Bio-inspired Adaptive Building Skins - Biotechnologies and Biomimetics for Civil Engineering - page 121

bioMASON are: loose pieces of aggregate, enzyme producing bacteria, an amount
of urea and an amount of calcium ions (Dosier 2011 ).
In addition to these materials, there are also applications of buildings which
attain adaptability by directly incorporating living organisms in the building
envelope construction, but do this while extending their functionality beyond what
is found in the original application domain. An example is the bio-reactive façade
of the BIQ house at the International Building Exhibition 2013 in Hamburg
(Fig. 5.4 ). The BIQ house is equipped with façade-integrated bio-reactors—
transparent containers with microalgae cultivated in the façade component. While
growing, the algae in these bio-reactors serve multiple functions at the same time:
they act as shading system, solar thermal collectors and absorb carbon dioxide.
After the cultivation phase, the algae can be separated from the water, to be used as
biomass with an expected energy gain of 30 kWh/m 2 per year (Wurm 2013 ).
Sweating polymers recently receive attention as a novel way for cooling
buildings without energy consumption (Rotzetter et al. 2012 ). Perspiration, the
way mammals release heat to their environment via moisture secretion is used as a
guiding principle for this concept. The technology uses thermoresponsive hydro-
gels, which enable utilization of evaporative cooling. At a critical switching
temperature of 32 C, the material undergoes a phase transition and accompanying
release of moisture in a sweating-like manner. Autonomous operation is ensured
by regeneration of the system with rain water. Experiments in a reduced-scale set-
up demonstrated an estimated energy-saving potential for cooling of up to 60 %
(Rotzetter et al. 2012 ).
Worldwide, avian mortality due to collisions with building facades is estimated
in the billions every year (Klem 2009 ), mainly because traditional windows appear
invisible for birds. In the search for solutions to this problem, bio-inspired prin-
ciples may form a valuable resource. The ultraviolet (UV) reflection pattern of
spider webs makes them discernable for the birds' sensory system. It is proposed
that window systems with similar UV reflecting properties can act as a significant
deterrent for collisions, with little or no obstructed view for humans (Evans Ogden
2014 ). Commercial products based on this proposition are currently entering the
market. The main challenge in making the technology successful is in finding a
coating composition that reflects a sufficient amount of UV light, yet does not
interfere with the windows' visual functioning. The importance of this issue is
reflected by the fact that the LEED green building rating system recently intro-
duced a pilot credit for bird-collision deterrence as part of the new biodiversity
category (Foster 2011 ).
An iconic example of a more indirect bio-inspired functional mechanism is the
self-cleaning capability of Lotus leaves. After studying the physical principles, this
advanced functionality has successfully been transferred in the form of coatings
for building cladding and fenestration systems (Pacheco-Torgal and Jalali 2011 ;
Solga et al. 2007 ). The deposition of a special hydrophobic layer prevents dirt from
building up because it gets washed away by the almost spherical droplets of water
(Parkin and Palgrave 2005 ).