Energy implications of reducing COVID-19 risk with different clean-air delivery solutions. A simulation study in a school

This paper presents simulations of energy use under different clean-air strategies to keep the number of secondary infections from one infected pupil in a classroom below 0.9 per week, thereby ensuring that total infections decline. Only airborne transmission of SARS-CoV-2 was simulated, and the infection risk in the far field. Simulations were made in the school building in a temperate climate (Denmark) during the heating season (October 1 to April 30). Infection risk was predicted using the Wells-Riley equation. The energy use was simulated using IDA ICE. The tested air-cleaning strategies included natural ventilation via window opening, with and without portable HEPA air cleaners; extract ventilation with exhaust fans, with and without portable HEPA air cleaners; and mechanical ventilation with heat recovery, with and without recirculation where an efficient filtration was installed. Additionally, ventilation scenarios were simulated to meet ASHRAE Standard 62.1 and Standard 241, as well as the Centers for Disease Control and Prevention's recommendations. The results showed that the most energy-efficient solution was adding portable air cleaners in classrooms, and the least energy-efficient was extract ventilation with an exhaust fan, which was also comparable to open windows at the same air change rate. Mechanical ventilation with heat recovery was more energy efficient than extract ventilation. Recirculating air through an efficient filter in the ventilation system was less energy-efficient than using portable air cleaners. The present simulations must be repeated in other climates before generalizations are made, because the predicted risk levels and energy use reflect the assumptions made. Nevertheless, the relative trends identified are expected to be broadly applicable. Consequently, the present results can be used to develop sustainable technical solutions that reduce the risk of infection through clean air delivery while using as little energy as possible.