The idea of holding a celebration for the millennium had been talked about since 1993 and even before. The Greenwich site had always been a possibility but other sites were also under consideration. In the latter part of 1995, the Millennium Commission invited bids with design proposals for several sites. Imagination Ltd joined with the NEC and Birmingham City Council to put forward a proposal for Birmingham. Buro Happold assisted Imagination in that bid. Imaginations proposal for content and design ideas was judged the best and they were subsequently asked to consider how they would transfer it to Greenwich. In the first months of 1996, Imagination, with assistance from Buro Happold, put forward a number of proposals for housing an exhibition in pavilions with a large arena for shows and displays. Richard Rogers Partnership was at that time working with British Gas and English Partnerships on the master plan for the whole of the gas works site. Their master plan had a circular road pattern at the northern end, which Imagination had incorporated into their exhibition plan.
Trang 1SERVICING THE DOME ENVIRONMENT
Tony McLaughlin BSc C Eng MCIBSE MASHRAE M Inst E
Partner, Buro Happold Consulting Engineers
S Y N O P S I S
The Millennium Dome is a fabric clad structure covering
some 80,000m2 which is to house a spectacular
exhibition for the duration of the Millennium Year This
paper describes some of the constraints on the
environmental engineering design, the servicing strategy
adopted, the cooling and electrical loads determined, and
how the environmental design evolved to meet the
changing development of the exhibit designs
I N T R O D U C T I O N - T H E M I L L E N N I U M
E X P E R I E N C E
The idea of holding a celebration for the millennium had
been talked about since 1993 and even before The
Greenwich site had always been a possibility but other
sites were also under consideration In the latter part of
1995, the Millennium Commission invited bids with
design proposals for several sites Imagination Ltd
joined with the NEC and Birmingham City Council to
put forward a proposal for Birmingham Buro Happold
assisted Imagination in that bid Imagination's proposal
for content and design ideas was judged the best and they
were subsequently asked to consider how they would
transfer it to Greenwich In the first months of 1996,
Imagination, with assistance from Buro Happold, put
forward a number of proposals for housing an exhibition
in pavilions with a large arena for shows and displays
Richard Rogers Partnership was at that time working
with British Gas and English Partnerships on the master
plan for the whole of the gas works site Their master
plan had a circular road pattern at the northern end,
which Imagination had incorporated into their exhibition
plan
The separate pavilions were four generous storeys high
and involved a considerable amount of construction work
leading to a difference between the costs of the designs
produced by Imagination to meet the brief, and the
Millennium Commission's budget The site was very
exposed to wind and rain coming off the river and there
was a worry about the impact of this on visitor
experience in the winter months Imagination was trying
to deal with this by covering the spaces between the
pavilions, which were arranged around a central show
arena
In May 1996, faced with time running out, Gary Withers
of Imagination and Mike Davies of the architects Richard Rogers Partnership suggested covering the whole site with a giant umbrella This would create a protected environment in which exhibition structures could be designed specifically for the exhibitions and be rapidly erected without the necessity for weather tight cladding
We in Buro Happold picked up that idea and suggested a fabric clad stressed cable-net structure supported by 12 masts This concept was welcomed by the client and engineering work got underway
T H E S I T E C O N D I T I O N S
Greenwich peninsula is an exposed site with the river Thames on "three sides "of the Dome site leaving it vulnerable to the winter winds from the east In the depth
of winter it can be an inhospitable place when the wind
is in the wrong direction Mike Davies reminded us many times that to the east there is no ground over 100m between Greenwich and the steppes of Moscow But like most southerly UK sites the met office offers the following synopsis, the prevailing wind is south westerly, the coldest month is January with a mean monthly temperature of 4oC and July is the warmest month with
a mean monthly temperature of 17.5oC As a matter of interest a temperature of 37.8oC was recorded at Greenwich in 1911 Greenwich is 7m above sea level
E N V I R O N M E N T A L E N G I N E E R I N G
THE 'UMBRELLA' CONCEPT
The concept of developing an "umbrella" environment is nothing new, as many of the mainline rail stations demonstrate What makes the Millennium Dome different is its physical scale and its intended purpose The dimensions of the Dome are huge: 320m in diameter, 50m high in the centre, with an enclosing wall structure 10m high and 1km long The contained volume is approximately 2.1 million cubic meters, which leads to a many well published and interesting statistic eg the weight of air inside the Dome is actually greater than that
of the structure that encloses it, not to mention the fact that it could contain 3.8billion pints of beer It is twice the size of Atlanta's Georgia Dome, previously the largest tensile-roofed structure in the world
Trang 2•mm U
Fig 1A The Environmental Concept
4 320m w>
Fig IB The Problem of Scale
S o l a r Reduction
The Creation of a M e s o E n v i r o n m e n t under the Dome roof from
w h i c h other s t r u c t u r e s ( c o r e & exhibition buildings) c a n s p a w n
F i g l C
design and passive control systems: mechanbal control systems:
• protection from solar radiation in hot weather • fresh air ventilation
• protection from precipitation in wet weather • air movement
• natural ventilation in hot weather • heating in winter
• wind protection in cold weather • comfort cooling in the core
• a smoothing of temperature or humidity accommodation and exhibits
Fig I D
When we first started work on the building services and environmental systems, it is fair to say that the Clients brief
was somewhat lacking, both in terms of what was likely to
happen inside the Dome, and even more so, what its form and operation was likely to be The driving issue was time The only design guidance we had, was to draw on our own previous experience and look at precedents The idea was to provide a services back bone which would give the desired flexibility for an exhibition theme which was still very much
in the melting pot Naturally this flexibility would also have
to have the capacity for the likely energy demands of the future exhibitions, all of which would be unique At the time, Imagination were leading the team, and it was with their extensive knowledge of past and present exhibitions, as well
as a lot of research into utility loads for existing exhibitions that we established the following energy demands:
Power supply 35MW Cooling demand 18MW Heating demand 2.5MW for the Dome air
intake systems
How these were delivered is addressed later in the paper
E N E R G Y B A L A N C E
Initially, one of the design team's primary concerns was the environmental implication of putting such high heat loads together with 35,000 visitors under a transparent roof What were the environmental conditions likely to be experienced
by the visitors? What would visitors expect? Would conditions be acceptable?
The roof is a double skin fabric, which allows 12% light transmission and has a shading coefficient of 0.08 Externally, the fabric is highly reflective (white), whilst internally the fabric is a white "matt" finish Initially, the architects and cost consultants preference was for a single skin structure but this had to be rejected environmentally, due to the need for increased solar protection of the double layer and, just as important, the need to provide some thermal insulative properties for the winter conditions The convincing argument was the much-reduced risk of condensation The inner fabric liner - which is not structurally taut as the outer layer - also assists in "softening" the enclosure's acoustic characteristics
The following energy balance diagram was first used to illustrate the problem and was the first simple step in our environmental analysis of the Domes environment
One of the underlying design objectives for the "umbrella" environment was that it should use the niinimum amount of energy to provide the transient environment within which the exhibition would operate Another advantage of the
"umbrella" is that it allowed the construction of the exhibition and core buildings under cover, free from the extremes of the British climate The downside of this latter point was that construction dust etc was trapped which eventually stained the inner liner
Trang 3Fig 2 Energy balance diagram
C O N D E N S A T I O N
The thermally lightweight, low insulation, high occupancy
characteristics of the Dome did give the design team some
concerns regarding the risk of condensation The arguments
for the inner liner were almost entirely based upon
environmental issues of which condensation was one The
others being solar protection, heat insulation in winter and
acoustic absorption
Buro Happold's TAS analysis of the volume indicted that
with the installed mechanical ventilation systems operating it
was possible to limit the build up of condensation We
looked at a number of operating scenarios which indicated to
us that the greatest risk of condensation on the internal skin
was late in the evening on a cold winters day with a
reasonable attendance We calculated that the build up of
moisture to be in the order of 30g/m2, this equates to a very
thin wetted surface less than 1mm thick Condensation
dropping is therefor unlikely
To validate our work we commissioned "The Centre for
Research in the Built Environment" at Cardiff University to
carry out an independent check This study made the
following observations;
surface condensation on the inner surface of the roof Whilst some condensation is likely it should not be sufficient to cause drips and will quickly evaporate as conditions improve
• Condensation risk in the Dome is however very sensitive to the ventilation of the space If ventilation rates do not reach those assumed, particularly in winter, there is a very high risk of severe condensation
on the inner skin As occupancy moisture builds up The simulations described in this report indicate that
ventilation rates should be greater than 0 3 air
changes per hour Thus natural ventilation alone may not be sufficient
• Condensation risk may be significantly reduced by continuous overnight ventilation, even in winter
• Condensation risk may be reduced by reduced by increasing the inner surface temperature
• Condensation risk will be increased by introducing internal water features, planting and other water vapour producing processes
• There is also the risk of condensation on the inner skin of the outer surface this could lead to staining or mould growth
V E N T I L A T I O N S T R A T E G I E S
Initial thoughts were for a totally naturally ventilated building, similar to the railway station environment referred to above, but this alone would never be sufficient because of the scale and usage of the enclosure
MM
This picture was taken from Building Services Journal April 1899
Trang 4Natural ventilation could not penetrate the depth of the
dome (particularly so in summer) and entering fresh air
would tend to rise a short distance in from the perimeter
as it picked up the internal heat gains Secondly the flow
restrictions imposed by the large scale perimeter
exhibition buildings would prevent air reaching the
centre Next, the team considered the use of underground
air ducts supplying a large displacement system
However, the desire to reduce the amount of ground
excavation to the absolute minimum due to the costs of
excavation in contaminated ground, made this
uneconomic Further, such a major displacement system
imposed on the plan at such an early stage of the design
process could impede the future placement of the
exhibition structures, so this solution was also rejected
The adopted ventilation strategy relies upon the
perimeter zone being naturally ventilated via open doors,
a permanently open strip at the top of the perimeter wall
and the natural leakage of the structure itself To move
air into the centre of the Dome, two 25m3/s air handling
units are located in each of the six core buildings
providing 300m3/s in total These air systems have a
modicum of heating, equivalent to the Building
Regulations uninsulated structure, which allows 25W/m2
of heating input This input is just sufficient to take the
chill off the incoming air The same applies in summer
when again, a modicum of cooling is added primarily to
assist the air in dropping into the occupied central zones
There is no attempt made to control the Dome
environment as a whole It will be a few degrees warmer
than the external environment in both winter and
summer The same large air handling units have variable
speed drives and can operate in full re-circulation mode
The full re-circulation option is used during shut down"
and rehearsal hours during the winter months
The following diagrams illustrate the applied layers of
ventilation
D E S I G N V E R I F I C A T I O N
TWO DIMENSIONAL MODEL
To verify the team's proposal, a three dimensional 360° CFD model was developed with AEA Technology in Didcot, Oxfordshire, acting as a sub-consultant to Buro Happold The model went through a number of refinements as the information on the exhibition structures began to filter through from the exhibition design teams As it stands today, the model has been generated by 700,000 cells, takes 450 MB of memory, and to run one scenario on AEA's most powerful machine takes approximately four days Outputs are air speed, air temperature, resultant temperature and a "Comfort Index" As stated earlier, the question posed by our client was what would the internal environment be like and to what is it comparable Buro Happold set about trying to establish comfort criteria for the space Fangers or Bedfords comfort criteria were not considered appropriate as they related primarily to "static" office
environments Instead criteria established by United
States Department of Transportation called the
"Relative Warmth Index" (RWI) was adopted This was developed for subways and train stations, so it was felt to
be the most relevant and appropriate for the Dome environment
RWI = M(Icw +Ia) + 1.13(t - 95) +RIa
74.2 where:
M = metabolic rate lew = insulation effect of clothing, clo
Ia = insulation effect of air boundary, clo
t = dry bulb temperature t-95 = difference between dry bulb and average
skin temperature
R = mean incident radiant temperature from
surrounding surfaces
The above are all imperial units
Explaining our results and "comfort" to our lay client was not an easy task, so the following diagrams were used to illustrate our results
Trang 5Fig 4 CFD plots with comfort criteria
Its worth noting, that as the model became more accurate, and our Client became more knowledgeable,
we reverted back to simply stating Resultant temperatures as our measure of the Domes environment The following diagrams illustrate some of the CFD model outputs
Hot S u m m e r Day
Fig 5a,b & c CFD plots
Ventilation tests to date on the installed systems
(Andrew Cripps paper)
Trang 63010 302.5 304.0 305.5 307.0
Temperature (K)
E N E R G Y D E M A N D S
PREDICTING THE LOAD
Formulating the Dome's energy demand twelve months
in advance of knowing what was going to happen within
the building, came to down to guesswork, albeit educated
guesswork We talked to a number of organisations who
had done "something" like it before, even if not on the
same scale, we did a lot of reading and research into
major exhibitions throughout the world, including asking
the Disney Corporation, whose advise was particularly
comforting - "Get your exhibition designs first before
establishing your energy loads"
The result is we have an all-electric building, this
decision taken against a brief for a temporary exhibition
(and at the time of the decision, also a temporary ^
building) Other energy supply methods were reviewed,
including Combined Heat and Power (CHP) The CHP
scheme was to be part of the total Greenwich Peninsula
development, initially be used to serve the Dome (this
being first load on-line) before commercial and domestic
loads came on line in the future Time, cost and lack of
funding saw this proposal stranded
Gas heating was excluded because of programme and the
cost of reinforcing the mains for the given demand At
the Dome, gas is only used for catering At first sight the
use of electricity as the Dome's sole energy source is
questionable, but when viewed against the Clients
programme, costs, the temporary exhibition brief and the
post exhibition legacy (an electrical infrastructure in
place for the future development of the Peninsula),
electricity proved the most attractive option
The following figure gives the current break down of areas:
SPATIAL BREAKDOWN OF AREAS WITHIN THE DOME
m?
Exhibition Area 35,000 Central Show Arena 14,750 Catering 3,900 Circulation 11,350 Retail 1,350 Toilets, plant, support 10,300
COOLING LOAD
The 18MW of cooling is split between the following functions as follows:
ELECTRICAL LOAD
The installed capacity of electrical power for the landlords' supplies, at 57.5MVA, is only slightly higher than our original estimate In providing this demand, the team set about standardising the size of transformers, the set up being:
• 2x 1.25MVA transformers for each of the six internal core buildings
• l x l 2 5 M V A transformer per exhibition
• 4x 1.25MVA for the central area buildings
• 4x 2.50MVA for the central show
• 9x 1.25MVA for the external buildings and landscape including "Baby Dome"
PLANT SELECTION
This standardisation of the primary M&E equipment was an early design objective set by the Client and the design team, based on the directive of an exhibition lifetime of two years, and the short design and build times available This directive was fundamental in the selection of services plant Tried and tested technology was used, albeit on a very large scale
Standard off-the-shelf plant was selected and positioned around the site
Trang 7The London International Financial Futures and Options
Exchange (LIFFE) was consulted by Buro Happold to
evaluate resale values of plant on the futures exchange, and
items were selected on this basis The type of transformer
specified, for example, was changed as a result of this input
as was the rated output of the packaged air-cooled chillers
Equipment is standardised throughout in order to increase
the likelihood of resale and minimise downtime if repairs are
required
S E R V I C I N G S T R A T E G Y
FUTURE F L E X I B I L I T Y
At the beginning, it seemed that we were faced with a
seemingly impossible task The site was a barren and
formless landscape, with little, if any, infrastructure, and
there was increasing public debate as to what to put in it
and if it should be built at all But with an immovable
completion date looming, design and construction work
on the Millennium Experience had to start
Faced with the uncertainty on the exhibition form and
content, the design team had to make some fundamental
decisions on how the services should be planned so that
the design and construction could progress well in
advance of any exhibition designers been appointed
There was much discussion and debate on the servicing
strategy and its intended flexibility as it was soon
realised this would have a major influence on the
exhibition layout and size A number of scenarios were
tested, including services within raised floors or above
ground service beams The adopted solution takes a very
pragmatic approach The dome is split into six equal
'pie' segments, each a mirror image of the other, the core
building being the 'heart' of each segment, with plant in
a pair of cylinders feeding into each segment External
plant such as the air cooled chillers, HV switchgear,
standby generators and water tanks are contained in the
twelve prominent service pods, or cylinders, around the
perimeter, these operate in pairs to service each of the six
segments All segments have equal capacities although
each pair of pods holds slightly different plant
From the cores, the services are distributed into a series
of six radial trenches, each six meters wide and 900mm
deep, and three circumferential trenches which run under
the Dome's ground slab and carry all cable and piped
services, including drainage The radial trenches are
generally arranged so an exhibition lies on either side
with an access route directly overhead Two major
exhibits are serviced from each, with any excess
continuing around the circumferential trenches to pick up
any secondary loads The radial trenches continue into
the centre of the Dome to supply the demands of the
central arena
As the siting of exhibits and public services was devised during construction, it was necessary to ensure that services would be available throughout the site when required Despite the uncertainties, the entire M&E services were designed in only nine months and their installation is now complete and commissioning started
in March 1999
Fig 6 Services Strategy
Fig 7 Early concept diagram for the service pods
T H E E X T E R N A L S E R V I C E P O D S
Included in all views of the exhibition since they first entered the public domain, the cylindrical pods surrounding the Dome are now entrenched in the minds
of everyone who has seen any photographs or models of the structure Housed within these aluminium-finned cylinders are all the primary services for the Millennium Experience Originally intended to be spherical, creating
a futuristic space-station look to the structure, they were
to hold part of the exhibition However, space constraints meant that the plant had to be moved outside
of the Dome The team liked the idea of using the now defunct exhibition spheres However, it became increasingly difficult to fit square plant into a round space, so the spheres are now cylindrical
Trang 8Fig 8 Architectural image
Fig 9
Each pod is split into three levels, plant not requiring
weather protection was left open to the elements, the
remainder was enclosed in packaged plantrooms
assembled off site by GEL and AC Engineering and
installed complete The contents of each pod varies due
to the way the required capacities have been apportioned
Where plant is not required, the space is left empty for
future expansion of exhibition demands
Two 750kW air cooled chillers are located on the top
level of each pod These are connected in parallel and
grouped onto a common header A chiller system (i.e a
'pie' segment) consists of four units, the pods working as
a pair, giving six systems in total to service the Dome and
site All systems run totally autonomous from each other
On floor two of the pods, one of each pair holds a
prefabricated packaged plantroom, which contain
close-coupled end-suction chilled water pumps to give a flow
of 132 1/s at a head of 200kPa to a common pipe system
which distributes around the Dome to null headers A
pressurisation unit and a controls system is also included
in this plantroom In eight pods London Electricity
packaged HV switchrooms are sited at this level
On the bottom level, a 92.5m3 sprinkler water tank is
sited in two pods, the volume required for the Category 3
Special system being too large for a single pod Separate
pump rooms have been installed as the tanks are more
than 30m apart A 500kW standby generator has been
installed in three pods, each generator servicing two
sectors
A C K N O W L E D G E M E N T S
Client:
The New Millennium Experience Company
Jennie Page, David Trench, Richard Coffey, Peter English
Architect:
Richard Rogers Partnership
Richard Rogers, Mike Davies, Andrew Morris, Stuart Forbes, Steve Martin, Adrian Williams, Mike Elkan, Laurie Abbott
Construction Manager:
MacAlpine Laing Joint Venture
Bernard Ainsworth, Gary Nash
Our sub-consultants:
Central Area:
Cundall Johnston and Partners
Ric Carr, Peter O'Halloran, Mike Golding
Lighting Designers:
Speirs and Major
Jonathan Spiers, Mark Major
Lift Consultants:
Dunbar + Boardman
Peter Boardman, Chris Meering
and most of all, to all my numerous colleagues at Buro Happold who have contributed to this project
R E F E R E N C E S
1 Constructing the Millennium Dome
Ian Liddell, Lecture to the RA, September 1997
2 The Design and construction of the Millennium Dome
Ian Liddell and Peter Miller The Structural Engineer, 6 April999
3 Servicing the Dome
Various, The Building Services Journal, April 1999
4 Subway Environmental Design Handbook Vol 1
U.S Dept of Transportation