The Reintroduction of Natural Ventilation to a 19th Century Opera House, Utilising Calibrated Computer Simulation and User Operation

The Royal Wanganui Opera House (RWOH), in Whanganui, New Zealand, was constructed in 1899, and now seats 830 people. This building was designed with a natural ventilation system; however, this system is no longer in operation and the RWOH has received regular complaints from patrons regarding indoor thermal comfort. Various options for mechanical systems to improve indoor comfort during summer performances have been considered, but have been deemed too costly. The RWOH is listed with Heritage New Zealand as a Category 1 heritage building. Without an effective ventilation scheme, the selection of the RWOH as a performance venue during peak summer months is threatened. The addition of a mechanical ventilation system will not only be costly, but also encounter issues complying with the building’s heritage listing. The potential benefits of a natural ventilation scheme for the RWOH regarding initial cost, thermal comfort, and on-going maintenance costs for the local Council are key drivers of this investigation. An additional benefit is the functional heritage value: restoring the building technology to its original design.
A calibrated Computational Fluid Dynamics (CFD) software analysis of the RWOH has been completed. Temperature and humidity monitoring devices were placed throughout the auditorium, stage, and roof space to gain data to calibrate CFD modelling of the space. Because temperature monitoring devices are reliable, cheap and readily accessible, temperature, rather than airflow, was selected as the calibration medium at multiple points in the auditorium for the ventilation simulations. The CFD analysis investigated the building’s potential for the reintroduction of a natural ventilation scheme in several incremental stages. Incremental changes to the operation of openings in the building have been completed: it saw reintroduction of natural ventilation airflows as tested through the CFD modelling. Staff at the RWOH were given an operation guide for the sold out performance of the New Zealand Opera School on Saturday the 21st January 2017, a performance that in previous years has sparked multiple complaints from the audience regarding comfort issues. No comfort complaints were received after this year’s Opera School Performance. While the weather during this key performance was not as warm or detrimental to the indoor thermal comfort as it has been in previous years, the owners and operators of the RWOH are now aware of the benefits the changes to the operation of the building’s ventilation openings has already achieved. The owners of the RWOH are interested in undertaking further stages of renovations in order to continue to improve the ventilation of the building for the future. The research team is currently devising a guide for the application of successful natural ventilation schemes to similar buildings throughout New Zealand.