Integration of Phase-Change Materials in Ventilated Façades: A Review Regarding Fire Safety and Future Challenges

: The increasing concerns about CO 2 emissions and climate change have pointed out the urgency of promoting sustainability in the building sector. One promising solution to enhance the energy efficiency of buildings and diminish environmental impact is the integration of phase-change materials (PCMs) into ventilated façade systems. This review article critically examines the current state of research on this innovative approach, with a particular focus on fire safety considerations. The paper explores the integration of PCM into ventilated façades, highlighting the potential for significant improvements in energy consumption, thermal comfort, and reductions in CO 2 emissions. However, the flammability of PCMs introduces substantial fire safety challenges that must be addressed to ensure the safe application of this solution. The fire safety of both ventilated façades and PCMs is approached, followed by specific fire safety concerns when PCMs are integrated into ventilated façade systems. The conclusion states that while the integration of PCMs into ventilated façades offers substantial environmental benefits, attention to fire safety is essential. This necessitates the implementation of rigorous fire protection measures during the design and construction phases. By addressing both the environmental advantages and fire safety challenges, this review aims to provide a comprehensive understanding of the potential and limitations of PCM-integrated ventilated façades, offering valuable insights for researchers, engineers, and policymakers in the field of sustainable buildings.


Introduction
The buildings sector is the most important source of carbon dioxide (CO 2 ) emissions in the European Union (EU), contributing most to total final energy consumption and greenhouse gas emissions, exerting a major impact on the environment and the sustainability of energy resources [1].In the face of rising CO 2 emissions and climate change, the European Commission proposed a revision of the Energy Performance of Buildings Directive (EPBD) in 2021, aligned with the EU's objective of climate neutrality by 2050 [2].Recently, a new version of the EPBD was launched in 2024 [3], which requires all new buildings to reach this standard by 2030, while promoting the use of solar energy and the integration of the life cycle concept of buildings to reduce emissions throughout their lifetime.
From an energy point of view, building façades are of particular importance as they play a key role in improving the energy efficiency of buildings [4].Studies have shown that it is the fundamental structure of a building, known as the building envelope, that exerts the greatest influence on its total energy consumption [5,6].An effective solution to solving these energy problems is ventilated façades [7].In addition to the energy efficiency of the construction, ventilated façades also feature an interesting architectural design [8].The energy efficiency of ventilated façades is achieved both in summer and winter, thanks to the natural convection obtained from the generated airflow [9].A ventilated façade is a "double" façade inside which there is a naturally ventilated air blade (normal or heavily ventilated).This allows the structure to "breathe".The air blade is located between the outer face of the thermal insulation layer and the inner face of the construction element (a structure that may or may not be thermally insulated, the outer face being opaque or glazed) [7].
A new technology that seems to revolutionize the field of construction involves the use of phase-change material (PCM) in construction [10].A study by Qudama Al-Yasiri conducted in 2022 highlights the benefits associated with incorporating PCM into the shell of a building in the extremely hot summer conditions of southern Iraq.Comparing two rooms-one with PCM and one without-PCM was found to bring significant benefits, including reduced indoor temperature and energy savings [11].The results indicate the advantages of PCM in the context of countries still using traditional energy sources, as well as the need for further research to improve the performance of PCM in construction.
Gonzalo Diarce et al. [12] highlight a higher thermal performance of a new type of ventilated active façade that includes a PCM in its outer layer.This innovation marks a significant advancement towards more sustainable construction solutions, particularly as ventilated façades are already known for enhancing the energy efficiency of buildings.Experimental results demonstrated that the melting and solidification processes of phasechange materials (PCMs) increased heat absorption during phase-change intervals, thereby reducing façade overheating.Computational simulations further supported this improvement in thermal performance, showing that the thermal inertia of ventilated façades with PCM surpasses that of traditional solutions evaluated in the study.The tests highlighted a façade energy efficiency of 10-12%, indicating considerable potential for reducing building energy consumption.Nonetheless, further research is required to study and optimize air circulation rates through the ventilated space to maximize the benefits of this technology for sustainable construction.
The structure of this article follows a logical progression, starting with an overview and gradually narrowing down to the main topic: the fire safety of ventilated façades with integrated PCM.It begins by introducing the concept of ventilated façades, then focuses on energy efficiency through a literature review on integrating PCM into these systems.The analysis then shifts to fire safety, first in a general context and then specifically addressing PCM.Finally, the paper integrates all previously discussed aspects regarding the fire safety of PCM-ventilated façades, proposing new research directions.
In this study, a keyword analysis was also conducted using a "word cloud" technique to highlight relevant terms and concepts associated with ventilated façades and PCM.The results presented in Figure 1 allow us to visualize and highlight words that frequently appear in the context of discussions about these technologies, as well as the relationships between them.Among the keywords that were highlighted are "ventilated facade", "PCM", "thermal energy storage", "fire safety", "double skin facade", etc.This analysis contributes to a deeper understanding of terminology and concepts associated with the topic of the article.The paper's workflow presented in Figure 2 illustrates the approach used in the article, which begins with the broader context of ventilated facades and then narrows the scope of the study to focus on the primary issue of phase change material integration for ventilated facade fire safety.
Figure 3 shows the articles studied by year of publication, between 1983 and 2024, revealing significant variations in research activity.It shows a gradual increase in publications over the years, with notable peaks in 2010, 2017, and 2018, where the number of publications reached six, ten, and fourteen, respectively.After a slight dip in 2019, there was another rise in 2020 and 2021, with nine and six publications, respectively.The trend continues with 11 publications in 2023.The chart indicates a general upward trend in the number of publications over the observed period.
More than 100 research papers, norms, and guidelines were investigated during the present study.Figure 4 shows the distribution of sources cited within this article.The bibliometric analysis identified a total of nine main sources, with the following participations.More than 100 research papers, norms, and guidelines were investigated during the present study.Figure 4 shows the distribution of sources cited within this article.The bibliometric analysis identified a total of nine main sources, with the following participations.More than 100 research papers, norms, and guidelines were investigated during the present study.Figure 4 shows the distribution of sources cited within this article.The bibliometric analysis identified a total of nine main sources, with the following participations.In the context of building safety, several notable incidents involving ventilated façades have sparked extensive discussions and reviews of safety regulations.Table 1 summarizes key examples of such fires, highlighting the impact of ventilated façades on the rapid spread of fire and the resulting consequences.The fire illustrated how a ventilated façade can facilitate the rapid spread of fire in high-rise buildings.The 32-storey building was nearly completely destroyed due to the flammable material used in its ventilated cladding.In the context of building safety, several notable incidents involving ventilated façades have sparked extensive discussions and reviews of safety regulations.Table 1 summarizes key examples of such fires, highlighting the impact of ventilated façades on the rapid spread of fire and the resulting consequences.The fire illustrated how a ventilated façade can facilitate the rapid spread of fire in high-rise buildings.The 32-storey building was nearly completely destroyed due to the flammable material used in its ventilated cladding.

The Address Downtown Fire
Dubai, UAE 2015 The New Year's Eve fire affected a 63-storey building with a ventilated façade.While there were no fatalities, the fire highlighted the risks associated with using flammable materials in tall buildings.Lacrosse Building Fire Melbourne, Australia 2014 The fire demonstrated the negative impact of flammable materials.

Ventilated Façades
The introduction of ventilated façades in building design has become a major topic of interest in construction, especially in the context of energy modernization, efficiency, and sustainability concerns.Various recent studies, such as the one conducted by Bikas et al., have highlighted the importance of ventilated façades as an intervention for the energy modernization of buildings [13].Pastori et al. addressed the assessment of the energy performance of a ventilated façade system through Computational Fluid Dynamics (CFD) modeling and a comparison with international standards [14].Ventilated façades have become increasingly important in building design, contributing to reducing summer thermal loads and, implicitly, energy consumption due to air conditioning systems.They benefit from the combined effect of reflecting solar radiation and natural or forced ventilation in the cavity of the façade.
The study developed a CFD modeling methodology to comprehensively evaluate the energy performance of a prefabricated wood and concrete ventilated façade module under various operating conditions.Numerical results, both global and local, were presented, focusing on heat flow, air velocity, and temperature within the façade cavity.The findings underscored the façade's efficiency dependence on solar radiation, the energy-saving benefits of natural convection, and the critical importance of designing an optimized façade geometry.
Mercader-Moyano et al. [15] aimed to design and analyze ventilated façade solutions based on the circular economy, with the goal of improving the energy conditions of resi-dential buildings.The results highlighted that implementing such a façade for building rehabilitation reduces energy losses through the building envelope, improves housing conditions, and decreases environmental impact.An energy consumption and CO 2 emissions analysis showed that the rehabilitated façade led to significant reductions compared to conventional methods, with energy consumption reduced by over 57% and CO 2 emissions by 51%.The study also indicated improvements in indoor environmental quality and reduced energy demand for domestic heating, contributing to overall environmental impact reduction.Additionally, the rehabilitated façade significantly reduced energy losses, with heat loss reduced by 32% and cooling losses by 18%.
However, ventilated façades face challenges such as higher initial costs and the necessity for careful design to ensure compatibility with existing building structures.
Looking forward, future research is trending towards utilizing innovative materials and advanced technologies to optimize the performance and durability of ventilated façades.There is a growing interest in integrating smart sensors for effective monitoring and control, as well as exploring eco-friendly and sustainable materials to reduce the carbon footprint of buildings.

Ventilated Façades with PCM Best-Practice Solutions
The proper design of building façades has been widely demonstrated to be a vital tool in efforts to improve the energy efficiency of buildings and reduce their ecological footprint [16][17][18].One effective method for storing thermal energy in buildings is through the use of sensible heat.This can be achieved by carefully selecting building materials with high thermal capacity.These materials absorb heat during the day and release it gradually at night, helping to maintain a consistent and comfortable indoor temperature.Additionally, integrating PCM into the building envelope is increasingly recognized as another beneficial option [19].
PCMs absorb and release heat during their phase-change process, transitioning between solid and liquid states.These materials provide enhanced thermal inertia, stabilizing indoor temperatures and reducing reliance on additional heating and cooling systems.Integrating PCMs into building envelopes can significantly enhance energy efficiency, thermal comfort, and construction durability.
The most commonly used types of encapsulations are microencapsulation and macroencapsulation, offering a wide range of shapes and sizes for the latter category [20].These techniques enable the precise and efficient distribution of PCMs within building structures, ensuring optimal performance in regulating indoor thermal conditions.
Adapting PCMs in building structures not only maximizes energy efficiency by reducing the energy consumption required for heating and cooling but also significantly contributes to reducing the carbon footprint of buildings.This represents a sustainable and cost-effective solution for enhancing residential comfort and overall building performance amidst global climate change and increasingly stringent energy efficiency requirements.
Croitoru et al. analyzed the integration of different types of phase-change materials (PCMs) into transpired solar collectors (TSCs), with a focus on improving heat transfer, including the use of nanomaterials.Thermal energy storage applied to TSCs is studied in terms of design criteria, material technologies, and impact on thermal conductivity.This review highlights the potential of integrating nanomaterial technology to enhance thermal performance.The use of nanomaterials in solar walls has the potential to significantly improve their performance.Integrating diverse materials such as graphene, graphite, metal oxides, and carbon nanoparticles can pave the way for improved thermal conductivity.
Materials with high thermal energy density, such as PCMs, have been widely used as solutions for storing large amounts of energy, thereby finding applicability in the field of solar thermal energy collection.A PCM thermal buffer can bridge the gap between solar energy availability and demand.Experimental research shows that for TSC systems, PCMs can increase the stability of the outlet air temperature and overall efficiency.[21] that tested the improvement of thermal performance in a building using a ventilated façade system with PCM placed in an air cavity.Two identical cubes in internal dimensions were constructed, one with PCM on the southern façade and one without PCM, to compare thermal efficiency.The PCM used, SP-22 from Rubitherm, with a melting point of 22 • C, was selected for storing solar energy during winters and providing nighttime cooling in summers.

Gracia et al. conducted a study
Both cubes were fully instrumented to measure interior wall temperature, indoor air temperature and humidity, the electric consumption of HVAC systems, and heat fluxes in PCM.Moreover, automations were installed to control fans and gates based on weather conditions and energy requirements.
The study explored various operational modes, including controlled fixed temperatures and free-floating temperature conditions, to evaluate the efficiency of the ventilated façade in reducing electric energy consumption and maintaining thermal comfort.Experiments were conducted under severe and mild winter conditions, demonstrating the system's ability to adapt PCM usage according to the building's heating and cooling demands.
Another study performed by Gracia et al. investigates the application of ventilated double-skin façades (VDSFs) and PCM to optimize energy efficiency in buildings, in a global context where strict regulations and efficient technologies are becoming increasingly important [22].The study highlights VDSFs as a promising solution due to their multiple benefits, including esthetic, acoustic, and thermal aspects.
The focus of this research is the integration of PCM (such as Rubitherm's SP-22) into the air cavity of the VDSF.The PCM has the ability to absorb and release heat according to temperature variations, significantly contributing to the reduction in energy consumption in buildings.In the cold season, the PCM absorbs solar heat to reduce the need for heating, while in the warm season, it solidifies at night to provide cooling during the day.
This study features an experimental component conducted in Puigverd de Lleida, Spain, where notable energy savings were achieved, particularly by reducing the electrical consumption of HVAC systems during the cold season.Additionally, a comprehensive numerical model was developed to simulate and optimize the thermal performance of the system under various global climate conditions, demonstrating the solution's adaptability across different building types and climates.
Thus, incorporating PCM in VDSFs emerges as an effective strategy for enhancing building sustainability, offering substantial energy savings and environmental benefits.The article underscores the importance of adopting tailored solutions to local climatic conditions and advocating for sustainable practices in the design and operation of modern buildings.
Curpek et al. conducted a study presenting a dynamic thermal model using the De-signBuilder simulation software platform v4.5 for a simple office building model equipped with an integrated ventilated photovoltaic (PV) façade/solar collector system in the climatic conditions of Bratislava, Slovakia [23].Thermodynamic simulations were used to evaluate the annual thermal performance of a ventilated PV façade combined with phase-change material (PCM).The study utilized simplified approaches to capture the system's critical aspects.The simulation results indicated that the natural ventilation of the PV façade, when integrated with PCM, could lower PV panel temperatures by over 20 • C on extreme days and delay peak temperature times by more than 5 h.
A study by Gracia et al. investigates the comparison of control strategies for a ventilated façade with PCM, focusing on energy savings, cost reduction, and lowering CO 2 emissions by decreasing energy demand for heating and cooling.These strategies enable maximum load transfer and the better integration of renewable energies in the sector [24].The high initial investment costs necessitate effective control to maximize energy benefits during operation.In this context, artificial intelligence techniques have proven effective in controlling active thermal energy storage units.The study employs a validated numerical tool to investigate the impact of various control strategies on the performance of a thermal energy storage (TES) system applied to the construction sector, specifically a PCM-ventilated façade utilizing free cooling.Three distinct strategies were developed to optimize cost savings, energy reduction, and CO 2 reduction across different climatic conditions.The results demonstrate robust benefits across all strategies tested, achieving average savings of 4.3%, 7.8%, and 16.7% compared to manual system operation.Furthermore, the study reveals that prioritizing cost optimization may compromise the energy and CO 2 reduction benefits typically associated with TES systems.
Another study by J. Curpeket et al. investigated the impact of integrating PCM into photovoltaic ventilated façades (BiPV) to enhance energy efficiency and thermal performance under real operating conditions [25].By incorporating PCM into the outer layer of the façade, the researchers aimed to mitigate overheating and improve temperature management in buildings.The PCM acts as a heat storage medium, absorbing excess heat from solar radiation and releasing it during cooler periods, such as at night or during high-temperature conditions.
The study shows that incorporating phase-change materials (PCMs) into BiPV ventilated façades offers substantial benefits for building energy efficiency and thermal comfort.This innovative technology effectively lowers the operating temperature of photovoltaic modules, efficiently stores heat within the integrated PCM, and maximizes solar energy utilization.Consequently, integrating PCM into BiPV ventilated façades presents a viable solution to optimize building energy performance, reduce reliance on active cooling, and enhance sustainability and thermal comfort.
A study by Bejan et al. demonstrates that integrating PCMs into solar collectors represents an innovative approach that can significantly enhance the efficiency and operational duration of these systems [26].Implementing organic PCM RT35 (paraffin) in a full-scale solar collector resulted in an 8.8% increase in maximum temperature and a 10.6% improvement in the coefficient of performance.Moreover, the useful operational time was extended by 110%, providing approximately 8 additional hours of efficient operation.These findings underscore the substantial potential of PCM in enhancing the energy performance of solar collectors, making them more effective and efficient solutions for heating fresh air in buildings.
Table 2 summarizes key research on the use of phase-change materials (PCMs) in ventilated façades.It highlights the type of façade and PCM used, the main findings, and the references.These studies demonstrate how PCMs can enhance energy efficiency and thermal comfort by managing heat storage and release, thus reducing heating and cooling needs in buildings.From this table, it is evident that there is a lack of research on the fire safety of these systems, indicating a need for further investigation in this area.Future research directions should focus on developing enhanced PCMs and intelligent control technologies to optimize the performance and durability of PCM-ventilated façades.This effort aims to make them more accessible and easier to integrate into building designs.

Fire Safety of Ventilated Façades
In the scientific community, the exploration of fire safety concerning ventilated façades remains insufficient, highlighting the critical need for developing and implementing additional fire safety measures for these façade systems.
In 2015, United Nations member states adopted the 2030 Agenda for Sustainable Development, outlining an action plan for global peace and prosperity.Central to this agenda are the 17 Sustainable Development Goals (SDGs), which urgently call for action from both developed and developing nations.Goal 11 specifically aims to create safe and sustainable cities and human settlements [27].
The façades of high-rise buildings pose significant fire risks, including rapid fire and smoke propagation and challenges in intervention and rescue operations, ensuring safe occupant evacuation, and prolonged fire duration.The increasing use of combustible materials in façade construction further exacerbates these concerns [28][29][30][31].
Recent trends show a shift in façade system configurations from simple to complex designs to meet diverse needs such as weather protection, insulation, and the esthetic enhancement of buildings.However, this evolution towards thinner, lighter, and more energy-efficient systems has also heightened the potential fire risk [32][33][34][35].
The study by Ankit Sharma et al. [36] underscores the significance of advanced technologies, particularly artificial intelligence (AI), in mitigating the risks associated with façade fires in high-rise buildings.AI solutions offer notable advantages in enhancing the speed and effectiveness of fire detection and response.
AI systems leverage data from various sensors and cameras installed within buildings, including information on local temperature, smoke presence, air movement patterns, and other indicators of fire.This real-time data analysis enables AI to swiftly pinpoint the location and severity of a fire outbreak.
Once a fire is detected, AI systems can provide actionable recommendations and support to human operators.They can autonomously trigger firefighting systems or alert firefighters to the precise location and severity of the fire, expediting response times and potentially minimizing damage and risk to occupants.
While the IFD guide [37] does not delve deeply into fire safety specifics, it relies on DIN 18516-1 [38] to offer precise directives and regulations for the design and installation of ventilated façades.
From a regulatory standpoint in Europe, the German standard [37] is pivotal in addressing fire safety measures for ventilated façades.This standard is widely recognized across Europe and referenced as a key resource for ensuring fire safety aspects.
Therefore, DIN 18516-1 serves as a critical framework for ensuring compliance with fire safety practices in the construction and design of ventilated façades throughout Europe.

Fire Safety of Phase-Change Materials
PCMs have become increasingly prominent across various industries, including latent thermal energy storage (LTES) systems, thermal management (TM), construction, aerospace, textiles, and others [39].These materials offer significant benefits due to their ability to store and release thermal energy during phase transitions, typically between solid and liquid states (melting and crystallization).
Over 500 distinct PCMs have been discovered and developed, each possessing unique characteristics and applications [40].These materials vary in chemical composition, operational temperature ranges, energy storage capacities, and other essential properties.
In the realm of building construction, PCMs are recognized for their effectiveness in reducing energy consumption for heating and cooling purposes [41,42].They function by storing latent heat during phase transitions, such as melting and crystallization, which occurs isothermally (at a constant temperature) [41].
PCMs significantly enhance thermal properties like thermal mass, specific thermal capacity, and thermal inertia.They have the capability to absorb and release substantial amounts of thermal energy during phase changes, thereby improving the energy efficiency and thermal performance of buildings.
Figure 5 illustrates the process of phase changes in PCMs, highlighting their critical role in managing thermal energy within building environments.R REVIEW 10 of 17 PCMs used in construction primarily undergo phase changes between the liquid and solid states and vice versa.These PCMs are broadly categorized into organic, inorganic, and eutectic types based on their chemical composition [43][44][45][46][47].Each category offers distinct properties suitable for various applications, as depicted in the figure above.
Historically, PCMs are classified into three generations [48].First-generation PCMs include salts and salt hydrates, second-generation PCMs encompass fa y acids and paraffins, while third-generation PCMs consist of polymeric PCMs and special metals [49].
In building construction, integrating PCMs into walls has become a common practice to enhance the heat storage capability of the building envelope.This integration significantly improves thermal comfort and energy efficiency by increasing the building's heat storage capacity [50][51][52].
PCMs store latent heat and undergo isothermal phase transitions between the liquid and solid states, such as crystallization and melting [53,54].Paraffins, according to a study by B.P. Jelle and S.E.Kalnaes, are widely used in various applications due to their superior properties and numerous advantages [55].Paraffins are high-molecular-weight hydrocarbons with a waxy consistency at room temperature, categorized into even-chain (n-paraffin) and odd-chain (iso-paraffin) subgroups.Their melting points range between 6 and 80 degrees Celsius, depending on the number of carbon atoms in their structure.
The latent heat of paraffins is mass-based, meaning there is no phase separation after the solid-liquid transition [56].Paraffins also exhibit low pressure and thermal conductivity [57], which is advantageous in certain applications as it reduces the risk of structural deformation or degradation when PCMs are incorporated.
While PCMs are effective for energy reduction in heating and cooling applications in buildings [32,33], their potential flammability remains a concern, limiting their widespread use across multiple sectors.However, studies have demonstrated that adding flame retardants can enhance the fire safety properties of PCMs, thereby mitigating their flammability and improving building fire protection [34,35].Alterations in PCM composition, such as incorporating flame retardants or hardeners, are viable strategies to enhance flame resistance and reduce the risk of PCMs igniting, as detailed in Table 3. PCMs used in construction primarily undergo phase changes between the liquid and solid states and vice versa.These PCMs are broadly categorized into organic, inorganic, and eutectic types based on their chemical composition [43][44][45][46][47].Each category offers distinct properties suitable for various applications, as depicted in the figure above.
Historically, PCMs are classified into three generations [48].First-generation PCMs include salts and salt hydrates, second-generation PCMs encompass fatty acids and paraffins, while third-generation PCMs consist of polymeric PCMs and special metals [49].
In building construction, integrating PCMs into walls has become a common practice to enhance the heat storage capability of the building envelope.This integration significantly improves thermal comfort and energy efficiency by increasing the building's heat storage capacity [50][51][52].
PCMs store latent heat and undergo isothermal phase transitions between the liquid and solid states, such as crystallization and melting [53,54].Paraffins, according to a study by B.P. Jelle and S.E.Kalnaes, are widely used in various applications due to their superior properties and numerous advantages [55].Paraffins are high-molecular-weight hydrocarbons with a waxy consistency at room temperature, categorized into even-chain (n-paraffin) and odd-chain (iso-paraffin) subgroups.Their melting points range between 6 and 80 degrees Celsius, depending on the number of carbon atoms in their structure.
The latent heat of paraffins is mass-based, meaning there is no phase separation after the solid-liquid transition [56].Paraffins also exhibit low pressure and thermal conductivity [57], which is advantageous in certain applications as it reduces the risk of structural deformation or degradation when PCMs are incorporated.
While PCMs are effective for energy reduction in heating and cooling applications in buildings [32,33], their potential flammability remains a concern, limiting their widespread use across multiple sectors.However, studies have demonstrated that adding flame retardants can enhance the fire safety properties of PCMs, thereby mitigating their flammability and improving building fire protection [34,35].Alterations in PCM composition, such as incorporating flame retardants or hardeners, are viable strategies to enhance flame resistance and reduce the risk of PCMs igniting, as detailed in Table 3.

Fire Safety of Ventilated Façades with PCM
PCMs are increasingly utilized across various fields, including their integration into ventilated façades.However, the perspective on fire safety concerning ventilated façades incorporating PCMs remains inadequately outlined, presenting a significant research challenge.Emphasizing fire safety concerns associated with PCMs in ventilated façades is paramount.
While PCMs offer substantial benefits in terms of enhancing energy efficiency and thermal comfort in buildings, it is critical to ensure that their deployment does not compromise occupant safety or structural integrity in fire scenarios.All materials used must conform to international standards that restrict fire spread [85].
Addressing these challenges necessitates extensive research and testing to evaluate the behavior of PCMs under fire conditions and to identify effective fire protection measures [86][87][88].Furthermore, there is a need to develop and refine regulations governing the use of PCMs in construction, striking a balance between energy performance and fire safety.These efforts should be supported by collaborative endeavors among researchers, industry stakeholders, regulators, and construction professionals.
A crucial initial step towards achieving these objectives involves constructing a model of a PCM-ventilated façade and subjecting it to controlled combustion to examine its fire reaction performance.For assessing the reaction to fire performance of ventilated façades integrating PCMs, it is essential to consider the aspects outlined in Figure 6 [89].3. Fire Safety of Ventilated Façades with PCM PCMs are increasingly utilized across various fields, including their integration into ventilated façades.However, the perspective on fire safety concerning ventilated façades incorporating PCMs remains inadequately outlined, presenting a significant research challenge.Emphasizing fire safety concerns associated with PCMs in ventilated façades is paramount.
While PCMs offer substantial benefits in terms of enhancing energy efficiency and thermal comfort in buildings, it is critical to ensure that their deployment does not compromise occupant safety or structural integrity in fire scenarios.All materials used must conform to international standards that restrict fire spread [85].
Addressing these challenges necessitates extensive research and testing to evaluate the behavior of PCMs under fire conditions and to identify effective fire protection measures [86][87][88].Furthermore, there is a need to develop and refine regulations governing the use of PCMs in construction, striking a balance between energy performance and fire safety.These efforts should be supported by collaborative endeavors among researchers, industry stakeholders, regulators, and construction professionals.
A crucial initial step towards achieving these objectives involves constructing a model of a PCM-ventilated façade and subjecting it to controlled combustion to examine its fire reaction performance.For assessing the reaction to fire performance of ventilated façades integrating PCMs, it is essential to consider the aspects outlined in Figure 6 [89].A very important aspect to keep in mind is that not all PCMs raise the issue of fire safety [90].The figure below shows in descending order the five PCMs that are flammable and have a high rate of heat release.
Table 4 comes as an extension of Figure 7 and, using the bibliographic references,  A very important aspect to keep in mind is that not all PCMs raise the issue of fire safety [90].The figure below shows in descending order the five PCMs that are flammable and have a high rate of heat release.
Table 4 comes as an extension of Figure 7 and, using the bibliographic references, highlights the characteristics of PCMs according to their level of fire safety.Studies and research in this area help us identify and understand more deeply the behavior of PCMs in fire conditions, which can help reduce the risk associated with them.Studies and research in this area help us identify and understand more deeply the behavior of PCMs in fire conditions, which can help reduce the risk associated with them.By investigating material properties and developing appropriate fire protection technologies, we can promote the safe use of PCMs in construction, thereby contributing to a safer and more sustainable built environment.
The main problems identified are reflected in Table 5-a self-assessment of the proposed problems and solutions.
The percentage analyses presented in Table 5 reflect a subjective evaluation of the issues associated with integrating PCMs into façade systems.They indicate several major concerns in the field, emphasizing the need to address legislative gaps, such as the absence of PCMs in fire safety regulations.Additionally, they highlight the importance of implementing standardized tests to assess PCM behavior in fire situations and the need to develop integrated design solutions, including fire barriers and flame-retardant materials.Another identified issue is the low level of awareness among stakeholders regarding the benefits and risks of PCM-integrated façade systems.Moreover, there is concern about the high initial costs associated with PCM integration in façade systems, requiring cost-benefit analyses and the development of more economical processes and materials.
These analyses provide a useful perspective for guiding future research and for formulating policies and strategies to facilitate the efficient and safe implementation of PCMs in construction while addressing the practical challenges identified.

Conclusions
This review article critically examines the integration of PCMs into ventilated façade systems, emphasizing their potential to enhance energy efficiency, improve thermal comfort, and reduce CO 2 emissions in buildings.PCMs achieve these benefits by leveraging their latent heat storage capabilities, which stabilize indoor temperatures and reduce the reliance on active heating and cooling systems.However, the integration of PCMs into ventilated façades also introduces significant challenges related to fire safety.
The flammability of many PCMs poses a notable risk that must be effectively addressed to ensure their safe application in building construction.Organic PCMs like paraffin wax and fatty acids are particularly flammable, whereas inorganic PCMs such as salt hydrates exhibit lower flammability risks.Mitigating these fire risks requires the incorporation of flame retardants and the development of non-combustible PCM alternatives.
To increase safety, updated fire safety regulations specific to PCM use in building façades are necessary.Integrated design solutions that include fire barriers and flameretardant materials are essential for ensuring the safety and efficacy of PCM-integrated systems.Future research directions should focus on developing PCMs with enhanced fire-resistant properties, exploring new compositions like inorganic and hybrid PCMs that balance thermal performance with reduced fire risks.
Furthermore, standardized fire safety tests tailored to PCM-integrated façade systems are needed.Experimental research and simulations should aim to deepen the understanding of PCM behavior under fire conditions and establish robust safety protocols.Comprehensive design strategies that integrate PCMs with advanced fire protection systems, such as smart sensors and real-time monitoring technologies, are crucial for enhancing safety measures.Additionally, conducting cost-benefit analyses of PCM integration in building façades will facilitate informed decision-making and promote wider adoption.Research into manufacturing processes and materials that reduce costs while maintaining performance and safety standards is also essential.
Increasing stakeholder awareness about both the benefits and risks associated with PCM-integrated façade systems is critical.Effective communication strategies can play a key role in disseminating knowledge and encouraging the adoption of safe and sustainable building technologies across the industry.

FireFigure 1 .
Figure 1.Keyword cloud for the references considered in the present review article.

Figure 3
Figure 3 shows the articles studied by year of publication, between 1983 and 2024, revealing significant variations in research activity.It shows a gradual increase in publications over the years, with notable peaks in 2010, 2017, and 2018, where the number of publications reached six, ten, and fourteen, respectively.After a slight dip in 2019, there was another rise in 2020 and 2021, with nine and six publications, respectively.The trend continues with 11 publications in 2023.The chart indicates a general upward trend in the number of publications over the observed period.

Figure 1 .
Figure 1.Keyword cloud for the references considered in the present review article.

Fire 2024, 7 , 17 Figure 1 .
Figure 1.Keyword cloud for the references considered in the present review article.

Figure 3
Figure 3 shows the articles studied by year of publication, between 1983 and 2024, revealing significant variations in research activity.It shows a gradual increase in publications over the years, with notable peaks in 2010, 2017, and 2018, where the number of publications reached six, ten, and fourteen, respectively.After a slight dip in 2019, there was another rise in 2020 and 2021, with nine and six publications, respectively.The trend continues with 11 publications in 2023.The chart indicates a general upward trend in the number of publications over the observed period.

Figure 3 .
Figure 3. Articles studied by year of publication.

Figure 3 .
Figure 3. Articles studied by year of publication.

Figure 4 .
Figure 4. Documents studied according to the cited source.

Figure 4 .
Figure 4. Documents studied according to the cited source.

Figure 7 .
Figure 7.The riskiest PCMs from the point of view of fire safety.

Figure 7 .
Figure 7.The riskiest PCMs from the point of view of fire safety.

Table 3 .
The main methods for reducing the flammability of PCM.

Table 5 .
Design and testing of secure façade systems that integrate PCMs efficiently and securely in legislation (%).