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Abstract The energy consumption for cooling takes up 50% of all the consumed final energy in Europe, which still highly depends on the utilization of fossil fuels. Thus, it is required to propose and develop new technologies for cooling driven by renewable energy. Also, thermal energy storage is an emerging technology to relocate intermittent low-grade heat source, like solar thermal energy and industrial waste heat as well as to exploit off-peak electricity, for cooling applications. This review aims to summarize the recent advances in thermally driven cooling and cold storage technologies, focusing on the formation and fabrication of adopted composites materials, including sorption materials, phase change materials, and slurries. Herein, first the classifications, selection criteria, and properties for these three types of materials is discussed. Then, the application potentials of all the materials are prospected in terms of economic analysis and sustainability.

In this paper, cement mortar IN200 integrated with solid–solid PlusIce X25 commercial PCM was fully characterized for the first time via experimental tests and numerical simulations. An experimental setup was designed and built to evaluate the thermal performance of the composite. Experimental results confirmed the expected advantages of the PCM-loaded plaster in terms of inner surface temperature, inbound heat flux reduction, and the enhanced damping effect on the average temperature. The experimental results were used to validate and calibrate a finite element model implemented in COMSOL Multiphysics® 5.6. The model was adopted to carry out a parametric analysis assessing the influence of PCM mass fraction, phase transition temperature, and PCM mortar thickness. The composite thickness was the most influential parameter, resulting in an energy saving increase from 3.29% to 72.72% as it was increased from 10 mm to 30 mm. Moreover, the model was used in a set of dynamic simulations, reproducing real Mediterranean climatic conditions to capture the transition process for a long period in buildings. The PCM mortar located on the interior side exhibited the highest reduction in both heat flux and inner surface temperature, representing a simple approach to achieving the best thermal comfort conditions.

This study focuses on the development and testing under lab-controlled conditions of a hybrid sensible–latent thermal energy storage (TES) system for domestic hot water (DHW) provision in residential buildings. The TES system’s design is based, for the first time in the literature, on a commercial tank-in-tank architecture integrating a macro-encapsulated commercial phase change material (PCM) inside the external tank to guarantee the safe provision of DHW and increase overall energy storage density at a reasonable cost. The PCM is a salt hydrate with a nominal melting temperature of 58 °C. The overall tank-in-tank TES volume is about 540 dm3. Almost one tenth of this volume is occupied by the PCM macro-capsules. The developed TES system was comparatively tested against the same configuration operated as a sensible TES. The obtained results showed the ability of the PCM to increase the thermal inertia inside the external tank, thus guaranteeing the quite stable provision of heat to the integral DHW tank during the stand-by periods. This effect was confirmed by the PCM’s ability to achieve an energy storage capacity up to 16% higher than the reference sensible TES system.

Abstract The lack of robust and low-cost sorbent materials still represents a formidable technological barrier for long-term storage of (renewable) thermal energy and more generally for Adsorptive Heat Transformations—AHT. In this work, we introduce a novel approach for synthesizing cement-based composite sorbent materials. In fact, considering the number of available hygrosopic salts that can be accommodated into a cementitious matrix—whose morphological properties can be also fine-tuned—the new proposed in situ synthesis paves the way to the generation of an entire new class of possible sorbents for AHT. Here, solely focusing on magnesium sulfate in a class G cement matrix, we show preliminary morphological, mechanical and calorimetric characterization of sub-optimal material samples. Our analysis enables us to theoretically estimate one of the most important figures of merit for the considered applications, namely the energy density which was found to range within 0.088–0.2 GJ/m3 (for the best tested sample) under reasonable operating conditions for space heating applications and temperate climate. The above estimates are found to be lower than other composite materials in the literature. Nonetheless, although no special material optimization has been implemented, our samples already compare favourably with most of the known materials in terms of specific cost of stored energy. Finally, an interesting aspect is found in the ageing tests under water sorption-desorption cycling, where a negligible variation in the adsorption capability is demonstrated after over one-hundred cycles.

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.

Phase change slurries (PCSs) have great potential as both a heat transfer fluid and an energy storage medium for cooling processes, cold energy storage, and cold energy transportation due to desirable thermophysical properties. One of the major benefits of PCSs compared to pure phase change materials is their fluidity, thus making them cooled or heated by a heat exchanger, pumped through pipes, discharged, and stored directly in a thermal energy storage tank. The use of encapsulated phase change slurries and gas hydrate slurry has thus attracted considerable interest as reflected in the literature with a rising number of publications and institutions involved in the area. The use of bibliometric techniques has found a recent interest in the literature to define the progress of different scientific topics and inspire researchers to identify novelties. In this paper, bibliometric analysis and a detailed systematic review are carried out to show the state-of-the-art development of PCSs for cooling applications. Research gaps and hotspots are identified to help define future perspectives on this topic.

Solar thermal energy coupled to a seasonal sorption storage system stands as an alternative to fossil fuels to supply residential thermal energy demand in climates where solar energy availability is high in summer and low in winter, matching with a high space heating demand. Sorption storage systems usually have a high dependency on weather conditions (ambient temperature and solar irradiation). Therefore, in this study, the technical performance of a solar-driven seasonal sorption storage system, using an innovative composite sorbent and water as working fluid, was studied under three European climates, represented by: Paris, Munich, and Stockholm. All scenarios analyses were simulation-based under optimal system control, which allowed to maximize the system competitiveness by minimizing the system operational costs. The optimal scenarios profit from just 91, 82 and 76% of the total sorption system capacity, for Paris, Munich, and Stockholm, respectively. That means that an optimal control can identify the optimal sorption storage size for each location and avoid oversizing in future systems, which furthermore involves higher investment costs. The best coefficient of performance was obtained for Stockholm (0.31), despite having the coldest climate. The sorption system was able to work at minimum temperatures of −15 °C, showing independence from ambient temperature during its discharge. In conclusion, a seasonal sorption system based on selective water materials is suitable to be integrated into a single-family house in climates of central and northern Europe as long as an optimal control based on weather conditions, thermal demand, and system state is considered.

In this study, the development and testing of a hybrid thermal energy storage (TES) including phase change material (PCM) macro-capsules inside a vertical sensible tank is presented. The storage was specifically developed for delivering hot water on board of ships. Accordingly, a commercial PCM was selected and tested. Subsequently, the hybrid TES was designed and tested under mimicked boundary conditions at lab scale, showing the possibility of increasing the volumetric energy storage density up to 30% compared to the sensible configuration. On this basis, two numerical models were developed: a detailed one, implemented in a Fluent environment, aiming at investigating the main parameters affecting the heat transfer efficiency inside the TES and a second one, implemented in an ESP-r environment to simulate the TES as a component to be implemented inside a more complex system, thus helping its accurate design and operation through a reliable modelling phase. Both models were satisfactorily validated against the experimental results, thus being made available for future investigations and design optimization.

The LiCl-based heat storage system exhibits a high-energy density, making it an attractive and one of the most investigated candidates for low-temperature heat storage applications. Nevertheless, lithium chloride, due to its hygroscopic nature, incurs the phenomenon of deliquescence, which causes some operational challenges, such as agglomeration, corrosion, and swelling problems during hydration/dehydration cycles. Here, we propose a composite material based on silicone vapor-permeable foam filled with the salt hydrate, hereafter named LiCl-PDMS, aiming at confining the salt in a matrix to prevent deliquescence-related issues but without inhibiting the vapour flow. In particular, the structural and morphological modification during hydration/dehydration cycles is investigated on the composite foam, which is prepared with a salt content of 40 wt.%. A characterization protocol coupling temperature scanned X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM) analysis is established. The operando conditions of the dehydration/hydration cycle were reproduced while structural and morphological characterizations were performed, allowing for the evaluation of the interaction between the salt and the water vapor environment in the confined silicon matrix. The material energy density was also measured with a customized coupled thermogravimetric/differential scanning calorimetric analysis (TG/DSC). The results show an effective embedding of the material, which limits the salt solution release when overhydrated. Additionally, the flexibility of the matrix allows for the volume shrinkage/expansion of the salt caused by the cyclic dehydration/hydration reactions without any damages to the foam structure. The LiCl-PDMS foam has an energy density of 1854 kJ/kg or 323 kWh/m3, thus making it a competitive candidate among other LiCl salt hydrate composites.

Abstract In the present work, adsorption performances of an innovative composite adsorber, based on SAPO-34-silicone composite macro-cellular foams, are reported. The choice of a foamed structure was assessed to improve the water vapor access towards the embedded zeolite keeping good adsorption heat pump dynamic performance. Depending on zeolite amount used as filler, zeolite/silicone foams evidenced a soft and open cell configuration (low zeolite content) or rigid and closed one (high zeolite content). Morphological analysis evidenced that the cellular structure of the foam is homogeneous and well distributed along the foam cross section. Adsorption tests showed that the adsorbent foamed samples have very effective adsorption capabilities indicating that the porous structure of the filled pure zeolite was not obstructed. SAPO-34 filler contributed actively, with an efficiency above 90%, to the adsorption performances of the composite foam. Starting from experimental equilibrium data, a simple thermodynamic analysis based on energy balances was carried out for air conditioning application. Results of the analysis demonstrated that foam technology can guarantee cooling COP up to 7% higher than that estimated for the typical adsorber solution based on loose adsorbent grains inside an aluminum finned-flat tube heat exchanger, which is very promising for practical application in adsorption heat pumps.

In order to reduce greenhouse gas emissions, current and future energy systems need to be made more efficient and sustainable. This change can be accomplished by increasing the penetration of renewable energy sources and using efficient technologies in energy generation systems. One way to improve the operation of the whole energy system is through the generation and end-use sector coupling. Power-to-heat energy conversion and storage technologies, in this view, are enabling technologies that can help in balancing and improving the efficiency of both thermal and electric grids. In the present paper, a comprehensive analysis of the role of heat pumps and thermal energy storage for sector coupling is presented. The main features of the analyzed technologies are presented in the context of smart electric grid, district heating and cooling and multi-carrier energy systems, and recent findings and developments are highlighted. Finally, the technical, social, and economic challenges in the adoption of investigated technologies are discussed.

A clear gap was identified in the literature regarding the in-depth evaluation of scaling up thermal energy storage components. To cover such a gap, a new methodological approach was developed and applied to a novel latent thermal energy storage module. The purpose of this paper is to identify some key aspects to be considered when scaling up the module from lab-scale to full-scale using different performance indicators calculated in both charge and discharge. Different normalization methods were applied to allow an appropriate comparison of the results at both scales. As a result of the scaling up, the theoretical energy storage capacity increases by 52% and 145%, the average charging power increases by 21% and 94%, while the average discharging power decreases by 16% but increases by 36% when mass and volume normalization methods are used, respectively. When normalization by the surface area of heat transfer is used, all of the above performance indicators decrease, especially the average discharging power, which decreases by 49%. Moreover, energy performance in charge and discharge decreases by 17% and 15%, respectively. However, efficiencies related to charging, discharging, and round-trip processes are practically not affected by the scaling up.

In the present paper, the numerical modeling of an innovative latent thermal energy storage unit, suitable for direct integration into the condenser or evaporator of a heat pump is presented. The Modelica language, in the Dymola environment, and TIL libraries were used for the development of a modular model, which is easily re-usable and adaptable to different configurations. Validation of the model was carried out using experimental data under different operating modes and it was subsequently used for the optimization of a design for charging and discharge. In particular, since the storage unit is made up of parallel channels for the heat transfer fluid, refrigerant, and phase change material, their number and distribution were changed to evaluate the effect on heat transfer performance.

The present work aims at the thermodynamic analysis of different working pairs in adsorption heat transformers (AdHT) for low-temperature waste heat upgrade in industrial processes. Two different AdHT configurations have been simulated, namely with and without heat recovery between the adsorbent beds. Ten working pairs, employing different adsorbent materials and four different refrigerants, have been compared at varying working boundary conditions. The effects of heat recovery and the presence of a temperature gradient for heat transfer between sinks/sources and the AdHT components have been analyzed. The achieved results demonstrate the possibility of increasing the overall performance when internal heat recovery is implemented. They also highlight the relevant role played by the existing temperature gradient between heat transfer fluids and components, that strongly affect the real operating cycle of the AdHT and thus its expected performance. Both extremely low, i.e., 40–50 °C, and low (i.e., 80 °C) waste heat source temperatures were investigated at variable ambient temperatures, evaluating the achievable COP and specific energy. The main results demonstrate that optimal performance can be achieved when 40–50 K of temperature difference between waste heat source and ambient temperature are guaranteed. Furthermore, composite sorbents demonstrated to be the most promising adsorbent materials for this application, given their high sorption capacity compared to pure adsorbents, which is reflected in much higher achievable specific energy.

With the aim of contributing to achieving the decarbonization of the energy sector, the environmental impact of an innovative system to produce heating and domestic hot water for heating demand-dominated climates is assessed is evaluated. The evaluation is conducted using the life cycle assessment (LCA) methodology and the ReCiPe and IPCC GWP indicators for the manufacturing and operation stages, and comparing the system to a reference one. Results show that the innovative system has a lower overall impact than the reference one. Moreover, a parametric study to evaluate the impact of the refrigerant is carried out, showing that the impact of the overall systems is not affected if the amount of refrigerant or the impact of refrigerant is increased.

In this study, the development and comparative characterization of different composite sorbents for thermal energy storage applications is reported. Two different applications were targeted, namely, low-temperature space heating (SH) and domestic hot water (DHW) provision. From a literature analysis, the most promising hygroscopic salts were selected for these conditions, being LiCl for SH and LiBr for DHW. Furthermore, two mesoporous silica gel matrixes and a macroporous vermiculite were acquired to prepare the composites. A complete characterization was performed by investigating the porous structure of the composites before and after impregnation, through N2 physisorption, as well as checking the phase composition of the composites at different temperatures through X-ray powder diffraction (XRD) analysis. Furthermore, sorption equilibrium curves were measured in water vapor atmosphere to evaluate the adsorption capacity of the samples and a detailed calorimetric analysis was carried out to evaluate the reaction evolution under real operating conditions as well as the sorption heat of each sample. The results demonstrated a slower reaction kinetic in the vermiculite-based composites, due to the larger size of salt grains embedded in the pores, while promising volumetric storage densities of 0.7 GJ/m3 and 0.4 GJ/m3 in silica gel-based composites were achieved for SH and DHW applications, respectively.

The need for innovative heating and cooling systems to decarbonize the building sector is widely recognized. It is especially important to increase the share of renewables at building level by maximizing self-consumption and reducing the primary energy demand. Accordingly, in the present paper, the results on a wide experimental campaign on a hybrid system are discussed. The system included a sorption module working as the topping cycle in a cascade configuration with a DC-driven vapor compression heat pump. A three-fluids heat exchanger with a phase change material (PCM), i.e., RT4 with nominal melting temperature of 4 °C, was installed on the evaporator side of the heat pump, for simultaneous operation as thermal storage and heat pumping purposes. The heat pump was connected to a DC-bus that included PV connection and electricity storage (batteries). Results showed that the energy efficiency of the heat pump in cascade operation was double compared to compression-only configuration and that, when simultaneously charging and discharging the latent storage in cascade configuration, no penalization in terms of efficiency compared to the compression-only configuration was measured. The self-sufficiency of the system was evaluated for three reference weeks in summer conditions of Athens climate and it was found that up to 100% of the electricity needed to drive the system could be self-produced for a modest cooling demand and up to 67% for the warmer conditions with high cooling demand.

Increasing the energy efficiency of residential and non-residential buildings is a crucial point towards the development of the sustainable cities of the future. To reach such a goal, the commonly employed intervention measures (for instance, on facades and glass) are not sufficient and efforts in reaching a fully renewable energy generation are mandatory. In this context, this paper discusses the applicability of a system with solar and biomass as the main energy sources in different climates for heating, cooling, domestic hot water and electricity generation in office buildings. The energy system includes solar thermal collectors with thermoelectric generators, a biomass boiler, a reversible heat pump/organic Rankine cycle and an adsorption chiller. The results showed that the system can operate with a share of renewables higher than 70% for all energy needs, with up to 80% of the overall energy demand supplied only by solar and biomass sources even in the northern locations.

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.

The thermal masses of components influence the performance of many adsorption heat pump systems. However, typically when experimental adsorption systems are reported, data on thermal mass are missing or incomplete. This work provides original measurements of the thermal masses for experimental sorption heat exchanger hardware. Much of this hardware was previously reported in the literature, but without detailed thermal mass data. The data reported in this work are the first values reported in the literature to thoroughly account for all thermal masses, including heat transfer fluid. The impact of thermal mass on system performance is also discussed, with detailed calculation left for future work. The degree to which heat transfer fluid contributes to overall effective thermal mass is also discussed, with detailed calculation left for future work. This work provides a framework for future reporting of experimental thermal masses. The utilization of this framework will enrich the data available for model validation and provide a more thorough accounting of adsorption heat pumps.

In this study, the definition of a new methodology for a preliminary evaluation of the working boundary conditions under which a seasonal thermal energy storage (STES) system operates is described. The approach starts by considering the building features as well as the reference heating system in terms of solar thermal collectors’ technology, ambient heat sinks/source, and space heating distribution systems employed. Furthermore, it is based on a deep climatic analysis of the place where the STES needs to be installed, to identify both winter and summer operating conditions. In particular, the STES energy density is evaluated considering different space heating demands covered by the STES (ranging from 10% up to 60%). The obtained results demonstrate that this approach allows for the careful estimation of the achievable STES density, which is varies significantly both with the space heating coverage guaranteed by the STES as well as with the ambient heat source/sink that is employed in the system. This confirms the need for careful preliminary analysis to avoid the overestimation of the STES material volume. The proposed approach was then applied for different climatic conditions (e.g., Germany and Sweden) and the volume of one of the most attractive composite sorbent materials reported in the literature, i.e., multi-wall carbon nanotubes (MWCNT)-LiCl, using water as the working fluid, needed for covering the variable space heating demand in a Nearly Zero Energy Building (NZEB) was calculated. In the case of Swedish buildings, it ranges from about 3.5 m3 when 10% of the space heating demand is provided by the STES, up to 11.1 m3 when 30% of the space heating demand is provided by the STES.

Salt hydrates, such as MgSO4∙7H2O, are considered attractive materials for thermal energy storage, thanks to their high theoretical storage density. However, pure salt hydrates present some challenges in real application due to agglomeration, corrosion and swelling problems during hydration/dehydration cycles. In order to overcome these limitations, a composite material based on silicone vapor-permeable foam filled with the salt hydrate is here presented. For its characterization, a real-time in situ environmental scanning electron microscopy (ESEM) investigation was carried out in controlled temperature and humidity conditions. The specific set-up was proposed as an innovative method in order to evaluate the morphological evolution of the composite material during the hydrating and dehydrating stages of the salt. The results evidenced an effective micro-thermal stability of the material. Furthermore, dehydration thermogravimetric/differential scanning calorimetric (TG/DSC) analysis confirmed the improved reactivity of the realized composite foam compared to pure MgSO4∙7H2O.