Studies of Alternative Ventilation Configurations to Mitigate Airborne Exposure Risks in Office Spaces

Casiano Armenta, Sandia National Laboratories
Nicole Naber, Sandia National Laboratories

The objective of this study was to evaluate the impact of alternative ventilation configurations on airflow patterns and potential exposure risks in office spaces. Two existing conference rooms at Sandia National Laboratories were modeled using computational fluid dynamics (CFD) simulations to characterize airflow patterns and potential airborne exposure risks in well-mixed and once-through (through-flow) ventilation conditions. Multiple scenarios were studied to evaluate the impact of occupancy. Experimental and visualization tests were also conducted to validate the well-mixed and through-flow models and findings.

The simulations demonstrated that the modified-return airflow configuration with through-flow conditions reduced pathogen concentrations in the space compared to the well-mixed airflow configuration. The experimentally measured air speeds generally matched the simulated airflow velocities, and a fog-purge visualization test was consistent with simulated results of plume movement and dissipation. The visualization tests demonstrated improvements in air change rate with the modified return, which promoted through-flow conditions, versus the original well-mixed ventilation configuration.

The results of this study demonstrate that minor modifications to a space that promote through-flow conditions can improve air quality and reduce pathogen concentrations. Sandia is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Learning Objectives

• Modification of the size and location of the return air grilles and changing the directional flow of the supply diffusers can be simple and offer a low-cost solution to reduce airborne exposure for the occupants given most general office areas have a heating, ventilation, and air conditioning (HVAC) design of a ducted supply and a plenum return;
• Reducing the airborne exposure for office occupants should not only be viewed for the COVID-19 pandemic, but also for the common cold and flu season, which will create a safer and healthier office space year-round;
• Implementation of CFD can be used from a safety point of view for not only laboratory spaces but also the common office areas and conference rooms; and
• Validating the CFD model can be achieved with simple visual tools and the purchase of expensive anemometer may not be required.

Biographies:

Casiano C. Armenta, PE, is a mechanical engineer in Facilities at Sandia National Laboratories, New Mexico. He is a Professional Mechanical Engineer (NM), a Certified Energy Manager (CEM) and a Green Building Engineer (GBE). He holds a BS in Engineering Technology from New Mexico State University and a MS in Mechanical Engineering from the University of New Mexico.

Nicole Naber, EIT, is a Mechanical Engineer in Facilities Operations at Sandia National Laboratories and has worked on testing, laboratory, and semiconductor manufacturing facilities. She has been a member of ASHRAE for 10 years and the Society of Women Engineers for 13 years. She holds a BS in Mechanical Engineering from the University of New Mexico.

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