d'Hères, France. Abstract: The Life Cycle Assessment (LCA) is a methodology to evaluate the building environmental impacts for the production, use and ...
ISBN: 978-84-697-1815-5
Simplified and reproducible building Life Cycle Assessment: Validation tests on a case study compared to a detailed LCA with different user’s profiles Authors: Bonnet, Romain1; Hallouin, Thibault1; Lasvaux, Sébastien2; Sibiude Galdric2 1 Bouygues Construction, Guyancourt, France 2 University Paris-Est, Scientific and Technical Centre for Buildings (CSTB), Saint Martin d’Hères, France Abstract: The Life Cycle Assessment (LCA) is a methodology to evaluate the building environmental impacts for the production, use and end-of-life phases. Two main barriers still limit the LCA to be largely used in the construction sector: time-consuming approach and non reproducible results between practitioners. In this study, we present a combined approach to conduct reproducible and simplified building LCAs. The simplified methods were defined based on the target group needs (e.g. construction companies). Each approach decreases the degree of freedom for the users while focusing on the main impact sources. Results show a deviation of results no more than 20% between the complete and simplified LCA methods. A better reproducibility between users is found for the simplified methods due to the predefined parameters (in opposite to the complete LCA). In addition, considerable time saving was reported. Our proposal should now be applied to a bigger sample of professionals of the construction sector to collect more feedbacks. Keywords: LCA, embodied impacts, buildings, simplification, reproducibility 1. Introduction The Life Cycle Assessment (LCA) is more and more recognized as a relevant methodology to evaluate the building environmental impacts for the production, use and end-of-life phases. It has been applied in the construction sector for many years and led to the development of several LCA softwares in Europe [1] [2]. Two main barriers still limit the LCA to be largely used with confidence in the construction sector. First, it is due to the time-consuming of a complete LCA study, especially for the assessment of the embodied impacts related to construction products integrated in a building. Unlike simple manufactured products, a building can be breakdown in dozens or hundreds of elements. Secondly, without detailed rules, we can still find very different results between two users on the same LCA tool depending on the chosen system boundaries, the quality of the bill of quantities, the user profiles and experiences. Previous studies already showed that the LCA embodied impacts for buildings can diverge due to the different scope of the modelling e.g., different boundaries, different LCA data, different representativeness of the studies [3]. A first requirement to harmonize LCA practice in the building sector is to rely on the same scope. In Europe, a first contribution was provided by the CEN TC 350 committee, which released two standards on products and buildings LCA [4]. In addition, a recent operational guidance InfoHub for building LCA (derived from the EeBGuide project) recommends using the EN 15804 and EN 15978 standards in the LCA practice [5]. The EeBGuide outcomes also proposed to go further 1276
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by developing different study types (screening, simplified and complete LCA) in a building LCA tool according to the stakeholders’ needs [6]. In this paper, we are interested in deepening the EeBGuide proposal for simplified LCA of a building. The interests of a simplified LCA method are mainly the reduction of the modelling time and the improvement of reproducibility between different users of the tool, due to the definition of harmonized parameters e.g., for LCA data or system boundaries. The simplified solutions have to be adapted to the user profiles and should be provided with guidance to be used in decision making. Moreover, the simplification should not decrease the accuracy of the global LCA results by keeping the sensitivity of results to major design parameters. Indeed, the simplification rules should be focused on the LCA tool interface by provided the limited number of parameters, based on empirical knowledge (e.g., previous LCA results of buildings can lead to the identification of the main impact sources and the simplified LCA method can benefit from them). In this study, we present a collaborative work with a LCA tool developer and a construction company conducted in the framework of a national research project [7]. A combined approach is proposed for reproducible and simplified building LCAs. 2. Scope of the study The simplified LCA methods are only developed and applied on new multi-residential buildings. This building type, in Europe and in France, mainly represents low energy buildings e.g. consuming less than 50 kWh/m²/year for the regulatory uses of the thermal regulation (heating, cooling, domestic hot water, lighting, auxiliaries). 2.1. System boundaries According to the EN 15978 standard “Sustainability of construction works, assessment of environmental performance of buildings, Calculation method”, module A (impacts related to the production of a product, its transport and the loss of the product on-site), module B (the number of replacement rates linked to the maintenance actions considered) and module C (end-of-life) are considered for the impacts related to the building products and technical equipment”. Figure 1 presents the system boundaries in relation to the three study types (screening, simplified and complete LCA) and the building type. This figure is derived from the EeBGuide InfoHub for building LCA [5]. Table 1 presents the nomenclature used to classify the elements according to the “HQE Performance” application rules [8]. 2.2. LCA data used Generic LCA data for building products and technical equipment are used in this study. These are based on Environmental Product Declaration (EPD) available in the national reference database INIES [9]. EPD are sector-specific LCA data, describing the impacts of one or several manufacturers that sold their products on a national market (e.g. the French market). When some EPD are missing for some products or equipment, generic data from the ecoinvent database are used. The generic LCA data based on EPD or ecoinvent are calculated following the NF P01-010 and EN 15804 standards from cradle-to-grave (i.e. for modules A, B and C cf. Figure 1) [4]. 2277
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Table 1: Nomenclature used to classify the elements according to the HQE Performance application rules
Classification of the building elements in 14 parts 1. External work 2. Foundations - infrastructure 3. to 7. Building products associated to the building envelope (superstructure) Structural elements Roof elements Interior walls Windows and joinery work Interior finishes 8. to 14. Technical equipment HVAC Sanitary facilities Electricity and communication network Safety equipment Lighting Lifts On-site electricity generating units (wind power, PV panels)
2.3. Environmental indicators Seven indicators were used based on the French and European standards for LCA in the construction sector. Table 2 presents the names, units and abbreviations of these indicators. Table 2: List of environmental indicators considered in this study
Indicators Total primary energy Water consumption Waste production Radioactive waste production Global Warming potential Acidification potential Photochemical ozone formation potential
Abbreviations PE WC WA RW GWP AP POCP
Units kWh l kg kg kg eq-CO2 kg eq-SO2 kg eq-C2H4
3. Development of simplified LCA methods Figure 1 presents the goal and scope of the simplified LCAs (cf. section 2) in relation to the targeted users’ group (construction companies). The simplified LCA methods are developed based on the outcomes of the EeBGuide InfoHub for building LCA. Screening and complete LCA are also reported to be consistent with the EeBGuide LCA guidance but are not described in this paper. The following requirements taken into account in the development of simplified LCA methods are as follows: • • •
Keep a good level of accuracy for the simplified LCA compared to a detailed LCA Reduce LCA modelling time by focusing on the main impact sources or on default values Involve third-party (e.g. a building stakeholder) to match the simplified LCA method to the user needs 3278
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Improve the reproducibility of LCA results by defining harmonised and predefined LCA data or system boundaries so that different practitioners can still achieve a similar LCA result (in opposite to complete LCA with a higher degree of freedom). With these key requirements in mind, the next sections present two simplified LCA calculation rules for the assessment of embodied impacts of new multi-residential buildings. They are the results of collaboration between a LCA tool developer (CSTB) and a building stakeholder (Bouygues Construction).
Figure 1: Goal and scope for the simplified LCA methods in relation to the targeted users’ group for the contributor “building products and technical equipment”
3.1. Pareto simplified LCA method The simplified LCA method “Pareto” is based on the general principle stating than “80% of the consequences are linked to 20% of the causes”. In LCA, it means, for a same building type, that only a limited number of building elements significantly contributes to a given environmental impact (e.g. the global warming). The Pareto calculation rules can be breakdown in three parts:
First, the definition of a reduced LCA using a harmonised and predefined list of elements associated to generic LCA data. Second, the calculation of ratios derived from the complete and reduced LCA results Third, the reduced LCA results per indicator are multiplied by the statistical ratios in order to compensate the neglected elements leading to the simplified LCA method “Pareto”.
In step 1, the elements that are mainly impacting in multi-residential projects are identified for instance reinforcing steel, foundation concrete and superstructure concrete. For the same 4279
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system boundaries (see Figure 1 and Figure 2), several building LCA case studies are conducted to derive the statistical ratio between the complete and the reduced LCAs. Ratios R are derived using the following formula:
Then, the ratios are applied to the reduced LCA results to convert them in simplified LCA results “Pareto”. The statistical ratios applied enable to keep the same level of completeness compared to a complete or detailed LCA while reducing the time spent by the practitioners. 3.2. EMMA simplified LCA method The simplified LCA method “EMMA” is based on the general principle arguing that the quantities of elements implemented in a building are linked to global parameters defined in early design stages e.g., net floor surface area, number of storeys, windows surface area, number of flats in a residential buildings. We mention that such approach has been used for many years in cost studies, by general contractors willing to reduce time spent in response to call to tenders. Here, the same approach is transferred to the environmental accounting. The EMMA calculation rules can be breakdown into three parts:
First, the definition of a list of elements Second, the building parameters that are linked to the elements (e.g., number of storeys etc.) Third, statistical ratio of quantities based on empirical knowledge within the construction company (e.g., taken from cost studies)
These three aspects can be determined from bill of quantities, invoices, or feedbacks from previous projects of the same building types. Yet, the overall reliability of this simplified LCA method will rely on the sample size of previous projects, and on the sound analysis of relationship between the building parameters and the quantities of elements. Main relationships for multi-residential buildings (mostly built in reinforced concrete in France) can be per linear, surface area or units of building elements. For instance, from the linear of facades, it is possible to have a proxy of the surface area of the facades based on the heights of each storey. Then, an automatic estimation of quantities of concrete, steel, insulation, interior coating can be derived (valid for loadbearing concrete structure). Similarly, the separation between wet and dry rooms in the building lead to two types of surface area also leading to the determination of cover floors (e.g., soft cover floors for dry rooms and ceramic tiles for wet rooms). Finally, quantities of elements can be derived from unit of equipment e.g., for HVAC. In that case, the statistical ratio of material quantities can be adjusted to the type of heating or ventilation system. In the end, a reduced amount of early design parameters enable to quantify all the elements. Then, a generic LCA data is associated. Then, the simplified LCA provides the same level of completeness as a complete LCA though with less 5280
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effort. This method is well fited for early ecodesing approach, because it is easier to compare different scenarios or variants. 4. Results The two simplified methods have been implemented in the ELODIE® LCA software for buildings [10]. The results presented in this section concerne the assessment of the embodied impacts of a real project of two multi-residential buildings located in France (see Figure 2). The net floor surface area is 4687 m² and each building has six levels above the ground and one underground car park. The LCA results are expressed per m² of net floor area per year. The baseline reference study period (RSP) is set at 50 years.
Figure 2: 3D view of the building in advanced design
4.1. Validation of the two simplified LCA with detailed LCA on the building case study Figure 3 presents the deviations in % between the simplified methods and a complete LCA. We notice a fairly good accuracy of the two simplified LCA methods with systematically more than 80% of the results of the detailed LCA. The POCP and WA indicators present the lowest level of accuracy for the Pareto method with 85% while for all the other indicators the error margin does not exceed 10%.
Figure 3: Results’ deviations between a detailed LCA and the two simplified LCA methods
4.2. Reproducibility tests of the two simplified LCA methods with different user profiles Results from Figure 3 show a fairly low loss of accuracy between the two simplified LCA and the detailed LCA. Figure 4 now presents a first pilot-test conducting on a sample of different 6281
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user profiles from a construction company. Nine different users representing different profiles in the construction company’s stakeholders (e.g., LCA practitioner with low experience vs. high expertise etc.) were asked to model the multi-residential building case study using these simplified methods. They use the same building design documents (program, plan, costing). Results of the case study showed a fairly good reproducibility when using these simplified tools and detailed guidance. The reproductibility with EMMA and with PARETO is quite similar.
Figure 4: Results’ deviations between the different user profiles for the two simplified LCA methods
Conducting simplified LCA also avoid spending a lot of time modelling elements per elements the building. As an illustration, Table 3 presents the average time needed for the different practitioners. Table 3: Average time spent by the different users for each type of LCA (complete, Pareto and EMMA) in the multi-residential case study
Indicators Complete LCA Simplified LCA – Pareto Simplified LCA – EMMA
Average time spent 12 hours 3 hours 8 hours
We notice that the time allocated by the construction engineers to the LCA drop from 33% with the EMMA simplified LCA to 75% with the Pareto method. As stakeholders cannot afford much time to conduct a LCA study especially in early design, such a compromise between accuracy, data requirements and efforts (time and cost) is probably the best method to invite more building stakeholders to the LCA approach. Further works should now be conducted to propose whole simplified LCA of building taking into account the embodied impacts but also the operational water and energy consumption. Similarly, further simplified LCA methods should be proposed to match the needs of other stakeholders (e.g. architects, thermal analysis design office etc.).
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Conclusions This paper presents a contribution towards simplified LCA following the general provisions and guidance of the EeBGuide European InfoHub on building LCA [5]. Simplified LCA is needed in construction LCA practices as practitioners do not have a lot of time to assess the environmental performances of their projects. This study showed the feasibility of simplified LCAs. Considerable time saving was reported between a simplified and a detailed LCA while keeping a fairly good accuracy. It would now be useful to validate the simplified LCA tools with a bigger sample of professionals of the construction sector to collect more feedbacks. In the same time, even if useful in early design or in quick LCA of new buildings, the practitioners should remain aware that the results of the simplified LCAs present a substantial uncertainty due to the reduced level of description of his project. However, if more time or more information is available, the practitioner will be able to precise the modelling and thus decrease the level of uncertainty linked to the level of description of the project. References [1]
Lasvaux S, Gantner J, Saunders T. “Requirements for building LCA tool developers, Deliverable 4.3”. European Project EeBGuide, 2012, 46 p., available online: www.eebguide.eu/eebblog/wp-content/uploads/2012/12/D-4.3.-Requirements-for-BuildingLCA-tool-designer.pdf
[2]
Peuportier B, Herfray G, Malmqvist T, Zabalza I, Staller H, Tritthart W, Wetzel C, Szalay Z. “Life cycle assessment methodologies in the construction sector: the contribution of the European LORE-LCA project”. SB11 Helsinki, 10 p.
[3]
Dixit M, Fernandez-Solis J, Lavy S, Culp C. Need for an embodied energy measurement protocol for buildings. Renewable and Sustainable Energy Reviews 16 (2012) 3730–3743
[4]
EN 15978: Sustainability of construction works – Sustainability assessment of buildings – calculation method. CEN – European Committee for Standardization. Brussels: CEN – CENELEC 2010.
[5]
EeBGuide Project “Operational Guidance for Life Cycle Assessment Studies of Energy Efficient Buildings Initiative” InfoHub available online: www.eebguide.eu, accessed 14/05/2014
[6]
Lasvaux, S., Gantner, J., Schiopu, N., Nibel, S., Bazzana, M., Bosdevigie B., Sibiude, G. 2014. Towards a new generation of building LCA tools adapted to the building design process and to the user needs? Proceedings of the International Conference on Sustainable Buildings, Construction Products & Technologies, SB13 Graz, 25-28 September 2013
[7]
Benefis, 2014. Accurate, simplified and reproductible Energy and Environnemental balance of buildings, building LCA research project funded by the French National Agency, www.agencenationale-recherche.fr/en/anr-funded-project/?tx_lwmsuivibilan_pi2[CODE]=ANR-11-VILD0001, accessed 24/04/2014
[8]
ASSOCIATION HQE. “HQE Performance: Première tendance pour les bâtiments neufs / First Trends for new buildings”. Report from the HQE Performance Test 2011. Available online: www.assohqe.org/hqe/IMG/pdf/HQE_Perf_-_BD_PPP.pdf
[9]
INIES, The French EPD database for building products, retrieved on 10/05/2013 from: www.inies.fr
[10] CSTB. ELODIE® LCA software for buildings, retrived on 10/05/2014 from: www.elodiecstb.fr
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