Thermal Energy Storage Volume Research Articles

Design and assessment of a concentrating solar thermal system for industrial process heat with a copper slag packed-bed thermal energy storage

Decarbonising the industrial sector is a key part of climate change mitigation targets, and Solar Heat for Industrial Process (SHIP) is a promising technology to achieve this. However, one of the drawbacks of SHIP systems is that they rely on an intermittent energy source. Therefore, sensible energy storage has emerged as a potential solution. In addition, solid byproducts have been proposed as a low-cost but effective material for thermal energy storage (TES). This work presents a SHIP system model coupled with a copper slag-packed-bed TES (PBTES) model using air as heat transfer fluid. The TES has been implemented to preheat the makeup water of the tank where steam is generated. A system design was carried out using a parametric analysis to find a solar field size and a corresponding TES volume. The resulting system was simulated, and the operating variables were analysed in detail. The results show that it is possible to generate 20% more energy due to the storage system. Additionally, a techno-economic analysis indicates that the SHIP with PBTES system results in a payback period of 14 years and a savings of CO2 emissions of 30tCO2.

Development and Experimental Characterization of an Innovative Tank-in-Tank Hybrid Sensible–Latent Thermal Energy Storage System

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.

Analysis of thermal energy storage tanks and PV panels combinations in different buildings controlled through model predictive control

The present study analyses the performance of a heating system controlled by a model predictive control strategy, where the impact of different combinations of thermal energy storage tank volumes and installed PV power capacities are analysed. The novelty of the paper lies in studying both economic and energy impacts of each equipment combination in different locations, buildings, and indoor occupancy schedules. The payback period, the reduction of the electricity grid consumption, and the behaviour of the coefficient of performance of the heat pump are studied in detail for all cases. Results point out that from an economic point of view, to invest in a thermal energy storage tank provides shorter payback periods in comparison to scenarios with PV panels, due to the high price of the solar elements. However, the energy performance analysis highlighted that the use of PV panels contributes to achieve up to 34%, 54%, and 90% of reduction of the electricity grid consumption in Helsinki, Strasbourg, and Athens, respectively. Finally, it is worth noting that the increase of the thermal energy storage volume improves the coefficient of performance of the heat pump.

Performance investigation of multiwall carbon nanotubes based water/oil nanofluids for high pressure and high temperature solar thermal technologies for sustainable energy systems

Nanofluids are of paramount importance for the development of efficient and competitive heat transfer fluids. The research paper presents a comprehensive study of the thermal properties for developing water and Therminol oil-based nanofluids to operate at high pressure and temperature, which will ultimately support the development of a more comprehensive understanding for nanofluids based heat transport phenomena. Multiwall carbon nanotubes were suspended in water and Therminol 66 at three different weight concentrations from 0.05% to 0.5% with Acacia Gum and oleic acid as surfactants for water and Therminol 66, respectively. The experimental results show more than a 35% enhancement in the thermal conductivity for both the water-based nanofluids and Therminol-66 based nanofluids. This thermal conductivity was also found to be similar with small increment at high pressures for both the base fluid and nanofluids, up to 70 bar pressure and 300 °C. Furthermore, the simulations carried out on parabolic trough collector solar thermal system using nanofluid properties and system advisor model software, showed an enhancement in energy production along with 10.37% reduction in real power purchase agreement price as well as 21% reduction on the thermal energy storage volume.

Analysis of a horizontal flow closed loop thermal energy storage system in pilot scale for high temperature applications – Part II: Numerical investigation

The storage system investigated in this work, namely the CellFlux system, consists of a regenerator type thermal energy storage volume which is coupled to a heat exchanger by a circulating intermediate working fluid. The numerical simulations in this work are based on experiments conducted with a large scale pilot plant having a bed length of more than 10 m. The storage volume is of a novel design with horizontal flow direction and is filled with hollow bricks as sensible heat storage material. So far, most publications focus on packed bed storage systems, often with molten salt or oil, only few consider regularly shaped channels with gaseous flow. For the investigation in this part of the publication, a one-dimensional dispersion concentric model for channel flow is implemented in MATLAB/Simulink.The analysis in part I of this publication has revealed a radial flow maldistribution, which can be predicted by a correction function correlated beforehand. The commonly used assumption of plug flow, however, will be afflicted with an error. Thus, the aim of this work is to determine the accuracy of the model both under the plug flow assumption and the application of aforementioned correction function. Three single blow experiments, where the storage is charged or discharged from a uniform initial temperature, are compared to the numerical model. The average temperature deviation between experiment and simulation reaches up to 10% without the correction function, but improves significantly through its application and then ranges between 0.4% and 4.8%.Moreover, studies based on larger experiments have either not observed or generally not addressed the effect of a flow maldistribution. This appears to be an issue for small scale experiments where typically more sophisticated models are applied. If it was possible to model the entire storage volume with the present 1D model, the flow maldistribution effects could average out. Also, computing effort would be low and allow simulations on system level. This approach was taken only by few authors so far, particularly for packed bed systems and was also not experimentally verified. In order to correctly depict the experimental set up, the model considers the different composition of the interior, such as flow distributors and inlet/outlet cones as well as the thermal heat capacity of the walls and losses to the environment. As a result the model shows good agreement with the experiments: the mean temperature difference of the exit temperature between experiment and simulation during cyclic operation remained below 5%.

Analysis of a horizontal flow closed loop thermal energy storage system in pilot scale for high temperature applications – Part I: Experimental investigation of the plant

A unique large scale pilot plant of the CellFlux thermal energy storage concept is experimentally investigated. This storage concept consists of a regenerator type thermal energy storage volume, which is coupled to a finned tube heat exchanger by a circulating intermediate working fluid. The system investigated in this work operates at a temperature of 390 °C and uses air as intermediate working fluid which is conveyed by a centrifugal fan. The storage volume has a bed length of over ten meters and is of a novel design, where the air flows in horizontal direction. Since this approach could cause a flow maldistribution, a thorough analysis is of major interest for the accuracy of subsequent numerical simulations. The experiments reveal that the mass flow along the centerline can be up to 20% higher than the mean bulk flow. A significant maldistribution between top and bottom area, however, is not observed. As an alternative to the typically used rock filling, the storage volume is equipped with standard hollow bricks. These bricks are cost effective but do not have a well-defined shape. Thus, the predictability of the pressure drop by correlations found in the literature is unclear. It turns out that the measured pressure drop is evenly distributed in axial flow direction but generally higher than expected from the assumption of pure channel flow. Further experiments are conducted to validate the heat capacity of the bricks and to derive a correlation for the inner heat transfer between bricks and storage walls. Eventually, the aim of the experimental investigation is a general proof of concept as basis for the numerical investigation. Thus, all specifications of the plant and the storage material are provided. The plant is analyzed towards plausibility of heat losses, showing that heat losses can be predicted well within the given uncertainties.

Sizing domestic air-source heat pump systems with thermal storage under varying electrical load shifting strategies

The demand for local heat storage to help manage energy demand in dwellings is likely to increase as the electrification of heat through heat pumps becomes more widespread. Sizing thermal energy storage systems has been an important topic in contemporary literature, but the effect of the electrical load shifting tariff and the service the householder receives in terms of space-heating and hot water delivered, however, has not and this is particularly important when households transition from conventional gas fired to low carbon technologies. This paper takes a whole system modelling approach to understand the impact of user demand patterns and load shifting scenarios on the volume of energy storage required for a heat-pump installation. The work uses monitoring data from several family homes to drive the simulation and finds that the level of service the householder receives is sensitive to their patterns of consumption, thermal energy storage volume and the electricity tariff, with some households being far more sensitive to tariff choice than others. The paper introduces a novel, quantifiable measure of service for space-heating and hot water systems that can be incorporated into thermal energy storage sizing procedures.

Introducing a hybrid photovoltaic-thermal collector, ejector refrigeration cycle and phase change material storage energy system (Energy, exergy and economic analysis)

In this study, an integrated system which including photovoltaic-thermal collectors, ejector refrigeration cycle and phase change material storage is developed and analyzed. The electrical power and refrigeration energy of the proposed system are about of 6666 kW and 5395 kW, respectively. The phase-change material storage sub-system consists of capric acid-lauric acid that in the absence of heat source of solar energy at night, 5395 kW refrigeration is released to cool at a temperature of 9 °C. The energy and exergy analyses are conducted and the obtained results show that overall thermal and total exergy efficiencies are about of 60.51% and 50.84%, respectively. The sensitivity analysis is performed to investigate the effect of the important operating parameters on the system performance. In this regard, Output temperature, generated heat energy and area of the photovoltaic thermal collectors; solar radiation, produced refrigeration and volume of thermal energy storage are selected. Also, the economic analysis is conducted and the obtained results indicate that the proposed system has an investment return period of 3.405 years and a prime cost of product of 20.45 US$ per ton of refrigeration.

Mixed integer linear programming for the design of solar thermal energy systems with short-term storage

In this paper a mixed integer linear programming (MILP) model is developed to facilitate the design of a solar domestic hot water system. The MILP model does so by optimising the area of roof mounted flat plate solar thermal collectors and the volume of thermal energy storage that are required to minimise the annual capital and operational cost of the overall energy system. A new formulation of the MILP is presented in which the model is decomposed into two sub-modules that are iteratively solved. One module determines the optimal sizing of the solar thermal collectors and storage tank. The other module optimises the hourly energy production of the solar collectors based on the impact that the collector inlet stream temperature has on the collector efficiency. This iterative formulation is compared to both a conventional MILP formulation and a dynamic simulation model to determine if the iterative formulation results in a design tool that is able to accurately represent the dynamic behaviour of a solar domestic hot water system, while maintaining the computational tractability and scalability of the model. The novel iterative MILP formulation is applied to a case study of an apartment building in Rheinfelden, Switzerland. The results indicate that conventional MILP formulations overestimate the amount of energy that solar thermal collectors are able to produce, resulting in an oversizing of the required thermal storage tank. However, the iterative MILP model more accurately predicts the energy production of the solar collector, leading to the more realistic sizing of the component technologies. This result is important when evaluating the financial feasibility of solar thermal collector systems in comparison to other renewable generation technologies, as an overestimation of the generation potential of solar thermal collectors may result in an incorrect assessment of their investment attractiveness.

Solar Hybrid Air Conditioner: Model Validation and Optimization

Solar air conditioners (A/Cs) have attracted much attention in research, but their performance and cost have to be optimized in order to become a real alternative to conventional A/C systems. In this study, a hybrid solar A/C is simulated using the transient systems simulation program(trnsys), which is coupled with matlab in order to carry out the optimization study. The trnsys model is experimentally validated prior to the optimization study. Two optimization problems are formulated with the following design variables: solar collector area, solar collector mass flow rate, solar thermal energy storage volume, and solar electrical energy storage size. The genetic algorithm (GA) is selected to solve the single-objective optimization problem and find the global optimum design for the lowest electrical consumption. To optimize the two objective functions simultaneously, energy consumption and total cost (TC), a multi-objective genetic algorithm (MOGA) is used to find the Pareto curve within the design variables' bounds while satisfying the constraints. The overall cost of the optimized solar A/C design is also compared to a standard vapor compression cycle (VCC). The results show that coupling trnsys and matlab expands trnsys optimization capability in solving more complex optimization problems. The results also show that the optimized solar hybrid A/C is not very competitive when the electricity prices are low and no governmental support is provided.

Thermal Energy Storage Thermal Response Model With Application to Thermal Management of High Power-Density Hand-Held Electronics

An important design objective that is unique to hand-held units is the need to constrain two temperatures: the maximum temperature of the electronic components and the maximum skin temperature of the hand-held unit. The present work identifies and evaluates, through parametric modeling and experiments, the passive thermal energy storage volume characteristics and phase change material composite properties that are most suitable for thermal control of small form-factor, high power-density, hand-held electronics. A one-dimensional transient analytical model, based on an integral heat balance, is formulated and benchmarked. The model accurately simulates the heat storage/recovery process in a semi-infinite, “dry” phase change material slab. Dimensional analysis identifies the time and temperature metrics and nondimensional parameters that describe the heat storage/release process. Parametric analysis illustrates how changes in these nondimensional parameters affect thermal energy storage volume thermal response.

Low temperature desalination using solar collectors augmented by thermal energy storage

A low temperature desalination process capable of producing 100 L/d freshwater was designed to utilize solar energy harvested from flat plate solar collectors. Since solar insolation is intermittent, a thermal energy storage system was incorporated to run the desalination process round the clock. The requirements for solar collector area as well as thermal energy storage volume were estimated based on the variations in solar insolation. Results from this theoretical study confirm that thermal energy storage is a useful component of the system for conserving thermal energy to meet the energy demand when direct solar energy resource is not available. Thermodynamic advantages of the low temperature desalination using thermal energy storage, as well as energy and environmental emissions payback period of the system powered by flat plate solar collectors are presented. It has been determined that a solar collector area of 18 m 2 with a thermal energy storage volume of 3 m 3 is adequate to produce 100 L/d of freshwater round the clock considering fluctuations in the weather conditions. An economic analysis on the desalination system with thermal energy storage is also presented.