Energy Storage Tank Research Articles

Model predictive control for optimal dispatch of chillers and thermal energy storage tank in airports

Cost of energy consumption is one of the biggest operational cost for airports, and it is increasing from time to time as airports expand to support growing number of passengers. Various factors affect the energy consumption including efficiency of airport Heating Ventilation and Air conditioning (HVAC) systems, which in turn depends on the efficiency of individual subsystems. In this paper, we present an optimal scheduling method for the central plant system at Dallas Fort Worth airport, involving chillers, pumps, and a thermal energy storage (TES) system. A model predictive control (MPC) problem is formulated to minimize both energy and demand charge costs while satisfying the cooling needs of the airport. The proposed Mixed-Integer Nonlinear Programming (MINLP) formulation includes performance curve based models for chillers and pumps and a simplified state of charge model for TES. The formulation also includes predictions of cooling load and chilled water return temperature. Simulation results for a month in summer show savings around 10% compared to the baseline. Initial recommendations based on insights from simulation results to the manual operation procedures resulted in significant savings. Field test results show a 7% chiller efficiency improvement.

Prediction of power generation output of compressed air energy storage tank based on temperature limitation

The pressure and temperature of the CAES system drop during the power generation process. This generation will be forced to stop when the temperature reaches the metal material limit. To avert the power generation process from stopping due to the temperature dropping too low, it is necessary to monitor and predict the power output of the CAES system in real time. By setting the relevant control operation logic, according to the temperature limit value of the gas canister, the minimum allowable temperature of the gas canister design, and the maximum value of the minimum allowable temperature of the pipe design between the gas canister and the heat exchanger, the minimum allowable temperature of the gas canister is obtained. the residual energy release energy and residual energy release time of the gas storage tank can be calculated by collecting relevant parameters in real time. It is verified by the simulation experiment of the 10 MW CAES system model. By monitoring the changes in parameters such as the temperature of the gas canister during the energy release process, the prediction model can calculate the compressed gas in the gas canister more accurately, and the power generation output can be predicted in the operation of the CASE system. Mastering the residual energy release energy and residual energy release time of the gas canister can arrange the operation mode in advance and improve the reliability of unit operation.

Experimental study on the thermal response of a metal foam dual phase change unit thermal storage tank

Adding fins or metal foam to phase change units can effectively enhance the heat storage efficiency of thermal energy storage (TES) tanks, thereby improving the reliability of TES tanks in coordinating renewable energy supply and demand. In this study, an experimental TES tank platform was designed and constructed to investigate how the addition of straight fins, metal foam, and straight fin/metal foam composite materials to paraffin affects the temperature response during the heat storage process. High-temperature water was selected as the heat transfer fluid (HTF) and injected from the top into the TES tank at the same paraffin fill level, and T-type thermocouples were arranged along the central axis of the phase change unit. TES tanks filled with either pure paraffin or composite phase change materials were tested by varying the HTF inlet temperature and velocity, and temperature response data were captured and recorded using a KEYSIGHT DAQ970A data logger. The results indicated that increasing the HTF inlet temperature significantly enhanced the heat storage rate while increasing the HTF inlet velocity had varying effects on different phase change units. A comprehensive analysis suggested that an inlet velocity of 1.3 m3/h (from a range of 0.8–1.8 m3/h) was reasonable. The addition of enhancement measures improved the temperature drift phenomena and effectively increased the temperature response rates and distribution uniformity. Moreover, the straight fin/metal foam composite material exhibited the best performance.

Vulnerability of Thermal Energy Storage Lining Material to Erosion Induced by Particulate Flow in Concentrated Solar Power Tower Systems.

Researchers from all around the world have been paying close attention to particle-based power tower technologies. On the King Saud University campus in the Kingdom of Saudi Arabia, the first integrated gas turbine-solar particle heating hybrid system has been realized. In this study, two different types of experiments were carried out to examine how susceptible prospective liner materials for thermal energy storage tanks were to erosion. An accelerated direct-impact test with high particulate temperature was the first experiment. A low-velocity mass-flow test was the second experiment, and it closely mimicked the flow circumstances in a real thermal energy storage tank. The tests were conducted on bare insulating fire bricks (IFBs) and IFBs coated with Tuffcrete 47, Matrigun 25 ACX, and Tuffcrete 60 M. The latter three lining materials were high-temperature-resilient materials made by Allied Mineral Products Inc. (AMP) (Columbus, OH, USA). The results showed that although IFBs coated with AMP materials worked well in this test, the accelerated direct-impact test significantly reduced the bulk of the bare IFB. As a result, lining substances must be added to the surface of IFBs to increase their strength and protection because they cannot be used in situations where particles directly impact their surface. On the other hand, the findings of the 60 h cold-particle mass-flow test revealed that the IFBs were not significantly eroded. Additionally, it was discovered that the degree of erosion on the samples of bare IFB was unaffected by the height of the particle bed.

Analysis and optimization of a sustainable hybrid solar-biomass polygeneration system for production of power, heating, drying, oxygen and ammonia

In this study, we introduce an innovative polygeneration system that combines solar and biomass energies to generate power, heating, hot air for the drying process, oxygen, and ammonia. The proposed polygeneration system comprises a solar tower subsystem (STS) integrated with two energy storage tanks (cold and hot), a gas turbine cycle (GTC), an organic Rankine cycle (ORC), a proton exchange membrane (PEM) electrolyzer, a thermoelectric generator (TEG), a cryogenic air separation unit (CASU), and an ammonia synthesis reactor (ASR). The GTC and the ORC equipped with the TEG are utilized for power production. The steam for the gasification process, hot air for the drying process and heating are produced by three regenerators. The PEM electrolyzer is used for the decomposition of water into hydrogen and oxygen, while the air separator (cryogenic method) is employed for the separation of air into nitrogen and oxygen. The separated oxygen is stored in an oxygen tank, while nitrogen and hydrogen are utilized for the ammonia generation. The system is evaluated from energy, exergy, economic and, environmental standpoints. Based on the findings, the proposed system is capable of generating approximately 163 MW of net power, 150 MW of heating, 100 MW of drying, 21.7 kmol/hr of oxygen and 23.24 kg/hr of ammonia. The total energy and exergy efficiencies, as well as the life cycle cost (LCC) and CO2 emissions are determined to be 70.68 %, 48.71 %, 1.175 × 109 $ and 381.3 kg/MWh, respectively. Additionally, a multi-objective Grey Wolf optimization algorithm is utilized to optimize the exergy efficiency, LCC, and CO2 emissions. The optimized results yield an exergy efficiency of 51.02 %, an LCC of 1.16 × 109 $, and a CO2 emissions of 359.73 kg/MWh. The proposed system demonstrates encouraging thermodynamic and economic performances, providing an appealing solution for efficient utilization of abundant solar and biomass resources.

Feasibility study: Economic and technical analysis of optimal configuration and operation of a hybrid CSP/PV/wind power cogeneration system with energy storage

In this study, a hybrid photovoltaic-wind-concentrated solar power renewable energy system and two cogeneration models are proposed. Evaluation criteria are employed, including the levelized cost of energy (LCOE) and the loss of power supply probability (LPSP). The optimal configuration and dynamic dispatch strategy of the hybrid system are determined through multi-objective optimization using the natural resources of Xining City. The economic feasibility of the system is assessed through comparison and analysis. The findings reveal that both cogeneration modes of the system effectively meet the power output requirements and dynamic thermal load. In thermal energy storage tanks' heat production mode without a battery storage system, the system achieves a minimum LCOE of 0.0526$/kWh and a maximum LPSP of 6.86%. With a battery storage system in this mode, the system attains a minimum LPSP of 4.83% and a maximum LCOE of 0.160$/kWh. Additionally, in the turbine spent vapor recovery heat supply mode, the system exhibits an LCOE of 0.127$/kWh and an LPSP of 4.96%, the system has better flexibility and wind-solar complementarity in this mode. This study also analyzed the importance of affordable electric energy storage for stable energy supply in hybrid energy systems.

Evaluation & optimization of solar-fossil-fuel-based multi-generation system with energy storage

The integrated solar energy hybrid system combines decentralized, energy-efficient approaches to various energy production methods, offering benefits such as improved efficiency, emissions reduction, cost-effectiveness, sustainability and reliability. Thus, in this study, the optimal design of a solar-fossil-fuel-based combined cooling, heating, power and freshwater generation system is presented. The main prime movers for generating power and heat concurrently are considered gas engines, diesel engines, gas turbines, and solid oxide fuel cell. The suggested system configuration contains a prime mover, two chillers, auxiliary boiler, desalination unit, parabolic trough collectors, photovoltaic panels, proton exchange membrane electrolyzer, thermal and cooling storage tanks. The genetic algorithm is considered as the optimization method for determining the lowest total annual cost. Various decision parameters are considered in this assessment, including the prime mover's capacity and operating under 12 partial loads, the number of prime movers, mass flow rate of the solar parabolic trough collectors, the electric cooling ratio, operation of 16 partial loads for chillers (with each chiller accommodating 8 partial loads), capacity of the auxiliary boiler, thermal and cooling energy storage tank capacities, number of photovoltaic panels, and the isentropic efficiency of the high pressure pump. The total annual cost comprises economic, energy, and environmental factors. Notably, the current system permits the purchase or sale of electricity to the grid. The optimal results disclosed a reduction of 27.08 %, 13.83 %, and a 23.80 % in the total annual cost of the system including the gas engine compared to the system with solid oxide fuel cell, diesel engine, and gas turbine, respectively. Furthermore, the system with solid oxide fuel cell showed fuel energy savings ratios of 48.6 %, 38.26 %, and 24.46 %, respectively, compared to the system including gas turbine, gas engine, and diesel engine. Additionally, in comparison to systems with solid oxide fuel cell, diesel engine, and gas turbine, the exergy efficiency of the system with gas engine is higher approximately 40.31 %, 3.04 %, and 92.50 %, respectively. The optimum total annual cost and exergy efficiency were determined to be 1.6708 ×106 $/year and 42.08 %, respectively, for the system utilizing the gas engine. Eventually, the comparison and analysis of optimal results from energy, exergy, economic and environmental perspectives were presented.

Optimization of PCM layer height of cascaded two-layered packed-bed thermal energy storage tank with capsules of varying diameters based on genetic algorithm

The packed-bed thermal energy storage (PBTES) technology exhibits significant potential for utilization in various energy sectors, including concentrating solar power, city heating systems and power peaking. This paper uses a genetic algorithm (GA) to optimize the phase change material (PCM) layer height arrangement of cascaded two-layered PBTES with capsules of varying diameters to enhance thermal performance during charging. The optimization process considers the oscillatory distribution of radial porosity, and the objective function utilized for assessing the thermal performance of the system is thermal energy storage (TES) rate density. The TES rate density for over 2000 different layer height arrangements was calculated. The findings indicate that the PCM layer height significantly influences the thermal performance of the tank in each layer. The charging performance is optimal when the layer height ratio of high and low melting point PCM is 12.05 % and 87.95 %, respectively, which is the optimal model. In comparison to the original model with equal bed height, the optimal model demonstrates a reduction in charging time of 28 %, increases the TES rate density by 17.68 %, and the greatest improvement in charging efficiency reached 31.28 %. And reduces the unit TES cost by 13 %. This study shows that GA is an effective tool for optimizing the structural arrangement of PBTES.

Experimental Evaluation of a Pilot-Scale Thermocline Thermal Energy Storage Combining Latent and Sensible Materials

This work presents the experimental evaluation of pilot-scale thermocline that integrates a layer of phase change material (PCM) at the top of a sensible heat storage material in a thermocline thermal energy storage (TES) tank. The TES is integrated to the MicroSol-R parabolic trough pilot plant at the PROMES research facility in Odeillo, France. The tank is filled with alumina spheres as sensible heat storage. The PCM is NaNO3 encapsulated in stainless steel horizontal tubes that fill about 5.5% of the tank volume. The charge is evaluated at three mass flow rates 2600, 3000, and 3900 kg/h at two different operating temperature ranges 285-315 ºC and 295-330 ºC. The discharge is studied at three mass flow rates 1600, 2000, and 3000 kg/h from 315 to 220 ºC and 330 to 225 ºC. The performance of the TES is analyzed with two main indicators: the thermocline thickness and the efficiency during the charge and discharge. The results indicate that lower mass flow rates during the charging process result in smaller thermocline thickness. Similarly, during discharge, the thermocline thickness reduces with lower discharge rates. Efficiency evaluation during discharge suggests that an optimal flow rate could be achieved.

Theoretical and experimental analysis of the impact of a recuperative stage on the performance of an ORC-based solar microcogeneration unit

Microgeneration ORC-based units driven by solar energy, which enable combined heat and power generation (CHP), are a promising solution for decarbonizing the domestic sector. However, the intermittent availability of solar energy, coupled with the variability in user demand for domestic hot water (DHW), can lead the system to frequent off-design conditions and a less reliable energy supply. Consequently, increasing attention has recently been focused on the technological and design solutions for improving plant performance and ensuring its continuous operation. This paper presents the results of an experimental campaign carried out to investigate the possible advantages – in terms of efficiency and savings of thermal energy in the upper source – of introducing a recovery heat exchanger (RHX) in the basic configuration of a solar ORC-based system. Tests were conducted on a fully instrumented ORC-based plant with two 12 kW electric heaters providing the thermal power recovered through the solar collectors. The RHX is introduced into a recuperative branch that can be bypassed by closing a dedicated three-way valve. The study aims to investigate the behavior of the ORC unit in the absence of solar radiation (with the electric heaters switched off) when the recovery unit is powered only by the hot water stored in the Thermal Energy Storage (TES) tank. Another purpose of the present work is to evaluate the benefits introduced by the RHX in reducing the temperature decrease of the TES hot water and, consequently, maximizing the operating time of the ORC-based unit. In order to support the experimental analysis, a comprehensive theoretical model of the unit was developed and validated against experimental data. The model was used as a software platform to optimize the plant design and recuperative branch configuration. The theoretical model was developed in the GT-Suite™ environment thus integrating a mono and zero-thermo-fluid-dynamic approach. In this way, a physical representation of the entire ORC-based unit is performed allowing also to define an optimal control strategy for maximizing plant performance under severe off-design and transient conditions.

CFD analysis and optimization of thermal stratification in a Thermal Diode Tank (TDT)

Thermal stratification is a common and natural phenomenon in energy storage tanks. This paper presents a Computational Fluid Dynamics (CFD) analysis of thermal stratification within a novel cold energy storage, termed a Thermal Diode Tank (TDT). The TDT is a well-insulated water tank equipped with heat pipes for unidirectional heat transfer from water to the ambient air. When integrated into a Refrigeration and Air-conditioning (RAC) system, it provides cooling water to reduce the condensing temperature. The research problem revolves around the impact of thermal stratification on TDT performance and the identification of the optimal TDT structure when thermal stratification is present. Therefore, this study aims to employ CFD to simulate temperature profiles within a TDT, both with and without an obstacle. With validated models, parametric analysis has been conducted to determine the optimal TDT structure. Several design parameters have been investigated, including tank orientation, heat transfer capacity, the ratio of obstacle axial height to TDT height (ho/H), and the ratio of obstacle hole diameter to TDT diameter (do/D). Key findings reveal that a vertical tank orientation is more conducive to improving the TDT assisted RAC system performance than a horizontal one. Increasing the TDT's heat transfer capacity also positively contributes to the system performance. Parameters of an optimal TDT structure include a ho/H ratio of approximately 0.43 and a do/D ratio of 0.4. It is found that the do/D ratio should be at least 0.15 to obtain positive stratification. Furthermore, the presence of thermal stratification can increase the system's Coefficient of Performance (COP) by up to 10 %.

Visualization study on double-diffusive convection during a rollover in liquid energy storage tanks

The growing global energy consumption and the transition to the renewable era highlight the urgent need for safe and energy-efficient liquid energy storage tanks. Rollover has been a severe hazard to the efficiency and safety of the storage tank accompanied by significantly enhanced mass and heat transport across the stratified layers, and rapid evaporation and mixing of the layers happen. However there is a lack of experiments sophistically designed for cryogenic storage applications, which leads to a lack of visualized and quantitative experimental data to understand the physics of rollover in energy storage tanks. In this study, a Z-type Schlieren system is established to visually reveal the double-diffusive convection patterns in a cylindrical experimental chamber. The concentrations of salt-water solutions are adjusted to simulate the density difference between the multi-component cryogenic fluids. Cross-correlation algorithm is adopted to analyze the transient velocity distributions in the stratified system. The rollover process is divided into four stages, namely the initial, transition, mixing, and stable stages. Effects of heat flux, concentration difference, and heating location on the rollover characteristics are parametrically investigated. Correlations are proposed with rescaled buoyancy ratio and density gradient, and satisfactory agreement with experimental data is achieved.

Enhancing energy efficiency of air conditioning system through optimization of PCM-based cold energy storage tank: A data center case study

Phase change material (PCM)-based cold energy storage systems (CESS) offer a promising solution for improving energy efficiency and cost-effectiveness in air conditioning systems. However, their limited heat transfer efficiency hinders widespread adoption. This study focuses on investigating the impact of key factors, including plate size, arrangement, and fin structure, on the charging and discharging processes of a PCM-based CES tank. The findings highlight the significant influence of PCM plate configuration and inlet flow rate on heat transfer performance in the storage tank. Notably, reducing the height of PCM plate from 50 mm to 10 mm while maintaining a consistent volume resulted in a remarkable reduction in charging/discharging time by 84.6 % and 87.9 %, respectively. Response surface models were developed to establish correlations between the number of fins, plate height, and inlet flow rate with the charging/discharging time of PCM plates, enabling the identification of the optimal solution for achieving faster charging/discharging times. Moreover, a case study in a data center retrofit project was conducted to evaluate the thermal performance of different PCM plate configurations. Despite the higher initial investment, the optimized solution demonstrated a higher effective utilization rate of the PCM-based CESS, leading to substantial energy savings and reduced carbon emissions.

Numerical Research on Thermodynamic Properties of a Thermocline in Thermal Energy Storage Tank Based on Modified One-Dimensional Dimensionless Model

The application of thermal energy storage (TES) has been proved effective to improve the energy utilization efficiency of renewable energy and industrial waste heat energy. In this paper, a modified one-dimensional dimensionless model for the thermocline thermal energy storage tank is derived to simulate the system more accurately. An adaptive strategy for solving region compartmentalization is proposed for reducing computing time. Based on the proposed model, the effects of three different parameters on the performance of the thermocline tank are studied. The results show that increasing the inlet velocity can reduce the thickness of the thermocline and improve the system efficiency. Increasing the temperature difference between hot and cold water leads to a thicker thermocline, but the thermal energy stored in the tank increases. Increasing the tank height has no effect on the motion characteristic of thermocline, but the system efficiency can be increased.

Charging characteristics of finned thermal energy storage tube under variable rotation

Solar photovoltaic-thermal (PVT) systems effectively offset the drawbacks of intermittent solar and low photovoltaic conversion efficiency. Thermal energy storage (TES) tanks of PVT systems with high charging efficiency and consistent thermal safety might achieve efficient utilization of solar energy for building. A new variable rotational strategy has been proposed to optimize the charging characteristics for TES tubes, taking into consideration the non-uniformity of melting. A series of simulations based on the volume-averaged model are conducted to investigate the thermal energy storage property of TES tubes under variable rotary mechanism. Qualitative and quantitative comparisons are made between variable rotation (ω = 1.5–0.5, 1.5–1.0, 1.5–2.0 rad·s−1), constant rotation (ω = 1.5 rad·s−1), and stationary systems. The focus of the comparison is melting efficiency, temperature distribution, and natural convection. The results indicate that rotation effectively shortens charging time, with a 57.62% and 15.73% reduction with variable rotary mechanisms of 1.5–1.0 rad·s−1 when compared with stationary and constant rotating tubes. Meanwhile, in the final moment, the greatest medium-temperature (55–65 °C) proportion of 90.58% and less low-temperature (25–55 °C) and high-temperature (65–70 °C) paraffin occupation of 4.67% and 4.75% could be obtained, reflecting the completed latent heat storage and stable thermal safety. The optimal variable rotation achieves improvements of 47.84% and 106.73% in time-integral Grashof number (Gr) and heat storage rate, compared with traditional stationary tubes.

Benefits through Space Heating and Thermal Storage with Demand Response Control for a District-Heated Office Building

Demand response techniques can be effective at reducing heating costs for building owners. However, few studies have considered the dynamic marginal costs for district heating production and taken advantage of them for building-level demand response. In this study, a district heating network in the Finnish city of Espoo was modeled to define dynamic district heat prices. The benefits of two demand response control approaches for a Finnish office building, the demand response control of space heating and a thermal energy storage tank, were evaluated by comparing them to each other and utilizing them together. A 5 m3 storage tank was installed in a substation of a conventional high-temperature district heating network. A new demand response control strategy was designed to make the most of the storage tank capacity, considering dynamic district heat prices and the maximum allowed return water temperature. The results indicate that the demand response control of space heating and the storage tank cut district heat energy costs by 9.6% and 3.4%, respectively. When employing the two approaches simultaneously, 12.8% savings of district heat energy costs were attained. Additionally, thermal energy storage provides more potential for peak power limiting. The maximum heating power decreases by 43% and the power fee reduces by 41.2%. Therefore, the total cost, including the district heat energy cost and the power fee, can be cut up to 22.4% without compromising thermal comfort and heat supply temperatures to ventilation systems.

Performance Evaluation and Optimal Design Analysis of Continuous-Operation Solar-Driven Cooling Absorption Systems With Thermal Energy Storage

Abstract A solar absorption cooling system consisting of a flat plate collector, thermal energy storage tank, and absorption chiller is analyzed in this work. A dimensionless model is developed from the energy balance on each component and the chiller’s characteristic performance curves. The model is used to determine the interaction and influence of different parameters such as tank size, solar collector area, chiller size, cooling load, cooling temperature, heat loss, and mass flow rates on the performance. From the analysis, smaller solar collector areas are required for lower cooling loads and smaller tank volumes. A specific cooling load of 1 × 10−5 will require a specific solar collector area between two and six times larger, depending on the initial tank temperature, than the area required for a baseline system that considers typical commercial design and operation parameters. A similar behavior was observed for the specific tank volume. For the baseline system, the minimum specific area of the collector of 9.57 is achieved for an initial tank temperature of 1.19. For a cooling load of 1 × 10−5, the optimum initial tank temperature will be 1.11 that results in a minimum specific solar collector area of 25.26. A specific tank volume of 4 × 10−4 will also have an optimum initial tank temperature of 1.11 that minimizes the specific solar collector area to a value of 28.18. The approach and analysis in this work can be used to determine design parameters for solar absorption cooling systems based on a proper relation among system’s dimensions to achieve optimum operation.

Thermal energy simulation of the building with heating tube embedded in the wall in the presence of different PCM materials

A large part of energy consumption around the world is spent on buildings. Improving and optimizing the thermal performance of buildings can reduce energy consumption. Phase change materials inside an envelope can act as a latent thermal energy storage tank and also prevent energy loss. In the present study, we have investigated the effects of adding PCM inside the wall of buildings, and a tube for heating is embedded inside the wall. The performance of the system has been evaluated based on computational fluid dynamics simulation in Open Foam software. PIMPLE algorithm and finite volume method were used to solve the governing equations. Three different arrangements of tubes are considered at the upper, middle, and bottom of the wall introduced as UTA, MTA, and BTA, respectively. Furthermore, it is assumed that the heat flux is in the range of solar heat flux that enters the system from the embedded tube. Three different tube arrangements, three heat fluxes, and two different types of PCMs have been investigated in this study to find the best integration of the system. The simulation results revealed that for Lauric acid, by increasing the heat flux from 200 to 400 Wm2, the melting time decreases from 9 to 2 h. Also, for Paraffin the melting start time reaches 2.5h from 10 h. Also, Lauric acid can store or discharge thermal energy for the long term. The highest percentage of stored energy is related to Lauric acid, which saves 13.8 % of the total input heat flux as latent energy and Paraffin stores up to 11.8 % of latent heat energy.

Evaluation of operational strategy of cooling and thermal energy storage tanks in optimal design of multi generation system

In this study, optimal design of solar combined cooling, heating, power, freshwater (FW) and hydrogen (CCHPWH) generation system using parabolic trough collectors (PTC), proton exchange membrane (PEM) electrolyzer and multi-effect evaporation with thermal vapor compression (MEE-TVC) is investigated. The CCHPWH + PTC system according to thermal energy storage (TES) tank with constant partial load (CPL) for chillers (case 1) and CCHPWH + TES + PTC including cooling energy storage (CES) tank system with variable partial load (VPL) strategy for chillers (case 2) in hot climate are compared to each other, and with CCHPWH system with CPL strategy (case 3) and with VPL strategy (case 4), respectively. The optimal results illustrated 0.64% reduction in the TAC of CCHPWH + TES + PTC + CES system with VPL strategy as compared to CCHPWH + TES + PTC system with CPL strategy. Notably, it was observed 4.55% and 4.67% decrement in the TAC of CCHPWH + TES + PTC + CES system with VPL strategy and CCHPWH + TES + PTC system with CPL strategy as compared to CCHPWH system with VPL and CPL strategy, respectively. As well as, energy and exergy efficiency of the CCHPWH + TES + PTC + CES system with VPL strategy in the optimal mood increased 11.85% and 19.05% in comparison with CCHPWH + TES + PTC with CPL strategy. Eventually, proposed cases were optimized and discussed from energy, exergy, economic, environmental.

Enhancing the performance of solar water heating systems: Application of double-layer phase change materials

An efficiently designed thermal energy storage (TES) tank is critical for enhancing the efficiency of solar water heating systems (SWHSs). This study describes the development of a hybrid sensible-latent TES tank in which a double-layer phase change material (PCM) with different melting points is integrated. To study its performance, a mathematical model of the SWHS with the hybrid tank was established in TRNSYS software. The results showed that when the volume of tank per unit area of solar collectors was in the range of 33.3–66.7 L/m2, the heat collection of the hybrid tank increased by 7.0%–15.6% and the heat supply increased by 7.6%–16.9% compared to that of the tank without the PCM. However, the effect of adding the PCM to the tank diminished when the volume of the tank was increased. The hybrid tank with the double-layer PCM achieved a twofold benefit of extending the heat supply time and maintaining a relatively high supply temperature compared to the tank with only a single-layer PCM. The effect of the hybrid tank on the thermal performance of the SWHS was prominent for the full-day and nighttime heating modes but was not significantly observed for the daytime heating mode.