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Energy conservation in buildings has been the focus of many studies since nearly one-third of global energy consumption is due to buildings. Phase change material (PCM) technology promises to be an attractive solution for energy saving in buildings since it is a passive and effective technology, as demonstrated in the literature. Therefore, this study focuses on the energy-saving performance of PCM-integrated buildings located in a Mediterranean climate to reveal their energy-saving potential. PCM is integrated both in external or internal south walls and roofs of buildings under four different climatic conditions. EnergyPlus, which is a well-known building simulation software, is adopted for building thermal analyses. The effects of melting temperature, location of PCM layer in the wall, thickness of PCM layer, type of envelope (wall or roof), and PCM double-layer system in the wall are investigated. The corresponding energy savings and CO2 emission reductions are obtained for the considered cases. The results showed that up to 41.6% reduction in energy demand can be obtained depending on the PCM application. Besides, PCM with a low melting temperature (21 °C) favored heating energy savings, while PCM with a high melting temperature (29 °C) favored cooling energy savings. Moreover, the double-layer PCM system provided higher energy savings than the single-layer PCM system, especially in warm and arid regions (Sousse and Tozeur).

The utilization of phase change materials (PCMs) in buildings leads to the reduction of energy consumption and maintaining the indoor temperature within the comfort range. The PCM performance strongly depends on the climatic conditions, causing a major challenge. To overcome this issue, the employment of a double-layer PCM system is introduced. The energy and economic assessments of various double PCM systems in the building located in different climatic conditions of Iran have been conducted for the first time. In this study, two PCM wallboards with different enthalpy and melting temperatures were embedded in the external walls of a residential building located in various climatic regions of Iran. The performance of the double-layer PCM system in five cities of Iran including Tehran, Isfahan, Shiraz, Tabriz, and Bandar Abbas during hot and cold months of the year was evaluated from energy and economic viewpoints. It was inferred that embedding a double-layer PCM system reduces the heating/cooling energy consumption compared to single-layer ones. It was concluded that the RT18/RT28 double PCM system was the best candidate to be employed in the external walls of the building located in Tehran and Shiraz, which reduced the total energy consumption of the building up to 6.26% and 5.17%. The RT18/RT22 double PCM system was the most efficient system for the building placed in Tabriz and Isfahan reducing the total energy consumption up to 4.41% and 3.87%, and the RT22/RT28 double PCM system had the best performance in the building located in Bandar Abbas, which could save 6.58% of total energy. Moreover, it was concluded that the use of a double PCM system reduced temperature fluctuations in the external walls. In addition, the economic analysis was performed using the dynamic payback period and the results revealed that the employment of a double-layer PCM system reduced the investment return period by up to 50%.

Nowadays, limited energy resources face ever-growing demands of the modern world. One engineering approach to mitigate this problem which has received considerable attention in recent years is using latent heat thermal storage (LHTS) systems, a significant opportunity which is provided by phase change materials (PCMs). In the present study, a numerical investigation was devoted to estimate the simultaneous freezing and melting processes of a double-layer PCM in terms of heat transfer and fluid flow phenomena. A double-pipe cylindrical channel with two compartments, A and B, was considered for locating two PCMs of RT28 and RT35 in various arrangements. The inner and outer walls were exposed to both hot and cold heat transfer fluids (HHTFs and CHTFs, respectively) beginning with solid or liquid initial state, which led to solid–liquid phase change process through PCMs. The numerical simulation was handled by a two-dimensional finite volume method (FVM) with a fixed Rayleigh number of 106 in which conduction and convection heat transfer mechanisms are taken into account. The effects of employing double-layer PCM and their arrangements, inner and outer walls’ boundary conditions, and initial statuses of PCMs are discussed, and the details of the compared results are shown in the form of temperature and liquid fraction variations over time.

A novel bifacial photovoltaic wall combining thermochromic material and double layers PCM (BPVW-TC+PCM) is proposed to passively regulate building heat gain and photovoltaic (PV) power generation through the dynamic color change properties of thermochromic glass and the latent heat storage capacity of the phase change material (PCM). Physical and numerical models of the composite wall system were developed, followed by numerical simulations to analyze indoor air temperature, PV power generation, and annual energy consumption in both ordinary and composite wall rooms. Additionally, optimization studies were conducted to determine the ideal phase change layer temperature and arrangement. The results indicate that this novel wall system significantly reduces indoor air temperature fluctuations and enhances PV power generation by approximately 16% in both summer and winter compared to conventional mono facial PV walls. The system achieves its lowest energy consumption when the high-temperature phase change layer is maintained at 28 °C and the low-temperature phase change layer at 18 °C, with both layers positioned on the interior side, resulting in an energy saving rate of 22.6%.

•An innovative BIPV system with double-layer PCM was proposed and established.•Dimensionless numbers were introduced, elucidating the relationship of double PCMs.•The influence of key parameters on the new system was clarified.•System dynamics were analyzed, highlighting PV and energy consumption synergy.•Energy and exergy analysis reflect the energy-saving potential of the new system. The integration of phase change material (PCM) with building-integrated photovoltaic (BIPV) presents a compelling approach to enhance solar energy utilization and mitigate indoor thermal loads, contributing to energy-efficient and low-carbon building development. Traditional BIPV-PCM structures, however, struggle to balance PV efficiency and thermal insulation, particularly with varying PCM wall positions. To address this situation, this study introduces a novel double-PCM BIPV composite envelope (BIPV-dPCM). An experimentally validated dynamic heat transfer model was developed and used to perform a comparative simulation analysis with three reference systems to quantify the energy-saving potential of the BIPV-dPCM, focusing on PV output and wall insulation effectiveness metrics. Further dimensionless parametric analysis were carried out to investigate the systematic performance of the two PCMs at different relativities. In addition, the coupled working mechanism of the BIPV-dPCM system concerning the power generation performance and thermal insulation performance under transient variations is explored. It was found that the BIPV-dPCM showcases superior thermoelectric coupling performance compared to three alternative enclosures. Incorporating two PCMs significantly enhances electrical exergy efficiency by 11.66 % and thermal exergy efficiency by 1.54 %, surpassing other reference systems. The increase in PCM latent heat ratio has a limited effect on performance gain. Notably, as the PCM thickness ratio exceeds 1, the decline in P value decelerates, for every 0.5 increment in the g, the P value diminishes by merely 0.2 %. The ideal h is identified between 1 and 1.5, with 1.5 being optimal for energy conservation objectives. Additionally, the self-sufficiency coefficient (SSC) of the BIPV-dPCM remains robust, sustaining a range of 55 % to 65 % over prolonged periods. This study offers novel perspectives and serves as a design reference for optimizing building energy systems and enhancing cooling efficiencies in subtropical climates. [Display omitted]

This study employs the effective heat capacity method within the COMSOL simulation framework to analyze the thermal performance of double-layer phase-change walls under typical summer climatic conditions in Zhengzhou, Henan Province. The model considers a wall structure with a total thickness of 100 mm and a height of 300 mm, where the exterior surface represents the outdoor environment, the interior surface represents the indoor environment, and the top and bottom boundaries are assumed to be adiabatic. A highly refined triangular mesh ensures numerical stability and solution accuracy. Special attention is given to the influence of Micro-PCM content on thermal storage characteristics. Simulation results demonstrate that increasing the Micro-PCM content substantially enhances the thermal regulation capacity of the double-layer phase-change walls. At a Micro-PCM volume fraction of 15%, the peak temperature of the double-layer phase-change wall is reduced by 4.33 °C compared to a conventional wall, while the attenuation factor increases to 16.88. Furthermore, the mean thermal delay extends to 440 min, the temperature amplitude decreases to 1.13 °C, and the peak instantaneous heat flux is reduced to 13.24 W/m2. These findings highlight the significant latent heat storage capacity and superior thermal modulation performance of double-layer phase-change walls, offering a valuable technical reference for the design of energy-efficient building envelope systems.

Phase change material (PCM) concrete walls represent a new type of energy storage wall. It is of great significance to study the fire resistance of PCM concrete walls to ensure the safety of these kinds of components in service. For this reason, fire resistance tests on eight PCM concrete partition wall specimens under the conditions of the ISO-834 standard fire curve were carried out. The tested wall structures included a solid wall and a double-layer wall with an air gap. The PCM used was paraffin phase change microcapsules, which were replaced with a fine aggregate according to the principle of equal volumes, at replacement proportions of 0%, 7%, 10%, and 14%. The test results showed that explosive spalling of the PCM concrete occurred when the double-layer wall specimen with a 10% replacement proportion was heated for 31 min, and the other seven specimens met the integrity requirements after heating for 90 min. The 100 mm thick ordinary concrete solid partition wall specimen did not meet the thermal insulation requirements after 90 min. The addition of PCM and the use of a double-layer structure with an air gap can both improve the wall’s thermal insulation performance; however, it is not the case that, the greater the amount of PCM used, the better the thermal insulation performance of the wall. The reasons that the PCM concrete spalled in the double-layer wall specimen with a 10% replacement proportion are discussed. This study provides critical insights into optimizing the PCM content and wall design for fire-safe energy-efficient buildings, offering practical guidance for sustainable construction practices.

In order to ensure thermal comfort of the wearer, clothing directly contacting to the skin has to have good thermoregulation properties. Various types of phase change materials (PCM) are used in the production of smart materials capable actively control the temperature of the body. PCM have the capacity to absorb, store and release heat energy. Their effectiveness is characterized by quantities of absorbed/released heat energy, expressed as enthalpy. Higher is the enthalpy better thermoregulation effect is achieved. The aim of the research was to determine the dependence of PCM efficiency on the structure of double layer knitted fabrics and to evaluate their durability of finishing with microcapsules. Double layer weft knitted fabrics of four different combined patterns, manufactured from cotton/PES, PES (Coolplus®, 4 channel profile fiber) and PES spun yarns of linear density 20.0 tex, were selected for investigations. In order to increase effectiveness of thermoregulation all fabrics were equally treated with organic PCM microcapsules MikrathermicTM P by padding method. These microcapsules have functional reactive groups on the shell surface which bind to fibres and can react with cellulosic and synthetic fibers without binders. The effectiveness of PCM on knitted fabrics treated with microcapsules was investigated in the temperature range of −10−+50 °C at 10 °C/min speed in heating and cooling processes with differential scanning calorimeter (DSC) Q10. Examinations (DSC thermograms) have showed that absorbed energy (cooling effect) of all investigated knitted fabrics is higher than released energy (heating effect). It was determined that the effectiveness of incorporated PCM depends on the structure of knitted farbics. The fibre composition of fabrics has the biggest influence on the initial effectiveness of PCM. The maximum effect of PCM (approx. 7.08-5.65 J/g) was received for knitted fabrics, produced from cotton/PES, and the smallest effect–from PES spun yarns. Investigating the durability of microcapsules to washing it was determined that the PCM effectiveness of various knitted fabrics meanly decreases approx. 1.4-2.7 times after 5 washing cycles. Treatment of samples to artificial day light showed that PCM on knitted fabrics are stable in comparison with applied dyes - colour difference ΔECMC after treatment reaches 1-2.4 value.