When Buro Happold began work on the Dome's building services at the beginning of 1997, the only thing that was fixed about the Dome was its footprint - almost everything else still had to be finalised. 'We knew where the mast positions were and we knew where the outline was,' says Ken Carmichael, Buro Happold M&E team leader.
'The biggest challenge was what was going inside it and where it was going. We had to try to design an infinitely flexible services infrastructure.'
In the absence of any information about the Dome's contents, Carmichael's team initially tried to design the services so that any activity could happen at any location. This led to a spider's web design that was too complicated to be feasible.
'It was designed so we could service anything no matter how large or small it was,' says Carmichael. 'It wasn't really practical in time or money, and it would have sterilised the groundworks for a long time. We pulled back from that position but kept the concept intact.'
The final solution sees the circular floor of the Dome split into six equal 'pie slices' and, instead of the spider's web, there are six radial plant tracks and three concentric ring trenches that link everything together and carry a total of 8km of services pipework. The primary plant - including chillers, pumps, sprinkler water tanks and the main plant rooms - is located in 12 pods outside the Dome.
From here, the services are fed into secondary plant rooms housed in six core buildings inside the structure. The trenches radiate out from these buildings, taking the chilled water, drainage and electrical cabling into the six sectors.
'We decided that any exhibitions that required full services would have to sit over a trench which we could service from the core plant rooms,' explains Carmichael. 'If they just need power and communications that could be done by running a conduit within the service finish.'
Lack of knowledge about the Dome's contents also defined the strategy for the design and procurement of the M&E equipment. 'To a certain extent there was a recognised strategy that we should overdesign the services,' says Carmichael. 'The client's brief was that it had to work.'
As a result, all the pipework from the primary services right through the secondary plant rooms and into the trenches is all the same size. It only reduces in size when it branches off to go into the individual zones. And the design team also standardised on one size for all but four of the Dome's 32 transformers.
The equipment specification was also dictated to some degree by consideration of what would happen to it after the Dome closes at the end of the year. 'It's clearly impossible to design a system that runs perfectly for one year then falls over after a year and a day,' says Carmichael. 'Chillers last between 10 and 20 years and transformers can last up to 40 years.'
As a result, the larger items were specified only after the team had consulted the London International Futures and Options Exchange (LIFFE) to find out the likely resale value of various pieces of plant. It had a big impact on the procurement of the transformers, some of which are located in the external pods. The specification was changed from standard cast resin transformers to some made of an organic ester material which is better for indoor use. These are likely to sell more easily - probably for a scheme in a developing country.
Right from the start both Buro Happold and main JV contractor McAlpine Laing were keen to see as much of the plant as possible prefabricated off site and delivered already containerised to the site. 'One of the cornerstones was to pre-package everything so there was no commissioning on site,' says Carmichael.
'Everything in the plant cylinders (pods) was pre-packaged, slid into place and just cabled up. Obviously the system as a whole then had to be tested, but all the commissioning had already been done.'
The decision to go for prefabrication was primarily because time was so tight, but there was also the issue of quality. 'They were building it all in a factory environment rather than on a wet dusty construction site,' says Carmichael. 'Here the main plant is outside, so having it containerised meant it was already waterproof when it arrived.'
His team was keen not to reinvent the wheel. 'We didn't want any plant that hadn't been tried or tested and proved in the field to be reliable,' he says. 'In most large buildings a short period of tweaking once it is occupied is normal, to get the systems working just right. But here there was no opportunity for that - the systems had to be fully functioning on day one.'
That is why computer controls are kept to a minimum, and there is no automated building management system. Buro Happold went for simple controls, with computers primarily as monitoring rather than operating tools. 'Modern building management systems usually only get commissioned six or eight months into the life of a building,' Carmichael points out.
When his team first started developing the building services strategy, the concept of the Dome was really no more than a giant umbrella - a covering to keep the worst of the elements off. There was always a plan for a central show, but that was originally going to be in an enclosed area that could be heated or cooled independently.
Once the architects opted for turning the Dome into a fully enclosed building with a massive central space inside, the M&E designers were faced with a new challenge: 2.1M.m3 of air that had to be maintained at a comfortable temperature. Buro Happold originally looked at natural ventilation, but there was obviously going to have to be heating in the winter and cooling in the summer if the Dome was to be comfortable for visitors and performers.
The result is a combination of natural ventilation, roof extraction, mechanical air supply and inner movement fans. Fresh air enters the building through the massive doors - three of which remain open even in winter - and warm air is delivered by 24 huge air handling units situated on top of the core plant areas.
Air is extracted by 12 extract fans located high up in the central arena area, and another 12 much larger fans, one inside each of the giant masts. Vents in a 60t aluminium cap at the centre of the Dome's roof aid the natural ventilation.
Fabricated by Baco, the 30m diameter cap was installed with the aid of a 50m high birdcage scaffold - the highest independent scaffold ever built, and one of 45 separate packages involved in the £40M M&E works.
Now that the Dome is open, Carmichael looks back with pride at what has been achieved. He describes the opening night, on 31 December 1999, as 'one of the most exciting times of my working life' - despite initial nerves about what would happen if the lights failed. He has now been seconded to NMEC for the year as the Dome's electrical manager.
One thing he can enjoy is seeing the 12 plant pods lit up at with red lights at night as part of the Dome's dramatic lighting display. 'I think they look wonderful,' he says. 'It's very exciting for us as building services engineers to see that because it expresses our work. For once you can see what we do.'