Estudio comparativo de eficiencia energética: Fachada ventilada frente a fachada vegetal

398 p. + anexosEn la actualidad se desarrollan multitud de investigaciones relacionadas con la rehabilitación energética lo que la ha convertido en un campo emergente en el sector de la construcción y de la arquitectura.El objetivo general de la tesis es evaluar la aplicabilidad de diferentes sistemas pasivos de rehabilitación de fachadas (fachada ventilada y fachada vegetal) y analizar los beneficios de la incorporación de dichos sistemas en el ahorro energético de edificios.Para ello, se ha realizado el estudio térmico y acústico en la rehabilitación energética de una fachada de doble hoja, analizando posibles mejoras sobre la envolvente desde puntos de vista técnicos.Todo el proceso de toma de datos se ha llevado a cabo en una célula de ensayos Paslink y el análisis de los datos así como el modelo matemático y las soluciones se han llevado a cabo bajo una metodología común, de forma que las secciones que componen la tesis están realizadas paralelamente tanto para el muro base como para las dos propuestas de rehabilitación estudiadas

Environmentally Sustainable Green Roof Design for Energy Demand Reduction

Green roofs are artificial ecosystems that provide a nature-based solution to environmental problems such as climate change and the urban heat island effect by absorbing solar radiation and helping to alleviate urban environmental, economic, and social problems. Green roofs offer many benefits in terms of heat and water conservation as well as in terms of energy costs. This work proposes the design of an extensive and environmentally sustainable green roof for the Faculty of Engineering building in Bilbao. The green roof will be made from the composting of food waste generated in the building’s own canteen. Therefore, the main objective of this study is to calculate the solar efficiency of a sustainable green roof, evaluate its thermal performance, and quantify the impact that its implementation would have on energy consumption and the thermal comfort of its users. The results obtained confirm that an environmentally sustainable green roof has a positive effect on summer energy consumption and that this effect is much greater when there is water on the roof, as shown by the difference in energy savings between the dry (−53.7%) and wet (−84.2%) scenarios. The data show that in winter the differences between a green roof and a non-vegetated roof are not significant. In this case, the estimated energy consumption penalty (0.015 kWh/m2) would be 10% of the summer gain

Thermal characterization of a modular living wall for improved energy performance in buildings

Vertical vegetation systems are an innovative passive method for decreasing the thermal energy demand of buildings while increasing the quality of urban life. The main objective of this work is to calculate the effectiveness of vegetation in reducing thermal loads analytically. For this purpose, the thermal energy performance of the modular living wall was compared with a traditional double façade construction system to evaluate the influence of vegetation using Stochastic Differential Equations models. The research was carried out experimentally using a real-scale PASLINK test cell. The thermal behaviour of a double leaf bare wall and the same double leaf wall converted into a modular living wall were calculated for different summertime and wintertime periods. In both studied cases, the temperature of the exterior surface of the bare wall is taken at the same place regardless of whether or not there is greenery system in the energy balance. With this simplification, the effect of the modular living wall can be identified within the estimated coefficients. The thermal resistance of the conventional double façade increased 0.74 (m2 K)/W over the non-greened wall, which represents a weighted increase of 49%. Additionally, the experimental results showed that the evapotraspiration processes that take place in the living wall lead to an increase in the combined convection-radiation coefficient, which reduces the overheating of the façade. Moreover, the effective solar absorptivity value of the outermost surface of the bare wall has been reduced an 85% thanks to the living wall, which confirms the high capacity of the living wall to reduce solar heat gains.This publication is part of the R+D+i project PID2021-126739OB-C22, financed by MCIN/AEI/10.13039/501100011033/ and “ERDF A way of making Europe”. This project has been made possible thanks to the agreement between the Basque Government and the University of the Basque Country UPV/EHU through of the ENEDI research group for the management and development of the Thermal Area of the Buildings Quality Control Laboratory of the Basque Government (ATLCCE). Open Access funding provided by University of Basque Country

Evaluation of the Thermal Performance of Two Passive Facade System Solutions for Sustainable Development

Sustainable development is essential for the future of the planet. Using passive elements, like ventilated facades based on insulation and air chambers, or living walls, which are solutions based on nature, is a powerful strategy for cities to improve their thermal environment, reduce energy consumption, and mitigate the effects of climate change. This approach allows for the quantification of the influence of passive surfaces on energy fluxes compared to bare surfaces. In addition, it delves into understanding how the incorporation of vegetation on building facades alters surface energy fluxes, involving a combination of physical and biochemical processes. This comprehensive investigation seeks to harness the potential of passive and natural solutions to address the pressing challenges of urban sustainability and climate resilience. This research uses a surface energy balance model to analyze the thermal performance of two facades using experimental data from a PASLINK test cell. This study uses the grey box RC model, which links continuous-time ordinary differential equations with discrete measurement data points. This model provides insight into the complex interplay among factors that influence the thermal behavior of building facades, with the goal of comprehensively understanding how ventilated and green facades affect the dynamics of energy flow compared to conventional facades. The initial thermal resistance of the bare facade was 0.75 (°C m2)/W. The introduction of a ventilated facade significantly increased this thermal resistance to 2.47 (°C m2)/W due to the insulating capacity of the air chamber and its insulating layer (1.70 (°C m2)/W). Regarding the modular living wall, it obtained a thermal resistance value of 1.22 (°C m2)/W (this vegetated facade does not have an insulating layer). In this context, the modular living wall proved to be effective in reducing convective energy by 68% compared with the non-green facade. It is crucial to highlight that evapotranspiration was the primary mechanism for energy dissipation in the green facade. The experiments conclusively show that both the modular living wall and open-ventilated facade significantly reduce solar heat loads compared with non-passive bare wall facades, demonstrating their effectiveness in enhancing thermal performance and minimizing heat absorption

Defining the cooling and heating solar efficiency of a building component skin: application to a modular living wall

[EN] The thermal evaluation of building components composed of a base wall with a solar passive skin solution, such as a vertical/roof greenery system, ventilated facade, reflective painting, etc., is usually performed as a whole. In this research, it has been proven that, independently of the base wall thermal inertia and insulation level, the temperature of the outermost surface layer of any building component during sunny hours is mainly dependent on the ambient air temperature and relative humidity, the incident global solar radiation and the building skin behaviour. The latter assumption has been proven on the south wall of a reference building simulated with TRNSYS. The south wall properties have been varied and the building has been subjected to different climates. The assumption's validity has been checked for twelve south wall cases: a combination of 2 thermal transmittance, 2 thermal inertia and 3 climates. Each case has been simulated for a whole year. Based on this finding and the local ambient conditions for sunny hours, the hypothetical achievable maximum and minimum temperatures for the outermost surface layer have been defined. Then, based on the outermost surface temperature experimental measurements, the cooling and heating solar efficiencies valid for any skin solution have been defined. Furthermore, the developed methodology has been applied to a vertical living wall tested for a whole year under the accuracy and quality procedure of the PASLINK method. In this way, the cooling and heating solar efficiencies were experimentally determined for this skin solution for both, the hot cold seasons. The study has shown that the cooling efficiency during the hot season is 90.8%. As expected, even during sunny summer hours, the presence of water positively affects the performance of the facade, as it brings the base wall external surface temperature close to the ambient wet bulb temperature, therefore reducing the cooling load of the building. For the cold season, the cooling efficiency was similar, at 90.3%, which means a heating efficiency of 9.7%. Again, even for sunny winter hours, the values of the external surface temperature tend towards the ambient air wet bulb temperature, resulting in an increase in the heating demand. These experimental efficiency values allow the heating or cooling behaviour of different skin solutions to be comparable with a single number that is independent of the base wall composition. In addition, independently of the base wall composition, once the experimental efficiency value of a given skin solution is known, it allows (during sunny hours) the base wall outermost surface temperature to be calculated with precision. The latter makes it possible to increase the accuracy of the estimation of the heating and cooling demands of such methods as the degree-day method.This work was supported by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund (grant number RTI2018-096296-B-C22) through the MONITHERM project 'Investigation of monitoring techniques of occupied buildings for their thermal characterization and methodology to identify their key performance indicators', project reference: RTI2018-096296-B-C22 (MCIU/AEI/FEDER, UE). Open Access funding provided by University of Basque Country

Prácticas de ordenador, adaptadas a la evaluación continua de grandes grupos, para problemas de transferencia de calor mediante el software EES

Tanto en la ETSI de Bilbao como en el resto de Escuelas Universitarias Técnicas de la UPV/EHU se imparte la transferencia de calor dentro de asignaturas con diversos nombres. En todas ellas se ha decidido seguir una guía docente similar en la cual la docencia magistral y de prácticas de aula se apoya mediante prácticas de ordenador y prácticas de laboratorio. Muchos de estos grupos tienen más de 75 alumnos y para poder aplicarles una evaluación continua se ha optado por la realización de siete prácticas de ordenador de 1,5 h cada una utilizando el software Engineering Equation Solver® (EES) además de tres prácticas de laboratorio. La primera práctica de ordenador se utiliza para aprender a utilizar el software. Durante las siguientes seis prácticas se realizan diversos ejercicios relacionados con la teoría explicada durante las clases magistrales. Estas seis prácticas están divididas en dos partes, durante la primera hora el alumno realiza ejercicios guiados por el profesor y con ayuda de apuntes. Durante la última media hora de la práctica el alumno es examinado y evaluado. El método de evaluación es todo o nada, se distribuyen una serie de ejercicios parecidos a los realizados durante esa práctica y el alumno deberá llegar al resultado solicitado, en caso de llegar al número exacto obtiene un 5% de la nota final y en caso de no llegar no obtiene nada. Tras la primera práctica introductoria, en las próximas tres prácticas se abordan problemas de conducción mediante diferencias finitas que resultarían inabordables mediante métodos analíticos. Luego se realizan dos prácticas con problemas de convección que requieren de un proceso iterativo para el cálculo de los coeficientes de convección. Finalmente se realiza una práctica de radiación en la que se plantea un sistema de ecuaciones complejo que sería costoso solucionarlo manualmente. En todas estas prácticas se abordan también estudios paramétricos que ayudan a la comprensión de los mecanismos de la transferencia de calor. Se consiguen cuatro objetivos fundamentales. Primero, el alumno es capaz de afrontar problemas de conducción transitorios con condiciones de iniciales y de contorno complejas. Segundo, se facilita al alumno la comprensión de los tres mecanismos de transferencia de calor. Tercero, indirectamente el alumno se familiariza con el uso del EES y con la programación de problemas de ingeniería. Por último, destacar que se han preparado las prácticas para su fácil corrección, esto permite al profesor realizar una evaluación continua sin tener que revisar decenas de ejercicios

Design of a Microscale Refrigeration System for Optimizing the Usable Space in Compact Refrigerators

This research aims to enter the miniature refrigeration machine sector with the objective of designing a small scale unit while maintaining a competitive coefficient of performance (COP), comparing with a Peltier plates system. To this end, a research of the current technology was carried out in order to obtain indicative values on the scales that were being worked on and their application. After the previous research, a refrigeration cycle was designed in EES (engineering equation solver). From this design, different conclusions were obtained: (1) The correct sizing of the compressor revolutions together with its displacement is crucial for the equipment to be able to provide the desired cooling capacity. (2) In order to obtain the desired cooling capacity in the microscale refrigeration system, the heat exchangers must have fins. (3) Of the analysed refrigerants, R600a is the best choice, as it shows favourable characteristics (high COP and low compression ratio) when working in this type of cycle.This work was supported by the Basque Government in the Elkartek call through the SOLRUC project “Knowledge acquisition for the design of new ultra-compact cooling solutions”, project reference: KK-2020/00115

Prácticas de laboratorio para la determinación experimental del coeficiente de convección

superficies se ha diseñado un equipo para la determinación experimental del coeficiente de convección sobre una placa plana. Constructivamente hablando el equipo está formado por una lámina calefactora colocada sobre la cara superior de una placa de madera. Al conectar la lámina calefactora a la red, se consigue una temperatura superficial superior a la de la cara inferior de la placa de madera, a la del ambiente y a la de las superficies que le rodean. De esta manera se logra que exista un intercambio de calor por conducción a través de la placa, por convección con el aire y por radiación con las superficies circundantes. Los objetivos de la práctica son varios. Por un lado, se busca que el alumnado aplique el balance de energía e identifique los diferentes mecanismos de transmisión de calor que intervienen. Por otro lado, a partir de la medida de diversas temperaturas durante la práctica, el alumnado debe calcular el coeficiente de convección que tiene lugar en esas condiciones. Además, el alumnado debe resolver el intercambio de calor por convección como si fuese un problema de clase, usando las correlaciones de convección existentes en la bibliografía relativa a transferencia de calor. Por último se le pide que calcule la diferencia entre ambos coeficientes de convección de manera porcentual. Una ventaja añadida del equipo es que puede ser igualmente utilizado para la realización de prácticas relativas al mecanismo de radiación

Eraikin pasiboen karakterizazio termikoa: landare-fatxada modular baten kasu-azterketa

Sistema berdeak sendotzen ari dira hirietako eskari termikoa murrizteko eta, aldi berean, hiriko bizitzaren kalitatea hobetzeko. Sistema berdeei lotutako onurak hainbat dira: biodibertsitatea handitzea, ekaitz-uren kontrola, energia aurreztea, tenperatura erregulatzea eta zarata arintzea. Landaredun sistema bertikalek errendimendu energetikoari egiten dioten ekarpenari buruzko ezagutza lortzeko, landaredun fatxada bati proba metodo-logikoak egin zaizkio Paslink zelda batean. Helburua landare-fatxada modular baten berokuntza- eta hozte-eskaria ezaugarritzea da. Emaitza nagusia isolamenduaren hobekuntza izan da. Erreferentziako fatxada 0.75 W/(m2°C) baliotik abiatzen zen, eta 1.22 W/(m2°C)-ko transmisio termikoko balioetara igaro zen landare-fatxadari esker; horrek esan nahi du isolamendu-ahalmena %30 handitu zela. Fatxada berdeek energia aurrezteko potentzialtasun handia dutela ondoriozta daiteke.; Modular living walls are being strengthened to reduce thermal demand in cities while improving the quality of life in the city. The benefits associated with green systems are increased biodiversity, storm water control, energy saving, temperature regulation and noise mitigation. In order to gain knowledge of the contribution of vertical plant systems to energy performance, methodological tests of the modular living wall have been conducted in a Paslink test cell. The objective is to characterize the heating and cooling demand of a modular living wall. The main result is the improvement of isolation. The reference façade started from a value of 0.75 W/(m2°C) and went to a thermal transmission value of 1.22 W/(m2°C) thanks to the green façade, which means that insulation capacity increased by 30%. It can be concluded that modular living walls have great energy saving potential

Consideration of the interactions between the reaction zones in the new extended Eddy dissipation concept model

The latest Direct Numerical Simulation (DNS) modeling results in flameless combustion suggest interactions between the combustion reaction zones. The New Extended Eddy Dissipation Concept (NE-EDC) model, where model coefficients are calculated based on local Reynolds and Damköhler numbers, was proposed to improve the standard Eddy Dissipation Concept (EDC) model's accuracy when modeling flameless combustion, but this model does not include the interactions between the reaction zones. In this work, a revised version of the NE-EDC model is presented, called here Generalized NE-EDC model, where the chemical time scale is calculated in detail, considering the reaction rates of CH4, H2, O2, CO and CO2, making the interaction between the reaction zones more realistic (in the NE-EDC only a one-step CH4 global reaction mechanism is considered). A comparative study of four global reaction mechanisms is carried out to select the best mechanism for chemical time scale definition: the adjusted Jones & Lindstedt (JL1); the adjusted Westbrook & Dryer (WD1); the adjusted Westbrook & Dryer (WD2); and the one-step CH4 global mechanism (1-step). The four global reaction mechanisms, in combination with the NE-EDC model, are applied to the Delft lab-scale furnace and the modeling results are compared against those experimental measurements. The NE-EDC modeling results, in combination with WD2, present a slight improvement over the other global mechanisms in flameless modeling