FEATURE

A section of the 1.4km thermal labyrinth that runs below Federation Square. Underground movement It is more than 10 years since Federation Square opened in . Of the milions who have visited the square in that time, few would know that below their feet lays one of the world’s best examples of decoupled thermal mass design: a thermal labyrinth. Sean McGowan reports.

Whether or not the of above, as well as delivering energy- , and a keynote Melbourne’s Federation Square resonates efficient cooling to the large atrium, and speaker at AIRAH’s coming The Future with you, what continues to be evident pre-chilled air to the refrigerated systems of HVAC conference. 11 years on from its opening is that in serving other buildings on the site. With fellow architect Peter Davidson, this project, form and function have both Bates was one of the primary architects of been paid heed to. “Unlike many ESD projects that go out of their way to paint wind turbines on Federation Square. The pair had formed The “function” credentials are evidenced the roof yellow – to call attention to their in by the inclusion of a 1.4km long thermal supposed ESD credentials – the systems in 1994, and three years later entered labyrinth located below the civic square at Federation Square are all about being the international design two-stage in the middle of the 3.8 hectare site. competition for the project. integrated and embedded in the design The labyrinth plays dual roles – that of and the architecture,” says Donald Bates, Short-listed for the first stage of the a structural support to the public plaza chair of Architectural Design at the competition, they formed a joint-

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venture agreement with long-established “Partially this was because in 1997–98, The labyrinth’s inclusion also forced a Melbourne architectural firm Bates fuel costs in were very low,” he rethink in respect to the fee mechanism Smart to undertake the second stage of says. “The small price difference in favour of the project for the services engineers, the competition. In late July 1997, they of a traditional cooling solution versus Atelier Ten. were announced as the winner. the labyrinth was seen as a cost saving “There was a slight ‘discipline’ barrier to to a project that had significant funding According to Bates, the idea to include the development of the labyrinth,” says pressures.” a thermal labyrinth as part of the design Bates. “Effectively, the development of the came about in the very earliest days of Time would show this to be a false labyrinth was to use a structural element their design work, when LAB collaborated economy, lending weight to Bates’ as an HVAC element. The concrete walls with London-based environmental engineering firm, Atelier Ten. assertion that making decisions only with of the labyrinth hold up the public plaza regard to existing energy costs is both above it. But these walls also operate as Having previously worked together on short-sighted and naïve. part of the cooling system. other design competitions, and with their offices in close proximity to one another, it made sense that discussions about the project’s engineering be included from the earliest stages. Here, indeed, was A capital project integrated design in practice. ACT’s Gungahlin College, Library, Canberra Institute Among a number of initiatives to come of Technology Learning Centre and Town Park project from this work was the thermal labyrinth. uses a thermal labyrinth. “They had previously produced a scheme The northernmost town centre of Canberra, Gungahlin is home to a recently in the UK for the Earth Centre in completed development featuring a new senior secondary college and small Doncaster, and it included a small-scale tertiary facility associated with the Canberra Institute of Technology (CIT), labyrinth under the main slab of the integrated with a community library, performing arts theatre and gymnasium. building,” recalls Bates of LAB. Naturally, each building features highly variable usage patterns, such that the Department of Education adopted the philosophy during design that the need Unlike many ESD projects for active within the secondary school be negated. that go out of their way to Rather, it directed the design team to achieve acceptable comfort control through passive design approaches alone. Those facilities shared with the paint wind turbines on the general public – such as the library, theatre and tertiary facility – were permitted active air conditioning. roof yellow – to call attention According to Cundall principal Caimin McCabe, M.AIRAH, the variety of to their supposed ESD functional uses in play, and the facilities’ different operating hours – as well credentials – the systems at as a strong passive design response being sought – led to the idea of a thermal labyrinth being implemented. Federation Square are all This was integrated into the structural solution below the paved courtyard about being integrated and between the library and CIT building and the main school building. embedded in the design “The selected location offered the ability for the thermal labyrinth to serve the college during school hours and the library ... CIT or the theatre after and the architecture’ hours, weekends and during school holiday periods,” he says. The labyrinth has been designed to achieve up to 9°C cooling of ambient air “The work undertaken during the in and 7°C heating in winter. competition design, as well as with other initiatives apart from the labyrinth, It provides a shared resource to the different parts of the development, convinced us that this would be an and offers a number of predicted benefits including: important feature of the sustainable • Passive comfort control within the learning hubs of the school during design of Federation Square.” the summer without the need for active cooling and pre-heating in winter. It also provides 100 per cent outside air ventilation all year round, and It would prove to be an astute decision. enhances the effectiveness of the natural stack ventilation strategy Eleven years on, the thermal labyrinth is adopted within the school. playing a major role in Federation Square becoming carbon neutral by the end of • A 30 per cent reduction in CO2 emissions associated with heating the year. and cooling of outside air required for the library and CIT spaces during library operating hours. At the time, however, Bates says the potential of the labyrinth had to be • A 46 per cent reduction in CO2 emissions associated with heating justified on more than several occasions and cooling of outside air required for the theatre. throughout the project’s duration.

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“The more the services engineers of labyrinth, cooling – or charging – the A glass-walled, high-volume structure Atelier Ten developed this design, the zigzag of 3m high corrugated pre-cast approximately 18m high, the Atrium more they eliminated the traditional concrete walls to the lowest night-time covers a floor area of approximately 2,040 pieces of equipment that define the costs temperature. sq m. The warmer air in this space is – and fees – of the services engineers. We displaced and evacuated through vents in had to find a different fee mechanism to the ceiling. allow them to develop the design.” T he small price difference Bates says the use of the labyrinth generally produces a 10–12°C I nside the labyrinth in favour of a traditional temperature differential between the The basic design and operation of daytime external temperature and that of cooling solution versus Federation Square’s thermal labyrinth the internal Atrium temperature. follows the rules of decoupled thermal the labyrinth was seen as Additionally, there are many days mass. throughout the year when the air from a cost saving to a project The labyrinth’s location – on top of the the labyrinth is not required in the open- structural slab above railway lines, but that had significant funding ended Atrium. At these times the system below the sloping surface of the public is used to provide pre-cooled air for the plaza – is unorthodox, and its size is pressures refrigerated systems that service the substantial. Yet the system works in ’ offices and cinemas of the Alfred Deakin much the same way as any other thermal During the day, the warmer ambient air is Building, housing SBS and the Australian labyrinth. then drawn through the labyrinth by the Centre for the Moving Image (ACMI). At night, fans draw the cool ambient air fans and is cooled as it comes into contact This significantly reduces the amount of from outside through vents placed along with the chilled (charged) walls. This energy required to cool these spaces. the southern edge of the development, air is then distributed into Federation close to the Yarra’s riverside. These fans Square’s large atrium via a displacement “The labyrinth reduces the cooling move the air through the 1,600 sq m system at floor level. loads on the Atrium, compared to a FEATURE

mechanically chilled, forced-air system, building in Luxembourg, designed with says that Melbourne’s large diurnal by more than 90 per cent,” says Bates. Foster + Partners. temperature ranges were identified early on as being ideal for a thermal labyrinth Compared to a mechanically chilled Despite many technological advances system. Yet it took some for a labyrinth to displacement air system, the reduction is in the HVAC field in the years since be confirmed as part of the final design. said to still be more than 40 per cent. Federation Square was completed, Bellew says little would change if the labyrinth “There were some concerns that, for the was designed today. labyrinth to be effective, it needed to be Dw ra ing inspiration in contact with the ground – which was Speaking from his London office, where somewhat problematical in the context the original design and operational T he labyrinth recouped of the site where the superstructure is diagrams of the Federation Square suspended above the railway tracks,” he labyrinth remain displayed on the wall, its slightly greater says. Atelier Ten principal Patrick Bellew says the firm’s work with thermal labyrinths construction costs within “It was therefore mooted as an idea with continues apace. the intention that the labyrinth would sit six years, and has been beneath the deck and between the railway Along with the Earth Centre and delivering substantial tracks. It only really emerged into the Federation Square labyrinths, Atelier design in its current form somewhat later Ten also designed a similar system at savings to Federation in the design process when a large volume Davis Alpine House at the Royal Botanic of unused space was identified beneath Square ever since Gardens in Kew, London. ’ the public plaza.” It has two thermal labyrinths under In that sense, he says the design is “We continue to look at systems that construction – one in Ankara, , somewhat opportunistic. However, once use many of the same ideas,” he says. beneath the headquarters of the the opportunity had been identified Turkish Contractors Association, and Reflecting on his involvement on the and the technical benefits analysed, a particularly large system beneath a Federation Square project, Bellew the architects fought passionately for

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its retention as a major environmental component of the scheme. Both Bellew and Bates reveal that there was a real desire within both the design and client teams to minimise the use of air conditioning and mechanical refrigeration as much as possible. With a design imperative that the large Atrium be open-ended and to face the public streets, the idea of introducing cooling was deemed illogical and expensive to operate. Searching for alternatives to offset heat gain in the Atrium without incurring substantial energy penalties, the labyrinth proved to be the answer. “The labyrinth solution allowed us to eliminate any form of mechanical cooling from this area,” Bellew says, “but still allowed us to guarantee the comfort for the occupants on warmer days.”

Macro v micro

According to Bellew, thermal labyrinths Federation Square’s Atrium building sits atop the thermal labyrinth cooling system. are particularly well suited to Melbourne because the night-time air is almost “The operation of the system has been “The design philosophy is quite always cool, due largely to the effect of the tested through some record temperatures straightforward at one level, but we use Southern Ocean. in the past few . And at a recent some unusual control arrangements to get reunion, reports from the Federation the most out of the system – in particular The Federation Square labyrinth has been Square management staff (FSM) were the control of the labyrinth cells in a series reported to take advantage of the micro- consistently positive – particularly as arrangement during the day, switching to climate created by the at to the benefit felt in the hottest weather a parallel operation mode at night during night. Bellew says, however, that the data without any supplementary cooling.” the purge cycle,” he says. “This adds to the sources drawn upon for analysis were not complexity of the modelling.” sufficiently refined as to provide this level of detail. Like any heating, ventilation The calculation of payback periods can also be complex. Rather, he says the design team was more and air conditioning system, focused on Melbourne’s macro weather “On Federation Square, we ran the energy conditions. Any advantage the Yarra there are rules to the design model with conventional chillers and River provides is a bonus. set-points as a reference case, and then of a thermal labyrinth ran the labyrinth, factoring in only the “Our analysis suggested that we could ’ fan energy for the labyrinth,” Bellew says. expect up to 15°C or even 20°C of Bellew says thermal labyrinths are “This gave us a projected energy saving.” potential cooling capacity on the notoriously “tricky” to model. hottest days of the year,” says Bellew, The design team then looked at the “add who returned to the city last year for a From its continuing work in the field, and omit” items on the capital cost, such commemorative lecture at the University Atelier Ten has evolved a method that as chillers, pipework and coils, and came of Melbourne’s Faculty of Architecture, combines dynamic simulation and some to a net additional cost. Building and Planning. CFD modelling to make assessments. Only then were they able to do a life-cycle and payback analysis. According to Bates, the labyrinth Did you know? recouped its slightly greater construction Although yet to be accurately modelled, Atelier Ten’s Patrick Bellew says an costs within six years, and has been area of exploration is the integration of phase change materials (PCMs) into delivering substantial savings to the concrete mix to extend the capacity and range of performance of thermal Federation Square ever since. labyrinths. Such a modification allows smaller footprints while achieving the same output. Eleven years on, Bellew says more attention would now be paid to reducing “It may be a while before we have enough certainty on performance,” the embodied carbon within labyrinth Bellew says, “to get the full benefit of this idea.” systems. Today, his firm works closely with structural engineers to design

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concrete walls to use the minimum In the ACT, a large system serves the able to provide beneficial passive cement content consistent with their Gungahlin Senior Secondary College cooling the following day,” McCabe says. structural integrity. as well as adjacent community library, According to McCabe, the benefits performing arts theatre and gymnasium This needs to be achieved while of thermal labyrinths can be further (see sidebar). maintaining the two critical issues enhanced if the heat-purge cycle of the associated with the design and Involved with these projects, and others thermal mass is used as a means to provide construction of labyrinth walls: surface both under construction and in design, a night purge, or a night ventilation area and air movement. is Caimin McCabe, M.AIRAH, principal strategy, to the building. This removes with Cundall. the heat stored within it, as well as reducing He says the spacing of the walls is also the need for cooling the following day. important – a function of the design McCabe says there are a wide range of velocity of the air through the chambers strategies being adopted around thermal “Importantly, a by-pass needs to be to ensure good heat transfer. labyrinths, both within Australia and incorporated within the design so that around the world. “If the air moves too fast, the convective the building is not overcooled overnight, heat transfer effect reduces and pressure requiring heating input the following drop – and therefore fan energy demand morning, but allow the thermal mass The labyrinth solution to be further cooled,” he says. – is increased,” Bellew says, adding that minimising fan energy use is important. allowed us to eliminate any McCabe cites one example he is aware “The other important factor is that the form of mechanical cooling of where the comfort control strategy for a rock-store labyrinth system was heat transfer effectiveness increases when from this area, but still the air turns the corners of the labyrinth. incorrectly commissioned as a traditional We believe it is because of the change allowed us to guarantee the air conditioning system. This resulted from laminar to turbulent flow, which in a reversal of the design intentions. comfort for the occupants increases the heat transfer.” In this instance, rather than running a Atelier Ten is using a concrete-filled profiled on warmer days purge cycle overnight to remove the heat block at its project in Turkey to achieve a ’ stored in the labyrinth during the day, degree of roughness on the surface, and to These include rock-store labyrinths, earth the heat was left in the rocks overnight. (or Canadian) tubes, earth-mounted reduce the amount of time that the air-flow “The implication and outcome of this next to the walls becomes laminar. concrete culverts, zigzag labyrinths and channel labyrinths. is that the rocks progressively heated Other than these factors Bellew says the up further and further to the point that construction of labyrinths, while time – “Like any heating, ventilation and air air passing through the rock store was consuming, is relatively straightforward. conditioning system, there are rules progressively cooled less and less,” he says. to the design of a thermal labyrinth,” “The most difficult issue is sometimes the McCabe says. “Ultimately, the rocks began to operate liability and warranty for the design, par- in reverse, adding heat to the air on ticularly when the project is using a ‘design The rules to which McCabe refers cover milder days so that the air entering the and build’ form of contract,” he says. air speed, turbulent airflow, length of run labyrinth came out hotter than it went and the material used. in, which created obvious comfort issues The underground “Air speed should be low to encourage within the offices.” movement the air to flow over the thermal mass and It is understood that once this error was not run down the centre of the thermal identified, the controls were modified to The number of thermal labyrinths in labyrinth without touching the sides,” he reflect the need for a night purge, and the Australia is greater than you might realise. says. “There is also a need for turbulent system has operated as intended since. ❚ Perhaps, like Federation Square, they are airflow to maximise connection of the the victim of remaining hidden below air to the exposed thermal mass through buildings – away from the public eye. ribbing of the boundary walls, rocks and A keynote of note fins in the airstream.” A little-known example is located below Victoria’s Parliament House in Additionally, ensuring sufficient length Melbourne. Likely built during the first of run within a labyrinth is critical to stage of construction in the 1850s, it getting the maximum cooling benefit out runs beneath the building to an adjacent of the system. It is also important that a park and was rediscovered during construction or bounding material with investigations into a proposed restoration poor thermal performance is used to of the building in the late 1990s. store and release energy.

More recently, thermal labyrinths have “A further very important step is to Donald Bates will be the keynote been used as key ESD elements at a ensure that the control logic of the speaker on day two of AIRAH’s number of Victorian schools – among ventilation fans drawing air through the The Future of HVAC conference. them the Suzanne Cory High School in labyrinth is correctly set up to facilitate a For more info, go to www.airah. Werribee and Hume Secondary College night-purge cycle to remove heat stored in org.au/TheFutureofHVAC in Broadmeadows. thermal mass overnight to prime it to be

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