Orchestral Manoeuvres

Cardiff Bay is set to come alive with music. Welsh voices will once more resonate in the Bay, but in the new Wales Millennium Centre the traditional male voice choir will be joined by arias, orchestras and schoolchildren. Scheduled to open on 26 November with a gala concert by HSBC’s Cymry for the World, the bulbous Centre will be home to the Welsh National Opera (WNO) and give a new stage for music and theatre.

On entering the majestic front entrance, visitors are led into the huge lungs of the centre. Naturally ventilated concourse areas filled with bars, shops, restaurants and art galleries flow through the six-storey building. The core of the centre is the Donald Gordon Theatre, a 1900-seat venue designed to adapt acoustically to suit different performances. Alongside this is a 250-seat studio theatre; a 150-bed accommodation block with attached studio that a Welsh youth organisation and the national dance company will use; plus rehearsal rooms, a recording studio and other WNO facilities.

To complete the centre required early involvement from the m&e contractors to meet co-ordination needs, acoustic demands and deal with the unusual ventilation system and immeasurable quantities of cabling involved.

Sir Robert McAlpine was appointed as main contractor in a two-stage tendering process. The firm brought in NG Bailey as m&e contractor at the second, fixed tender stage and worked “back to back” with it. “Because it’s design and build, a job like this is not standard so there is a lot of risk involved. By getting involved with Baileys early on and getting a secured price for all the m&e work, we share some of that risk, which is what partnering is all about,” explained McAlpine m&e manager Joel Thorogood.

The design of the m&e continued for at least the first ten months on site. When McAlpine started work in March 2002 Arup was involved in much detailed design. Before each slab was poured the teams had to ensure design was complete and all builders’ work holes included.

“Although Arup had done the initial design work, when we started on site the design became our responsibility,” said Thorogood, “so Arup, and the architects all came under our employ. That’s why we were involved in the early stages.”

To ease the process all teams relocated to site. “Before piling took place we had a site set up and 40 cabins, all open plan, connected together over two floors. We could all draw on each other all the time and get the information right,” explained Thorogood. Included here was a drawing review room. Rather than distributing each drawing to individual teams a single version was placed here and all had a responsibility to review it and mark their comments before it was reworked. “The benefit was that everyone gets to see what others’ comments are and no-one has to collate the details,” said Thorogood.

Services for songs

In terms of servicing, the studio and accommodation block effectively stands alone. It is served by rooftop boilers and cooled by a variable refrigerant system.

The main centre is served by a single system in terms of heating and chilled water pipework. “There is one secondary circuit and only one secondary pump that does the whole building,” Thorogood explained. This design meant flushing and commissioning of the system could not be carried out until the building was virtually complete.

The separate areas of the centre were constructed almost in tandem. The steel frame was erected by October 2002, then the floor slabs poured before the brick walls were built. As the walls were going up, the installation of services followed through on a floor by floor basis.

“It is an incredibly complicated building structurally and service co-ordination-wise,” stressed Thorogood. The main theatre seating is constructed on cantilevered steel beams stretching above and across the main entranceway. This made it difficult to install services and close working between structural and m&e teams was essential.

This was also true for other services within the concourse. Much is installed within the ceiling of the full-height area. To ensure a smooth process, the entire area was filled with scaffolding and the work carried out in strict sequence.

Similarly, at roof level services had to be considered early in the build. All ahus in the fifth floor plantroom concealed under the roof were craned into position and the structure built around them.

The centre makes use of an ice storage cooling system. Two heavily insulated 6 x 3 x 2 m ice tanks in the basement provide the energy required. In these a labyrinth of pipes circulates glycol at -12°C to build a giant ice cube. The centre makes use of cheaper night-time energy to produce the ice and use of ice for top-up means that the chillers can be run on full load for longer, increasing their efficiency and allowing a smaller chiller size. During performances when loads peak, the system can draw on the chillers and the ice together to meet the demand. Installation of the system was relatively simple, reported Thorogood. “The most difficult thing with the tanks was, because they were in one piece, we had to get them in the building before we built any of the external elevation or any of the downstairs walls; basically the building was built around them.”

The biggest issue on the m&e installation was the cabling. “There are thousands of miles of cabling,” stressed Thorogood. Every socket and outlet has its own radial circuit feeding back to the same dimmer room rather than indirectly through local distribution boards. This was necessary to give the client the flexibility and demanded. In the orchestra pit for the main stage collapsible cable trays allow sections of the stage to move on spiral lifts while not disrupting the electrical supplies; however this adds yet more length to the cabling.

Making music not noise

Acoustics are a critical part of the services design, particularly in the main theatre. “If you can hear the services at all, it’s too noisy,” explained Thorogood. But before considering the noise from any services the location of the centre posed its own questions. The Bute Tunnel, a busy dual carriageway, runs under one corner of the site and there were worries over acoustic breakthrough. To ensure this was not an issue when the piles were being put in, Arup set up measuring equipment on top of the pile caps at night and a lorry was hired and driven back and forth through the tunnel. The data proved no action was needed.

Structurally all rooms are segregated. Many rooms in the main centre are of box-in-box construction, where the actual ‘floating’ floor is isolated from the slab by rubber-housed jacks and the walls are double-skinned, with the internal wall connected to the floating floor and tied with rubber interceptors to the external wall attached to the slab. The roof also has been isolated from the main theatre.

The ductwork for the ventilation system throughout is massive and the airflow very slow. “The air is like a small trickle and there’s no noise,” said Thorogood, “The idea is to make everything as big as you can and make it as slow as you can.” The sections entering the rooms are clad with acoustic material to remove any noise before the critical spaces are reached.

Noise from electrical sources also had to be considered and top of the list was lighting. “We had a lot of input in the early days in terms of acoustically testing light fittings and lamps to make sure there was no problems with filament buzz because they were all dimmable,” explained Thorogood.

Most of the low level seat lighting is low voltage, bringing a need for step-down transformers. Placing transformers in the seat legs was rejected due to the noise levels. Instead remote, step-down, multi-load transformers were used.

Phase two of the build will involve construction of a 500-seat theatre and facilities for live tv and radio performances, completing the triangular footprint of the site and rounding the arts extravaganza the city now boasts.