50–84.50 €/m2, CO2 reduction up to 39.10 kgCO2/m2, and a simple payback period (SPP) of 0.30 maximum up to 1.20 years. The outputs of this study can bring benefits in terms of reduced energy consumption and CO2 footprint, and the proposed COIT value can be applied not only in Albania but in other regions that exhibit similar climate conditions.