Search Results (67)

Heating, ventilation, and air-conditioning (HVAC) systems account for the largest share of energy consumption in European Union (EU) buildings, representing approximately 40% of the final energy use and contributing significantly to carbon emissions. Latent thermal energy storage (LTES) using phase change materials (PCMs) has emerged as a promising strategy to enhance HVAC efficiency. This review systematically examines the role of latent thermal energy storage using phase change materials (PCMs) in optimizing HVAC performance to align with EU climate targets, including the Energy Performance of Buildings Directive (EPBD) and the Energy Efficiency Directive (EED). By analyzing advancements in PCM-enhanced HVAC systems across residential and commercial sectors, this study identifies critical pathways for reducing energy demand, enhancing grid flexibility, and accelerating the transition to nearly zero-energy buildings (NZEBs). The review categorizes PCM technologies into organic, inorganic, and eutectic systems, evaluating their integration into thermal storage tanks, airside free cooling units, heat pumps, and building envelopes. Empirical data from case studies demonstrate consistent energy savings of 10–30% and peak load reductions of 20–50%, with Mediterranean climates achieving superior cooling load management through paraffin-based PCMs (melting range: 18–28 °C) compared to continental regions. Policy-driven initiatives, such as Germany’s renewable integration mandates for public buildings, are shown to amplify PCM adoption rates by 40% compared to regions lacking regulatory incentives. Despite these benefits, barriers persist, including fragmented EU standards, life cycle cost uncertainties, and insufficient training. This work bridges critical gaps between PCM research and EU policy implementation, offering a roadmap for scalable deployment. By contextualizing technical improvement within regulatory and economic landscapes, the review provides strategic recommendations to achieve the EU’s 2030 emissions reduction targets and 2050 climate neutrality goals. Full article

The innovation in thermal storage systems for solar thermal power generation is crucial for achieving efficient utilization of new energy sources. Molten salt has been extensively studied as a phase change material (PCM) for latent heat thermal energy storage systems. In this study, a two-dimensional model of a vertical shell-and-tube heat exchanger is developed, utilizing water-steam as the heat transfer fluid (HTF) and phase change material for heat transfer analysis. Through numerical simulations, we explore the interplay between PCM solidification and HTF boiling. The transient results show that tube length affects water boiling duration and PCM solidification thickness. Higher heat transfer fluid flow rates lower solidified PCM temperatures, while lower heat transfer fluid inlet temperatures delay boiling and shorten durations, forming thicker PCM solidification layers. Adding fins to the tube wall boosts heat transfer efficiency by increasing contact area with the phase change material. This extension of boiling time facilitates greater PCM solidification, although it may not always optimize the alignment of bundles within the thermal energy storage system. Full article

This paper presents the results of a numerical study on transient temperature distributions and phase fractions in a thermal energy storage unit containing phase change material (PCM). The latent heat storage unit (LHSU) is a compact shell-and-tube exchanger featuring seven tubes arranged in a staggered layout. Three organic phase change materials are investigated: paraffin LTP 56, fatty acid RT54HC, and fatty acid P1801. OpenFOAM software is utilized to solve the governing equations using the Boussinesq approximation. The discretization of the equations is performed with second-order accuracy in both space and time. The three-dimensional (3D) computational domain corresponds to the inner diameter of the LHSU. Calculations are conducted assuming constant thermal properties of the fluids. The experimental and numerical results indicate that for paraffin LTP56, the charging time is approximately 8% longer than the discharging time. In contrast, the discharging times for fatty acids RT54HC and P1801 exceed their charging times, with time delays of about 14% and 49% for RT54HC and 25% and 30% for P1801, according to experimental and numerical calculations, respectively. Full article

The decarbonization of residential cooling systems requires innovative solutions to overcome the mismatch between the renewable energy availability and demand. Integrating latent thermal energy storage (LTES) with heat pump/air conditioning (HP/AC) units can help balance energy use and enhance efficiency. However, the dynamic behavior of such integrated systems, particularly under low-load conditions, remains underexplored. This study investigates a 5 kW HP/AC unit coupled with an 18 kWh LTES system using a bio-based Phase Change Material (PCM) with a melting temperature of 9 °C. Two configurations were tested: charging the LTES using either a thermostatic bath or the HP/AC unit. Key parameters such as the stored energy, temperature distribution, and cooling capacity were analyzed. The results show that, under identical conditions (2 °C inlet temperature, 16 L/min flow rate), the energy stored using the HP/AC unit was only 6.3% lower than with the thermostatic bath. Nevertheless, significant cooling capacity fluctuations occurred with the HP/AC unit due to compressor modulation and anti-frost cycles. The compressor frequency varied from 75 Hz to 25 Hz, and inefficient on-off cycling appeared in the final phase, when the power demand dropped below 1 kW. These findings highlight the importance of integrated system design and control strategies. A co-optimized HP/AC–LTES setup is essential to avoid performance degradation and to fully exploit the benefits of thermal storage in residential cooling. Full article

Thermal energy storage (TES) is likely to play a significant role in the decarbonisation of domestic heat, allowing consumers to shift their energy consumption away from peak demand periods and reducing overall strain on the grid. Phase change materials (PCMs) are a promising option for TES, in which energy can be stored in the latent heat of the melting of the PCM; these offer greater storage densities than sensible heat TES and have the benefit of releasing stored heat at a consistent temperature (the crystallisation temperature of the PCM). One of the key difficulties for PCM-based TES is state of charge (SoC) estimation (the estimation of the proportion of energy stored in the TES unit up to its maximum capacity), particularly during idle periods while the unit is storing heat. SoC estimation is key to the implementation of TES, as it enables the effective control of the units. The use of a resonator within the PCM for SoC estimation could potentially provide a global estimate of the SoC, since the resonator passes through the full depth of the PCM in the unit. The SoC could be inferred by measuring the vibrational response of the resonator under excitation, which varies depending on the melt state of the PCM. This paper presents findings from a test rig investigating this proposal, including discussions on the features required from the resonator response for SoC inference. Full article

Latent heat thermal energy storage systems play a crucial role in aligning energy supply with demand, enhancing the efficiency of energy usage, thereby aiding in energy conservation and emissions reduction, and promoting the efficient use of renewable energy. Therefore, we constructed an experimental apparatus for a shell-and-tube latent heat storage. This apparatus was utilized to investigate how varying the inclination angle of the heat storage device, the inlet temperature of the heat transfer fluid (HTF), and water flow direction affect both the heat transfer behavior and the thermal efficiency of the system. The findings indicate that as the inlet temperature rises, the melting rate of the phase-change material (PCM) increases; when the inclination angle is 0°, for every 5 °C increase in water temperature, the time required to reach thermal equilibrium is shortened by 2 h, and the time needed for the PCM to transition from a solid to a liquid state is correspondingly reduced by 2 h. Additionally, the temperature variation trend of the phase-change material remains fundamentally consistent at different inclination angles. However, as the angle increases from 0° to 90°, there is a gradual reduction in the melting rate. Whether the water enters from the top or bottom, the melting rate of the PCM remains almost unchanged, and the stabilized temperature of the PCM is also nearly the same. Full article

The conversion and storage of renewable energy into thermal energy is an important part of the low carbon economy. The goaf of a deep mine offers the possibility of large-scale thermal energy storage due to its sufficient underground space. Since the repositories are built inside the goaf backfill and there are few studies on their heat storage capacity and effectiveness, this paper builds an experimental platform based on the similarity theory and selects the geometric similarity ratio of 1:15 to study the phase change heat storage performance of the backfill mine heat storage. Under the typical operating conditions, the temperature distribution of the PCM inside the cylindrical storage unit was analyzed. At the end of heat storage, the temperature distribution of the PCM was 0.93–0.98, but at the end of heat release, the temperature distribution of the PCM was not uniform. At the same time, the heat is reasonably corrected, so that the thermal energy charging effectiveness is increased to 0.98, and the total effectiveness of thermal energy charge and discharge remains 0.87. The parameters of the storage unit are analyzed in detail by changing the water temperature, the flow velocity and the ratio of heat storage and release time of the circulating medium. The experimental results show that when the heat release water temperature is constant and only the heat storage water temperature is changed, the higher the water temperature, the higher the total effectiveness of thermal energy charge and discharge. On the contrary, when the heat storage water temperature is constant and the heat release water temperature is reduced to 14 °C, the total effectiveness of the heat release is increased by 7.5%. When the flow state is in transition, the total effectiveness decreases. The longer the heat storage/release time, the smaller the TSTD_ave inside the PCM and the more uniform the temperature distribution. By restoring the experimental data to the engineering prototype, the repositories installed in the goaf were able to store and extract 422.88 GJ and 375.97 GJ of heat, respectively. Finally, the environmental assessment of the C-LHSU showed that the carbon emissions per unit heating area of the CFB, GWHF and GHF were reduced by 88.1%, 84.2% and 83.0%, respectively. The experimental results show that the cylindrical phase change heat reservoir has higher heat transfer energy efficiency, which provides a theoretical basis and engineering reference for efficient heat storage and utilization in deep mine goafs. Full article

Thermal energy storage systems utilising phase change materials offer significantly higher energy densities compared to traditional solutions, and are therefore attracting growing interest in both research and application fields. However, the further development of this technology requires effective methods to enhance thermal efficiency. We propose a horizontal periodic shell-and-tube structure as an efficient latent heat thermal energy storage unit. This research aims to analyse heat transfer not only between the tube containing the heat transfer fluid and the phase change material but also between adjacent shell-and-tube units. The results obtained for a single cell within the periodic structure are compared with those of reference single shell-and-tube units with insulated adiabatic and highly conductive shells. The enthalpy–porosity approach, combined with the Boussinesq approximation, is applied to address the heat transfer challenges encountered during melting and solidification. The periodic horizontal shell-and-tube structure proves to be an efficient latent heat thermal energy storage unit with short melting and solidification times. In contrast, the non-periodic case with neglected conduction in the shell increases the melting and solidification times by 213.8% and 21%, respectively. The shortest melting and solidification times were recorded for the case with a periodic horizontal shell-and-tube structure and shell aspect ratios of 0.44 and 1, respectively. Full article

Thermal energy is very crucial, and Phase Change Materials (PCM) provide methods to store it. The objective of this study is to investigate the effect of changing the angle of the Latent Thermal Energy Storage Unit (LTESU) on the amount of time required to melt the PCM. Stearic acid (PCM) was enclosed in a housing to subject it to thermal energy at different orientations. Changing the angle enhances the buoyancy force exerted on melted PCM as thermal energy is added, causing a difference in density. This density difference produces flow currents that circulate the melted PCM in the enclosure due to the hot PCM rising and surrounding the cold PCM that occupies the space left by the hot PCM. These currents are responsible for the distribution of thermal energy throughout the enclosure so that naturally turbulent flow will transfer more heat energy as compared to laminar flow. It was noted that the least amount of time needed to charge the stearic acid was at 60°. An improvement of 16.67% in terms of melting time was observed with respect to the reference case. Full article

The efficiency and economy of an ASHP (air source heat pump) can be significantly improved in a cold area by combining it with a TESU (thermal energy storage unit). The work of looking for a phase change material with a suitable temperature range, a large thermal capacity, and high conductivity has been always on the road. This paper prepared 10 CPCMs (composites of a phase change material) by using the vacuum adsorption method, which consists of LA (lauric acid) as the phase change material and EG (expanded graphite) as the skeleton matrix for its high thermal conductivity and porous characteristics. By characterizing and analyzing their basic properties, surface morp\hology, and stability, a suitable CPCM for the TESU coupled with the ASHP heating system is found. The leakage experiment results show that the maximum effective content of LA absorbed in 100-mesh EG of a CPCM is 80%, and that in 200-mesh EG, it is 90%. Among 10 CPCMs, CPCM3, with a mass ratio of LA:EG/8:2, is considered the more satisfactory one for the TESU proposed by this paper, because its performance shows good stability, its phase transition temperature is 40.98–41.94 °C, its latent heat is 164.34–168.28 kJ/kg, and especially, its thermal conductivity is 8.15–8.33 W/(m·K). This paper will be followed by performance research on TESUs coupled with ASHP heating systems. Full article

Latent Heat Transfer Thermal Energy Storage (LHTES) units are crucial in managing the variability of solar energy in solar thermal storage systems. This study explores the effectiveness of strategically placing layers of anisotropic and uniform metal foam (MF) within an LHTES to optimize the melting times of phase-change materials (PCMs) in three different setups. Using the enthalpy–porosity approach and finite element method simulations for fluid dynamics in MF, this research evaluates the impact of the metal foam’s anisotropy parameter (Kn) and orientation angle (ω) on thermal performance. The results indicate that the configuration placing the anisotropic MF layer to channel heat towards the lower right corner shortens the phase transition time by 2.72% compared to other setups. Conversely, the middle setup experiences extended melting periods, particularly when ω is at 90°—an increase in Kn from 0.1 to 0.2 cuts the melting time by 4.14%, although it remains the least efficient option. The findings highlight the critical influence of MF anisotropy and the pivotal role of ω = 45°. Angles greater than this significantly increase the liquefaction time, especially at higher Kn values, due to altered thermal conductivity directions. Furthermore, the tactical placement of the anisotropic MF layer significantly boosts thermal efficiency, as evidenced by a 13.12% reduction in the PCM liquefaction time, most notably in configurations with a lower angle orientation. Full article

Preservation of perishable food produce is a major concern in the cold chain supply system. Development of an energy-efficient on-farm cold storage facility, hence, becomes essential. Integration of thermal storage into a vapor compression refrigeration (VCR)-driven cold room is a promising technology that can reduce power consumption and act as a thermal backup. However, designing a latent heat energy storage heat exchanger encounters challenges, such as low thermal conductivity of phase change materials (PCMs) and poor heat exchanger efficiencies, leading to ineffective charging–discharging cycles. The current study investigates the effect of the integration of a Phase Change Material (PCM) in terms of the selection of the PCM, the optimal positioning of the PCM heat exchanger, and the selection of heat exchanger encapsulation material. Numerical analysis was undertaken using 3D Experience software (version: 2024x.D31.R426rel.202403212040) by creating a 3D model of a 3.4 m³ micro-cold storage unit to understand the inner temperature distribution profile. Further, the experimental setup was developed, and tests were conducted, during which the energy consumption of 1.1 kWh was recorded for the total compressor run time of 1 h. Results indicated that an improved cooling effect was achieved by positioning the PCM trays on the wall opposite the evaporator. It is seen that a temperature difference in the range of 5 to 7 °C exists between the phase change temperature of PCM and the optimal storage temperature depending on the encapsulation material. Hence, PCM selection for thermal storage applications would have an important bearing on the material and configuration of the PCM encapsulation. Full article

This work examines the thermal stability testing results of Mg84Cu16 as a new phase change material for its potential use in latent thermal energy storage systems for 488 °C transition temperatures. The results obtained in a previous study [1,2] showed that the Mg84-Cu16 alloy is one the most promising materials for thermal energy storage applications due to their eutectic nature and because the highest thermal conductivity (106 W/mK) was reported in the 400–550 °C temperature range. To confirm these results, the thermal stability of this alloy and its behavior with container materials during its use in industrial conditions were evaluated. In the first part, the Mg84-Cu16, with latent heat of 232 J/g, was subjected to short-term thermal cycling tests in 30 melting/solidification cycles in order to identify any potential changes in their thermophysical and structural properties. Variations in thermophysical properties were analyzed using the DSC technique. The evolution of the eutectic microstructure was examined via SEM. The second part of this study studies the compatibility between the selected materiel and the different containment materials, such as SS304, SS316, and INCONEL, in order to identify the most suitable stainless steels that can be used in the construction of thermal energy storage unit for the Mg84Cu16 alloy. Full article

This paper reports the vapor pressure and enthalpy of vaporization for a promising phase change material (PCM) guanidinium methanesulfonate ([Gdm][OMs]), which is a typical guanidinium organomonosulfonate that displays a lamellar crystalline architecture. [Gdm][OMs] was purified by recrystallization. The elemental analysis and infrared spectrum of [Gdm][OMs] confirmed the purity and composition. Differential scanning calorimetry (DSC) also confirmed its high purity and showed a sharp and symmetrical endothermic melting peak with a melting point (T_m) of 207.6 °C and a specific latent heat of fusion of 183.0 J g⁻¹. Thermogravimetric analysis (TGA) reveals its thermal stability over a wide temperature range, and yet three thermal events at higher temperatures of 351 °C, 447 °C, and 649 °C were associated with vaporization or decomposition. The vapor pressure was measured using the isothermogravimetric method from 220 °C to 300 °C. The Antoine equation was used to describe the temperature dependence of its vapor pressure, and the substance-dependent Antoine constants were obtained by non-linear regression. The enthalpy of vaporization (Δ_vapH) was derived from the linear regression of the slopes associated with the linear temperature dependence of the rate of weight loss per unit area of vaporization. Hence, the temperature dependence of vapor pressures ln P_vap (Pa) = 10.99 − 344.58/(T (K) − 493.64) over the temperature range from 493.15 K to 573.15 K and the enthalpy of vaporization Δ_vapH = 157.10 ± 20.10 kJ mol⁻¹ at the arithmetic mean temperature of 240 °C were obtained from isothermogravimetric measurements using the Antoine equation and the Clausius–Clapeyron equation, respectively. The flammability test indicates that [Gdm][OMs] is non-flammable. Hence, [Gdm][OMs] enjoys very low volatility, high enthalpy of vaporization, and non-flammability in addition to its known advantages. This work thus offers data support, methodologies, and insights for the application of [Gdm][OMs] and other organic salts as PCMs in thermal energy storage and beyond. Full article

Compared to sensible heat storage, latent heat storage provides higher energy density due to the enthalpy difference of the storage medium undergoing a phase change. However, the heat storage capability of phase change materials is opposed by low thermal conductivity. To enable sufficient heat transfer within a latent heat storage unit, phase change materials can be used in combination with a metallic matrix. One approach is the infiltration of phase change materials into additively manufactured metallic lattice structures. In this work, the fabrication of aluminum lattice structures through laser powder bed fusion is described. During fabrication, the cell size and the strut diameter were varied to obtain specimens of different geometries. To obtain the thermal conductivity of the fabricated lattices, measurements were conducted based on the transient plane source method. Additionally, finite element simulations were carried out to evaluate the effect of fabrication and measurement uncertainties. The thermal conductivity of the fabricated lattices was found to be between 3 W/(m·K) and 130 W/(m·K). The numerically and analytically performed calculations provide good estimations of the experimentally obtained data. Full article