Termite mounds reveal secret to creating ‘living and breathing’ buildings that use less energy

Newswise — Within the realm of about 2,000 documented termite species, a portion serve as ecological creators. Certain genera, such as Amitermes, Macrotermes, Nasutitermes, and Odontotermes, construct mounds that can stretch up to eight meters in height, placing them among the most colossal biological formations globally. Over millions of years, natural selection has diligently refined the architecture of these mounds. Should human architects and engineers observe and contemplate the approaches of termites, what valuable insights might they gain?

In a recent publication in Frontiers in Materials, scientists demonstrated how termite mounds can impart knowledge on creating pleasant indoor environments in our constructions without relying on energy-intensive air conditioning systems, thereby reducing carbon emissions.

Dr. David Andréen, the study's primary author and a senior lecturer at Lund University's bioDigital Matter research group, stated that their research reveals the potential of utilizing the "egress complex" – an elaborate system of interconnected tunnels found within termite mounds – to facilitate innovative airflow, heat distribution, and moisture control within human architecture.

Termites from Namibia

Andréen, together with his co-author Dr. Rupert Soar, an associate professor at Nottingham Trent University's School of Architecture, Design, and the Built Environment, focused their investigation on Macrotermes michaelseni termite mounds in Namibia. These mounds are home to colonies comprising over a million individual termites. At the core of these mounds, one can find the mutually beneficial fungus gardens cultivated by the termites as a food source.

The researchers specifically investigated the egress complex, an intricate network of tunnels within the termite mounds. These tunnels, measuring between 3mm and 5mm in width, connect larger conduits within the mound to the outside environment. During the rainy season (from November to April), when the mound is actively expanding, the egress complex extends across the north-facing surface of the mound, directly exposed to the midday sun. However, during other seasons, termite workers block these tunnels. The purpose of this complex is believed to be twofold: facilitating the evaporation of excess moisture while ensuring adequate ventilation. But how exactly does it achieve these functions?

In their research, Andréen and Soar delved into the arrangement of the egress complex and its ability to facilitate oscillating or pulse-like airflow patterns. To conduct their experiments, they utilized a scanned and 3D-printed replica of a fragment from the egress complex that was originally collected from the wild in February 2005. This fragment had a thickness of 4cm and a volume of 1.4 liters, with approximately 16% of its composition comprising tunnels.

During their investigation, the researchers employed a simulation technique using a speaker to induce oscillations of a CO2-air mixture through the 3D-printed fragment of the egress complex. They monitored the mass transfer using a sensor to measure the airflow. The results of their experiments revealed that the airflow was most pronounced when the oscillation frequencies ranged between 30Hz and 40Hz. At frequencies between 10Hz and 20Hz, the airflow was moderate, while frequencies between 50Hz and 120Hz exhibited the least airflow.

Turbulence helps ventilation

Based on their findings, the researchers reached the conclusion that the tunnels within the egress complex interact with the external wind blowing on the termite mound in a manner that promotes improved airflow for ventilation. When wind oscillations occur at specific frequencies, turbulence is generated inside the mound. This turbulence effectively facilitates the removal of respiratory gases and excess moisture from the central region of the termite mound. Therefore, the intricate design and arrangement of the egress complex contribute to enhancing mass transfer of air, aiding in the ventilation process.

Dr. Rupert Soar elaborated on the significance of the egress complex's design in the context of building ventilation. Traditional HVAC (Heating, Ventilation, and Air Conditioning) systems often face challenges in maintaining the delicate balance of temperature and humidity within a building while facilitating the movement of stagnant air outwards and fresh air inwards. However, the structured interface of the egress complex provides a solution by enabling the exchange of respiratory gases based on concentration differences between its different sides. As a result, the conditions inside the mound, and by extension, the building, can be effectively maintained without disrupting the ventilation process.

In their study, the authors proceeded to conduct simulations of the egress complex using a series of 2D models that gradually increased in complexity. The models ranged from simple straight tunnels to more intricate lattice formations. To observe the mass flow, they utilized an electromotor to drive an oscillating body of water, which was made visible through the use of dye, through the tunnels. The researchers were surprised to discover that the electromotor only needed to move the air back and forth a few millimeters (representing weak wind oscillations) for the ebb and flow to propagate throughout the entire complex. Notably, the required turbulence was only observed when the layout of the complex possessed a lattice-like structure.

Living and breathing buildings

The researchers' conclusion is that the egress complex has the ability to facilitate ventilation in termite mounds through the power of wind, even when the wind intensity is low.

Andréen envisions a future where building walls incorporate networks resembling the egress complex, using emerging technologies like powder bed printers. These networks would enable the circulation of air through embedded sensors and actuators, operating with minimal energy consumption.

Soar concluded by highlighting the significance of complex structures found in nature, such as the egress complex, for advancing construction-scale 3D printing. He emphasized that the ability to design intricate structures like those in nature is essential for achieving progress in this field. The egress complex serves as an exemplar of such complexity and has the potential to address multiple challenges simultaneously. It can contribute to maintaining comfort within homes while effectively regulating the flow of respiratory gases and moisture through the building envelope.

"We stand at the threshold of a transformative shift towards construction that emulates nature: the prospect of designing a building that truly lives and breathes may soon become a reality."