Cleanroom Airflow Alignment Metric Rδ

This study proposes and validates a novel metric, the Cleanroom Airflow Align- ment Metric (Rδ ), to quantify and optimize vertical airflow alignment in ceiling- mounted Fan Filter Unit (FFU) cleanrooms. By formulating a simplified one- dimensional energy balance between alternative airflow pathways (horizontal-to- vertical vs. vertical-to-horizontal), Rδ enables rapid assessment of FFU operating strategies without requiring full CFD simulations.The proposed Rδ index was validated through both CFD analysis and in-situairflow measurements, showing strong correlation with deflection angle and air age metrics. Sensitivity analysis confirmed that Rδ is robust against uncertainties inair density, floor resistance coefficients, and wall roughness assumptions.