A Study on Carbon Emission Reduction in the Entire Process of Retrofitting High-Rise Office Buildings Based on the Extraction of Typical Models

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The building sector is one of the largest contributors to carbon emissions globally, with high-rise office buildings being a major source due to their energy-intensive operations. This study aims to address the critical issue of carbon emission reductions through the retrofitting of existing high-rise office buildings, focusing on the entire life cycle of these buildings, including the embodied, operational, and demolition phases. Existing research has primarily concentrated on energy consumption and carbon emissions during the operational phase, neglecting the carbon impact of the retrofitting process itself. This research seeks to fill that gap by quantifying the carbon reduction benefits of retrofitting across all life-cycle stages. Using data from 100 high-rise office buildings in Hangzhou’s Gongshu District, five typical models were extracted based on their construction eras and architectural features. Retrofitting strategies tailored to these models were developed, and the carbon reduction benefits were calculated using the carbon emission factor method. The primary findings indicated that the shape and orientation of buildings are crucial factors influencing the carbon reduction benefits of retrofitting. Buildings oriented east–west tend to exhibit greater carbon reductions after retrofitting. During the embodied and demolition phases, retrofitting emissions remain similar for models constructed in the same era due to consistent material inputs. However, emissions vary for models from different eras, primarily due to differences in envelope materials and subsequent material consumption. High-rise office buildings constructed between 2007 and 2021 demonstrate higher overall retrofit carbon reduction rates compared to those built before 2007, despite the latter achieving greater reductions during the operational phase. The shorter remaining lifespans of pre-2007 buildings diminish their life-cycle carbon reduction advantages. Notably, complex-shaped buildings from the same era do not necessarily exhibit lower overall retrofit carbon reduction rates compared with rectangular or L-shaped buildings, with comparable reductions per unit area. This suggests that complex-shaped buildings should not be disregarded for retrofitting based solely on shape considerations. Furthermore, the remaining lifespan of a building significantly impacts its post-retrofitting carbon reduction benefits; longer lifespans result in greater benefits, and vice versa. In practical engineering applications, structural reinforcement measures can be implemented prior to retrofitting to extend a building’s structural lifespan, ultimately enhancing its carbon reduction benefits.