Are we overestimating radiant effects? Re-examining view factors in the seated posture

• The Anterior/Posterior symmetry assumption is not valid when the occupant is seated on a stool or chair. • The presence of an office chair decreases the projected area factor by up to 86 %, and the mean radiant temperature by up to 1.9C. • No significant difference between adult and child radiation data was found in the seated posture. • Tabulated data of projected area factors are provided for all manikins for both positive and negative elevations. Radiant heat exchange plays a critical role in occupant thermal comfort, and can be leveraged to increase building energy efficiency through radiant heating and/or cooling systems and personal comfort systems, for example. However, the view factors and projected area factors f p of seated occupants, necessary for the adequate design of these systems, remain underexplored and often rely on outdated assumptions. This study investigates the impact of two long-standing simplifications—anterior-posterior (A/P) symmetry and the neglect of seat shading—on radiation data for both adult and child occupants in the seated posture. Using numerical manikins in various seated configurations (floating, on a stool, and on a chair), f p values are calculated and tabulated, and their influence on view factors and mean radiant temperature is assessed. Results indicate that the A/P symmetry assumption holds only where no seat is present (as if the occupant were floating), and seat shading significantly reduces radiant exposure—up to 86 % for an adult in an office chair. Comparisons between adult and child manikins reveal minimal differences (<12 %) in the seated posture, suggesting that age-specific radiation data may be less critical for seated children than previously found for standing postures. Two test cases demonstrate that using standard view factors relying on these assumptions overestimates t ¯ r by up to 2 °C, which could compromise occupant thermal comfort. These findings call for updated design and evaluation practices to account for seat shading effects in indoor spaces where occupants remain in the seated posture for prolonged periods.