Phase change materials for cold energy storage: Insights from three decades of research trends,advancements,and future directions

Thermophysical properties and material enhancement of PCMs

Cluster 1 comprises terms including charging, cold storage system, cool TES, nanofluids, nucleating agent, nucleation, PCM, solidification, stability, subcooling, supercooling degree, thermal conductivity, and viscosity. It can be seen that this cluster comprises the fundamental thermal science and materials engineering principles that govern PCM cold storage systems, with research demonstrating how critical thermophysical properties determine system performance and efficiency. The presence of thermal conductivity in this cluster indicates a primary factor in heat transfer efficiency, with multiple studies showing significant enhancements through nanoparticle additions. For example, Sathishkumar et al. (2016) found that graphene nanoplatelets increased thermal conductivity by 12% in liquid and 56% in solid for water-based nanofluids. Similarly, Kumaresan et al. (2021a) achieved a 36% enhancement in thermal conductivity using graphitised mesoporous carbon, while Sathishkumar and Cheralathan (2022) reported a 53.15% improvement at −10°C with functionalised multi-walled carbon nanotubes. Furthermore, Sundaram et al. (2023) observed a thermal conductivity enhancement of up to 59.1% with graphene nanoplatelets, and Srinivasan and Ponnusamy (2024b) achieved a 30.75% improvement in solid-state properties using hybrid nanofluid formulations.

Viscosity in this cluster influences fluid flow characteristics and thermal performance, with Sundaram et al. (2023) noting that higher nanoparticle concentrations increase viscosity, subsequently reducing energy storage density and solidification rates. Nanofluids emerge as advanced heat transfer enhancement techniques throughout the literature, with water-based formulations outperforming pure PCM systems. Chandrasekaran et al. (2014b) prepared nanofluids using multi-wall carbon nanotubes and achieved a 25% reduction in freezing duration compared to pure deionised water. In another study, Chandrasekaran et al. (2014a) utilised copper oxide nanoparticles in a water-based nanofluid PCM, as shown in Figure 7. The authors demonstrated a 35% reduction in solidification time due to enhanced heat transport properties. Nanda Kumar and Chandrasekaran (2021) investigated Al₂O₃ nanofluid PCMs, demonstrating enhanced thermal properties for faster heat dissipation and higher operating temperatures.

OPEN IN VIEWER

Figure 7.

Experimental setup for studying heat transfer characteristics of CuO nanofluid PCM in a spherical capsule during solidification (Chandrasekaran et al., 2014a) (Reproduced with permission from Elsevier, License number: 6038410516783).

Nucleation and nucleating agents play a pivotal role in controlling crystallisation behaviour and mitigating problematic subcooling phenomena across multiple investigations. Vikram et al. (2019) used sodium chloride and D-sorbitol as nucleating agents, reducing subcooling from −5.4°C to −2.8°C in deionised water systems. Chandrasekaran et al. (2014b) employed Pseudomonas as a nucleating agent, eliminating subcooling in nanofluid PCMs and improving phase change reliability. Chandrasekaran et al. (2014a) further proved that nucleating agents eliminated subcooling problems, allowing evaporators to operate at higher temperatures in chiller systems.

Solidification processes in Cluster 1 exhibit central phase change behaviours that determine energy storage efficiency and system performance characteristics. For instance, Sathishkumar et al. (2016) found that graphene nanoplatelets reduced solidification time by 25% due to their enhanced thermal conductivity and increased specific surface area. (C. Chen et al., 2022a) numerically analysed the solidification behaviour, reporting a 30.1% reduction in solidification time at a 1.2 wt% graphene nanoplatelet concentration. In addition, Jeevarathinam et al. (2024) achieved a 40% reduction in solidification duration using 5 wt% natural graphite flakes in deionised water.

Subcooling and supercooling degrees indicate critical temperature control challenges that affect system reliability and operational efficiency. Sathishkumar et al. (2016) reduced subcooling from −7°C to −2.5°C by adding graphene nanoplatelets, enabling more predictable phase change behaviour. (Mulawarman et al., 2018) effectively reduced water supercooling using glycerol and propylene glycol as nucleating agents, allowing faster and more reliable freezing processes. Sundaram et al. (2023) achieved a reduction of up to 47.6% in supercooling using gum Arabic-stabilised graphene nanoplatelet formulations, thereby improving the predictability of phase change.

Charging represents the energy storage phase during which PCM systems accumulate thermal energy for subsequent release during discharge cycles. Sathishkumar et al. (2016) observed accelerated energy charging during 78% of the total solidification time, with the innermost 9% of the volume solidifying over a duration of 22%. Kumaresan et al. (2021b) demonstrated that micro-particle enhanced PCM stored roughly 94% of cool energy in a shorter time than base PCM formulations. Kumaresan et al. (2021a) showed that nanofluids achieved 96% cool energy storage in accelerated charging mode, improving system efficiency. Cool TES systems benefit from enhanced PCM formulations that address fundamental thermophysical property limitations in conventional materials. Rakkappan et al. (2021) investigated the 1-decanol/expanded graphite composite PCM as a superior alternative to ice for cold TES applications, as shown in Figure 8. Their composite PCM stored latent heat at relatively higher wall temperatures than ice, requiring much lower temperatures for solidification. In the work of Bharathi et al. (2024), the authors developed a nanocomposite-enhanced fatty acid eutectic PCM using coconut shell-activated carbon cobalt oxide, achieving 73% thermal conductivity enhancement at 0.1 wt%.

OPEN IN VIEWER

Figure 8.

An experimental setup for investigating the energy storage characteristics of spherically encapsulated 1-decanol/expanded graphite composite PCM (Rakkappan et al., 2021) (Reproduced with permission from Elsevier, License number: 6042120070184).

Cold storage systems utilise advanced PCM formulations to overcome traditional ice-based limitations, thereby enhancing thermal performance and operational flexibility. Ajour et al. (2024) simulated unsteady solidification processes in advanced cold energy storage systems using alumina nanoparticle-enhanced water-based PCM formulations. The analysis revealed that increasing the nanoparticle concentration improved the cold storage rate by 36.37%, while the effects of nanoparticle size were found to be nonlinear and complex. Stability in cluster 1 comprises thermal cycling durability and chemical compatibility, ensuring long-term system performance and material integrity under repeated operational cycles. Sundaram et al. (2023) investigated stability using different surfactants and found that gum Arabic-stabilised formulations demonstrated the highest stability and thermal performance characteristics. (Srinivasan and Ponnusamy, 2024a) achieved the highest stability with sodium dodecylbenzene sulphonate, characterised by a −42.7 mV zeta potential and an average particle size of 212.6 nm. In another study, Srinivasan and Ponnusamy (2025) found that a hybrid nanofluid PCM using the anionic surfactant SDBS exhibited the greatest stability, with the smallest particle size and the highest zeta potential.

Experimental validation and performance assessment of PCM cold storage systems

Cluster 2 comprises cold storage tank, cool storage, experiment, heat transfer, micro-encapsulation, n-tetradecane, paraffin, performance, phase change, PCM, and thermal performance. The cluster focuses on experimental validation and performance assessment of PCM cold storage systems. The emphasis on experimental methodology indicates the critical importance of empirical validation in PCM research. Cold storage tanks represent practical implementation scales, and micro-encapsulation addresses advanced PCM packaging techniques for enhanced durability and containment. Specific materials like n-tetradecane and paraffin are commonly studied organic PCMs with suitable melting points for cold storage applications. Heat transfer and thermal performance metrics are central to system evaluation. This cluster highlights the transition from theoretical understanding to practical implementation, emphasising the need for experimental characterisation to validate system performance, optimise operating parameters, and demonstrate the commercial viability of cold energy storage technologies.

The experimental methodology forms the basis of this research domain, as demonstrated by multiple studies that emphasise empirical validation over theoretical modelling alone. Torregrosa-Jaime et al. (2013) conducted an extensive experimental analysis of a paraffin-based cold storage tank containing 1450 kg of paraffin with 18 spiral-shaped coils. Their experimental approach revealed that natural convection influences the melting process during phase change operations. The study identified that roughly 31% of the paraffin remains unutilised due to poor coil contact with the storage medium. The study achieved optimal performance in terms of system efficiency at the lowest HTF supply temperatures and mass flow rates.

n-Tetradecane, an organic PCM, has been used across multiple experimental studies due to its suitable thermophysical properties for cold storage applications. For instance, H. Zhang et al. (2022) enhanced n-tetradecane thermal conductivity by developing tetradecane/expanded graphite composite PCMs for high-power cold storage applications. The study composite achieved a thermal conductivity of 21.0 W/m·K, representing nearly a 100-fold improvement over the raw n-tetradecane’s performance characteristics. The innovative spiral wave plate cold storage tank, utilising composite materials, improves power and energy density, reaching a 40 kWh/m³ capacity. In addition, the predictive models for maximum paraffin loading and thermal conductivity yielded errors of only 1.7% and less than 10%, respectively. S. Wu et al. (2010) developed thermal performance simulations of a packed bed cool TES system utilising n-tetradecane as the primary PCM. The authors examined the temperatures of PCM and HTF, as well as variations in solid and liquid fractions, and the rates of cooling and heating during storage and release throughout operational cycles. S.-M. Wu and Fang (2012) further investigated the dynamic charging performance of cool energy storage systems with coil pipes using n-tetradecane and aqueous ethylene glycol solution. The findings revealed that increasing or decreasing the flow rate and inlet temperature enhances cool storage rates and reduces charging time requirements. According to their findings, the system achieved a cool storage capacity of approximately 103 MJ in about 5 h under optimised operational parameters.

Paraffin-based systems dominate experimental cold storage research due to their favourable phase change characteristics and commercial availability for practical applications. The work of D. Li et al. (2019) examined the thermal control performance of tube-fin cool storage heat exchangers filled with paraffin PCM. The experimental study incorporated graphene powder enhancement to improve solidification rates and thermal management capabilities for electronic device applications. Graphene powder improved solidification rates, increasing thermal control time by 114.8% at 800 W heating power. Under maximum heat flux of 1000 W, heat control times were 40, 29, and 25 min for 0%, 2.5%, and 5% graphene mass fractions, respectively. X. Wu et al. (2019) enhanced pure paraffin (RT4) thermal conductivity by preparing composite PCMs with varying carbon nanotube mass fractions. The experimental evaluation achieved thermal conductivity improvements of 30.3% in solid and 28.5% in liquid at 3% carbon nanotube concentration. In addition, when applied in vertical open-type refrigerated display cabinets, composite PCMs reduced internal temperature fluctuations during defrosting, with 3%-carbon nanotube composites decreasing temperature differences by 92.0% and 12.2%, respectively.

Micro-encapsulation represents an advanced PCM packaging technique that addresses durability, containment, and enhanced performance requirements in practical cold storage applications, as investigated across several studies. For example, Fang et al. (2013) synthesised polystyrene/n-tetradecane composite nanoencapsulated PCMs using ultrasonic-assisted mini-emulsion in situ polymerisation techniques. The nanoencapsulated PCM formed uniform spherical capsules with an average diameter of 132 nm, achieving melting and freezing points of 4.04°C and −3.43 °C, respectively. The materials yielded corresponding latent heat of 98.71 J/g and 91.27 J/g with a maximum specific heat of 4.822 J/g K. In addition, the good mechanical stability demonstrated through freeze-thaw cycling indicated a strong potential for cool energy storage applications, as indicated by their experimental characterisation. Moinuddin et al. (2021) micro-encapsulated ester-based non-paraffin PCMs into organic shells using in situ polymerisation techniques. The authors’ micro-encapsulated PCM showed good morphology and chemical stability, with a latent heat of 65.32 kJ/kg and an onset melting temperature of 8.57°C.

Likewise, heat transfer mechanisms and thermal performance metrics constitute central evaluation criteria for experimental validation of cold storage system effectiveness and operational efficiency. H. Zheng et al. (2024) utilised computational fluid dynamics to analyse the performance of carbon nanotube composite phase change cold storage spheres with annular fins. The study addressed the challenges of low thermal conductivity, high shell thermal resistance, and overall system inefficiencies through enhanced heat transfer mechanisms. Incorporating carbon nanotubes into annular-finned paraffin cold storage spheres reduced cooling time by 48 min and increased efficiency by 61.7% compared to traditional systems. Carbon nanotube additions outperformed fin enhancements in isolation, and optimal fin geometry and refrigerating medium flow rates further enhanced convective heat transfer. In the work of Dogkas et al. (2020), the authors experimentally investigated cold TES systems using organic PCMs (A9 and A14) for building cooling applications. The A9 organic PCM yielded efficient fan coil unit operation, maintaining a water temperature difference exceeding 5°C for over half of the tank capacity. The system achieved heat transfer rates exceeding 5 kW for 32 min with A9 and 24 min with A14.

Phase change behaviour and system performance optimisation are critical aspects of experimental validation that determine the commercial viability of cold energy storage technologies. In this context, Yedmel et al. (2024) developed a novel cold storage system combining TES using paraffin-based PCMs with thermosiphon loops. The thermosiphon-assisted TES system delivered 97% of stored cold energy to display cabinets, prolonging acceptable temperature maintenance during compressor shutdowns. With a cold accumulator, the air temperature remained within an acceptable range for 72 min, compared to only 3 min without accumulation capability. C. Yao et al. (2018) developed shape-stabilised PCM-wallboards (PCMW) using paraffin and expanded perlite to enhance building thermal inertia. The paraffin-based PCMW exhibited latent heat values of approximately 67 J/g, with melting and freezing points of 27.6°C and 23.6°C, respectively. Experimentally, PCMW reduced indoor temperature by up to 2.53 K under typical northern China weather conditions, with numerical simulations demonstrating average temperature reductions of 9.22 K during summer office hours.

Commercial viability assessment through experimental characterisation facilitates the optimisation of operating parameters and demonstrates the practical implementation potential for widespread adoption. Y. L. Shao et al. (2020) compared encapsulated ice thermal storage (EITS) systems with theoretical encapsulated organic PCM systems utilising paraffin waxes. The system achieved three times the cold energy storage capacity of conventional chilled water tanks and 9.37% higher capacity than EITS systems. This improvement resulted from greater solidification in encapsulated organic PCM systems, with HTF flow rate impacting the solidification ratio and energy storage. Yuan et al. (2024) investigated the physical hardening effects of wax-based materials, including paraffin characteristics, on low-temperature properties after extended cold storage periods. F-T waxes and Montan waxes with typical paraffin characteristics deteriorated in their low-temperature rheological performance after 72 h of cold conditioning, with grade losses of up to 6.2°C and increased thermal stress, confirming the physical hardening impacts on long-term system performance and operational reliability.

Heat exchange technologies and PCM-based ice storage system integration

Cluster 3 contains terms including charging rate, heat exchanger, heat transfer enhancement, ice storage, ice storage system, ice-on-coil, nanoparticles, numerical modelling, PCM, and TES. This cluster represents advanced heat exchange technologies and system integration approaches that have been extensively investigated in multiple research studies. Heat exchangers are critical components determining overall system efficiency, as demonstrated by Abdelrahman et al. (2020), who experimentally evaluated a twin concentric helical coil configuration immersed in distilled water as a PCM (Figure 9). The core component is an insulated acrylic tank containing two concentric helical coils, where ice formation occurs during the charging process and melts during discharge. The entire system is monitored through a laptop-based data acquisition system, which is connected to temperature sensors and controllers distributed throughout the circuit. The HTF circulation is managed by a pump and regulated through multiple valves, with flow rates measured by dedicated flow metres to ensure precise control of experimental conditions. The system operates with separate charging and discharging reservoirs, each equipped with electric heaters for temperature control. A bypass pipe enables flexible flow management across various operational modes. The refrigeration circuit comprises a complete vapour compression cycle, including a compressor, condenser, evaporator (a tube-in-tube heat exchanger), and expansion valve, all housed in an outdoor unit. This setup enables controlled cooling of the HTF, facilitating the formation of ice on the helical coils. The study revealed that approximately 90% of the energy storage capacity was achieved within 59–74% of the total charging time under the tested conditions.

OPEN IN VIEWER

Figure 9.

Experimental set-up for ice storage system using twin concentric helical coil (Abdelrahman et al., 2020) (Reproduced with permission from Elsevier, License number: 6042120287984).

Additionally, heat transfer enhancement techniques, such as the use of nanoparticles, improve thermal performance. Chandrasekaran et al. (2024) reported that iron oxide nanoparticles in deionised water achieved a 50% mass frozen state with an enhanced surface heat flux of up to 200% at −6°C. The addition of these nanoparticles reduced chiller operational time by 75% through optimised container design and partial charging. Afsharpanah et al. (2022) further revealed that copper foam occupying 3% of the container volume accelerated the phase change rate by 84.6%, outperforming the 24.3% improvement achieved by equivalent CuO nanomaterials alone. When copper foam was combined with high-porosity and CuO nanomaterials at a concentration of 0.03, the phase change rate increased by 92.5%.

Likewise, ice storage systems indicate an established cold energy storage technology with proven commercial viability and reliability. Al-Shannaq et al. (2019) enhanced thermal conductivity by encapsulating water within high-thermal-conductivity graphite spheres, achieving a 12-fold increase in effective thermal conductivity. This enhancement reduced freezing and melting times by 53.7% and 44.4%, respectively, compared to non-graphite spheres. The graphite matrix minimised supercooling by acting as a nucleating agent, addressing a key challenge in ice storage applications. Ice-on-coil configurations indicate common implementations that have been extensively studied for optimisation. Mousavi Ajarostaghi et al. (2023) investigated solidification processes in ice-on-coil systems using combined experimental and numerical approaches. The study modified the evaporator design, featuring four connected horizontal coils, which enhanced the ice thickness by up to 14.71% after 180 min, particularly at the bottom sections of the coils. Q. Lin et al. (2019) applied lattice Boltzmann modelling to simulate transient solid-liquid phase change in ice-on-coil tanks containing nine horizontally aligned pipes. The study identified three distinct melting stages and found that high-temperature pipe placement in upper tank sections maximised melting rates.

The charging rate in this cluster emphasises the dynamic performance characteristics crucial for practical applications and system responsiveness. In view of this, Almeshaal and Sakr (2023) numerically investigated packed-bed ice storage systems with Al₂O₃ nanoparticles dispersed in water capsules. The findings indicated that 90% of stored cool energy could be charged in 12–77% of total charging time, depending on coolant conditions. In addition, increasing the coolant flow rate reduced full charging time by up to 69.2% at double the flow rate. Ding et al. (2022) proposed foam freezing as a high-performance charging method, identifying an optimal foam bubble radius of 0.6 mm, which achieved a cold energy charging coefficient of 237.1 W/m² K. This approach outperformed traditional ice ball and ice-on-coil methods in charging efficiency. Yan et al. (2023a) experimentally set up an ice-on-coil TES system designed to study dynamic melting processes, as shown in Figure 10. The system centres on an ice-storage tank containing serpentine coils, where ice formation and melting occur, monitored by strategically placed thermocouples that measure temperature distributions throughout the melting process. A thermostatic bath (Alpha RA 24) provides precise temperature control for the HTF, which circulates through the system via a circulation pump. Both float-type and turbine flow metres measure flow rates to ensure accurate monitoring of fluid dynamics. The fluid flow is regulated by ball valves and bypass valves, allowing for controlled experimental conditions. A nozzle system facilitates proper fluid distribution within the storage tank. Temperature and flow data are continuously collected through a data logger system connected to a computer for real-time monitoring and analysis of the melting characteristics. The authors revealed that dynamic circulation systems improved average discharge rates by 60.7–89.2% while reducing ice melting duration by 45.3–54.3% compared to static systems. In the work of Laouer et al. (2024), the authors employed lattice Boltzmann methods to analyse the partial melting of ice embedded with copper and alumina nanoparticles. The simulations revealed that a 6% concentration of copper nanoparticles reduced the melting time by 12.4%, with copper particles proving slightly more effective than alumina. The modelling approach captured the complex interactions between Rayleigh numbers and nanoparticle volume fractions that affect energy storage efficiency.

OPEN IN VIEWER

Figure 10.

(a) Experimental setup of dynamic melting process in an ice-on-coil storage system (Yan et al., 2023a) (Reproduced with permission from Elsevier, License number: 6042120531367).

Integrating PCMs with conventional ice storage systems signifies a hybrid approach, maximising energy density and reliability. For example, Niu and Zhang (2009) investigated the performance of micro-encapsulated paraffin slurry for building cooling applications in temperate temperature ranges. Full latent heat storage was achievable at 5°C due to supercooling effects, and an effective cooling storage capacity existed between 5 °C and 18 °C. This demonstrates the potential for PCM integration with passive cooling methods for diurnal storage applications. Yan et al. (2023b) explored alumina nanofluid as PCM in ice-on-coil systems, finding reduced freezing times but negative impacts on melting performance. However, implementing spiral finned coils improved system performance by reducing the melting time by 24% and increasing the average discharge rate by 74.4%.

Calcium chloride hexahydrate systems and micro-encapsulated PCM slurries

Cluster 4 comprises terms such as calcium chloride hexahydrate, crystallisation, energy storage, freezing, ice, melting, mpcm (micro-encapsulated PCM) slurry, natural convection, phase change energy storage, and supercooling. Calcium chloride hexahydrate (CaCl₂·6H₂O) has attracted significant attention due to its favourable thermophysical properties for cold storage applications. For instance, Cao et al. (2022) developed a composite PCM using calcium chloride hexahydrate with glycerol as a temperature regulator and achieved a melting temperature of 11.8°C and phase change enthalpy of 112.86 J/g. X. Han et al. (2022) optimised the calcium chloride hexahydrate system by incorporating methanol and glycerol, resulting in a material with a phase transition temperature of 10.4 °C and a latent heat capacity of 120.75 J/g. Zou et al. (2018) enhanced the performance of calcium chloride hexahydrate by incorporating urea and ethanol, achieving a phase change temperature of 11.62 °C and an enthalpy of 127.2 J/g·C. Li et al. (2022) developed a tailored calcium chloride hexahydrate composite (CCH-UNSC4) with an optimised composition, achieving a phase change temperature of 9.51 °C and a latent heat of 99.08 J/g. The work of M. Li et al. (2023) created a gel-like PCM from calcium chloride hexahydrate with an 8.15°C melting temperature and 93.80 J/g latent heat capacity.

The crystallisation process in these calcium chloride hexahydrate systems indicates a fundamental aspect of phase change energy storage mechanisms. Crystallisation behaviour directly influences the energy storage capacity and thermal performance of PCMs during solidification. The controlled crystallisation of calcium chloride hexahydrate enables efficient energy storage through the release of latent heat during phase transitions. C. Li et al. (2022) demonstrated that proper crystallisation control in their composite system resulted in thermal cycling stability over fifty cycles. Allouche et al. (2015) found that MPCM slurry could store 53% more energy than water in equivalent tank volumes. Yu et al. (2018) found that MPCM slurries yield higher cold energy storage capacity than traditional packed pebble bed systems. L. Zheng et al. (2017) confirmed that MPCM provides higher energy transport effectiveness for cold storage applications.

The energy storage enhancement achieved through PCMs signifies a critical advancement in thermal energy management systems. Freezing processes are crucial to PCM performance, primarily affecting energy storage efficiency and heat transfer characteristics. S. Zhang and Niu (2010) investigated the freezing behaviour of micro-encapsulated paraffin slurry systems for building cooling applications in temperate temperature ranges. H. Xu et al. (2018) demonstrated that MPCM slurry enhanced temperature differences during freezing processes compared to pure water systems. The freezing characteristics directly influence the effectiveness of PCMs in practical cold storage systems. Ice formation and behaviour in this cluster characterise the fundamental PCM development considerations for cold storage applications operating near water-freezing temperatures. The interaction between ice formation and PCMs affects system performance and energy storage capacity. In addition, melting characteristics determine the energy release patterns and thermal performance of PCMs during discharge cycles in cold storage systems. Cao et al. (2022) achieved controlled melting behaviour through the incorporation of glycerol, resulting in an optimised melting temperature suitable for air conditioning applications. X. Han et al. (2022) concluded that the addition of methanol influenced the melting characteristics, achieving the desired phase transition temperatures for cold energy storage.

Supercooling is a critical challenge in PCM development, affecting energy storage reliability and system performance predictability. S. Zhang and Niu (2010) found that full latent heat storage required temperatures around 7°C due to supercooling effects in micro-encapsulated paraffin systems. Cao et al. (2022) reduced supercooling to 1.22°C by adding barium hydroxide octahydrate as a nucleating agent to calcium chloride hexahydrate systems. X. Han et al. (2022) demonstrated effective supercooling reduction through barium carbonate incorporation, facilitating easier nucleation in composite PCMs. Zou et al. (2018) achieved a 0.95°C reduction in supercooling by adding strontium chloride hexahydrate to calcium chloride hexahydrate composite systems. C. Li et al. (2022) achieved an ultra-low supercooling degree of 0.39°C through an optimised composite formulation in their tailored calcium chloride hexahydrate system. Luo et al. (2023) reduced undercooling to 1.75°C by integrating expanded graphite into shape-stabilised PCM systems. The supercooling mitigation strategies represent essential developments for reliable PCM performance in practical cold storage applications.

Expanded graphite enhancement and cold chain logistics applications

Cluster 5 comprises cold chain, cold chain logistics, cold energy storage, expanded graphite, modified expanded graphite, PCMs, and thermal properties. This cluster bridges materials science with practical cold chain applications through comprehensive research initiatives. Cold chain logistics is the primary market driver for cold energy storage technologies, encompassing food preservation, pharmaceutical distribution, and the transportation of temperature-sensitive cargo across various operational environments. Therefore, integrating PCMs within cold chain systems improves temperature control and energy efficiency. For instance, Liu et al. (2024b) reported that glycine-based water composites reduced the pre-cooling time for strawberries by 56.60% compared to conventional ice. Their research enabled adequate refrigeration for up to 17.86 h within the critical temperature range of 1.54 °C to 3.39 °C. This advancement illustrates how enhanced PCMs can improve logistics efficiency and maintain product quality during transportation. The pharmaceutical sector benefits from these innovations, as demonstrated by G. Zhang et al. (2023), who showed that tetradecane-dodecanol-decanoic acid/expanded graphite composites extended the cold preservation time for vaccines by 50.4 times.

Expanded graphite and its modifications are thermal conductivity enhancers and structural supports for PCMs, addressing the typically low thermal conductivity limitation. X. Chen et al. (2024) achieved thermal conductivity improvements eight times higher than pure PCM through SiO₂-coated expanded graphite incorporation. The authors’ composite material achieved a thermal conductivity of 5.183 W/m·K and demonstrated thermal cyclic stability over 200 cycles. Zhou et al. (2024) reported even more substantial enhancements, achieving a 22.52-fold increase in thermal conductivity to 5.18 W/m·K with their dodecane–hexadecane/expanded graphite composite. These improvements address fundamental limitations that previously restricted PCM applications in demanding cold chain environments. The structural support function proves equally critical, as demonstrated by Y. Chen et al. (2022b), who achieved high adsorption rates of 92 wt.% in expanded graphite matrices. This capability prevents material leakage and maintains phase change functionality throughout operational cycles.

In addition, modified expanded graphite suggests an advanced approach to optimising PCM performance through surface chemistry manipulation and enhanced compatibility in this cluster. For example, Liu et al. (2024c) employed Triton X-100 surfactant modification to improve compatibility between expanded graphite and glycine water-based materials. The modified expanded graphite increased the adsorption capacity to 82.87% and achieved a thermal conductivity 4.08 times higher than that of pure glycine water-based PCM. Liu et al. (2024a) utilised cetyltrimethylammonium bromide modification to enhance the adsorption capacity from 73.96% to 84.05%. This modification approach demonstrates systematic material optimisation for specific application requirements. W. Wu et al. (2025a) further advanced this concept through hydrogen bond-enhanced hydrophilic modification of expanded graphite with cationic surfactants. The authors’ approach increased thermal conductivity by 80.85% and achieved cycle stability with only 17.0% latent heat attenuation after 1000 cycles.

The focus on thermal properties highlights the critical importance of material characterisation for optimising applications across various temperature ranges. X. Xu et al. (2023) developed materials with phase transition temperatures of −0.7 °C and latent heat values of 170.4 J/g. Their research focused on the 0–8 °C range, which is crucial for cold chain logistics applications. J. Tang et al. (2024a) optimised octanoic acid–tetradecanol mixtures, achieving phase-transition temperatures of 11.4 °C with latent heat between 150 and 155 J/g. This temperature range is suitable for building air conditioning and intermediate cold storage applications. Zhou et al. (2024) achieved a sub-zero phase change temperature of −12.09 °C with a high melting enthalpy of 178.75 kJ/kg. These diverse temperature ranges demonstrate the material's adaptability to specific operational requirements.

Cold energy storage applications benefit from enhanced PCM formulations that combine high latent heat capacity with improved thermal conductivity characteristics. L. Tang et al. (2024b) developed composite materials with a thermal conductivity of 5.64 W/m·K and a latent heat of 263.1 J/g. The material maintained insulation box temperatures below 8 °C for 1124.1 min. Liu et al. (2024d) achieved thermal conductivity increases of 510% compared to base materials and maintained a latent heat of 144 J/g. The study approach reduced temperature differences inside the cold storage apparatus from 6.7 °C to approximately 1 °C. The work of T. Wu et al. (2025b) established that incorporating expanded graphite enhanced thermal conductivity more than tenfold without affecting the phase change enthalpy. This optimisation enabled cold storage densities exceeding 100 kWh/m³ and maximum power densities exceeding 200 kW/m³. X. Xu et al. (2023) revealed that cold storage panels with built-in charge cold coils achieved 58.1% shorter charging times compared to conventional charging methods. This improvement directly translates to operational efficiency gains in cold-chain transportation systems. The materials also reduced energy consumption through improved thermal management and reduced temperature fluctuations during storage and transport operations.

Numerical modelling, packed bed systems, and renewable energy integration

Cluster 6 includes the following terms: latent heat, numerical modelling, packed bed, PCM, renewable energy, and TES. This cluster comprises the critical intersection of latent heat storage technology and sustainable energy integration, utilising numerical modelling and practical implementation strategies. Latent heat storage fundamentally distinguishes PCMs from conventional sensible heat storage systems by providing higher energy density capabilities. This advantage is demonstrated through multiple research initiatives that have systematically investigated the thermal performance characteristics of PCM-based cold storage systems. Numerical modelling is the foundation for advancing PCM cold storage technology, allowing precise system design optimisation and performance prediction across various operating conditions. The modelling approaches that researchers have developed to facilitate an understanding of complex thermal dynamics within packed bed configurations allow for a systematic evaluation of design parameters and operational strategies. Packed bed configurations are the most practical and scalable implementation approach for large-scale TES systems in industrial and commercial applications. These configurations offer efficient heat transfer characteristics and maintain structural integrity and operational reliability under varying thermal loads.

Integrating PCM cold storage systems with renewable energy sources addresses fundamental sustainability concerns and simultaneously provides essential grid stabilisation capabilities for modern energy networks. This integration strategy facilitates effective load shifting and energy management, particularly in accommodating the intermittent nature of renewable energy generation. In view of this, Cheng and Zhai (2018) highlighted the effectiveness of cascaded packed bed cool TES units using multiple PCMs, achieving optimal thermal performance with a 24-stage configuration that reduced charging time by 15.1% compared to single-stage units. The research established that strategic temperature difference management (6°C) between phases enhances solidification heat transfer characteristics without compromising the quantity or quality of cold energy stored. The cascaded approach applies numerical modelling principles to optimise system performance through a systematic arrangement of PCM. Muthaiyan et al. (2021) advanced the practical application of packed-bed cool storage units by integrating residential air conditioning systems with rooftop solar PV power generation systems. The study revealed that latent heat storage systems can effectively support the integration of renewable energy and maintain reliable cooling performance for residential applications. The study yielded average coefficient of performance values of 1.0, 0.93, and 0.89 for HTF setpoint temperatures of −6°C, −9°C, and −12°C, respectively, highlighting the relationship between operating temperature and system efficiency. The cooling load delivery capabilities ranged from 2.25 kW during initial operation to 0.3 kW during the sixth cycle, highlighting the importance of thermal resistance management in maintaining consistent performance throughout discharge cycles.

The work of J. Wang et al. (2023) contributed to the advancement of numerical modelling techniques through their investigation of multi-stage cold storage packed beds utilising modified sodium sulphate decahydrate-based PCMs. The authors achieved a 7.3% increase in cold storage density compared to single-stage systems through strategic PCM modification and optimal filling ratio implementation (4:2:4). The enhanced thermal stability and storage performance revealed the effectiveness of combining advanced material modification with system design for air conditioning applications. The study validated the feasibility of multi-stage PCM systems for emergency cooling applications, providing one hour of reliable cooling capacity through optimised TES management. In the work of Tafone and Romagnoli (2023), the authors expanded the application scope of PCM cold storage by investigating liquid air energy storage systems integrated with cascaded latent heat cold TES. The numerical investigation revealed higher performance characteristics of cascaded PCM-based high-grade cold storage compared to conventional single PCM configurations. The cascaded system achieved enhanced charge phase capacity ratio (0.87 versus 0.81) and improved discharge phase utilisation factor (0.87 versus 0.80), resulting in a 6% improvement in liquefaction performance with specific energy consumption of 0.27 kWhe/kgLA. This research exemplifies the potential for integrating renewable energy through advanced PCM cold storage technologies, which enhance overall system efficiency and operational sustainability.

X. Li et al. (2018) investigated the dynamic characteristics of TES units incorporating multiple PCMs in spherical capsules for conventional air conditioning applications. The authors established that multi-PCM TES units offer a higher charging capacity than conventional single-PCM systems, with a 4:2:2 proportion yielding optimal performance characteristics. The study found that lowering the HTF inlet temperature reduces charging time, facilitating operational optimisation in practical applications. Additionally, the dynamic characteristics analysis highlighted the importance of systematic PCM selection and arrangement in maximising TES efficiency in packed bed configurations. In the work of Al-Shannaq et al. (2019), the authors addressed thermal conductivity limitations by developing a novel graphite-water composite sphere for cold energy storage applications. The experimental investigation discovered that encapsulating water within high thermal conductivity graphite spheres increased the effective thermal conductivity by a factor of twelve, reducing freezing and melting times by 53.7% and 44.4%, respectively. The graphite nucleating effect minimised supercooling phenomena and maintain consistent phase change behaviour throughout operational cycles. The study established that HTF inlet temperature and flow rate adjustments influence freezing time and melting rate, demonstrating system adaptability for various cooling applications and renewable energy integration scenarios.

In other studies, Grabo et al. (2021) developed an advanced packed-bed TES system using a non-spherical super-ellipsoidal macro-encapsulated latent heat storage capsule designed to enhance packing density and heat transfer characteristics. The capsule design increased storage capacity by over 20% compared to conventional spherical capsules, thereby boosting energy density from 51.5 kWh/m³ to 64.1 kWh/m³. The system delivered a thermal power output of about 4 kW during phase change processes, indicating practical applicability for large-scale TES applications. The numerical modelling approach accurately predicted charging and discharging behaviour within ±0.82 K of the experimental data, validating the effectiveness of advanced modelling techniques for system design optimisation. Khattari et al. (2021) provided a detailed analysis of positive latent cold storage systems for industrial applications through numerical modelling of their dynamic and thermal behaviour during discharge periods. The findings indicate that maintaining the HTF temperature near the PCM melting point leads to quasi-stabilisation of the outlet temperature, while reducing the fluid flow rate extends the energy discharge duration. For multi-PCM systems, the amount of latent energy released depends on PCM placement order, HTF flow rate, and inlet temperature, highlighting critical design considerations for industrial cold storage applications and renewable energy integration strategies. The work of Tafone et al. (2021) emphasised the practical application of cryogenic PCMs in liquid air energy storage systems through innovative cold TES solutions. The experimental and numerical investigation of packed bed units revealed improved thermal performance by reducing thermocline effects and extending discharge duration through the thermal buffering effects of PCM. The research achieved a 17% reduction in liquefaction-specific consumption (0.272 kWhe/kg LA) compared to 0.330 kWhe/kg LA, thereby enhancing both thermodynamic efficiency and economic viability. The economic analysis revealed payback periods of less than 3 years, establishing PCM integration as a cost-effective advancement for renewable energy storage technology that supports grid stabilisation and sustainable energy management objectives.

Economic viability and phase change slurry applications in air conditioning

Cluster 7 comprises terms such as air conditioning, cold storage, cooling, economic analysis, phase change slurry, and thermal storage. This cluster focuses on the practical applications and economic viability of PCM cold storage systems. The term ‘air conditioning’ refers to a major application area where cold energy storage can help shift peak load and reduce energy costs. For example, Sao et al. (2024) reported that integrating cylindrical PCM containers with air conditioning units resulted in coefficient of performance (COP) improvements of up to 94.49%. The enhanced performance resulted from optimised airflow rates, which reduced PCM discharging time and increased power savings. Y.-X. Huang et al. (2025a) provided clear evidence of economic viability through their evaluation of an integrated active-passive cooling system. The authors proposed that the system reduced HVAC operation time by 22.4% and lowered total energy consumption by 26.1%. The most significant finding was the 118.6% reduction in electricity costs compared to traditional active cooling systems. This economic performance was achieved through effective load balancing via peak shaving and valley-filling strategies.

The phase change slurries offer an implementation method that combines the benefits of PCMs with fluid handling capabilities. Ma et al. (2009) investigated micro-encapsulated PCM slurry based on Rubitherm RT6 for secondary cooling applications. The authors identified optimal concentration levels that maximised energy transportation capability and system effectiveness. The study confirmed the feasibility of direct micro-encapsulated PCM slurry implementation in air handling units for improved energy continuity. Vorbeck et al. (2013) further validated phase change slurry applications through pilot-scale testing in a 5 m³ storage tank and found that phase change slurry could store more than twice the heat compared to water systems. However, the higher viscosity resulted in approximately five times greater pumping energy requirements, illustrating the trade-off between thermal efficiency and energy input. The emphasis on cooling applications highlights the primary market focus for cold energy storage technologies. Jia and Qi (2025) investigated phase-change cold storage systems using aluminium rods with PCM at a 6°C phase-change temperature. The study's comparative analysis revealed the differential impacts between water-based and phase-change composite systems for thermal storage and release applications. F. Yang et al. (2025) advanced cooling technology through flat micro-heat pipe arrays in simultaneous charging and discharging modes. The optimisation efforts resulted in a 28.62% reduction in steady-state time and a 30.63% increase in cold storage capacity. This cluster demonstrates the practical implementation perspective, emphasising that technical performance must be balanced with economic considerations.

Energy efficiency, solar energy integration, and sustainability

Cluster 8 comprises terms including energy efficiency, energy saving, latent heat storage, PCMs, sensible heat storage, and solar energy. This cluster focuses on energy conservation and the integration of solar energy across various cooling applications. Energy efficiency and energy saving are the primary drivers for PCM adoption, primarily in reducing peak energy demand and improving system performance. The thermal properties of PCMs show significant energy efficiency improvements across multiple applications. For example, Y. Xu et al. (2024) achieved a 9.7% increase in COP and a 24.5% increase in heating COP for their solar-heat-driven ejection-compression hybrid cooling system with subcooling storage. Y. Zhang et al. (2025) reported a 19.4% improvement in cooling performance through the integration of hydrate-based latent heat storage with carbon dioxide water-source heat pump systems. These findings highlight the substantial energy efficiency gains that can be achieved through the implementation of PCM in advanced cooling technologies.

The comparison between latent heat storage and sensible heat storage highlights the fundamental advantages of PCMs in terms of energy density and temperature stability. Latent heat storage through PCMs has a higher TES capacity than conventional sensible heat storage systems. Roy et al. (2023) found that PCM-based heat exchangers maintain stable temperatures for 55 min during compressor shutdown at high ambient temperatures. The results revealed that PCM integration reduces compressor on-off cycles from six to one per hour, decreases compressor run time by 31%, and achieves overall energy savings of approximately 40%. Energy-saving achievements through PCM implementation extend beyond basic thermal management to system optimisation. Natarajan et al. (2023) developed a hybrid portable solar cold storage system, which achieved a 17.9% reduction in energy consumption compared to conventional cold storage systems. The PCM-based solar cold storage system maintained chamber temperatures within permissible ranges and consumed less energy than traditional systems. The work of Reddy et al. (2023) found that bio-based PCM systems, combined with air washers, achieve a 7–17% reduction in overall electrical energy consumption during the peak summer months. In addition, the system shifts 5–10% of energy demand from peak hours to off-peak hours under tropical climate conditions. Liang et al. (2024) optimised PCM-based cold energy storage tanks by reducing the plate height from 50 mm to 10 mm, achieving reductions of 84.6% and 87.9% in charging and discharging times, respectively. Rivera and Moraga (2024) found that PlusIce E-10 improved freezer energy efficiency by 11.4% while reducing temperature fluctuations in food products and PCM plates.

Solar energy integration is a sustainable cooling solution, primarily relevant to solar-driven cooling systems and thermal energy management. Combining PCMs with solar energy systems creates synergistic effects that enhance energy efficiency and environmental sustainability. For example, Y. Xu et al. (2024) developed a novel solar-assisted ejector-compressor hybrid refrigeration system incorporating subcooling storage at intermediate temperatures. The system demonstrated reduced energy storage volume, thermal leakage, and overall system size, while maintaining higher performance characteristics. In the work of J. Gao et al. (2025), the authors analysed the active heat storage and release characteristics of embedded capillary dual-effect PCM plates, focusing on solar thermal energy and sky radiation cooling. The dual-effect PCM system effectively meets seasonal indoor energy demands for both summer cooling and winter heating applications. The system reduces primary energy consumption by 185.7–282.1 MJ/m²/year compared to concrete roof systems and achieves 22.6% energy savings compared to single-effect PCM systems.

Similarly, integrating solar energy with PCM cold storage systems is also applicable to remote agricultural applications with limited grid connectivity. In view of this, Natarajan et al. (2023) developed a 5 kW, 2-ton prototype solar cold storage system equipped with multiple sensors and a microcontroller system for remote monitoring and temperature control. The system operates continuously for 24 h, sustaining banana fruit preservation quality within acceptable parameters. In the work of Abbassi et al. (2022), the authors developed mathematical models for encapsulated PCM TES tanks within TRNSYS software, enabling the simulation and performance investigation of latent heat energy storage systems integrated with solar energy applications. The model validation achieved errors less than 2% for one-dimensional simulations and 10% for two-dimensional simulations compared to experimental data.

It is worth noting that cluster 8 further demonstrates the environmental and efficiency benefits of PCM cold storage systems, emphasising their role in sustainable energy systems. The environmental advantages extend beyond energy efficiency, including substantial reductions in carbon emissions and enhanced system sustainability. Peng and Lo (2024) conducted an economic analysis, demonstrating that the adoption of PCM leads to a 32% reduction in electricity costs, annual energy savings of 118,411 kWh, and a reduction in carbon emissions of 60,272 tons per year. (Y. Zhang et al., 2025) aligned their research with the objectives of carbon neutrality and the Kigali Amendment, demonstrating how PCM integration supports global environmental sustainability goals. The average COP during cold storage reached 2.54 at gas cooler inlet water temperatures of 32°C, indicating efficient thermal management under varying operational conditions. Combining high-efficiency thermal storage with renewable energy sources marks a significant step toward environmentally responsible cooling technologies that reduce energy consumption while maintaining performance standards. Abbassi et al. (2022) found that PCM tanks effectively track solar irradiation variations and minimise building cooling and heating loads by 22.5% and 18%, respectively. Seasonal cooling storage with PCM tanks achieves approximately 7% savings in total energy consumption, highlighting the long-term benefits of integrating TES.

Refrigeration systems and solar-powered cold storage applications

Cluster 9 comprises the following terms: air-conditioning, cold thermal storage, refrigeration, slurry, solar cooling, and storage. This cluster represents established cooling and refrigeration applications where PCMs demonstrate operational advantages. Air-conditioning applications benefit substantially from PCM integration, as demonstrated by W. Lin et al. (2014), who developed a ceiling ventilation system enhanced by solar PV thermal collectors and PCMs, which achieved maximum air temperature rises of 23.1°C in winter and substantially increased thermal comfort coefficients to values as high as 0.9921. The system utilised solar radiation in winter and sky radiative cooling in summer, demonstrating the versatility of PCM-enhanced air conditioning solutions. (Riffat et al., 2022) further advanced air-conditioning applications through their experimental study of a novel PCM chilled ceiling panel incorporating transparent membrane covers integrated with solar photovoltaic-driven vapour-compression cooling systems. The findings revealed that the PCM chilled ceiling system effectively stored excess cooling energy for night-time use and prevented moisture condensation through infrared-transparent membrane barriers. The work of L. Zheng et al. (2019) revealed the effectiveness of micro-encapsulated PCM cooling storage in solar air conditioning systems, achieving energy-saving rates of 30.5%. It also maintained indoor temperatures between 18°C and 22°C, with transient thermal efficiency showing consistent variation trends with solar radiation intensity.

Likewise, cold thermal storage in this cluster highlights the fundamental application where PCMs offer temporal energy management capabilities for peak load reduction and energy cost optimisation. Zhai et al. (2014) conducted experimental investigations of phase change cold storage tanks integrated into solar air-conditioning systems, signifying good feasibility and stability with charging and discharging processes completed within 230 and 220 min under steady conditions, respectively. The system achieved charging and discharging capacities of 1016.1 kJ and 942.8 kJ, respectively, highlighting the substantial energy storage potential of cold thermal storage applications. MONSALVE et al. (2018) assessed integrated household refrigerators with eutectic PCMs, indicating that PCM decreased compressor cycling periods and reduced energy consumption significantly. The study's thermal characterisation of two different eutectic PCMs (PLUSICE E-10 and 19.5 wt.% NH4Cl) provided essential data for optimising cold thermal storage performance in domestic applications.

Similarly, refrigeration applications indicate the primary market areas where cold thermal storage provides significant operational benefits through enhanced temperature stability and reduced energy consumption. In view of this, Jilte et al. (2023) designed and evaluated a novel milk chiller latent storage system based on PCMs for storing coolness and keeping milk at safe storage temperatures around 4–5°C over 12 to 24 h. The system reduced the milk temperature from udder temperature (∼35°C) to storage temperature within 60 min and maintained chilled conditions for up to 12 h without requiring continuous refrigeration. The integrated portable design supported switching between solar PV and grid power sources, revealing the feasibility of overcoming power availability challenges in remote locations. Maiorino et al. (2025) developed a compact autonomous solar-powered refrigerator prototype that integrates solar PV systems, batteries, and PCMs to preserve perishable goods in off-grid areas, as shown in Figure 11. The authors’ prototype maintained internal temperatures ranging from +4°C to −20°C while incorporating 22 l of water-based PCM to stabilise internal temperatures and mitigate battery size limitations. The system maintained medical samples at −21°C within a ± 1°C range during simulated conditions, demonstrating robustness for field deployment and vaccine preservation applications.

OPEN IN VIEWER

Figure 11.

Solar-powered vapour compression refrigerator prototype showing (a) closed configuration with folded solar panel lid and (b) open configuration with deployed solar panel for maximum solar energy collection (Maiorino et al., 2025) (Published under open access with permission from Elsevier).

Slurry systems in this cluster permit enhanced heat transfer characteristics and improved pump ability for large-scale cold thermal storage applications where conventional solid PCMs face transport limitations. The improved heat transfer properties of slurry systems facilitate more efficient thermal energy exchange, thereby maintaining the fundamental energy storage benefits of PCMs. Integrating slurry systems with conventional refrigeration equipment enables scalable implementations suitable for industrial and commercial applications that require substantial cooling capacities. Solar cooling is a sustainable solution that integrates renewable energy sources with thermal storage capabilities. For instance, the work of Jarimi et al. (2024) developed solar PV-assisted DC vapour compression systems with low-cost ice gel thermal batteries for off-grid building cooling applications, as shown in Figure 12. The solar panels power a DC compressor that circulates refrigerant through the cycle, where it absorbs heat at the evaporator (T6–T7), gets compressed and heated (T1–T2), and then releases heat through the condenser (T3–T4). The ice gel thermal battery stores excess cooling capacity during peak solar generation, maintaining consistent operation when solar input is insufficient. The expansion valve controls refrigerant flow between the high and low-pressure sides. At the same time, the fan coil unit distributes conditioned air throughout the building (T8–T10), providing sustainable cooling without grid dependency through the integration of TES. The system achieved at least 50% better performance than grid-reliant systems, with lower levelised cooling costs of $0.06/ kWh. J. Yao et al. (2020) analysed solar-assisted heat pump systems coupled with built-in PCM heat storage based on PV/T panels for stable residential heating in high-latitude regions. The system achieved heating COP up to 5.79, representing 70% improvements over conventional air conditioning systems while delivering electrical, thermal, and overall efficiencies of 17.77%, 55.76%, and 75.49%, respectively. The system maintained underfloor heating temperatures between 22°C and 31°C after 39 h of operation.

OPEN IN VIEWER

Figure 12.

(a) Layout of solar PV cooling system (Jarimi et al., 2024) (Reproduced with permission from Elsevier, License number: 6042120973508).

The storage systems in this cluster underscore the fundamental role of PCM technology in temporal energy management, where cooling demands fluctuate throughout operational cycles. Rahimpour et al. (2022) evaluated PCMs in building insulation to improve the self-consumption of residential rooftop solar systems in Australian conditions. The findings indicate that PCM integration reduced annual electricity costs by 10.6% in Brisbane to 19% in Adelaide and unexpectedly led to slight decreases in solar PV self-consumption, ranging from 1.5% in Brisbane to 2.7% in Perth. Mandal and Saxena (2023) assessed latent energy storage systems for thermal management applications in hot and dry climatic conditions, finding that incorporating PCMs in building elements reduced heat transfer by up to 50% and increased energy storage capacity by 22%. The research discovered that using PCMs in solar PV panels passively improved efficiency by 0.5–3% without requiring auxiliary power input.

Building-integrated TES and thermal comfort enhancement

Cluster 10 comprises terms such as buildings, cold TES, metal foams, numerical simulations, PCMs, and thermal comfort. This cluster focuses on building-integrated cold storage systems and advanced heat transfer enhancement technologies that optimise architectural thermal management applications. For example, Yeşilata et al. (2025) investigated the integration of capric acid-based PCMs into 3D-printed polylactic acid plates with varying geometries of cavities to enhance TES and improve building energy efficiency through passive thermal regulation. The results indicate that spherical cavity geometries yielded improved thermal performance, reducing heat loss by 5.35% to 11.03%, enhancing heat retention by 2.69% to 4.77%, and sustaining stable phase-change temperature windows of 29.7°C to 30.3°C. Philip et al. (2020) explored novel eutectic PCMs composed of lauryl alcohol and stearyl alcohol for cold TES applications to enhance thermal comfort in buildings. The developed eutectic PCM exhibited a melting point of 22.93°C and a latent heat of fusion of 205.79 J/g, demonstrating favourable thermophysical properties, thermal stability, and cycling reliability for indoor temperature regulation applications. In the work of Abhijith and Sreekumar (2023), the authors developed a binary eutectic of palmitic acid and lauryl alcohol for latent heat TES, aiming to enhance indoor thermal comfort in buildings. It was observed that the eutectic PCM achieved phase transition temperatures of 20.25°C with a latent heat of 155.59 J/g, exhibiting favourable thermophysical properties and corrosion resistance suitable for integration with conventional cooling systems.

Sun et al. (2020) explored double-layer radiant floor systems incorporating two different inorganic PCM layers with distinct melting points to regulate indoor thermal comfort effectively across seasonal variations. The double-layer radiant floor system extended thermal comfort duration, achieving 2.2 times longer comfort in winter and 1.7 times longer in summer compared to reference rooms. The system enhanced energy savings by reducing active system operation time, thereby enabling peak load shifting and economic cost reductions through optimised thermal conductivity of PCM composites. M. J. Huang et al. (2025b) developed sustainable radiant floor heating systems integrating composite PCMs enhanced with expanded graphite powered by air source heat pumps to reduce power consumption and improve thermal comfort. The PCM-expanded graphite system enhanced heat retention capacity by 37% compared to systems using metal mesh, while maintaining 0.7°C higher floor surface temperatures when combined with copper powder. The integration of PCMs in building applications leverages their inherent ability to absorb and release substantial quantities of thermal energy during phase transitions while maintaining relatively constant temperatures. X. Gao et al. (2018) proposed coupled cooling systems that combine phase-change chairs (PCC) and phase-change plates (PCP) to enhance temperature control and thermal comfort in isolated, high-temperature environments. Their combined PCC and PCP cooling system outperformed individual PCP systems, reducing room temperature by 1.4°C within the first 50 h and decreasing the occupied system volume by 31.4%, thereby demonstrating enhanced thermal comfort and space efficiency.