Impact of climate variability on optimal thickness of wall insulation: A numerical study across five cold cities using long-term numerical simulations

In cold climates, winter heat loss through building walls significantly impacts energy consumption. Several previous experiments showed that while simple steady-state methods such as the Degree-Days approach are often used for estimation, they lack accuracy in capturing transient effects. In this paper, we employ a numerical transient simulation method to evaluate heat transfer through the southern and northern wall in five cold cities over the six-month heating season. Temperature profiles and heat loss are analyzed for both uninsulated and insulated walls using glass wool with varying thicknesses. The optimal insulation thickness is determined by assessing thermal performance across different scenarios. The results will help determine how to increase energy and financial efficiency at the same time in cold climates. As a result, it was found that for the south wall, the optimum insulation thicknesses are (33, 25, 30, 32, and 26 cm), and the life cycle energy savings are (564.56, 300.12, 448.01, 516.41, and 302.38 Euros per square meter) for the cities of Ulaanbaatar, Copenhagen, Edmonton, Hokkaido, and Warsaw, respectively, while the payback time are (1.79, 2.71, 2.09, 1.92, and 2.75 years).