Sorption Thermal Energy Storage Research Articles

Sorption thermal battery with solar powered absorption chiller for various building cooling applications

In the proposed sorption thermal energy storage (STES) system, the thermal energy storage (TES) tanks are integrated with solar assisted-absorption chiller (AC) to perform extended operation while matching the incompatibility of time gap between the renewable energy heat source and cooling demand of the building. In this study, the operating characteristics of sorption thermal battery (STB) at discharging process and storage capacity of STES charging process are studied. The feasibility study is conducted for four different types of buildings (hotel, hospital, single-family house, and office) to investigate the optimized discharging cooling capacity of STB and the optimized TES ratio. Under the condition of the 200 kWh of the building cooling load and cooling area of 181.63 m2, the most effectively meeting the demand is shown in the hotel, in which STES responds to 78.1 % of the cooling demand with 7.5 kW discharging cooling capacity of STB and 55 % charging the storage capacity of the STES system. The optimum energy storage density is 68.2 kWh/m3 and coefficient of performance is estimated of 0.41. The optimized STES can meet the cooling demand as much as 67.4 % for the hospital and 26.9 % for the single-family house. The office doesn’t require to apply the STES due to the absence of the cooling load at discharging period.

Exploration adsorption characteristics of zeolite 13X depending on humidity and flow rate in sorption thermal energy storage applications

Sorption thermal energy storage (STES) systems utilizing zeolite 13X present a promising solution to pressing global energy challenges. In this study, we explore the influence of absolute humidity and flow rate on the heat release process within a STES system, with a focus on local and overall performance considering temperature profile, degree of adsorption reaction, and average thermal power. A numerical model has been developed to investigate the adsorption kinetics of zeolite 13X and water, which is validated through experiments on pressure drop and transient temperature changes. In this study, we introduce P(%), a novel factor providing a holistic perspective of the adsorption process throughout the reactor. Through the analysis of P(%), we elucidate the link between the adsorption reaction, local heat transfer characteristics, and average thermal power within the reactor. Our findings reveal that increasing absolute humidity and flow rate accelerates the adsorption reaction of zeolite, leading to reduced discharge time. Our findings indicate that the adsorption reaction rate significantly decreases when P(%) approaches 95%. It is noteworthy, however, that the specific threshold of P(%) can vary based on the adsorbent type or reactor design. Despite this, P(%) can be utilized as a factor to establish the criteria for optimal control of STES. This research provides a guideline for optimum operational control and reactor design of STES systems.

Optimal control of a solar-driven seasonal sorption storage system through deep reinforcement learning

Deep reinforcement learning (DRL) has demonstrated its effectiveness in the control of energy systems, although it has not yet been applied to sorption thermal energy storage (TES) systems. The operation of sorption TES systems is notably more complicated compared to other TES variants. The discharge of a sorption TES occurs at a particular desorption and evaporation temperature. Achieving a continuous and efficient discharge of a sorption TES is a challenging control task if heat required at the evaporator is obtained from the sun or the environment. Its operation is especially complicated during winter, because of the limited availability of solar irradiation and low ambient temperatures. Thus, this study analyzes for first time in the literature the competitiveness of deep reinforcement learning to control a solar-driven seasonal sorption TES system and compares it against traditional optimized rule-based control strategy. The system, located in Central Europe, supplied domestic hot water and space heating to a single-family house. Two DRL models were developed and trained to operate the system under two different sets of data: 120 winter consecutive days and 60 winter non-consecutive days. The results showed that the DRL control strategy reduced the system operational costs by 28% in a 60 winter days scenario. For a 120 winter days scenario, the operational cost savings decreased to 13% because the smart control performed worst once the sorption TES was fully discharged. These results were derived from a four-year validation data set, bolstering their robustness. The study demonstrates the successful application of DRL in controlling a solar-driven seasonal sorption TES system, yielding considerable economic savings compared to an RBC strategy. Subsequent work will consist of implementing the smart control strategy at prototype level to assess its performance.

Effect of charging operating conditions on open zeolite/water vapor sorption thermal energy storage system

Sorption thermal energy storage (STES) is one of the most promising solutions to realize inter-seasonal thermal energy storage for building heating. However, the analysis of charging operation parameters on the thermal energy storage performance of STES system is insufficient. In this paper, a STES experimental bench using zeolite 4A/water vapor as the sorption working pairs was built, and the charging/discharging experiments were conducted. The thermal energy chain during the full charging-discharging process was analyzed. The experimental results indicated that approximately 60% of the thermal energy provided by the heater was directly lost through the reactor outlet in the charging process, which seriously hindered the improvement of the thermal energy storage performance of the STES system, such as the coefficient of performance (COP). In addition, the influence of charging conditions on the thermal energy storage performance of the system was also investigated. Both the improvement of charging temperature and the reduction of charging air humidity are beneficial to enhancing the thermal energy storage performance of the STES system. When the charging temperature was 150 °C, the energy storage density of zeolite reached a maximum of 251 kWh/m3. The COP of system reduced by 28% when the relative humidity of charging air rose from 20% to 70%. The effect of the volume flow rate of charging air on the thermal energy storage performance of the system is insignificant. The COP of system maintained around 0.212 at different charging air volume flow rates.

Sorption Thermal Energy Storage Performance of Nanoporous Metal–Organic Frameworks and Covalent Organic Frameworks by Grand Canonical Monte Carlo Simulations

Sorption Thermal Energy Storage Performance of Nanoporous Metal–Organic Frameworks and Covalent Organic Frameworks by Grand Canonical Monte Carlo Simulations

Performance of sorption thermal energy storage in zeolite bed reactors: Analytical solution and experiment

Sorption thermal energy storage (STES) has the advantage of high energy storage density and low heat loss, which has been considered as one of the promising solutions to achieve carbon neutrality in buildings. An insight into the thermal energy storage performance of reactors enables the optimization of STES systems. In addition, the analytical solution is concise and understandable in physical significance. In the present work, the perturbation theory was introduced to derive the analytical solutions for the fluid and solid temperatures in the reactor during the discharging process. Subsequently, a zeolite 13X STES system was built to conduct charging and discharging experiments. Based on the derived analytical solution, the fluid temperature at different axial positions in the reactor and energy storage density (ED) of zeolite were calculated and compared with the measured data. The results showed that there was a good agreement between the experimental test and the analytical solution, in which the maximum deviation of the energy storage density was less than 4 %. The analytical solution could obtain specific functional expressions for STES performance parameter of ED and further receive the results quickly.

Experimental evaluation of a hybrid solar dryer with flexible open sorption thermal energy storage unit on demand for burdock root drying

Solar drying represents an attractive way to implement an efficient and green development strategy. The viability of open sorption thermal energy storage (OSTES) can compensate for the inherent shortcomings of intermittency and instability of solar energy for ensuring the continuity of the drying process. Nevertheless, the existing solar-powered OSTES technologies only allow a batch mode while being severely restricted by sunlight's availability, thereby heavily limiting the flexibility in managing OSTES on demand. Herein, a novel proof-of-concept that a standalone solar dryer integrated with a reversible solid-gas OSTES unit is presented. Using in situ electrothermal heating (in situ ETH) could rapidly release adsorbed water of activated carbon fibers (ACFs) in an energy-efficient manner to achieve a charging process with faster kinetics. Applying electrical power by a photovoltaic (PV) module, particularly during sunlight-absent or insufficient time, allowed multiple OSTES cycles to proceed. Moreover, ACFs cylindrical cartridges can be flexibly interconnected in either series or parallel, forming universal assemblies with well-controlled in situ ETH capacity. The mass storage density of ACFs with a water sorption capacity of 570 mg/g is 0.24 kW·h·kg-1. The desorption efficiencies of ACFs are higher than 90%, corresponding to 0.057 kW·h maximum energy consumption. The resulting prototype can diminish the fluctuation of air humidity along the night and provide a relatively steady and lower air humidity for the drying chamber. The energy-exergy and environment analysis of the drying section for both setups are estimated, respectively.

Optimizing the discharge process of a seasonal sorption storage system by means of design and control approach

Sorption thermal energy storage systems have higher energy densities and low long-term thermal losses compared to traditional energy storage technologies, which makes them very attractive for seasonal heat storage application. Although they have a lot of potential at material level, its operation and system implementation for residential application requires further study. The performance of a seasonal sorption thermal energy storage system strongly depends on the discharging process during the cold season. The present study analysed through numerical simulations different scenarios to enhance the thermal performance of a solar-driven seasonal water-based sorption storage, which supplied space heating and domestic hot water to a single-family house in a cold climate region. All studied scenarios were analysed under optimal control policy. The results indicated that the sorption storage could increase by 9 % its energy density if conservative and constant discharging temperature set points are considered, due to fewer interruptions during the discharge. The energy density of the sorption storage driven by solar energy was highly impacted by the weather conditions, and by the type and availability of low-temperature heat source. Indeed, the energy density of the sorption storage increased by 22 % using a water tank to assist the evaporator of the sorption storage, instead of a latent storage tank. The use of a dry-heater to assist the evaporator with environmental heat was not suitable for the climate studied due to the low hours of operation. The sorption storage system composed of 20 modules of LiCl-silica gel could obtain an energy density and a COP of 139 kWh/m3 and 0.39, respectively, if a constant low-temperature heat source (i.e, geothermal or waste energy) was available.

Experimental and numerical investigation of multistage sorption energy storage system

In this paper, thermal energy storage is utilized to store heat from solar energy and also use waste heat to counterbalance the demand and supply of energy. A laboratory multistage closed sorption thermal energy storage (STES) unit is designed and tested to study the performance of a cascade sorption system. The experimental unit consists of three sorbent reactors, an ammonia cycle, and an oil cycle. Composite sorbents namely, MnCl₂, CaCl₂, and Nh₄Cl are used with ammonia as sorbate. Expanded natural graphite (ENG) is mixed with sorbents to increase the thermal conductivity and improve the mass transfer performance of sorbents. Further, a computational fluid dynamic model using COMSOL Multiphysics is built to study the performance of triple, double, and single closed STES systems. For the triple experimental STES system, a charging temperature up to 155 °C is used. At Nh3 pressure of 7.5 bar, the discharging temperatures are found to be 132.9 °C, 99.1 °C, and 60.3 °C for MnCl₂-ENG , CaCl₂-ENG , and Nh₄Cl-ENG composite sorbents, respectively, while a total energy storage density (ESD) of 3474.28 kJ/kgsalt has been achieved. For a double experimental STES system, a charging temperature up to 105 °C is used. Discharging temperatures are found to be 95.3 °C and 60.1 °C for CaCl₂-ENG , and Nh₄Cl-ENG composite sorbents, respectively, and a total ESD of 2471.94 kJ/kgsalt is achieved at Nh3 pressure of 7 bar. A parametric study is carried out to study the effect of different parameters on the performance of STES system at different arrangements. Increasing the inlet oil temperature during discharge results in a reduction of total ESD. For the specified design condition, the optimum oil mass flow rate is found to be 0.04 kg/s to achieve the highest ESD.

A novel passive polymer-sorbent thermal battery for low-temperature energy applications: A numerical feasibility study

Sorption thermal energy storage (STES) systems offer great potential for meeting the growing energy needs and increasing the use of renewable energy resources. However, the complexity and large-scale of current STES technologies lead to relatively low-efficiency systems, severely limiting their widespread implementation. To address this challenge, this study presents a novel and compact smart-polymer sorbent (SPS) thermal battery with passive material-enabled mechanisms for controlled low-temperature thermal energy storage applications. A numerical model is established to investigate the coupled heat and mass transport processes underlying the working behavior of the SPS battery. It is also used to reveal the interdependence of the two processes and the limiting factors for the battery's thermal performance. The heating performance of several SPS battery designs was studied as an example, focusing on their application for cold environment thermal protection. Moreover, the influence of various design parameters was examined, including sorbent selection, void fraction, relative humidity, gate thickness, and gate-to-sorbent area, along with their implications to the coupled mass-heat transport processes. The results revealed that diffusion-based mass transport is the limiting process affecting the SPS battery thermal performance. The numerical simulation results also indicated that the sorbent selection should consider their low recharge temperature (40 °C–100 °C) and less pronounced temperature-dependent adsorption behavior to maximize the heating performance of the SPS battery. In addition, the SPS battery heating efficiency could be enhanced by increasing the sorbent void fraction to 0.35, relative humidity (RH) to 40 %, and gate-to-sorbent area to 60 % while decreasing the gate thickness to 0.1 μm effectively, which facilitate the diffusion-controlled mass transport process. Lastly, a single layer SPS battery is beneficial for thermal regulation at low temperatures; however, using distributed battery designs had a significant thermal performance enhancement benefit of 90 % compared to the single layer design. Hence, our study reveals the complex coupling effects of the heat and mass transport processes within the proposed SPS battery and provides insights and guidance (e.g., materials selections and SPS design) for engineering emergent small-scale passive STES applications.

Thermal performance assessment and control optimization of a solar-driven seasonal sorption storage system for residential application

The present paper analyzed the thermal performance and control optimization of a solar system based on seasonal sorption storage for domestic applications. The system control, which could choose between 41 operational modes, was optimized based on operational costs and maximization of sorption system use. The system was composed by 17.5 m2 of evacuated tube collectors, 3.6 m3 of composite sorbents based on lithium chloride and a stratified water tank. High efficiency of a sorption storage system was obtained when continuous charges or discharges occur, which, in this study, depended on weather conditions (ambient temperature and solar irradiation). The operational economic benefits were maximized using a sorption system with 9% less capacity and, therefore, less storage volume. The sorption thermal energy storage system obtained energy densities of 90 and 106 kWh/m3. The whole system could supply 35% of the total thermal demand of a single family house in Nuremberg. The study concluded that the control optimization of a seasonal sorption system is a key factor to make the technology competitive, define its optimal size and, therefore, maximize its energy density in further designs.

Experimental analysis of a high-performance open sorption thermal storage system with absorption-crystallization-adsorption processes

Sorption thermal energy storage is one of the promising solar thermal energy storage considering its long-term storage ability. Since the common sorption thermal storage suffers from low sorption capacity, a high energy storage density enhancement mechanism is always essential for a cost-effective and compact storage system. With three-phase sorption thermal storage, high energy storage density from the crystallization sorption process can be achieved. However, such a sorption process brings significant challenges, including crystal blockage issues in absorption system or solution leakage handling problems in adsorption system, which need to be resolved. Here, we showed a high-performance sorption thermal storage that can attain high energy storage density via a full liquid-to-solid state sorption process. Such a process is achieved by adopting moist air as heat and mass transfer media, which enables liquid absorption, crystallization, and solid adsorption in a simple configuration simultaneously. The lab-scale model achieved high energy storage density in the range of 333–405 kWh/m3 resulting from the heat of absorption and crystallization of LiCl, which is the record value for liquid absorption systems. The energy storage density obtained from the dual liquid and solid sorption processes is enhanced by 278 % compared with that of the conventional cycle at 70 % RH (relative humidity) and temperature lift of 10 °C. With simple construction and high energy storage density, the proposed system has great potential in real applications.

Sorption characteristics of K2CO3-based thermochemical material for thermal energy storage

The selection of a suitable thermochemical material (TCM) is essential for sorption thermal energy storage (TES) systems. Among many TCMs, K2CO3 is considered a promising candidate. A major challenge in the application of pure K2CO3 for TES is the low sorption rate, which can be improved effectively by employing a porous matrix. In this study, we prepared a K2CO3-based composite with a salt content of 85.7% by using a solution impregnation method. Immediately afterwards, its sorption characteristics were investigated at different thicknesses, morphologies and working conditions. The result showed that the sorption rate of the K2CO3-based composite is more than four times higher than that of pure K2CO3, and the mass and volume heat storage densities are approximately 608.5 kJ/kg and 214.7 kWh/m3, respectively, indicating that this composite may be competitive in TES applications.

Thermophysical characterization of magnesium chloride and its application in open sorption thermal energy storage system

Sorption thermal energy storage is considered as a promising method to reduce energy consumption of building heating. MgCl 2 ⋅6H 2 O could be a good candidate due to its high energy storage density. This paper first summarizes phase equilibrium lines of four MgCl 2 hydration/dehydration processes to evaluate reaction enthalpy and entropy variation. Thermal diffusivities and specific heat of MgCl 2 , MgCl 2 ·6H 2 O and MgCl 2 -ENG composite are determined which are compared with common counterparts of MgSO 4 ·7H 2 O and MgSO 4 -ENG. Then the performance of open sorption thermal energy storage system is assessed in terms of various sorbents. Results show that the obtained thermal conductivities of MgCl 2 ·6H 2 O range from 0.15 W m −1 K −1 to 0.96 W m −1 K −1 at the temperature range of 15–70 °C while thermal conductivities of MgSO 4 ·7H 2 O range between 0.29 W m −1 K −1 and 0.68 W m −1 K −1 at 20–45 °C. At 20 °C testing temperature, thermal conductivities of composite MgCl 2 are improved which range between 0.97 W m −1 K −1 and 2.92 W m −1 K −1 under the condition of 500–900 kg m −3 density and 67–80% mass ratio of salt. Besides, MgCl 2 composite is preferable for open sorption thermal energy storage which could achieve stable heat output for more than 4 h under the conditions of 15.4 °C inlet temperature, 40% relative humidity and 0.26 m s −1 air velocity. • Light flash method proves to be suitable to measure thermal diffusivity of hydrates. •Thermal conductivity of MgCl 2 ·6H 2 O is between 0.15 W m −1 K −1 and 0.96 W m −1 K −1 . •Thermal conductivity of composite MgCl 2 ranges from 0.97 W m −1 K −1 to 2.92 W m −1 K −1 . •MgCl 2 -ENG composite is a desirable candidate for open sorption thermal energy storage.

Assessing the suitability of alkali-activated metakaolin geopolymer for thermochemical heat storage

This study investigates the suitability and potentials of using alkali-activated metakaolin geopolymers as sustainable low-cost thermochemical heat storage materials via water sorption and/or hydration reactions. Four different alkali-activated metakaolin geopolymer formulations were assessed. The cyclic water sorption capacity and moisture diffusion coefficients were assessed via two continuous water vapor sorption/desorption cycles using the dynamic water vapor sorption (DVS), proving the regeneration ability of geopolymers for sorption thermal energy storage. The thermochemical properties of geopolymers, including the dehydration enthalpy and activation energy, were determined. For the amorphous sodium aluminosilicate hydrate gel (N-A-S-H) with bulk Si/Al ratio of 1.5, the mass and volumetric energy storage capacity of 827.9 J/ghydrate sample and 350 kW h/m3 were achieved, with a charging temperature of around 120 °C. The outcomes of this study suggest that alkali-activated metakaolin geopolymers have the potential to be used for both low-temperature water sorption thermal energy storage and medium temperature hydration/dehydration thermochemical energy storage. The energy storage performances of metakaolin geopolymers are closely related to their aluminosilicate framework structures and surface textural properties. The partial crystallisation of the amorphous N(K)-A-S-H gel, resulting in the formation of micropores, which does not seem to affect the maximal water uptake but increases the proportion of the chemically bound water. The presence of the amorphous mesoporous aluminosilicate gel N(K)-A-S-H gel in geopolymers leads to desorption hysteresis at relative humidity higher than 30 %. Further optimisation of the synthesis approach, aluminosilicate framework structures, micro and mesopore structures will be required to optimise their overall thermal energy storage performances.

Hybrid thermochemical sorption seasonal storage for ultra-low temperature solar energy utilization

The effective upgrading and utilization of low or ultra-low temperature heat (below 50 °C) could meet a significant fraction of space and water heating loads. To fulfill this goal, hybrid sorption thermal energy storage (TES) to recover ultra-low grade solar heat below 50 °C is investigated, aiming to address the issue of winter heating in severe cold regions. A water-based solar photovoltaic-thermal (PVT) system is integrated to provide heat and electricity for a sorption TES system. Composite ammonium chloride is used for thermodynamic prediction in terms of weather conditions in different places. It is demonstrated that when water temperatures increase from 31.4 °C to 51.2 °C, energy efficiencies of hybrid sorption TES system under theoretical and selected working conditions in Hangzhou increase from 0.52 to 0.57 and from 0.33 to 0.38, respectively. The overall exergy efficiencies of hybrid TES with the PVT system under theoretical and selected working conditions increase from 0.059 to 0.062 and from 0.046 to 0.057, respectively. The overall exergy efficiency of the hybrid system in Helsinki is 0.55, which is 4.3% higher than those in Hangzhou. One remarkable fact is that hybrid sorption TES integrated with the PVT system is quite promising especially for severe cold regions.

Artificial Neural Network Simulation of Energetic Performance for Sorption Thermal Energy Storage Reactors

Sorption thermal heat storage is a promising solution to improve the development of renewable energies and to promote a rational use of energy both for industry and households. These systems store thermal energy through physico-chemical sorption/desorption reactions that are also termed hydration/dehydration. Their introduction to the market requires to assess their energy performances, usually analysed by numerical simulation of the overall system. To address this, physical models are commonly developed and used. However, simulation based on such models are time-consuming which does not allow their use for yearly simulations. Artificial neural network (ANN)-based models, which are known for their computational efficiency, may overcome this issue. Therefore, the main objective of this study is to investigate the use of an ANN model to simulate a sorption heat storage system, instead of using a physical model. The neural network is trained using experimental results in order to evaluate this approach on actual systems. By using a recurrent neural network (RNN) and the Deep Learning Toolbox in MATLAB, a good accuracy is reached, and the predicted results are close to the experimental results. The root mean squared error for the prediction of the temperature difference during the thermal energy storage process is less than 3K for both hydration and dehydration, the maximal temperature difference being, respectively, about 90K and 40K.

Multi-functional three-phase sorption solar thermal energy storage cycles for cooling, heating, and heat transformer

Abstract Thermal energy storage based on sorption method is attractive in view of energy storage density, storage period, and flexibility. Three-phase sorption thermal energy storage is advantageous from high energy storage density, but its temperature lift is low. Besides, further energy storage density enhancement is needed to make the storage system more compact. In this paper, multi-functional three-phase sorption thermal energy storage cycles are proposed to achieve higher temperature lift and energy storage density simultaneously, in which different applications can be evident including interseasonal heating, combined cooling and heating in summer, and heat transformer in summer and winter. The performance of the proposed cycles for three operating modes is evaluated analytically with a working pair of LiCl/H2O, due to its high absorption and crystallization enthalpy. Results showed that the multi-functional three-phase sorption thermal energy storage cycles obtained a temperature lift of 65°C and an energy storage density up to 1307 Wh/kg, which cannot be realized with a conventional three-phase cycle. Moreover, combined cold and heat storages at 15°C and 60°C, respectively, and discharging temperature more than 100°C are achieved. With these proposed cycles, a wider range of applications could be expected for three-phase sorption thermal energy storage.

Development of a sorption thermal energy storage to support the thermal management of hybrid vehicles

Development of a sorption thermal energy storage to support the thermal management of hybrid vehicles

Development of a sorption thermal energy storage to support the thermal management of hybrid vehicles

Development of a sorption thermal energy storage to support the thermal management of hybrid vehicles