Urban indoor bioaerosol - source strength, human activities, and mitigation

Bioaerosols are recognized as one of major indoor air pollutants. These particles are found to deposit on the coils of heating, ventilation and air conditioning (HVAC) systems, which will then disperse to the indoor spaces to degrade the air quality and affect the occupants’ health. In Singapore, the problem can be exaggerated due to the prevalent use of HVAC systems. Unfortunately, there is no experimental data on the deposition of bioaerosols on HVAC cooling coils. This project investigated the bioaerosol deposition on coils under dry mode (with cooling coils off) and wet mode (with cooling coils on). The deposition of two groups of bioaerosols, bacteria and fungi, were further examined. In this experiment, a fin-and-tube cooling coil system with fin spacing 3.1 fins/cm running under air velocities from 1.0-2.0 m/s was studied. Air samples that contained bioaerosols were collected for DNA extraction and the subsequent quantification tests including Qubit and qPCR. The particle deposition measured by optical particle counter was used to facilitate the interpretation of the obtained experimental data. It has been found that the bioaerosol deposition increases with the increasing air velocity and particle size. Operating modes also affected deposition on cooling coils since the presence of condensed water under wet mode could trap more bioaerosols. Fungi had a higher deposition fraction than bacteria on coils. The results suggest that cooing coils can be an important sink for bioaerosols and hence act as the source of indoor air quality problems. Further studies are recommended for the viability of the deposited bioaerosols and their resuspension mechanisms.Bachelor of Engineering (Environmental Engineering