Spatiotemporal distribution and the passive dispersal of fungal spores through HVAC systems

Heating, ventilation and air conditioning (HVAC) systems are widely used to regulate indoor temperature and air quality of modern buildings. The central supply and exhaust system cause the dispersal and removal of bioaerosols. This study presents results from ex situ experiments conducted to a better understanding of the spatiotemporal distribution, passive dispersal and removal of fungal spores through HVAC systems. The study was conducted in a 50 square meters by 3 m high instrument room in a research building with HVAC systems. Plates with Aspergillus flavus colony were attached upside down on the edge of the ceiling vent to imitate the mildew growing. Fungal spores were released for 10 min, collected and counted by the settle plate method in 2 h. Results show that A. flavus spores dispersed to 3.6 m in 2 min and were evenly distributed in the room within 8 min. The concentration of spores decreased from 48 to 3–6 CFU/plate after 60 min and was lower than 1% after 120 min. Our results suggest that airborne fungal spores disperse and remove by HVAC systems efficiently. Without the external and internal source, the HVAC system could greatly reduce the fungal amount in the indoor air to the background level within one hour. This study provided the observed data of the transmission and retention of internal or external biological contaminants through HVAC system.