Industrialised, Integrated, Intelligent sustainable Construction - I3con

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SUSTAINABLE CONSTRUCTION HANDBOOK 2 complex architecture of the interface that termites build - the mound - to manage the environment in their collectively constructed space – the nest [31]. New rapid manufacturing and free-form fabrication techniques make it now feasible to build walls that incorporate some of these design principles (Figure 10). Imagine, for example, porous walls that are permeated with a complex reticulum that, like in the termite mound, acts as a low-pass filter for turbulent winds. In this instance, an interior space of a building could be wind-ventilated without having to resort to tall chimneys, and without subjecting the inhabitants to the inconvenient gustiness that attends to the usual means of local wind capture, namely opening a window. Now, it is the windows that are the barriers and the walls that connect the inhabitants to the world outside. Or, imagine a cladding system that mimics the mound’s complex interface at the surface conduits and egress tunnels (Figure 10). One could employ such claddings as whole-building wind-capture devices, which greatly expands a building’s capacity for wind capture. Or, imagine a wall that is tuned for differential mass exchange where the high-frequency components of turbulent winds can evaporatively cool a porous wall’s surface layers and provide natural cooling for air forced through the walls by wind’s lower-frequency components. The possibilities, we hope you will agree, are large. 244 Beyond biomimicry Indeed, the possibilities may be more than large: they may be vast. This is because the termite mound is not simply a structural arena for interesting function. It is itself a function, sustained by an ongoing construction process that reflects the physiological predilections of the myriad agents that build and maintain it. The mound, in short, is the embodiment of the termites’ “extended physiology” [29, 32, 33]. This raises the intriguing idea that building design can go “beyond biomimicry”, to design buildings that do not simply imitate life but are themselves “alive” in the sense that termite mounds are. Figure 11. The standard negative feedback model for regulating the built environment Realizing the living building is predicated upon there being a clear idea of what distinguishes living systems from non-living ones. Unfortunately, most of the criteria that are commonly put forth by biologists - cellular organization, replication, heredity, reproduction, self-organization, low entropy - are not very informative for building designers. Remarkably, they are not even particularly helpful in the life sciences. Reproduction, for example, is not a useful criterion for recognizing living systems, such as the biosphere, that do not reproduce. Nor is a concept like self-organization much help: many complex non-living systems, like clouds, are self-organizing, so how are these to be distinguished as not-life? Fortunately, there is one feature that reliably distinguishes life in a variety of contexts and scales. That is homeostasis, the tendency of living systems to gravitate toward a particular adaptive state in the face of disruptive perturbations. Realizing the living building therefore means realizing the homeostatic building. The idea of homeostasis is nothing new to architects and engineers, of course: it is standard practice to outfit buildings with systems to regulate particular properties of the built environment: temperature, humidity, air quality and so forth. The focus here is on machines that do work to manipulate a property through negative feedback control (Figure 11). Thus, a property is sensed, its deviation from some desired value is assessed, and a machine is activated that does work to offset the deviation. Such systems range in complexity from simple house thermostats to sophisticated Building Energy
HANDBOOK 2 SUSTAINABLE CONSTRUCTION Management Systems, but all have in common that they are firmly rooted in the building-as-machine design tradition. Homeostasis is more than simply self-regulation, however. It is a fundamental property of life that, among other things, confers upon living systems an impressive capability for emergent self-design [30]. Thus, regulation of an environmental property - the essence of the building-as-machine - is but one of many outcomes of a larger systemic homeostasis that engages every aspect of the system’s architecture and function. The termite “extended organism” is a remarkable example of this capability. A termite colony’s oxygen demand varies considerably with colony size: small colonies may comprise a few thousand individuals, while the largest colonies may have populations upwards of two million [34]. Despite this large variation in demand, oxygen concentrations do not differ appreciably with colony size: oxygen concentrations in very large colonies are similar to those in much smaller colonies (Figure 12, [15]). Yet, there is no machine in the termite mound that does the work to offset the perturbation that a negative feedback system might demand. Nor is there any evidence of an “oxygen-stat”: termites are not particularly sensitive to quite large oxygen perturbations. How, then, is oxygen concentration regulated? Figure 12. Oxygen concentration in several nests of Macrotermes michaelseni. Symbols represent means +/- 1 standard deviation. Mound size is a surrogate for colony metabolic demand. Part of the answer is that it is not simply the property of oxygen concentration that is regulated. What is regulated, rather, is multiphasic processes of which one outcome is a steady oxygen concentration. Because the mound is an extended organism, this process extends to the mound, which is itself a process. Thus, mound structure is as impressively regulated as oxygen concentration. How termite colonies manage this seamless integration of structure and function remains largely obscure, but some interesting features are starting to emerge. There is a common link, for example, in the termite-mediated movement of soil that makes the mound both process and structure: this is why it is possible for the mound’s structure to reflect the termites’ collective physiology. Understanding the termite colony as an extended organism therefore involves understanding what guides this ongoing termite-driven stream of soil through the mound. Surprisingly, negative feedback, so essential to the building-as-machine paradigm, appears to play only a minor role in the termite extended organism. Rather, there is a kind of swarm intelligence at work. Soil translocation is organized into discrete foci of intense activity that is driven by a multiplicity of positive and negative feedback loops involving termites, the structures they build and the intensity of local AC perturbations of the environment (Figure 13). To complicate matters, the multiple foci compete with one another for workers, with more intensely active foci drawing workers away from less intense foci, the outcome of the competition both determining and being determined by the structures that result. To complicate things further, the entire process is modulated by the availability of liquid water. 245
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Industrialised, Integrated, Intelligent sustainable Construction - I3con

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