Phase change materials (PCMs) offer strong potential for reducing building energy demand. This study aims to develop lightweight structural mortars with improved indoor thermo-regulation by incorporating a form-stable PCM (FSPCM). The FSPCM was produced by impregnating expanded vermiculite (EV) with n-octadecane at a 40 wt% ratio. The reference mortar was prepared using EV as a lightweight aggregate at 25 wt% relative to cement. To obtain thermally enhanced composites, this EV fraction was replaced with FSPCM at substitution levels of 25-100 %. All mixtures were characterized to evaluate their physical, mechanical, and thermal performance. The mixture completely replaced with FSPCM showed the most significant improvements, achieving a thermal conductivity of 0.456 W/mK, density of 1.07 g/cm3 , and compressive strength of 8.81 MPa. DSC analysis of the FSPCM revealed melting and solidification temperatures of 25.76 and 25.42 degrees C, with latent heats of 100.4 and 99.5 J/g. Thermo-regulation tests confirmed effective reduction in indoor temperature fluctuations. A preliminary cost-performance evaluation, based on unit material prices and experimentally observed thermal benefits, indicates that FSPCM-integrated mortars may provide favorable life-cycle economics despite higher initial material costs. In conclusion, the EV/n-OC composites demonstrate strong potential as sustainable and energy-efficient building materials.

Improving the thermal behavior of building envelopes plays a significant role in minimizing energy consumption and regulating indoor thermal comfort. The use of phase change materials (PCMs) in wall components offers an important approach to passive heat regulation in buildings. In this regard, the implications of PCM placement for hollow brick structures under real outdoor conditions have been adequately addressed in the literature. This study presents an experimental assessment of the effects of integrating different microencapsulated phase change material (MPCM) configurations into brick hollows on thermal performance, taking into account the same real environmental conditions, while also providing a general approach in terms of energy savings and environmental benefits. The findings highlight that the MPCM additive demonstrates effective performance in reducing peak temperatures and regulating thermal fluctuations. The proposed MPCM-containing bricks (OUT2, IN2 and FULL) provide a maximum advantage of 7.04 degrees C and 4.47 degrees C in minimizing indoor heat gains and losses during the daytime (heating period) and night (cooling period) respectively. Among the configurations tested, IN2, despite having a significantly lower MPCM ratio, provided almost the same thermal and energy advantages as FULL and offered the highest cost-performance efficiency. This highlights the critical role that MPCM placement plays in terms of thermal efficiency. The analyses also show that MPCM efficiency is more pronounced under conditions where solar radiation is concentrated. According to annual heating and cooling energy performance analyses based on experimental measurements, a significant reduction in heat flow in both heat gain and heat loss directions was observed with MPCM integration compared to the reference. The MPCM integration resulted in annual building-scale energy savings of 279-631 kWh by reducing cooling and heating loads by approximately 3.06 kWh/m2 and 12.71 kWh/m2 respectively. Consequently, the building's total annual CO2 emissions decreased by approximately 10.49 kgCO2/m2 & sdot;year. The economic savings achieved by minimizing heatingcooling loads and reducing CO2 emissions reached 88.83 USD. The novelty of this study lies in investigating different MPCM layouts in hollow brick structures under real outdoor conditions, and all findings demonstrate that an optimized MPCM placement can maximize thermal performance and economic return without increasing material usage. Furthermore, it has been shown that the MPCM-brick system offers economically, environmentally sustainability and energy-efficient innovative structural solutions in building envelope designs.

Latent heat storage techniques, mainly phase change materials (PCMs), are essential for improving the use of energy in buildings by effectively storing surplus thermal energy and discharging it as required, thus decreasing demand for energy and promoting environmentally friendly practices. Nonetheless, issues like as PCM leakage and weak interfacial connection have hampered their broad adoption. Therefore, the present investigation introduces an exciting technique by incorporating shape-stable PCM (SSPCM) within concrete, employing a unique blend of biodegradable and sustainable resources for energy-saving construction designs. The SSPCM was evaluated for its physico-chemical, thermal, and mechanical characteristics by mixing Arabic gum (AG) with Ethyl stearate (ES) in different proportions. The optimal ES ratio within AG was 25 wt% with no leakage observed. The phase change of optimal AG/ES SSPCM occurs at 28.9 degrees C with an enthalpy of 61.6 J/g (endothermic) and 59.8 J/g (exothermic). Also, following 500 consecutive thermal cycles, the newly created AG/ES SSPCM demonstrated outstanding chemical and thermal stability. The AG/ES addition resulted in a notable decrease in the thermophysical properties of concrete due to the low load-bearing, low density and reduced heat transfer rate of SSPCM. Yet, AGCON-100 possess sufficient compressive strength for use as an insulation concrete. On the other hand, because of the AG/ES's capacity to absorb and store heat, the thermoregulation tests showed that AGCON-100 with AG/ES SSPCM maintained lower temperatures (-2.6 degrees C) during warm times and higher temperatures (0.5 degrees C) during cold periods. These outcomes underscore the capacity of AG/ES SSPCM to improve temperature control and diminish the ecological effect in structures, thus contributing to the achievement of sustainable development goals.

This study presents the development and evaluation of a novel and sustainable solar air heater (SAH) incorporating an enhanced compact heat-absorbing structure made from recycled aluminum radiator fins, designed to improve thermal and exergetic-performance while promoting material-reuse and sustainability. The reuse of waste radiator materials provides a multilayered-fin configuration that increases the effective heat-transfer surface area, enhances turbulence, and reduces overall heat loss without additional manufacturing cost. A comparative methodology was employed to assess the influence of this compact thermal-storage element on SAH performance under typical Autumn and Spring conditions. The baseline and modified SAH models were evaluated using dimensionless performance parameters and validated through experimental testing. The average thermal-efficiency of the baseline system was 64.81 %, while the compact heat-exchanger-integrated system reached 78.54 %, indicating a significant improvement of about 13.7 percentage points (21 % relative increase). Furthermore, the oriented-configuration (ochxSAH) provided an additional 3.23 percentage points improvement, corresponding to a further 4 % performance gain. The heat loss rate for chxSAH increase 5.9 % that accompanied a much larger rise in useful heat-gain, confirming improved energy utilization efficiency. These gains were achieved through the improved energy-saving capacity of the recycled radiator-based absorber and its ability to maintain higher outlet temperatures. To complement the experimental study, a machine-learning (ML) approach was applied to predict SAH efficiency. The ML results validated the superior thermal and exergy performance of the sustainable SAH design, demonstrating that integrating waste-material-based compact heat exchangers can enhance system efficiency while supporting circular-economy principles in solar-thermal technologies.

Extraction of natural aggregates for concrete not only depletes non-renewable resources but also causes habitat loss, groundwater disruption, and carbon emissions. At the same time, sustainable and energy-efficient construction demands materials capable of reducing operational energy. Integrating phase change materials (PCMs) into cementitious systems is promising for passive thermal regulation, yet conventional methods (microencapsulation, coatings) suffer from leakage, poor dispersion, and weak bonding. This study proposes replacing natural stone with 3D-printed smart aggregates embedding 50 wt% methyl palmitate (MP), combining structural compatibility with latent-heat storage. Concretes with natural aggregates (NA), synthetic aggregates (AA), and PCM-integrated aggregates (AAPCM) were compared in this study. At 28 days, compressive strength dropped from 92.99 MPa (NA) to 58.39 MPa (AA) and 44.34 MPa (AAPCM); ultrasonic pulse velocity decreased from 4.49 to 4.26 to 3.91 km/s. Thermal conductivity reduced by similar to 52% (1.26 -> 0.606 W/mK). DSC confirmed latent-heat storage of 224 J/g (MP) and 109 J/g (AAPCM) with >99% retention after 500 cycles. Outdoor tests showed up to 5 degrees C surface cooling and delayed heat release near 26 degrees C. Thus, PCM-integrated aggregates mitigate the environmental burden of quarrying while delivering thermally adaptive concretes, suitable for fa & ccedil;ades, pavements, and energy-resilient building envelopes.

Phase change materials (PCMs) are becoming a key component in the design of next-generation textiles that can control temperature in response to ambient temperature for the goal of heat management. The high heat capacity of methyl palmitate (MP) was directly impregnated into porous diatomite in this study at four ratios (40%, 50%, 53%, and 55% by weight). The leakage test showed that composites with 53% and 55% MP exhibited leakage, whereas composites with 40% to 50% MP did not exhibit any leakage. Consequently, the cellulosic fabric coating method employed composites containing 50 wt% MP. A two-component silicone matrix that can be cured at room temperature was mixed with MP/Diatomite composite (MPDIA) in three ratios (10%, 20%, and 30% by weight). The resulting composite‑silicone mixture was then applied to the fabric surface. FTIR results showed no chemical interaction between diatomite and MP. The fabrics coated with MPDIA‑silicone mixture exhibited melting enthalpy (from 7.4 to 24.2 J/g) and freezing enthalpy (from 7.1 to 23.8 J/g). After 600 thermal cycles, no significant difference was observed in either the phase transition temperatures or latent heats of the coated fabrics. SEM-EDS analyses demonstrate that the coating layer maintains its durability on the textile surface, exhibiting resistance to 10 washes. Under solar exposure conditions, the thermoregulation performance of coated fabric with paste containing silicone and 30% MPDIA (CFMPDIA30) were experimentally assessed. Due to latent heat release, PCM-integrated fabric provided brief nocturnal heating while lowering peak daytime temperatures by up to 6.4 °C under intense solar radiation. A dominant and long-lasting cooling impact with a time-limited heating contribution was established by temperature difference analysis.

The modern days construction sector faces growing pressure to adopt materials that are both energy-efficient and environmentally responsible. This research presents bio-polyurethane foam (PBF) carrier impregnated with polyethylene glycol (PEG) as novel building material. The resulting composite using PEG as phase change material (PCM) simultaneously tackles two building-related issues: reducing the carbon footprint associated with cement production and lowering the operational energy demand of buildings through passive thermal regulation. Test results showed that the melting point of PEG-impregnated PBF composites was found to be to be 22.3 degrees C while the melting enthalpy was recorded as 78.3 J/g. The developed composite provided a nighttime cooling of up to 10 degrees C compared with geopolymers without PCM. With a 28-day compressive strength of 22 MPa, the material is suitable for use in elements subjected to low-to-medium load levels, especially in non-load-bearing or secondary load-bearing applications such as residential slabs, floors, and non-load-bearing walls. These results suggest strong potential for use in partition walls, wall blocks, and insulation panels designed to moderate indoor temperature fluctuations in energy-efficient buildings.

This study addresses the development of new composite materials based on natural biomass and renewable resources in response to the increasing demand for solar photothermal energy storage composites. The raw materials used include gypsum, moss biomass (MBM), and ethyl palmitate (EP) as the phase change material (PCM). The highest ratio shape-stable PCM in gypsum was determined to be 10%. The composites prepared with this ratio were then added to the gypsum matrix at 2.5%, 5%, 7.5%, and 10%, respectively, to produce the final composite panels. The morphological, thermal, and chemical properties of the shape-stable MBM/EP composites were investigated using SEM, TGA, and DSC analyses. Furthermore, the solar thermal regulation performance of the produced gypsum-based composite panels was tested under open-air conditions. The phase transition temperature and melting enthalpy of the shape-stable MBM/EP composites were determined to be 19.5 degrees C and 173.2 J/g, respectively. The shape-stable MBM/EP composites exhibited a melting enthalpy of 171.2 J/g, with only a minor decrease after 500 cycles. Under conditions where the ambient temperature exceeded 46.38 degrees C, the internal temperature of the PCM-containing cabinets was measured at least 12.15 degrees C lower than that of the gypsum-only cabinets. On the other hand, when the temperature dropped to approximately 15 degrees C, the core temperature of the PCM-containing cabinets was observed to be approximately 4.70 degrees C higher. This study presents an innovative approach for the development of environmentally friendly gypsum/moss/PCM composites for use in thermal energy storage systems.

Improving the energy efficiency of building materials is critical for reducing environmental impacts. This study develops and evaluates bio-based polyurethane composites (BPUCs) incorporating lauryl alcohol (LA) as a phase change material (PCM) for lightweight cementitious systems. The composites were synthesized from modified castor oil (MCO), commercial polyether polyol (CPP), and methylene diphenyl diisocyanate (MDI), and systematically characterized to assess their thermal, mechanical, microstructural, and environmental performance. Differential scanning calorimetry, thermogravimetric analysis, hardness, tensile, and thermal conductivity tests were performed, followed by outdoor thermal regulation testing using a full-scale cabin setup. Results show that increasing LA content improves bulk density (38.9-67.6 kg/m3), hardness (7.1-15.2), and thermal conductivity (0.026-0.038 W/m & sdot;K), while moderately reducing tensile strength (243-138 kPa) and strain (89-43 %). The optimized composite, BPUC-LA-6, achieved a latent heat storage of 127.8 J/g and enhanced thermal stability, with activation energy increasing from 108.47 to 164.13 kJ/mol. When incorporated into lightweight cementitious composites (BLWC3), the system reduced peak surface temperatures by up to 6.5 degrees C and maintained nighttime warmth by approximately 2 degrees C, confirming its effective thermal energy storage behavior. Energy simulations across different Turkish climate zones indicated heating energy reductions up to 60 % in severe climates, accompanied by proportional decreases in CO2 emissions. The economic analysis showed annual savings between $0.65 and $4.39 per square meter depending on the heating source, with a payback period of 2-15 years. This work presents a scalable bio-based polyurethane-PCM system that integrates renewable materials with high PCM loading, offering a practical route to energy-efficient and low-carbon building materials.

Lightweight concrete systems made by employing PCMs and natural waste aggregates are a promising material to minimize heating and cooling needs in buildings. But most systems utilize natural minerals or fly ash-based carriers with finite storage capabilities and are not validated under real-world conditions. There is, however, a dearth in the literature of waste-derived, carbon-rich ashes which can act as stable porous hosts for lightweight aggregates and organic PCMs. This study covers the gap by applying reclaimed heavy fuel oil ash as a new bifunctional carrier, impregnated with lauryl alcohol, and integrated into lightweight concrete to produce a 50:50 (heavy fuel oil ash-PCM):cement blended concrete composite. The impregnated ash showed thermal stability at approximately 150 degrees C and the absorbed lauryl alcohol was also about 20 degrees C in melting and has the latent heat capacity of 110-120 J/g. In concrete, the ash impregnated had a peak temperature of 1-3 degrees C reduction on the internal surface with direct sunlight, as compared to the diatomite control when both mixed. Outdoor cabin experiments indicated reduced daytime heat gain and delays in nighttime cooling, suggesting a significant thermal buffering effect. This implies that the composite obtained from waste could alleviate daily temperature variations, enhance its indoor thermal comfort, and decrease heat transfer through building envelopes. This work makes a solid foundation in the development of thermal performance and the sustainability of lightweight building materials by linking material-scale characterization to component-level outdoor testing and paving a way further from the aforementioned studies.

The integration of phase change materials (PCMs) with biomass-derived biochar offers a sustainable and energy-efficient approach for developing composites with enhanced thermal functionality. In this study, a leakage-resistant composite was prepared by impregnating olive waste pulp (OWP)-based biochar (BC) with 45 wt% lauryl alcohol (LOH). The OWP-BC/LOH composite was incorporated into concrete by partially replacing sand at 10 %, 15 %, and 20 % to produce advanced materials for building energy conservation. Extensive tests covering morphological, physical, mechanical, thermal stability, thermal energy storage (TES), and solar thermoregulation were conducted. The compressive strengths of TES-integrated concretes were 45.31 MPa, 37.94 MPa, and 28.48 MPa for 10 %, 15 %, and 20 % replacements, respectively. While lower than the control, these values remain acceptable considering the improved thermal regulation. At 20 % replacement, apparent porosity, water absorption, and dry unit weight were measured as 23.3 %, 14.91 %, and 1869.11 kg/m3, respectively. FTIR analysis confirmed strong interactions between OWP-BC and LOH. DSC results revealed a melting point of 20.18 degrees C with a latent heat capacity of 111.9 J/g, maintaining stability after 600 heating-cooling cycles. TGA analysis indicated that the working temperature range was well below the onset of thermal degradation, ensuring long-term durability. Thermal conductivity decreased by 13 %, reaching 0.93 W/m & sdot;K. Furthermore, solar thermoregulation tests showed that 20 % OWP-BC/LOH concrete provided effective daytime cooling and nighttime heating. The use of OWP-BC/LOH composites could potentially reduce annual building energy consumption up to 27 kWh m-2 y-1 and lower CO2 emissions by

This study proposes a novel bio-derived, sustainable, and shape stabilized composite phase change material (PCM) and evaluates its performance within cement mortars. The PCM composite was produced by impregnating an organic PCM into activated carbon (AC) obtained from pomegranate peel waste (PPW). The micro and mesoporous structure of the AC was used as physical host for the PCM. To evaluate the performance of PCM composite, characterization tests and analyses were performed to verify structural stability, chemical compatibility, and thermal reliability. The optimum PCM loading was found to be 45 wt% to achieve high latent heat storage capacity, negligible or no leakage, and robust cycling stability. Subsequently, mortar specimens incorporating the biochar shape-stabilized PCM (AC-PCM) composite were prepared and tested for compressive strength, porosity, water absorption, thermal conductivity, and thermoregulation under realistic conditions. The PCM composite has a melting temperature of 26.32 degrees C and an enthalpy of 116.8 J/g that confirms its applicability for low-temperature thermal storage in build environments. Mortars with 20 vol% composite achieved a 28-day compressive strength of 33.44 MPa. While this represents a 43.5% decrease compared to the control mix, the mechanical performance remained within acceptable limits. Open field thermoregulation tests revealed that the PCM-enhanced mortar reduced peak indoor temperatures by 8.9 degrees C. Hence, the Bio-AC-PCM incorporated mortar offers an eco-friendly and mechanically viable approach to climate-resilient and energy-efficient construction materials.

3D printing of cementitious materials is a novel approach to fabricating structural components with many applications, including rapid structural recovery in remote areas since it can function almost autonomously. However, since the newly built components are instantly exposed to the outside environment, their thermal properties can have major impact on their energy efficiency and the long-term operating costs for heating, ventilation, and air conditioning (HVAC) systems. To address this challenge, and for the first time, this study combines an outdoor thermal monitoring system with a detailed material performance evaluation for 3D printed concrete (3DPC) containing melamine-formaldehyde-based phase change materials (PCMs). To uncover the impact of PCMs in 3DPC sections, a series of standardized and advanced tests, including nano-indentation, mu CT scanning, SEM, and thermal efficiency measurements, were performed. Results show that the inclusion of PCM increased total porosity from 14.44 % to 21.49 % and water absorption from 8.57 % to 11.20 %. Surface hardness decreased from 1296.11 MPa to 764.58 MPa, accompanied by a higher variability (standard deviation rising from 256.60 MPa to 414.55 MPa) for PCM-containing samples, as compared to the reference 3DPC samples. The addition of PCMs also reduced thermal conductivity by similar to 10%, while it also remained stable after 100 cycles of freeze-thawing. The results of the study are found to be significant and contribute to the development of energy-efficient and resilient materials.

As global energy demand continues to rise, improvement of energy-efficient composites in construction is becoming increasingly critical. This work investigates physico-mechanical, and thermal performances of lightweight cementitious composites enhanced with bio-activated wood based-activated carbon (WAC) and phase change materials (PCMs), specifically Lauric acid and Myristic acid. The PCM impregnated WAC was replaced with the scoria up to 30 %. This research evaluates the impact of combining WAC and PCM on cementitious composites' performance, focusing on critical parameters as compressive strength, thermal conductivity, porosity, and dry unit weight. Results show that unit weight and compressive strength gradually lessen as the proportion of WAC increases. Specifically, the LWC-WAC30 mixture demonstrates a 32.3 % lower dry unit weight and an 83.7 % lower compressive strength compared to the reference lightweight concrete (R-LWC). Although mechanical performance is reduced, the improved thermal behavior, including lower peak temperatures and minimized thermal fluctuations, shows that these composites remain well-suited for thermal energy storage (TES) and passive building applications. Thermoregulation experiments conducted in a controlled setting demonstrated the PCM's effectiveness in stabilizing internal temperatures, achieving decrement of peak room center temperatures of up to 4.58 degrees C for cycles of elevated ambient temperatures. Furthermore, study emphasizes the innovative application of WAC as a sustainable medium for PCM integration, presenting a novel strategy that utilizes natural materials to enhance thermal performance while preserving structural integrity. These results underscore the considerable potential for employing WAC-PCM composites within the construction sector, particularly in the creation of energy-efficient and resilient building materials.

A diffuse reflective (DR) surface in a concentrating photovoltaic thermal system (CPVT) system can provide uniform solar energy dispersion, minimizing hot spots, uneven lighting, and efficiency loss compared to costlier, highly reflective (HR) surfaces. This study uniquely compares the performance of HR-CPVT and DR-CPVT systems, highlighting the significant thermal and electrical efficiency of HR-CPVT while demonstrating the cost-effectiveness of DR-CPVT. The direct comparison of these systems under varying conditions provides novel insights into the trade-offs between high performance and economic feasibility. The performances of CPVTs were examined under various seasonal and weather conditions. The advantage of HR-CPVT was less pronounced in autumn due to seasonal effects. In the summer season, the cooling effect of water becomes more prominent, and the HR-CPVT outperformed the DR-CPVT by 6.1 to 8.5 %, depending on the mass flow rate in terms of overall efficiency. This advancement majorly arises from thermal efficiency. HR-CPVT achieved about a 5.6-7.9 % larger thermal efficiency. However, the electrical efficiency difference was minimal (similar to 0.5 %) and diminished to 0.1 % in the afternoon due to practical PV power generation limits. Despite its high reflectivity, HR-CPVT showed only marginal exergetic benefits over DR-CPVT. The simple payback period was calculated to be 3.65 years for HRCPVT, while it was only 3.19 years for DR-CPVT due to its lower installment cost. RSM analysis accurately predicts the experimental results.

With growing global energy demand and the urgent need to reduce carbon emissions, developing sustainable materials with thermal energy storage capabilities has become essential. This study introduces, for the first time, a flexible polyurethane biocomposite (FPB) containing directly integrated unencapsulated coconut oil-based phase change material (CO-PCM), without micro-shells or encapsulation. This novel approach simplifies fabrication, reduces cost, and enhances thermal and mechanical performance through direct polymer-phase change material interaction. Flexible polyurethane biocomposites incorporating varying concentrations (0 %, 15 %, 30 %, and 45 %) of CO-PCM were synthesized using a two-step method involving polyether polyol, isocyanate, and a catalyst. Increasing CO-PCM content improved the physical and thermal properties of the composites. At 45 wt% CO-PCM, bulk-density increased by 51 %, Shore A hardness by over 43 %, and tensile strength by 14 %, while strain decreased from 82 % to 53 %. Thermal conductivity improved by 15 %, and activation energy rose by 30 %, indicating enhanced thermal stability. The composites were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Thermoregulation tests showed that the FPB with 45 % CO-PCM reduced peak surface temperatures by up to 6.8 degrees C during the day and retained 2.4 degrees C more heat at night, contributing to stable indoor thermal conditions. Energy simulations across four climate zones revealed that FPB-45 could reduce heating energy demand by up to 26 % compared to conventional expanded polystyrene (EPS) insulation. CO2 emission analysis indicated up to 10 kg/m2 annual reduction, and up to $1.80/m2 annual savings when using fuel oil, proving its technical and economic viability.

This study examines the impact of phase-change thermochromic (TC) coatings on the durability, color stability, and thermal regulation of poplar wood, focusing on potential applications in energy-efficient buildings. By applying accelerated weathering tests, the study assessed how TC pigments (red or yellow) at varying concentrations affect wood properties. The results showed that TC-treated wood undergoes significant color shifts depending on pigment concentration and temperature. For instance, at 25 degrees C, the color change (Delta E*) reached 71.07 for red-20 samples and 68.30 for yellow-20, with increased lightness (L*) at higher temperatures. Unlike untreated samples, TC-coated wood exhibited a whitening tendency as temperatures rose to 38 degrees C and 50 degrees C, suggesting a promising thermal regulation capability. Accelerated weathering tests revealed that TC-treated wood experienced greater color changes than control samples, though varnish coating helped reduce discoloration. Notably, thermal regulation tests demonstrated that TC-treated wood helps maintain cooler indoor temperatures during hot conditions and warmer temperatures in cold conditions, highlighting potential energy efficiency in building environments. This study provides a foundation for utilizing thermochromic materials in construction, offering insights into their weathering and thermal performance. Future studies should focus on optimizing TC formulations and assessing durability in real-world settings.

This study examined the enhancement of thermal properties in wood through impregnation with tallow (TW) and myristic acid (MA) to create a bio-based phase-change material (BPCM) suitable for energy-storing interior building materials. Poplar sapwood was impregnated with TW/MA mixtures in ratios of 30:70, 50:50, and 70:30. Leakage tests revealed a maximum leakage of 2.8% for the 30:70 ratio at 70 °C for 20 min. The weight percentage gain (WPG) reached 112.0%. Fourier transform infrared spectroscopy (FTIR) confirmed the physical combination of the TW/MA mixture and poplar wood. The mixture exhibited a phase-change temperature of 50.5 °C and latent heat of 172 J/g. The differential scanning calorimetry (DSC) results showed a latent heat capacity of 73.6 J/g and a melting temperature of 45.9 °C for the ratio of 50:50. Thermoregulation tests demonstrated an indoor temperature that was sustained within tolerable ranges and reduced room temperature fluctuation. Thermal conductivity decreased by 41.4% in tallow impregnated samples but increased by 10% in the TW/MA mixture. Wood samples impregnated with phase-change materials exhibited 90.71% fungal resistance. Overall, BPCMW showed promise for the practical storage and release of solar thermal energy, with tallow-impregnated wood (TW-W) displaying a superior performance, offering significant benefits in reducing building heating and cooling loads.

Non-imaging concentrators enhance photovoltaic thermal system efficiency by improving solar energy capture. However, selecting the optimal concentrator geometry remains challenging due to efficiency, cost, and acceptance angle constraints. This study optimizes concentrating photovoltaic thermal (CPVT) design using compound parabolic (CPC), V-trough, and compound hyperbolic (CHC) concentrators with varying truncation levels and incidence angles. By integrating Grey Relational Analysis (GRA) and Response Surface Methodology (RSM), forty-eight CPVT configurations were uniquely analyzed to identify the best balance between performance, geometry, and cost. The results indicate that V-trough achieved the highest thermal efficiency (66.2% at 0 degrees) and was particularly effective at small angles. CPC maintained stable efficiency across configurations, with moderate truncation (55%), reducing material costs while preserving performance making it a cost-effective option. CHC exhibited the steepest efficiency decline (64.9% to 30.0%) as the incidence angle increased. Due to lower PV temperatures, electrical efficiency improved with incidence angle and smaller reflectors, peaking at 30 degrees with 0.42 truncation. Truncation effects varied by concentrator type, with CPC being the least sensitive. GRG analysis shows that CHC remains more stable at higher incidence angles. RSM identifies incidence angle as the most influential performance factor, indicating that sun tracking may be necessary at larger angles. These findings provide a structured framework for CPVT system optimization, offering insights into the role of truncation and incidence angles in enhancing efficiency and economic feasibility, supporting large-scale adoption by reducing material costs while maintaining energy output, and making it a sustainable solution for enhanced solar energy utilization.