A series of long, rippled concrete walls helps to passively cool a large atrium at the Federation Square cultural arts and media center in Melbourne.
Patrick Bellew is very keen on termites. Not just any termites. Barossa termites.
The blind wood-munching critters found in Africa are best known for building massive, finely engineered nests that can reach 20 feet in height and come with fully integrated passive temperature control.
“The system can control the temperature in the queen's chamber, at the heart of the nest, to within 1ºC throughout the year, even in the extreme heat of the African day,” says Bellew, founding director of London- and New York-based building environmental engineering consultants Atelier ten. In order to achieve such a precise level of temperature control, Bellew says the termites rely on three fundamental physical principles—convection, thermal mass, and evaporative cooling. These principles can be applied to high-performance building design to reduce reliance on mechanical systems.
“Outdoor air is drawn through tunnels into a subterranean chamber, which has a large contact surface area with the ground to help cool the space on hot days and warm the space on cold days,” he explains. When the central core becomes too warm or the air too stale, the termites unblock openings to ventilation shafts to exhaust the air out the top of the nest and induce the convective draft that drives the system.
In extreme heat, the arrangement is supplemented by evaporative cooling, says Bellew. “The termites travel tens of meters down tunnels to the water table to collect minute quantities of water to place into the system.”
Federation Square cultural arts and media center in Melbourne; Photo: David Simmonds
In the world of biomimicry, where science looks to nature for the most efficient solutions, Bellew and his fellow engineers at Atelier ten have used the intuitive science of the Barossa termite nest as a source of inspiration. During the past decade, the designers have applied much of what they learned from Africa's white ants to develop buildings that minimize—or even eliminate—the need for energy-hungry HVAC mechanical systems.
“Successful low-carbon buildings need to be 80% about passive design, using natural forces to minimize reliance on systems,” says Bellew. “What could be more inspiring as a role model than a tiny, blind insect that builds vast structures that intuitively exploit the physical laws to produce a comfortable environment in even the most extreme weather conditions?”
Atelier ten first applied its concrete labyrinth concept on the Planet Earth Galleries for the Earth Centre in Doncaster, England. The design eliminated the need for mechanical cooling for the exhibit space. Rendering: Atelier ten
The firm has successfully implemented this innovative approach on several building projects in Europe and Australia, including the Alpine House glasshouse at the Royal Botanical Gardens Kew outside London and the Federation Square cultural arts and media center in Melbourne.
At the heart of Atelier ten's basic design philosophy for mass-cooled buildings is a subterranean passive thermal storage system composed of what Bellew describes as a labyrinth of concrete tunnels that are an integral part of the actual building structure but are thermally decoupled from the spaces that they serve. During the summer months, warm outside air is drawn into the subterranean chamber using low-pressure mechanical fans and, with the control of dampers, is channeled slowly through the labyrinth, where it cools before being routed into the interior space of the building.
With the use of dynamic thermal analysis modeling
Earth ducts: Another method for cooling buildings
If you're not ready to take on an all-out labyrinth project just yet, Bellew suggests a slightly different decoupled thermal storage approach: earth ducts.
Widely used in Germany and other parts of Europe, this method involves burying long runs of concrete or steel pipe several feet below grade. Warm outside air is drawn into the duct using low-pressure mechanical fans, where it gradually cools as it passes through the duct and is then routed into the interior space of the building. In most cases, earth ducts work in parallel with conventional mechanical cooling and heating systems to help reduce energy costs.
“We recently completed a study of earth ducts for use in U.K. big-box retail and found that, with the appropriate systems, we can virtually eliminate heating and cooling loads,” say Bellew.
software, Atelier ten's engineers are able to optimize the size, scale, and configuration of the concrete labyrinth based on the location of the project, design of the building, and desired interior environmental conditions. For instance, at Federation Square, where daytime temperatures can reach 40ºC, computer analysis showed that long, rippled concrete walls would perform better than smaller, flat walls. The design maximizes heat exchange by increasing the surface contact area and roughness.
“The air is almost always cool at night in Melbourne,” says Bellew. “We use night cooling to flush the heat of the day, along with some of the moisture, out of the concrete by running the system throughout the night so that the mass is cool the following day.” The flow of air can be controlled through the various chambers to respond to external conditions and allow the heat to be flushed out of the concrete quickly at night. Typically, the air travels 300 meters down the passageways during the day and 100 meters at night when it is being flushed.
The design eliminated the need for mechanical cooling for the center's atrium, saving significant mechanical plant space and upfront equipment cost. Plus, Bellew says the concrete labyrinth “will last for several generations, where conventional equipment would have to be replaced several times.” When cooling is not needed in the space, the air can be diverted to an adjacent museum to help cool the gallery spaces.
While decoupled thermal storage systems like the one implemented at Federation Square require significant upfront investment in infrastructure, Bellew says much of the upfront cost is offset with downsized mechanical systems and ongoing operational savings. For instance, Bellew says the annual energy consumption for cooling the atrium space at Federation Square is just 10% of that which would have been required for a more conventional overhead cooling system.
“The payback period for the additional cost of the labyrinth in Melbourne was less than 10 years, with a potential design life of 100 years or more,” says Bellew. “Of course, upfront costs can vary depending on whether you have to excavate to build the labyrinth or are using found space, as was the case with Federation Square.”