Priority Ranking of Energy Efficiency Renovation Measures for Existing Buildings Under Budget Constraints: A Hierarchical Decision-Making Framework Integrated with Carbon Revenue Analysis

Reducing carbon emissions while carrying out urban renewal has put existing residential buildings in the spotlight for low-carbon transformation. These buildings typically consume large amounts of energy and offer significant savings potential, making them a priority in the building sector. Addressing the challenges of limited capital, long payback periods, and inadequate comprehensive benefit assessment in building energy retrofits, this study introduces a carbon trading mechanism and develops a priority decision-making framework based on life-cycle cost–benefit analysis and net present value rate (NPVR). Five typical retrofit measures (grouped into four simulation categories), including external wall insulation, roof insulation, window replacement, lighting upgrade, and rooftop photovoltaic (PV) system, are evaluated through TRNSYS energy simulation applied to an aging residential building in Xi’an, China. The results demonstrate that lighting system upgrades and rooftop PV installation yield the highest economic returns and investment efficiency, while building envelope insulation measures, despite delivering substantial energy savings, exhibit lower NPVR due to high initial investment. Sensitivity analysis reveals that electricity price is the dominant factor influencing economic viability, whereas carbon price under current market conditions exerts limited influence on retrofit prioritization. The proposed framework provides a quantitative decision-support tool for building owners and policymakers to optimize retrofit investment strategies under budget constraints.