MATERIAL FLOW ANALYSIS IN THERMAL ENERGY STORAGE. Lídia Rincón, Gabriel Pérez, Marc Medrano, Luisa F. Cabeza

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1 MATERIAL FLOW ANALYSIS IN THERMAL ENERGY STORAGE Lídia Rincón, Gabriel Pérez, Marc Medrano, Luisa F. Cabeza GREA Innovació Concurrent Edifici CREA, Universitat de Lleida, Pere de Cabrera s/n, Lleida (Spain) Phone: , Fax: ABSTRACT Material Flow Analysis (MFA) is a method to analyse the flows of a material in a well-defined system under study. MFA is considered as one important tool of industrial ecology along with instruments such as Life Cycle Assessment or Design for Environment. The goal is to get a transparent understanding of the material flows, to calculate indicators and to develop strategies and measures for improving the material flow systems. Given that the positive effect of incorporating PCM (phase change materials) in the envelop of a building has been demonstrated in terms of energy efficiency, the goal of this paper is to use the methodology of MFA to evaluate the effect of the use of PCM in a building. With this methodology energy consumption, the consequent CO 2 emissions, and the environmental impacts produced in all the phases of the life of each material will be studied. 1. DEMATERIALIZATION OF CONSTRUCTION Standard economic assessments consider neither the environmental damage nor the value of the run out resources. That means that it does not account the external costs. Therefore, the value that it is given to the resources is much lower than the real cost to the Earth, as establish the Ecological Economy. There are limits in natural production of required resources as well as in the dump sites (air, water and earth). Required construction materials in buildings are subject to these physical limits which are gradually closer to saturation. More detailed information can be found in Martínez-Alier (2008). Current economical system is exceedingly inefficient. In order to reach the required liveability standards we are consuming more materials and natural resources than in other previous period, and that represents environmental and economic impacts. Direct materials required for building one standard square meter in Catalonia is about 2.5 tones. Only for housing in the province of Lleida it is required an amount of almost 1,750,000 tones per year of stone (sand, gravel, crushed stone, etc) mainly used for building the foundation and structure and about 650,000 tones per year of ceramic (clay bricks, roof tiles, vitrified tiles, etc) mainly used in façades (figure 1). This high amount of materials means about 500 kg CO 2 /m 2 per year emissions only for the fabrication of the materials, about 20 times more than the emissions produced by use phase of the building (about 30 kg CO 2 equivalent per year). More detailed information can be found in Cuchí (2005) and Cuchí & Pagès (2007).

2 Tones Aggregate Stone Ceramic Cement Water Precast Lime Precast Steel Wood Other Mortar Concrete Figure 1. Total amount of materials used for new constructed building of housing in Lleida per year (average between ). Source: own compilation. More data can be found in IDESCAT, Ministerio de Fomento and Cuchí (2005). Construction sector in Catalonia has a big impact in natural environment, not only because of the occupation of urban ground but also because of the big amount of raw materials extracted that produces damage on it. The 90% of raw extracted materials in Catalonia are minerals. From this amount, 94% are used in construction sector. In order to reduce the high materials consumption of this sector it is necessary to act in two ways: the first one is to reduce the material intensity (T/m 2 ) of buildings and infrastructures and the second one is to lower the number of new buildings. That would help to tend to the dematerialization of Catalonia. The building sector is responsible for one third of the total emissions that are attributed to the Spanish Estate accounting the total greenhouse effect emissions (GEG) produced by all the activities used for building plus the energy consumed during the useful period of the building. More detailed information can be found in Cuchí & Pagès (2007). CO 2 emissions related to the fabrication of the main consumed materials by construction are more than 7 million tones per year. The transport of products of construction produces about 1 million tones of CO 2 per year. More detailed information can be found in Sendra (2008). In order to accomplish the Kyoto Protocol it is necessary to take measures on construction sector. But not only emissions are the problem, but also the accumulation of construction wastes -mainly stone and brick- that are saturating the dumping sites for wastes. In front of this problem, a solution is required: the dematerialization of building sector. The aim of this paper is to offer an overview about how PCM can contribute to a dematerialization of the building sector by the improvement in resources use efficiency. That is to say to reduce the amount of required materials in building keeping the standard comfort in habitability, so the environmental impacts would decrease. 2. SEARCHING NEW MATERIALS FOR DEMATERIALISING BUILDINGS Research in new building materials which increase the energy efficiency of buildings -in terms of heating and air conditioning- and at the same time reduce the high materials consumption is convenient if it is intended to do research in sustainable development. Phase Change Materials (PCM) are offered as innovative materials which are able to improve the properties of the materials used in the envelope of the building (façades and cover). With this paper, it is aimed to

3 offer an overview of the Life Cycle of PCM and to assess the energetic and environmental benefits that the incorporation of these new materials can bring in the current construction systems. 3. PCM IN BUILDINGS ENVELOPES Building envelope comprises the exterior enclosure (or façades) and the cover. The materials and construction solutions from the envelope are relevant in order reduce the energy demand from heating and cooling. Therefore, the energy consumption of the building during its lifetime is directly related with the envelope. It is the responsible of the energy consumption during the use phase of a building. On the other hand, the embodied energy of the fabrication of its materials means a total energetic consumption of almost 30% for the enclosure and 7.6% for the cover. More detailed information can be found in Cuchí (2005). Both energy consumption in use phase and embodied energy in materials make of the envelope the main responsible of energy consumption in buildings. Therefore, the envelope is a key point where to act in order to minimize the energetic consumption of heating and cooling in use phase as well as energy consumed for fabricating the materials. The envelope has lost its structural function and then it has just an enclosure function. It is the protector third skin between the environment where we inhabit and us. It makes possible the comfort in the interior of the building. For accomplishing this function it is not necessary for the façade to be that heavy as it is now. The same function could be done with fewer materials. Reducing the amount of materials in the envelope would help to dematerialize the construction. The main materials that constitute the façades of a typical building in Catalonia are ceramics and insulation. Ceramic constitute the 20% of the total amount of materials used for constructing a building. Mainly it is located in the exterior enclosures with a 45%. It means that façades are constituted of 254 kg of ceramic per constructed square meter, which means emissions about 98 kg CO 2 and 1,200 MJ of energy consumption. As regards to thermal insulation, these materials do not represent a big part of the total amount of materials in a building (below 1%), but they mean a high energy consumption in the total because they are highly processed materials whose fabrication require great quantity of nonrenewable energy, like polyurethane or polystyrene (with 70 MJ/kg and 100 MJ/kg respectively in front of the values of 2.8 MJ/kg for bricks). Polystyrene means about 1,000 MJ of energy necessary for building one square meter of typical construction. More detailed information can be found in Cuchí (2005). PCM used in building envelopes makes possible the reduction of the volume of materials and at the same time improves the thermal behaviour of the interior of the building. For example, in the case of a concrete envelope it is experimentally proved that the addition of PCM in this material increases a lot the thermal capacity and, therefore its thermal lag also increases while the phase change takes place. Variation in walls with PCM temperature is almost zero when fusion or solidification takes place. It is also experimentally proved that this concrete increases, in specific climatic conditions, the time of comfort inside the cubicle with PCM compared to the concrete cubicle without PCM. When PCM effect and air conditioned are combined, then it is proved that PCM allows saving energy. Particularly a reduction of the 5% of consumption energy in summer period is reached. It is not a very high number but it must be considered that there is only a 5% of PCM in concrete. More detailed information can be found in Castellon (2008).

4 Other experimental studies with PCM in alveolar brick façade and usual brick with polyurethane insulation façade are demonstrate the improvement in energy saving. In these two cases the results of the energy savings during summer period are evident. Just because of the fact of introducing a small volume of PCM in the insulation, thermal inertia increases significantly. The results studied for the summer period show that there is an improvement of the energy saving between the typical constructed façades and the PCM façades of % for the polyurethane insulation and of % for the alveolar brick. It means that with just a little addition of PCM in the insulation (about 1% of the total weight) the comfort in the interior building can be reached saving about 16 % of the energy required for cooling. More detailed information can be found in Castell (2009). So that, with less thickness of material is possible to improve the thermal behaviour of the envelope, just adding a little quantity of PCM. If the thickness of the façades is not any more necessary for having a good thermal behaviour and a good thermal lag because we are using thin façades, how much material is possible to save in construction? An overview of the potential material savings can be done just with some basic data. A comparative has been made among the thickness of walls required for having the same thermal storage capacity in façades within brick, concrete wall and a façade with the product Micronal PCM SmartBoard: 12 cm, 9 cm and 1.5 cm respectively (figure 2). More detailed information can be found in the product data sheet (BASF). Figure 2. Comparison of thickness between brickwork, concrete wall and plaster with PCM wall having the same thermal heat storage (BASF). In Lleida between 2000 and 2007 there has been an average of 1,300,000 m 2 of constructed surface every year. This means an amount of ceramic about 652,500 tones per year and an energy consumption of 3,039,542 Giga Joules per year required for the fabrication of this material (figure 3). If it was possible to substitute the 10% of this amount by including PCM with the equivalent thermal inertia, a first approach would consider material savings of 65,250 tones of ceramic per year. That means the savings of 3,800 tones of CO 2 every year in the fabrication of bricks. More detailed information can be found in Cuchí (2005). This detailed comparison study to assess the real improvements if a typical Mediterranean construction is to be replaced by a lighter building using PCM with the same thermal inertia is under work. Of course a comparison between the brick saving and the energy consumed during all the life cycle of this product which contains PCM is necessary. A research in this sense is required for compare the real energy and economic saving of incorporating PCM in construction.

5 Energy (GJ) 3x x Ceramic Steel Cement Aluminium Precast mortar Additive Aggregat e Stone Lime PVC Precast Wood concrete Other Figure 3. Total amount of embodied energy in main construction materials for new constructed buildings for housing in Lleida per year (average between ). Source: own compilation. More data can be found in IDESCAT, Ministerio de Fomento and Cuchí (2005). There are different kinds of PCM. The main PCM used in building materials are salt hydrates and paraffins (figure 4). More detailed information can be found in Castell (2009). Life Cycle Assessment would be required in order to get the real cost of the material and to get the comparison with the conventional construction materials in façades. Salt hydrate Paraffin Figure 4. RUBITHERM phase change materials (PCM). The main inconvenient of this new construction material is the current high market price of PCM, quite high because it is an almost unknown material in construction sector, and its use is still experimental. But the goal is to get the real cost of the material. That means not only its market price but also its environmental cost that its use means (understood as an improvement in the energy saving of the building plus the saving materials in the construction of the building). The saving in energy and materials may compensate the over cost of a still unknown material. Nowadays the use of PCM is so innovative and so limited that we can not still introduce it in the material flow analysis of the construction materials, but it allows making a balance of the saving of materials if its use was incorporated in actual construction. 4. METHODOLOGY The main tool used for this research is the Material Flow Analysis (MFA). It consists in determining and quantifying all the flows that are inputs and outputs in a system with the goal of assessing the total interchange of resources between the system and the environment.

6 For this account, one of the parts to study is the Life Cycle Assessment of the Phase Change Material. Next, environmental problems will be detected and real economic cost will be determined, accounting all the phases of fabrication of the materials and the phase of use of the building. MFA of main construction materials will be done in the region of Lleida. The balance between the material consumption in typical construction and the materials required in construction with PCM will show the total economic, energetic and environmental saving of introducing PCM in construction. The final goal is to prove its economical and environmental feasibility and check out which would be the improvement of introducing PCM in construction systems. 5. CONCLUSIONS A first approach in the results demonstrates the improvement in the energy consumption of the building due to the incorporation of PCM in the façades. The reduction of energy that it involves makes possible to reach an optimal point between the required material in the construction of exterior enclosures of the building and the interior thermal comfort. The increase of the thermal lag of the enclosure allows the reduction of the thickness of the material requirement, like brick, concrete or alveolar brick, some of the main used construction materials. Due to the large amount of built surface per year in Catalonia even a small reduction per square meter of those materials means a big volume of the totality per year. The decrease of required materials, even if they are just a small part of the façade, would involve a big volume of materials every year, a very significant amount. A detailed comparison study to assess the real improvements if a typical Mediterranean construction is to be replaced by a lighter building using PCM with the same thermal inertia is under work. This study will give results on the environmental, energy and economic potential savings for the total residential buildings in Lleida. ACKNOWLEDGEMENTS The work was partially funded by the Spanish government (project ENE C02-01/CON). Dr. Marc Medrano would like to thank the Spanish Ministry of Education and Science for his Ramon y Cajal research appointment. REFERENCES BASF the Chemical Company, Micronal PCM SmartBoard TM, SmartBoard Technical Data Sheet Castell Casol A.O. (2009). Analysis and implementation of thermal energy storage using phase change materials for cooling applications.. Ph. D. Thesis. GREA Innovació concurrent. University of Lleida, Spain. Castellón C. (2008). Use of microencapsulated phase change material in buildings. Ph. D. Thesis. GREA Innovació concurrent. University of Lleida, Spain. Cuchí A. (2005). Arquitectura i sostenibilitat. Edicions UPC. Cuchí A., Pagès A. (2007). Sobre una estrategia para dirigir al sector de la edificación hacia la eficiencia en la emisión de gases de efecto invernadero (GEI). Universitat Politècnica de Catalunya. EUROSTAT (2001). European Statistical Office. European Commission. Economy-wide material flow accounts and derived indicators. A methodological guide. Luxembourg: Office for Official Publications of the European Communities.

7 IDESCAT. Web de l estadística oficial de Catalunya. [ Martínez Alier J. (2008). La crisis económica, vista desde la economía ecológica. Ecología Política. Número 36. Crisis económica y financiera. Ministerio de Fomento, Boletín nº /3/2008, datos aportados por los visados de Dirección de Obra de los Colegios de Arquitectos Técnicos (Obras en Edificación). Sendra, C. (2008). Anàlisi dels fluxos de materials de sistemes. Avaluació del Metabolisme Material a Diferents Escales. Departament Enginyeria Química. Institut de Ciència i Tecnologia Ambiental (ICTA)Universitat Autònoma de Barcelona.