Similarity analysis between helium and fire smoke in sub-scale wind tunnel test for investigation of smoke spread during photovoltaic roof fires

The increasing number of photovoltaic (PV) roof fires brings huge concern to PV fire safety issues. There is a vital necessity to investigate the mechanism of smoke spread from PV roof fires. In this study, a helium test method was developed to replace the real fire smoke to investigate smoke spread from the PV roof fire. The helium test in the wind tunnel was conducted with PIV to measure the fluid velocity and helium volumetric fraction with various roof angles. CFD simulation of FDS was conducted and validated for helium test and fire smoke test, where the average NRMSE between experiment and simulation results are 11.95% (velocity) and 19.04% (helium volumetric fraction). Then, dimensionless numerical analysis was performed to justify the similarity theory of the helium test method, which illustrates an average of 0.39% for velocity and 1.95% for dimensionless temperature between the helium test and fire smoke test. Furthermore, a region of separation flow had been found on the leeward side of buildings to blow smoke into the building from the PV roof fire through the skylight. The key parameters are proposed for roof angle, i.e., the 15° roof scenario has the highest risk of smoke spread from PV roof fire; correspondingly, the 45° and 60° roof scenarios are safest.