C O N T E X T 1 0 7 : N O V E M B E R 2 0 0 8 23 the 1980s, was also inadequate and eventually fell into disuse. In 2002 the hall was closed due to concerns about the safety of the structure. A team was commissioned to design a wide-ranging refurbishment. The structure is a mixture of steel frame, load-bearing masonry, and filler joist concrete slabs. The slabs were constructed from concrete that included crushed clinker from coal-fired boilers. Clinker concrete is not very strong, and it is susceptible to mechanical and water damage. The acid in clinker attacked the steel filler joists. It was assumed that the clinker concrete would have to be replaced but, following work by the structural engineers, a design was developed in which much of the clinker concrete could be retained. Designing a new ventilation system within the constraints of the existing building, with its less than ideal air distribution, required a pragmatic approach. In consultation with the client, it was decided to aim for reasonable standards of thermal and acoustic comfort without recourse to mechanical cooling. A scheme was designed that did not include mechanical cooling but would not preclude it being added at a later stage, should it be required. In the few years before closure, the auditorium had been filled to capacity only rarely, but the refurbished hall is likely to have a full house on many occasions. The most onerous conditions for the auditorium ventilation system will be a sell-out concert on a warm summer evening. A range of options for the ventilation of the auditorium was considered. It was concluded that only a displacement system could be sympathetically integrated with the listed interior. The advantage of a displacement system is that with good distribution, mechanical cooling can be avoided as most of the heat from occupants and lighting is excluded from the occupied zone. Also air can be introduced at a higher temperature than with an overhead supply system. An energy-efficient, low-pressure-loss system was developed, using the principles of a displacement ventilation system. The constraints of the existing building established the duct area, which largely determines the pressure required from the fans to drive the system. Fresh air drawn in from the external light well between the Royal Hall and the adjacent Exhibition Hall is filtered, heated, and drawn by a fan through large sound attenuators and into the basement corridor. The corridor reverts to a supply air duct as originally conceived by Stott, but with the both ends sealed by an air lock.The walls of the corridor are lined with acoustic absorbing foam and perforated sheet metal, resulting in very low noise levels of concert-hall standard. Intervention in the historic fabric was minimal. The existing chair store beneath the grand circle and the ceiling void below the upper circle are used as distribution plena. Decorative grilles mounted in the face of the grand circle balcony supply air to the flat floor, with underseat diffusers below the fixed seating. The once-operable lights in the lanterns over the ambulatories have been refurbished and motorised to allow warm air to exhaust at high level or to allow more make-up air in. These are used in combination with the 1980s fan cowls that have had their fans replaced with motorised dampers. The ambulatories adjacent to the auditorium space will be used as the principal interval bars. For certain events the ambulatories may even be open to the auditorium during the performance. The existing roof lights to these areas have been motorised to provide a natural means of ventilating these spaces and a further route for ventilation air when ambulatories are open to the auditorium. This avoids the need for a separate air system supply to serve these principal foyer spaces.The supply fan serving the auditorium is speed controlled to allow an appropriate amount of air to be delivered to the space based on occupancy, using a combination of carbon dioxide and temperature sensors. Airtightness is always a challenge in an existing building. Working closely with the architect and contractor ensured that the construction of the refurbished building fabric and builderswork elements of the ventilation system were detailed and built to minimise air leakage. Several pressure tests were carried out, supplemented by smoke tests with a theatrical smoke generator to help visualise air movement. Restored to its original glittering glory, the Royal Hall was re-opened by the Prince of Wales in January 2008. Once again it draws a wide range of visitors and the ventilation system, discreetly integrated with the fabric, is maintaining comfortable conditions during performances. David Clark is a partner of Max Fordham LLP. The design team for the refurbishment of the Royal Hall consisted of Burrell Foley Fischer (architect), Price and Myers (structural engineer) and Max Fordham (services engineer). Left: A computational fluid dynamics analysis of summer conditions Right: A computational fluid dynamics model of auditorium ventilation Images: Max Fordham LLP
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