On the path to “net zero” energy stadiums

BEST PRACTICE EXAMPLES FROM AUSTRALIA

Authors Russell Lee, Managing Partner at COX (left) Dr Matthias Irger, National Head of Sustainability at COX

The challenge to achieve the goals of the Paris Climate Change Agreement to limit global temperature increases to avoid catastrophic impacts requires action by all sectors, including sport and leisure. With about 40 % of carbon emissions attributable to buildings and cities, transforming the way we design our built environment is fundamental to combatting the climate emergency. With reference to recent projects in Australia, such as the Ken Rosewall Arena, Queensland Country Bank Stadium, Sydney Football Stadium, and Optus Stadium, the authors discuss design principles and their impact on a “net zero” facility.

Many sports organisations around the world have now joined the UN Sports for Climate Action Initiative, which aims to “act, educate, measure and promote” the need to reduce carbon footprint. Sports facilities inherently provide a formidable challenge to achieve net zero carbon emissions due to their large energy consumption on game days and material used in construction and operation, as well as their significant water use and waste.

The need to extend roof coverage to protect spectators from rising heat, rain and wind exacerbates the challenge of reducing embodied carbon in stadia: how do you protect from “more” but achieve this protection by using “less”?

These concerns are particularly acute in Australia where life is more affected by rising temperatures and extreme weather that has the potential to cancel events and put the wellbeing and enjoyment of both athletes and spectators at risk. Three core principles for approach to sustainability As a signatory to Architects Declare, COX acknowledges the global climate and biodiversity emergency, and we understand the importance of protecting and regenerating the natural environment. By 2030, COX aims for all our new projects to be carbon neutral in our operations and achieve a 50 % reduction in embodied carbon emission. Additionally, COX is pursuing broader environmental goals such as achieving net zero water and zero waste amid a circular economy, increasing climate resilience and enhancing native biodiversity.

COX’s approach to sustainability follows three core principles – firstly the fundamentals of good passive design should be achieved to the degree possible on any given site, secondly the amount of embodied energy within the proposed fabric of a design minimised, and thirdly any active systems appropriate to the site and the brief are fully explored before pen is put to paper.

Queensland Country Bank Stadium – Photo: Andrew Rankin

Passive design When applied to stadia, passive design remains one of COX’s key design considerations including solar management with adequate sun protection for spectators and glass facades, natural ventilation, access to daylight and the use of light coloured, reflective materials for the building envelope.

Just as in any other building typology, facilitating natural ventilation in sport buildings can significantly reduce the reliance for HVAC systems, systems that can be expensive to run and can quickly have trickle down impact on ticket costs as energy costs continue to rise. Furthermore, the COVID pandemic and the primacy of public health has made access to fresh air even more important, especially in high-density venues which are often cited by media as potential “super spreader” events.

Upgrading Ken Rosewall Arena The redevelopment of Ken Rosewall Arena at Sydney Olympic Park allowed us to optimise the roof shape and operable facade to improve airflow inside the stadium and thus the thermal comfort of users as far as possible without the use of energy-consuming active conditioning. It was a combination of budgetary restraint and our “resilience” approach to design that also allowed us to upgrade this facility rather than advocate for its replacement. This is not always possible, or the most cost-effective outcome in the medium and long-terms, but it is always a starting point for our design and is usually a way to minimise the carbon footprint of our work.

Queensland Country Bank Stadium Another example is Queensland Country Bank Stadium in Townsville, located in Australia’s tropical northeast. The stadium is rotated approximately 25 degrees east of North to align with the prevailing afternoon winds, the most frequently used timeslot for both sporting and entertainment events. The stadium takes advantage of the local natural breezes in two key ways – the open-ended horseshoe design allows the breeze to enter the bowl and the bowl is orientated toward the breeze to cool spectators, athletes, and employees. It’s almost a “back to the future” design, but one that is very modern in its form and realisation.

“The fundamentals of good passive design should be achieved to the degree possible on any given site.“

Apart from maximum temperatures and rainfall, wind speed is a significant climatic influencer on the design of Queensland Country Bank Stadium. Townsville is within a cyclonic region and has wind loads that are about 50 % higher than Queensland’s capital Brisbane, and 100 % higher than Sydney, for instance. Therefore, the weight of steel required in response to these conditions is proportionate to these increased loads. However, the architectural and engineering teams have worked hard to design a roof structure that responds efficiently to the wind but also minimises material used. The roof is a combination of membrane to the truss forms and metal deck to the infill panels. The membrane produces the same visual shading as a solid roof panel whilst significantly reducing the weight of the roof, creating a sense of openness and an overarchingly light and minimal expression. This expression, created for efficiency but crafted for elegance, has already become a unique identity element for the stadium. This minimal, ultra-efficient form also enables it to stand out from other global venues, so much it has been commented in the media that the stadium evokes the leaf forms of the Pandanas tree, endemic to eastern Australia.

Ken Rosewall Arena – Photo: Cameron Hallam

Embodied carbon The most efficient way to reduce the embodied carbon footprint of new stadia is the adaptive reuse of existing structures and avoid complete demolition of outdated venues where possible.

As most of the carbon is usually embedded in the concrete bowl and foundations, retaining those would yield the largest carbon saving, while roofs are generally easier to dismantle and recycle.

The lighter the roof, the less materials are used As demonstrated by the redevelopment of Ken Rosewall Arena, it is possible to reuse much of the existing bowl superstructure, substructure, and piling. It was found that the existing structure could support the new lightweight PTFE fabric roof. The circular form used creates a very efficient self-resolved tension structure. Again, by working together with our engineering partners we were also able to realise a form that evokes a sense of lightness and elegance in its form and representation. This strategy minimised the use of resources relative to the protection afforded by the extended roof cover.

The lighter the roof, the less materials are used and the lighter the building, which in turn reduces the amount of concrete required for foundations. It sounds easy and obvious. But in a project and complex as a 40,000-seat stadium the opportunities to complicate and “add in” arrive daily in the design process so that it’s easy to see where projects can become unnecessarily “heavy”. structural engineers Schlaich, Bergermann and Partner – the roof of the new Sydney Football Stadium (Allianz Stadium) and it is now reported to be the lightest stadium roof in the Southern Hemisphere. And again, this lightness is achieved without sacrificing coverage and guest comfort. This is exemplified by the fact that 100 % of the 42,500 seats are within the drip line of the roof.

“The most efficient way to reduce the embodied carbon footprint of new stadia is the adaptive reuse of existing structures [...].”

Business cases may demand for new built Unlike Ken Rosewall Arena, the legacy of Sydney Football Stadium was deemed unsuitable for an upgrade, based on an extensive series of studies and business cases. The central requirement to extend the utilisation of the stadium and enhance patron amenity was beyond what any economic “upgrade” could deliver.

The new stadium does boast some impressive statistics from recycling approximately 87 % of construction and demolition waste, to exceeding energy and water efficiency benchmarks by 20 %. The stadium’s lightweight roof structure uses 40 % less steel than a typical venue of the same size, and the building hosts integrated solar panels and water harvesting solutions.

Where concrete is unavoidable, we specify concrete with a high degree of ash or slack and recycled aggregate to minimize its embodied carbon. Replacing concrete and steel with timber is the next frontier in the journey to carbon neutral stadia.

Energy Whether designing a new stadium or redeveloping an existing one, minimizing operational energy use is paramount. Apart from reducing running costs by saving electricity, it also reduces the need to offset emissions for stakeholders who seek to entertain carbon neutral events.

Reducing lighting energy Artificial lighting is generally the greatest contributor to electricity use in stadia. By allowing daylight to penetrate deep into the building, the translucent PTFE roofs of Ken Rosewall Arena, the new Sydney Football Stadium and Perth’s Optus stadium have proven an excellent strategy to reduce the need for artificial lighting, while providing shade and rain protection. It is an elegant solution that becomes a feature of a venue and an enhancer of experience rather than feeling like an omission; capturing the golden light of dusk in one of the concourse bars at Queensland Country Bank Stadium has already become a noteworthy experience for patrons for example.

The emergence of new technology is an important factor in continuously decreasing the operational energy in our stadia designs over time. All COX projects incorporate efficient LEDs for interior and external lighting. On-site energy generation All our contemporary stadia designs include considerations for on-site renewable energy generation and incorporate solar PVs and provisions for future installation where feasible. While the large roof area lends itself to the installation of PVs, they can also be installed to shade car parks and pedestrian walkways. The arrival of solar PV films will further support their integration in the next generation of ultra-lightweight structures.

Anaerobic digesters using organic waste to produce electricity out of biogas is another technology perfectly suited for stadia. Sports and entertainment venues produce a large amount of organic waste from food leftovers and grass clippings, which can either be locally composted or transformed to energy. A commitment to a plastic-free environment in combination with on-site organic waste treatment significantly reduces the amount of waste sent to landfill and diminishes fossil fuel emissions from garbage trucks.

While surplus energy can be fed into the grid and power nearby buildings and precincts, on-site renewable energy generation is most efficient when supported by batteries as they help to manage disparities between energy demand and generation and stabilize the electricity grid.

Water collection and use Conversing potable water is another important consideration, particularly in Australia with its great rainfall variability and regular droughts, which are also predicted to worsen due to climate change. While stadia have a substantial

demand for water on game days and pitch irrigation, a typically large roof area provides a great opportunity for rainwater harvesting and reuse to flush toilets and irrigate.

The new roof at Ken Rosewall Arena for example was designed to enable the collection of rainwater from at least 90 % of the enlarged roof surface with a projected plan area of approximately 8,000 m². The fall and guttering of the roof can collect rainwater which can then be fed into a future tank in the next stage of the development, with the aim of water reuse for non-potable uses. In a predominantly dry and warm Sydney climate the on-site capture, storage and re-use of all water types is essential in enhancing landscape, maintaining amenity, and reducing costs.

At Queensland Country Bank Stadium, up to 500,000 litres of rainwater storage from roof run off is used for toilet flushing, post-game wash down and cooling tower water demand on match day. Rainfall is not the issue in the tropical North of Australia, however diverting water appropriate for non-landscape use is an important route to efficiency of operation.

Multifunctionality offers sustainability For all the debate around the use of sustainable materials and an understandable reticence to “knock down and rebuild” the key to the success of any leisure facility – from community centres to mega stadia – lies in their utility and in their utilisation. The intensity with which they are used by their codes, teams, events, entertainers, governments, schools and so on is a true measure of their success and a key element to their sustainability.

Longevity is one important measure, but so is multifunctional utilisation – if one venue can fulfil the role where three or four were previously needed then this becomes a net success in the ambition of a more sustainable future. If a venue is used 14 times a week versus the three delivered by the preceding facility, how should we then view them through the lens of longevity and sustainability?

The new Sydney Football Stadium for example houses three elite code franchises of football; Rugby Union, Rugby League and Soccer, and is also ready-made for everything from superstar concerts to community events.

Perth’s Optus stadium designed by COX in association with Hassell and HKS Architects is another successful example of multifunctionality. The multi-purpose stadium has been designed with current and future flexibility in mind and accommodates Australian Rules Football, Cricket, Rugby Union and League, and entertainment events. The 60,000seat stadium includes the widest range of hospitality options in any sports venue within Australia including the innovative locker room, coaches club, sky terraces, corporate suites, club lounges, a 2,000-person function room, retail and over 50 food and beverage outlets.

Community – cultural and social impacts When looking at the carbon footprint of stadia on an annual per capita basis, it becomes clear that attendance is key. A stadium development represents a massive investment – not only in monetary terms but also in terms of carbon emissions. The obvious goal is to fill the stadium with as many events and spectators throughout the year as possible.

A focus of our design ethos is the desire to enhance the civic life of our cities. Stadia are a rare and very singular opportunity to express this ethos to its fullest. It’s inarguable that

the denizens of our cities (eight out of ten Australians in fact) see climate action as a core focus for government and climate change as an existential threat to our society. As such, a presciently designed stadium with flexibility and community at its heart can materially contribute to both objectives and deliver a more sustainable and more culturally inclusive and vibrant city. As designers, you cannot get clearer motivation than this.

We always talk about our projects, but especially our sporting venues, and their need to “give more than they take”. It is this ethos that best expresses COX’s approach to a sustainable future of stadia design.

What are the next steps?

For existing facilities, we are also seeing operators and management companies hard-baking a continual review of ever more sustainable practices as part of their periodic, and in some cases, their daily operational reviews. This is probably the biggest and most important area of progress, where there’s been a rapid shift from a “net zero” objective being ”nice to have” to one that’s both central and a “guiding operational ambition”. As this has now moved from the niche or specialist realm and into a more mainstream management enterprise, literally everything is on the table from base construction materials through to software that optimises the solar harvesting and storage and then manages to the minute how this power is deployed based on the climatic requirements of the day and the nature and needs of the event being staged.

Optus stadium – Photo: Peter Bennetts

Optus stadium – Photo: John Gollings