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Trends for heating energy in European Cities are the decarbonization of energy sources and the reduction of heat loads. District heating (DH) networks are key systems to reach the targets due to the cost competitiveness and high performance levels they show. However, DH networks require a conversion to adapt for the need of the future. It is necessary to reduce the operation temperature so that it is possible to increase the performance of renewable systems and operation criteria needs to be adopted for the introduction of weather-dependent, distributed heat sources such as solar systems. In this paper is presented the RELaTED, a novel DH networks scheme with decentralized Ultra-Low Temperature performance. This way, it is possible the adaptation of new and existing networks to several operational schemes. Transitory phases for the conversion of actual DH and how this affects the whole system are discussed along the paper.

Thermal conductivity plays an important role in energy storage when the materials are charging and discharging. This paper presents an experimental investigation of the evolution of thermal conductivity up to 600 °C in different concretes. Moreover, the thermal conductivity was measured during thermal fatigue cycles when temperature ranged between 300 and 600 °C, simulating the operation conditions in a storage system of molten salts in a Concentrating Solar Power Plant (CSP). Five concrete compositions were analysed using diverse types of aggregates with different thermal response, covering a wide range of the initial thermal conductivity. The results confirm that the loss of thermal conductivity with temperature during the first heating is mainly due to the free water loss. Moreover, the type of aggregate influences the overall thermal performance of concrete due to its thermal conductivity and the volumetric differences with the cement paste. Siliceous aggregates underwent the highest decrease of thermal conductivity of concrete (+50%) with regard to room temperature. Regarding the cooling phase, thermal conductivity recovers between 20% and 40% depending on the type of aggregate. The outcomes of the present study demonstrate that the assumption of a constant thermal conductivity value in numerical simulations to predict its thermal capacity for energy storage is not appropriate. Es una corrección a un artículo publicado en: Sol. Energy 214 (2021) 430–442. Peer reviewed

[EN]The expected performance of an innovative Pumped Thermal Energy Storage (PTES) system based on a closedloop Brayton-Joule cycle and integrated with a Concentrated Solar Power (CSP) plant are analysed in this study. The integrated PTES–CSP plant includes five machines (two compressors and three turbines), a central receiver tower system, three water coolers and three Thermal Energy Storage (TES) tanks, while argon and granite pebbles are chosen as working fluid and storage media, respectively. A sizing of the main components of the integrated plant has been firstly carried out for the design of an integrated PTES-CSP plant with a nominal net power of 5 MW and a nominal storage capacity of 6 equivalent hours of operation. Specific mathematical models have been developed in MATLAB-Simulink to simulate the PTES and CSP subsystem in different operating conditions, and to evaluate the thermocline profile evolution within the three storage tanks during/charging and discharging processes. A control strategy has finally been developed to determine the operating modes of the plant based on the grid service request, the solar availability, and the TES levels. The performance of the system during a summer and a winter day have been analysed considering the integration of the PTES subsystem in the Italian energy market for arbitrage. Results have demonstrated the technical feasibility of the hybridization of a PTES system with a CSP plant and the ability of the integrated system to participate to energy arbitrage, although a lower exergy roundtrip efficiency (about 54 %) has been observed with respect to the sole PTES system (about 60 %).

The use of concrete is showing great potential as thermal energy storage material for concentrating solar power plants (CSP) due to its versatility, relatively low cost, and the possibility to reach a high operating temperature, above 500ºC thus increasing the plant efficiency. However, actual configurations based on concrete show different drawbacks including difficulties during the manufacturing on-site, different thermal expansion coefficients between concrete and pipes, and poor thermal conductivity of concrete. In order to address those challenges, this study proposes a new TES concrete tank concept based on three main pillars: modularity, improved concrete formulation, and direct contact concept. A preliminary assessment of the thermal performances of the new concept was analyzed through simulations showing the temperature distribution of the modules. Unión Europea 789051 “NextGenerationEU”/PRTR Ministerio de Ciencia e Innovación RTI2018-093849-B-C31 - MCIU/AEI/FEDER, Ministerio de Ciencia, Innovación y Universidades RED2018-102431-T- MCIU/AEI Ministerio de Ciencia, Innovación y Universidades MCIN/AEI/10.13039/501100011033

This work is partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31 - MCIU/AEI/FEDER, UE) and the Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (AEI) (RED2018-102431-T). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is a certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme. This project has received funding from the European Union´s Horizon 2020 research and innovation programme under the No 764025 (SWS-Heating). Alicia Crespo would also like to acknowledge the financial support of the FI-SDUR grant from the AGAUR of the Generalitat de Catalunya and Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya.

The accelerated growth of cities entails challenges in all sectors, and specifically, it has a close relationship with the construction sector. The Dominican Republic is a country where urban growth is increasing considerably, representing a problem of great magnitude in terms of the construction of social housing to reduce the housing deficit. In the social housing projects in Santo Domingo, the energy conditions are non-existent. There are no previous studies on the thermal comfort of those buildings. For this reason, this study seeks to analyze thermal comfort and energy efficiency in these types of housing through an energy simulation.The energy simulation is carried out through OpenStudio, which uses the Energy Plus calculation engine. A type of model was analyzed for the determination of temperatures and ranges of thermal comfort to evaluate its behavior for 24 hours in different months. The calculations obtained from the energy consumption due mainly to the variation of the comfort temperature indicate that the temperature variation is very similar in the selected months, with a maximum temperature of 27.3ºC in the hottest month and a minimum temperature of 26 .8ºC in the coldest month. Finally, due to the warm climate that prevails in the area, a high comfort temperature is recorded in these types of dwellings. To improve the comfort conditions in this type of dwelling, it is necessary to add thermal insulation and control the solar gains effectively.

Libro focalizzato sulle tecniche di caratterizzazione di sistemi e materiali per accumulo termico

This paper analyses the possible applications of medium temperature solar concentration technologies, Compound Parabolic Collector, Linear Fresnel Collector and Parabolic Trough Collector in the Spanish industrial sector. Results of this study allow evaluating whether or not solar technologies are an alternative to conventional sources. This possibility is analyzed energetically, economically and environmentally. Results show that the percentage of solar use is decisive in determining the true thermal energy generation cost. The other essential parameter is the solar field area due to produce economy of scale that reduces investment costs. Fluid temperature has significant influence mainly in Compound Parabolic Collector technology. Results obtained in this paper collect multiple alternatives and allow comparing for different scenarios the suitability to replace conventional energy sources by thermal energy obtained from medium temperature solar concentration technologies from an economic perspective. For instance, for percentage of solar use equal to 100%, the lowest thermal energy generation costs for each technology are 1.3 c€/kWh for Compound Parabolic Collector technology, fluid temperature of 100 °C and industrial process located in Seville, 2.4 c€/kWh for Linear Fresnel Collector technology, fluid temperature of 170 °C and industrial process located in Jaen, 3.3 c€/kWh for technology, fluid temperature of 350 °C and industrial process located in Jaen. These costs are lower than conventional energy sources costs.