CFD Analysis of Demand Control Ventilation (DCV) for Laboratory Facilities
ASHRAE Journal, Vol. 66, no. 6, June 2024
Author
Kishor Khankari
Abstract:
This CFD study evaluated the impact of demand control ventilation on the concentration levels and the resulting exposure (dose) of occupants during the accidental spill scenario in a laboratory. A three-dimensional transient CFD model was developed to study the transient dispersion of contaminants in a laboratory space under a controlled release of a contaminant. Newly developed metrics of Spread Index (SI)TC and Purge Time (PT)TC were employed to evaluate the effectiveness of the DCV system.
These analyses indicate that the demand control ventilation systems can reduce the time required for recovering the laboratory environment after an accidental spill of chemicals. This is achieved by increasing the ACH levels after the onset of the spill which enhances the rate of removal (purge time) of contaminants. Increased airflow rate due to increase in the ACH also enhances the dilution of contaminants. The Spread Index (SI)BZ that indicates the extent of the spread of contaminants in the breathing zone reduced by 37 percent due to the DCV. The Purge Time (PT)TC – the time required for the ventilation system to bring the concentration levels below a certain acceptable threshold value reduced by almost 7 minutes.
However, the concentration levels in front of the occupants and the resulting exposure showed significant spatial variations. The analyses indicate that exposure levels will depend on the location of the occupant. Interestingly, the DCV does not show an immediate impact in reducing the occupant exposure. On the contrary, the exposure levels either increased or remained unchanged for a long time after the onset of DCV. The benefit of DCV in reducing occupant exposure can be realized mostly during the decay phase after the release of chemical vapors (source) stops.
There are several parameters including the layout of supply diffusers and exhausts; the system lag in starting the DCV system, and the locations of sensors that can impact the effectiveness of the demand control ventilation need further evaluation. CFD can be a valuable tool in analyzing and optimizing demand control ventilation systems.
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About the author
Dr. Kishor Khankari
ASHRAE Fellow, ASHRAE Distinguished Lecturer
Dr Kishor Khankari is the founder of AnSight LLC. As a specialist in Computational Fluid Dynamics (CFD), his passion for solving engineering problems and providing sound scientific solutions has led to innovations and optimized designs in the industry.
A noted expert in his field, he has a Ph.D. from the University of Minnesota and has published in several technical journals and trade magazines. As a well sought-after speaker Dr. Khankari makes regular presentations in various technical conferences and professional meetings worldwide.
