Phase Change Material Thermal Energy Research Articles

Benefits of zeotropic mixture for heat pump water heater with phase change material thermal energy storage

Integrating heat pump water heater (HPWH) into latent heat thermal energy storage (LHTES) with phase change material (PCM) has been recognized as a promising way to mitigate the energy use for heating water in the building sector. This paper uses zeotropic mixture R1234yf/R1234ze(Z) in HPWH and spherical PCM encapsulations in LHTES. The mathematical model is established and validated. Effects of zeotropic mixture composition, working fluid flow rate and heat transfer fluid (HTF) flow rate are discussed to reveal the instantaneous behaviors and overall performance of the integrated system. The results indicate that as the charging process progresses, the condensing pressure of the system steadily increases, leading to a decline in COP. By employing zeotropic mixtures, the system performance can be effectively improved, with the highest COP of 2.68 when the mass fraction of R1234ze(Z) is 70 %, which represents an 18.1 % and 6.8 % improved COP compared to R1234yf and R1234ze(Z), respectively. A smaller refrigerant flow rate or a larger HTF flow rate contributes to a higher COP. For heat storage capacity in LHTES, a higher mass fraction of R1234ze(Z) and a larger refrigerant flow rate are preferable, while a smaller HTF flow rate is beneficial. Finally, a multi-objective optimization is carried out. Results suggest that the best overall performance is achieved with a COP of 2.70 and a heat storage capacity of 629.24MJ, under conditions of the mass fraction of R1234ze(Z) at 70 %, a refrigerant flow rate of 0.28 kg/s, and an HTF flow rate of 0.46 kg/s.

Deployment of Dedicative Nanoadditives to Enhance the Thermal Behavior and Effectiveness of Heat Transfer Performance of Eutectic Compound

ABSTRACTTwo nanoprecursors with capping agents were incorporated in stearyl alcohol–adipic acid combination phase change material (PCM) in this study. The addition of nanomaterials made the eutectic reliable in the manner of its thermal properties like higher enthalpy, degradation point, and more compatible with the metal encapsulation materials when compared with the pristane eutectic. The importance of nano‐metal oxides in parent material was shown by the reduced time frame of the PCM's thermal energy storing and releasing process for space heating applications. The specific heat capacity of both the aluminum and titanium oxide nanocomposites were greater than the eutectic, which indicates that the material can retain more energy. The thermal conductivities of base material and nanocomposite PCMs were 0.2686, 0.2815, and 0.4395 W/mK at 40°C, and the highest percentage increment of nanocomposites was seen as 9.19% and 63.62% at varied encircled temperatures. The crystal structure and chemical disintegration were evinced with the X‐ray diffractometer results of the composites.

Residential Micro-CHP system with integrated phase change material thermal energy storage

This paper presents an analysis and experimental investigation of the effect of integrating Phase Change Material (PCM) within a heat exchanger within a Micro Combined Heat and Power (Micro-CHP) system intended for residential applications. A commonly used Micro-CHP layout is replicated in a test rig to characterise the performance of two alternative heat exchanger arrangements. The first is a conventional arrangement where the exhaust gas produced by the prime mover is directed to an air-to-water heat exchanger to heat water and store it in a tank. In the second arrangement, PCM material is encapsulated within specially designed compartments in a heat exchanger to store part of the exhaust thermal energy from the prime mover while heating the water in the storage tank. The time needed to heat the water and discharge heat is compared for both cases, as well as the amount of thermal energy stored during the same operating period. The study also explored the potential to improve the designed unit by using different PCM materials. The test results show that adding 4.7 L capacity paraffin compartments within the heat exchanger extended the discharge time of the hot water by over 400 %, which reflects a marked improvement in the heat storage capacity of the system. This would result in a significant increase in the viable operating period of a CHP system. The one-dimensional analysis revealed that replacing the paraffin with ClimSel C58 PCM can reduce the charging time of the water tank by around 54 % improve the heat storage capacity by factor of 2.35 comparing to Paraffin. The proposed heat exchanger with encapsulated PCM has a potential in other applications such as storage of excess renewable energy or integration with heat pumps to improve matching of supply and demand and thus flexibility of an energy system with integrated intermittent renewables.

Thermal management of high-powered short-duration electronics aided by a phase change material thermal energy storage

Quantifying the performance of phase change materials (PCMs) for thermal energy storage in high-power short-duration electronics applications requires performing tests that push the material to its limit. This involves designing experiments to test solid-liquid PCMs in near real-world thermal load conditions to test its performance. Conventional cooling methods are sized to manage the maximum loading the cooling system will be subjected to in its operation, even if this loading occurs for a short period of time. This design ethos is inefficient and results in heavy and expensive equipment being used in an application where it will be underutilized most of its useful life. In this work, a PCM thermal energy storage (TES) device was built using a plate-and-frame heat exchanger and investigated to determine the suitability of this system to manage the temperature of high-power electronics with a low duty cycle. These experiments showed how a PCM-TES can be used in conjunction with conventional temperature management equipment to create a reliable cooling solution while allowing the conventional cooling components to be decreased in size and capacity. This work shows that, for a given application, a cooling system can be more efficiently designed with the use of a PCM-TES and opens the door to additional research on this topic.

Numerical investigation of an amalgamation of two phase change materials thermal energy storage system

In the last three decades, many researchers have published their findings on the storage of thermal energy using various phase transition materials (both organic and non-organic). One of their goals was to have a higher heat storage capacity with a shorter heat charging cycle for thermal energy storage. This study looked into a floating capsule thermal energy storage system (TESS). A number of spherical capsules filled with beeswax were placed in a paraffin-filled cylindrical shell. With heat transfer fluid flowing through three hexagonal tubes arranged at 120° inside the TESS core, the two phase change materials (beeswax with a thermal conductivity of 0.25 W/mK and paraffin with a thermal conductivity of 0.23 W/mK) were charged and discharged. For the proposed TESS, a mathematical model was created and utilised to forecast thermal energy storage capacity and charging/discharge times for various configurations. In TESS, a 70–30% mixture of the two PCMs results in a 21.5 percent increase in heat storage capacity when beeswax alone is used, and an 8.4 percent decrease in storage capacity when paraffin alone is used. For a heat storage capacity of 7300 kJ, the model estimates charging and discharging times of around 2.6 and 3.2 hours, respectively.

Scale-Up Considerations of the Sundial Rotating Fresnel Solar Collector

In the frame of the ASTEP project two prototypes of the Sundial collector, together with a Phase Change Material Thermal Energy Storage, will be tested integrated with the industrial processes of two sites. However, the size of the pilot systems will not be optimized for commercialization. The present work considers the scale-up of the concept for one of the pilot industrial sites: a dairy industry located in Greece, and how will the thermal losses of the system must be considered with the increased aperture, thermal storage size and energy output. For the scaling up of the system, the capacities of the Sundial, demand and TES were doubled and multiplied by 10, and the thermal losses of both nominal conditions and annual performance were considered. The results showed that the ratio between the piping heat losses and the total available energy decreased when scaling-up the system both in the nominal and in the annual results. Hence, the heat losses lost importance when scaling up, when more energy was available. These facts should be considered when evaluating the performance of the pilots and feasibility of the concept.

Development and experimental investigation of full-scale phase change material thermal energy storage prototype for domestic hot water applications

The paper presents an experimental analysis of the full-scale phase change material (PCM) thermal energy storage (TES) prototype that is designed for use in domestic hot water preparation systems. The PCM-TES prototype is based on the external arrangement of organic PCM and a custom-made compact fin-and-tube type of heat exchanger. The prototype has been designed, constructed, and tested according to the Ecodesign Directive requirements for water heaters and hot water storage tanks. Several parameters have been analysed, including the heat transfer fluid (HTF) temperature and mass flow rate, heat transfer rate, accumulated and released energy, and quantity of domestic hot water (DHW) delivered. Additional attention was paid to the reliability and repeatability of the results. Experimental research allowed to determine the quantity and temperature of DHW at a constant mass flow rate of 0.1 kg/s. The prototype unit showed that it can deliver 99.1 l of hot water at 40 °C for up to 15 min and 39 s, while the use of lower temperature DHW (up to 37 °C) allows to increase the quantity of hot water delivered up to 156.2 l. Experimental results showed the viability of the prototype, areas for improvement and further possibilities for its optimization. Overall, the study results are relevant for developing latent heat thermal energy storage systems using fin-and-tube heat exchangers in tanks and the feasibility of integrating such systems into DHW systems.

Adaptive machine learning based control of multi-temperature, multi-module latent thermal storage ensembles

Phase change material thermal energy storage systems can be used to alleviate disparities in renewable energy supply and demand. Performance of such systems can be enhanced using a cascade of multiple phase change materials but efficiency benefits currently rely on precise optimization of design parameters. Therefore, there is motivation to develop storage technologies which provide greater flexibility for applications with dynamic operating conditions. In this study, a novel system is proposed called a multi-temperature, multi-module ensemble which consists of multiple phase change materials combined in series and parallel configurations. The system is optimized and controlled by an artificial neural network trained using a multi-objective optimization scheme. The performance for the novel system is compared to two baseline systems: a single phase change material system and a cascaded system. Across a wide range of fixed operating conditions, the results show that the ensemble reduces the rate of exergy destruction by 60% compared to the single module system and achieves a 10 °C improvement in performance for matching target outlet temperature compared to the cascaded system. Over a dynamically changing load profile, the results show that the multi-temperature, multi-module ensemble with artificial neural network controller is the preferable design as it achieves the excellent exergy efficiency of a cascaded system while maintaining the flexibility needed to respond to dynamically changing operating conditions. Furthermore, this novel approach widens the potential applications of latent thermal energy storage by providing a means to standardize manufacturing to drive down system cost and allowing the system to adapt to unforeseen design parameters.

Phase-Change Material Thermal Energy Storage for the Smart Retrofitting of Existing Buildings

This article presents the use of phase-change material (PCM) thermal storage within the Horizon 2020 HEART project (Holistic Energy and Architectural Retrofit Toolkit), aimed at decarbonising the European building sector through the retrofitting of existing structures into energy-efficient smart buildings. These buildings not only reduce energy consumption, but also incorporate advanced technologies for harnessing green energy, thereby promoting environmental sustainability. The HEART project employs state-of-the-art technologies for electricity production/dispatching and heat generation/storage, managed by a cloud-based platform for the real-time monitoring of parameters and optimising energy utilisation, enabling users to control their environmental comfort. The article provides a detailed examination of one of the project’s demonstration sites in Italy, focusing on various components such as heat pumps, photovoltaic systems (PV), controllers, and particularly emphasising the significance of storage tanks. The study involved the measurement and analysis of three heat storage tanks, each with a total volume of 3000 L. These tanks utilised PCM modules for latent heat storage, significantly enhancing overall heat accumulation. Water served as the heat transfer fluid within the tanks. Through meticulous calculations, the article quantifies the accumulated heat and presents a comparative evaluation between PCM-based storage tanks and conventional water tanks, showcasing the advantages of PCM technology in terms of increased heat retention and efficiency.

Heat pump water heater enhanced with phase change materials thermal energy storage: Modeling study

A promising solution to improve the first hour rating (FHR) of a heat pump water heater (HPWH) involves employing a secondary tank which contains phase change material (PCM) capsules. To better understand the influence of PCM thermal storage on the HPWH operational performance, a dynamic model was developed to simulate and analyze the behavior of a newly developed HPWH technology that incorporates PCM storage into a standard HPWH to optimize key parameters such as the uniform energy factor and FHR. Mathematical models of several key components of the proposed HPWH-PCM integrated thermal energy storage (TES) system, e.g., water heater tank, PCM TES tank, evaporator, compressor, and expansion valve, have been elaborated. Also, a model-based control co-simulation platform was developed to integrate a embed PCM storage HPWH dynamic model with a control model for better supporting control design, analysis, verification, and validation. The model accuracy has been validated through comparing simulation results with lab test results, with a mean average percentage error of <5.5% for most of the selected performance variables. In addition, using the developed co-simulation platform, the demand response control strategy was studied to evaluate the load flexibility of the combined HPWH-PCM storage system by shifting system power usage to outside of the 3.5 h peak load period.

Dynamic modelling of a compressed heat energy storage (CHEST) system integrated with a cascaded phase change materials thermal energy storage

Carnot batteries represent an emerging thermo-mechanical energy storage technology based on the conversion of surplus electricity into medium–low temperature heat, and subsequent conversion of the heat into electricity. A promising Carnot battery’s configuration is the Compressed Heat Energy Storage (CHEST) that combines a high-temperature heat pump (charge phase), an Organic Rankine Cycle (discharge phase) and a thermal energy storage (TES) system. As of now, all the literature studies on CHEST were designed to store the thermal energy into a cascaded TES combining a pressurized water storage for the sensible section and latent heat material for the evaporation and condensation sections. The objective of the present work is to numerically investigate a novel configuration of the TES system utilizing a cascade of multiple phase change materials (PCMs) in place of the cascade of sensible heat and phase change materials presented in literature, aiming to enhance both the energy density and the round trip efficiency of the system. The comparative technical analysis has been carried out by developing for the first time a dynamic numerical model of the CHEST system. Indeed, while the current literature studies on CHEST are only focused on preliminary analyses to define the general thermodynamic potential and to identify the limits of the overall system, this paper overcomes this gap and presents a detailed dynamic analysis of the CHEST with focus on TES modelling. Notably, the authors developed a plant model in MATLAB that blends together algebraic and differential sub-models detailing the transient behaviour of the CHEST system. The results are of interest for academia and industry and contribute significantly to the development of a more efficient CHEST system. Indeed, by enhancing the thermal buffer effect typical of PCM media, the cascaded TES augments both the COP of the high-temperature heat pump (4.13 vs 3.79) and the electric efficiency of the ORC (11.69 % vs 11.31 %). As a result, the novel CHEST system based on cascaded PCMs is capable to achieve a round trip efficiency of 47.6 % and an energy density of 6.9 kWhe/m3, simultaneously increasing the respective values of the state-of-the-art solution by 13 % and 100 %, respectively.

Phase change material based thermal energy storage applications for air conditioning: Review

• Application of PCM TES for indoor environment control is presented. • From assessments made, 5% energy savings can be achieved by using PCM TES. • PCMs integration in AC unit enhance its coefficient of performance by ∼ 1.8% least. • Optimized PCM TES units can reduce CO 2 emissions by 30%. Phase change material thermal energy storage is a potent solution for energy savings in air conditioning applications. Wherefore thermal comfort is an essential aspect of the human life, air conditioning energy usages have soared significantly due to extreme climates, population growth and rising of living standards. Resultantly research efforts have shown increasing innovation towards the integration of phase change material based thermal energy storage technology with space heating/cooling systems to achieve significant savings. The review therefore focuses on the previous published experimental and theoretical works to organize these important milestones, analyze energy saving avenues as well as giving highlights on best practices and widely accepted techniques and recommendations for all reviewed studies to achieve cost cutting but accurate results. It also discusses the useful enhancements that can be implemented for optimum performance of the PCMs. The reviewed potential benefits of PCMs integration in air conditioning units include enhancements in the coefficient of performance by ∼1.8% at minimum, at least 5% energy savings and estimated reduction of CO 2 emissions by about 30%.

Phase change material thermal energy storage design of packed bed units

Heat transfer enhancement and optimization are found to be essential for the PCM (phase change material) thermal energy storage design. In this work, the performance advantage of the packed bed PCM storage unit design is analyzed in comparison, and the impacts of key geometric parameters of a packed bed unit were numerically investigated. The optimized shell-and-tube design, based on the hexagonal circle configuration, serves as the benchmark for the comparison. The thresholds of the bed and PCM-capsule diameter ratio,D/d, is found, above which the effective energy storage capacity of the packed bed would be higher than that of an optimal shell-and-tube unit. The threshold of D/d can be quantitatively correlated to the superficial velocity of the heat transfer fluid, providing a pathway for the tailored design of a packed bed PCM thermal storage system. In conclusion, it was found that packed bed units are advantageous due to their larger surface-to-volume ratio, in particular in large-scale applications. This work proposes a numerical analysis based framework to design packed bed PCM storage units in comparison with shell-and-tube units so that a proper type of PCM thermal storage design can be selected under a specific geometric and operational condition.

Nanofibers for Renewable Energy

Electrospinning is a straightforward technique for the fabrication of nanofibers with the potential for various applications. Thermal energy storage systems using electrospun nanofibers have gained researchers’ attention due to its desirable properties such as nanoscale diameter, large surface area, excellent thermal conductivity, and high loading and thermal energy storage capacity. The encapsulation of phase change materials (PCMs) in electrospun nanofibers for storing renewable thermal energy can be achieved by uniaxial electrospinning of a blend of PCM and polymer, coaxial electrospinning of a PCM core and a polymer sheath, or post-electrospinning absorption. The PCM content and thermal energy storage capacity of different PCM composite nanofibers are compared in this chapter. The drawbacks of traditional electrospinning PCM encapsulation techniques and benefits of post-electrospinning encapsulation methods are discussed.

Latent Thermal Energy Storage Application in a Residential Building at a Mediterranean Climate

An innovative thermal energy storage system (TESSe2b) was retrofitted in a residential building in Cyprus with a typical Mediterranean climate. The system comprises flat-plate solar collectors, thermal energy storage tanks filled with organic phase change material, a geothermal installation consisting of borehole heat exchangers with and without phase change material and a ground source heat pump, an advanced self-learning control system, backup devices and several other auxiliary components. The thermal energy storage tanks cover the building’s needs at certain temperature ranges (10–17 °C for cooling, 38–45 °C for heating and 50–60 °C for domestic hot water). A performance evaluation was conducted by comparing the TESSe2b system with the existing conventional heating and cooling system. The systems were simulated using commercial software, and the performance of the systems and the building’s energy needs were calculated. Based on the energy quantities, an economic analysis followed. The equivalent annual primary energy consumption with the conventional system resulted in being 43335 kWh, while for the storage system, it was only 8398 kWh. The payback period for the storage system was calculated to be equal to 9.76 years. The operation of the installed storage system provided data for calculations of the seasonal performance factor and storage performance. The seasonal performance factor values were very high during June, July and August, since the TESSe2b system works very efficiently in cooling mode due to the very high temperatures that dominate in Cyprus. The measured stored thermal energy for cooling, heating and domestic hot water resulted in being 14.5, 21.9 and 6.2 kWh, respectively. Moreover, the total volume of the phase change material thermal energy storage tanks for heating and domestic hot water was calculated to be roughly several times smaller than the volume of a tank with water as a storage medium.

Thermal energy storage using phase change material: Analysis of partial tank charging and discharging on system performance in a building cooling application

Thermal energy storage coupled with phase change materials is a technology that offers the potential to shift and in some case reduce building cooling loads and increase energy efficiency. This simulation study uses a TRNSYS building and HVAC system model to investigate whether partially charging and discharging a phase change material thermal energy storage tank can improve the operational characteristics required by a light-weight commercial building located in a Mediterranean climate. The results indicate that partial charging and discharging can lead to better energy performance of the phase change material thermal energy storage HVAC system. If the phase change material thermal energy storage tank is not required to operate at maximum capacity (i.e., maximum charge), energy savings are possible by only partially charging the tank. Further energy efficiency gains are also possible by control of the heat transfer fluid flow rates in the HVAC thermal energy storage system loops. Generally, higher charging loop flow rates and lower discharge loop flow rates produce better energy performance. Charging a phase change material thermal energy storage tank above 90% is not recommended, as at very high charge fractions, the energy performance decreases considerably, while the charging time increases significantly.

Development of a Fuzzy Logic Controller for Small-Scale Solar Organic Rankine Cycle Cogeneration Plants

Solar energy is widely recognized as one of the most attractive renewable energy sources to support the transition toward a decarbonized society. Use of low- and medium-temperature concentrated solar technologies makes decentralized power production of combined heating and power (CHP) an alternative to conventional energy conversion systems. However, because of the changes in solar radiation and the inertia of the different subsystems, the operation control of concentrated solar power (CSP) plants is fundamental to increasing their overall conversion efficiency and improving reliability. Therefore, in this study, the operation control of a micro-scale CHP plant consisting of a linear Fresnel reflector solar field, an organic Rankine cycle unit, and a phase change material thermal energy storage tank, as designed and built under the EU-funded Innova Microsolar project by a consortium of universities and companies, is investigated. In particular, a fuzzy logic control is developed in MATLAB/Simulink by the authors in order to (i) initially recognize the type of user according to the related energy consumption profile by means of a neural network and (ii) optimize the thermal-load-following approach by introducing a set of fuzzy rules to switch among the different operation modes. Annual simulations are performed by combining the plant with different thermal load profiles. In general, the analysis shows that that the proposed fuzzy logic control increases the contribution of the TES unit in supplying the ORC unit, while reducing the number of switches between the different OMs. Furthermore, when connected with a residential user load profile, the overall electrical and thermal energy production of the plant increases. Hence, the developed control logic proves to have good potential in increasing the energy efficiency of low- and medium-temperature concentrated solar ORC systems when integrated into the built environment.

Integrating paraffin phase change material in the storage tank of a solar water heater to maintain a consistent hot water output temperature

The temperature of the hot water withdrawn for a solar water heater varies throughout a day. However, for process heat applications, constant temperature water can be required from a solar water heater. This is usually achieved by providing additional auxiliary heat input. Disadvantageously, such extra water heating incurs additional cost and, if met from fossil fuels, produces greenhouse gas emissions. An alternative approach of using a phase change material to moderate variations in the outlet temperature of hot water from the store is examined in this paper using an experimentally-validated CFD model of a solar water heater with a phase change material thermal energy storage in the hot water tank. The CFD model was solved by COMSOL Multiphysics. For a particular solar water heating system, incorporating an encapsulated paraffin wax phase change material has been shown to able to deliver up to 1200 L of hot water at a temperature of 60 °C ± 2 °C for more than 8 h.

Experimental and numerical study on the effect of multiple phase change materials thermal energy storage system

Nowadays, thermal energy storage using Phase Change Materials (PCMs) receives a great interest due to its high energy storage density especially for low and medium temperature storage applications. Nevertheless, PCM suffers from the low thermal conductivity during the charging and discharging of heat. In this study, the multiple PCM technique has been investigated as a thermal enhancement technique in a shell-and-tube heat exchanger. The investigations have been conducted experimentally and numerically using different PCM arrangements and working conditions for Paraffin wax. The experimental work shows higher average temperature of PCM in the multiple PCM arrangement than the other two arrangements of low and high PCM arrangement. The conducted numerical analysis focuses on the geometrical parametric study by varying both the radial and the axial dimensions of the cylindrical storages. The results show that longer PCM storage enhances the melting time compared to the wider PCM storage for the same amount of PCM.

Performance investigation and sensitivity analysis of shell-and-tube phase change material thermal energy storage

This paper presents the development, experimental testing, and numerical investigation of water-based phase change material (PCM) thermal energy storage (TES) using the shell-and-tube design with different tube layouts including single serpentine, double serpentine, and spiral. Sodium acetate trihydrate (SAT) with a melting temperature of 58 °C was used as the storage medium. The major contribution of this study is the sensitivity analysis and performance comparison of the shell-and-tube PCM TES units with different tube layouts. A quasi-three-dimensional dynamic model of the PCM TES unit was developed and used to predict the performance of the TES unit under different design and operating conditions, which was validated against the experimental data. A global sensitivity analysis was implemented to quantify the influence of the design parameters on the performance of the PCM TES unit. The results showed that the inlet water temperature was the most influential parameter, followed by the tube length, water flow rate, tube layout, and PCM thermal conductivity. The PCM TES module with the spiral tube layout and the double serpentine tube layout generally outperformed that with the single serpentine tube layout. The time required to charge the PCM to a liquid fraction of 0.95 was reduced by 16.0% if changing the tube layout from single serpentine to spiral and when the tube length was 4,055 mm. The findings obtained from this study could be potentially used to guide and facilitate the design of the shell-and-tube PCM TES units.