CFD Analysis of Residential Kitchen Ventilation with Gas Stove
Airflow Patterns Matter!
Airflow patterns in the kitchen impact the flow behavior of pollutants. Understanding the nature of airflow patterns and the flow path of pollutants plays a critical role in determining the pollutant exposure levels of occupants. The dispersion of pollutants and their flow path can depend on several inter-related factors. These factors include exhaust flow rates, design of the exhaust hood, size and location of make-up air openings, location, and capacity of the burners used during cooking, cooking practices, and user behavior in operating the kitchen ventilation system. Physical testing of all these parameters under controlled conditions for a variety of conditions is time and labor-intensive, if not impossible. Computational Fluid Dynamics (CFD) analysis provides a feasible alternative for systematic evaluation of these parameters and gaining insights into the performance of kitchen ventilation.
With the help of CFD simulations, we investigated the impact of exhaust fan flow rates on the spread of Nitrogen Dioxide (NO2) and its concentration levels in a typical kitchen. Unlike our previous study with the mass balance approach which predicted only a “volume-averaged” concentration, this CFD study predicts the spatial distribution of NO2 concentration in the space.
Analysis of Exhaust Fan Flow Rates
Our CFD analyses indicate that the exhaust flow rate of 75 cfm or less is inadequate for the effective removal of pollutants from a kitchen space. Increasing the exhaust flow rate reduces the spread of pollutants and high-concentration zones. High exhaust flow rates also remove the pollutants quickly from the kitchen. Turning on the exhaust fans in the nearby bathroom can supplement the capacity of the hood exhaust fan.
Thermal Plume Can Protect!
These analyses further indicate that the thermal plume – hot air rising from a person and the buoyancy of hot gases released during the cooking can help reduce the NO2 exposure. Such thermal stratification causes the pollutants to accumulate near the ceiling and migrate along the ceiling. Thus it moves the pollutants up and away from the breathing zone of occupants. Thermal plume from a person can form a “protective shield” which helps reduce pollutant exposure.
During the first few minutes of the cooking when the burner is ON, the occupant NO2 exposure levels remain low, however, the exposure level starts increasing during the purge phase when the burner is turned off. Interestingly, this analysis indicates that the NO2 exposure level remains significantly below the EPA acceptable level of 100 ppb-hr for all exhaust fan flow rates.
CFD is a valuable tool in analyzing and optimizing kitchen ventilation systems.