High Latent Heat Capacity Research Articles

Experimental study on the dynamic integration of PCM in building walls for enhancing thermal performance in summer condition

Passively integrating phase change material into the walls to enhance the thermal performance of the building has been a promising solution in recent years. As the PCM has a high latent heat capacity, it leads to damping the high variations of temperature and provides an obvious benefit in energy saving and indoor comfort. However, the traditional passive integration method of the PCM limited the utilization of the PCM. The thermal resistance between the PCM and the indoors restrains the thermal response of the PCM, and it between the PCM and the outdoors reduces the impact of outdoor heating or cooling on the PCM. In this study, a dynamic PCM integration in the building envelope method was proposed and experimentally investigated. A PCM layer and an air layer were combined to be integrated into the wall assembly, which allows the position of the PCM layer and the air layer could be changed to adjust the thermal resistance (air layer) between the PCM and indoors and outdoors. The results showed that this dynamic method can dramatically reduce the indoor temperature and the heat flux across the interior surface of the wall. Compared to the envelope with only static PCM layer configurations, the dynamic PCM provided a reduction of 9.1% in the indoor average temperature and a reduction of 116.0% in the peak heat flux during the experiment's three days, as well as the dynamic PCM, exploited more latent heat than the other static configurations. Considering the energy performance, the dynamic integration of PCM showed a 100% reduction in heat gain through the interior surface compared to the envelope with only a static PCM layer under summer conditions.

Sustainable solar-powered seawater desalination enabled by phosphorene-decorated watermelon-like phase-change microcapsules

Solar-powered interfacial evaporation is considered as an emerging innovative technology for seawater desalination; however, it suffers from insufficient evaporation efficiency under intermittent solar irradiation. Aiming at realizing sustainable solar-powered seawater desalination for clean water production, we have designed a new type of watermelon-like phase-change microcapsules as a photothermal absorbent material for a solar interfacial evaporator. This type of phase-change microcapsules was prepared through rational layer-by-layer microencapsulation with a ZrO2 nanoparticle-containing n-docosane core as a phase-change material (PCM) for solar photothermal harvest and prompt thermal response, a ZrO2 shell for the leakage prevention of the molten n-docosane core, and a polydopamine coating layer together with its surface-decorated phosphorene nanoflakes for high-efficient sunlight absorption and fast water transportation. The resultant microcapsules are featured by a watermelon-like microstructure as confirmed by transmission electron and scanning electron microscopy. They also exhibit a high light absorption efficiency of 84.95 %, a high latent heat capacity of 146.2 J g−1, and good wettability. Equipped with the watermelon-like phase-change microcapsules, the developed solar interfacial evaporator obtained an evaporation rate of 3.09 kg m−2 h−1 under one-sun illumination for seawater desalination. The PCM core within the microcapsules can store solar photothermal energy as latent heat under sufficient solar irradiation and then release it under evaporation conditions without sunlight illumination, thus enhancing the water evaporation efficiency. This enables the developed evaporator to increase its total evaporation mass by 31.5 % on a cloudy day in comparison with the conversional solar evaporator without a PCM, indicating a remarkable enhancement in the evaporation performance under intermittent solar irradiation. The developed solar interfacial evaporator exhibits great potential for application in sustainable solar-powered seawater desalination.

Integrating MXene Film With Recyclable Polyethylene Glycol-co-Polyphosphazene Copolymer as Solid-Solid Phase Change Material for Versatile Applications.

Phase-change materials (PCMs) stand a pivotal advancement in thermal energy storage and management due to their reversible phase transitions to store and release an abundance of heat energy. However, conventional solid-liquid PCMs suffer from fluidity and leakage in their molten state, limiting their applications at advanced levels. Herein, a novel Zn2+-crosslinked polyethylene glycol-co-polyphosphazene copolymer (PCEPN-Zn) as a solid-solid PCM through dynamic metal-ligand coordination is first designed and synthesized. The as-synthesized PCEPN-Zn is further integrated with an MXene film to construct a double-layered phase-change composite through layer-by layer adhesion. Owing to the introduction of MXene film with low emissivity, good light absorptivity, and nonflammability, the resultant phase-change composite not only presents a high latent-heat capacity, good thermal stability, high thermal reliability, and excellent shape stability, but also exhibits a superior self-healing ability, good recyclability, high adhesivity, and good flame-retardant performance. It can be easily adhered to on most objects for various application scenarios. With a combination of the excellent functions derived from PCEPN-Zn and MXene film, the developed phase-change composite exhibits broad prospects for versatile applications in the thermal management of CPUs and Li-ion batteries, thermal infrared stealth of high-temperature objects, heat therapy in the clinic, and fire-safety for various scenarios.

Experimental and numerical investigation of a double spiral tube heat exchanger in a novel composite phase change material

Phase change energy storage technology effectively harnesses energy, and phase change materials have been garnered significant attention due to their high latent heat capacity. The heat transfer capacity and phase transition of HCNT − CH3COONa·3H2O/Na2HPO4·12H2O composites in a double spiral tube heat storage unit were investigated. The effects of different flow rates and temperatures on the heat transfer characteristics of phase change materials were studied, and the thermal performance of the storage units was evaluated by calculating the power, energy and energy efficiency ratios. The phase change process of the composite during heat transfer was further revealed via simulation, and the heat storage and heat release of the composite were compared with those of other phase change materials. The results show that the effects of the flow velocity on the transformation time and power of the phase change material are negligible. However, an increase in flow rate can significantly increase the heat storage and heat release of the phase change unit. In particular, when the flow rate is 4 LPM, the energy efficiency ratio can reach 76.6 %. When the temperature increases from 80 °C to 90 °C, the melting time decreases by 30.23 %, indicating that increasing the temperature has a significant effect on the phase transition process. Through simulation calculations, the composite phase change material shows significant performance advantages under the same working conditions; its heat storage capacity is 108 % greater than that of the other materials, and the heat release capacity is 206 % greater, which indicates that it has greater energy storage and release efficiency and a better thermal energy conversion capacity. In addition, the experimental and simulation results also reveal the existence of a diagonal region of slow phase transition in the heat storage unit. In summary, this paper analyses the heat transfer performance of a double spiral tube heat storage device, provides a theoretical basis for practical application, and provides an important reference for improving the performance of a phase–change energy storage system.

Phase change hydrogel formed by osmotic pressure for thermal energy storage

The present study investigates the potential of latent heat storage using phase change materials (PCMs) to reduce building energy consumption, addressing the common challenges of PCM leakage and compatibility with construction materials. We introduce a novel phase change hydrogel, created by encapsulating polyethylene glycol (PEG) within a superabsorbent polymer (SAP) network through osmotic pressure. The structural and thermal characteristics of the PEG/SAP composite were analyzed using differential scanning calorimetry (DSC), thermal gravimetric analysis (TG), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and polarizing optical microscopy (POM). Results demonstrated that PEG effectively filled the SAP network, forming a stable composite structure, with PEG as the core and SAP as the supporting matrix. The composite achieved a remarkable PEG mass fraction of 80 %, yielding a melting enthalpy of 129.7 J/g and a peak melting temperature of 51.89 °C. Additionally, PEG/SAP exhibited robust thermal stability up to 300 °C. Notably, when incorporated into cement, surface temperatures of phase change cement decreased by 12 °C compared to conventional Portland cement under constant heating. This approach highlights high latent heat capacity, low production costs, and straightforward fabrication, positioning PEG/SAP as a promising solution for large-scale applications in building energy conservation.

Fabrication of boron nitride/copper oxide@multi-walled carbon nanotubes composites for enhancing heat transfer and photothermal conversion of phase change materials

To realize the efficient storage and conversion of solar energy by phase change materials (PCMs), low photothermal conversion efficiency and poor heat transfer performance remain great challenges. Herein, polyethylene glycol (PEG)-based composite PCMs with excellent photothermal conversion performance and exceptional thermal management capability were obtained by using boron nitride/copper oxide@multi-walled carbon nanotubes (BN/CuO@MWCNTs) as the thermal conductive and photothermal conversion enhancement fillers. The results indicate that owing to the bridging effect, the introduction of CuO and MWCNTs on the BN surface can construct additional heat transfer paths, resulting in a high thermal conductivity of up to 2.35 W/(m·K) for the as-prepared PEG/BN/CuO@MWCNTs composite, which is about 9-folds enhancement than pristine PEG. Simultaneously, the supercooling degree of PEG in PEG/BN/CuO@MWCNTs is effectively suppressed due to the synergistic nucleation effect of BN, CuO and MWCNTs. Additionally, the PEG/BN/CuO@MWCNTs composites not only exhibit a high latent-heat capacity of 154.5 J/g and a high photothermal conversion efficiency of 92.2 %, but also show favorable shape stability and durable reliability. This work offers a workable solution for the synergistic enhancement of photothermal conversion and thermal management, which can effectively promote the practical application in solar energy conversion and storage.

Carbon-intercalated halloysite-based aerogel efficiently encapsulating phase change materials with excellent photothermal conversion and energy storage

Latent heat storage systems based on organic phase change materials (PCMs) are considered to be an efficient solar energy utilization strategy, but leakage vulnerability and insensitivity to sunlight of PCMs limit their further application in energy storage. In this work, a new hierarchical porous aerogel was constructed with the carbon intercalated halloysite nanotubes (CHNTs) as the assembly units for PCMs encapsulation to improve the load weight, stability and sunlight absorption. The CHNTs were first successfully synthesized through intercalation and carbonization, with the aim of increasing their specific surface area and sunlight absorption.Subsequently, the CHNTs/polyvinyl alcohol (PVA) aerogels with 3D honeycomb structure were prepared by self-assembly using a freeze-drying method, which can significantly promote the encapsulation ratio of lauric acid (LA) in the pores of both aerogels and CHNTs. The CHNTs can not only improve compressive strength of the aerogels and shape stability of the composite PCMs, but also enhance light absorption ability of the composites compared to pristine HNTs. As a support material, CHNTs aerogel (CHNP) loaded more than 92 wt% PCM (LA@CHNP) and exhibited an extremely high latent heat capacity (170.9 J/g). The LA@CHNP had good structural and thermal stability in 300 cycles without visible leakage. Besides, solar energy absorption increased from 43 % to 98 %, and the solar-to-thermal energy conversion efficiency increased to 95.88 %, which could be attributed to 3D porousness and carbon nanolayers of the CHNTs. We have successfully synthesized an eco-friendly and facile composite LA@CHNP, which will contribute to the design of advanced composites with excellent solar energy storage properties, and provide a new direction for the application of carbonized materials.

Flexible phase change film with motion sensing and tactile recognition for wearable thermal management

Phase change materials (PCMs) have gained significant interest in personal thermal management technologies owing to high latent heat capacity and isothermal phase transitions. However, achieving simultaneous thermal and wearing comfort remains a formidable challenge due to their solid rigidity and liquid leakage. In this work, a polyetheramine-based conductive phase change film was developed by introducing ion transport network and tetradecanol as phase change components encapsulated within the skeleton network. The film possesses adjustable heat storage density (79.5–163.4 J/g) and exceptional flexibility at room temperature. On the basis of desirable thermal regulation ability and ideal wearability, the film was successfully applied in the personal thermal management field and effectively regulated the human body temperature. Moreover, the film realized human motion sensing and object tactile recognition in real time with construction of the inner ion transport channels. This successful exploration provides a promising and scalable route towards intelligent wearable thermal management.

Sustainable energy synergy for historic building: Conservation retrofit solution of hygrothermal control

Historic buildings require groundbreaking retrofit technology to prevent damage to the exterior appearance of the exterior. This paper presents a retrofit technology to increase the energy efficiency of old historic buildings that were heavily exposed to hygrothermal conditions. The study employed an innovative interior finishing material composed of diatomaceous earth and microencapsulated phase change materials to achieve a trade-off between performance improvement and heritage conservation. Based on previous studies, an optimal formulation was identified through evaluation. The developed retrofit technology displays crack resistance, high latent heat capacity, and remarkable moisture stability. Our analysis revealed that the application of this retrofit solution would effectively reduce moisture levels and mitigate condensation risks without compromising the building’s historical integrity. The retrofit technology yielded a reduction in cooling and heating energy consumption by over 10% while concurrently addressing moisture stability through a decrease in the thermal transmittance of the exterior walls. By utilizing passive technologies and the unique properties of diatomaceous earth, our pioneering research on the sustainable preservation of historic buildings has laid the foundation for widespread retrofit adoption in heritage conservation.

Investigation on the synergistic effect and thermal properties of poly-hydroxyethyl methacrylate encapsulated graphene quantum dot-paraffin hybrid nanofluid

In this study, a novel water-based hybrid nanofluid was developed using poly-hydroxyethyl methacrylate-encased graphene quantum dot-paraffin nanocomposite (HEMA GQD-P). Graphene quantum dots (GQD) with an average size of 10 to 15 nm were synthesized by citric acid nucleation and the HEMA GQD-P nanocomposites were synthesized by an emulsion polymerization reaction. The emission spectra of GQD obtained using photo-luminescent spectroscopy confirm the occurrence of quantum confinement effect. The synthesis of HEMA GQD-P was carefully carried out to ensure its optimal properties. The synergistic effect due to high thermal conductivity of GQD and high latent heat capacity of paraffin were recognized in the enhanced properties of nanocomposite and hybrid nanofluid. The latent heat capacity of the synthesized nanocomposite was found to be 21.8 % higher than the pure paraffin. The prepared hybrid nanofluid possesses high dispersion stability at pH 7 and the thermal conductivity of the hybrid nanofluid enhances with an increase in nanoparticle concentration. A maximum thermal conductivity enhancement of 53 % (±2) was obtained for the hybrid nanofluid (0.3 vol%) at 30 °C. The present work reveals that the encapsulation of GQD-paraffin in a poly-hydroxyethyl methacrylate shell creates nanocomposites with high heat transfer properties. The synergistic effect of the HEMA GQD-P enhances their potential in the preparation of hybrid nanofluids with enhanced properties for desired thermal management applications.

Thermal response to periodic heating of a heat sink incorporating a phase change material

Phase change materials (PCMs) can effectively dampen temperature fluctuations due to their high latent heat capacity, leading to decreased average cooling requirements in various engineering applications. However, there are few design guidelines for PCM-based heat sinks and there is limited experimental research on their performance in high heat flux, periodic heating conditions. In this work, we present a 0-D and 1-D nondimensional analytic model for PCM-based heat sinks subject to sinusoidal heating. We formally define the four possible responses of PCM-based heat sinks and derive expressions to predict their effectiveness. We test experimentally two PCM-based heat sinks to validate these expressions – an air-cooled system and a water-cooled system. The operating PCM is Field's metal (32.5-Bi, 51-In, 16.5-Sn), a eutectic alloy with a melting temperature of 60 °C. Thermocouples are embedded in the system to measure the evolution of the system's temperature over time. We apply a sinusoidal heat input and study the parametric response of these heat sinks under a wide range of heat flux amplitudes (1-100 W/cm2) and periods (5–640 s), while also varying the external heat transfer coefficient (1,700-18,700 W/m2K), ambient temperature (20–45 °C), and thickness of PCM (1–4.4 mm) to comprehensively validate these proposed models. The experimental results are plotted in phase space and show good agreement with the analytic predictions.

Research Progress of Photovoltaic Cooling Systems Based on Phase Change Materials: An Overview

Photovoltaic technology plays a crucial role in harnessing renewable energy. While photovoltaic panels directly convert solar energy into electricity, more than 50% of solar radiation is lost as waste heat, diminishing the overall efficiency of the panels. This study reviews various cooling technologies for photovoltaic systems, focusing on the use of phase change materials for cooling in photovoltaic systems. Phase change materials, known for their high latent heat capacity, are extensively used in thermal energy storage applications. Incorporating phase change materials in photovoltaic systems can increase thermal storage potential by 30–50% compared to conventional systems, leading to a 70% extension in heat storage duration and various levels of enhanced power output. The main purpose of the article is to review the advantages and disadvantages of various technologies, determine the research direction of phase change materials for cooling systems in photovoltaics, and ensure the reliability of this technology.

Multi-stimuli-responsive shape memory flexible composites based on magnetic melamine/polydopamine/phosphorene complex foams and polyethylene glycol

We have developed a novel type of flexible multi-stimuli-responsive shape memory composite system based on a melamine/polydopamine (PDA)/Fe3O4/phosphorene (PR) complex foam and poly(ethylene glycol) (PEG). The system was constructed through coating PDA on the skeleton of the melamine foam and then decorating the PDA layer with Fe3O4 and PR nanosheets, followed by vacuum impregnation of PEG. The resultant composites exhibit an intrinsic thermal-driven shape memory behavior with a high shape recovery ratio of around 100% thanks to their high latent heat capacity derived from the loaded PEG. The introduction of magnetic Fe3O4 nanoparticles and PR nanosheets not only enhances the thermal conductance of the composites but also generates good magnetic and photothermal responsiveness. This enables the composites to obtain good light- and magnetic-driven shape memory capabilities in a shorter shape recovery period. This study offers a new strategy for developing smart materials with multiple and effective response to light, heat, and magnetism.

Unidirectionally Structured Magnetic Phase-Change Composite Based on Carbonized Polyimide/Kevlar Nanofiber Complex Aerogel for Boosting Solar-Thermo-Electric Energy Conversion.

To realize highly efficient solar-thermo-electric energy conversion for clean electricity power generation, we have developed a new type of unidirectionally structured magnetic phase-change composite comprising a carbonized polyimide (C-PI)/Kevlar nanofiber (KNF) complex aerogel as a 3D carbon skeleton porous supporting material, CoFe2O4 nanoparticles as a magnetic additive, polyethylene glycol (PEG) as a phase-change material, and polypyrrole as a photothermal absorption coating layer. The as-fabricated C-PI/KNF complex aerogel exhibits a unidirectional microstructure, high porosity, robust skeleton frame, ultralight weight, and high thermal conductance. Featured with such unique structure and characteristics, the complex aerogel can offer an effective heat and electron transfer method to ensure highly efficient solar-thermal conversion and photothermal energy storage of the developed composite. The developed composite exhibits a high latent heat capacity of over 150 J g-1, outstanding shape stability along with a low leakage of 0.2 wt %, good thermal cycling stability, and high photothermal conversion efficiency of 84.8%. Based on the Seebeck effect, a solar thermoelectric generation system (STEGS) was constructed with the hot side coupled with the developed composite and the cold side immersed in air and ice water. Under 2.0 kW m-2 solar irradiation, the developed STEGS in ice water obtained maximum output voltage and current of 259.7 mV and 27.1 mA, respectively, which are significantly higher than those in air. The output power of the developed STEGS in an ice water environment is 50.6% higher than that in air under 4.0 kW m-2 solar irradiation. More importantly, the developed STEGS in ice water continuously generated output voltage and current for about 810 s without solar irradiation thanks to the latent heat release by the PEG component within the developed composite. In addition, the introduction of magnetic CoFe2O4 can accelerate solar-thermal conversion through periodic electron motion by the Néel relaxation or Brownian relaxation. This resulted in an increase in the maximum output voltage and current by 13.7 and 11.5%, respectively, under an alternating magnetic field as a result of the magnetism-accelerated solar-thermo-electric conversion. This study offers an innovative approach for developing PCM-based advanced functional materials for solar energy utilization in clean and sustainable electricity generation.

Eco-Friendly Flame-Retardant Phase-Change Composite Films Based on Polyphosphazene/Phosphorene Hybrid Foam and Paraffin Wax for Light/Heat-Dual-Actuated Shape Memory.

Multiactuated shape memory materials are a class of promising intelligent materials that have received great interest in the fields of self-healing, anticounterfeiting, biomedical, soft robotic, and smart thermal management applications. To obtain a light/heat-dual-actuated shape memory material for thermal management applications in fire safety, we have designed a type of halogen-free flame-retardant phase-change composite film based on polyaryloxyphosphazene (PDAP)/phosphorene (PR) hybrid foam as a support material and paraffin wax (PW) as a phase-change material (PCM). PDAP was synthesized as a flexible foam matrix through the ring-opening polymerization of hexachlorocyclotriphosphazene, followed by a substitution reaction of aryloxy groups. The porosity of the PDAP foam is improved by introducing PR nanosheets, facilitating a high latent heat capacity of the PDAP-PR/PW composite films for thermal management applications. The PDAP-PR/PW composite films can implement rapid shape recovery within 65 s in the heating process, which is much shorter than that of the corresponding film without PR nanosheets (185 s). Furthermore, the PDAP-PR/PW composite films also exhibit light-actuated shape memory behavior thanks to their good solar-to-thermal energy absorption and conversion contributed by PR nanosheets as a highly effective photothermal material. More importantly, the presence of PR nanosheets imparts an excellent flame-retardant property to the PDAP-PR/PW composite films. The PDAP-PR/PW composite film can be self-extinguished within 2 s after the flame. Through an innovative integration of flexible polyphosphazene foam, PR nanosheets, and solid-liquid PCM to obtain a sensitive actuating response to light and heat, this study offers a new approach for developing multiactuated and eco-friendly flame-retardant shape memory materials to meet the requirement of applications with a requirement of fire safety in soft actuators, thermal therapy, control devices, and so on.

Double-layered hydrogels based on phase change material and pen ink for continuous and efficient solar-driven seawater desalination

A novel double-layered hydrogel based on the polyacrylamide matrix, pen ink, and phase-change microcapsules was developed to construct a hydrogel-based evaporator for efficient and continuous seawater desalination. The n-eicosane (core)@crystalline TiO2 (shell) phase-change microcapsules were fabricated through interfacial polycondensation, and the resulting phase-change microcapsules obtained a considerably high latent-heat capacity of 187 J·g−1. The upper layer of the hydrogel exhibits a high solar absorptivity of over 90 % due to the introduction of pen ink as a solar absorber, which helps the hydrogel-based evaporator to gain an excellent photothermal energy conversion capability. A high evaporation efficiency of 93.89 % was obtained for the developed hydrogel-based evaporator along with a high evaporation rate of 1.85 kg·m−2·h−1 under one-sun illumination. The phase-change microcapsules dispersed in the lower layer of the hydrogel can act as a latent heat-storage unit to store a great quantity of photothermal energy through melting phase change by the phase change material core. This imparts a consecutive evaporation capability to the developed hydrogel-based evaporator. As a result, its water production was increased by 11 % under 50-min one-sun illumination and 50-min non-illumination.

Composite phase change material based on Al alloy with durability of over 10,000 cycles for high-temperature heat utilization

High-temperature latent heat storage (LHS) technology using alloy-based phase change materials (PCMs) is promising for high-temperature heat applications owing to its high heat storage capacity at a constant temperature. Microencapsulated PCMs (MEPCMs) coated with stable ceramics can help prevent corrosive reactions observed in alloy PCMs during heat storage. Because MEPCMs are considered as ceramic particles, a composite PCM can be prepared by compositing them with a sintering aid. In this study, composite PCMs consisting of MEPCM with Al–12 mass% Si alloy (melting point: 577 °C) particles with diameters of 31.7 or 68.2 μm, and α-Al2O3 as the sintering aid were prepared. The MEPCM used in the preparation of the composite PCM included alumina hydroxide and various alumina polymorphs as coatings. Pellet-like compacts were successfully produced by mixing each MEPCM with α-Al2O3. After heat treatment, the composite PCMs retained their shape. In particular, the latent heat capacities of the composite PCMs made from small and large MEPCMs with α-Al2O3 coatings were 171 and 231 J g−1, respectively. Moreover, the composite PCMs retained their shape and more than 80 % of their latent heat capacity after 10,000 and 1000 cycles. The developed composite PCMs, with their high latent heat capacity and durability, can be employed for high-temperature heat applications.

The Performance Evaluation of Photovoltaic Integrated Organic Phase Change Material in a Single Container using Indoor Solar Simulator

Photovoltaic panels convert sunlight, a renewable energy source, into electrical energy. The abundant irradiance will heat the photovoltaic panel, reducing the panel's efficiency. This study proposes using PCM 36 as a cooling technique to reduce the temperature of the photovoltaic panel, which is low-cost and has higher latent heat capacity. The indoor solar simulator study is performed to meet the IEC 60904-9 standard. The research process starts with validating PCM 36, sun simulator testing, validating the photovoltaic panel, and fabricating a container to place the PCM 36 at the rear side of the photovoltaic panel to cool down the temperature. The final experiments are conducted indoors, using three different irradiance levels and a one-hour photovoltaic panel operation under the sun simulator. The optimal results reveal a 31.67% reduction in temperature and a 6.83% increase in electrical efficiency at a maximum of 40 minutes, 500 W/m2 irradiance, with a 9 mm thickness of PCM 36. Throughout this study, the efficiency of the photovoltaic system is enhanced by effectively reducing the temperature within the optimal range by incorporating phase change material.

A novel method to evaluate phase change materials' impact on buildings' energy, economic, and environmental performance via controlled natural ventilation

The construction industry consumes a significant portion of global energy, with space conditioning in buildings accounting for a substantial 34% of energy usage. Notably, the energy consumption of a building is significantly influenced by its envelope. Researchers widely acknowledge that incorporating phase change materials (PCM) into the building envelope is a promising way to enhance energy efficiency and mitigate CO2 emissions in the building sector, owing to their high latent heat capacity. However, PCM must be completely charged after each cycle to exploit its full potential. Natural ventilation is a viable technique to facilitate the charging and discharging cycle of PCM within a 24-h period. To this end, the present study utilized EnergyPlus simulations to optimize the cooling energy savings of a residential building incorporating PCM into its envelope for PCM melting temperatures, considering various ventilation strategies across 45 cities in 15 climate zones worldwide. In order to evaluate the latent heat utilization of PCM and its improvement facilitated by natural ventilation, two novel indicators, namely HS and HR, were formulated to represent the heat stored and released by PCM during a 24-h cycle, respectively. In addition, following an economic analysis of PCM integration, a comprehensive environmental evaluation was carried out, which included the carbon intensities (CI) of all fuel sources contributing to power generation. The study's findings reveal substantial energy savings across all climate zones when controlled natural ventilation is coupled with PCM, and the newly proposed indicators precisely quantify the performance of PCM in all scenarios evaluated. In the arid climate zone (A), combining PCM and natural ventilation enhances energy savings, albeit to a similar extent as using ventilation alone. However, the integration of PCM with temperature-controlled ventilation yields striking energy reductions of up to 72.8%, 85.3%, and 61% in arid (B), warm temperate (C), and snow (D) climate zones, respectively. The cost-benefit analysis reveals a minimal return period of as short as five years in climate zone C. In the same climate zone C, the in-depth environmental analysis reveals a maximal reduction of 42,004 CO2-e kg/year in carbon emissions. In conclusion, this research study demonstrated that integrating PCM with controlled natural ventilation offers a practical, sustainable, and cost-effective solution with eco-friendly and energy-efficient outcomes.

Flexible phase-change composite films for infrared thermal camouflage and photothermal energy storage

To meet the requirement of multipurpose applications in infrared thermal camouflage and solar photothermal energy storage, we have developed a series of multifunctional composite films based on polyurethane (PU) as a flexible matrix and double-layered phase-change microcapsules as an additive. The double-layered microcapsules were first constructed by encapsulating n-docosane as a phase-change material in a titanium dioxide shell, followed by depositing a polyaniline (PANi) functional layer. Then, the microcapsules were incorporated into the PU matrix to form the composite films through in situ polycondensation. A high latent heat capacity of over 130 J g−1 was achieved by the microcapsules as a result of a high n-docosane loading. This can generate an effective thermal buffer for the composite films and thus endow them with a good thermal camouflage capability. The composite films also show good solar energy-storage performance thanks to their superior sunlight absorptivity derived from the PANi coating layer of the microcapsules. The composite films present a much higher surface temperature (68.6 °C) than pure PU film (41.9 °C) under simulated sunlight irradiation for 1488 s. In addition, the composite films exhibit a self-cleaning surface and high flexibility. Integrating the double-layered microcapsules and flexible PU matrix may provide an innovative strategy for developing flexible functional films for infrared thermal camouflage and photothermal energy storage applications.