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- ItemOpen AccessExperimental evaluation of different macro-encapsulation designs for PCM storages for cooling applications(Elsevier, 2023) Rehman, Omais Abdur; Palomba, Valeria; Vérez, David; Borri, Emiliano; Frazzica, Andrea; Brancato, Vincenza; Botargues, Teresa; Ure, Zafer; Cabeza, Luisa F.Extensive research has been conducted on utilizing phase change materials for cooling applications, making it one of the most explored techniques in this domain. This research paper presents a comprehensive performance evaluation of a latent heat thermal energy storage unit featuring three distinct macro-encapsulation designs for phase change materials. The study aims to assess the thermal performance, efficiency, and practical applicability of these macro-encapsulation designs in a storage system. The PCM macro-encapsulation designs under investigation include cylindrical and rectangular shapes, each possessing different geometry. Two different configurations have been considered in this study. One configuration contains same PCM mass in order to have similar storage capacity while the other configuration has maximum PCM mass that can be inserted inside the tank. The used phase change material is a salt hydrate with melting temperature of 17 °C. The experimental setup consists of a controlled test rig that simulates real-world conditions and enables the comparative analysis of the three designs. Key performance parameters such as the charging and discharging time, temperature profiles, heat transfer rate, and energy storage/retrieval rates are measured and analysed. The results obtained from the experimental study provide valuable insights into the thermal behaviour, energy storage capacity, and overall effectiveness of the three macro-encapsulation designs. It is important to mention that use of an encapsulation design is highly dependent on application. The findings of this study contribute to the understanding of the impact of different macro-encapsulation designs on performance of thermal energy storage units. The results serve as a basis for optimizing macro-encapsulation designs, improving the efficiency and reliability of latent heat storage systems, and promoting their wider adoption in various energy management applications.
- ItemOpen AccessAnalysis of a heat pump-based energy system exploiting a low GWP refrigerant in different European climates(EDP Sciences, 2023-08-25) Rehman, Omais Abdur; Palomba, Valeria; Frazzica, Andrea; Cabeza, Luisa F.The objective of this research is to assess the operation of a heat pump (HP) under varying climatic conditions in Europe. To achieve this, a Dymola model is developed for a solar-assisted reversible water-to-water HP that utilizes a low global warming potential (GWP) refrigerant, R1234ze(E), and includes thermal and electrical energy storage systems. Experimental data is used to validate the primary components of the model. Simulations are conducted for both summer and winter seasons to determine the system’s overall annual performance. The analysis covers energy exchange between the system and the grid and utilizes key performance indicators such as self-sufficiency and self-consumption index. Furthermore, a techno-economic analysis is conducted to determine the payback period of the heating and cooling energy system based on the components’ capital expenditure and available incentives.
- ItemOpen AccessLactic acid production from cow manure: Technoeconomic evaluation and sensitivity analysis(MDPI, 2023) Garrido, Ricard; Cabeza, Luisa F.; Falguera Pascual, VíctorRecently, the industrial focus has shifted to renewable raw materials due to the exhaustion and rising pressures about environmental and political issues. Lignocellulosic biowaste can be derived from a range of sources, such as animal manure, forestry waste, and agricultural waste, and it can be transformed into lactic acid through a biochemical process. There are 942.63 million cattle in the world and annually generate 3.7 billion tons of manure, which could be used to produce lactic acid. The economic viability of a lactic acid plant from cow manure has not yet been determined and is, thus, considered in this study. Using the modeling program Aspen Plus data and other sources, as well as collecting all economic inputs, the feasibility analysis of a lactic acid plant handling cow manure is assessed in this paper. Three scenarios are calculated to check the feasibility depending on the plant size: scenario I handles 1,579,328 t·year-1, scenario II handles 789,664 t·year-1, and scenario III handles 315,865 t·year-1. The results demonstrate that treating the tested lignocellulosic biomass for the manufacture of lactic acid is economically feasible because the economic analysis shows positive net present values for scenarios I, II, and III. The technoeconomic analysis reveals that the minimum lactic acid selling price for scenario I is 0.945 EUR·kg-1, which is comparable to the cost of commercial lactic acid produced from starch feedstock. Scenario II achieves a minimum selling price of 1.070 EUR·kg-1, and scenario III 1.289 EUR·kg-1. The sensitivity analysis carried out reveals that the factor with the biggest impact on the NPV is the yield. Moreover, this study provides a model of industrial application and technoeconomic evaluation for lactic acid production from cow manure.
- ItemEmbargoA transient heat losses model for two-tank storage systems with molten salts(Elsevier, 2023) Tagle-Salazar, Pablo D.; Prieto, Cristina; López-Román, Antón; Cabeza, Luisa F.Concentrating Solar Power (CSP) is a proven and mature technology for energy supply. In recent years, electricity generation based on this technology has increased worldwide, to a large degree due to its high dispatchability when coupled with an energy storage system. Commercially, most plants store the energy in molten salts in a two-tank configuration. This study focuses on this storage configuration and proposes a mathematical model for the thermal losses in these tanks, both at nominal conditions and during transients. With this model at its core, a computational tool for thermal performance analysis in OpenModelica is developed. This dynamic thermal model includes the estimation of local heat loss due to assembly defects, which are heat flows that cannot be determined by theoretical modelling. The development of a semi-empirical correlation for estimating local heat loss is also presented. Simulation results showed that this local heat loss may represent a share about 40% of the total heat loss in a small-scale tank. A comparison of the characteristics of the model proposed in a previous work is also presented to establish the innovation of the model. Two thermal storage systems with different tank designs and sizes were simulated to compare the results using the present model with data available in the literature. Results show good agreement in transient thermal behaviour of heat flows, temperatures, and cooling rates when compared with data from other authors for the same tank.
- ItemOpen AccessRenovation assessment of building districts: Case studies and implications to the positive energy districts definition(Elsevier, 2023) Guarino, Francesco; Rincione, Roberta; Mateu Piñol, Carles; Teixidó Cairol, Mercè; Cabeza, Luisa F.; Cellura, MaurizioAs the built environment is among the main contributing sectors to climate change, it is needed to investigate new paradigms to push decarbonization efforts towards the ambitious objectives defined internationally. It is a shared understanding that shifting the perspective from the single building to the district perspective is required to fully take into consideration the complexity of all interactions undergoing within the built environment, thus the concept of Positive Energy District emerged as a district with annual net zero energy import and net zero CO2 emission working towards an annual local surplus production of renewable energy. In this framework, this paper explores the investigation of the potential for achieving the level of Positive Energy District in a group of nonresidential buildings in Balaguer, Catalonia, Spain. These buildings, occupying 8,825 m2 in the city centre, require significant refurbishment for improved energy performance. The analysis includes building energy modelling and simulation, renovation studies, several alternative balance calculations, and carbon emissions assessment. The paper also considers mobility and embodied energy and their impact on energy/carbon balances. The results show that Positive Energy Districts carbon and primary energy balances are not met with rooftop PV installations when retrofitting an existing district towards the Positive energy target but further significant PV areas (roughly + 50%) are required to meet merely the use stage balances: negative results are traced when mobility and embodied energy are computed. A formulation alternative to the simple mathematical balance to facilitate the diffusion of Positive Energy District as catalyst of urban decarbonisation could be needed, including context factors and alternative systems (e.g., rating systems).
- ItemOpen AccessExperimental evaluation of the thermal degradation of solar salt under different gas covers(Elsevier, 2023) Prieto, Cristina; López-Román, Antón; Cabeza, Luisa F.Commercial concentrating solar power (CSP) plants use solar salt (60-40 wt% NaNO3-KNO3) as thermal energy storage media due to its proven performance. Nevertheless, at high temperatures its decomposition can become a problem, hindering the possibility to rise operating temperatures. Therefore, this paper studies the decomposition of solar salt using different cover gases, dry air and oxygen. Results show that the use of oxygen as cover gas, instead the commercially used dry air, slows down the thermal decomposition of solar salt, reducing the amount of NOx and nitrites formation.
- ItemOpen AccessHardware-in-the-loop tecniques for complex systems analysis: Bibliometric analysis of available literature(MDPI, 2023) Cabeza, Luisa F.; Vérez, David; Teixidó Cairol, MercèSimulating complex systems in real time presents both significant advantages and challenges. Hardware-in-the-loop (HIL) simulation has emerged as an interesting technique for addressing these challenges. While HIL has gained attention in the scientific literature, its application in energy studies and power systems remains scattered and challenging to locate. This paper aims to provide an assessment of the penetration of the HIL technique in energy studies and power systems. The analysis of the literature reveals that HIL is predominantly employed in evaluating electrical systems (smart grids, microgrids, wind systems), with limited application in thermal energy systems (energy storage). Notably, the combination of electrical hardware-in-the-loop (EHIL) and thermal hardware-in-the-loop (THIL) techniques has found application in the assessment of vehicle thermal management systems and smart cities and, recently, has also been adopted in building systems. The findings highlight the potential for further exploration and expansion of the HIL technique in diverse energy domains, emphasizing the need for addressing challenges such as hardware-software compatibility, real-time data acquisition, and system complexity.
- ItemOpen AccessLactic acid production from cow manure: Experimental process conditions analysis(MDPI, 2023) Garrido, Ricard; Falguera Pascual, Víctor; Pérez Navarro, Omar; Acosta Solares, Amanda; Cabeza, Luisa F.The production of cow manure far exceeds the quantity that can be utilized in primary applications such as fertilizer or for the generation of biogas. As a result, alternative value‐added applications are being investigated. The purpose of this study is to evaluate the production of lactic acid, using cow manure as the raw material. The methodology involved the implementation of thermochemical pretreatment for the cow manure, followed by simultaneous saccharification and fermentation for lactic acid production. Response surface methodology based on a central composite design was employed to analyze the simultaneous saccharification and fermentation process. The factorial design of the experiments was carried out with three factors, cow manure concentration, temperature, and enzyme concentration, with 80 g∙L−1, 50 °C, and 212.5 IU/gCMDry Matter as central point values, respectively. Following the addition of Bacillus coagulans DSM2314 inoculum to enzymatically hydrolyzed cow manure at pH 5.0, after a 24 h period the concentration of lactic acid was recorded at 13.65 g∙L−1, with a conversion efficiency of 33.1%. Studies were conducted until 48 h to analyze time impact. Characterization studies for native cow manure and that pretreated using acid reagent were conducted. Sugar content and by‐product formation were analyzed, resulting in 23.24 g∙L−1 of sugar remaining as the maximum after fermentation, while low values of furfural (1.04 g∙L−1), 5‐hydroxymethylfurfural (1.35 g∙L−1), and acetic acid (1.45 g∙L−1) were found. Optimal conditions were calculated at 24 and 48 h with R software, obtaining the lactic acid, with yields of 13.4 g∙L−1, 36.28% (for 24 h) and 15.27 g∙L−1, 32.76% (for 48 h), respectively. Experimental and statistical studies of enzymatic hydrolysis and fermentation stated that cow manure was a feasible substrate for the production of lactic acid.
- ItemEmbargoEvaluation of cross-contamination in indirect thermal storage system in concentrated solar plants(Elsevier, 2023) Prieto, Cristina; López-Román, Antón; García-Rivero, Guillermo; Bartolí, Esther; Cabeza, Luisa F.Solar concentration technology is fully dispatchable due to the use of thermal energy storage systems, in particular, commercial parabolic trough power plants use indirect storage systems based on molten salts. This system includes a heat exchanger to transfer energy between the thermal oil from the solar field and the salts used in storage. In addition, some content of water is considered by cross-contamination in the steam generator of the power block. This study analyses the compatibility between both fluids in the event of cross-contamination in the equipment. The degree of compatibility between a triphasic system made up of a mixture of sodium nitrate and potassium nitrate salts (60:40), heat transfer fluid (DP:DPO), and water, when they were subjected to 390 ºC for a period of 312 h (two weeks). The study shows how thermal oil undergoes complete thermal-oxidative degradation without high impact on the composition of the salts.
- ItemOpen AccessApplication of deep learning techniques to minimize the cost of operation of a hybrid solar-biomass system in a multi-family building(Elsevier, 2023) Zsembinszki, Gabriel; Fernàndez Camon, César; Borri, Emiliano; Cabeza, Luisa F.Concerns related to climate change put renewable energy at the centre of most of the policies aimed at achieving a deep decarbonisation of the building sector. The combined use of two or more renewable energy sources in the same energy system can lead to an increase in the total share of renewable energy and in the flexibility of the system. In this direction, the SolBio-Rev project aims to develop an innovative system that uses solar thermal collectors and a biomass boiler to meet energy demand in buildings in different climatic regions. An advanced control that used deep reinforcement learning techniques was considered in this paper to find an optimal control strategy for a specific SolBio-Rev system installed in a standard multi-family residential building located in Madrid. The advanced control was developed to minimize the total cost of operation of the system. The results indicated that the advanced control strategy achieved a cost reduction of 35% in winter, compared to a standard rule-based control strategy. However, the improved control was not able to produce a significant cost reduction in summer.