Seminar 27 -- Is it Time to Separate from the Mixing Factor?

2023 ASHRAE Annual Conference

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The well-mixed environment is commonly invoked and often misunderstood. While mixing is a ventilation design scheme with many appropriate applications, engineers sometimes say "well-mixed" when they actually mean "effective ventilation." Mixing creates a more uniform contaminant or temperature distribution, which can be an inappropriate target. This thinking is carried further when mixing factors are used to specify higher volumetric flow rates when space concentration is not uniform. Control of toxic/infectious material using safety factors multiplied by mixing factors increases further the required flow with an exponential rise in energy cost. We explore alternative benchmarks available through CFD and direct-reading instruments.