GENERAL CONSIDERATIONS
A theatre is a building with vast volumes that either contain a lot of occupants for a short period of time, or are left empty for the major part of the day. When the grand public volumes (foyer, auditorium and stage) are unoccupied, it is not necessary to supply fresh air to heat the building. For that purpose, radiant heating is supplied with baseboard units positioned on the peripheral walls. When the theatre is occupied, the mechanical units are activated for fresh air, heating and cooling.
There are 4 mechanical units that serve the theatre: 3 are located on the roof of the foyer, 1 on the backstage roof. The roof of the auditorium and stage is left free of any mechanical equipment. This is normally done for acoustical purposes, to prevent noise or vibration transmission to the auditorium.
Units 1 and 2 are positioned on a raised galvanized steel platform to prevent the machines from being buried in snow during the winter season. The galvanized steel panels on either side of the roof create an acoustic barrier, preventing the noise of the units to escape and be a public nuisance. This creates a confined space where snow is likely to accumulate.
AUDITORIUM-FOYER
Mechanical unit no. 1 serves both the foyer and the auditorium. Initially, there were 2 units, one for the foyer and one for the auditorium, to ensure better control. As the project was over budget, solutions had to be found to reduce costs. The mechanical engineer eliminated one unit and designed the ducts so both spaces could be served by a single unit. This explains in part the complexity of the ducts in the mechanical room on level 3. To have one unit service two spaces, the assumption was made, and accepted by the client, that the foyer and the auditorium would not be occupied at the same time. Therefore, as people first arrive in the foyer, the mechanical system allots 80% of its capacity to ventilate the foyer and 20% to the auditorium to keep minimal air treatment. When occupants move from foyer to auditorium, the demand for cooling detected by thermostats shifts space. This activates motorized dampers in ducts that open and close to redirect air in the auditorium.
In the auditorium, air is supplied by the ceiling. This choice, favored by the mechanical engineer, gives the audience fresh air that gently falls from the ceiling. Return air is taken from the back of the balcony ceiling, to create air movement in the direction of spectators seated at balcony level. Other return grills are located on the walls on either side of the proscenium. To avoid costly solutions, no air return is located under the orchestra floor, being a slab on grade with no access.
In the foyer, air distribution is solely done by the ceiling. Supply air is located parallel to the depth of the building, above the curtain wall windows on the sides, to avoid condensation during winter. Electric baseboards also run along the curtain wall to supply hot air against the glass in winter. The remaining air is supplied from the center of the ceiling. Return plenums are located perpendicular to supply, along the front and back wall.
Unit no. 1 supplies the serving public spaces: catering room, storage, entry hall, ticket office and service corridor, considered an extension of the foyer, as well as the toilets in the basement.
STAGE
Unit no. 2 strictly serves the stage area. Air is supplied by the ceiling and returned on either side of the stage curtain. Supply and return ducts run between the girders to minimize building height, this being normal practice.
For acoustic considerations, air velocity is reduced by half in ducts to avoid hearing air movement. To reduce air speed, all ducts were doubled in their width and height. Coordination between acoustics, structure and ventilation required changes and compromises from both mechanical and structural engineer. Some ducts were split in two to fit between girders. This situation is also true for unit no. 1 serving the auditorium. The plan of level 4 shows this clearly.
A specific consideration for a theatre: Air pressure on both sides of the curtain separating stage and auditorium has to be balanced to avoid a draft and curtain movement. During a play, the loading dock garage door must be closed, to prevent air draft to penetrate the stage and create movement in the curtain. This is also true for any window.
ADMINISTRATION
The administration section, located above the main entry on level 2 between the front facade and the foyer, contains offices that are occupied during day time. The spaces occupy a small volume and have requirements radically different form the auditorium or stage. The engineer specified a separate mechanical unit to service them, for efficiency and flexibility.
Within the administration, one element stands out as a major volume to be treated: The glass facade. This high volume, more than a service corridor, is the iconic figure of the theatre and counts for more than half of the cooling and heating requirements. Opposing views between the architect and the mechanical engineer on the necessity of the corridor's height were expressed: the first wanting a tall unbroken transparent facade, the second, a reduced volume to minimize mechanical equipment and energy consumption.
BACKSTAGE
The backstage area contains services spaces for the stage, separated between actors and technicians. Like the administration, some of these spaces are occupied on a daily basis. An independent mechanical unit as been provided for flexibility and energy efficiency.
BASEMENT
This area is serviced by mechanical unit 1. Extraction in the toilets and technical rooms is given by independent units located on the mechanical room's roof on level 4.
Toilets are in negative pressure, preventing odors from contaminating circulation spaces. For maximum ceiling height in the waiting hall, there is no suspended ceiling: Acoustic liner is directly applied against the bare concrete slab. To avoid visual clutter, ventilation ducts and sprinklers are located on the peripheral walls, hidden within a lowered gypsum ceiling in the toilets.