Implementing building retrofitting strategies to halve campus office building carbon emissions by 2035 : a case study in Hong Kong with techno-economic analysis

Abstract

Operational energy consumption contributes significantly to carbon emissions in buildings, presenting critical environmental challenges. Previous research identified three primary retrofitting approaches to mitigate carbon emissions: renewable energy generation, reducing occupant demand, and improving building system efficiency. However, few studies have integrated these strategies to evaluate energy reduction potential in office buildings located in hot-summer humid cities such as Hong Kong. This study compiled integrated retrofitting strategies from benchmarking projects, such as Leadership in Energy and Environmental Design (LEED) certified buildings, to address operational energy and carbon reduction goals in Hong Kong. The combined retrofitting strategies were adapted to address occupant needs, renewable energy generation, lighting, windows, and mechanical ventilation and air conditioning (MVAC) systems for two campus office buildings (Block M and Block Z) in Hong Kong. EnergyPlus was used to simulate energy performance, and life-cycle costs of the strategies were also analyzed. The results show that operational carbon emissions decreased by 50.1 % in Block M and 50.5 % in Block Z, aligning with Hong Kong's 2035 carbon reduction goal. Among the strategies, MVAC upgrades, particularly chiller improvements, achieved the largest energy savings, followed by LED lighting and renewable energy systems, while non-renewable building envelope upgrades contributed the least. Shallow strategies, such as increasing cooling setpoints, adopting daylight sensors, and reducing ventilation rates, provided moderate energy savings. Life-cycle cost analysis revealed that shallow retrofits and LED systems offered the shortest payback periods, followed closely by MVAC strategies. In contrast, strategies involving exterior scaffolding installations, such as windows system upgrades and building envelope integrated photovoltaics, had longer payback periods despite their significant energy consumption reductions. While most strategies achieved payback within 14 years, the window upgrade with double-silver low-e glass required 24 years due to its high initial cost. These findings can assist decision-makers and designers in selecting suitable retrofitting strategies in hot-summer humid regions.