Costs of Modernization and Improvement in Energy Efficiency in Polish Buildings in Light of the National Building Renovation Plans

Long-term renovation strategies (LTRSs) play a central role in achieving the European Union’s objective of a climate-neutral building stock by 2050. In Poland, the challenge is particularly acute: a majority of the building stock was constructed before 1990 and does not even meet basic thermal performance standards. In view of the state of the buildings in Poland and the assumptions made about obtaining the necessary energy parameters in the coming years, it is necessary to undertake thermal modernization measures. The purpose of the paper is to assess the economic efficiency of the variants of modernization of building stock in Poland, taking into account the constraints related to improving energy efficiency. Additionally, the article also points out the problem of discrepancies resulting from climate zones that may significantly affect the final primary energy results (on average, 5–15%). In order to achieve the objectives, the paper focuses on the analysis of energy sources. According to the overall score in the analytic hierarchy process (AHP) method, the best solutions, with a global priority of 0.46, are renewable energy sources (RESs). The evaluation of selected fuel types in the 2055 perspective, using the technique for order preference by similarity to ideal solution (TOPSIS) method, indicate favorable environmental performance by sources based on electricity, i.e., air-source heat pumps, ground-source heat pumps, and electric heating, which achieved the highest relative closeness to the ideal solution. Heat pump systems can reduce energy consumption by 26–41% depending on the building and heat pump type. The final analysis in the paper concerns different options for thermal modernization of a model single-family house, taking into account different energy sources and stages of thermal modernization work. The scenario involves the simultaneous implementation of all renovation measures at an early stage, resulting in the lowest investment burden over time and the most favorable economic performance.