Qingyan Chen

To achieve building carbon neutrality by 2050, the Hong Kong government has set a 30-40% electricity saving target for commercial buildings. Although energy retrofitting is recognized as a key pathway to this target, it remains uncertain whether, and which, existing strategies can successfully achieve it. To address this gap, this study proposed a techno-economic assessment framework to explore suitable retrofitting strategies based on large-scale building simulation. A total of 10,000 EnergyPlus-based commercial office building models were generated. Eight commonly used retrofitting strategies were then evaluated using these models. The results identified high-efficiency chillers, LED lighting, and increased cooling temperature setpoints as the most effective strategies, delivering average electricity savings of around 30.3% for Hong Kong office buildings. However, a considerable portion of the buildings were found unable to achieve a saving rate above 30%. To reveal the underlying reasons, this framework employed XGBoost and SHAP analysis to identify the crucial building characteristics that affected the energy saving rate. The framework identified the chiller COP, cooling temperature setpoint, and HVAC type as the three most important characteristics. Further analysis indicated that most office buildings with air-cooled chillers achieved the 30-40% electricity saving target. In contrast, office buildings with water-cooled chillers met this target only when equipped with variable air volume boxes and using low cooling temperature setpoints. This study provides a comprehensive guideline for energy retrofitting in commercial office buildings in Hong Kong, contributing to the achievement of building carbon neutrality by 2050.

Contaminant transport and flow distribution are very important during an elevator ride, as the reduced social distancing may increase the infection rate of airborne diseases such as COVID-19. This investigation used a computational fluid dynamics (CFD) model based on the RNG k–ϵ turbulence model to predict airflow and particle transport in an elevator-lobby area with moving passengers. The CFD results showed a complex airflow pattern due to the downwash air supply from the ceiling and the upward thermal plumes generated by passengers. This investigation studied different respiratory activities of the index patient, i.e., breathing, coughing with and without a mask, and speaking. The results quantitatively compare the risk of infection among different respiratory activities. During an elevator ride, the infection risk was generally low because of the short duration. However, if the index patient talked in an elevator, the infection risk would be relatively high, as two passengers in the closest proximity to distance would be infected.

Yixuan Wang, Qingyan Chen, Duygu Ataman. Proceedings of the 4th Workshop on Evaluation and Comparison of NLP Systems. 2023.