ACR Journal

CMYK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 33 VENTILATION Ventilation Strategies There has been surprisingly little research into the practical implications of di erent ventilation strategies and how they could influence indoor virus transmission. Some research papers have looked at spreader and super-spreader events and identified either a lack of ventilation or air conditioning as the key contributors to the spread of infection indoors. However, most commonly used air conditioning systems only recirculate stale air, so they do not provide any ventilation. There are various claims of disinfection and purification systems being e ective against the virus, but the claims seem to be based on laboratory research rather than real-life scenarios. A fanned air purifier could have the opposite e ect if it blows purified air straight past an infected person, picking up their breath and distributing virus-carrying aerosols around the room. Previous research, mainly using pre- existing computational fluid dynamics (CFD) covering various ventilation and comfort systems, shows a significant di erence between natural and mechanical ventilation strategies, as the two measures handle the air very di erently. One utilises buoyancy and stratification, and the other employs air-mixing as a design objective 3 . We couldn’t call this research conclusive since we were missing ventilation measure specific CFD simulations in a like-for-like, matching environment and real-life test data. Monitoring air distribution We teamed up with Building Services Research and Information Association (BSRIA) and Brunel University, London, to conduct a real-life Indoor Environment Study, with financial support from Innovate UK. The study was carried out in a 40m 2 oce, with four desks and four ‘droids’ (or DIN-men - white cylindrical tubes built in accordance with BS EN 142240:2004), complete with masks, screens, various ventilation systems and a comprehensive suite of monitoring equipment. We sourced and installed various ventilation, comfort, and ‘purification’ measures, including a wall mounted air conditioning unit; hybrid ventilation, popular in schools; typical top-down, ceiling void ducted HVAC, mostly used in larger oce buildings and various air purifiers. We also tested di erent natural ventilation approaches from open windows to façade integrated systems. We ‘infected’ one of the droids, using easily detectable CO 2 gas as a proxy for the infected breath, delivered at a real-life velocity of 3.5m/s. Body temperature was also mimicked to ensure we replicated a typical environment as closely as possible. The flow of that ‘breath’ was monitored through various scenarios, using a multitude of CO 2 sensors at multiple heights and locations. We also monitored the impact of various provisions on occupant comfort - Figure 5. Spread of infected breath throughout the unventilated office measured using exhaled CO 2 proxy. Figure 6. Spread of infected breath throughout the top down mechanically ventilated office. Figure 2. Schematic illustrating ventilation flows with the various flow elements such as the body plume, inlet flows, stratification and arrows indicating entrainment and mixing (Cambridge University Press) 2 Figure 3. Pre-existing CFD simulations of typical airflow in Naturally Ventilated classrooms (Ventive) 3 Figure 4. Setup of the Indoor Infection Spread test office.