Distribution characteristics, growth, reproduction and transmission modes and control strategies for microbial contamination in HVAC systems: A literature review

With the outbreaks of SARS, MERS, H7N9 and many other epidemic diseases, microbial contamination has become a significant focus in both HVAC and epidemiology fields. HVAC systems are the “respiratory system” of modern buildings, regulating indoor temperature, humidity, airflow and cleanness. However, they will be the sources of microbial contamination worsening indoor environment and threatening occupants' health if they are improperly designed or operated. To prevent and reduce microbial contamination, it is essential to have an overall understanding of microbial characteristics in HVAC systems. Therefore, this paper provides a comprehensive review of the distribution characteristics, growth and transmission modes of microorganisms in HVAC systems, as well as the microbial control strategies. In specific, this study reviews the HVAC components where microorganisms primarily grow and the corresponding microbial species. Afterwards, this study analyses factors that can decide the microbial growth and reproduction, and then presents the mould growth partition diagram that identifies the suitable conditions for microbial growth. Moreover, main factors that can affect the transmission of microbial aerosol in HVAC systems are also summarised. Based on these, effective strategies for constraining microbial contamination are put forward. Besides, this study further clarifies current situations and future directions of the studies on the microbial contamination in HVAC systems. Overall, this study can inform HVAC engineers and epidemiologists with a basic understanding of how to reduce indoor microbial contamination and preserve better indoor environments.