Energy, Environmental, and Economic Assessment of a Deep Energy Retrofit in a Greek School Building

School buildings are characterized as energy-intensive buildings, while indoor thermal comfort and air quality remain inadequate. This study addresses the fragmented assessment of school building renovations by integrating energy performance, indoor thermal comfort, and life-cycle environmental and economic impacts into a unified evaluation framework. Multiple energy, environmental, and economic indicators are calculated to enable a multidimensional evaluation of alternative renovation strategies. Emphasis is placed on the school’s potential role as an active prosumer within a renewable energy community and the identification of trade-offs between environmental benefits and economic feasibility. For this purpose, a school building located in Kifissia, Greece, is investigated using two in-house developed tools: T-DEOS, an energy simulation tool, and VERIFY, a life-cycle environmental and economic assessment tool. To identify the most efficient renovation strategy, four holistic strategies that involve multiple passive building envelope technologies, highly efficient energy systems, and renewable energy systems are examined, whereas the building is considered to participate in a local renewable energy community. According to the analysis, the optimum renovation strategy is calculated to result in more than 79% energy savings for heating and a 7.09% enhancement of indoor thermal comfort conditions during the school’s occupied hours. The electrification of the building energy systems along with rooftop PV electricity generation results in a self-sufficiency rate of approximately 52% and a self-consumption rate of almost 19%. Finally, the optimum scenario results in a 95% decrease in annual operational expenses compared to the existing school state.