星空传媒

Parabat Garga is under no illusions about the scale of the task his company faces. As project director for Amec Services, he is responsible for the detailed design, procurement, installation and commissioning of the mechanical services for a large part of BAA鈥檚 Heathrow Terminal 5 project. 鈥淚t is one of the largest M&E installations ever undertaken by a UK contractor,鈥� he says.

The 拢4.2bn terminal under construction in west London is said to be the biggest construction project in Europe. It includes a 396 m long, 176 m wide, 40 m high glass-clad main terminal building; a 442 m 脳 52 m satellite terminal (itself bigger than Terminal 4); a 4000-space multistorey car park and tunnel extensions; and a new station for the Heathrow Express and the Tube鈥檚 Piccadilly Line (see site plan below). All this construction is taking place between two of the world鈥檚 busiest runways, with planes taking off and landing every 90 seconds. If you add to this the challenge of getting men and materials to the site through a single access gate, time constraints on delivery vehicles on the nearby M25 and an immovable construction programme, you can see just why the scheme is such a challenge.

Despite the gargantuan nature of the project and the tricky site constraints, Garga is making some astounding claims. He says the contractor will undertake its share of the 拢600m of services work with less than half the site labour that would conventionally be required. Not only that, but he insists Amec will actually 鈥渃ut six months from the project鈥檚 original build programme鈥�.

Garga can only make these impressive declarations because Amec has decided to make extensive use of off-site manufacturing techniques. Prefabrication of a building鈥檚 services is not new; pre-assembly has been used on a variety of buildings, including London鈥檚 Tower 42 and Birmingham鈥檚 National Exhibition Centre. However, the challenge for Garga and his team is to prove that modularisation can work on such a complex project.

Sitting in the design office dressed in a tweed jacket, Garga looks more the academic than construction revolutionary. It is when he talks construction, however, that his radical principles come to the fore. 鈥淭he conventional approach is to erect 80% or more of the M&E services on site, which is a laborious and time-consuming activity; on this site, however, Amec is assembling over 60% of the services off site,鈥� he explains. In addition to increasing productivity, Garga says that this approach is superior in other areas: 鈥淎ssembling the services in a factory is safer for the operatives; their workspace is cleaner and consequently the quality of their work is better; there are fewer men on site; and there are fewer materials to be delivered to and stored on site鈥�.

On site, the main terminal鈥檚 roof is almost complete. Architect Richard Rogers Partnership鈥檚 design features a huge wave-form roof supported on a series of X-shaped tubular steel abutments. The building鈥檚 fully-glazed facades appear to hang from this roof like glass curtains. Rogers designed the roof and facade structure to be completely independent of anything inside the terminal; this gives BAA great flexibility for the future and, more importantly, it allowed construction of the building鈥檚 shell to commence while the layout of the interior was still being finalised.

Consulting engineer DSSR developed the concept design for the terminal鈥檚 services in partnership with fellow consultants Mott MacDonald and Parsons Brinkerhoff. The basic plan is to take the main services 鈥� electric power, heating and chilled water 鈥� from a separate energy centre to the south of the main terminal building, pipe them through underground tunnels into the basement of the new terminal and its satellite, and then direct them through the terminal鈥檚 basement to 11 key riser points within the terminal itself. In addition to the pipework, these risers will also house ventilation plant, IT rooms and staircases.

The consultants opted to use a constant volume air displacement system to keep conditions inside the terminal comfortable. This works by drawing fresh air into the terminal through an enormous builderswork duct in the terminal鈥檚 basement, where it is filtered and heated before being ducted to the base of each of the 11 risers. These risers are, in effect, a series of five plantrooms stacked one on top of the other; one air-handling plantroom for each of the building鈥檚 five main floors 鈥� 55 plantrooms in total. The fresh air is supplied to each air handling unit, with exhaust air expelled through eight chimneys mounted on the terminal鈥檚 roof.

The initial concept from the consultants was handed over to services contractors to design and install. The consultants then have a watching brief as 鈥渃oncept guardians鈥� according to Garga. Along with Amec, other services contractors working on the scheme include Crown House Engineering, on the 拢350m satellite terminal, and Balfour Kilpatrick, on an 拢80m services contract for a railway station and tunnels.

We鈥檝e modularised all the primary distribution pipework on a scale never seen before in the UK

Jim Hutchison, services project leader, Amec

Amec developed a modular system for the off-site manufacture of services for the main terminal building and its energy centre. Each module consists of a rectangular steel frame into which all the service pipes, ducts, electrical cable trays and even some of the plant are installed. Groups of these modules will be pre-assembled in the fabricator鈥檚 yard before being delivered to site to ensure they fit together and to enable some systems to be commissioned before leaving the site. 鈥淭he modules are small enough to fit on the back of a lorry,鈥� says Garga. More than 5000 modules based on 11 standard module types will be supplied to the main terminal building alone.

Jim Hutchison, Amec鈥檚 services project leader, starts his tour of the project at the terminal鈥檚 energy centre. This grey, industrial shed houses 43 MW of heating and 27 MW of cooling plant for the main terminal building and its satellite. In the future it will also be home to the plant for a second satellite building, to be constructed under the scheme鈥檚 second phase.

Stepping into the energy centre, the first thing to catch your eye is a line of four giant chillers lining the north wall. The size of each 6.6 MW chiller meant it had to be delivered in three sections, jacked into position and then assembled. BAA鈥檚 specification for an energy-efficient, environmentally friendly cooling systems means all the chillers use ammonia as a refrigerant. The chillers are in the process of being connected to eight roof-mounted wet cooling towers, with their pipework modules craned into position on the roof.

At the eastern end of the energy centre is the terminal鈥檚 heating plant. Two enormous cylindrical boilers, their burners still sheathed in polyethylene wrapping, lie on skids waiting to be moved into their final position. Once Amec receives delivery of a smaller third boiler, all three can finally be manoeuvred into place.

High overhead the building鈥檚 ceiling is a maze of pipework and ductwork. 鈥淲e鈥檝e modularised all the primary distribution pipework in the energy centre on a scale never seen before in the UK,鈥� Hutchison says. The modules were installed in what Hutchison describes as 鈥渢rains鈥�. Each train comprises 10 modules bolted together on the ground. The modules house all the pipework and ductwork and cable trays and even come complete with sections of the energy centre鈥檚 mezzanine floor. The 10 modules are lifted as a complete assembly in a single 100-tonne lift using strand jacks. 鈥淭he advantage is you are lifting the floor up with the pipework so that you don鈥檛 have men working at height,鈥� Hutchison explains. 鈥淎nd once the modules are installed you can work underneath them immediately,鈥� he adds.

From the energy centre, heating and cooling pipework snakes to the main terminal and its satellite through 1.5 km of tunnels. Outside the energy centre, a scaffolding lid covers the hole where pipework modules were lowered into the underground ducts. In addition to the 600 mm diameter cooling pipework, the tunnel modules contain heating, cold water, drinking water and sprinkler pipework. 鈥淭he distances involved lend themselves to modularisation,鈥� says Hutchison. The project鈥檚 phasing means that there is still one leg of pipework still to be installed before it can be cleaned and flushed.

Beneath the main terminal, the heating and cooling mains split to serve three subterranean 鈥渨et鈥� plantrooms. From here the mains branch out to feed the base of each of the 11 service risers. Currently Amec has installed about 60% of the pipework in the building鈥檚 basement.

On the terminal鈥檚 ground floor, or apron level as it is known in airport parlance, the first modules to form the service risers are being installed, beneath the terminal鈥檚 giant roof. A mezzanine floor partially fills the space beneath the roof, within which 11 huge voids rising up to the roof mark the positions where the service risers have yet to be installed.

We鈥檙e aiming to have 70%of the building鈥檚 services prefabricated by the end of the project

Parabat Garga, project director, Amec

Work on Riser S1 is the most advanced, with the top two plantroom levels already in place close to the roof鈥檚 underside. At the moment a team of five men from a specialist lifting company are grappling with the four modules that will form the riser鈥檚 basement plantroom. Each module was delivered to site on the back of a truck. A specially constructed gantry then lifted the module clear of the vehicle before placing it on a motorised bogy. Inside the terminal, the module is transferred from the bogy to a lifting frame. Once all four modules are in place and have been bolted together, the competed assembly will be lowered into position using four strand jacks. Four outriggers will support the plantroom from the floor slab to allow the lifting frame to be removed.

Amec is using two fabrication companies to assemble the modules. Babcock Engineering Services, in Rosyth, Scotland, will put together the more complex core modules, while Kent-based WS Britland will assemble the pipework distribution modules. Wisely, Amec involved the fabricators in the design of the modules to speed production. 鈥淚f you design the modules to suit the manufacturing facility you will get a more cost-effective design,鈥� Garga explains.

Before construction started in earnest, a series of sample modules were constructed. This allowed the fabricators to establish an assembly methodology and enabled the designers and erectors to review the module鈥檚 construction and set a workmanship benchmark for subsequent modules.

Using fabricators based in other parts of the country has other advantages for the T5 site. Garga says that having the modules manufactured off-site helps ensure there is a workforce available to put them together, while reducing the demand on skilled workers on site. The modules will be delivered to site directly from the fabricators as they are needed. 鈥淚f we need to make an adjustment to programme, we can stockpile the modules off-site,鈥� he says.

However, Amec has not modularised everything. The pipework has been delivered in modules, but it is delivered without insulation. According to Garga it is more cost effective to apply insulation in long lengths, preferably later in the project when the possibility of damage has diminished. And, although the cable trays are part of the modules, cabling contractor EDF will not roll out the power cables until later in the programme. 鈥淚t is uneconomic to lay the cables as modules,鈥� Garga says.

One of prefabrication鈥檚 benefits is that it is compatible with state-of-the-art design systems. Before the modules are assembled, their virtual, digital forms are inserted into the T5 single project model (see page 29), which allows Amec to eliminate several nightmare scenarios in advance. In addition to detecting any clashes, the model allows what Garga describes as 鈥渃onstruction studies鈥� to take place: this is where the service modules are put together into runs and risers to work out the most efficient way of assembling them.

Amec has also involved BAA鈥檚 facilities managers in the design of the system in what Garga calls 鈥渇ront to back engineering鈥�. He says: 鈥淲e wanted to ensure the services are efficient to run and maintain so we involved people that will operate the plant throughout its life.鈥� The single project model allows BAA鈥檚 facilities management team to 鈥渨alk through鈥� the building to check for access problems when servicing the plant. Once everybody is satisfied, the 3D CAD models are transferred directly to the fabricators for construction. 鈥淲e realised we needed to plan our process in a different way. We did it through web-based technology to plan the logistics, manufacturing data and materials flow,鈥� explains Garga.

With 60% of the building鈥檚 services prefabricated, you would have thought Garga would be satisfied. Not a bit of it: 鈥淲e鈥檙e aiming to raise that figure to 70% by the time we near the end of the project,鈥� he says. The first modules to form the terminal鈥檚 risers are starting to be installed 鈥� the pressure is now on Garga to prove his claims if the terminal is to open as scheduled on 30 March 2008.