siliconindia | | AUGUST 20199ported to the whole space, including the other occupants' breathing zones. In such cases, even if the distance between the infected person and a potential receptor is long, the ex-haled infectious droplets can still be inhaled by the recep-tor and cause cross infections. Thus, the person-to-person airborne infectious disease transmission in buildings with mixing ventilation can be rather significant.Current Trend of Building Ventilation DesignTo reduce the airborne infectious disease transmission in buildings, researchers proposed several advanced ventila-tion design systems. For example, displacement ventilation was originally proposed for reducing energy consumption for cooling. Displacement supply air diffusers are installed at the lower level of the walls, while the exhausts are in-stalled at the ceiling level. Cool air is supplied to the room at a low speed. As the cool air tends to stay at the lower level of the room, a layer of cool air is formed. When the cool air encounters a heat source, such as a person, the air is heated and moves upwards. The upward airflow goes through the heat source and brings the heat to the exhausts. This is also known as the buoyancy effect. The heat remov-al efficiency is significantly improved in this way. From the perspective of removing exhaled infectious droplets, the displacement ventilation system is also advantageousas the fresh air also goes upwards with the buoyancy effect, so that the exhaled droplets can be directly brought to the exhausts without travelling to other occupants' breathing zones. Therefore, the cross infections due to airborne trans-mission can be minimized.The traditional approach to achieve the optimal design of air distribution in buildings is to conduct small or full-scale experiments in a simulated environment or with trial-and-error tests. The whole process may take a few months and cost a lot of money & resources. With the rapid de-velopment of advanced computer modeling techniques, the design can be completed more efficiently. Currently, the most popular and powerful computer aided design tool for air distribution in buildings is Computational Fluid Dy-namics (CFD). To obtain the information on airflow distri-bution, CFD numerically solves a set of partial differential equations for the conservation of mass, momentum (Navi-er-Stokes equations), energy and turbulence quantities. The solution includes the distributions of air velocity, pressure, temperature and turbulence parameters. Based on the cal-culated airflow, we can continue to solve the droplet equa-tions to obtain information about person-to-person infec-tious droplet transport in buildings. Through the computer simulations, the effectiveness of the air distribution system on controlling airborne infectious diseases transmission can be correctly evaluated to assist the building design.The Way Forward in Building DesignThe inverse design technique using genetic algorithm and adjoint method, combined with CFD has been developed in recent years to directly achieve the optimal design of air distribution systems to minimize the airborne infectious diseases transmission in buildings. In comparison with the traditional trial-and-error experiment method, applying the inverse design approach with CFD in building design can reduce design time down to a tenth, depending on the com-puting resources available. The users only need to install the relevant inverse design software and learn how to oper-ate it. As the initial setup costs of adapting to inverse design are not high, it is expected such that advanced technologies will be widely used by the industry practitioners in design-ing green and healthy buildings in the long run. Through the computer simulations, the effectiveness of the air distribution system on controlling airborne infectious diseases transmission can be correctly evaluated to assist the building design
< Page 8 | Page 10 >