• Energy Research

The energy consumption in the built environment represents one of the major contributors of carbon emissions to the atmosphere. This leads to the need for a transition in the building sector and the introduction of policies that pursue high efficiency in residential and non-residential buildings with an increasing share of renewables. The benefit of the use of thermal energy storage is widely recognized to increase the efficiency of energy systems in different building typologies, to help in the introduction of renewable energies in buildings and to reduce the energy demand needed for heating and cooling. Nowadays, different thermal energy storage technologies are available, including sensible, latent, and sorption and chemical reactions (also called thermochemical) energy storage. Although in the past twenty years, the scientific literature showed an increasing trend in the research of thermal energy storage integrated to the building sector, it was only in recent years that this concept was extended to the built environment, which includes residential and non-residential buildings, districts, and urban networks. This paper provides a comprehensive review and classification of thermal energy storage technologies applied in the built environment considering the trends and the future perspective of the past and current research. This work was partially funded by the Ministerio de Ciencia, Innovación y Universidades de España (RTI2018-093849-B-C31 - MCIU/AEI/FEDER, UE) and by 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 GREiA (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 workshop brought together a selection of H2020 EU-funded projects involving experts from the biomass, geothermal, solar thermal, and heat pump sectors to discuss a common strategy for increasing the use of renewable energy technologies for heating and cooling for buildings and industry.

Thermal energy storage (TES) tanks for cold storage can be used for peak load shaving. This paper presents and evaluates a mathematical model where a TES tank is filled with commercial phase change material (PCM) flat slabs. The 2D model is used for simulating the outlet temperature of the heat transfer fluid, and also the heat transfer rate during the discharging process. The study includes the use of an approximation of the PCM specific heat (cPCM;old) which corresponds to the parameter calculated in the previous iteration of the implicit finite difference method. Thus, an evaluation of the different model parameters is performed, based on the comparison between the computational time and accuracy of the different simulations. Moreover, the uncertainties in different input variables are also analysed in order to find out which variable should be known more accurately. The results show that using the approximated parameter cPCM;old is a good solution for reducing the computational time despite a slight error increase in the case of using small time step in the simulation. Moreover, the inlet HTF temperature, and melting temperature, density and specific heat of the PCM are the main parameters to take into account in terms of uncertainty variables evaluation. The research leading to these results has received funding from the [EuropeanCommunity’s] Seventh Framework Programme([FP7/ 2007-2013] [FP7/2007-2011])under grant agreementn_262285.The work was partially funded by the Spanish Government (ENE2011- 22722, ENE2011-28269-C03-01 and ULLE10-4E-1305). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2009 SFR 534).

The adoption of thermal energy storage (TES) systems based on phase change material (PCM) remains limited by their low thermal conductivity, which restricts power density. Existing heat transfer enhancement techniques are often costly or come with significant drawbacks, leaving a gap for an effective and affordable solution. This study highlights metal wool as a promising alternative, offering low cost, ease of application, and retrofitting potential. While previous experiments demonstrated substantial improvements in power density using copper wool, a comprehensive numerical model to further optimize this technique is presented here. The model, incorporating CFD simulations and uncertainty analysis, was validated for bulk PCM and two copper wool-PCM composites before being extended to a wool material analysis. First, possible alternatives to copper as wool material were tested, highlighting aluminum as a viable candidate. Then, the proposed composite was found to match the discharging performance of a PCM with an effective thermal conductivity of 2.5 W/mK, a value rarely achieved by conventional enhancement techniques. Additionally, a techno-economic comparison revealed that copper wool delivered a 14.7-fold increase in thermal conductivity relative to liquid PCM at ¿6 per kg of PCM additivated¿a performance unmet by metal foams and nanocomposites. These findings confirm metal wool as a viable cost-effective and high-performance solution for improving TES systems, partially bridging the gap between efficiency and affordability. A.R. and E.C. acknowledge funding under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3—Call for tender No. 1561 of 11.10.2022 of Ministero dell’Università e della Ricerca (MUR); funded by the European Union—NextGenerationEU. This work was partially funded by the Ministerio de Ciencia e Innovacion’ - Agencia Estatal de Investigacion’ (AEI) (PID2021-123511OB-C31-MCIN/AEI/10.13039/501100011033/ FEDER, UE and RED2022-134219-T). This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Department de Recerca i Universitats of the Catalan Government for the quality accreditation given to their research group (2021 SGR 01615). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This paper is part of the RYC2023-044196-I, funded by MCIU/AEI/ 10.13039/501100011033 and FSE+. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101036910

Abstract A heat pump coupled to thermal energy storage (TES) tanks is experimentally tested under simulated summer conditions and the results are presented in this paper. The cold TES tank is used for shifting the cooling load of a small house-like structure. The study evaluates the thermal behaviour of the TES tank for cold storage and the application of the system for space cooling. For the analysis, two different configurations of the tanks are compared: a water tank and a PCM tank. The PCM tank is filled with a commercial macro-encapsulated PCM, which has a phase change temperature of 10 °C. The results point out that the PCM tank is able to supply 14.5% more cold and to maintain the indoor temperature within comfort 20.65% longer than the water tank. However, it needs 4.55 times longer to charge the tank.