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MONDO ARC

The National Assembly for Wales, Cardiff, Wales

Issue 30 April / May 2006 : Architectural : Government

Architect: RICHARD ROGERS PARTNERSHIP Lighting Consultants: BDSP PARTNERSHIP & DPA LIGHTING


Delivered on budget (£41.5 million) and in time to be opened by the Queen on St. David’s Day, the Senedd has attracted as much good publicity as the Scottish Parliament gained bad. here, Matthew Winter of consulting engineers and lighting designers for the project, BDSP, gives a personal account of Cardiff’s latest iconic building.

The Philosophy
The royal opening by Her Majesty the Queen of the Senedd building for the National Assembly for Wales (NAfW) on St. David’s day this year marked a key moment in the eight year history of the project, as this completes the third and last of the parliamentary buildings.
The project, originally conceived and won in competition in 1998 with Architects Richard Rogers Partnership (RRP) and ARUP to provide a new home for the Assembly, was subsequently re-tendered in 2001 under a ‘design and build’ procurement route with the same design team led by the Main Contractor Taylor Woodrow Construction.
The building, situated in a prime position on the waterfront of Cardiff Bay, adjacent to the Grade I listed Pierhead Building and the new Welsh Millennium Centre, looks out over Cardiff Bay offering a spectacular panorama of sky and water. The architectural concept was one of placing the electorate above the elected whilst offering maximum transparency and openness – symbolic of true democracy.
New accommodation in the building primarily comprises Public Spaces, Committee Rooms, A.M. Offices and a central Debating Chamber. The elevated public concourse, also known as the main hall, supported by exhibition areas and a public café sits above the private members’ areas.
The Client’s Brief required that the new Assembly Building meet the Assembly’s constitutional responsibilities for sustainable development and achieve an “Excellent” rating under the Building Research Establishment Environmental Assessment Method (BREEAM).
In response, the environmental design strategy for the building as a whole was one first and foremost of reducing energy demand, followed by the application of renewable energy sources and only then covering any residual demand by using highly energy efficient technologies. In adopting such an approach the building is predominately naturally ventilated, uses ground source heat exchangers, a biomass boiler and rainwater harvesting. This philosophy is also reflected in the lighting design and could broadly be described using the following three step approach:
1. Maximise and control natural daylight penetration - to provide an optimised uniform daylight profile and minimise dependence on artificial lighting;
2. Install an artificial lighting scheme that would provide a stimulating dynamic visual experience whilst using energy efficient light sources;
3. Link controls to deliver the best cross-over between natural and artificial lighting to reduce energy consumption whilst still giving end users some individual control over their personal environmental space.
The artificial lighting scheme was implemented on the idea of zoning / sub-zoning to meet specific criteria of each individual space. Energy efficient lamps, photometry and control gear were also carefully selected and harmonized with algorithmic controls for daylight linking and constant illuminance monitoring, optimising energy input and extending lamp life.

The Public Space (Main Hall)
As a visitor to the new building, the first area of the building you enter, after the security, entrance is the main hall. The over-sailing roof of the main hall, and by default the whole building, has been carefully configured so as to maximise daylight availability to the spaces below, whilst at the same time providing the necessary levels of shading during the peak summer months only. The focus here was on controlling ‘overheating’ rather than maximising shading, as the latter will invariably reduce daylight availability in the main hall, as opposed to finding an optimum balance between lighting and thermal control. Outside these times, direct sunlight is purposely allowed to penetrate into the main hall to enliven the public space and make the visitors feel that they are as much ‘outside’ as ‘inside’.
To give confidence to the architectural design of the space and achieve the aims of daylighting and shading, the main hall was extensively analysed through computer modelling (Radiance). The simulations also provided a visual means of communication with the client and architect in technical aspects of the lighting design.
Results of daylighting computer simulations showed that daylight levels in the main hall would be very good over large parts, with daylight factors in excess of 5% in many areas and over 2% throughout the building. With the building now complete, daylight levels are being recorded and first findings show positive results, confirming the computer simulation predictions.
When it came to the artificial lighting design many alternative proposals were analysed, with the final solution based on recessing the luminaires, wherever possible, into the timber clad soffit of the main hall. This solution enabled the lights to form an integral part of the undulating geometry of the roof. As per the daylight simulations, computer modelling was carried out to assess the proposals.
The artificial lighting design concept for the main hall can be categorised into two generic elements – a ‘downlighting’ strategy that serves primarily the functional activities taking place within the main hall and an ‘uplighting’ strategy to complement the dynamic wave form of the timber clad soffit.
The downlight element of the lighting had to achieve a general maintained level of illumination of around 150 lux at floor level and a overall uniformity (ratio of maximum to minimum illuminance) of no more than 5:1. This has been achieved using WE-EF medium beam projectors concealed within apertures in the timber clad ceiling structure. Due to the height of the luminaires and the volume of the public space, metal halide lamps were selected for their efficacy and long lamp life. Uplighting of each dome is achieved by 4 medium beam WE-EF projectors, fitted with standard ‘off the shelf ‘ linear spread lenses, located in pairs at opposite ends of each dome and concealed within the ceiling structure. The use of these lenses help distribute the light beam very wide horizontally, but very narrow vertically. This allows the domes to be lit with good uniformity whilst allowing the curvature of the domes to be expressed.
In terms of controls, the uplight element of the artificial lighting is time clock controlled to coincide with times of darkness, whereas the downlight element is daylight linked ‘on/off’ only, owing to the characteristics of the discharge lamps (non dimmable). The selection of a metal halide CDM lamp also gave the freedom to select a lamp with a higher colour temperature of 4200K, to more closely coincide with the colour of natural daylight.
During the design phase, Taylor Woodrow Construction and MJN Colston proposed an alternative manufacturer to supply the luminaires as a competitive means of assessing the scheme. A comprehensive study was conducted by BDSP to see how the two schemes compared. Fundamentally the Light Output Ratio (i.e. efficiency of the luminaire as a unit) and the light distribution of the alternative fittings was significantly less when compared against the original scheme. These characteristics are critical to the success of an energy efficient scheme. Once applied (i.e. remodelled) the uniformity of illumination of the alternative scheme was shown to be inferior to that originally designed and so the alternative proposal was not pursued.

 

The Private Space (Committee Rooms, A.M. Offices and Debating Chamber)
Committee Rooms and A.M. Offices flank the Debating Chamber. These spaces are naturally lit via a set of roof lights and vertical glazing facing onto internal courtyards. The rooflights are provided with roller blinds for solar control – automatically controlled by the lighting control system with the provision for local control - whereas the vertical glazing elements are fitted with blinds for privacy. Unconventionally, these are activated from below (ground level) and unfurl upwards thereby enabling the user to be provided personal privacy whilst still maintaining transparency and thereby daylight penetration at high level.
Artificial lighting in these spaces is delivered by a homogeneous raft luminaire designed in conjunction with RPP and MJN, specifically for the project. The raft luminaires house independent T5 fluorescent lamps for up and down lighting, voice alarm speakers, and in some areas smoke detectors. The luminaires are scene controlled, the default being daylight linked.
Whilst the brief for the Debating Chamber differed from the other parts of the building in that it had to comply with a Media Operation Plan, which in essence focused on the requirements of broadcasting, the chamber itself is unmistakably meant to be read and perceived as a daylit space by both Assembly Members and the watching public.
The vision was to permit daylight penetration into the heart of the building – the chamber – allowing internal conditions to vary naturally with the passage of time, thus providing a vital psychological connection with the outside. This would also enhance the quality of the space for the users (Assembly Members), whilst at the same time provide conditions appropriate for broadcasting as apposed to focussing purely in televising needs, which would otherwise have created the ideal broadcasting environment – a dark studio space.
To resolve such differences, discussions were held with different broadcasting consultants/experts and it soon became evident that there was clearly a wide variety of opinions on what constitutes the ideal requirements for televising/broadcasting and how artificial and natural light should be mixed (if at all).
Natural daylight penetrates into the debating chamber via a glazed lantern seated on the domed roof beneath a rotating wind cowl and is then reflected into the space below via a series of concentric aluminium rings which make up the chamber funnel. A conical mirror, suspended under the lantern, reflects daylight from low angle winter sun into the chamber below and can be raised / lowered to suit the required daylight levels including ‘grey-out’ conditions for selected broadcasting needs.
Extensive daylighting simulations were undertaken, for the whole year to ensure that the optimum design solution could be found. This process involved investigating different glazing materials, assessing the benefits of integrating light reflectors into the glazed lantern structure, researching different geometric shapes of both the lantern itself as well as the mirrored cone, investigating the impact of different materials and finishes of the funnel as well as assessing various combinations thereof.
All of these daylight studies were based on achieving the required illuminance levels of 500 lux and uniformity of 0.8 (min/average) across the working plane, whilst at the same time complying with the broadcasting requirements. Direct solar access, resulting in patches of sun and shadow are only permitted when the debating chamber is not in session. This philosophy was purposely adopted to generate some dynamism within the space.
In line with the Media Operation Plan, the artificial lighting design for the debating chamber required that the artificial lighting achieve a horizontal illuminance of 500lux with a colour temperature of 5000K and colour rendering of 1A/1B, suitable for colour balancing by the host broadcaster, televising the proceedings during daylight hours.
As with the daylighting studies, numerous computer modelling simulations assessing various artificial lighting strategies and luminaire configurations were undertaken to achieve both a technically compliant and an architecturally simple yet elegant solution.
Following some early investigations on CTB filters, the choice of CDM lamp was reviewed and the installed design for the Debating Chamber is based on the use of 70W 4200K ceramic discharge metal halide CDM-T lamps. The choice of metal halide lamps, as the predominant light source, was based on the lamps performance: comparably good colour rendering, long lamp life as well as significantly higher energy-efficiency compared to a conventional tungsten halogen solution. By using a lamp with a higher colour temperature, a lower strength CTB filter was used to raise the correlated colour temperature (CCT) up to approximately 5000K resulting in lower losses. The laboratory results by which the choice of CTB filter was finally concluded was conducted in conjunction with iGuzzini.
To house the 70W CDM-T lamp, the selected iGuzzini floodlight, which best suited the spatial constraints, had to be modified as it had been designed for a CDM-TC lamp. This required that a prototype luminaire be manufactured then photometrically and thermally tested in Italy by iGuzzini to obtain true project specific performance data. These figures in way of digital photometric data were fed back into the BDSP lighting model to verify the initial lamp selection and overall design.
The result is a Chamber lit by a single ring of 80 x 70W CDM-T metal halide floodlights recessed into the base of the funnel and set at oblique angles, with the aluminium rings starting immediately above.
As the metal halide lamps cannot be dimmed, the floodlights were arranged in four banks (i.e. 25%) to achieve daylight compensation. In this manner they could be switched according to the daylight levels.
A further eight floodlights are installed higher up between the tubes to illuminate the surface of the funnel. At the perimeter of the chamber, WILA circular T5 fluorescent lamps are recessed into the acoustic panels.
In conclusion, the artificial lighting design coupled with daylight successfully complements the overall low energy concept for the whole project, enabling the Senedd to set new standards in environmental performance.

techical information

Architect: Richard Rogers Partnership (John Lowe)
Lighting Consultants: BDSP Partnership (Matthew Winter) & DPA Lighting (Barry Hannaford)
Environmental & Building Services Engineers: BDSP Partnership (Matthew Winter)
Civil & Structural Engineers: ARUP (Gabriel Hyde)
Set Advisor: Department Purple (Russell de Razario)
M&E Contractor: MJN Colston (Peter Davies)
Contractor: Taylor Woodrow Construction (Jerry Williams)
Lighting Manufacturers: Main Hall - WE-EF Medium beam projector floodlights; Whitecroft Raft fluorescent luminaires (courtyards)
Debating Chamber - iGuzzini CDM T floodlights; Wila Circular recessed fluorescent downlights
Committee Rooms/A.M. Offices - Whitecroft Raft fluorescent luminaires (bespoke design)

www.bdsp.com

 

welsh assembly
The Main Hall features good daylight distribution throughout all public spaces; at dusk artificial lighting is automatically energised
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The public realm, view of reception area and elevated events area. All up and downlights are energised for photographic purposes pic: redshift photography
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