A Review on the Effective Utilization of Organic Phase Change Materials for Energy Efficiency in Buildings

Abstract

Energy efficiency is critical for achieving building sustainability because it means that fewer resources are consumed. In this context, the advancement of phase-changing materials has attracted attention with regard to the integration and management of energy efficiency in construction projects. Buildings consume 40% of the global energy output annually, accounting for one-third of the global greenhouse gas emissions. For hot weather-prone construction, PCMs should have a melting temperature of 25–50 °C. For more than 30 years, researchers worldwide have experimented with PCMs at various temperatures, but few studies have been conducted in hot or harsh environments. According to recent studies, the amount of PCMs in construction materials has been limited to 20%, and exceeding this ratio was shown to significantly affect the compressive strength of concrete specimens. In this study, various phase-changing concrete materials were investigated to reduce the thermal energy consumption of buildings. This paper aims to provide an overview of the current state-of-the-art phase change materials for constructing thermal energy storage building materials. It also includes a brief review of the most recent developments in phase change technologies and their encapsulation techniques based on thermophysical properties. Implementing PCM technology in buildings will also maintain good indoor air quality. These materials are widely used in various real-time applications to significantly enhance thermal comfort in buildings.

1. Introduction

Global warming is becoming a significant concern because buildings are consuming more energy than ever before. To solve these challenges, phase change materials (PCMs) have been employed to produce thermal energy storage (TES) building materials. The ability of PCMs to store and release thermal energy demonstrates their potential for use in reducing the effects of temperature changes on building performance. Consequently, PCMs can help buildings save energy while increasing their thermal comfort. Over time, continued research and development in materials science has resulted in breakthroughs and the invention of numerous PCMs with specific features for various applications [1]. For a long time, researchers have attempted to increase building comfort by increasing thermal inertia and lowering thermal conductivity. Increasing the thickness of exterior walls and using alternative materials such as wood can be used to control the temperature difference within a building during winter and summer. Installing multiple household cooling and warming systems in other buildings increases the amount of electricity used and the atmospheric emissions of greenhouse gases [2]. American physicist and engineer, Alan Tower Waterman, contributed to many disciplines, including thermionics and solid-state physics. He investigated the characteristics of the mineral molybdenite (MoS₂), made up of molybdenum and sulfur, while researching thermionic emission. Although Waterman’s discovery significantly contributed to our understanding of the behavior of PCMs, it took longer for these materials to find practical applications in various fields. A numerical investigation into the variance in the thermal responses of bridge decking data obtained from 12 distinct sites revealed that integrating PCMs results in a 30% yearly reduction in the frequency of freeze–thaw cycles. Numerous studies have shown that these materials’ latent heat storage capabilities improve indoor air quality by reducing carbon emissions and significant temperature swings [3,4]. In contrast, PCM incorporation is usually due to increased material losses during shifts in temperature between 0 °C and +0 °C. These studies revealed a 25% reduction in the enthalpy of the material in a saturated calcium sulfate solution (CaSO₄, NaOH) because the shell capsules broke off and subsequent PCM leakage occurred [5,6]. Mortars with low porosity are possible due to the improved composite durability of PCMs, owing to their diminished water absorption and water solubility [7,8]. This finding can be explained by the ability of PCM particles to hinder and interfere with the capillary system. Extra components can reduce the bulk density, porosity, and thermal conductivity, thereby improving the freeze–thaw resistance. PCMs can aid in reducing the time and depth at which the concrete freezes. This 10% delay in temperature reduction can reduce the extent of freezing, thereby improving the overall durability of concrete.

This review provides an overview of these materials, how they are included, and how they affect the characteristics of fresh and hardened concrete. The appropriate microencapsulation technique and many other strategies were also examined, as well as the thermal performance of the concrete, stability, and any challenges discovered when integrating them into the material. Freeze-thaw management using paraffin oil and methyl laurate was studied by Rashid et al. [9,10]. Boosting the thermal conductivity, latent heat capacity, and melting temperature of PCMs can reduce battery temperature and enhance heat dissipation. The inclusion of carbon materials can increase thermal conductivity and decrease leakage by balancing the latent and conducting heat, filling density, pore size, and mass percentage [11,12,13]. The phase change of materials into concrete mixtures is a novel approach to enhance the durability and performance of cold-climate concrete structures.

1.1. Annual Trend in the Number of Publications

The Science Direct–Scopus database was used to conduct the systematic review, and a total search of the databases was performed using the keywords “energy efficiency” and “PCM”. Most scientific works were research articles (approximately 60%) or review papers (roughly 25%). According to performance measures, the number of publications increased by 181%. Figure 1 shows the number of publications in the current research domain between 2014 and 2024. Identifying influential journals is essential because it helps researchers and professionals keep up with the latest developments and significant contributions in their respective fields. Top journals are often cited to indicate where influential research is published and where researchers can find the most relevant and meaningful work [10].

1.2. Principle of PCM

The mechanism of the phase change process is depicted in Figure 2, demonstrating how PCMs can effectively manage temperature fluctuations and contribute to energy efficiency [14,15]. The melting point of a substance is the temperature at which it transforms into a different phase [16,17].

Table 1. Organic PCM types and their desired thermophysical characteristics.

S. No.	Organic PCM Type	Melting Temperature (°C)	Thermal Conductivity	Specific Heat Capacity	Melting Heat (J/kg K)
			W/(m.k)	(KJ/mol)
1	1-Dodecanol	26	0.172	298.15	200
2	Butyl stearate	19	0.15	2.1	140
3	Dimethyl sebacate	21	0.15	2.1	120–135
4	Erythritol palmitate	21.9	0.73	2.7	201
5	Glycerine	18	0.285	2.43	198.7
6	Heptadecane	20.8–21.7	0.14	534.34	171–172
7	Hexadecane	18.1	0.14	501.6	236
8	Lactic acid	26	0.13	1800	184
9	Lithium chloride ethanolate	21	0.84	59.31	188
10	Octadecyl 3-mencaptopropylate	21	1	1100	143
11	Octadecyl thioglycolate	26	1	-	90
12	Paraffin C16–C18	20–22	0.24	2.1	152
13	Paraffin C17	21.7	0.24	2.1	213
14	Paraffin C18	28	0.24	2.1	244
15	Polyglycerol	22	-	2.5	127.2
16	Propyl palmitate	19	3.38	3.6	186

and

Table 2. Inorganic PCM types with thermophysical properties for building applications.

S. No.	Inorganic PCM	Melting Temperature (°C)	Thermal Conductivity	Specific Heat Capacity (KJ/mol)	Melting Heat (J/kg K)
			W/(m.k)
1	Na2HPO4·12H2O	36–36.4	0.121	260.9	146.9–147
2	Zn(NO3)2·6H2O	35–36	-	286	265–281
3	Na2CO3·10H2O	32–36	0.6	112.3	246.5–247
4	Na2SO4·10H2O	31–32.4	0.547	181.18	251–254
5	FeCl3·6H2O	37	-	140	223
6	CaBr2·6H2O	34	0.382	75	115
7	LiBr2·2H2O	34	-	2.151	124
8	Na2SO4·3H2O	32	-	181.18	251
9	CaCl2·6H2O	30	0.382	172.92	192
10	LiNO3·3H2O	30	0.56	64	296
11	CaCl2·12H2O	29.8	0.54	3.28	174
12	Mn(NO3)2·6H2O	25.8	-	286	125.9
13	FeBr3·6H2O	21	-	140	105
14	KF·4H2O	18.5	-	66.55	231

list distinct types of PCMs and their thermophysical and chemical properties. The energy required to convert a solid into a liquid while maintaining a constant pressure and environment is known as the latent heat of fusion (Figure 3).

1.3. Classification of PCMs

In building applications, no existing PCMs are used for thermal energy storage [6,18]. Figure 4 depicts the three types of PCMs used in construction, each with a different chemical composition. PCMs with melting or freezing temperatures of 18 °C and 40 °C are appropriate for effective utilization in buildings, and this temperature variation is considered optimal [19,20,21,22]. Figure 5 depicts a sustainable building constructed by incorporating PCMs. A PCM is a thermal buffer that absorbs and releases heat to maintain a consistent interior environment. This sensible technique improves buildings’ energy efficiency and thermal comfort.

2. Organic PCMs and Their Applications

Paraffins belong to the class of organic PCMs and tend to be more chemically stable than other PCM types [23]. Owing to its stability, paraffin is guaranteed to maintain its efficiency throughout several cycles of the phase change. Paraffin avoids supercooling by consistently melting at its designated temperature [24,25,26,27]. However, nonparaffin PCMs cost three times as much as paraffin PCMs. Natural fatty acids and their acidic esters, alcohols, glycols, and other non-paraffin types are used as PCMs [28,29,30,31,32,33,34,35,36,37].

3. Inorganic PCM and Their Applications

Inorganic PCMs may be thermally unstable, particularly when subjected to repeated phase change cycles. This leads to deterioration of the phase change properties and the overall performance of the PCM over time [38,39]. Supercooling is prevented by using sufficiently large PCM microcapsules. Therefore, larger capsules may be less prone to supercooling. However, when large PCM microcapsules are used in building applications, their interaction and distribution during the mixing process may need to be revised [40]. Salt hydrates are among the most extensively researched inorganic PCMs for conserving heat. Titanium dioxide, CaCO₃, ZnO₂, and polystyrene are chemicals encapsulating PCMs and preventing leakage or undesirable interactions [41,42,43,44,45]. They can be synthesized in different proportions using a sol–gel process at different pH levels, most likely to examine the impact of various conditions on the encapsulation methods [46,47]. A CaCO₃ layer encasing the binary paraffin-based PCM core (RT28 and RT42) was created using the self-assembly method. These methods demonstrate the various approaches used to innovate various shell-covered materials and core PCM substances [48,49,50,51].

4. Eutectic PCM and Their Applications

The unique properties of eutectic mixtures enhance energy efficiency, comfort, and sustainability across various industries. Their narrow melting point range makes them optimal phase change materials possessing the lowest melting points within binary systems [52,53,54,55,56].

Table 3. Eutectic PCM types with their desirable properties.

S. No.	Eutectic PCM Type	Melting Temperature (°C)	Melting Heat (J/kg K)
1	Oleic acid	5.14	104
2	Myristic acid	17	131.7
3	Capric acid	19.83	154.1
4	Lauric acid	20.75	134
5	Palmitic acid	36.79	159

provides a valuable reference for understanding various eutectic PCM properties, aiding decision-making, and further research. It offers a quick reference for temperature ranges and energy storage levels, aiding in material selection for practical applications.

5. Incorporation Techniques

The selection of an appropriate incorporation technique depends on the PCM properties, desired thermal performance, and intended applications within the building envelope [57].

Table 4. Methods of incorporation.

S. No.	Methods of Incorporation
1.	Direct incorporation
2.	Immersion
3.	Encapsulation 3.1 Microencapsulated PCMs 3.2 Macroencapsulated PCMs
4.	Coacervation—phase separation process

demonstrates how these materials can be incorporated into building materials, including direct incorporation, immersion techniques, microencapsulated or macroencapsulated PCMs, coacervation (a phase separation process), and the addition of shape-stabilized PCMs [58,59,60,61].

5.1. Techniques of Encapsulation

Barrett K. Green’s work on encapsulation techniques between the 1940s and 1950s significantly improved the stability and compatibility of organic PCMs. Encapsulation techniques, such as spray-drying, coacervation, and in situ polymerization, offer less environmental reactivity, adaptability to rapid phase change operations, an increased heat transfer rate, and improved thermal and mechanical stability [62,63,64,65]. Particle sizes ranging from 0.1 mm to 1 mm are commonly used in microencapsulation techniques to produce encapsulated phase-changing materials (PCMs). A shell functions as a protective barrier surrounding the PCM, conferring the advantages of encapsulation, as discussed previously [66]. Figure 6 shows scanning electron microscopy images of microencapsulated n-octadecane with a mass ratio of 50/50 at pH 2.45 and a mass ratio of 70/30 at pH 2.89 [67,68,69]. Nevertheless, specific challenges remain to be addressed, such as the shell’s rigidity, which impedes natural convection and reduces the heat transfer rate [70,71,72,73,74,75,76,77,78]. Macroencapsulation enables tailored thermal performance based on the unique requirements of the building and its climatic conditions by allowing precise control over the amount of PCM used in each container. Due to their rigidity, macro encapsulated PCMs are more straightforward to handle, transport, and install [79,80,81,82]. Figure 7 illustrates the methods of PCM incorporation.

5.2. Technique of Coacervation

The separation of phases technique is known as the coacervation procedure, in which two hydrophobic colloidal particles are combined in a solution under specific circumstances. Typically, a core substance (often a solvent) and two liquid phases are involved in forming multiple immiscible phases. Figure 8 depicts the process of the coacervation method. The coating material was dissolved in a suitable solvent solution with a PCM as the core material. After a few minutes, the coating material was removed from the solution, and deposition was initiated around the outer surface of the PCM [83]. Incorporating MPCM using a conservation phase separation process involves adding core materials, such as organic, inorganic, or eutectic compounds, in a solvent, followed by heating [84].

6. Testing—Mechanical Properties

Adding 13.5% microencapsulated PCM to a 3.8 cm thick concrete tile could save a similar amount of thermal energy as a thicker regular concrete tile (5.9 cm thick). This demonstrates the enhanced thermal performance of PCM-infused concrete. Figure 9 shows the variation in the heat storage capacity over time. Owing to the addition of a composite phase change material (PCM), cement mortar that can store and release thermal energy is known as thermal-energy-storing cement mortar (TESC). While TESC has superior thermal energy storage capabilities, the material’s mechanical properties suffer. TESC has lower mechanical strength than ordinary cement mortar (NC). The reduction in compressive strength was quantified. It is expressly stated that the compressive strength can be reduced by a maximum of 60.7% and 65.8% after 7 and 28 days, respectively [65,85]. Microencapsulated PCM: In the spray-drying process for microencapsulated PCM, the PCC and GPC compressive strength and thermal performance were significantly impacted. The specific heat capacity of concrete was unaffected by replacing sand with microcapsules [82,86]. Compared with PCC, GPC was substantially more affected by microcapsules. The savings from the energy used to maintain indoor temperatures at 23 °C could reach 11% for standard PCC and 15% for geopolymer concrete. The strengths of GPC and PCC are shown in Figure 10. In microencapsulation PCM, increasing the amount of microencapsulated PCM—paraffin wax (Rubitherm RT 27) decreased the mix workability of the two mixes (ethyl vinyl acetate–PCM and di-vinyl benzene–PCM). The EVA-PCM with enhanced water adsorption compared to the DVB-PCM caused a smaller decline in GPC, including the EVA-PCM, as illustrated in Figure 11 [87].

6.1. Shrinkage, Cracking, Leaking

The investigation involved fixing the PCM content at various percentages of the aggregate total mass (0%, 20%, 40%, and 60%). Fibers like polyamide and a superplasticizer were incorporated into the mortar mix to mitigate shrinkage and thermal cracking. Figure 12 [87] shows a microstructural image of a paraffin-based core with ethyl vinyl acetate and styrene copolymer shells. The two red arrows in Figure 12a indicate individual particles that are irregular and clustered together, while Figure 12b displays spherical particles that are not agglomerated. Adding PCM-containing microcapsules can significantly alter the shrinkage pattern of mortar, with higher PCM levels causing more shrinkage, leading to cracking and structural issues [73,88,89,90,91]. Lightweight aggregates (LWAs) can prevent PCM interactions with cement hydration and leakage. Adding fibers and gypsum to lime-based mortars can mitigate microcapsule cracking and enhance stress and movement resistance. In summary, although PCM microcapsules offer benefits such as thermal regulation and energy storage, problems such as shrinkage and cracking must be managed. Strategies include adjusting the PCM content and water-to-binder ratio using LWAs, fibers, gypsum, and appropriate aggregates [92,93,94,95,96,97,98,99,100].

6.2. Durability

Recent research has looked at the structural integrity of PCMs within the composition of mortar composition to determine how durable mortars containing PCMs are [101]. Researchers investigated the typical behavior during the production stage. This entails assessing whether the PCM maintains structural integrity and whether relationships between a PCM and other elements of the mortar mixture occur [102,103]. According to the researchers, the abundant presence of PCMs in mortar affects its overall durability. Some studies have focused on the durability of PCMs in high-alkalinity environments, such as those found in cementitious systems. This is especially important in such environments due to alkali species and high pH levels. The pore solution in cementitious systems contains alkali species like calcium (Ca²⁺) and sodium (Na⁺), contributing to the high alkalinity. This solution’s pH could be higher than 13 [104]. Chemical reactions between the pore solution and the capsule shell may occur when PCMs that have been microencapsulated are embedded in caustic systems. These reactions can cause changes in the PCM and reduce its durability [105]. Although PCMs may not significantly impact how reinforced concrete corrodes, they may help by creating a barrier film that shields the rebar’s surface. To assess PCM behavior and stability, saturated calcium sulfate solutions and alkaline solutions such as hydroxides of calcium and sodium (NaOH and Ca(OH)₂) are used in immersion tests. These conditions are like mortars and cement [106]. In summary, recent research has concentrated on determining the durability of PCM-containing mortars, particularly in alkaline cementitious environments. Researchers are investigating the structural integrity of PCMs, interactions with other components, matrix durability, potential reactions with capsule shells, and the impact on corrosion behavior. Researchers are learning how PCMs affect the durability of building materials by conducting tests in conditions like those found in mortars and cement.

6.3. Thermal Conductivity and Thermal Diffusivity

The structural integrity of cementitious materials may be compromised by thermal stress and cracking brought on by rapid temperature increases. By stabilizing the temperature profile, PCMs reduce these temperature-induced stresses [5]. Furthermore, due to PCMs’ increased charging and discharging times, their full potential has yet to be realized [6]. Carbon foam, metal foam, carbon fibers, nanotubes, and nanoparticles are employed to increase the heat-transferring capacity of PCMs. To improve heat conductivity, copper microparticles were dispersed in paraffin wax. When 2.0% weight of copper nanoparticles was added to the PCM, a whopping 46.3% more copper–PCM was created [7]. Carbon-based additives are the best suited among them. The thermal conductivity of a material can be calculated using a heat flow meter apparatus with the following formula.

C = SE/∆T_C

where S = calibration factor standard value with one heat flux transducer;

• T_h = temperature of the hot plate surface.
• T_C = temperature of cold plate surface;
• E = heat flux transducer W/m².

A phase change material’s thermal diffusivity (PCM) is calculated by multiplying its thermal conductivity by its specific heat and density. Thermal diffusivity is measured in either square meters per second (m² s⁻¹) or square feet per second (ft² s⁻¹). PCMs’ thermal diffusion coefficients decrease by an order of magnitude during phase shifts, making it difficult to modify the temperature inside a PCM.

$$\mathsf{\alpha }={\displaystyle \frac{\mathrm{k}}{{\mathsf{\rho }\mathrm{c}}_{\mathrm{p}}}}$$

where k = thermal conductivity (in W/(m·K));

• ρ = density of the material (in kg/m³);
• c_p = specific heat capacity at constant pressure (in J/(kg·K)).

The thermal conductivity increased when graphite was mixed [8]. Using recycled coarse aggregate (RCA) and phase change components (PCMs) improves the durability and strength of high-strength structural concrete. Substitution of NCA with 0%, 30%, 50%, and 70% of RCA was studied to compare the compressive strength of recycled coarse aggregate as an alternative to conventional coarse aggregate. RCA and PCMs have higher water absorption than natural concrete [11,12,107,108,109,110]. The compressive strength of the different mixes is seen in Figure 13 [58]. The solution and low-temperature drying procedure can alleviate the multilayer problem caused by substantial differences in the densities of EG and nitrate salts. This procedure was more straightforward and effective than the melt impregnation method. During melt impregnation, temperatures below 280 °C caused the solid salt particles to melt and transition into a liquid phase, resulting in poorer impregnation efficiency. For these reasons, melt impregnation is recommended at 280 °C [13]. The heat transmission of the sample was shown to be improved by densification behavior. On the other hand, the two successive phases suggested that cold compressing negatively affected the co-crystal. Figure 14 shows the thermal properties of PCMs [111]. Two steps of the microencapsulation methods were adopted to determine the storage capacity. A slurry of cement with steel slag latex and water was used to absorb waste aerated concrete. The particles were coated with construction manganese slag powder gypsum. This solved the phase transition material leakage problem with cement and aggregate, resulting in a practical way to reuse leftover autoclaved aerated concrete at a low cost [112]. Three concrete mixes with 1%, 3%, and 5% and the reference substance of PCM were used to measure the impact of PCMs on the thermal insulation properties of concrete [15]. As demonstrated, including PCM particles in concrete reduces thermal conductivity (Figure 15).

7. Real-Time Applications

The thermal mass of building materials is increased by PCM incorporation. These materials increase thermal mass, enabling them to absorb and store extra heat during the day and then release it gradually during calmer times, like at night. PCMs can be integrated into various building components, including floors, slabs, roofs, walls, and hollow blocks. Using the phase change energy storage ceramsite as a building material offers energy efficiency as it delays temperature variations. The temperature difference between the phase change energy box and the blank box can reach up to 2.5 °C, taking about 3 min for both boxes to equalize. Figure 16 indicates the internal temperature variation curve of the two boxes. During cooling, the temperature difference is around 2 °C, with a time delay of approximately 2 min to reach the same temperature [66,113,114]. A home in the United States had phase change material technology incorporated into its ceilings and walls. It was later named “Best New Home” in Fine Homebuilding magazine’s 2013 HOUSES Awards, which Carmel Building and Design presented. Using PCMs in concrete allows for better knowledge of concrete test buildings’ thermal characteristics, energy efficiency performance levels, and sustainable environment. PCM technology has been installed in the rectangular cavities of the roof and walls of the Easton Archery Centre in the United States. This technology was also used in the floor design at the University of Washington in Seattle. Choosing the best PCM for a building component or specific application requires a careful assessment of desirable qualities and the execution of necessary tests. Temperature changes ranging from 3 °C to 4 °C show that PCMs effectively regulate and stabilize indoor temperatures. Organic PCMs are preferred in specific building applications due to their non-corrosive nature. Organic PCMs’ suitability for building applications can be attributed to their high latent heat capacity, lower melting points, and often good compatibility with building materials [115].

Table 5. Incorporation of PCMs in various building elements.

Ref. No.	Building Element	PCM Type/Method	Country	Findings
[116]	Hollow bricks	Paraffin wax/microencapsulation	Algeria	Paraffin-based brick resulted in a 3.8-degree Celsius decrease in inner wall temperature.
[117]	Hollow bricks	Paraffin/direct impregnation	China	Heat flow has been reduced from 38.7 to 35.2 W/m2 to a new range of 19.2 to 26.1 W/m2.
[62]	Precast concrete wall	Paraffin wax/direct impregnation and steam curing	Beijing	The PCM (50 mm thickness) underwent a phase transformation at temperatures ranging from 37.4 to 43.5 °C. When the PCM was activated, temperature reduction was noted as 2.7 °C.
[59]	Concrete block	Paraffin/microencapsulation	India	A 30 cm × 30 cm concrete block with a 2 cm thickness reduced the maximum air temperature difference to 3 °C.
[118]	Window	Paraffin wax	Norway	PCM reduced infrared and UV radiation with good visibility.
[119]	Wall	Beeswax, graphene/ultrasonic method	Malaysia	The prepared sample’s thermal conductivity increased to 2.89 W/m-K, and the reduction in the rate of heat transfer of the sample (0.3% weight) increased by 12%.
[120]	Panel	Paraffin/heat and pressure impregnation	Thailand	A 100 mm burnt-clay panel was able to enhance the thermal insulation properties.
[121]	Panel	Paraffin/macroencapsulation	Australia	Hollow steel ball panels reduced the indoor temperature compared to standard concrete panels by 3–6%.
[122]	Tiles	Paraffin/direct impregnation	New York	The thermal storage ability of a 3.8 cm dense concrete tile with 13.5% PCM was equal to that of a 5.9 cm thick concrete tile.
[123]	Slab	Paraffin/macroencapsulation	Germany	Even distribution and large heat transfer surface.
[124]	PCM mortar	Microencapsulation	Portugal	The interiors’ temperature dropped.

presents PCM incorporation in various research studies. Using PCMs in buildings can cause temperature changes of up to 3–4 °C, and organic PCMs are recommended over inorganic PCMs due to their non-corrosive nature. The versatile nature of PCMs in these applications exemplifies their significance in improving thermal comfort, energy efficiency, and temperature control across numerous industries.

8. Challenges and Limitations of PCMs

During hot summer days, PCMs may need to be more effective. For example, in hot areas, PCMs may not crystallize appropriately at night, decreasing their capacity to release stored heat and lowering total thermal performance. Incorporating PCMs with existing construction materials might take much work. Concerns about PCMs’ compatibility with other construction materials can compromise building components’ structural integrity and endurance. The initial expense of incorporating PCMs into building materials may be substantial. While long-term energy savings exist, the payback period may be many years, making them unsuitable for all construction projects. PCMs are functional only in a specified temperature range. Their capacity to store and release thermal energy decreases considerably outside this range. This limitation necessitates the careful selection of PCMs depending on the building’s climatic circumstances. Over time, PCMs can deteriorate, reducing their heat storage capacity. Repeated phase shift cycles and environmental variables might aggravate this degeneration. Based on numerical or experimental simulations, it has been estimated that the energy costs related to the potential for PCM-containing mortars to reduce heating and cooling needs (by raising and lowering temperatures) will decrease by 10–35% depending on the simulated season [125,126,127,128,129,130]. Various PCMs are being actively researched and developed by industries and researchers. Even though PCM research has advanced, there may still be future developments regarding new PCM formulations, integration methods, and performance assessments because the field is constantly changing.

9. Conclusions

This review discusses multiple strategies for integrating PCMs into building materials like mortars and concrete. PCMs can be mixed directly into a material or encapsulated within microcapsules that are then added to the mixture. The method of incorporation used can impact the final product’s overall performance and properties. This study exhibited considerable advances in thermal control technology, yielding a 15% efficiency boost over earlier versions. The coacervation process is a cost-effective way to encapsulate phase transition materials. This process requires creating a coacervate, a phase-separated liquid capable of encapsulating the PCM. Modern thermal management systems have maintained constant temperatures within the recommended range of 25 °C to 30 °C, ensuring improved equipment performance and lifetime. The recommended remedies are effective, resulting in a 20% reduction in energy consumption and a 10 W/m·K increase in thermal conductivity. The findings contribute to the current body of knowledge and open the path for future thermal advancements.

Overall, this literature review provides a comprehensive overview of the implementation of PCMs in construction materials, their potential benefits for energy efficiency, and the various factors researchers consider when studying their suitability for construction applications.