CIBSE Case Study: The Art of the Impossible
CIBSE Case Study: The Art of the Impossible
Back to CIBSE Case Studies OverviewArticle from the November 2014 edition of the CIBSE Journal written by Andrew Pettifer.
Innovative engineering and careful restoration transformed an Australian Beaux Arts beauty into a global investment bank's HQ. Arup's Andrew Pettifer FCIBSE explains how a Sydney belle became hi-tech real estate.
Fifty Martin Place is a historic building in the heart of Sydney's financial district. Constructed between 1925 and 1928 - for what was then the Government Savings Bank of New South Wales - it is a rare Australian example of the American-influenced, inter-war Beaux Arts style. Macquarie Group, Australia's only global investment bank, acquired the building in 2012 to create its new corporate headquarters. This was a radical step in the Australian property market where, typically, commercial property is owned and managed by real estate investment trusts. The fact that Macquarie was to be an owner-occupier opened up opportunities both to refurbish an important heritage building, and to create a world-class workspace, specifically designed to meet the bank's corporate objectives of enhanced performance through connectivity, collaboration and sustainability.
Consequently, 50 Martin Place has become the largest historic refurbishment in Australia to be awarded a Six Star Green Star rating - representing "world leadership" - by the Green Building Council of Australia. The design strategy involved the creation of a glass, domed roof - to house client facilities and meeting rooms - and an enlarged, open-edged atrium. The atrium is the centrepiece of the project, enhancing daylight penetration through the core of the building, while accommodating open stairs that provide connectivity between office floors.
The strategy presented Arup, the sustainable design and building services consultant for the project, with a number of challenges. The first was to remove as much plant as possible from the roof to free up space for client use. Plant that remained at roof level - including cooling towers, standby generators and smoke exhaust fans - was carefully integrated into the new glazed structure, to minimise the intrusion into the architectural form. Other plant was sensitively relocated to reduce the impact on the historic fabric of the building. This included the conversion of original water tanks into fan- and boiler- plant rooms, and the relocation of chillers from the roof to the basement. An existing light well was used as a fresh-air intake, and worked in tandem with the atrium, which acted as the exhaust air path. The office air conditioning solution uses passive chilled beams, coupled with fresh air supply delivered through a 250 mm-high raised-access floor. The combination is Australia's first example of such an approach (see panel, "Air conditioning").
Seeing the light
Given the heritage of 50 Martin Place, its façade has far less glazing than contemporary buildings, and access to daylight and views is well below modern expectations. A key design objective of the project, therefore, was to bring daylight, sky views, and interconnectivity from the top of building to its core. This was achieved through the transparent new roof structure and the enlargement of the existing narrow atrium, to increase daylight penetration into the building, while creating a visual point of connection to the outdoors. Innovative glazing technology - comprising triple glazing with an inbuilt extruded mesh - creates a high-performing fabric. The result is superior thermal comfort, ample daylight, and extensive sky views. Architecturally, the result is a transparent volume, clearly demarcating the new and the old, and respecting the history of the building.
Extensive daylight analysis was conducted, to demonstrate to the Heritage Council of NSW the environmental benefits of increasing the atrium size. The analysis quantified the benefits of increasing the atrium width for daylight penetration on the floor plates, and within the atrium. Further studies were conducted to determine the best configuration for the internal stairs interconnecting the atrium to ensure the stairs allowed as much daylight as possible to reach the bottom of the space. The results of the analysis showed daylight reach within the atrium would extend three storeys deeper, compared with the existing building. Useful daylight penetration into the office space was increased by approximately 150%. Modelling was also undertaken to assess sunlight penetration, and an automatic blind system will shade the atrium floor during the relatively few hours in a year when the sun is sufficiently high to penetrate the office space.
The office lighting layout was developed to reinforce the structural and ceiling grid in the original building, and to expose the historic fabric previously hidden behind the ceiling. The offices and atrium have perimeter, ceiling-mounted daylight sensors that dim the adjacent lighting when sufficient daylight reaches the work desks. To maximise the effect of the widened atrium, it was decided not to add any further equipment to light the void. Vertical circulation lighting is managed using integrated balustrade lighting in the stair. This also plays on the perforated balustrade panels, giving the stair the appearance of a glowing ribbon rising up through the generous space. At high level, the need to mount luminaires beneath the glazing has been avoided by the design of self-illuminated glass bridges. At the base of the atrium, an indirect mirror system is used to redirect light to the traders. The luminaires and mirrors are mounted to the exposed beams at the perimeter of the void, to provide clear views up through the atrium.
Fire Safety Engineering
While the large open atrium allows daylight to penetrate deep into the building, it did provide the engineers with a tough challenge in terms of fire safety. The Building Code of Australia limits the number of floors that can be connected via openings to two above ground, although any number may be connected via a sealed atrium. The requirements for a sealed atrium are onerous, with glazing and wall-wetting systems, smoke exhaust, emergency power, multiple exit routes for any balconies, and, importantly, no real connection to the floors. This did not meet Macquarie's desire for the atrium to be open and therefore enhance connectivity and collaboration within the business. To achieve an open-edged atrium - and provide the required interconnectivity - a performance-based, fire-engineering design was developed by Arup's fire engineers. In the event of fire, the non-fire floors are smoke-separated from the atrium by a combination of drop-down smoke curtains and glazed panels, required to resolve tricky etailing around large heritage beams.
The fire floor remains open to the atrium, and large smoke exhaust fans extract from the top of the atrium at a rate of 40 m 3/hr, while make-up air comes from automation of existing heritage balcony doors at level two,combined with the general supply air system. The new client floors constructed within the glass-dome roof extension are open to the atrium. For these floors, exiting through a smoke-proof construction to fire-escape stairs - off an external terrace - enables occupants to move to a place of relative safety before evacuating.
This approach allows for high-occupant numbers to be accommodated within the client entertaining areas.
Sprinklers are provided throughout the building to keep fire sizes low. Smoke detection - including beam detection in the atrium - provides for early warning, while pressurised escape routes give people time to evacuate the fire floor and those adjacent to it, simultaneously. There is staged evacuation for the remaining floors. Another significant task was to upgrade the numerous styles of heritage luminaires on the original staircases and the halls, some of which were gas mantle luminaires. To upgrade the historic fittings, a number of diffuse LED sources were developed, effectively replicating the optical distribution of older tungsten lamps, while increasing the lumen output to meet the egress requirements.
50 Martin Place demonstrates how new life can be breathed into a historic building, to create an exciting contemporary workplace. The project highlights that the unique characteristics of such a construction requires highly bespoke engineering solutions. The result, however, is a building that is prudent in the reuse of existing resources, energy efficient in performance, and, most importantly, meets the client's objectives of creating an inspiring and efficient place to work.
The general office air-conditioning solution uses passive chilled beams, coupled with dehumidified fresh air supply, delivered through swirl outlets in a 250 mm-high raised-access floor, acting as a plenum. Raised-access flooring systems are not common in the Australian commercial market, and the combination of chilled beams with supply air through the floor at 50 Martin Place is the country's first example of such an approach. Mindful of the potential leakiness of the heritage structure, the raised floor plenums went through rigorous pressure testing on site, to ensure that performance requirements were met. The swirl outlets were specified to have an adjustable throw pattern of +/-30 degrees from the vertical, to provide occupants with the opportunity to adjust the air distribution in their vicinity.The ceiling-level services have been carefully arranged to complement the original ceiling design, and allow the 1920s structural grid to be exposed. Passive chilled beams enabled the ceiling to be pushed up within the beam structure, resulting in a 270 mm-deep ceiling zone, bordered by a 450 mm-deep structural beam grid. Full factory testing of the beams, acting in combination with the specified floor diffusers, allowed the design to be verified before installation. To avoid the need for long and deep ductwork runs from the side core configuration at each level, supply air is introduced into the shallow floor plenum by 12 new supply air risers. These are distributed around the perimeter and served from lateral distribution of ductwork accommodated within a 900mm-deep floor at level one.
Partway through demolition, sections of the original, ornate, pressed-metal ceiling cornices were discovered on level one, which was being converted into the main trading floor. The in-desk cooling specification allowed the ceilings and chilled beams in these areas to be omitted, and the cornices fully restored and exposed. The trading floor also extends across the base of the atrium, which again - with no ceiling immediately above - suited an in-desk cooling solution. Cooling units are integrated into the desks and underfloor displacement delivers fresh air drawn from the raised access floor in combination with chilled beams on other levels.
This is the first commercial installation of in-desk cooling in Australia. The chilled-beam and in desk cooling solutions require a well-sealed building, particularly in the Sydney climate, which experiences sustained periods of high temperature and humidity. The building fabric was pressure tested by Arup during the early design phase and performed surprisingly well, with only window seals needing replacement.