Thermal Comfort in Mechanically Ventilated Theatres

Auditoria require blackout conditions and have a relatively high occupancy with raised carbon dioxide levels from the audience and a significant heat load from lighting and stage equipment. Maintaining an acceptable indoor environmental quality has long been a challenge for designers and engineers. Performance theatres are of vital importance to the United Kingdom, with a large number of historic and modern buildings; they play an important role in terms of cultural and economic impact. With England having a rich theatrical tradition, it's vital to improve thermal comfort and indoor air quality in existing theatres, and provide a guideline for designing new theatres. There has been relatively little published on thermal comfort in theatres.

The aim of this research is to learn whether mechanically ventilated theatres are thermally comfortable and whether the introduction of mechanical ventilation to naturally ventilated theatres provides significant improvements to thermal comfort and indoor air quality. The emphasis is on identifying the causes of discomfort in the case studies of the research. The method employed to undertake this research consisted of interviewing the facilities managers of the theatres, comprehensive post-occupancy data collection during both summer and winter, and modelling the case studies with Computational Fluid Dynamics (CFD) to help determine the impacts of different air distributions on the air flow pattern and occupants' comfort in the auditoria. Several issues were found in the theatres with different mechanical ventilation systems; these characteristics can affect the audience and the theatre sector in five areas: transmission of contagious bacteria and viruses such as COVID-19, thermal comfort dissatisfaction, perception of air freshness, the audience alertness and the production companies' interests. The results of the research suggested that mechanically ventilated theatres are not necessarily more comfortable than the naturally ventilated theatres and, based on the type of mechanical ventilation and air distribution system, some factors need to be considered. Regardless of the air distribution strategy in a theatre, it is essential to prevent unintended recirculation of air externally between inlets and outlets by providing enough distance between them and locating exhaust outlets downwind of fresh air intakes.

With a downward ventilation system, the extract grilles need to be located on the run of the raked seating rather than the rise and the right levels of extraction rates need to be provided. It is also important to provide at seat extraction by designing extract grilles underneath each seat in the Stalls, Circle and the Upper Circle. With a displacement ventilation system in a theatre, it is essential to introduce the supply air into the auditorium with a low velocity to avoid local discomfort. Providing extracts over each level can prevent a high CO2 concentration in the Upper Circle. Additional extraction at the very centre of the ceiling also helps to extract the stale air from the Stalls. With a mixed ventilation system, where both the supply and the extract are located at high level, it is advisable to prevent the cold draughts around the whole body by supplying the fresh air at a low velocity and an air temperature of 18℃- 19℃. It is also necessary to prevent the migration of the stale air from the Circle and the Upper Circle to the Stalls by providing appropriate levels of extraction and perhaps by introducing more supply air, in particular, to the Stalls.

The outcome of this research can provide the researchers and designers with useful information regarding thermal comfort and air quality in mechanically ventilated theatres. In addition, findings from this research can help the theatres companies and engineers to provide/ maintain acceptable levels of thermal comfort and indoor air quality for the existing theatres and future theatre design. The methods developed and outcomes from this research could also be applied to other types of buildings such as lecture theatres and cinemas to improve their thermal comfort and IAQ.