Modelling and analysis of a metal hydride cooling system

La tesis doctoral que se presenta a continuación ha sido realizado en el Instituto de Ingeniería Energética de la Universidad Politécnica de Valencia, y parcialmente en el instituto de Stuttgart (Alemania) "Institüt für Kernenergetik und Energiesysteme" (IKE). El presente estudio consiste en el modelado y validación de un sistema de producción de frío basado en la absorción/desorción de hidrógeno en metales. La instalación experimental que se ha modelado se halla en el instituto IKE. En primer lugar, los materiales utilizados se han caracterizado tanto desde el punto de vista de las curvas P-C-T de equilibrio como de la cinética de absorción/desorción de cada aleación. En segundo lugar, se ha desarrollado un modelo completamente dinámico basado en las reacciones de transferencia de calor y masa que ocurren en los reactores. Los resultados se han validado con una amplia gama de medidas de IKE en régimen transitorio, obteniendo un ajuste muy bueno para diferentes ensayos. Finalmente, mediante la utilización del modelo, se han optimizado las condiciones de operación y las propiedades de los materiales, alcanzando así mejores prestaciones en refrigeración.Payá Herrero, J. (2010). Modelling and analysis of a metal hydride cooling system [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8911Palanci

Aprendizaje activo del alumnado en la asignatura “Energía solar fototérmica”

[EN] The present work describes the methodology which has been applied in the subject “Energía solar fototérmica” of the Universitat Politècnica de València. With the aim of promoting an active student participation, different methods have been continously applied such as continously mixing theory and problems, self-assessment tests, projects or business games. In comparison with previous years, the attendence was very high (92% mean value). The evaluation system which was chosen (60% practical work) seems a good strategy to assimilate concepts and develop competences according to 94% of the students. 88% of them agrees that their personal involvement and active participation is essential to reach this goal. In the subject, the students have to defend an oral presentation in groups of two. 75% of the students support that this work was favourable to develop oral communication skills.[ES] En el presente trabajo se describe la metodología adoptada en la asignatura de “Energía solar fototérmica” de la Universitat Politècnica de València. Con el objetivo de favorecer el aprendizaje activo de los alumnos, se plantea una metodología basada en intercalar frecuentemente teoría con problemas, tests de autoevaluación, prácticas, proyectos o juegos de empresa. Frente a experiencias anteriores en la misma asignatura, se consiguió una asistencia altísima (92% de media). El sistema de evaluación escogido (60% mediante trabajos prácticos) parece favorable a un 94% de los alumnos de cara a asimilar mejor los conceptos. Un 88% de ellos considera que la participación activa en clase favorece la asimilación de conceptos y el desarrollo de competencias. En la asignatura, los alumnos realizan una presentación en grupos de dos. Un 75% de los alumnos está de acuerdo en que ésto mejoró su capacidad para comunicar resultados en público.Payá Herrero, J. (2017). Aprendizaje activo del alumnado en la asignatura “Energía solar fototérmica”. En In-Red 2017. III Congreso Nacional de innovación educativa y de docencia en red. Editorial Universitat Politècnica de València. 824-833. https://doi.org/10.4995/INRED2017.2017.6795OCS82483

Incorporación de técnicas para favorecer el aprendizaje activo en la asignatura “Evaluación técnico-económica de sistemas energéticos”

[EN] The present work describes the active learning approach followed in the subject “Techno-economical assessment of energy systems”. In first place, the employed techniques are described and in second place, the results are discussed from the point of view of the teacher and the students, by means of a survey which was answered by 34 of the 36 students. The results indicate that the students have a very positive perception with respect to their training when adopting techniques such as group discussion, evaluation with projects or oral presentations. A novel aspect has been including half an hour of autonomous work of the students in each practical lesson, where they had to solve on their own typical simulation errors. 73% of the students agreee that this method developed their autonomy. Globally, and although the results are very positive (97% satisfaction with the teacher and 86% with the subject), the teaching can still be improved by further working on the teaching material (contents) aswell as by better adapting the project to the contents and competences which are developed through the subject.[ES] El presente trabajo describe la metodología de aprendizaje activo adoptada en la asignatura de “Evaluación técnico-económica de sistemas energéticos”. En primer lugar se describen las distintas técnicas empleadas en clase y en segundo lugar se comenta su utilidad tanto desde el punto de vista del profesor como de los alumnos, a través de un sondeo al que contestaron 34 de los 36 alumnos matriculados. Los resultados muestran que los estudiantes perciben de manera muy positiva en su formación técnicas como presentaciones orales de los alumnos, evaluación por proyectos o discusión en grupos. Un aspecto novedoso ha sido incluír en las prácticas media hora de trabajo autónomo de los alumnos para detectar problemas típicos de simulación. 73% de los alumnos indican que esto aumentó su autonomía. Globalmente, aunque los resultados son muy buenos (97% de satisfacción con el profesor, 86% con la asignatura en general), todavía hay margen de mejora sobre todo en los contenidos y en el enfoque del proyecto, para que sea más acorde con los conceptos y competencias trabajados en la asignatura.Payá Herrero, J. (2017). Incorporación de técnicas para favorecer el aprendizaje activo en la asignatura “Evaluación técnico-económica de sistemas energéticos”. En In-Red 2017. III Congreso Nacional de innovación educativa y de docencia en red. Editorial Universitat Politècnica de València. 834-840. https://doi.org/10.4995/INRED2017.2017.6796OCS83484

Incorporación y seguimiento interanual de una actividad práctica de aprendizaje basada en proyectos

[EN] The present work presents a teaching methodology which consists on a competition where the students have to design, build and test the heating capacity of a solar cooker. A detailed description is provided for the activity, along with the time-evolution and progressive enhancements which have been introduced from the academic course of 2016-2017 until 2019-2020. Finally, the results are discussed on the basis of a same survey answered by the students at the end of each course. The students agree that the competition helps to better assimilate the main concepts, to share different options and develop critical skills. The students also consider that they learn more because they have more personal involvement. From the point of view of the instructor, the activity has entirely fulfilled the objectives which were to increase the student interest, participation and concentration in the classes, and to promote a deep learning.[ES] En el presente trabajo se presenta una actividad de enseñanza-aprendizaje que consiste en una competición en la que los alumnos diseñan, construyen y ensayan la capacidad de cocción de una cocina solar. Se detalla la actividad, así como la evolución temporal y mejoras incorporadas desde el curso 2016-2017 hasta el 2019-2020. Finalmente, los resultados se comentan en base a una misma encuesta realizada a los alumnos al final de cada curso. Los alumnos están de acuerdo en que dicha competición favorece la asimilación de conceptos, permite compartir y contrastar distintas opiniones, así como desarrollar su capacidad crítica. Los alumnos también consideran que aprenden más pues tienen una mayor implicación. Desde el punto de vista del profesor, la actividad ha cumplido íntegramente con los objetivos iniciales planteados, que eran de aumentar el interés de los alumnos, su participación, concentración en clase, y favorecer un aprendizaje profundo en la materia.Payá Herrero, J. (2021). Incorporación y seguimiento interanual de una actividad práctica de aprendizaje basada en proyectos. En IN-RED 2021: VII Congreso de Innovación Edicativa y Docencia en Red. Editorial Universitat Politècnica de València. 70-81. https://doi.org/10.4995/INRED2021.2021.13458OCS708

Methodology for the calculation of the shadow factor on roofs and facades of buildings in urban areas

[EN] The present paper presents a systematic methodology to obtain the shadow factor on roofs and facades of buildings. The approach is based on the use of Geographic Information Systems (GIS), and helps to obtain, accurately and on urban scale, the incident solar irradiance on each surface of any building. Given the characteristics of the entire urban area, the solar gain of the buildings can consequently be calculated more accurately than with a stand-alone building model. A good quantification of the solar gain is essential, for instance, to better evaluate the consumption of Air-Conditioning systems. This approach can also be useful to size and simulate the introduction of PV panels in facades or roofs of urban regions, or to carry out a climate-sensitive urban design and planning. This approach is based on a vector-based 3D model of the buildings or trees of the urban region. Open data of cadastral cartography and LiDAR altimetric data are used as inputs. Using the previous 3D model and solar geometry data, analytical models are applied to calculate the shadow of each tree or building on any desired surface. The mentioned methodology has been implemented in R and has been applied to buildings of Valencia (Spain). The results have been validated with SketchUp, both for horizontal and vertical surfaces, and the error has been calculated for different hours of the day.Viana-Fons, JD.; Gonzálvez-Maciá, J.; Payá-Herrero, J. (2019). Methodology for the calculation of the shadow factor on roofs and facades of buildings in urban areas. Universidad de Castilla-La Mancha José Antonio Almendros Ibáñez. 870-877. http://hdl.handle.net/10251/180701S87087

Dynamic Modelling and Techno-Economic Assessment of a Compressed Heat Energy Storage System: Application in a 26-MW Wind Farm in Spain

[EN] One of the main challenges for a further integration of renewable energy sources in the electricity grid is the development of large-scale energy storage systems to overcome their intermittency. This paper presents the concept named CHEST (Compressed Heat Energy STorage), in which the excess electricity is employed to increase the temperature of a heat source by means of a high-temperature heat pump. This heat is stored in a combination of latent and sensible heat storage systems. Later, the stored heat is used to drive an organic Rankine cycle, and hereby to produce electricity when needed. A novel application of this storage system is presented by exploring its potential integration in the Spanish technical constraints electricity market. A detailed dynamic model of the proposed CHEST system was developed and applied to a case study of a 26-MW wind power plant in Spain. Different capacities of the storage system were assessed for the case under study. The results show that roundtrip efficiencies above 90% can be achieved in all the simulated scenarios and that the CHEST system can provide from 1% to 20% of the total energy contribution of the power plant, depending on its size. The CHEST concept could be economically feasible if its capital expenditure (CAPEX) ranges between 200 and 650 k€/MWThis work has been partially funded by the grant agreement No. 764042 (CHESTER project) of the European Union's Horizon 2020 research and innovation program.Sánchez Canales, V.; Payá-Herrero, J.; Corberán, JM.; Hassan, A. (2020). Dynamic Modelling and Techno-Economic Assessment of a Compressed Heat Energy Storage System: Application in a 26-MW Wind Farm in Spain. Energies. 13(18):1-18. https://doi.org/10.3390/en13184739S1181318Nikolaou, T., Stavrakakis, G. S., & Tsamoudalis, K. (2020). Modeling and Optimal Dimensioning of a Pumped Hydro Energy Storage System for the Exploitation of the Rejected Wind Energy in the Non-Interconnected Electrical Power System of the Crete Island, Greece. Energies, 13(11), 2705. doi:10.3390/en13112705Shi, J., Yang, Y., & Deng, Z. (2009). A reliability growth model for 300 MW pumped-storage power units. Frontiers of Energy and Power Engineering in China, 3(3), 337-340. doi:10.1007/s11708-009-0032-yArgyrou, M. C., Christodoulides, P., & Kalogirou, S. A. (2018). Energy storage for electricity generation and related processes: Technologies appraisal and grid scale applications. Renewable and Sustainable Energy Reviews, 94, 804-821. doi:10.1016/j.rser.2018.06.044Jockenhöfer, H., Steinmann, W.-D., & Bauer, D. (2018). Detailed numerical investigation of a pumped thermal energy storage with low temperature heat integration. Energy, 145, 665-676. doi:10.1016/j.energy.2017.12.087Steinmann, W.-D. (2017). Thermo-mechanical concepts for bulk energy storage. Renewable and Sustainable Energy Reviews, 75, 205-219. doi:10.1016/j.rser.2016.10.065Thess, A. (2013). Thermodynamic Efficiency of Pumped Heat Electricity Storage. Physical Review Letters, 111(11). doi:10.1103/physrevlett.111.110602Guo, J., Cai, L., Chen, J., & Zhou, Y. (2016). Performance optimization and comparison of pumped thermal and pumped cryogenic electricity storage systems. Energy, 106, 260-269. doi:10.1016/j.energy.2016.03.053Attonaty, K., Stouffs, P., Pouvreau, J., Oriol, J., & Deydier, A. (2019). Thermodynamic analysis of a 200 MWh electricity storage system based on high temperature thermal energy storage. Energy, 172, 1132-1143. doi:10.1016/j.energy.2019.01.153Frate, G. F., Antonelli, M., & Desideri, U. (2017). A novel Pumped Thermal Electricity Storage (PTES) system with thermal integration. Applied Thermal Engineering, 121, 1051-1058. doi:10.1016/j.applthermaleng.2017.04.127Mateu-Royo, C., Mota-Babiloni, A., Navarro-Esbrí, J., Peris, B., Molés, F., & Amat-Albuixech, M. (2019). Multi-objective optimization of a novel reversible High-Temperature Heat Pump-Organic Rankine Cycle (HTHP-ORC) for industrial low-grade waste heat recovery. Energy Conversion and Management, 197, 111908. doi:10.1016/j.enconman.2019.111908Benato, A. (2017). Performance and cost evaluation of an innovative Pumped Thermal Electricity Storage power system. Energy, 138, 419-436. doi:10.1016/j.energy.2017.07.066Benato, A., & Stoppato, A. (2019). Integrated Thermal Electricity Storage System: Energetic and cost performance. Energy Conversion and Management, 197, 111833. doi:10.1016/j.enconman.2019.111833Maximov, S., Harrison, G., & Friedrich, D. (2019). Long Term Impact of Grid Level Energy Storage on Renewable Energy Penetration and Emissions in the Chilean Electric System. Energies, 12(6), 1070. doi:10.3390/en12061070Steinmann, W. D. (2014). The CHEST (Compressed Heat Energy STorage) concept for facility scale thermo mechanical energy storage. Energy, 69, 543-552. doi:10.1016/j.energy.2014.03.049Hu, B., Wu, D., Wang, L. W., & Wang, R. Z. (2017). Exergy analysis of R1234ze(Z) as high temperature heat pump working fluid with multi-stage compression. Frontiers in Energy, 11(4), 493-502. doi:10.1007/s11708-017-0510-6He, Y.-L., Wang, R., Roskilly, A. P., & Li, P. (2017). Efficient use of waste heat and solar energy: Technologies of cooling, heating, power generation and heat transfer. Frontiers in Energy, 11(4), 411-413. doi:10.1007/s11708-017-0525-zHassan, A. H., O’Donoghue, L., Sánchez-Canales, V., Corberán, J. M., Payá, J., & Jockenhöfer, H. (2020). Thermodynamic analysis of high-temperature pumped thermal energy storage systems: Refrigerant selection, performance and limitations. Energy Reports, 6, 147-159. doi:10.1016/j.egyr.2020.05.010Steinmann, W.-D., Bauer, D., Jockenhöfer, H., & Johnson, M. (2019). Pumped thermal energy storage (PTES) as smart sector-coupling technology for heat and electricity. Energy, 183, 185-190. doi:10.1016/j.energy.2019.06.058Pereira da Cunha, J., & Eames, P. (2016). Thermal energy storage for low and medium temperature applications using phase change materials – A review. Applied Energy, 177, 227-238. doi:10.1016/j.apenergy.2016.05.097Cecchinato, L. (2010). Part load efficiency of packaged air-cooled water chillers with inverter driven scroll compressors. Energy Conversion and Management, 51(7), 1500-1509. doi:10.1016/j.enconman.2010.02.008The Turbocor Family of Compressors Model TT300, Danfoss TURBOCOR. Datasheetwww.turbocor.com,USAPalkowski, C., Zottl, A., Malenkovic, I., & Simo, A. (2019). Fixing Efficiency Values by Unfixing Compressor Speed: Dynamic Test Method for Heat Pumps. Energies, 12(6), 1045. doi:10.3390/en12061045Estadísticas del Sistema Eléctrico | Red Eléctrica de Españahttps://www.ree.es/es/estadisticas-del-sistema-electrico/3015/3001OMIP Operador del Mercado Ibérico de Energía—Polo Portuguéshttps://www.omip.pt/El Mercado de Restricciones Técnicashttp://mifacturadeluz.com/mercado-de-restricciones-tecnicas/Puerto Escandón (España)—Parques eólicos—Acceso en línea—The Wind Powerhttps://www.thewindpower.net/windfarm_es_2253_puerto-escandon.phpFederico Bava DS D2.1 Case studies: User Requirements and Boundary Conditions Definition. CHESTERhttps://www.chester-project.eu/wp-content/uploads/2018/11/CHESTER_D2.1_Case-Studies_v5.0.pdfEstado actual de la energía termosolar (CSP)—HELIONOTICIAShttp://helionoticias.es/estado-actual-de-la-energia-termosolar-csp/Gallo, A. B., Simões-Moreira, J. R., Costa, H. K. M., Santos, M. M., & Moutinho dos Santos, E. (2016). Energy storage in the energy transition context: A technology review. Renewable and Sustainable Energy Reviews, 65, 800-822. doi:10.1016/j.rser.2016.07.028Smallbone, A., Jülch, V., Wardle, R., & Roskilly, A. P. (2017). Levelised Cost of Storage for Pumped Heat Energy Storage in comparison with other energy storage technologies. Energy Conversion and Management, 152, 221-228. doi:10.1016/j.enconman.2017.09.04

Thermal characterisation of compact heat exchangers for air heating and cooling in electric vehicles

[EN] The use of air conditioning in all-electric cars reduces their driving range by 33% in average. With the purpose of reducing the energy consumption of the vehicle and optimising the performance of the batteries, the mobile air-conditioning can be integrated with the temperature control system of the powertrain by means of a coolant loop. In such layouts, the air-to-coolant heat exchangers must operate efficiently in both air heating and cooling modes. Dynamic simulation tools comprising the entire thermal system are essential to assess its performance. In this context, fast but accurate models of the system components are required. This paper presents the thermal characterisation of a commercial compact louvered-fin flat-tube heat exchanger (heater core) for this novel application, based on an experimental campaign comprising 279 working points that reflect real air-conditioning (heating and cooling) working conditions. A general methodology to fit a single correlation of the global heat transfer coefficient for both dry and wet working conditions is explained. The semiempirical correlation developed is employed in a single-node model of the heat exchanger that requires minimal computation time. The present model predicts the heat transfer rate with an average deviation of 3.5% in the cases with dehumidification and 1.9% in the cases when the heat exchanger remains dry.This work has been supported by the European Commission under the 7th European Community framework program as part of the ICE project ‘‘MagnetoCaloric Refrigeration for Efficient Electric Air-Conditioning”, Grant Agreement no. 265434. B. Torregrosa-Jaime acknowledges the Spanish Education, Culture and Sport Ministry (Ministerio de Educación, Cultura y Deporte) for receiving the Research Fellowship FPU ref. AP2010-2160.Torregrosa-Jaime, B.; Corberán, JM.; Payá-Herrero, J.; Delamarche, JL. (2017). Thermal characterisation of compact heat exchangers for air heating and cooling in electric vehicles. Applied Thermal Engineering. 115:774-781. https://doi.org/10.1016/j.applthermaleng.2017.01.017S77478111

Performance analysis and modelling of a 50 MW grid-connected photovoltaic plant in Spain after 12 years of operation

[EN] This study aims to estimate the performance and losses of a 50 MW photovoltaic (PV) utility-scale after 12 years of operation. The PV plant has monocrystalline and polycrystalline silicon modules and is located in the central region of Spain with an annual insolation of 1976 kWh/m2. Monitoring data over the entire year 2020 has been analyzed and filtered to assess the performance results following the IEC 61724 standard guidelines. The annual average reference yield, final yield, performance ratio and capacity utilization factor are of 5.44 h/d, 4.28 h/d, 79.24%, and 19.77%, respectively. Besides the experimental analysis, this work improves the estimation of the daily performance ratio, especially in days with low insolation. Two different modelling approaches have been assessed and compared. In first place, a physical model has been adopted, based on the most common losses, and including an exponential expression to account for low irradiance losses. In second place, statistical models have been used, with either multiple linear regressions or random forest algorithms. In contrast with other published models which require many inputs, the best accuracy has been reached with the random forest model using only the ambient temperature and solar irradiance as predictors, obtaining a RMSE of 1% for the PR and for the energy production.The authors gratefully acknowledge the operation & maintenance staff of the PV Power Plant in Olmedilla de Alarcon ¿ for providing the measured data of the solar PV power plant.Fuster-Palop, E.; Vargas-Salgado, C.; Ferri-Revert, JC.; Payá-Herrero, J. (2022). Performance analysis and modelling of a 50 MW grid-connected photovoltaic plant in Spain after 12 years of operation. Renewable and Sustainable Energy Reviews. 170:1-17. https://doi.org/10.1016/j.rser.2022.11296811717

Development and validation of a dynamic thermal model of a minibus using TRNSYS

[EN] The current paper presents a dynamic thermal model of a vehicle including two thermal zones, one for the front region (driver) and one for the back (passengers). The model, developed in TRNSYS, is able to predict the cabin¿s thermal behaviour under variable ambient temperatures and solar radiation. A minibus was used to validate the model using experimental data for ambient temperature, solar radiation and the indoor temperature of a minibus parked both inside and outside a garage in Torino (Italy). The proposed model accurately reproduces the warm-up and cool-down of the cabin. In addition, the model has been used to calculate the cooling load of the cabin during a summer day, and to quantify the thermal loads under variable ambient conditions. In future work, the model will be used to predict the dynamic performance of the A/C system in an urban driving cycle and to optimise the compressor control strategy.Daniela C. Vásconez-Núñez acknowledges the financial support provided by the CONVOCATORIA ABIERTA 2013-SEGUNDA FASE program, which was funded by the SENESCYT (Secretaría Nacional de Educación Superior, Ciencia, Tecnología e Innovación) (Grant No 2014-AR3R7463) of Ecuador.Vásconez-Núñez, DC.; Gonzálvez-Maciá, J.; Corberán, JM.; Payá-Herrero, J. (2018). Development and validation of a dynamic thermal model of a minibus using TRNSYS. International Journal of Vehicle Design. 77(1/2):87-107. https://doi.org/10.1504/IJVD.2018.098272S87107771/

Reproducibility of solidification and melting processes in a latent heat thermal storage tank

This study analyzes the reproducibility of solidification and melting tests in a tank containing 181 kg of paraffin for cold storage at around 8 °C. Firstly, an experimental campaign of 10 identical tests was carried out. The performance is practically the same in terms of PCM temperatures and thermal power, with a maximum deviation of 2% in the capacity of all tests. In a second campaign, the impact of the initial conditions was studied. The results indicate that fixing a same mean PCM temperature at the beginning of the tests is insufficient to ensure an accurate reproducibility. Depending on the heat transfer rate during the preparation tests, the capacity differed in up to 33%. In tanks with such quantities of PCM, fixing a uniform initial PCM temperature is hardly possible, thus it is important to prepare the tank with same operation conditions.Bosholm, F.; López Navarro, A.; Gamarra, M.; Corberán Salvador, JM.; Payá Herrero, J. (2016). Reproducibility of solidification and melting processes in a latent heat thermal storage tank. International Journal of Refrigeration. 62:85-96. doi:10.1016/j.ijrefrig.2015.10.016S85966