Industrialised, Integrated, Intelligent sustainable Construction - I3con

More documents

Recommendations

Info

SUSTAINABLE CONSTRUCTION HANDBOOK 2 penetrate to the lower chimney and subterranean tunnels, and the rapid transients that drive flows in the superficial tunnels (Figure 9). These disparities in frequency of AC wind energy, along with variations in wind speed, wind direction and the distribution of surface porosity on the mound, can set up a slow back-and-forth “sloshing” of the boundary between nest and mound air, enhancing the mixing of the two air masses there [15]. Another interesting impedance-based mechanism involves so-called high-frequency ventilation, or HFV [21]. This is a respiratory therapy that is used to sustain gas exchange in lungs that have suffered mechanical damage and cannot sustain the large volume changes that normally accompany respiration. High frequency ventilation imposes minuscule volume changes on the lung, but at a much higher frequency, 10-20 Hz as opposed to the normal ventilation frequency of 0.2 Hz. According to one theory, HFV works by driving the lung at the resonant frequency of the airways, enhancing diffusion and promoting pendelluft ventilation [20, 22]. A form of high-frequency ventilation may also occur in termite mounds, but here driven by particular bandwidths of the frequency spectrum of turbulent winds. The extensive array of long, large-calibre tunnels in termite mounds can extend for more than 2 metres in length. These resonate strongly at frequencies of about 20-30 Hz, which sits comfortably within the frequency bandwidth of turbulent winds, typically 1-100 Hz. If the mound’s tunnels are “tuned” to capture the AC wind energy in this narrow frequency band, it may set air in the tunnels resonating, driving a kind of HFV that could promote gas exchange without large bulk flows of air through the nest. More likely, however, is a structural distribution of wind capture that matches a distribution of resonant frequencies. For example, the air spaces in the mound offer a variety of path lengths for transient wind energy to follow, ranging from a few centimetres in the superficial egress tunnels, to metres in some of the deeper and larger calibre tunnels. Thus, transient winds at the upper end of the frequency spectrum could do work in the shorter superficial tunnels, while lower frequency transients do work in the deeper and longer tunnels. This opens the possibility for discriminatory mass transfer mechanisms in termite mounds (and termite-inspired buildings) similar to those that operate routinely in lungs. Evaporative cooling through panting works this way, for example. Panting cools a dog by elevating the rate of evaporative mass loss from the mouth and lungs, driven by an increased lung ventilation [23-26]. This poses a physiological quandary: how to increase water vapour flux without simultaneously increasing carbon dioxide flux, which could cause severe upsets of the body’s acid-base balance. The quandary is resolved by the lung’s impedance. Driving the lungs at the resonant frequency of the thoracic cage increases the lung’s impedance. The higher-frequency ventilation preferentially enhances evaporation from the upper respiratory passages. The lung’s high impedance to these high frequencies leaves CO2 flux at the deeper, mixed regime level unchanged. Similar discriminatory schemes may operate in termite mounds too. For example, termites tightly regulate the nest’s water balance, which is often undermined by percolation of ground water into the nest following rains [27, 28]. At the same time, termites also tightly regulate the concentrations of oxygen and carbon dioxide within the nest [15]. Termites are thus faced with a physiological quandary similar to the one panting dogs must face: how to evaporate water faster from the nest without simultaneously disrupting the balance of respiratory gases. Termites accomplish this by actively transporting water to the superficial parts of the mound in wet soil, where it is deposited around the egress tunnels. Because it is precisely these regions that should be ventilated most strongly by rapid wind transients, evaporation can be enhanced without also increasing respiratory gas flux that depends strongly upon low-frequency transients. 242
HANDBOOK 2 SUSTAINABLE CONSTRUCTION Figure 9. Hypothetical pendelluft ventilation in the termite mound and nest. Top. Array of forces acting on the deep air masses in the mound and nest. Middle and bottom. Pendelluft flow that arises in response to variation in wind speed and direction. How buildings can be like lungs This enhanced conception of how termite mounds work is immensely liberating because it opens a veritable new universe of termite-inspired building designs. No longer need such designs be constrained by the long-prevailing models of induced-flow and thermosiphon flow: a good thing, since these mechanisms rarely operate in natural mounds anyway. In contrast, a clear vision of how termite mounds actually work literally opens a whole new spectrum of wind energy to explore and exploit. Figure 10. Some imagined biomimetic designs. Top left. The surface conduit-egress tunnel complex. Top right. A rendering of a building enveloped by porous “surface conduits.” Bottom. The block elements for an artificial surface conduit. Consider, for example, the traditional conception of the wall. In most building designs, walls are erected as barriers to isolate spaces: internal spaces from the outside world, internal spaces from one another and so forth. Yet spaces, if they are to be occupied and used, cannot be isolated. Resolving this paradox is what forces building designs to include infrastructure - windows, fans, ducts, air conditioning, heating etc - all essentially to undo what the erection of the walls did in the first place. In short, the paradox forces building design toward what we might call the “building-as-machine” paradigm (BAM). Living systems, which also are avid space-creators, resolve the paradox in a different way: by erecting walls that are not barriers but adaptive interfaces, where fluxes of matter and energy across the wall are not blocked but are managed by the wall itself [29, 30]. This is illustrated dramatically in the 243
Page 1:
Industrialised, Integrated, Intelli
Page 4 and 5:
SUSTAINABLE CONSTRUCTION HANDBOOK 2
Page 6 and 7:
Page 8 and 9:
Page 10 and 11:
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
Page 64 and 65:
Page 66 and 67:
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
Page 100 and 101:
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162 and 163:
Page 164 and 165:
Page 166 and 167:
Page 168 and 169:
Page 170 and 171:
Page 172 and 173:
Page 174 and 175:
Page 176 and 177:
Page 178 and 179:
Page 180 and 181:
Page 182 and 183:
Page 184 and 185:
Page 186 and 187:
Page 188 and 189:
Page 190 and 191:
Page 192 and 193:
Page 194 and 195:
Page 196 and 197:
Page 198 and 199:
Page 200 and 201:
Page 202 and 203:
Page 204 and 205: SUSTAINABLE CONSTRUCTION HANDBOOK 2
Page 260: SUSTAINABLE CONSTRUCTION HANDBOOK 2
show all

Industrialised, Integrated, Intelligent sustainable Construction - I3con

Create successful ePaper yourself

Delete template?

Save as template?