Life Cycle Assessment of zero- emission façade construction

Transcription

1 Life Cycle Assessment of zero- emission façade construction Speakers: Barecka, M. 1 ; Zbiciński, I. 1 ; Heim, D. 1 1 Lodz University of Technology, Lodz, Poland Abstract: In the research of zero- emission building design, façade solutions like ventilated panels, photovoltaic panels and phase change materials (PCM) are used in order to reduce the energy demand and the environmental impact of the façade during operational phase. However, considering all phases of the life cycle of a façade, some solutions being energy- efficient in the operational phase, may have a significant environmental impact on the production or disposal phase. Therefore, the Life Cycle Assessment (LCA) is needed in order to measure the sustainability of selected configuration of the façade. In this work, LCA was calculated for three different façade solutions: opaque insulating panel with glass finish, opaque insulating panel with photovoltaic finish and opaque insulating panel with glass finish and PCM in the insulation. The panels are to be included in an experimental façade which will be constructed within the framework of German- Polish Energy Efficiency Project. The energy gains from different façade solutions were obtained from ESP-r software (a modeling tool for the simulation of building energy performance). The LCA calculations were performed applying two tools: Material Input per Service Unit (MIPS) and Ecopoints 99 (using SimaPro software). The LCA scores, proportional to the panel surface- were used in optimization process of façade configuration to find out the most sustainable solutions and point out the environmental loads of each façade design. The results- LCA scores, show that although the panels with photovoltaic finish have 25% higher environmental impact in the production phase, the energy gains in the operational phase compensate environmental impact generated in production and disposal phase. Key words: LCA, façade, PV,PCM, energy Introduction Reduction of general energy consumption is doubtlessly one of the greatest challenges of sustainable development. In Poland, the energy consumption in buildings is responsible for about 40% (1) of energy use and a similar relation is observed on a global level. Therefore, a special attention should be paid to improvement of energy efficiency of buildings, commercial and residential ones. The high energy demand of buildings comes mainly from the need for maintain the thermal indoor comfort (temperature between 20 0 C-26 0 C). The reduction of energy consumption for heating or cooling is expressed in the concept of zeroenergy building, also known as zero- emission building (2). The terms stand for the buildings which has zero (or close to zero) energy demand. One of the major parts of ZE building is the façade, since it is the major surface by which the building loses the energy. A plenty of innovative solutions were studied for façade design, enabling the signification reduction of heat loses. However, considering all phases of the life cycle of a façade, some solutions being energy- efficient in the operational phase, may have a significant environmental impact on the production or disposal phase. Therefore, the Life Cycle Assessment (LCA) is needed in order to measure the sustainability of any configuration of the façade. The result of LCA should be equally considered with energy performance of the façade in the design processes. 1

2 Analyzed systems and major assumptions In the frame of this paper, three different façade solutions were considered: opaque insulating panel with opaque glass finish, opaque insulating panel with photovoltaic finish and opaque insulating panel with glass finish and PCM in the insulation. The panels are to be included in an experimental façade which will be constructed within the framework of German- Polish Energy Efficiency Project (3). The data on façade panels was supplied by the producer- Stoispo company (4). The detailed data on LCA of the CIS photovoltaic panel was taken from the literature (5). The panel 3-D schemes of panels are presented in the figure 1. Fig D schemes of analyzed panels solutions.mw stands for mineral wool insulation, PCM- phase change material, PV- photovoltaic finish. All the panels are based on the same insulation layer (20 cm of mineral wool, λ=0.033 W/mK) and equipped with the same alumina- stainless steel support system. The external part of the façade solution is separated from the insulation with an air gap, enabling the ventilation of the façade system. The main difference in the construction of three panels is the finish and insulation layer (the external layer of panel exposed to the outer environment conditions). The first panel is finished with a layer of opaque glass, whereas the second one is finished with a layer of CIS photovoltaic (nominal power 80Wp). The third panel has exactly the same construction and finish as the first one, but in its structure a layer of 6 mm of phasechange material (PCM) was integrated. The PCM, based on caprylic acid (melting point C) is added in order to minimize heat loses in winter or undesired heat gains in the summer by active insulation. An alternative solution for PCM shape stabilization is proposed within this analysis. Instead of microencapsulation of PCM, the PCM will simply be placed between two layers of polyethylene foil, creating a structure similar to 3D ice cube bags. The goal of the LCA analysis in to express and compare the environmental impact expressed for a functional unit- panel of dimensions of 120 cm per 60 cm. The façade lifetime is estimated to be 25 years. The building façade containing the analyzed panel is supposed to be orientated to west and well exposed to the sunlight radiation. Due to the lack of exact data on every stage of the life cycle of the façade, the crucial life stages were identified in collaboration with industrial partner. According to the analysis, the most important environmental impacts are related to the panel production stage and its maintenance. The use of materials on the production and maintenance stage is presented for the glass finish panel in the simplified process tree (fig. 2) obtained from SimaPro software. 2

3 Fig. 2. Simplified process tree for glass finish façade panel. Since the role of the façade panel is to prevent the heat loses/ gains, the energy that is transferred by the façade is a loss from the point of view of analyzed system. Therefore, the energy that is needed to recompense the heat loses via façade is responsible for the environmental impact of the panel. In order to include this important term in the LCA analysis, ESP-r simulation engine for building energy performance was used. Basing on the software, a model of different façade solutions were developed. The internal temperature for the simulations was 20 0 C in winter and 26 0 C in summer, and the CIS photovoltaic nominal conversion efficiency was assumed to be 12%. The simulation results enabled to estimate the energy flow via the façade in the winter and summer season (for climate data for Poland, Lodz Region). The energy flow was recalculated on electrical energy demand assuming 98% system efficiency for electric heating (no need for cooling was required according to the simulation results). The electric energy demand was integrated in LCA analysis, considering the European Union electricity mix for the co-ordination of production and transmission of Electricity (UCPTE), Medium Voltage. This electrical energy demand was further considered in LCA analysis (table 1). The energy obtained from the photovoltaic panel in winter was subtracted from the energy demand for heating. In summer period, the energy from photovoltaic is supposed to be used on site for other purposes than heating and to be an extra product of the façade, therefore this energy in included in the data inventory as negative value (-141 kwh of energy consumed by façade in summer). Table 1. Energy loses via different façade solutions and electrical energy demand for heating. Energy (kwh/ year) Glass finish CIS PV finish panel Glass finish+ panel PCM panel Loses in winter Energy gains from PV Electric energy demand for heating 5.41 extra available

4 No other impacts of the façade were recognized on the maintenance stage of façade lifetime, since according to the industrial partner data no extra washing, replacement or painting is needed. On the disposal phase, the façade needs to be decomposed to the recyclable elements (aluminum, steel, etc.) and the environmental impact related to the recycling or disposal of those elements is already considered in the LCA coefficients used in the data inventory in for the production stage. The energy demand for the reconstruction of the façade is supposed to be equal for every panel solution, therefore is not considered in this comparative analysis. Impact assessment The LCA analysis was carried out in accordance to International Standardization Office (EN ISO and updates) recommendations. The assessment was performed in four stages: goal and scope definition, inventory analysis, impact assessment, and interpretation. The choice of LCA tool applied for the assessment is generally left to the analyst. Since there is no obligatory LCA tool on the legal level, the industrial partners or costumers may be exposed to certain inaccuracies coming from estimating of LCA with different methods. Therefore, in the frame of this project, two LCA tools were compared in order to prove if significant differences comes from the method selection. MIPS (Material Input per Service Unit) MIPS is a concept originally developed at Wuppertal Institute for Climate, Environment and Energy (Germany). The method bases on assumption that every material-input becomes an output (waste, emissions) and therefore measuring the inputs enables an approximation of the overall environmental impact of a analyzed unit. The analysis is based on adjusting to every input in the lifetime of a product a factor of Material Intensity. The Material Intensity factors express how many kilograms of natural resources are consumed within the whole lifetime of given material (6). Material Intensity Factors were elaborated by experts, are available online and constantly updated. The factors database cover the majority of building materials. Eco-points 99 (egalitarian version) The Eco-points enable to express the LCA of a product or service by expressing the assessment of damage to the environmental that is caused by the life cycle of a product. There are three damage categories considered: Human Health (unit: DALY= Disability adjusted life years), Ecosystem Quality (unit: PDF*m2yr; PDF= Potentially Disappeared Fraction of plant species) and Resources (unit: MJ surplus energy Additional energy requirement to compensate lower future) (7). The SimaPro software was used for LCA calculation applying this method. The data inventory of the inputs related to the façade panel life cycle was introduced to the software and on the basis of the SimaPro databases the environmental damage was calculated and expressed as points. Results and interpretation The values of LCA scores obtained with Ecopoints 99 and MIPS tool are presented in the figure 3, separately for production phase, operational phase and whole life cycle. 4

5 a) tones of natural resources PV finish Glass finish+pcm Glass finish Production phase Operational phase Total LCA b) Fig. 3. LCA scores for three façade solutions: a)mips values, b)ecopoints 99 values. 5

6 Since the values for each method are expressed in different units (kilograms of natural resources/ points of environmental damage), they were further presented in a relative way (each value divided by the highest score obtained with the method), to make them easily comparable. The normalized LCA scores for three façade solutions considered is presented in the figure Relative LCA score PV finish Glass finish+pcm Glass finish Ecopoints 99 MIPS -3-4 Fig. 4. Normalized LCA scores for three façade solutions. However the panel with photovoltaic finish has higher impact on production stage, the energy gains from the panel in the whole life cycle recompense this impact totally, leading to negative value of environmental impact- what means that this product allows a great environmental saving. This concept is only valid if LCA as a comparative tool is considered, aiming to choose the best façade design among the possible solutions. The photovoltaic panel itself cannot be claimed to have a zero or negative environmental impact. However, being analyzed in comparison to other façade solutions, the advantage of energy production makes it highly environmentally friendly in comparison to a solution that does not produce any extra energy. The energy aspect has doubtlessly the higher impact on the final LCA score, since the greater part of environmental damage is attributed to fossil fuel consumption (figure 3b). Due to this fact, the operational phase of the façade contributes mostly to environmental impact and therefore should be carefully optimized. Considering the economic aspect of applying the photovoltaic panels instead of glass finish panels, the simple payback period of extra investments cost is assumed to be about 6 years, without considering the possible rise of energy price and assuming that all electricity produced on site will be consumed on site. Considering the panel with PCM layer, the energy saving achieved was very low, therefore hardly recompensed the extra materials use on the production stage. The difference of LCA for a panel with and without PCM addition was small enough to be neglected at it may be assumed that the LCA for the panel with PCM is almost equal to the impact of the panel 6

7 without it. In order to make the PCM addition environmentally justified, the better energy performance of the material should be achieved. The LCA results obtained with different tools- MIPS and Ecopoints gave similar results only for the panel with glass finish and glass finish with PCM inside. Environmental impact of PV panel is significantly different according to the method used, however it has a negative value in both cases. The most important part of LCA for photovoltaic façade is related to the operational phase and electricity production. Therefore, the use of different environmental impact coefficients for electricity production in the LCA tools considered has a decisive impact on final LCA score. Conclusions Resuming, due to energy gains in the lifetime of façade, the panel with photovoltaic finish proves to be the most suitable opaque solution from the environmental point of view, as far as the façade is well exposed to the sunlight radiation. Application of this façade solution allows not only to reach the goal of zero- emission building in the terms of energy consumption, but also in terms of general, long- term environmental impacts. Due to the long life cycle of a building, the decisive factor is energy demand for heating (even for very efficient insulating systems), related to the maintenance phase. Therefore, improving the energy performance of any façade solution is the most efficient way to reduce the environmental impact. Acknowledgements This work was funded by The National Centre for Research and Development as part of the project entitled: Promoting Sustainable Approaches Towards Energy Efficiency in Buildings as Tools Towards Climate Protection in German and Polish Cities: developing facade technology for zero-emission buildings (acronym: GPEE). The authors wish also to acknowledge also the support of the Sto-ispo company in providing the inventory data for LCA analysis. References (1) National Action Plan for Energy Efficiency in Poland, available online: (last access: ) (2) Marszal, A.J., Heiselberg, P, Bourrelle, J.S., Musall, E., Voss, K., Sartori, I., Napolitano, A. (2011). Zero Energy Building A review of definitions and calculation methodologies, Energy and Buildings, 43/4: (3) German- Polish Energy Efficiency Project, (4) Sto-ispo website: (5) Raugei, M., Bargigli, S., Ulgiati, S. (2007). Life cycle assessment and energy pay-back time of advanced photovoltaic modules: CdTe and CIS compared to poly-si, Energy, 32: (6) Material Intensity Factors calculated by Wuppertal Institute for Climate, Environment and Energy, available online: (last access: ) (7) Ecopoints 99 egalitarian version, available within SimaPro software support 7