Carbon dioxide concentration levels and ventilation rates of naturally ventilated university classrooms in the hot summer and cold winter area of China

Abstract

Poor indoor air quality has been shown to bring a negative influence to students’ learning performance and human health. Most college students in China spend more than 10 hours each day having lessons and studying in classrooms of teaching buildings, which originally designed to be mechanically ventilated with ceiling fans. Unlike in the northern China, there is no heating system for classrooms during winter in many cities of hot summer and cold winter area. Recently wall-mounted split units without fresh air introduction were installed just in some classrooms to provide air conditioning. Thus all the doors and windows of classrooms are closed when being occupied in winter to compromise thermal comfort. Complaints about poor IAQ are very common in university classrooms. Reasons for high levels of CO2 concentrations are dense opulation and inadequate ventilation, in some cases of which can beblamed on the building design. Investigation of IAQ and ventilation performance in classrooms of this area would provide valuable information for future teaching building design and natural ventilation utilization in universities. In this field study CO2 concentration were monitored in classrooms of a typical teaching building in Nanjing city, and then ventilation rates were estimated. The findings show that these classrooms have lower average CO2 concentration levels (981 ppm) in May compared to that in November (1838 ppm) which is higher than recommended in several standards. A peak reading of 4500 ppm was observed during an examination when all the doors and windows closed. It was confirmed that with windows or doors shut, the classrooms would not have sufficient ventilation. Just opening the corridor windows could not efficiently reduce indoor CO2 concentration, while opening top-hung windows works without influencing thermal comfort, which need further study. Window type is very important for good natural ventilation performance. These types of classrooms and buildings are widespread and results found here may apply elsewhere in many other cities in China.