A systematic review on COVID-19 related research in HVAC system and indoor environment

•COVID-19 related research in HVAC system and indoor environment is reviewed.•HVAC system, filtration, and indoor improvements measures are examined.•Building operation guidelines from different countries are compared.•Impact on building energy consumption and research recommendations are provided. The on-going COVID-19 pandemic has wrecked havoc in our society, with short and long-term consequences to people's lives and livelihoods - over 651 million COVID-19 cases have been confirmed with the number of deaths exceeding 6.66 million. As people stay indoors most of the time, how to operate the Heating, Ventilation and Air-Conditioning (HVAC) systems as well as building facilities to reduce airborne infections have become hot research topics. This paper presents a systematic review on COVID-19 related research in HVAC systems and the indoor environment. Firstly, it reviews the research on the improvement of ventilation, filtration, heating and air-conditioning systems since the onset of COVID-19. Secondly, various indoor environment improvement measures to minimize airborne spread, such as building envelope design, physical barriers and vent position arrangement, and the possible impact of COVID-19 on building energy consumption are examined. Thirdly, it provides comparisons on the building operation guidelines for preventing the spread of COVID-19 virus from different countries. Finally, recommendations for future studies are provided. [Display omitted]