Natural Ventilation Technique of uNVeF in Urban Residential Unit Through a Case Study

The scientific technique of urban residential units with natural ventilation is a critical aspect of sustainable architecture and urban planning for enhancing indoor air quality and reducing airborne disease transmission in a built urban environment. This technique involves an urbanized Natural-Ventilation effectiveness Factor (uNVeF) combined with the regression analysis of all corresponding parameters of wind direction with its velocity, achievable air change rate per hour, openable window combination, and height of urban residential unit. Through 25 scenarios of the case study, it demonstrates and evaluates the effectiveness of natural ventilation in an urban residential unit with 13.9 m² located on the thirty-fifth floor in the Hong Kong public residential building. The results confirmed the statutory compliance with the local statutory requirement of a minimum natural ventilation rate(Practice Note for Authorized Persons, Registered Structural Engineers and Registered Geotechnical Engineers). A maximum 60.1 air change rate per hour (ACH) was measured when 75% of the opened windows, which corresponds to a uNVeF of 0.953. Notably, the fully opened windows scenario resulted in a lower natural ventilation rate due to undetermined external factors. Lower floor level can still achieve 1.5 ACH with modification of several window opening scenarios at the lowest floor. It indicated that occupants should pay attention to adjusting the window opening strategies. The achievable natural ventilation can reduce the COVID-19 infection risk by 96.1% at 35/F and 93.4% at 1/F (lowest floor) compared to the 1.5ACH baseline condition. The higher the natural ventilation rate correspond to lower the COVID-19 infection risk. These findings highlighted the uNVeF technique can optimize window opening area and the effectiveness of natural ventilation in addressing health concerns.