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Since occupants spend most of their time indoors, an energy-saving and comfortable indoor environment are particularly important. The differences in the metabolic rate of occupants make them have different requirements for their thermal environment. To save energy under the comprehensive needs of occupants for thermal environment, the combinatorial optimization strategy based on NSGA-II and improved the TOPSIS method is proposed in this study. Firstly, the physical model of the CFD simulation is verified by experiments. Secondly, the specific operation cases corresponding to combinations of different levels of factors are determined via the RSM method, and the ventilation performance prediction model considering the metabolic rate differences and outdoor weather changes is established. Thirdly, supply air velocities and temperatures are optimized by using Pareto-based NSGA-II; the Pareto optimal solution set under different outdoor temperatures is obtained. Finally, based on the Pareto optimal solutions at different outdoor temperatures, the optimal strategy under dynamic outdoor air temperature is obtained by improved TOPSIS by the CRITIC method. The optimization of ventilation parameters significantly improved the ventilation performance, and the results show that the predicted mean vote, energy consumption, vertical air temperature difference between head and ankle levels and the local mean age of air for different metabolic rates decrease by 64.1%, 4.74%, 24.83% and 7.39% on average, respectively. Moreover, the relative energy saving rate increases as the metabolic rate increases, and the strategy facilitates adaptation to outdoor weather changes and meets the individual needs of occupants for the indoor environment. This has important implications for achieving the global goal of energy efficiency and emission reduction. Full article

During the normalization phase of the COVID-19 epidemic, society has gradually reverted to using building space, especially for public buildings, e.g., offices. Prevention of airborne pollutants has emerged as a major challenge. Ventilation strategies can contribute to mitigating the spread of airborne disease in an indoor environment, including increasing supply air rate, modifying ventilation mode, etc. The larger ventilation rate can inevitably lead to high energy consumption, which may be also ineffective in reducing infection risk. As a critical factor affecting the spread of viral contaminant, the potential of ventilation modes for control of COVID-19 should be explored. This study compared several ventilation strategies in the office, including mixing ventilation (MV), zone ventilation (ZV), stratum ventilation (SV) and displacement ventilation (DV), through analyzing ventilation performance and infection risk for the optimal one. By using ANSYS Fluent, the distributions of airflow and pollutant were simulated under various ventilation modes and infected occupants. The SV showed greater performance in mitigating infection disease spread than MV, ZV and DV, with an air distribution performance index (ADPI) of 90.5% and minimum infection risk of 13%. This work can provide a reference for development of ventilation strategies in public space oriented the prevention of COVID-19. Full article

The analysis of ventilation strategies is fundamentally affected by regional climate conditions and local cost databases, in terms of energy consumption, CO₂ emission and cost-effective analysis. A systematic approach is covered in this paper to estimate a local economic and environmental impact on a medium-sized space located in two regions during supply-and-installation and operation phases. Three ventilation strategies, including mixing ventilation (MV), displacement ventilation (DV) and stratum ventilation (SV) were applied to medium-sized air-conditioned space with this approach. The trend of the results for three ventilation systems in the life cycle assessment (LCA) and life cycle cost (LCC) analysis is SV < DV < MV. The result of CO₂ emission and regional LCC shows that SV is the lowest one in both regional studies. In comparison with the Hong Kong Special Administrative Region (HKSAR) during 20 Service years, the case analysis demonstrates that the percentage differences in LCC analysis of MV, DV & SV in Guangdong are less than 20.5%, 19.4% and 18.82% respectively. Their CO₂ emission of MV, DV and SV in Guangdong are more than HKSAR in 10.69%, 11.22% and 12.05%, respectively. The present study could provide information about regional effects in the LCA and LCC analysis of three ventilation strategies emissions, and thereby help set up models for decision-making on high efficiency and cost-effective ventilation strategy plans. Full article