Natural ventilation in buildings based on termite mounds
A team of mechanical and civil engineers at Loughborough University, UK, hopes to construct buildings that can create comfortable living conditions by extending our use of renewable forms of energy. How so? By unlocking a few of the mysteries found in the termite mounds on the plains of Namibia, Africa.
Architects have long been inspired by termite mound architecture and many examples exist of the resulting chimney-style, passive, ventilation systems. However, the species of termites, Macrotermes michaelseni, currently being studied by Dr Rupert Soar do not create mounds that are visibly open to air but still achieve the same level of ventilation. They build highly complex structures that ensure a constant internal environment (homeostasis) in which the insects can thrive, regardless of the fluctuating external conditions. ‘Both mounds and termites are able to control their internal environment as closely as an organism,' says Soar. ‘But the amazing thing is this is a pile of mud, not even humans have achieved the same level of complexity in our buildings.'
The team designed and built the world's largest slice and scan machine and shipped it to Namibia last summer, armed with international experts and funding from EPSRC. Erected over a termite mound, the device scanned the mound for two months and produced a slice image of every millimetre of the structure, even below ground. In addition, the team measured variables including local weather, internal moisture levels, temperature, metabolic rates, mound permeability, and oxygen and carbon dioxide concentrations. The 2,000 2D scanned images that have been accumulated are now being re-assembled into a 3D computer model from which simulations of flow and regulation can be performed.
The research is ongoing, tackling interesting questions as to how the termites maintain all the variables within equilibrium. Are the termites constantly interacting with the structure to get suitable airflow? ‘We have seen them opening and closing small access channels to the outside like windows,' suggests Soar.
Initial research also indicates a complex vein-like and thin capillary geometry that enables a method of respiration through the mound's skin, similar to the way a lung works.
What about the materials' properties? Soar explains that there appears to be a threshold response to moisture at any single location on the clay and aggregate-blended skin. ‘Most clays expand within a tight moisture range. In mounds, if the sun shines and dries out the clay below the threshold, it will encourage permeability and ventilation. If it rains, the clay swells and becomes impermeable. It is an incredibly smart structure.'
The team sees potential for this research to eventually influence the construction of buildings, although Soar stresses that their theories have yet to be proven. One idea is that rather than look at moisture as a problem, humans could, like termites, also incorporate the threshold response to moisture in walls, using the ‘buoyancy' of moisture that occurs with heat for ventilation and evaporative cooling.
Additionally, he sees scope for creating walls with capillary-like structures that drive moisture for water recovery through evaporative cooling, and control air exchange and temperature, lowering our reliance on non-renewable energy through passive regulation using the energy around us.
So how could these structures be built into the walls of our homes? By printing them using massive, mobile machines that can print 3D building structures ‘as if you were printing ink onto paper', suggests Soar. His team is collaborating with the University of Southern California, USA, to build these machines. ‘There is no limitation to how complex the structure is that you print. We [can] scan nature itself, manipulate the information with advanced modelling techniques and then print the structure into our homes.'
Soar adds, ‘If, as some people are suggesting, brick firing is going to end in ten years, then there are companies already looking at printed unfired clay structures. We are already printing panel systems with channel and ducts for all the pipework.'