A new ventilation performance index considering relative changes in environmental parameters: A numerical study

Abstract

The ventilation index plays a crucial role in evaluating and selecting ventilation systems. However, existing studies focus only on the "effectiveness" of ventilation systems but usually ignore the "extent of the effect" caused by ventilation, and no relevant indexes are available. To address this issue, this study aims to propose a new ventilation index named the equivalent ventilation number (EVN), which considers the relative change in environmental parameters. The application potential of the EVN index was numerically examined in a virtual hospital ward setting with varying air changes per hour (ACH), thermal loads, air distribution patterns, contaminant source intensities, and local air supply rates. The results demonstrate that the highest average temperature-based EVN and CO2-based EVN are obtained when ACH increases from 6 h−1 to 12 h−1 and local supply air velocity increases from 0 m/s to 1 m/s, with values of 0.66 and 1.49 respectively. Furthermore, EVN values differ across different ventilation conditions and locations. The effect of changing ventilation conditions on ventilation performance assessed by heat removal effectiveness and temperature-based EVN, as well as contaminant removal effectiveness and CO2-based EVN, is opposite in 4 out of 10 cases and 3 out of 10 cases, respectively. The average EVN values calculated based on temperature and contaminant changes differ among all cases, with the largest difference of 1.2. The proposed EVN is anticipated to be an effective index for quantifying and comparing the "extent of the effect" caused by ventilation systems under various ventilation conditions.