COVID-19 : Computational Fluid Dynamics (CFD) Airflow Assessment and Analysis

Airflow Patterns Matter!

The recent COVID-19 pandemic has raised concerns about the effects of space air distribution on the spread of airborne contaminants. Airflow patterns and the resulting flow path of airborne contaminants play a crucial role in the dispersion and accumulation of airborne contaminants and probable locations of surface deposition. Airflow patterns can also play an important role in reducing the risk of contaminant exposure by the proper layout of supply diffusers and exhaust grilles. The airflow patterns and the flow path of airborne contaminants can depend on several inter-related factors including:

• the number, location, and type of supply diffusers;
• supply airflow rates (air change rates) and associated diffuser throws;
• supply air temperature;
• number, size, and locations of return/exhaust grilles;
• the location and strengths of various heat sources in a room;
• an arrangement of furniture and other obstructions to airflow;
• location, type, and capacity of in-room air cleaners;
• and importantly, the relative positions of contaminant sources in space.

Air Changes per Hour (ACH)

Often high supply airflow rates or air change rates per hour (ACH) are specified to cover the risk of COVID-19 exposure in indoor spaces. Although high supply airflow rates can reduce the overall concentration of contaminants, it may not ensure acceptable concertation levels everywhere in the occupied zone. Importantly, locations of high concentration, especially those in the breathing zone of occupants, can pose potentially higher exposure risk. Ideally, the clean supply air should sweep the contaminants from the breathing zone without significant recirculation and stagnation that generally create pockets of high concentration. At the same time, the clean air should not escape or short-circuit the space without the collection and removal of contaminants from the breathing zone. Since the air takes the path of least resistance the effectiveness of ventilation depends on several factors related to the design and operation of HVAC systems.

Computational Fluid Dynamics (CFD)

Systematic investigation of the combined effects of all the variables that affect airflow patterns and the flow path of contaminants using physical testing in indoor facilities is time and resource-intensive, and sometimes impossible. Computational Fluid Dynamics (CFD) analyses, if performed properly with adequate expertise, can predict airflow patterns and the probable flow paths of airborne contaminants in a space. Such analysis can be employed as a valuable design tool in developing appropriate mitigation strategies for existing spaces and during the early stages of new designs to optimize occupant comfort and indoor air quality and to minimize the concentration of airborne contaminants. CFD analyses are based on the fundamental physical laws and involve numerical solution of equations of air motion, heat transfer, transport of airborne contaminants, and similar other transport processes.

Figure 1: CFD analysis of a laboratory space indicates that by simply adding a one more exhaust grille the spread of the airborne contaminants (Spread Index) reduced by about 40 percent.

Figure 2: CFD analysis of a hospital patient room indicates that by relocating and increasing the size of a return can significantly help in reducing the spread of airborne pathogens.

Guidance for HVAC Layout to Optimize Airflow Distribution

• Increase the number and size of return/exhaust grilles in a space.
• Place return/exhaust grilles away from the occupied zone to avoid stagnation of contaminants.
• Minimize turbulence of the supply air in the occupied breathing zone by appropriate selection of supply airflow rates and supply diffusers.
• Promote “single pass” sweep layout for HVAC designs.
• Perform Computational Fluid Dynamics (CFD) analysis to optimize the HVAC layout to improve the ventilation effectiveness.

AnSight CFD Solutions for COVID-19 Airflow Assessment

Our proprietary procedures for CFD analyses help minimize the spread of airborne contaminants and provide:

• Valuable insights into the complex airflow patterns, flow path of airborne contaminants, and the concentration levels of contaminants in indoor spaces which can lead to appropriate mitigation strategies to reduce the spread of airborne contaminants.
• Our insightful flow animations which help in visualization of airflow patterns and in revealing any stagnant zones with unacceptable levels of contaminant concentration.
• Valuable insights into the impact of various design and operating parameters on the ventilation effectiveness using our proprietary methodology of Spread Index.
• Optimization of HVAC layout including location, type, and capacity of the in-room air cleaners to minimize the spread of airborne contaminants in the breathing zone.

Check our publication

CFD Analysis of Airflow Patterns and Probability of Infection in Indoor Spaces – A Concept of Aerodynamic Containment