Passive Cooling with Phase Change Materials for Sustainable Buildings: Review

Explore the review of passive cooling with phase change materials for sustainable buildings. This comprehensive literature review examines how phase change materials enhance energy efficiency, reduce environmental impact, and improve indoor comfort by utilizing natural cooling processes. It highlights current research, applications, and future prospects, providing valuable insights into sustainable architecture practices.

Highlights

• PCM technology conserves energy, stabilizes temperatures, enhances solar control, and reduces consumption by 14–90%.
• Windows incorporating PCM panels can lower heat transfer by up to 66% and decrease solar gain.
• Combining PCMs with nocturnal radiative cooling reduces surface temperatures by more than 13° Celsius.
• Solar-powered desiccant air conditioning systems with PCM achieve an average of 75% energy savings and a 60–90% reduction in peak load.
• Surfaces infused with PCM cut energy usage by 20%-66%, providing adaptive thermal regulation in various climates.

Abstract

Boston Brand Media brings you the interesting news - Phase Change Materials (PCMs) represent a groundbreaking technology with significant potential to enhance sustainable and energy-efficient cooling in buildings. These materials store and release latent heat during phase transitions, facilitating thermal energy storage and temperature regulation. This extensive literature review examines various strategies for implementing passive cooling with PCMs in buildings. PCMs improve multiple passive cooling methods, including solar control, ground cooling, ventilation-based heat dissipation, radiative cooling, and thermal mass-based heat modulation. The review covers PCM classifications, encapsulation techniques, melting enthalpies, integration into building envelopes, and performance across different climates.

Findings indicate that PCM walls can delay heat transfer by 2 hours and mitigate external temperature fluctuations. Windows with PCM panels reduce heat transfer by 66%. Combining PCMs with nocturnal radiative cooling results in interior surface temperature reductions exceeding 13°C. Natural ventilation with PCMs can achieve energy savings of up to 90% in hot climates. The combination of free cooling and PCM thermal storage reduces charging times by 35% and enhances heat transfer. Simulations suggest that strategic placement of PCMs in lightweight building walls can reduce heat flux and overall energy consumption. Despite challenges related to scalability, compatibility, reliability, and recycling, PCM solutions hold significant promise. Thoughtful integration of PCMs into building design can substantially improve thermal performance and energy efficiency. Experimental validations confirm energy reductions ranging from 14% to 90%, demonstrating the versatility of passive cooling techniques using PCM thermal storage and heat transfer capabilities across various climates.

1. Introduction

Over the past three decades, global energy consumption for space cooling has more than tripled since 1990. This surge impacts not only electricity grids but also greenhouse gas emissions and urban heat islands. Recent temperature records underscore the urgency of addressing this trend. Inadequate access to indoor cooling increases the risk of heat stress, affecting thermal comfort, productivity, and health.

Addressing cooling needs sustainably is crucial. The Net Zero Emissions by 2050 initiative outlines three key goals for 2030: 1) "Build better" through policy support, targeting 20% of existing building floor area globally and ensuring all new constructions are zero-carbon-ready, emphasizing passive cooling solutions. 2) Advocate for moderating air-conditioning set points to 24–25°C. 3) Improve efficiency, aiming for the highest efficiency rating for new air-conditioning equipment by 2035.

Heating and cooling in buildings constitute a major portion of energy consumption, challenging sustainability. The 2022 International Energy Agency (IEA) report shows building energy demand reached 133 exajoules (EJ) in 2022. A crucial transition toward sustainable energy practices is depicted in the Net Zero Scenario, highlighting the progress toward net-zero emissions by 2030.

To address the trajectory of increasing energy usage and its environmental consequences, implementing stricter building codes, retrofitting existing structures, and investing in passive solutions and energy-efficient technologies are essential.

These measures aim to meet the growing demand for thermal comfort while minimizing environmental impacts. Passive cooling methods are promising alternatives to traditional energy-intensive cooling systems, using natural elements and strategic design principles to regulate indoor temperatures effectively.

Figure 2 categorizes various passive ideas for heating and cooling, detailing different techniques. By sharing data on these passive cooling methods, their potential to revolutionize building energy use is highlighted, promoting a shift towards more sustainable and resilient built environments.

2. Passive cooling concepts

Passive cooling principles are essential to sustainable building design, leveraging natural mechanisms to maintain thermal comfort while minimizing energy use. In convective cooling, air acts as the cooling medium, using various forms of natural ventilation to remove excess heat from buildings. This process harnesses the buoyancy effect or natural wind speed, exemplified by techniques like solar walls, solar chimneys, and cross ventilation. Maintaining good indoor air quality is crucial for occupant well-being, and ventilation is key to removing pollutants like CO2. However, balancing ventilation and thermal comfort can be challenging, as traditional methods might reduce heat and increase the need for heating. Mechanical ventilation with heat recovery can function independently for a single room, but centralized systems require integration with existing air-handling units.

Natural ventilation stands out as a primary passive cooling strategy, facilitating air movement through building openings to enhance indoor air quality and reduce dependence on mechanical cooling systems. Another method, night ventilation (NV), utilizes cooler nighttime temperatures to dissipate accumulated heat, promoting energy efficiency. Additional strategies include shading techniques like overhangs and vegetation, which reduce solar heat gain and help regulate internal temperatures. Similarly, thermal mass materials, such as concrete or stone, absorb and gradually release heat, fostering a stable indoor environment.

2.1. Passive cooling classification

The classification of various passive cooling strategies for heating and cooling is documented in Fig. 2. These strategies can be broadly categorized into five classes, each with distinct approaches to optimize indoor climate control.

1. Solar Control Strategies: These focus on managing solar radiation through building orientation, shading devices, wall/window design, and climate considerations.
2. Passive Desiccant Systems: These use desiccant materials to naturally control humidity levels, enhancing comfort without relying on energy-intensive systems.
3. Heat Dissipation: This involves natural methods for removing heat to create comfortable indoor environments while reducing energy consumption. Techniques include passive ventilation systems, evaporative cooling, and convective cooling.
4. Mechanical Ventilation Systems: Complementary methods like nocturnal ventilation and radiative cooling support these natural processes.
5. Heat Modulation: Encompassing free cooling and thermal mass techniques, free cooling utilizes natural processes like cross-ventilation, while thermal mass focuses on storing and releasing heat using PCMs in windows, roofs, ceilings, and wallboards.

2.2. PCMs classification

PCMs exhibit a variety of features and can be classified from four primary viewpoints: chemical composition, temperature range, microstructure, and application, as shown in Fig. 3. PCMs are broadly classified into two main groups based on their chemical composition: organic and inorganic.

1. Chemical Composition:some text
   • Organic PCMs: Derived from carbon-based compounds, including paraffins, fatty acids, esters, and bio-based materials, known for their high latent heat storage capacity. They are widely used in building materials and textiles.
   • Inorganic PCMs: Made of non-carbon-based substances like salts and metals, characterized by high thermal conductivity. They are commonly used in electronics cooling and solar energy storage.
2. Temperature Range:some text
   • Low-Temperature PCMs: Operate below room temperature, typically used for domestic and commercial refrigeration.
   • Medium-Low Temperature PCMs: Suitable for typical room conditions, applied in heating and cooling buildings.
   • Medium-Temperature PCMs: Used for solar-based heating, hot water, and electronic applications.
   • High-Temperature PCMs: Designed for applications above room temperature, such as absorption cooling, waste heat recovery, and electricity generation.
3. Microstructure:some text
   • Microencapsulated PCMs: Small particles enclosed within a thin shell, enhancing dispersibility and integration into various materials.
   • Macro-encapsulated PCMs: Larger containers offering controlled release properties for specific applications requiring more controlled heat exchange.
4. Application:some text
   • Building Materials: Integrated into diverse applications, including insulation, windows, wall, and roofing systems, to optimize indoor comfort and reduce reliance on active heating and cooling systems.

The relationship between PCM melting enthalpy and temperature is illustrated in Fig. 4 for different PCM groups. Organic PCMs typically have lower melting enthalpies at moderate temperatures, making them efficient for energy absorption and release. Inorganic PCMs display higher melting enthalpies at elevated temperatures, suitable for significant heat storage applications. Eutectic mixtures combine elements from both categories, offering versatility across a broad spectrum of thermal conditions.

2.2.1. Temperatures

PCMs can be classified into four temperature ranges based on their melting points, with specific focus given to working temperature ranges. This review addresses four working temperature intervals:

1. Low Temperature Range: −35 °C to +5 °C, used in refrigeration.
2. Medium Low Temperature Range: +5 °C to +40 °C, common in building heating and cooling.
3. Medium Temperature Range: +40 °C to +80 °C, for solar heating and electronic applications.
4. High Temperature Range: +80 °C to +300 °C, for absorption cooling and waste heat recovery.

2.2.2. Microstructure

Encapsulation is crucial for PCM thermal storage systems, involving two primary methods: macro-encapsulation and microencapsulation.

• Macro-encapsulation: Enclosing PCM in large containers, suitable for diverse shapes and sizes, commonly used in exterior walls and precast slabs.
• Microencapsulation: Enclosing small PCM particles in a thin shell, enhancing heat transfer and preventing leakage, though more costly.

2.2.3. Chemical composition

The selection of PCMs for building applications depends on parameters like melting point, latent heat, and thermal conductivity.

• Melting Point: Defines the temperature at which PCM changes phase, critical for activation within desired temperature ranges.
• Latent Heat: Indicates energy storage capacity, higher values enhance temperature regulation.
• Thermal Conductivity: Facilitates efficient heat transfer, crucial for quick response times and overall performance.

PCMs with phase change temperatures between 18 and 30 degrees Celsius, aligning with thermal comfort requirements for different seasons as defined by ASHRAE. This classification ensures PCMs maintain optimal indoor conditions, contributing to sustainable and energy-efficient building designs.

2.2.4. Application

Phase Change Materials (PCMs) are substances with a high heat of fusion, capable of storing and releasing large amounts of energy. This makes them useful across various applications, including electronics, textiles, energy storage, and buildings. The application of PCMs in the building industry will be comprehensively reviewed in the following sections.

2.2.4.1. Electronics

Maintaining the operational temperatures of electronic components within specified limits is crucial globally. Research has utilized a one-dimensional thermal model to optimize advanced packages through phase change cooling, which alleviates thermal transient effects in high-power electronic packages. To address the challenge of poor thermal conductivity during PCM phase changes, Thermal Conductivity Enhancers (TCEs) like internal fins, metal networks, PCM-based heat sinks, and nanoparticles are incorporated. Studies on heat sink geometry have identified optimal volume fractions for enhanced thermal performance. The use of multiple PCMs in thermal energy storage systems improves thermal efficiency by reducing exergy loss and enhancing overall performance. Experimental studies reveal extended thermal regulation periods and lower temperatures when various PCM arrangements are used in heat sinks.

2.2.4.2. Textiles

PCMs enhance thermo-regulation in textiles by absorbing, storing, and releasing heat. When temperatures drop, the stored heat is released as the PCM solidifies, regulating temperature and maintaining thermal comfort. PCMs in textiles are applicable in clothing, technical textiles, and interior textiles. Since the 1980s, NASA and textile companies have developed thermo-regulated garments using PCM technology to control temperature changes in harsh environments. PCMs can reduce excess heat and sweating during physical activity or in hot conditions. Techniques for incorporating PCMs into textiles include filling hollow fibers, adding during spinning, and coating or laminating fabrics. Each method has trade-offs between thermal performance, weight, and durability. PCM textiles hold promise for temperature regulation in protective clothing, bedding, and medical products, with ongoing research focused on improving encapsulation and heat transfer.

2.2.4.3. Energy Storage

PCM thermal energy storage (TES) enhances the viability of solar technology, especially in low or no insolation conditions. Key applications of PCM TES include solar water heaters, cookers, air heaters, and greenhouses. In solar water heaters, PCM layers beneath tanks absorb heat from water during daylight hours through latent heat storage, although poor heat transfer between the PCM and water can limit effectiveness. Solar cookers use PCM TES to capture and store solar energy for evening cooking. Solar agricultural greenhouses use encapsulated PCMs for daytime heat storage and nocturnal heat release, regulating temperatures to improve plant quality. PCM TES is also increasingly integrated into solar thermal power plants to balance energy supply and demand fluctuations, and in home heating applications to store heat during off-peak hours for daytime space heating. Despite challenges related to durability and cost-performance ratios, PCM TES offers significant sustainability benefits through more intelligent use of solar energy.

3. Incorporation of PCMs into Building Envelopes

Integrating PCMs into building applications focuses on enhancing human thermal comfort and analyzing temperature variations on building envelope surfaces. Aligned with the European Union's goal of reducing primary resource consumption by 80% by 2050, the Holistic Energy and Architectural Retrofit Toolkit (HEART) aims to create nearly zero-energy buildings. The HEART toolkit envisions smart buildings that integrate electric, thermal, and information flows, requiring a transition to intelligent management systems and energy-efficient technologies. Key components of the HEART project include a Decision Support System, prefabricated insulation, universal Photovoltaic (PV) tiles, power controllers, heat pumps, storage units, battery packs, and smart fan coils. Buildings account for 40% of the European Union's total energy consumption, making effective renewable energy harnessing imperative. Integrating PCMs into thermal storage systems aims to enhance energy efficiency and sustainability in building applications.

3.1. Solar Control Techniques

Integrating PCMs into passive cooling techniques redefines solar control. PCMs, known for their latent heat absorption and release, add dynamism to passive cooling. Incorporated into building elements like walls and windows, PCMs act as thermal batteries, absorbing excess heat during high solar exposure and releasing it when temperatures drop. This approach enhances overall thermal performance, offering efficient temperature regulation without heavy reliance on active cooling. PCMs are a cutting-edge solution for sustainable and innovative solar control in building design.

3.1.1. Climate

The use of passive PCM cooling in various climates has been examined using the Köppen-Geiger climate classification system, based on temperature, rainfall, and other characteristics. Several studies show the effectiveness of PCMs in different climates:

• Equatorial Singapore: Exterior PCMs reduce annual heat gain by 21–32%.
• Warm Temperate Lleida, Spain: PCMs mitigate temperature swings, resulting in a 15% energy drop and 1–1.5 kg/year/m² CO2 reduction in summer.
• Snowy Beijing: Shape-stabilized PCMs reduce daily maximum temperatures by 2°C.
• Mediterranean Egypt: PCM ceiling panels reduce indoor temperatures by 7°C and cooling energy by 14%.
• Rome and Abu Dhabi: Effective passive cooling in roofing with PCM at temperatures of 25–31°C.
• Semi-arid and arid Vicuña and Calama: Enhanced PV power generation (5.8% and 4.5%, respectively) with a 40mm layer of CaCl2–6H2O.

3.1.2. Building Orientation

Strategic building orientation is crucial in maximizing solar gains during winter while mitigating excess heat in summer, which is a cornerstone of energy-efficient passive design. Integrating PCMs into selectively oriented building envelopes and walls enhances solar control and thermal regulation capabilities. Ideally, buildings should have their longest facades facing south for consistent solar exposure, minimizing extensive east or west-facing walls that are prone to excessive summer sun. Overhangs and shading devices can further minimize high-angle summer sunlight. Enhancing south walls with PCM insulation layers, panels, or modules allows for the absorption of intense solar gains during the day through latent heat storage as the PCM melts. The stored heat is then released slowly as ambient temperatures cool, creating a thermal buffering effect that maximizes winter solar gain benefits while curbing overheating risks in summer. Strategically placing PCM layers in east, west, or roof assemblies helps manage solar loads based on orientation. Varying PCM melting points and positioning PCMs internally or externally allow for tuning thermal inertia, leading to improved occupant comfort and energy efficiency. In cooling-dominated climates, an elongated east-west axis is preferred to minimize east and west solar exposure. External shading projections and high-performance glazing should be optimized to meet codes. PCM integration remains beneficial for additional solar control. Key findings from various studies focusing on the impact of PCMs on building orientations for ideal solar gain.

3.1.3. Shading Devices

Shading devices, such as overhangs and louvers, play a crucial role in reducing the need for artificial lighting and internal heat generation. Emphasizing passive shading instruments enhances energy efficiency, highlighting their role in sustainable architectural design through various shading methods. Implementing different shading strategies, including passive, active, and hybrid shading, maximizes energy conservation and supports passive cooling in buildings.

key studies analyzing the energy and comfort improvements from integrating PCMs into different shading systems. Shading devices with PCMs demonstrate substantial benefits, including a 5% reduction in cooling load and an 8% increase in savings due to variations in angles and length. The application of PCMs to shading systems results in a 44% decrease in cooling energy consumption and a 34% improvement in comfortable hours. Combined with other strategies, such as insulation and PV panels, these findings underscore the potential of PCM-enhanced shading devices in achieving significant energy savings and enhancing building performance. These studies verify the promising potential for PCM-enhanced shading devices as a passive cooling technique, meriting further real-world testing and optimization.

3.1.4. Wall Construction

The integration of Phase Change Materials (PCMs) in wall construction has become a promising approach for effectively managing excess solar heat gains and enhancing energy efficiency in buildings. The PCM-Enhanced Wall System, explored through theoretical modeling and energy demand analysis, investigates the relationship between energy savings and factors such as optimal melting points and ventilation strategies. Double Skin Façades (DSF) are prominent, with mathematical modeling and simulations in temperate continental climates highlighting their potential. Key configurations such as dual-PCM melting temperatures, thicknesses, and multistep placements are emphasized for optimal performance.

Cavity walls, essential components in building envelopes, play a crucial role in reducing energy loss. Parametric studies and numerical models demonstrate the importance of PCM layer locations within the cavity, identifying optimal thicknesses and phase transition temperatures for efficient space cooling. This comprehensive examination,  delves into cooperative initiatives aimed at advancing sustainable and energy-efficient building methods.

Key findings include:

• PCM-Enhanced Wall Systems: Theoretical modeling and energy demand analysis show that optimal melting points and ventilation strategies significantly influence energy savings.
• Double Skin Façades (DSF): Simulations underscore the importance of configurations like dual-PCM melting temperatures, thicknesses, and multistep placements in temperate climates.
• Cavity Walls: Studies identify optimal PCM layer locations, thicknesses, and phase transition temperatures to maximize space cooling efficiency.

This thorough review illustrates the collaborative efforts to promote sustainable and energy-efficient construction practices, demonstrating the potential of PCMs in wall construction to enhance building performance and reduce energy consumption.

3.1.5. Windows

Windows significantly influence a building's heating and cooling load, despite advancements in coatings, sealed glazing, and tight gaskets. The ventilated window (VW) concept aims to regulate outdoor airflow through the double window cavity, reducing solar heat gain in summer, minimizing room heating load, and enhancing thermal comfort by using solar radiation to preheat ventilation air in winter. However, the pretreated supply air temperature often falls short of room temperature.

To address this limitation, Phase Change Materials (PCMs) provide additional thermal storage in the VW, creating an active system for enhanced performance. PCMs can store excess heat during the day and release it during cooler periods, improving overall thermal regulation.  Various research outcomes related to the use of windows for sunlight exposure in passive cooling techniques.

Key points include:

• Ventilated Window (VW) Concept: Focuses on regulating outdoor airflow to reduce solar heat gain, minimize heating load, and enhance thermal comfort by preheating ventilation air with solar radiation.
• Challenges: Pretreated supply air temperature often does not reach room temperature.
• PCM Integration: Provides additional thermal storage, creating an active system that enhances window performance by storing and releasing heat as needed.

This integration of PCMs into windows demonstrates a promising approach to improving energy efficiency and thermal comfort in buildings, leveraging passive cooling techniques to optimize performance and reduce reliance on mechanical systems.

3.2. Passive Desiccant Cooling

Passive desiccant cooling systems are an innovative solution to energy-efficient air conditioning, gaining prominence in recent literature. They are noted for their ability to precisely control indoor temperature and humidity by combining desiccants with other passive strategies. Significant progress has been made in integrating Phase Change Materials (PCMs) with desiccants, as these elements work synergistically to manage dynamic thermal conditions effectively. Research findings on the topic, showcasing various investigations in this field.

Key points include:

• Energy-Efficient Air Conditioning: Passive desiccant cooling systems provide an energy-efficient alternative to conventional air conditioning, focusing on temperature and humidity control.
• Integration with PCMs: Combining PCMs with desiccants enhances the system's ability to handle dynamic thermal conditions, improving overall efficiency and effectiveness.
• Research Findings: Studies have explored various configurations and materials to optimize passive desiccant cooling systems, with promising results for indoor climate regulation.

Research in passive desiccant cooling systems has demonstrated their potential for achieving energy-efficient air conditioning through innovative designs and material integrations, paving the way for more sustainable building climate control solutions.

3.3. Heat Dissipation Techniques

3.3.1. Evaporative Cooling

Evaporative cooling is a compelling alternative to traditional air conditioning systems, especially suited for hot and arid climates as well as temperate regions. This method offers economic benefits and contributes to environmental sustainability by leveraging the substantial enthalpy of water evaporation to absorb heat from the surrounding air. This process significantly reduces air temperature while increasing humidity.

Evaporative cooling is classified into two main types: direct evaporative cooling (DEC) and indirect evaporative cooling (IEC).

• Direct Evaporative Cooling (DEC): Involves direct contact between the air stream and water, using the sensible heat of the air to evaporate the water, which lowers the air temperature and increases humidity. The efficiency of DEC depends on the moisture content of the intake air.
• Indirect Evaporative Cooling (IEC): Utilizes a heat-exchanging wall to separate dry and wet air streams, preventing additional moisture in the product air. Combining IEC with other cooling systems can enhance overall performance by focusing on cooling effectiveness, temperature reduction, and climate conditions.

Experiments in Bangalore, India, demonstrated that a hybrid PCM-based storage system enhances solidification behavior, speeds up charging duration, and increases the heat transfer rate. This integrated system outperforms conventional systems, presenting a promising approach for energy-efficient building cooling or integration with existing HVAC systems.

A study on a solar-powered solid desiccant air conditioning (SPSDAC) system with a PCM unit showed energy efficiency with coefficients of performance (COP) surpassing exergy efficiency, ranging from 1.83% to 1.99%. The system's mean overall thermal storage capacity reached 1817.7 W, demonstrating its potential for sustainable cooling solutions.

3.3.2. Convective Cooling

PCMs play a critical role in enhancing convective cooling through various ventilation strategies:

• Natural Ventilation: Integrating PCMs into building materials optimizes cooling by absorbing and releasing heat, stabilizing indoor temperatures, and enhancing comfort.
• Mechanical Ventilation Systems: These systems, including Trombe walls, solar chimneys, and buoyancy-driven stack ventilation, incorporate PCMs to absorb and release solar heat, facilitating convective airflow. In solar chimneys, PCMs release stored heat to enhance cooling, while in buoyancy-driven stack ventilation, PCMs optimize air circulation.
• Nocturnal Ventilation: Designed for nighttime cooling, this method benefits from PCMs that absorb excess heat during the day and release it at night, improving air exchange and thermal radiation. PCM-enabled nocturnal ventilation enhances energy efficiency by utilizing the material's capacity to store and release energy.

Multiple studies in this field, providing an overview of their findings. These studies highlight the effectiveness of PCMs in enhancing convective cooling methods, contributing to energy efficiency and improved indoor climate control.

3.3.3. Radiative Cooling

Radiative Cooling (RC), which utilizes the Earth's atmosphere and sky as a heat sink, has been used for centuries, notably in ancient ice-making practices. This passive cooling method has gained contemporary significance in building energy efficiency. Solar reflectance, emissive radiators, and materials like polymers and inorganic particles play a crucial role in influencing RC during the day. However, challenges remain in developing novel radiative radiators, which could potentially lead to supercooling and increased heating demands.

Integrating Phase Change Materials (PCMs) into building envelopes provides a solution by buffering against supercooling and enhancing thermal capacity. Studies summarized highlights the potential and applications of RC, emphasizing system optimization, climatic considerations, and material constraints.

Key points include:

• Historical Context: RC has been employed for centuries, particularly in ancient ice-making.
• Modern Application: Gains contemporary significance in improving building energy efficiency.
• Material Influence: Solar reflectance, emissive radiators, and materials like polymers and inorganic particles are critical to RC effectiveness during the day.
• Challenges: Developing novel radiative radiators can lead to supercooling and increased heating demands.
• PCM Integration: Buffers against supercooling and enhances thermal capacity, making RC more effective and reliable.

Various studies that explore the potential and applications of RC, focusing on optimizing systems, considering climatic factors, and addressing material limitations. These studies underscore the importance of integrating RC with PCMs to improve thermal management and energy efficiency in buildings.

3.4. Heat modulation

3.4.1. Free Cooling

Free cooling (FC), a vital aspect of passive cooling, utilizes nocturnal coolness to counteract daytime heat in buildings. This technique leverages a structure's thermal mass and its effectiveness can be significantly enhanced by incorporating Phase Change Materials (PCMs). With their latent heat storage capabilities, PCMs optimize FC by reducing system sizes and boosting overall efficiency. Careful selection of PCM melting temperatures allows for tailored application across various climates. The integration of FC and PCMs represents an innovative and sustainable solution, offering cost-effective management of daytime heat accumulation through strategic nocturnal cooling processes in building design.

Key points include:

• Thermal Mass Utilization: FC exploits the building's thermal mass to absorb and store cool nighttime air, which is released during the day to mitigate heat.
• PCM Integration: Enhances the effectiveness of FC by utilizing the latent heat storage properties of PCMs, thereby optimizing system performance and efficiency.
• Tailored Applications: Selecting appropriate PCM melting temperatures ensures that FC can be effectively applied in various climatic conditions.
• Cost-Effective Solutions: This combination provides a sustainable and economical method for managing daytime heat through nocturnal cooling.

Multiple investigations scrutinizing the integration of PCM and FC principles of energy efficiency. These studies highlight the benefits and potential of using PCMs to enhance free cooling in building designs, demonstrating improvements in energy efficiency and indoor thermal comfort.

Summary of Findings

• Efficiency Improvements: Studies show that PCM-enhanced free cooling systems can reduce the need for mechanical cooling, leading to significant energy savings.
• Optimal Melting Points: Research indicates that the careful selection of PCM melting points is crucial for maximizing the efficiency of free cooling systems.
• Case Studies: Various investigations have demonstrated the practical application of PCM-FC systems in different climatic regions, confirming their versatility and effectiveness.

In conclusion, the integration of free cooling and PCMs offers a promising approach to improving building energy efficiency and thermal management. By capitalizing on nocturnal coolness and the latent heat storage properties of PCMs, this method provides a sustainable and cost-effective solution for managing heat accumulation in buildings.

3.4.2. Thermal Mass

The integration of Phase Change Materials (PCMs) into thermal mass components such as wallboards, windows, roofs, and ceilings is a compelling approach for enhancing passive cooling strategies. Various techniques for PCM incorporation—direct incorporation, immersion, vacuum impregnation, encapsulation, and shape stabilization—cater to different building elements, ensuring a comprehensive and effective approach to passive cooling.

Applications in Building Components

1. Walls: PCM-infused materials in walls absorb and release latent heat, stabilizing indoor temperatures by mitigating temperature fluctuations throughout the day and night .
2. Windows: Windows with PCM coatings reduce heat gain during daylight hours, lowering the reliance on active cooling systems and improving indoor thermal comfort .
3. Roofs: Roofing materials embedded with PCMs enhance the building’s ability to absorb and release solar heat, contributing to energy efficiency and thermal regulation .
4. Ceilings: PCM integration in ceilings aids in maintaining thermal stability by absorbing excess heat during the day and releasing it when temperatures drop, thus improving overall indoor climate control .

These applications illustrate the flexibility and effectiveness of PCMs in various building components, highlighting their importance in the design of sustainable and energy-efficient buildings. The specific benefits and integration techniques for PCMs across different building elements.

Summary of Findings

• Walls: PCM-infused walls provide enhanced thermal inertia, reducing peak indoor temperatures and improving occupant comfort.
• Windows: PCM-coated windows offer significant reductions in solar heat gain, contributing to lower cooling loads.
• Roofs: PCM-enhanced roofing materials provide superior solar heat management, aiding in both heating and cooling efficiency.
• Ceilings: Incorporating PCMs in ceilings helps in maintaining a stable indoor temperature, reducing the need for mechanical heating and cooling.

By integrating PCMs into the thermal mass of buildings, designers can significantly improve energy efficiency and indoor thermal comfort. These materials offer a versatile and effective means of leveraging natural thermal storage capabilities, contributing to more sustainable building practices. The diverse techniques for PCM integration ensure that these benefits can be tailored to various climates and building designs, further underscoring the potential of PCMs in passive cooling strategies.

4. Conclusion

The integration of Phase Change Materials (PCMs) into building envelopes offers a promising solution for enhancing energy efficiency and thermal comfort. However, challenges such as scalability, compatibility with various building materials, reliability in real-world conditions, and end-of-life considerations for responsible disposal or recycling must be addressed. Overcoming these hurdles through targeted research efforts is essential to fully leverage the benefits of PCMs. Future research avenues include exploring bio-based and composite PCMs to enhance thermal conductivity, optimizing PCM layer positioning and configuration, and developing tailored encapsulation methods for diverse building components. Additionally, investigating the combination of multiple PCMs with staggered melting points holds potential for improved thermal regulation. Ensuring seamless integration with conventional building materials, rigorous testing, and sustainability considerations, including life cycle assessments and eco-friendly alternatives, are paramount. Furthermore, developing a universal design rule or workflow would serve as a valuable reference for navigating energy-efficient building design challenges across different climates and architectural styles.

The analysis highlights the transformative impact of PCMs on energy efficiency and thermal performance across various applications, such as:

• Solar Control Techniques: Reducing heat loads by up to 75%.
• Building Orientation: Achieving 70-90% energy savings in south-facing walls during peak summer.
• Shading Devices: Reducing cooling energy consumption by up to 44%.
• Wall Construction: Energy savings of 15-47.6%.
• Window Design: Energy savings of up to 62.3% and 41.53%.
• Climate-Specific Applications: Reducing annual heat gain and mitigating temperature swings.
• Passive Desiccant Cooling: Achieving up to 75.82% energy savings and peak electrical reductions from 60.87% to 90%.
• Evaporative and Convective Cooling Strategies: Reducing cooling energy consumption by 3.32-59.19%.
• Radiative Cooling: Achieving a 10% overall cost saving.
• Heat Modulation Techniques: Reducing charging duration by 34.8%.
• Thermal Mass Optimization: Reducing energy consumption by up to 90%.

The integration of PCMs has shown significant potential for contributing to the development of intelligent, nearly zero-energy buildings and aligning with ambitious energy reduction goals, such as the EU's target of an 80% reduction. Addressing the identified challenges and pursuing the outlined research directions are crucial to unlocking the full potential of this innovative technology and paving the way for widespread adoption in the construction industry, ultimately promoting sustainable and energy-efficient buildings.

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Source: sciencedirect‍