Five alive

The installation of m&e services at Heathrow Terminal 5 took a huge leap forwards as 2006 approached. After years of highly detailed planning and co-ordination, the installation of the central service chimneys in the main terminal building began.

Five chimneys, each weighing around 100 tonnes and reaching 15-m high are being installed along the central spine of the new building, T5A. These, plus three similar, smaller chimneys positioned on the airside stretch of the building (closest to the runway) are central to the m&e services strategy and provide the comfort cooling of T5A. In mid-November the first of the five main chimneys began to take shape on site.

Responsibility for the design and installation of the m&e services on the majority of T5A was awarded to Amec.

It has been working on the services design since November 2002.

Structural design

One of the most unusual and successful aspects of the chimney design at T5 was Amec's decision to modularise much of the m&e plant and prefabricate it offsite.

All eight chimneys are constructed of prefabricated steel modules, based over four floor levels. These modules comprise the vast majority of the m&e services needed for the terminal building including general ventilation ductwork, smoke extract, kitchen extract systems, control systems, cabling containment, lighting, small power, communications infrastructure and fire alarms.

As well as containing the services, the chimneys were designed holistically with the building and provide a continuation of the structure to the roof. Items such as escape and access stairways and floors for the services maintenance were built into the prefabricated modules. The development of the chimneys was carried out using 3D modelling and collaborative working with the supply chain (see box, ‘Model features').

"Ideas were developed around the needs of the project," explains George Adams, Amec's T5 engineering manager. "The key driver for the modules is the time benefit - to save time and give programme assurance. The business benefits from this far outweigh any capital savings." The use of prefabrication reduced traditional onsite interfaces by around 60%. The resulting lower level of operatives and build activity on site, contributed to programme certainty.

"The key benefit was a six-month reduction on the critical path of the programme, which was estabished three years ago. Modularisation was not an add-on, it is an integral part of the building," Adams stresses. "It's getting close to plug-and-play technology."

Off-site working

Around 60% of the services were prefabricated offsite. "Any more than this and it would not have been cost-effective," explains Adams.

There were two types of services module used in the project, large-scale versions that slotted together to form the chimneys and plantrooms, plus smaller units for distribution of services around the site. Prefabrication was split between two locations according to module size. The larger units were manufactured by Babcock Engineering Services at its facility in Rosyth, Fife; the distribution units were produced by WS Britland in Dover, Kent. "The Scottish site had the capacity and size to deal with the large modules; the Kent facility is more focused and able for mass production," explains Adams. The integrated supply chain approach used at T5 meant the various suppliers delivered directly to the assembly yards to Amec's instructions.

"The main benefit of the prefabrication sites chosen was that they had a very large capability, so if Amec wanted to increase the number of manufacturing streams to meet the demands of the build programme this was possible," explains Adams. "Say there is one production line making the modules, a second, third and fourth line could be started up alongside this, duplicating the work and increasing the number of modules being produced at the same time," he adds.

This flexibility to change manfacturing output to meet the demands of the site was essential. "Parallel manufacturing was a major part of the prefabrication strategy and the ability to set up multiple streams was vital," stresses Adams.

Manufacturing of a complete airside chimney from cutting of the steel to the finished product ready for installation takes around five weeks. The main chimneys also follow this five-week programme. This timescale was dictated by the factory's production cycle. "The factories were confident about making the modules in five weeks," explains Adams. "This is where the flexibility to have extra production streams was essential, so that if more modules were needed over the five-week period, another stream comes online to produce them."

The chimneys were erected at the prefabrication yards and inspected before being dismantled for delivery to site (see ‘Building blocks'). One of the few components to be installed traditionally is the cabling; a design exercise showed this to be the most cost-effective method.

The services are set to complete by March 2007, with commissioning due to end by September 2007. T5A is due to usher its first passengers to the skies on 30 March 2008.