Low-temperature Thermal Storage Research Articles

Examination of Operational Methods for a Low-Temperature Aquifer Thermal Storage Air Conditioning System Based on Operational Performance and Considerations of Thermal Storage and Pumping Volume Balance

Aquifer Thermal Energy Storage (ATES) systems are garnering attention as high-efficiency air conditioning technologies that contribute to the realization of a carbon-neutral society. This study focuses on an ATES system constructed in Japan, characterized by its complex geological conditions and thin aquifer layers. Detailed actual performance data measured over four years are presented, and performance analysis results show that a COP of 5 was achieved for the overall building cooling and heating system. In addition, the study provides a detailed analysis of the imbalance in heat quantity, remaining heat storage, and other factors based on actual data, identifying operational issues and summarizing specific improvement measures. Finally, as a proposal for a sustainable operational method to balance the cumulative heat storage and pumping volume of cold and hot water, specific operational procedures are summarized, including setting the return water temperature for the next season based on the dimensionless average pumping temperature of the previous season, and a flowchart is presented. There is no prior research that shows such specific operational procedures, and this can be considered an important achievement of this study.

Multi-objective optimization of multi-energy complementary system based on cascade utilization of heat storage

A multi-energy complementary system driven by solar energy and central grid is proposed to supply electricity and cooling/heating, in which a dual-tank thermal storage system is integrated to achieve cascaded solar heat energy utilization. The system integrates parabolic trough solar collectors, high-temperature and low-temperature thermal storage tanks, and an organic Rankine cycle to form an operational loop. The low-temperature thermal storage tank drives an absorption heat pump independently. Excess photovoltaic power drives the ground source heat pump for heating/cooling. Three indicators are defined and compared to show the renewable energy penetration rate in the complementary system. A multi-objective optimization model considering economic performance and renewable energy rate is constructed to optimize the system configurations. Three sets of objective functions are compared through the optimization Pareto frontiers. Then, the TOPSIS method is employed to select the optimum configuration through setting different weights of optimization objectives. Compared with the reference system, the proposed multi-energy complementary system improves the energy, economic and environmental benefits by 59.21%, 24.27% and 11.31%, respectively. Through a variety of equipment (PV, ORC, AHP, TES), solar energy supplies 86.2% and 72.2% of total electricity and heat loads, respectively.

A multi-vector community energy system integrating a heating network, electricity grid and PV production to manage an electrified community

Electrification in energy supply–demand plays a critical role in domestic heating and road transport, delivering an electrified community to reduce carbon emissions. This solution, however, places a significant power demand increase on the distribution networks. To ensure the security of electricity supply, an efficient energy system and energy demand reduction are essential. In this paper, a multi-vector community energy system, applying an electrified heating network, electric vehicle smart charging, community-scale peak shaving and photovoltaic (PV) generation, is demonstrated in three models to manage an electrified community. Firstly, a heating network model, comprising a central ground source heat pump, low-temperature district heating system, electric heaters and thermal storage, is established to measure the optimum distribution temperature. Next, an electrified community model illustrates hourly electricity demands and performances of a community energy system, which is then used to identify the required degree of housing thermal efficiency improvement (i.e., heating demand reduction). The third model evaluates decentralised PV/storage units to maintain the power demand below a targeted power. Modelling results show that the demand ratio of domestic hot water to space heating determines the distribution temperature, which indicates the temperature is increasing with growing housing thermal efficiency. Moreover, the electrification of a community could increase the peak power demand on the highest demand day by over five times, converting heating demands into electricity directly. This significant peak demand can be possibly reduced to only a 33% increase by employing a community energy system. The model of PV/storage units is validated through a 12-week assessment. Ultimately, a modelling tool is developed by assembling the mentioned models, providing four pathways to attain electrification. Users can adjust specific parameters and database to align with the local conditions. The results indicate the requirements of building a community energy system and electricity demands in the highest consumption period.

Experiments on a novel metal hydride cartridge for hydrogen storage and low temperature thermal storage

Even though metal hydrides have been mainly studied for hydrogen storage, their applications can be extended to thermal energy storage by utilizing the exothermic and endothermic reactions during the hydride formation and decomposition processes, respectively. In this paper, a low temperature hydride, La0.75Ce0.25Ni5 is experimentally investigated for hydrogen storage and thermal energy storage applications. Heat and mass transfer characteristics of a novel scalable cartridge type reactor is studied at various heat transfer fluid temperatures and hydrogen supply pressures. Maximum hydrogen storage capacity of 1.38 wt% and a gravimetric thermal energy storage capacity of 127.01 kJ.kgMH-1 at about 70% efficiency were achieved. The energy storage capacity achieved during experiments is compared with the theoretically possible output by defining a performance index, namely, the energy storage effectiveness, and its maximum value was found to be 0.67 at 20 °C and 20 bar.

Review of Technologies and Recent Advances in Low-Temperature Sorption Thermal Storage Systems

Sorption thermochemical storage systems can store thermal energy for the long-term with minimum amount of losses. Their flexibility in working with sustainable energy sources further increases their importance vis-à-vis high levels of pollution from carbon-based energy forms. These storage systems can be utilized for cooling and heating purposes or shifting the peak load. This review provides a basic understanding of the technologies and critical factors involved in the performance of thermal energy storage (TES) systems. It is divided into four sections, namely materials for different sorption storage systems, recent advances in the absorption cycle, system configuration, and some prototypes and systems developed for sorption heat storage systems. Energy storage materials play a vital role in the system design, owing to their thermal and chemical properties. Materials for sorption storage systems are discussed in detail, with a new class of absorption materials, namely ionic liquids. It can be a potential candidate for thermal energy storage due to its substantial thermophysical properties which have not been utilized much. Recent developments in the absorption cycle and integration of the same within the storage systems are summarized. In addition, open and closed systems are discussed in the context of recent reactor designs and their critical issues. Finally, the last section summarizes some prototypes developed for sorption heat storage systems.

Experimental thermal study of a new PCM-concrete thermal storage block (PCM-CTSB)

Phase change material concrete as a new building envelope has been widely used in passive building energy conservation, but less research has been done for it as a heat storage block in an active low-temperature thermal storage system. To enhance the heat storage capacity of PCM-concrete, overcome the PCM leakage problem and reduce the cost of heat storage, clastic light shale ceramsite (CLSC) was used to absorb paraffin to prepare PCM-CLSC aggregate and PCM-concrete thermal storage blocks with different PCM weight percentage (0, 2 wt%, 4 wt% and 6 wt%). The absorption, compatibility, thermal and mechanical properties of PCM-CLSC aggregate and PCM-concrete thermal storage blocks have been tested. To improve the charging and discharge rate, the active thermal storage and release system has been designed. Besides, the study presents the effects of PCM weight percentage and the characteristics of heat transfer fluid (HTF) on the performance of an active thermal storage system. The experimental results show that PCM-CLSC aggregate has good absorption and compatibility. The thermal conductivity and compressive strength of PCM-concrete thermal storage blocks decreased with the increase of PCM weight percentage, and the average specific heat capacity increased by 12.54% (2 wt% PCM), 31.60 (4 wt% PCM) and 41.23% (6 wt% PCM), respectively. Also, by increasing the PCM weight percentage, HTF flow rate and inlet temperature, it is possible to improve the heat storage and release capacity while effectively increasing the heat transfer rate and reducing the thermal resistance.

A comprehensive parametric, energy and exergy analysis of a novel physical energy storage system based on carbon dioxide Brayton cycle, low-temperature thermal storage, and cold energy storage

Low-temperature energy storage system is an important development direction of physical energy storage technology, which can avoid the technical difficulties caused by high-temperature conditions. In this paper, a novel physical energy storage system based on carbon dioxide Brayton cycle, low-temperature thermal storage, and cold energy storage was proposed. Water was chosen as the working medium for thermal storage, and ice slurry was chosen as the working medium for cold energy storage. The working processes of this low-temperature carbon dioxide energy storage system were introduced in detail and the corresponding thermodynamic model was established. In addition to the evaluation based on power efficiency and exergy efficiency, thermal energy utilization efficiency and cold energy utilization efficiency were defined to assess the feasibility of the independent operation of the system. Parametric analysis was carried out to analyze the effects of several important parameters on system performance. The results showed that, for the system under the basic working condition, power efficiency was 55.7%, exergy efficiency was 52.87%, thermal energy utilization efficiency was 83.3% and cold energy utilization efficiency was 89.5%. The total exergy destruction was 48.07 kW and the largest exergy destruction came from the compressor. According to the sensitivity analysis, in turbomachinery, turbine efficiency had the greatest influence on power efficiency as well as exergy efficiency, and when turbine efficiency increased by 1%, both power efficiency and exergy efficiency increased by 0.634%. There was an optimum for pressure ratio to get the maximum values of power efficiency and exergy efficiency, and the optimum was 6.5. The decrease of the pressure drop in heat exchangers could increase power efficiency and exergy efficiency whereas the decrease of minimum temperature difference in heat exchangers could increase the four efficiencies. Measured in terms of the degree of influence, heat exchanger3 had the greatest influence and should be paid more attention. As to the cooling medium, the increase of the inlet temperature of water could increase power efficiency and exergy efficiency. Besides, there was an optimum for the mass flow rate of water to maximize power efficiency and exergy efficiency. Finally, it should be noted that, to ensure that the storage of cold energy during the charge process could meet the demand of cold energy during the discharge process, all the parameters studied needed to be carefully set. Relevant research provided important guidance for understanding the thermodynamic performance of the low-temperature energy storage system with carbon dioxide as the working fluid.

Air-Cycle Energy-Saving IH Rice Cooker Based on Phase Change Heat Storage

This device combines phase change heat storage with air circulation, and proposes a new three-dimensional honeycomb grid structure on the phase change material carrier structure. The reasonable use of steam residual heat and the use of a segmented electromagnetic coil structure reduce the heat loss and power consumption of IH rice cooker. Utilizing the hot steam generated in the heating stage of the rice cooker, the low-temperature waste heat is recycled in the low-temperature phase-change thermal storage module designed by the device. At the same time, the electromagnetic coil is segmented. Besides, the fuzzy control is used to determine the actual amount of rice to be cooked to determine the number of coil segments used in the heating stage to reduce power consumption.

Thermodynamic analysis of a novel compressed carbon dioxide energy storage system with low‐temperature thermal storage

Research projects on new electrical energy storage (EES) systems are underway because of the role of EES in balancing the electric grid and smoothing out the instability of renewable energy. In this paper, a novel compressed carbon dioxide energy storage with low-temperature thermal storage was proposed. Liquid CO2 storage was employed to increase the storage density of the system and avoid its dependence on geological formations. Low-temperature thermal energy storage technology was utilized to recycle the heat of compression and reduce the challenges to system components. The system configuration was introduced in detail. Four evaluation criteria, the round trip efficiency (RTE), exergy efficiency (ηEx), thermal efficiency (ηTE), and energy density (ρE) were defined to show the system performance. Parametric analysis was carried out to examine the effects of some key parameters on system performance and the genetic algorithm was adopted for system optimization. The calculated results show that, for the novel EES under the basic working condition, its RTE is 41.4%, ηTE is 59.7%, ηEx is 45.4%, and ρE is 15 kWh m−3. The value of ρE increases with the increasing pump outlet pressure for a fixed value of pressure ratio, and the changes of RTE, ηTE, and the total exergy destruction of the system (ED,total) with pump outlet pressure are complicated for different values of pressure ratio. When both pressure ratio and pump outlet pressure are high, the values of RTE and ρE can be maximized whereas the value of ED,total can be minimized. Besides, no matter how pump outlet pressure and pressure ratio change, the exergy destruction of the system mainly come from compressors and regenerators, which accounts for about 50% of the total exergy destruction.

Numerical study of a thermal storage tank enclosed PCM capsules

Low-temperature thermal storage has a huge potential in residential use for regulating the energy supply. This paper proposes a new thermal storage system consisting of modular units. Users can combine different numbers of the units to achieve the desirable energy demand. In this study, a single unit was studied. The hydrated salt was used as the phase change material (PCM) and it was packed in spherical capsule. The phase change situation of each PCM balls were analysed with numerical simulation method. The results showed that the PCM balls in different position had different change rate. In the charging process, the thermal stratification happened after the middle part of the unit, the down layer PCM balls took 30% more time than upper layer to be melted completely. In discharging process, considered the user requirement, the low inlet velocity may fit the single unit. The thermal stratification also happened in the discharging process, and it is most obvious in the middle part.

Off-design performance of CAES systems with low-temperature thermal storage under optimized operation strategy

Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. However, the current research on off-design performance of CAES systems, especially in the aspects of advanced compressed air energy storage systems and operation strategies, is deeply insufficient. The complete off-design model of a compressed air energy storage system with thermal storage (TS-CAES) and optimal regulations by adjusting variable inlet guide vane (VIGV) and variable stator vane (VSV) is established for the first time. Using this model, we uncover the off-design characteristics common in TS-CAES systems caused by changes in load, ambient temperature, and operation type (constant pressure operation and sliding-pressure operation), and which is conducted under the optimal regulation strategy for the compression and expansion sections. It is found that system parameters fluctuate around a balance position with load fluctuation. But under the optimal operation, the fluctuation of the system efficiency and energy density is relatively small. System efficiency and energy density increase marginally with the decrease of ambient temperature, and thermal storage temperature increases linearly and markedly with rise in ambient temperature. We also found that system efficiency under constant pressure operation is decreased by 1.74 percent compared to that under sliding-pressure. This study will provide theoretical support for the design, operation, and control of TS-CAES systems.

Enhanced performance of air-cooled thermal power plants using low temperature thermal storage

This paper presents the essentials of low temperature thermal storage (LTTS), a novel technique whereby thermal energy storage is employed to achieve sub-ambient condensation in air-cooled Rankine cycle power plants. It summarises work which was undertaken to explore the potential and the range of application of LTTS. The technology is most effective at geographical locations with large average daily temperature ranges, and high summertime temperatures. Hourly normal temperature data was sourced for five potential deployment sites, which provided a representative sample of different climate types. A steam turbine, a condenser, an air-cooled heat exchanger, and a chilled water thermal energy storage tank formed the LTTS configuration – a techno-economic model of which was developed to simulate system behaviour. The size of the air-cooled heat exchanger, the fan speed of the air-cooled heat exchanger, and the hours of charge, discharge, and bypass of the thermal energy storage tank were all modelled as variables to determine the effects of component sizes and operating patterns. LTTS performance was benchmarked by comparison with a direct air-cooled condenser model. Results presented in this paper include daily plant output, annual power output, and payback period. This study shows that LTTS can deliver all the advantages of dry-cooling, without suffering the usual performance degradations. The inherent flexibility of LTTS allows for configurations to be customised to exploit the prevailing site climate, and capitalise on the local power demand pattern. There are also clear indications that, in suitable climatic settings, LTTS outperforms traditional air-cooled thermal power plants by offering up to 10% additional generating capacity. Coupled to this are payback periods as short as 2.5 years, ensuring LTTS can be considered a viable alternative to current air-cooling strategies.

High Carnallite-Bearing Material for Thermochemical Energy Storage: Thermophysical Characterization

Thermochemical energy storage has a high material-related energy density and low energy losses over time compared to sensible and latent energy storage. Considering economic and ecological aspects, there is a great opportunity in using low cost or even waste materials from the mining industry, as thermochemical energy storage medium. In this study, a systematic analysis of a high carnallite-bearing material, comparable to the natural waste, for thermochemical energy storage was performed. The material displays gradual decomposition and poor reversibility of hydration reaction at temperatures above 150 °C. However, the reversibility is significantly higher and the decomposition is slower between 100 and 150 °C under pH2O = 25 kPa. The reversible behavior of the hydration reaction of carnallite, between 100 and 150 °C, is stable for 15 cycles when the material is exposed at 150 °C for short periods of time (t < 20 min). Following this path, any potential application of this material is definitely limited to low temperature thermal storage or thermal upgrade. Taking the low material cost into account, one of the potential applications of this material could be in the context of long-term heat storage. For this purpose, the temperatures of dehydration can be below 150 °C and the temperatures of rehydration close to 40 °C.

Design of SBS-Modified Bitumen Stabilizer Powder Based on the Vulcanization Mechanism

In order to improve the problem of the bad thermal storage stability of Styrene-Butadiene-Styrene Block Copolymer Modified Bitumen (SBS-modified bitumen), the vulcanization reaction was selected as the basic mechanism for the research and development of the stabilizer. Sulfur, tetramethylthiuram disulfide (TMTD), zinc oxide, butylated hydroxytoluene (BHT), kaolin (Al2O3·2SiO2·2H2O) and carbon-white (SiO2) were used as raw materials, and 32 kinds of components with different contents of raw materials were designed. The 48-h segregation softening point and other modified bitumen technical indicators, such as ductility, penetration, penetration index, viscosity, and so on, were tested and analyzed. The fluorescence microscope test was also conducted to explore the crosslinking situation based on the vulcanization reaction. The results show that the component with good performance of the SBS-modified bitumen stabilizer powder was S:TMTD:ZnO:BHT: Al2O3·2SiO2·2H2O = 60:16:4:20:1250 or S:TMTD:ZnO:BHT:SiO2 = 60:16:4:20:625. The optimum content of stabilizer powder was 0.9% (S/modified bitumen). The stabilizer was dry powder and can be directly put into bitumen. It can cross-link SBS and especially has an effect on preventing SBS segregation. The technical performance of SBS-modified bitumen with stabilizer powder, such as hot temperature performance, low temperature performance, anti-aging performance and thermal storage stability, all meet the relevant specifications.

Parameter and layout optimization of a high temperature solar combined cycle using low temperature thermal storage

A novel high temperature solar supercritical carbon dioxide (S‐CO2) and organic Rankine cycle (ORC) combined power system with low temperature thermal storage is introduced. The heat releasing of the S‐CO2 can be used as the heat source of the ORC. This system could keep high thermal efficiency, whereas thermal storage temperature is far lower than the maximum temperature of the system. Previous work has proved that the system efficiency can be kept at 38% when the thermal storage temperature is in the range of 220∼230°C. Basic relationship among system efficiency, power ratio and thermal storage temperature are analyzed. The key parameters of the system are optimized under certain constraints. Three possible improved layouts of this system are discussed in the end. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1234–1243, 2017

Experimental Study on Thermal Performance of Beeswax as Thermal Storage Material

Thermal energy storage is one of the key areas of energy conservation. Identification and applications of thermal storage materials are the primary concerns for fabrication of an efficient thermal energy storage system. In this study, Beeswax was introduced as a natural phase change material for low-temperature thermal energy storage. Surface characterization of beeswax was done using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and Fourier Transform Infra-red Spectroscopy (FTIR). Thermal properties of beeswax were determined by Differential Scanning Calorimetry (DSC). A shell and tube type thermal storage unit was fabricated to study the thermal performance of beeswax as the thermal storage material. Storage material formed the shell part while hot fluid was allowed to pass through the centrally placed copper tube. Temperature variation with time was studied at nine points of thermal storage units. Effect of various flow rates and inlet temperature of heat transfer fluid (HTF) on the heating profile of beeswax was studied. Objective of this study is to analyse potential of beeswax as thermal storage material and its application for low-temperature thermal storage.

Storing surplus solar energy in low temperature thermal storage for refrigeration applications

In this paper a thermodynamic analysis of a concept approach based on a possible form of load management for photovoltaic energy is presented. By using the surplus electricity for driving a compression chiller it is possible to load a low temperature thermal storage. This cold storage can be used to cover the cooling demand of domestic refrigerator and freezers. A parameter study was performed to evaluate the energetic efficiency for this system in a single family home. A short economic evaluation compares the concept to a system without storage and to a system with battery storage.

Modelling study, efficiency analysis and optimisation of large-scale Adiabatic Compressed Air Energy Storage systems with low-temperature thermal storage

The key feature of Adiabatic Compressed Air Energy Storage (A-CAES) is the reuse of the heat generated from the air compression process at the stage of air expansion. This increases the complexity of the whole system since the heat exchange and thermal storage units must have the capacities and performance to match the air compression/expansion units. Thus it raises a strong demand in the whole system modelling and simulation tool for A-CAES system optimisation. The paper presents a new whole system mathematical model for A-CAES with simulation implementation and the model is developed with consideration of lowing capital cost of the system. The paper then focuses on the study of system efficiency improvement strategies via parametric analysis and system structure optimisation. The paper investigates how the system efficiency is affected by the system component performance and parameters. From the study, the key parameters are identified, which give dominant influences in improving the system efficiency. The study is extended onto optimal system configuration and the recommendations are made for achieving higher efficiency, which provides a useful guidance for A-CAES system design.

Performance prediction of a small-size adiabatic compressed air energy storage system

The problem of decentralized energy storage is of crucial importance for the development of renewable energy resources. In the first stage of their development, RES have relied on the possibility of connecting to the grid. However, with increased RES share, pressure is being put on the electrical grid system, resulting in the necessity of extensive load modulation of traditional plants (hydroelectric and fossil), and also on the development of large energy storage facilities (hydro-pumped, CAES, batteries,…). From the point of view of distributed energy systems, connected to smart grids, it is rather interesting to develop local energy storage systems, which can help to decrease the load on the grid infrastructure, possibly paving the way to complete off-grid operation. The case study is a Small-Size Advanced Adiabatic Compressed Air Energy Storage (SS-AA-CAES), developed from existing components (compressors, heat exchangers, vessels, expander,…) and coupled to a local PV field. The system operates trying to separate pressure energy and heat, and promoting regenerative/recuperative use of this last with low-temperature thermal storage (hot water) to cover the necessary time lag. The system also represents a CHP solution, as the hot water recovered from compressor cooling is available for heating purposes. A thermodynamic model of the system was built, used for design, and a simulation covering system operation over one year was performed. The results show that the system could be recommended (possibly with the support of battery storage) for use in applications where complete off-grid operation is preferable, or where it is important to minimize the impact of the grid infrastructure, such as in natural parks and remote areas.

Ancillary services for the electrical grid by waste heat

This paper proposes a method to provide ancillary services to the electrical grid with waste heat recovery. The thermal flexibility needed to provide variable electrical output is provided by connecting the thermal source to a thermal grid and a thermal storage unit. Large capacity low heat grade thermal storages are cheaper and more readily available than large capacity electrical storage solutions, and hence thermal storage is preferable.In this paper, the dimensions of a low temperature thermal storage buffer to balance the variability of a wind- or solar plant is determined. It is calculated that a spherical storage tank of 25 m diameter and 90–130 °C would be sufficient to balance the unpredictability of a 100 MW plant of either solar- or wind energy.