The performance of portable HEPA air cleaners in naturally ventilated classrooms- A systematic literature review

Abstract

Increasing the supply of fresh air via natural ventilation is a good strategy for mitigating airborne COVID-19 transmission. This is particularly relevant to New Zealand, being that the majority ofschools’ classrooms are naturally ventilated. However, the effectiveness of natural ventilation is dependent on outdoor temperature and wind conditions, which are unable to be controlled. In situations where there are limitations which prevent or severely limit window-opening, either due to design or environmental conditions, the performance of natural ventilation can be compromised. In these cases, systems that assist ventilation can aid the performance of natural ventilation to achieve an appropriate amount of air changes, in order to mitigate COVID-19 transmission. A well publicised method of providing additional airborne COVID-19 transmission mitigation alongside natural ventilation is the use of portable High Efficiency Particulate Air (HEPA) air cleaners/purifiers. Leading authorities confer that HEPA air cleaners are only to be considered a supplementary measure, second to fresh air ventilation as they do not affect CO2 levels. The aim of this paper was to review the available literature on the performance of HEPA air cleaners in naturally ventilated classrooms. Using the replicable search processes of a systematic literature review from medical research practice, 142 articles were retrieved from four search databases (ScienceDirect, Scopus, PubMed, and Google Scholar). Through analysis of these 142 articles, there were only seven articles that empirically investigated the methods of assisting natural ventilation in classrooms through HEPA air cleaners in the context of the COVID-19 pandemic. This demonstrates that there is a significant gap within the existing relevant literature, requiring further research to support them.