CASE STUDY | FAIRFIELD HALLS The jet nozzles are angled between five and 15 degrees from horizontal, depending on their location in the auditorium to ensure good air movement across the audience seating. Noise is minimised using attenuators, lined plenums and by controlling regenerated noise. The ventilation system has pre-sets, calibrated to suit different situations, says Chan. For example, during recording sessions, the facilities team can select a mode that achieves the lowest noise levels and provides sufficient fresh air for an orchestra without an audience. Where new finishes have been applied to the hall, these have been selected to match the acoustic performance to the original finish they replaced. The one significant addition to the hall is what Chan terms acoustic banners. These are rolls of sound-absorbing material hidden in banner boxes at high level on the walls. For the majority of events, the banners will remain furled, but they can be unfurled to adapt the reverberation time of the hall for speech-based events, for example. Max Fordham tested the halls acoustics as part of the commissioning process. Acoustic testing was done during the night to minimise the influence from other noise sources, says Chan. The acousticians have also used the Covid-19 lockdown as an opportunity to make additional measurements to validate the Concert Hall acoustics and quantify the effect of the acoustic banners. Ventilating the Ashcroft Theatre The ventilation system for the 800-seat Ashcroft Theatre is very similar to that of the Concert Hall, with fresh air delivered via wall-mounted jet nozzles and extracted through ceiling grilles; Chan describes it as Concert Hall lite. Two AHUs serve the theatre; one supplies fresh air to the stage and the front of the auditorium, and the other the rear. As with the Concert Hall, we have front and rear AHUs, which can be turned on or off individually depending on occupation levels, Chan explains. These AHUs have heating coils, heat-reclaim wheels and a recirculation facility, with the ability to add cooling in the future. The AHUs are located in a plantroom above the stage. Ducts transport the tempered air from the units and through the ceiling void above the auditorium, to supply branches that drop down in the walls of the auditorium to feed the jet nozzles. Routing the ductwork through the ceiling void was much more of a challenge for the theatre. Unlike the Concert Hall, which is supported on a concrete frame, the roof of the theatre is supported by a series of dense steel trusses, which Chan describes as the bane of his life. He says the original ventilation system must have been designed alongside the steelwork very accurately to ensure the ducts could be threaded through the forest of angled steel. Id be lying if I said everything went in as wed designed it, without hitting a single beam, Chan says, laughing. Some of the voids and risers could only be accessed from scaffolding; when we started to open them up, we discovered things such as downstand beams that were not on historic drawings. As with the Concert Hall, the challenge The foyer has been decluttered as part of the Halls refurbishment The venue is currently closed because of the pandemic 46 October 2020 www.cibsejournal.com CIBSE Oct20 pp44-47 Fairfield Halls Supp.indd 46 25/09/2020 16:43