Bridging financial and environmental payback gaps: a life cycle-based retrofit framework for net-positive university campus buildings

Decarbonization of existing educational building stock is critical for meeting global climate mitigation targets. However, the misalignment between financial feasibility and environmental urgency often hinders deep renovation projects. This study develops a comprehensive retrofit implementation framework that integrates dynamic energy performance analysis with Life Cycle Assessment (LCA) to resolve this conflict. Utilizing a representative faculty building in a mild-continental climate (Cfb) as a case study, the research evaluates a phased ‘inverted pyramid’ retrofit strategy. Unlike traditional validation methods reliant on variable utility bills, this study employs a standard-based ‘Asset Rating’ methodology compliant with national (TS 825) and international (ASHRAE 90.1) protocols to ensure the reproducibility of the proposed strategies. Simulation results indicate that a coordinated strategy—combining envelope thermal upgrades with heat pump electrification—reduces Energy Use Intensity (EUI) by 50.3% (from 1269 to 630 MJ/m2). The subsequent integration of a 464 kWp photovoltaic system transforms the facility into a Net-Positive asset, exporting an 87 MWh surplus annually. A novel contribution of this research is the quantitative exposure of the ‘Payback Gap’: while the retrofit yields a Financial Payback Period of 7.1 years (under conservative fiscal scenarios), the Carbon Payback Period is validated at approximately 0.8 years. Sensitivity analysis further confirms that while financial ROI is susceptible to market volatility (±20%), the environmental benefit remains robust. Consequently, the study provides an evidence-based roadmap for policymakers, validating the necessity of prioritizing Carbon ROI alongside traditional cost metrics to accelerate the transition to climate neutrality.