The effect of local exhaust and supply air terminal on the mitigation of indoor airborne transmission risk and on the thermal comfort.

Nowadays, people spend the majority of their time indoors. It is important to ensure a healthy indoor environment for the occupants as well as their well-being. Moreover, it is important to guarantee clean air to the occupants without compromising their thermal comfort. Generally, the improved IAQ is in contrast with energy-saving measures. For this reason, there is a crescent interest in focusing only on the occupied zone with the application of local exhausting. The thesis focuses on the effects of the application of local exhaust and the locations of air terminal devices on indoor airborne transmission. The study was conducted in a test chamber at Aalto University, set up as a meeting room. The room hosted 6 occupants, including an infected person simulated by a breathing manikin. The pathogen or virus exhaled by the manikin was simulated by the tracer gas SF6. Every experiment lasted 3 hours, considering the average occupation time of a meeting room. The configuration studied was in the cooling season with two different heat gains, 36 W/m2 and 67 W/m2. All the cooling power requested was provided by the cooled supply air, with an indoor set-up temperature of 25.5°C. For each heat gain, the air terminal device-perforated duct was located at three different locations. In two configurations the air was supplied from the floor level, on the window side, or on the corridor side. Also, the performances were studied placing the perforated duct at the height of 1.7 m on the corridor side. To analyse the IAQ, the contaminant concentration, the contaminant removal efficiency, and the infection risk were calculated. Moreover, the effects on thermal comfort were analysed for each of the 6 occupants. The vertical thermal gradient, the air velocity, the heat removal efficiency, and the draught risk were calculated. The obtained results showed that the ventilation system studied allows to reach very low infection risk values, in particular supplying from the floor level. The infection risk reached with the lifted configuration is still within the limits, with a risk of 1.5% after 3 hours. The window configuration is the best one for removing pollutants, reaching a CRE of 5.56. On the other hand, the corridor case shows more uniformity of contaminant concentration among the different occupants of the room. However, the higher heat gains often lead to high airflow rates that cause local discomfort. In particular, close to the supply air inlets it is often measured a very high air velocity and draught risk.