Mathematical modelling to aid in the transition towardsmore sustainable buildings
- Autores: Alba Torres Rivas
- Directores de la Tesis: Laureano Jiménez Esteller (dir. tes.), Dieter Boer (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2020
- Idioma: español
- Tribunal Calificador de la Tesis: Rubén Ruiz Femenia (presid.), Joan Manel Vallés Rasquera (secret.), Mariana Palumbo (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The importance of the environment and sustainability is becoming an awareness for the policies and the society. For that reason, a new market of cost-effective, environmentally friendly and sustainable products. Methodologies and studies to evaluate the performance of those products can show new potentialities and improvement trends. The building sector is not an exception and multiples studies are evaluating new alternative technologies.
This sector represents one of the main energy consumers worldwide, with a 40% of the total annual energy consumption and being the responsible of a third part of the greenhouse gas emissions (GHG). Many countries have taken that into account and have dictate energy measures to reduce the energy demand and the GHG associated. To achieve those improvements, multiple strategies can be applied, such us energy efficient equipment, double-glazed windows, building insulation or renewable energy technologies, such as solar panels.
Building insulation has shown to be a promising alternative reducing the energy demand associated to heating and cooling, without compromising the thermal comfort inside the building. Following this trend, a wide range of insulation materials are available or have been developed, providing multiple alternatives. Despite the improvements that those materials provide in buildings demand, some materials have an important energy embodied that may counter effect the global energy consumption associated to the alternative (accounting the manufacture, installation, dismantling and disposal of the materials). Neglecting the associated impact of those materials may lead to sub-optimal solutions, which suggest that an initial evaluation of the alternatives would help in the early stages of building design or retrofit.
In this thesis we present several studies to analyse the possibilities of bio-based materials, as they provide good thermal properties and low embodied energy. Firstly, bio-based materials have been analyse in terms of cost, environmental impact and condensation risk, providing a systematic methodology to identify the possibilities of the different materials in different climate conditions. Secondly, a methodology to assess the combination of those materials in panels or fiber mats is carried out with an initial evaluation of the efficiency (in terms of cost and environmental impact) of the materials to identify the most promising alternatives to combine and systematically generate efficient combination of the materials. This promising alternative can propose materials with intermediate properties which could benefit in some applications (e.g., improving moisture buffering or acoustic insulation, among others).
To illustrate the possibilities of the methodology, a house-like cubicle has been considered, varying the insulation materials and thicknesses of the insulation with the objective to achieve the minimum cost and environmental impact without condensation risk. Despite that, the proposed methodology can be applied to other building models and with other variables or objective functions.
The first chapter of the thesis describes the methodology to asses a multi-objective optimization (MOO) with the evaluation of the moisture transfer to evaluate the condensation risk in different climates. It minimizes the cost and impacts associated during the whole life cycle, considering the construction materials and the energy consumed to achieve the comfort during the operational phase. The results provided are further evaluated to reduce optimal Pareto frontier alternatives to those without the condensation risk.
The environmental impact, is carried out following a life cycle assessment (LCA) methodology from cradle-to-gate (from extraction until end of life), based on the ReCiPe methodology. ReCiPe has a total of 17 specific impact which are aggregated into three different damage groups (human health, ecosystem quality and resources), which are further clustered into a single indicator which is used in this approach.
This approach has shown important improvements with bio-based materials, achieving reductions in terms of cost and environmental impact comparing to a reference insulation material, polyurethane (PU). For the case of Lleida, the best economic alternatives are provided by 24cm of cotton and wool (a reduction of 28% compared to PU), whereas 86cm of corn is the best environmentally friendly alternative (with a reduction of 26% compared to PU). Despite being optimal solutions, any of those can be implemented without condensation risk, which proves the necessity of implement this further analysis for bio-based materials. Excluding those non-feasible solutions, other Pareto optimal solutions improve the performance of PU, 22cm of hemp is the most compromise solutions between cost and impact without condensation risk. All the solutions of PU are dominated by different bio-based materials. The second chapter evaluates the efficiency of different combinations of insulation materials and thicknesses, with the objective to propose materials combination for sandwich panels or fiber mats which facilitate the installation process and provide materials with more balanced properties. For that reason, the material-thickness combinations have been evaluated in terms of cost and environmental impact, following a cradle-to-utilization variant (from the extraction until the use phase). The chosen LCA methodology used is ReCiPe with the 17 specific impacts which are considered inputs. Those inputs and the economic one are analysed with an objective reduction method to identify redundant objectives which are excluded from the further analysis without losing efficient solutions.
All the material-thickness combinations (from now DMUs) are evaluated with Data Envelopement Analysis, which provides for each alternative an efficiency score which divide the DMUs in efficient (efficiency score of 1) and non-efficient solutions (efficiency score < 1). Furthermore, for each non-efficient DMU an efficient alternative is provided, which are potential composites (materials-thicknesses combinations of different materials). All the composites are filtered to exclude non-feasible materials that are not attractive to the market, and the others are also evaluate to prove their performance. This methodology has been applied in a cubicle-like building, but can be carried out in other buildings or with different materials.
For the selected case study, 12 out of 42 solutions are efficient, while from the 30 proposed composites only 10 are finally retained due to their appealing properties. The methodology proposed also proved to properly predict composite performance generating a good methodology in the early stages of materials designs. Furthermore, it is important to identify the potential of those methodologies in a bigger scale, to evaluate this potential a methodology to quantify and analyse the building stock of a region is assessed for the residential sector. The proposed methodology quantifies and evaluates the whole stock of each municipality of the selected area, enabling to analyse the special characteristics of the different areas, size of municipality and climate conditions. The main barrier in this methodology is to big amount of individualities of the building stock that makes impossible to gather all the information, due to that reason it is important to simplify and cluster the characteristics of the building stock maintaining as much individualities as possible. For that reason, the key parameters that define the residential stock have been identified as year of construction, amount of dwellings, the building typology and building surface. It is important to know that the different categories of each of the key parameters may be different depending in the area selected, in this case study 12 clusters have been defined with a specific energy demand and building characteristics.
This analysis quantification has been assessed for the region of Catalonia (north-east area of Spain), which policies are encouraging to achieve what they call an Energetic transition agreement, which copes with the idea to provide renewable energy by small suppliers (i.e., building stock of the municipalities). In order to generate this energy, PV panels have been installed in the available roof area of the buildings, analyzing a total of 947 municipalities of different sizes and characteristics.
Following this methodology, we can conclude that, for the selected area, residential buildings can supply approximately a 20% of the electricity demand. According to the size of the municipality this self-consumption rate decreases as the size increase, with an important change of tendency of municipalities bigger than 50000 inhabitants where it decreases until a factor of self-consumption of 8% for the specific case of Barcelona. Furthermore, this methodology enables the possibility to evaluate the effect of refurbishment of the actual building stock, which has been carried out in four different alternatives, reducing the energy demand by specific amounts (e.g., energy reductions achieved by an insulation material). For this illustrative example 4 different alternatives have been proposed, a reduction of 60% and 80% and fixing an energy demand of 30kwh/m2 and 15kwh/m2. This example illustrates the effect of building retrofit, varying from a 20% of self-consumption until more than 100% of self-consumption for the majority of municipalities with an important measures of building retrofit. Despite that, we can conclude that this measure of self-production is not able to produce all the energy required for the whole area in any case, which means that the building stock would always require an extra generation of different sources or technologies (e.g., solar farms).
