Scaling method between sub-scale helium and full-scale smoke tests of smoke spread during solar roof fires

Increasing numbers of photovoltaic or solar panels have been installed on building roofs worldwide. Meanwhile, fires from solar roofs were also reported to increase when they are overheated. During a solar roof fire driven by wind and thermal buoyancy effects, the toxic smoke can spread around and infiltrate back into the building and creates major concerns over occupants’ health and safety. To understand this complex heat and mass transfer process, it is possible to conduct full-scale fire studies, which are often constrained by the cost, so the associated studies have been found inadequate in the literature. In comparison, a sub-scale experiment in a wind tunnel can be a cost-effective method for understanding the mechanism of the smoke spread from solar roof fires. However, this may require a fireproof wind tunnel, and the use of actual fires in a lab context often creates safety and cost concerns and is thus impractical. Therefore, this study proposes a scaling method for conducting sub-scale wind tunnel tests with helium to generate a similar thermal plume and smoke spread behavior as an actual fire. The method was demonstrated by comparing the similarity of a 1/15 scale helium experiment in a wind tunnel and a full-scale smoke test by computational fluid dynamics (CFD) simulations using a fire dynamics simulator (FDS). A good agreement was found with an average difference of 7.02% for dimensionless velocity and 7.87% for dimensionless temperature. The difference among all cases was less than the maximum of 21.66%, which occurred only in the transient 45° roof scenario near the free stream region close to the indoor space. Therefore, the proposed scaling method of the wind tunnel helium test is justified in this paper when studying the smoke spread during solar roof fires. •CFD simulations of wind tunnel helium tests by FDS were validated.•A new scaling method for the wind tunnel helium test was proposed.•The new method was confirmed by the similarity of temperature and velocity at different scales.•A full-scale smoke spread can now be predicted by a sub-scale helium test in a wind tunnel.