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CASE STUDY 125 Old Broad Street, London

FOCUS ON: HEATING & VENTILATION

Hammerson's redevelopment of the former London Stock Exchange at 125 Old Broad Street, London EC2, will create a total net internal area of 31,000m¦, comprising ground-floor retail space and 26 office floors.

The original facade will be replaced with a highly engineered envelope, designed by Grimshaw, that will let in more daylight and improve thermal and solar performance. The building will be extended by 1,500mm around the perimeter to create more usable floor space.

The office areas will be conditioned by a two-pipe, fan-coil system with electric reheat. After examination of the building's load profile, which is cooling-dominated, this was found to be more economical than a fourpipe system. The new facade and the geometry of the building, combined with local zone controls, will ensure that the amount of electricity used for heating is minimal.

The layout of the building, with its rectangular core, lent itself to an economical services distribution layout, with every point on the floorplate close to a riser. This enabled the design team to maximise the floor-to-ceiling height. Particular attention has been paid to the design of the ceiling, with sprinkler heads, lighting, slot diffusers, PA speakers and firealarm detectors and sounders incorporated into a race-track of multi-service tiles running concentrically around the core. This allows the majority of the ceiling to be plain white.

A special 'N-shaped' plenum has been designed to bridge over the light fittings and distribute air to the two runs of slot diffusers on either side of the tile.

The new engineering systems will be to shell-and-core for the ground-floor retail and to Cat-A fit-out on the office floors.

Construction started this April following the appointment of Bovis Lend Lease as main contractor. Practical completion is scheduled for December 2007.

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