A comparative study of the effects of ventilation-purification strategies on air quality and energy consumption in Beijing, China

In countries suffering from heavy ambient air pollution, ventilation is a problem, as ventilation intakes outdoor air pollutants, such as particulate matter with an aerodynamic diameter less than 2.5 μm (PM_2.5), while removing indoor air pollutants. Thus, it is important to identify appropriate ventilation-purification strategies to build healthy indoor environments with low energy consumption. This study reports the comparison of two sets of strategies, i.e., mechanical ventilation with filters and natural ventilation with indoor air cleaners, in respect to energy consumption and the PM_2.5 and carbon dioxide (CO₂) exposure of occupants in a typical apartment in Beijing, China. A dynamic mass balance model was employed to calculate the PM_2.5 and CO₂ exposure concentrations, while the energy consumption of heating and cooling was simulated with the Designer’s Simulation Toolkit. It was found that natural ventilation with air cleaners provided lower PM_2.5 exposure compared with that of mechanical ventilation with filters; however, mechanical ventilation achieved a lower CO₂ exposure concentration. The annual cooling, heating, and fan energy consumption of natural ventilation strategies are lower than those of mechanical ventilation strategies. With respect to natural ventilation, an infiltration rate of 0.3-0.4 h^-1 was the preferred setting, which led to low PM_2.5 and CO₂ exposure with lower energy consumption. The basic requirements for controlling indoor PM_2.5 could be met if the threshold is set at 25 μg/m³. The results provide guidelines on how to combine multiple ventilation purification strategies to improve indoor air quality with lower energy usage.