Influence of air changes per hour on hydrogen leaks in mechanically ventilated enclosures

Abstract

The integration of hydrogen energy systems into nearly zero-emission buildings (nZEB) is emerging as a viable strategy to curtail greenhouse gas emissions associated with energy use in these buildings. However, the indoor or outdoor placement of certain hydrogen system components or equipment necessitates stringent safety measures, particularly in confined environments. This study aims to investigate the dynamics of hydrogen dispersion within an enclosure featuring forced ventilation, analyzing the interplay between leakage flow rates and ventilation efficiency both experimentally and numerically. To simulate hydrogen's behavior, helium gas, which shares similar physical characteristics with hydrogen, was utilized in experiments conducted at leakage flows of 4, 8, and 10 L/min, alongside a ventilation rate of 30 air changes per hour (ACH). The experiments revealed that, irrespective of the leakage rate, the oxygen concentration returned to its initial level approximately 11 min post-leakage at a ventilation rate of 30 ACH. This study also encompasses a numerical analysis to validate the experimental findings and assess the congruence between helium and hydrogen behaviors. Additionally, the impact of varying ACH rates (30, 45, 60, 75) on the concentrations of oxygen and hydrogen was quantified through numerical analysis for different hydrogen leakage rates (4, 8, 10, 20 L/min). The insights derived from this research offer valuable guidance for building facility engineers on designing ventilation systems that ensure hydrogen and oxygen concentrations remain within safe limits in hydrogen-utilizing indoor environments.