{"id":455459,"date":"2026-03-31T10:36:41","date_gmt":"2026-03-31T10:36:41","guid":{"rendered":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/what-is-the-recommended-way-to-model-co-exhalation-from-people\/"},"modified":"2026-03-31T10:44:26","modified_gmt":"2026-03-31T10:44:26","slug":"what-is-the-recommended-way-to-model-co-exhalation-from-people","status":"publish","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/what-is-the-recommended-way-to-model-co-exhalation-from-people\/","title":{"rendered":"What is the recommended way to model CO\u2082 exhalation from people?"},"content":{"rendered":"

<div>Hello everyone,<\/div><div> <\/div><div>I am performing a CFD simulation of indoor airflow and CO\u2082 distribution in a lecture hall using ANSYS Fluent with the Species Transport model (CO\u2082 treated as a passive scalar).<\/div><div> <\/div><div>I have some questions regarding how to correctly define CO\u2082 sources and boundary conditions:<\/div><div> <\/div><div>CO\u2082 from occupants (breathing):<\/div><div>What is the recommended way to model CO\u2082 exhalation from people?<\/div><div>Should it be defined as:<\/div><div>a mass source term (kg\/s) in a small volume near the mouth, or<\/div><div>a boundary condition (e.g., velocity inlet with specified CO\u2082 mass fraction)?<\/div><div>CO\u2082 concentration at supply air diffusers:<\/div><div>For the supply air, I set the CO\u2082 concentration to 0.001283  ( AHU set 28% outdoor air and 72% indoor air ,so 500 ppm, mass fraction = 0.000725 , 1000 ppm, mass fraction = 0.0015 , 0.000725*0.28 + 0.0015*0.72 = 0.001283 ).<\/div><div>Is this the correct approach?<\/div><div>CO\u2082 setting at return outlets (pressure outlet):<\/div><div>For return air outlets, should I define the backflow CO\u2082 mass fraction as outdoor concentration (500 ppm), or should it be left unspecified?<\/div><div>General modeling approach:<\/div><div>Is it more appropriate to model CO\u2082 as a volumetric source distributed in the occupied zone, or as localized sources at each occupant?<\/div><div> <\/div><div>My goal is to obtain realistic CO\u2082 distribution and evaluate ventilation effectiveness in the breathing zone.<\/div><div> <\/div><div>Any suggestions or best practices would be greatly appreciated. Thank you!<\/div><\/p>\n","protected":false},"template":"","class_list":["post-455459","topic","type-topic","status-publish","hentry","topic-tag-fluent-ansys-1"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t