Seasonal Thermal Storage Research Articles

Performance analysis of cross seasonal thermal storage solar soil source heat pump drying system

Performance analysis of cross seasonal thermal storage solar soil source heat pump drying system

Techno-economic optimization and feasibility of PCM-based seasonal thermal energy storage systems for district heating and cooling

Phase change materials (PCM) are an attractive seasonal thermal energy storage solution for load shifting due to relatively high energy density. Nevertheless, the choice of the right design parameters, such as storage size and phase-change temperature, is nontrivial, as these are tightly linked to the expected seasonal operation of the storage. This paper presents a combined design and operation optimization framework for sizing PCM-based seasonal thermal storage, which can capture dynamic behaviour of the storage in sensible and latent phases, and its impact on the efficiency of connected heat pumps and chillers. The proposed method, formulated as a mixed integer quadratically-constrained programming problem, was applied to a case study of heating-dominated district. It was found that the optimal PCM melting temperature equals to the heating demand supply temperature, thus removing the need of a heat pump to discharge the storage. The optimal operation of storage requires a full charging and discharging cycle of both latent and liquid phase. Higher CO2 emission price does not lead to a significant reduction of CO2 emissions, but the storage size does, leading to a higher heating coverage ratio of the storage, and consequently CO2 emissions and cost savings, which can be further enhanced with PV integration. The economic analysis indicates that, unless other benefits such as storage volume reduction are accounted for, PCM cost should drop by a factor 4 to make this solution economically viable for seasonal storage.

Experimental and numerical investigations of the energy performance of a solar seasonal thermal storage heating system under different operation modes in cold-region tunnels

Solar seasonal thermal storage heating (SSTSH) system is a new type of energy-efficient and environment-friendly anti-freezing technology in cold-region tunnels. The purpose of this study is to investigate the energy performance of an SSTSH system operated in different modes by using field experimental tests and numerical simulation. The experimental system is installed in Tianshan Shengli Tunnel of Xinjiang, China. Three operation modes including single heat storage, single heat extraction, and combined operation mode are investigated under different flow rates and inlet temperatures. The thermal performance, system operational efficiency and borehole wall temperature are analyzed and compared under various modes. The experimental results indicate that for the single heat storage operation mode, the thermal storage performance can be improved by enhancing the flow rate and inlet temperature. However, when ensuring the thermal storage amounts, a lower flow rate or inlet temperature should be employed to improve system efficiency. For single heat extraction operation mode, the heat extraction performance is effectively improved by lowering the inlet temperature, while the coefficient of performance (COP) is decreased. It is advisable to maintain a higher inlet temperature to improve operational efficiency of heat extraction. For the combined operation mode, the simulation shows the heat extraction performance of the SSTSH system can be greatly improved by the increasing the heat storage inlet temperature. When the heat storage inlet temperature increases by 5 °C, the growth rate of the average heat extraction amount is 2.45 W/m during the combined operation mode. The seasonal heat stored raises the surrounding rock temperature to a higher level, which is beneficial for increasing the COP of the heat pump, and effectively addresses the thermal imbalance in cold regions. The combined operation mode of the SSTSH system is recommended for the tunnel heating in cold regions.

Experimental investigation on dynamic thermal storage and extraction performance of seasonal thermal storage

The initial investment for a buried pipe system using soil as a seasonal thermal storage medium is costly and not suitable for small rural buildings. To promote the cost-effective heating in rural areas, this study proposes a novel seasonal thermal storage system utilizing water and soil as thermal storage medium with copper rods to enhance thermal transfer between water tank and the surrounding soil. An experimental platform was established to discuss the temperature variation characteristics and investigate the thermal performance under different operating modes and experimental parameters. The results show that the temperature of the soil without copper rods is linearly related to the depth, while the highest temperature at the end of the copper rods occurs at the middle depth. The soil with short copper rods exhibits the most rapid thermal storage response and a relatively shorter thermal extraction response time. Intermittent operation can significantly enhance the thermal extraction rate and outlet temperature of the thermal storage unit, whereas the energy storage efficiency decreases with the extension of the downtime. The soil contribution rate of the thermal storage unit is influenced by the operational duration, initial temperature of the water tank and outdoor ambient temperature.

Super‐liquid‐repellent thin film materials for low temperature latent heat thermal energy storage: A comprehensive review of materials for dip‐coating

AbstractWhen discharging latent heat thermal energy storage (LHTES) systems, performance is influenced by the formation and adherence of a solid layer of phase change material (PCM) on heat eXchange (HX) surfaces. Super‐liquid‐repellent thin films (STFs) may be able to reduce solidifying PCM adhesion on HX surfaces during discharging, delay PCM solidification to lower temperatures, and by modifying nucleation sites potentially enable long‐term seasonal thermal storage. Techniques employed previously to fabricate sintered polymeric STF coatings include chemical vapour deposition, dip‐coating, spray‐coating, spin‐coating, layer‐by‐layer (LbL) assembly, sol‐gel, anodizing, electrodeposition, electrospinning, so on. Dip‐coating is considered attractive for fabricating thin films on simple and complex surface geometries due to process maturity, scalability, flexibility and cost‐effectiveness. To identify suitable materials for preparing STFs on metal HX surfaces using the dip‐coating process, more than 200 journal articles published in English during the period 2010 to 2022 were reviewed and the potential role of STFs in LHTES applications was assessed. The review identified key areas and applications stimulating STF material developments and formulations. The dip‐coating of potential STF materials was classified under three major themes driving current research and development (R&D) activities, that is, high performance thin films, eco‐friendly thin films and fundamental research formulations. This review provides a platform from which to develop coatings and HX systems to enable the cost‐effective implementation of STFs for improved heat transfer in future mobile/stationery LHTES systems.

Numerical modelling of a high temperature borehole thermal energy storage system: Norway case study

Global warming is threatening life on earth. Utilising renewable energy is considered as the most effective measure to minimise anthropogenic CO2 emissions. High-temperature borehole thermal energy storage (BTES) systems have a world-wide potential to reduce energy consumption, increase energy utilisation of waste heat and provide efficient seasonal heat storage. Hybrid application of BTES and solar energy leads to net zero emissions. In this study HT-BTES is evaluated for seasonal thermal heat storage and recovery. To this end, a CMG STARS model was built and validated using the existing 100-wells BTES system in Norway. Then, the model was used to evaluate BTES thermal performance and thermal recovery efficiency. Sensitivity analysis was also conducted to study the dynamics of storage temperature in the BTES under different operating conditions, such as heat carrier flow rate, injection temperature, and charging period. Results of this case study show that the model-predicted temperatures during charging and discharging are in good agreement with the existing BTES system. In 5 years of operation, 35.5% of the heat injected into the BTES system was recovered, while the significant heat remained in the borehole region and lost to surrounding rock (64.5%). BTES was found very sensitive to flow rate, the charging period and injection temperature. Borehole depth has a minimal effect on BTES storage temperature at constant studied injection temperature.

Effect of climate on the optimal sizing and operation of seasonal ice storage systems

Seasonal thermal storage systems can reduce the temporal mismatch between renewable energy availability and energy demand. Ice storage systems exhibit a non-linear behaviour in the heat exchange and storage processes, complicating the formulation of optimal design and operation problems. In this work, we propose a mixed-integer quadratically-constrained programming formulation, which minimizes the Levelized Cost of Energy for space heating and cooling, including sizing of a supporting PV array. The optimization was repeated for different storage volumes, finding the system optimal operation in each case –and thereby the optimal system sizing. The heating and cooling demands were computed from an archetypal office building, placed in three reference locations with cold and semi-arid, warm and humid continental, and temperate and humid continental climates. Results show that the optimal PV size decreases with growing ice storage volume, and an ice storage works best in a temperate continental climate, covering up to 47% of the cooling demand with a 250 m 3 storage.

Modelling of solar assisted district heating system with seasonal storage tank by two mathematical methods and with two climatic data as input

The goal of the study is to present two independent solutions capable of modelling the thermal behaviour of the solar assisted district heating systems with seasonal thermal storage. The study uses a new approach in modelling the thermal behaviour of the solar assisted district heating systems, by using two calculation methods: the analytical method and TRNSYS to perform the simulations, and by using two climatic data as input: EnergyPlus and Meteonorm. The heat demand of the buildings, the shares of energy produced by the solar thermal system, and by the gas boiler used as backup, and a very large number of the system parameters: temperature variation in each layer of the seasonal heat storage tank, temperatures, and flow rates on all the circuits, etc. were calculated. The results were compared using three parameters: Mean Deviation, Mean Bias Error and Root Mean Square Error. All the results calculated with the two methods were found to be very close. The annual solar fraction was found to be in the range of (34.9–50.2) %, depending on the type of the considered solar thermal collector, the combination of calculation method and climatic data as input. The study proves that both analytical method and TRNSYS can be used successfully to simulate the thermal behaviour of solar assisted district heating systems with seasonal heat storage.

Refined modeling and co-optimization of electric-hydrogen-thermal-gas integrated energy system with hybrid energy storage

To further explore the multi-energy complementary potential on multi-time scales under variable operating conditions, a refined modeling and collaborative configuration method for Electric-Hydrogen-Thermal-Gas Integrated Energy Systems (EHTG-IES) with hybrid energy storage system (HESS) is proposed in this paper. To commence with, an advanced operation model for the EHTG energy conversion equipment is formulated by incorporating their nonlinear operating characteristics under variable operating conditions. Next, the distinct features of HESS with different energy medium are accurately depicted with various effective linear-reduction and relaxation strategies. Then, the coupling design day method and the intra-day and inter-day state superposition strategy are combined to efficiently model the time horizon. Lastly, a co-optimal configuration model of the EHTG-IES is devised, with the aim of minimizing total annual cost. The case study validates that the refined modeling of coupled components leads to a 3.18% reduction in cost and 5.05% reduction in carbon emissions significantly. This paper also assessments the synergy and substitution benefits of multiple low-carbon technologies and finds that diurnal and seasonal hydrogen storage have a large part of overlapping roles, and hydrogen-based system contributes a deeper utilization of seasonal thermal storage. The sensitivity analysis indicates that the current carbon tax policy has a negligible impact on the carbon emissions, equivalent to about 1% of the gas price, but appropriately increasing attention on low carbon allows for an emission decrease of 28.62% at a cost increase of 4.38%.

Dynamic characteristics and energy efficiency evaluation of a novel solar seasonal thermal storage - heating system

This paper proposes solar seasonal thermal energy storage system compounded with long-term and short-term energy storage tanks for a single-family dwelling, which using assisted water source heat pump to further improve the systems stability. With the objective of improving the solar energy utilization efficiency and reducing the primary energy consumption, the dynamic simulation model of the “heat collection-heat storage-heat supply” system under the non-stationary boundary conditions throughout the year is established. The energy transfer and conversion law of each subsystem and the dynamic operation characteristics are analyzed through simulation method. The system cooperative control strategy is proposed and parameter optimization is carried out. Results indicate that the annual heat collection efficiency of the water source heat pump composite system has been improved by 2.2 % compared with the electric auxiliary heating system. Meanwhile, the heat storage efficiency and the solar energy guarantee rate increased by 5.8 % and 8.3 %, respectively. Moreover, the optimal water source heat pump composite system not only improves energy efficiency and achieves the cost savings compared with the electric auxiliary heating system, but also reduces carbon dioxide emission by 10.3 %, which have great advantages for energy saving and emission reduction.

New, 3D binder-jetted carbons with minimal periodic surface structures

This study focuses on the design, additive manufacturing, and characterization of porous carbon-based structures in the form of a triply periodic minimal surface (TPMS) with outstanding mechanical properties and oxidation resistance, combined with good electrical and thermal conductivity. Binder jetting (BJ) of graphite-carbon black powders was used to 3D print computational models of three TPMS with different topologies and geometric porosities. Infiltration and pyrolysis (PIP) with furan resin was then performed to densify the parts. Composite materials, comprising a highly disordered carbon matrix binding well-crystallized graphite grains, were obtained. The printed and pyrolyzed samples are highly porous TPMS cylinders with diameter, height and a surface thickness of ∼19 mm, ∼33 mm and 0.76 mm, respectively. The samples have a skeleton intrinsic porosity of 20%, of which 8% is open, meaning that the material could potentially be further infiltrated and densified. Nevertheless, the samples have better mechanical properties than compressed carbon-graphite composites, as well as 3D-printed carbon produced by direct ink writing and stereolithography. High-temperature tests showed that, although the amorphous carbon matrix is more prone to oxidation than the graphite grains, the overall oxidation resistance remains exceptionally high. These properties allow for applications as Joule resistors and in seasonal thermal storage.

Energy, Volume and Cost Analyses of High Temperature Seasonal Thermal Storage for Plus Energy House

The article analyzes the impact of different filling materials for a seasonal heat storage stack that can be used to heat an innovative plus-energy house in Poland. The storage medium is of the sensible heat type. Twelve filling materials and nine thermal insulation materials readily available in the local market were analyzed. Seven variants comprising a combination of the stack’s filling and thermal insulation materials were selected and then grouped into three classes: advanced, medium, and simple technology. Using a mathematical model, energy analysis of the year-round operation of the HVAC installation in the analyzed building was performed for each of the seven variants. The conducted analyses revealed that for each combination of filling and thermal insulation material, there is an optimal maximum temperature of the stack, at which the volume of the stack is the smallest or its costs are the lowest. The obtained results were evaluated to determine the ideal variant combination, and two solutions were recommended: clinker brick and fireplace wool, for which the stack volume is 23 m3 and the total cost is EUR 12,500; and concrete block and glass wool, for which the stack volume is 27 m3 and the total cost is EUR 1700.

Reduced order 1 + 3D numerical model for evaluating the performance of solar borehole thermal energy storage systems

This study presents a computationally efficient numerical model for solving the fluid flow and heat transfer phenomena in co-axial boreholes heat exchangers arranged on a rectangular grid (N × N) drill hole pattern. Such systems of boreholes are an integral component of a Solar-Borehole Thermal Energy Storage System for seasonal thermal storage application. The numerical model couples a one-dimensional fluid flow and convective heat transfer model in the heat exchanger with a three-dimensional model of conductive heat transfer in the strata. In addition to solving mass and heat transfer in borehole systems, it integrates a solar thermal collector system and building dynamic thermal load to design a Solar- Borehole Thermal Energy Storage system for a 182-unit residential apartment building. Simulation also considers and evaluates the conductive, convective, and radiative thermal losses of the system. The model is validated using experimental data from a coaxial borehole heat exchanger and compared to the results of a commercial finite volume solver for multiple co-axial boreholes. The computational cost of developed numerical model is reduced by a factor of 194 compared to a commercial finite volume solver. Solar- Borehole Thermal Energy Storage system simulation is performed for a period of five years considering hourly fluctuations in solar irradiance and building dynamic thermal energy demand. Parametric study is performed on depth and spacing of boreholes, and mass flowrate in the solar thermal collectors. It is found that a system of 100 boreholes, each 100 m deep, linked to 674 solar thermal collectors can provide the heating for the building with a total thermal demand of 5600 GJ per year.

A Simulation of a Sustainable Plus-Energy House in Poland Equipped with a Photovoltaic Powered Seasonal Thermal Storage System

This article describes the innovative photovoltaic powered seasonal thermal storage—PVPSTS system. It was used in the design of a plus-energy detached single-family house with a usable area of 98 m2. This area meets the requirements of the latest building regulations in Poland. The building, with the innovative HVAC installation, was subjected to energy analysis, and a numerical model was also developed. The model was tested based on TMY data for the location of Wroclaw, Poland. Analysis of the results allowed the authors to learn the specifics of the operation of the system throughout the year and to also define its efficiency. The required size of the storage stack was determined to be 1.6 × 1.6 × 0.3 m. The photovoltaic installation, which was integrated with the roof, can produce 48 GJ of electricity per year. This is five to six times more than the building’s heating needs, and any excess energy can be exported to the power grid.

Semi-analytical modeling of large-scale water tank for seasonal thermal storage applications

Buildings consume large amount of energy for cooling in summer and heating in winter. A renewable energy-based district heating using seasonal thermal storage can better serve for a lower carbon space heating for buildings. The research objective is to propose a first semi-analytical model of large-scale water tank storage as an efficient and flexible tool for further development of TES. A new idea of “three-zone method” is proposed for detailed heat and mass flow inside water storage with least increase in computational burden and better capture of internal non-uniform thermal distribution. All three modes of charging, discharging and standby are modeled separately with high flexibility. A modified finite cylindrical source model for TES was proposed, for the first time, for transient heat transfer in the ground, which is inspired by analytical model of ground source heat pump. A complete comparison was made between the new semi-analytical model and validated reference data, which shows a good match in temperature profile in different locations. This study will pave a way for a further systematical study on seasonal thermal storage.

Techno-economic analysis of a hybrid district heating with borehole thermal storage for various solar collectors and climate zones in Pakistan

Fossil fuels are being used to accommodate domestic heating needs all over the world, and the alarming rise in carbon footprint is demanding the world to shift towards renewable energy technologies. A key strategy to lessen household fossil fuel consumption is a solar hybrid district heating network integrated with seasonal thermal energy storage (TES). The objective of this study was to analyze and compare the thermo-economic performance of solar hybrid district heating systems integrated with borehole TES systems in ' 'Pakistan's five climate zones and identify the best suitable solar thermal collector technology. Based on the solar energy incident on different types of thermal collectors, a validated TRNSYS model was used to investigate the dynamic performance indices i.e., solar fraction, system efficiency, and thermal storage efficiency. The heat demand model and weather-related data were changed as input to the system. Based on mentioned performance indices, out of 5 different cities having different climates, climate Zone-C(Quetta), having a continental semi-arid climate, is selected as the most suitable, and Zone-E(Karachi) has tropical desert climate as the least favorable among five different zones with a seasonal storage efficiency of 61% and 19% respectively. The solar fraction is about 91%, also up to the mark as the proposed system utilizes both solar energy and auxiliary systems. Further, the implementation of different thermal collector technologies Parabolic Trough Collector, Evacuated Tube Collector & Flat Plate Collector, revealed that the thermal efficiency of ETC is best among all, with the highest value of 65%, followed by PTC at 44%, and FPC shows the least efficiency of 36%. The economic analysis shows that the model embedded with ETC has a minimum payback period of 6.90 years, followed by an FPC of 7.22 years and a maximum for PTC of 7.38 years. The analysis presented in the current study provides guidelines for researchers and policymakers to identify acceptable location-based best solar thermal collector technologies coupled with seasonal thermal storage for district space heating.

Study on heat transfer process of insulated floating cover of water pit for solar seasonal thermal storage

Water pit thermal energy storage (PTES) can transfer the solar energy heating from the non-heating season to the heating season, which can efficaciously cope with the mismatch problems in energy intensity, usage time and space of solar energy heating system. The long-term PTES system is stable and efficient, avoiding the idleness and waste of the collector field. The insulating floating cover is the most expensive part of PTES and it is also the key factor to determine whether the thermal stratification of the PTES can be formed. This project studied the heat transfer process of insulated floating cover with a finite element model of a 500 m3 water pit in Yanqing, China, and the result is validated by experimental data. The difference between the numerical simulation consequences and the experimental consequences is about 5.6%, and the comprehensive heat transfer coefficient of the insulated floating cover can reach 0.186 W/(m2 K). The verified numerical model can intuitively display the temperature distribution and other key parameters of the insulating floating cover, which provides an important reference for the design and manufacture of the insulated floating cover.

Analytical modeling and validation of the thermal behavior of seasonal storage tanks for solar district heating

In the context of the complex worldwide energy crisis, the solar district heating and the embedded seasonal storage tanks can contribute to the increase of energy efficiency in district heating systems. The analytical investigation of the thermal behavior of the storage tanks allows the evaluation of the reduction in energy consumption, that can be achieved, and the correct sizing of both solar fields and storage tanks.The study presents complete analytical models for fully mixed and stratified seasonal storage tanks, integrated in solar district heating systems. The provided validation of both models was realized by comparison with results available in the literature. Three and five comparisons were conducted for the fully mixed model and for the stratified model, respectively.The Mean Deviation (MD), Mean Bias Error (MBE) and Root Mean Square Error (RMSE) were used in the validation process. For the fully mixed model, in all the comparisons, the differences between the storage tank temperature provided by the model and the corresponding temperature from the reference are lower than 16.7 °C (occasionally). MD is lower than 2.9 °C, while MBE is lower than 5.9 % and RMSE is lower than 9.9 %. For the stratified model, in all the comparisons the differences between the storage tank temperatures provided by the model and the similar temperature from the references are lower than 2.35 °C. MD is lower than 0.5 °C, while MBE and RMSE are lower than 1.55 % for all the comparisons. The reasonable differences between the model and the reference, in the case of the fully mixed tank and the neglectable differences in the case of the stratified tank, validated both analytical models, that can be further used with high confidence, in investigations related to the thermal behavior of solar district heating systems with seasonal thermal storage.

Assessing the potential of seasonal thermal storage for local energy systems: Case study for a neighborhood in Norway

District heating has an important role in the shift to carbon-neutral energy systems through enabling the use of heat sources that would otherwise be wasted to cover buildings’ heating demands. The availability of many renewable and surplus heat sources is however in opposite phase with the heating demand, creating a demand for seasonal thermal energy storage. This study performs a techno-economic assessment of the heat supply system of a residential area in Norway, where seasonal storage storing excess heat from a waste incineration plant is being planned. A heat supply solution combining seasonal storage and low-temperature district heating was compared with two more conventional alternatives: high-temperature district heating and direct electric heating.The study shows that the seasonal storage is not cost optimal under the conditions assumed, in particular regarding the electricity market; however, the total costs were only 3% higher compared to electric heating. Seasonal storage additionally allows to reduce the use of peak heating units in the district heating system in the winter, thus reducing the costs and emissions related to heat production, and district heating alone has a significant impact in alleviating the pressure on the power grid. The peak power demand was reduced by 28% when investing to low- or high-temperature district heating, and seasonal storage was shown to enable up to 31% reduction in the peak heating demand. Moreover, it was shown that higher electricity prices in the winter and reduced grid capacity increase the economic viability of the solution and could make it competitive.

Application Prospect of Solar Water Heating System with Seasonal Thermal Storage in Rural Area of Northern China

In the past few decades, the traditional method of coal-fired heating in rural area of northern China has been exposed many environmental problems. Therefore, as a kind of clean and renewable energy, solar resource has attracted more and more attention. To ensure long-term domestic heating requirement in the countryside, seasonal thermal storage was developed to overcome seasonal variability, the main drawback of solar energy. However, the application prospect of this technology in rural area of northern China still remains to be discussion. This study selected six identical country seats (with 1800m 2 heating area) in Beijing as the model, and from three aspects of climate condition, thermal performance, economic and environmental impact, analyzed the application conditions of solar water heating system with seasonal thermal storage in space heating and domestic hot water. The results show that with 420m 2 solar collectors and 905m 3 seasonal storage tank, the proposed system can meet most demand of space heating and domestic hot water for six buildings, and its equivalent annual cost is acceptable compared to other heating systems despite high one-time cost may become the main problem of its advancement in the countryside of northern China.