Air Change Rate (ACR) or HVAC Configuration—Which Makes Labs Safe?

March 18, 2020
1 p.m. – 2 p.m.
Eastern Time

 

Often high airflow rates or air change rates per hour (ACH) for laboratory spaces are presumed to cover the risk of chemical exposure. Previous analysis indicated that high ACH does not necessarily create diluted indoor environment at all the time for all the occupants. With increasing ACH the overall concentration levels in the space (detected in the exhaust duct) decrease, however, the flow path of the contaminants remains almost similar. The HVAC configuration including the location and type of supply diffusers, diffuser throws, size and locations of exhaust grilles, locations and strengths of heat sources, location and size of fume hoods, and arrangement of furniture and other airflow obstructions can influence the flow path of contaminants, which in turn, determines the strength and location of high concentration zones in labs.

This presentation with the help of Computational Fluid Dynamics (CFD) analysis will demonstrate the effect of HVAC configuration on the ventilation effectiveness of HVAC system. This study investigates the impact of number and location of exhaust grilles on the flow path of contaminants and the resulting transient and spatial distribution of contaminant concentrations in a typical lab. Time varying concentration levels are predicted at the face level of three occupants located at three different locations in the lab as well as in the exhaust duct. Based on these concentrations the time varying chemical exposure (dose) for each occupant is calculated. The ventilation effectiveness of the HVAC system is analyzed with the help of two non-dimensional indices: Spread Index (SI)TC and Purge Time (PT)TC. (SI)TC quantifies the percent of the room volume presumed to be the high risk zone, where the contaminant concentrations are higher than the desired target concentration (TC). Whereas the (PT)TC evaluates the time the ventilation system takes to bring the lab environment below the target concentration. This analysis shows the distributed exhaust strategy with three exhaust grilles significantly reduced the (SI)TC values resulting in reduced concentration levels and chemical exposure (dose) of occupants. Interestingly the occupant closer to the exhaust grilles shows high level of exposure than the one closer to the contaminant source. The analysis results will be presented with insightful animations showing the progression and movement of contaminant cloud in the space.

Learning Objectives:

  • Understand the impact of location and number of exhaust grilles on contaminant concentration levels and on exposure levels (dose) of occupants;
  • Understand the impact of air change rates per hour (ACH) on the relative exposure levels (dose) of occupants and how do they vary with time and location in the lab space;
  • Understand the definitions of Spread Index (SI)TC and Purge Time (PT)TC and how they can be employed to evaluate the ventilation effectiveness of laboratory HVAC systems; and
  • Understand how Computational Fluid Dynamics (CFD) can be employed in evaluating the ventilation effectiveness of laboratory HVAC systems and optimizing the ventilation system designs for the labs.

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Instructor Biography

Dr. Kishor Khankari, Ph.D. is the President AnSight LLC. A specialist in Computational Fluid Dynamics (CFD), he works closely with his clients to provide engineering insights and optimized design solutions using analytical techniques. Kishor has several years of experience in providing consulting services and insights through analysis to a wide variety of engineering problems involving fluid flow, heat transfer, mass transfer, and other similar engineering processes. Dr. Khankari has developed a patented technology of a wind band design of exhaust fan assembly systems. He has developed several easy-to-use analytical software tools, which are regularly used by design engineers in a variety companies including those in the critical facility and automotive industries.

A noted expert in his field, he has a Ph.D. in CFD from the University of Minnesota and has been regularly publishing in technical journals and trade magazines. Dr. Khankari is an eloquent speaker and has made several presentations worldwide on topics related to design and optimization of HVAC systems at various technical conferences and professional meetings. ASHRAE recognized him as a Distinguished Lecturer. Dr. Kishor Khankari is ASHRAE Fellow and recipient of the ASHRAE Distinguished and Exceptional Service Awards. He is currently leading ASHRAE Multi Task Group (MTG) on Air Change Rates and I2SL technical group on Ventilation Effectiveness for Laboratories. He is past President of Detroit ASHRAE Chapter, past Chair of ASHRAE Technical Committee TC9.11 Clean Spaces, and past Chair of ASHRAE Research Administration Committee (RAC). He is member of ASHRAE Environmental Health Committee (EHC) and voting member of ASHRAE Technology Council. He serves on Industry Advisory Board for Architectural Engineering discipline of Lawrence Technology University.

 

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