Pressure equalization and wind loads on roof-mounted solar arrays

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There has been a substantial increase in the quantity of installed roof-mounted photovoltaic (PV) arrays in Canada in the last few years and an almost threefold increase globally in the past decade. Wind is often the governing design load, but currently there are no appropriate provisions in building codes for such loads and there is a great deal of uncertainty about how to handle them. Accurate knowledge of these loads is particularly important for the installation of PV arrays on existing roofs, where there is often limited structural capacity available to withstand the additional weight and ballast of the arrays. It is important to resolve these issues in order to have greater penetration of solar power generation into suburban and urban areas. Roof-mounted solar arrays rely on an aerodynamic mechanism called pressure equalization. What this means is that design wind loads on roof-mounted arrays should be substantially less than those acting on the roof structure. Multi-layer cladding systems on buildings also rely on pressure equalization to reduce the loads that these systems need to withstand. However, pressure equalization is a significant unresolved issue of wind loading on buildings. So, while it is desirable to maximize pressure equalization, there is currently only limited theory to predict or model this phenomenon, and key parameters are missing in existing formulations. In order to be able to optimize design and building code approaches, much greater information is required. Thus, the objectives of the current proposal are (i) to develop an analytical model for pressure equalization, and (ii) to apply the results to the situation of roof-mounted PV arrays. This work is done in the context of the applicant's research program, which is focussed on the development of better design standards and models for the loading and responses of structures in extreme wind. Novel experiments, using technology developed for the 'Three Little Pigs' Project, will be conducted. At least six graduate students, and several undergraduate students, will receive training on this project.