ACTIVE CERAMIC ENVELOPES: SUSTAINABILITY AND ARCHITECTURAL INTEGRATION OF FUNCTIONS

Claudio VARINI Dr.Arch.

University of Florence, Florence, Italy claudio.varini@taed.unifi.it

Keywords: Active Ceramic envelopes, photovoltaic, photo catalytic, building technologies, Ecotiles

Summary Walls and roofs such as fur and not such as shell, sensitive to exterior agents and structured for transferring energy to the architectural organism; agents capable of preserving the optimum conditions for its functioning through time and with a long useful life. These are the characteristics of the Ecotiles, research project in the finalization stage in the TAED department of the University of Florence. Ceramic materials as reliable starting point: by performances, useful life, contained cost and cultural rooting on the one hand, and by the development of the widely diffuse productive potential worldwide, on the other. The high effectiveness photovoltaic function and photo catalytic function are integrated into ventilated systems -also permitting the control of thermal excursions- that are the basic functions of the project aimed of reaching an esthetical and functional integration through a real innovation over traditional ceramics. The effective architectural integration, through modular components (admitting 24 to 90 degrees applications) until today only reached in glass roofing and facades and partiality with metallic supports, becomes a fundamental vehicle for the diffuse sustainability oriented innovation acceptance: flexibility of use and greater complexity design spectrum in respect to ventilated facades and photovoltaic roofs are the elements proposed in the Ecotiles system.

1. How can traditional materials harmonically integrate active functions? A new horizon for architecture, technology and the industry has opened over the functionalized surfaces, framed by the process and product innovation. In further detail we recognize in the energetic and environmental topics some indispensable development fields for envelopes. The question that immediately arises is if new materials must correspond to new functions, or else, if it is possible to find a valid response on traditional materials. And, by traditional I refer to brick. Will they be in condition of providing satisfactory answers to the more urgent effective and sustainable management of energetic resources for improvement comfort at a cost allowing the opening of a place in the market? With the presence of non traditional materials and complex and performing solutions it is valid to ask oneself if bricks have reached its physiological limit, or else, if there is field for short and middle term real innovations. The answer is on the capacity of the material for assuming new functions and responds to yet unsatisfied needs. The construction industry is just beginning to give answers that imply an active position facing the decrease of energetic and air quality improvement costs, and this is the field where the ECOTILES research project takes place. The project foresees the photovoltaic functionalization of brick ventilated enclosures. Objective: Integrated systems capable of responding to the functional and aesthetic instances oriented to industrial transferability. The action field of the project is limited to the technological viability demonstration (and the economic convenience level) of an active ceramic enclosures system, being fully aware that times and resources necessary for reaching effective innovation are different. But, why the need of inventing active roofs and facades? First we consider the urgency of giving technological response to energetic and environmental problems; second, its has been considered that traditional ceramics are materials that due to its behavior throughout time by extension of applications, aesthetic and physical-mechanical characteristics can be effectively integrated to advanced technologies. It is also considered that in addition to its long useful life and its recyclable condition, it dramatically decreased the impact on the environment. The aggregation of technology and value aimed at promoting the introduction of the industry is sought so that the same brick making company will produce not only simple pieces, but system finite components. For this purpose, it is necessary to attach to the production normal cycle processes capable of functionalizing the surface at sight.

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Figure 1 Photovoltaic panels on a ceramic roof. It is precisely the energetic and environmental combined action applied to bricks what can have a transcendental impact: innovation is technologically possible, economically attractive, demanded by the standards, object of economic and fiscal advantages, in addition to responding to the demands of the potential users. Therefore, the project proposes both, the innovation of the process and of the product. It is an analogous step to the one taken by ventilated facades pioneering companies when conceiving a system made-up by dry applied ceramic pieces and supported by a connection and anchoring sub-structure. What is being stated is not just the production of single industrial pieces with low aggregated value, but the supply of systems components with advanced characteristics and functions. In order to reach that point, it is necessary to specifically investigate the compatibility between ceramic surfaces and materials making-up the external functionalized layer, and to experimentally assess stability and functioning under extreme conditions. The point is to catalyze energy and resources in order to combine the project and productive actions with those of applied research that until now, within this horizon, have operated in separate ways. The governmental commitments for the application of the Kyoto Treaty favors the utilization of renewable energetic sources, as well as solutions capable of decontaminating the atmosphere, and paradoxically, these are the consequent restrictions to the application of the treaty [the increase of thermal effectiveness, decrease of energetic consumption, pushed by the required energetic standards and certifications] allowing projects, such as ECOTILES, to respond to one or more of these demands, to have a non negligible appeal and greater possibilities of having an impact on the construction market. This impact also depends from other two mandatory components: the integration of the “functionalized enclosures” system to architecture and facilities and the functional elements aspect dimensionally, formally and chromatically integrated to the aesthetics of architecture without building a useful but unpleasant foreign body.

Figure 2 Shell v/s skin If we look at - for instance - photovoltaic panels and installations currently in the market, we notice that frequently the proposed technological solutions respond to the functional box logic, this is, of an overlapped technological element, partially integrated and some times “uncomfortable”. In the project the enclosure has been conceived not so much as a shell, but rather as a skin, therefore not as a durable surface, but as a complex system of integrated superficial and “subcutaneous” functions as the natural ventilation and a continued superinsulation layer. The complexity of matters demands the contribution of specialized knowledge and synergy among the experts in order to avoid the Frankenstein effect. The project is not referred to a sole disciplinary area, and it operates within a filed in some aspects unexplored, but there are recent experimental investigations and applications to which we can refer to for analogy purposes.

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Figure 3 Building with glass funcionalized surfaces in Peking The glass manufacturing industry is a pioneer in the active decks field reaching significant results, both in dealing with thermal aspects as well as in regards to functionalization: let us see for example double skins, or the use of the nanomaterial. The crystal has certain advantages with respect to the terracotta for it is not porous due to the smooth surface and the absence of impurities that can compromise the photovoltaic functioning; but this is a technologically solvable problem. On the other hand, the cement production industry has recently experienced the photo catalytic functions, inserting metallic oxide in constructions with satisfactory results. Figure 4 Photocatalytic cement covering Why then should we start from bricks? Starting from bricks is starting from a known element: its raw material is present worldwide, its use transcends millenniums, its behavior and durability are well known, and they enjoy an excellent acceptance due to its color, texture and the content-cost relationship. Starting from a known and widely diffused material permits to join continuity and innovation without radically modifying the aspect of constructions. It is precisely the experience of “secondary effects” revealed by new construction materials (such as pathologies or early aging) that makes us trust on the ceramic support based on solid and reliable grounds of knowledge in terms of useful life and its behavior throughout time and facing atmospheric agents.

2. Transfer to the brick making industry Transfer to the brick making industry can consequently benefit from the basis provided by useful information and also set the specific limits or advantages. In regards to the terracotta, there are at least three crucial points for reaching the production innovation and two points for process innovation:

2.1 Functionalization of the at sight surface in terracotta While there are different contextual conditions that can favor at least the diffusion of active enclosures, two types of fictionalization are considered: the first one is the energetic and implements photovoltaic technology; the second, the environmental one that takes advantage of photo catalytic properties of the metallic oxide. With both functions there are various material selection possibilities, consequently of Technologies and effectiveness levels.

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2.1.1 Photovoltaic Second and third generation technologies are studies with close attention, superior in effectiveness in respect to those of wafers currently used; the analysis is not limited to silicon, but it analyzes the cadmium tellurium (CdTe) and copper diseleniurum (CIS) industrial transfer possibilities. Today, the microcrystalline silicon is the most compatible material with industrial transferability thanks to an advantageous cost-performances relationship; nonetheless, the presence of market speculative phenomena, but the materials that have yielded superior results in experimental tests are different, even when these results are conditioned to stability, due to the toxicity of some components or due to the cost of the raw material. Leaving aside for a moment the aesthetic aspects, the election between these, the market acceptance possibilities depend in great part of the relationship between the cost of the raw material and the effectiveness of the cells, besides the global cost of the elements installed and integrated in the architecture. Today, the first generation panels have much too long cost covering times in order to have greater diffusion, even when being true that among the renewable sources it is the photovoltaic the one that more rapidly approaches the threshold of competitiveness with fossil fuel. Figure 5 Flexible photovoltaic thin film. All projections show a continuous and rapid growth of production and applications, but in terms of percentages the PV provides a minimum part of the energy used. The time necessary for reaching a balance point is subject to many variables but is not easy for the owner to cover the expenses of an investment that gives results only several years later; on the other hand the statements of some producers that promise to decrease to few months the balance point has not lead massive diffusions due to law effectiveness, duration and support compatibility problems. Other discrimination is in the production technology: the need of thermal process of vacuum chambers has a strong impact on the final costs of the functionalized tiles in terracotta. And in certainly is in this direction that vast research is being developed aimed at favoring processes permitting to increase the production speed, the compatibility with the conventional productive process for reaching more rapidly payable final costs. An envelope integrated system with functionalized surfaces cannot yet do without the aesthetic component: the acceptance of magnificent architecture with black bands as if they were censoring intervention it is rather difficult. It is then opportune to seek the harmony of architecture playing with forms and colors integrating functionality with aesthetics. In order to obtain it, we must get acquainted with the energetic and productive aspects: texturized surfaces solutions are technologically possible, the selective chromatic distribution according to defined designs; this solutions can be applied to materials that already have serigraphic machinery on its production process, while it would be too much costly for the brick making industry.

2.1.2 Photocatalytic The photocatalysis process accelerated the oxidation process and it naturally happens, but, facing the high concentration of polluting substances present especially on the urban and metropolitan areas, avoids its accumulation and permits the rapid decay of organic and inorganic substances present in the air. It is an analogous process to photosynthesis, but with the advantage of being always active, also in the cold months characterized by the increase of harmful emissions. The solar radiation itself activates a photochemical reaction in the presence of a catalyzer. Nitrogen and carbon oxides and other volatile and semi-volatile compounds are deposited on the surface of the buildings and decay in the presence of ultraviolet radiation (3% of the spectrum) and soon also within the visible spectrum (15%) when the surfaces are coated with titanium dioxide. The reference values on concrete prove that 1000m2 of functionalized surface purify 200.000m3 of polluted air of a city, which corresponds to the transformation of 25 kg of polluters per year, equivalent to the work of 30 trees of high steam of over 50 years of age. Titanium dioxide has another fundamental property: it is super hydrophilic. The water drops that enter in contact with the surface quickly cover it completely, washing it and releasing it from pollution substances, moss, and bacteria. Contrary to photosensitive materials, the titanium dioxide has the advantage of being transparent, therefore impacting with respect to the ceramic support color.

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Figure 6 Outline of photocatalytic process.

2.2 Configuration and aspect of the components The elements of the systems in terracotta are subject to an analogous design to that one of other tiles for ventilated facade. When in dealing with surfaces subject to post-cooking carving, relatively large sizes are preferable due to eminently economic criteria. Taking into account the modest semiconductors effectiveness, such of amorphous silicon the task of maximizing the absorption of photons is delegated to the configuration of the surface; for the purpose we intervene on the modeling of pieces being aware of the fact that the incidence of solar rays plays a primary important role on energetic efficiency. Another crucial aspect to be considered is the chromatic aspect; the application of photovoltaic films, even with a width of few nanometers, grants the support a dark or black color. Different compositions of the semiconductors can lead to chromatic variations, which imply a decrease on the efficiency that by itself is not high. This problem implies to chose if larger extensions of photovoltaic tiles are preferable, but with a less dark design or coloration, or if more efficient tiles occupying a shorter surface are preferred. A third door is also still opened: the one that links more efficiency to better aspect… Figure 7 Conventional ventilated wall with terracotta surface.

2.3 Photovoltaic Installations In regards to normal ventilated facades, an installation capable of transporting energy from the cells to the users or to the network are required. Special care must be given to the connections and to the integration of the network cabling.

2.4 Production Process One of the crucial aspect of the process innovation is on the structuring of the surface preparation and finalization treatments within a consolidated production chain, for non conventional treatment requiring special thermal and environmental conditions are required and, therefore the introduction of new machines.

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Figure 8 Outline of process of production of photovoltaic surface.

2.5 Part fixation, removal and substation process The anchoring aspect of the metallic framework supporting structure, of the tiles to it, as well as all operations carried out at the work site for permitting the connection to the electrical network make part of the project; a study of the process that goes from the installation of piping to the connection of the external network and of each Photovoltaic tile is made. Same is applicable to control interventions and the eventual replacement of parts subject to damage or malfunctioning. Beyond the technical aspects it results notorious that the experimented technology should be able to conjugate a series of advantages between operators and users capable of making it acceptable within a speculative and substantially traditional market. The road of architectural integration together with the increase of efficiency at incorporated costs is the goal that pursues, even when being aware that the mechanisms that must be activated for always getting closer to a more sustainable building are diverse and heterogeneous. Tending to Reduction of Energy consumption is one of the principal goals without forgetting that in perspective we could look forward to a Positive Energy Building. Meanwhile, photovoltaic energy production is promoted for direct use with the possibility of immersion in the energy excess network (in Europe Electricity Production companies pay this contribution very well and from 10 to 20 years); minimizing the environmental impact in energy production. There still remains the question about the political support and economic incentives favoring the production and diffusion of surfaces capable of decontaminating urban environment with modest incremental costs. This is technologically feasible since long ago.

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