Melting Temperature Of Phase Change Material Research Articles

Assessment of latent heat thermal storage systems operating with multiple phase change materials

Abstract Latent heat thermal storage (LHTS) systems employing phase change materials (PCMs) offer several advantages compared to sensible heat storage units. However, they exhibit an inherent poor thermal performance owing to poor heat transfer, poor thermal conductivity of PCMs, and so on. Methods such as replacing single PCMs with multiple PCMs, addition of fins, micro/macro/nano-encapsulated composite PCMs and dispersion of high conductivity particles to PCMs have been suggested and studied in the past by different authors as a means for performance enhancement of LHTS systems. While extensive literature is available on the last three methods, studies on multiple PCMs are very limited. It is rather difficult at this stage to conclude on the benefits and merits/demerits of the method, given the limited data available in the open literature. Therefore, there is a need for consolidation and compilation of the existing literature to understand and assess the performance of LHTS units operating with multiple PCMs. An attempt is made in this paper to assess the performance of multiple PCM based thermal storage systems by carrying out a comprehensive review of available literature on the topic. Studies have evinced that single PCM units replaced with multiple PCMs offered superior performance with enhanced charging/discharging rates and better energy/exergy efficiencies. Also, past investigations reveal optimal melting temperatures of PCMs, optimal melting temperature difference between PCMs, optimal mass and so on to obtain an optimal performance of multiple PCM systems. Relevant published data were compared and discussed to understand the research trend over the years. Discussions were extended covering the challenges involved with multiple PCMs highlighting the scope for further research. An overall summary based on the survey has been presented for a concise understanding of key findings published in the open literature.

Analysis of the Thermal Storage Performance of a Radiant Floor Heating System with a PCM.

This study first reviewed previous studies on floor heating systems based on the installation of a phase change material (PCM) and the current status of technical developments and found that PCM-based research is still in its infancy. In particular, the improvement of floor heat storage performance in indoor environments by combining a PCM with existing floor structures has not been subject to previous research. Thus, a PCM-based radiant floor heating system that utilizes hot water as a heat source and can be used in conjunction with the widespread wet construction method can be considered novel. This study found the most suitable PCM melting temperature for the proposed PCM-based radiant floor heating system ranged from approximately 35 °C to 45 °C for a floor thickness of 70 mm and a PCM thickness of 10 mm. Mock-up test results, which aimed to assess the performance of the radiant floor heating system with and without the PCM, revealed that the PCM-based room was able to maintain a temperature that was 0.2 °C higher than that of the room without the PCM. This was due to the rise in temperature caused by the PCM’s heat storage capacity and the emission of waste heat that was otherwise lost to the underside of the hot water pipe when the PCM was not present.

Latent Heat Thermal Capacitor in Heat Exchangers- a Computational Investigation

The main objective of this study to evaluate the performance of phase change material (PCM) in smoothing outlet temperature of double tube heat exchanger subjected to fluctuating inlet temperature. A computational fluid dynamics (CFD) model is formulated, validated and utilized to investigate the conjugate heat transfer between heat transfer fluid (HTF) and PCM inside the heat exchanger. Three organic-based PCMs, i.e. n-octadecane (C18H38), n-eicosane (C20H42) and myristic acid (CH3(CH2)12COOH), were investigated to study the importance of PCM melting temperature on the performance of the PCM based thermal capacitor. The effect of heat transfer fluid inlet Reynolds was evaluated as well. The result confirms the potential usage of PCM as smoothing device (thermal capacitor). Moreover, the outlet temperature fluctuation was found to decrease as the inlet Reynolds number increases. Selecting PCM with appropriate melting points is crucial in ensuring successful application of PCM as thermal capacitor for specific application.

Comparative analysis of the PCM application according to the building type as retrofit system

It is necessary to reduce the environmental load by reducing the energy consumption in the building sector. As one of the preferred methods, phase change materials (PCMs) are considered to be promising to store and discharge thermal energy. Recently, many studies of PCM applications in buildings by simulation tools have been conducted. However, there is not much research on glass curtain wall building (GCW) systems applied to PCM installation compared to conventional wall-based buildings (CWB). The objective of this paper is to investigate the optimization of PCM applied to GCW and to evaluate the building energy performance by EnergyPlus. A building model was selected from ASHRAE Standard 90.1–2013 prototype buildings, and Baltimore, Duluth, and Miami in ASHRAE climate classification was used as the input climate data. In this study, the experiment used Shape-stabilized PCM (SSPCM) with mixing ratio of n-octadecane and n-heptadecane (7:3), selected owing to the energy efficiency in the thermal comfort range based on ISO 13790. Considering PCM application to GCWs and CWBs, it is important to apply the optimized PCM considering the different approaches between GCWs and CWBs. In addition, a PCM melting temperature of 25 °C was the most suitable setting for the retrofit. PCM installation on a wall, a floor, and a ceiling with the same melting temperature was the most effective approach.

Sensible and latent heat energy storage systems for concentrated solar power plants, exergy efficiency comparison

Different options of sensible and latent heat storage systems comprising different types of heat transfer fluids, heat storage media or phase change materials (PCMs) have been compared considering the upstream and downstream requirements of a concentrated solar power cycle. For an optimal system, analysis of both the energy efficiency and exergy recovery of the storage system and the whole cycle of heat to power is necessary. This study provides this analysis, comparing a two-tank sensible storage system to latent heat shell and tube storage system, using an analytical method, ε-NTU. For the case of molten salt as the PCM and sCO2 as the heat transfer fluid, results show 4.02% higher exergy recovery for the two-tank system at a working temperature range 450–700 °C compared to 450–660 °C for the latent heat storage system where the upper limit is the PCM melting temperature. Compared to the Carnot cycle efficiency (the highest rate of useful energy (exergy) recovery for an isentropic process) of 70%, the overall efficiency of the two-tank system, the base case of molten salt/sCO2, molten salt/Na, and molten metal/sCO2 are 57.41%, 53.39%, 55.21%, and 53.55%, respectively. The gap in efficiency between the sensible and latent heat storage systems decreases by lowering the thermal resistance of heat transfer fluid side and/or the PCM side. Specifically, the gap in efficiency decreases 45% by using liquid Na instead of sCO2 and a 4% decrease is observed when replacing molten salt with a molten metal like aluminium as the PCM. Using PCMs with higher melting temperature is preferred with liquids with high thermal conductivity like Sodium. For a heat transfer fluid such as sCO2 with low thermal conductivity, a higher inlet fluid temperature and/or a low temperature PCM can provide high exergy efficiency. For a specific combination of PCM and heat transfer fluid, an optimal melting temperature exists depending on the inlet temperatures during charging/discharging and the thermophysical properties of the media. The study shows that PCM storage provides opportunities to minimise causes of irreversibilities to achieve simultaneous high volumetric energy density and high exergy recovery for CSP application in comparison with the conventional two-tank sensible storage.

Experimental evaluation of phase change material in radiant cooling panels integrated with thermoelectric modules

This study proposes a phase change material for use in radiant cooling panels integrated with thermoelectric modules (PCM–TERCP) and evaluates its performance characteristics during the solidification and melting process of phase change materials in design conditions. The PCM–TERCP consists of phase change materials (PCMs), thermoelectric modules (TEMs), and aluminumpanels. TEMs operate to freeze the PCM, and PCM stores the cooling thermal energy to maintain the constant surface temperature of the panel for radiant cooling. The main purpose of thermal energy storage systems is the shift of the electricity consumption from day-time to night-time during the summer season. Therefore, PCM–TERCP can implement off-peak operation according to which energy is expected to be saved. The melting temperature of PCM and the target surface temperatures of the bottom panels of PCM–TERCP were designed to be 16°C. Additionally, the room temperature and mean radiant temperature (MRT) was set to 24°C, while the thickness of the PCM pouch was 10 mm. As a result, the solidification process required 4 h and the total input power was 0.528 kWh. Correspondingly, the melting process can operate passively over a period of 4 h. In most cases, the operating temperature was lower than 19°C, which validates the temperature response of PCM–TERCP.

Improving system performance of a personal conditioning system integrated with thermal storage

An innovative personal conditioning system called Roving Comforter (RoCo) comprises of a miniature vapor compression cycle (VCC), storing its condenser heat in a phase change material (PCM) thermal storage with helical refrigerant tubes. In the present study, we analyze its system performance with different PCM by using a validated dynamic model in Modelica®. Mathematical equations and programming decisions for implementation of PCM model in Modelica are discussed. Higher melting temperature of PCM results in higher power consumption during cooling operation, but reduced power consumption during recharge operation (solidification of PCM). Thus, it is necessary to identify the appropriate temperature of PCM that maximizes its coefficient of performance (COP), since RoCo operates with alternating cooling and recharge operations. The PCM melting and solidification from the helical coil geometry is captured with empirical correlations obtained from experiment. Various regimes observed in these asymmetric processes are discussed. An increase of 11% in the COP is observed. The article highlights modeling details and interesting insights of system performance of a vapor compression cycle integrated with PCM, which are increasingly being developed in recent times.

Numerical Investigation of Energy Saving Characteristic in Building Roof Coupled with PCM Using Lattice Boltzmann Method with Economic Analysis

Due to their characteristics of high energy storage density and a nearly constant melting temperature, phase change materials (PCMs) could be inserted into the roof of green buildings in order to reduce the energy consumption and ameliorate the room thermal comfort. In this paper, an enthalpy based multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) was developed to calculate the transient phase change conjugate heat transfer with solar radiation inside the green building’s PCM roof in the hot summer and cold winter areas of China. The effect of the PCM melting temperature on the variation of the roof internal temperature was investigated and the energy saving characteristic of the PCM roof under an intermittent energy utilization condition was also analyzed by comparing with the performance of the roof filled with sensible insulating materials (SIMs). Then, the life cycle incremental costs and incremental benefits of a PCM roof and SIM roof were studied by using the comprehensive incremental benefit model so that the green building roof could be economically evaluated. The results indicate that a temperature rise inside the roof during summer cooling time could be delayed due to the latent heat of the PCMs. It was also found that the melting temperature and the thickness of the PCM layer should be chosen appropriately for enhancing the energy saving amount of a PCM roof. Based on this, the PCM roof could have a better energy saving capability than the SIM roof. During the winter heating time, as the environment temperature and the room temperature are both below the PCM melting temperature, the PCM roof does not have a latent heat characteristic so that it performs like a SIM roof. Furthermore, due to the high price of PCMs, the incremental cost of green building is increased, which makes the PCM roof have a negative comprehensive incremental benefit. Under this circumstance, developing PCMs with a low price and stable chemical properties is a key scientific bottleneck for a wider application of PCM roofs in the architecture engineering field.

Significance of PCM arrangement in cooling vest for enhancing comfort at varied working periods and climates: Modeling and experimentation

Personal cooling vests that incorporate phase change material (PCM) have been utilized to improve thermal sensation of people working outdoors in different fields (firefighting, construction, military, police, etc.). In this study, an integrated fabric-PCM and bio-heat model was validated through human subject testing to determine the extent to which it could detect thermal and comfort responses when varying the arrangement of a fixed number of PCM packets in the cooling vest. The modeling approach was utilized for given PCM melting temperature to determine the number of packets needed and their optimal arrangement at moderate (35 °C) and hot (40 °C) environments for 45, 60 and 90 min working durations. The findings showed that when full coverage of the torso is not needed, optimal arrangements were those having full back coverage with the remaining packets on the upper front. Lower front cooling did not show significant improvement in comfort over upper front cooling. That effect was more evident when lower front PCM packets were used at the 40 °C hot environment. As the working duration increased, less differences were detected in skin temperatures and comfort between the optimal and worst cases since a higher PCM coverage area was necessary.

Numerical Thermal Characterization and Performance Metrics of Building Envelopes Containing Phase Change Materials for Energy-Efficient Buildings

Residential and commercial buildings consume nearly 40 percent of total USA energy use and account for one-third of total greenhouse gas emissions. The challenges are how to effectively promote energy efficiency in buildings to respond to the high financial burden of energy consumption, while reducing pollution. Phase change materials (PCMs) have been used as passive energy storage for building systems. Along this vein, this study aims to numerically elucidate the design parameters of building envelopes strengthened by PCM layers, and unveil their impacts on building energy efficiency. Critical design variables, such as the thickness of the PCM layer, the latent heat of PCMs, or melting temperature of PCMs were selected for a parametric study, while performance metrics were used to assess building efficiency. Results revealed that PCM-enabled building walls exhibited different levels of improvement, in terms of reduction of peak temperature and temperature swings. Among the variables, the selection of the proper melting point for a PCM was identified as the most crucial parameter for determining building energy efficiency, while the heat of fusion was also observed as a critical property of PCM for building potential. Findings also demonstrated that the placement of the PCM near the interior wall surface could achieve higher efficiency, as compared to other cases. Results also showed that the thermal conductivity of PCM has a minimum contribution to energy storage capacity.

Mathematical modelling and sensitivity analysis of solar photovoltaic panel integrated with phase change material

It is reported that every degree rise in photovoltaic (PV) temperature could lead to a decrease in electricity output by 0.4–0.65%. Phase change material (PCM), which could absorb great amount of heat without raising the temperature of itself, is employed in this study to control PV module temperature and increase power generation. This kind of integrated system is the so-called PV-PCM system. In recent years, some work has already been conducted in using PCM for PV panel thermal regulation both numerically and experimentally, while some issues are still unsolved or unclear, for example, limited number of cases in simulation, difficulties in modelling PCM convective effect, the impact and uncertainty resulting from some common assumptions in numerical simulation. To examine these issues, an improved thermal resistance model through applying enhanced conductivity method is developed to incorporate PCM convective effect in 1-D model, offering a good compromise between accuracy and simplicity. The numerical simulation result illustrates that neglecting PCM convective and radiative heat transfer will cause significant errors. Finally, based on simulation of over 300 cases, the two-variable analysis demonstrates that every 100 W/m2 increase in solar radiation can lead to about 5 °C increase in peak temperature, and an optimal performance can be achieved when the melting temperature of PCM is slightly higher, such as 5 °C, than the ambient temperature.

Multiple Phase Change Material (PCM) Configuration for PCM-Based Heat Sinks—An Experimental Study

A small-scale phase change material (PCM)-based heat sink can regulate the temperature of electronics due to high latent-heat capacity. Three different heat sinks are examined to study the effects of PCM combination, arrangement of PCMs in multiple-PCM heat sink, PCM thickness, melting temperature and intensity of heat source on the thermal behavior of heat sink. Results are obtained for the temperature distribution across the heat sink and the PCM melting profile. It is concluded that (i) PCM combination RT50–RT55 increases the thermal regulation period and also reduces the heat sink temperature at the end of the operation, (ii) the RT58–RT47 arrangement slightly reduces the maximum temperature as compared to RT47–RT58, (iii) As PCM thickness increases from 30 mm to 60 mm, the thermal-regulation-period increases by 50 min, (iv) As the PCM melting temperature increases, the thermal-regulation-period and the heat sink temperature increase and (v) The thermal-regulation-period decreases as the power rating increases from 1 to 2 W.

How to enhance thermal energy storage effect of PCM in roofs with varying solar reflectance: Experimental and numerical assessment of a new roof system for passive cooling in different climate conditions

In last decades, the effectiveness of thermal energy storage (TES) systems for energy efficiency has been widely studied when integrated to building envelope, often as latent strategy by means of Phase Change Materials (PCM). In this view, the present study investigates the dynamic thermal performance of an innovative cool polyurethane-based membrane with PCMs inclusion for roofing applications. Such membranes were developed in previous works when the new composite material was characterized in terms of thermal-optical and morphological properties, when integrating PCMs with transition point at 25 °C and 55 °C. In this work, such materials is finally implemented into a roof multilayer structure, and additional experimental tests are carried out in a dedicated environmental simulation chamber, where the thermal performance of the novel lightweight roof stratigraphy is investigated. To this aim, two types of membranes for roofing applications, i.e. the innovative proposed cool membrane and a more traditional dark bitumen membrane, are considered. These two roof configurations are tested with and without the integration of PCMs, with varying the melting temperature range, in two different climate boundary conditions, i.e. Mediterranean climate of Rome, Italy, and Hot desert climate of Abu Dhabi, UAE. Moreover, numerical analysis of the roof thermal behavior is carried out through transient heat transfer calculation. Therefore, the two roof configurations are simulated and compared, in the same selected climate conditions and with varying PCMs.Findings of coupled experimental tests and numerical analysis show that the combination of cool membrane and PCMs with suitable melting temperature range allows to significantly reduce the roof surface temperatures and, therefore, the heat flux through the roof. In detail, results of numerical analysis demonstrate how in Rome the integration of PCMs with melting point around 25 °C and 45 °C in the cool and the dark roof membrane, respectively, has a great effect in reducing the external roof surface temperature. On the contrary, in Abu Dhabi, the configuration allowing the higher inward heat flux reduction is represented by the integration of PCMs with melting point around 35 °C and 55 °C in the cool and dark membrane, respectively. On the other hand, experimental tests show how the inclusion of a PCM layer with melting point around 25 °C and 31 °C under the cool and dark coating membrane, respectively, allows the best thermal performance in both climate conditions. Therefore, this work showed the promising effectiveness of PCMs inclusion to improve the thermal performance of waterproof membranes for roofing applications. However, as demonstrated, the selection of the proper PCM melting temperature should be operated by taking into account not only the climate conditions, but especially the roofing medium and the position in the roof stratigraphy where thermal energy storage materials are integrated. In fact, roof coating thermal behavior is largely influenced by its thermal-optical properties, e.g. solar reflectance and thermal emittance.

Numerical comparison between single PCM and multi-stage PCM based high temperature thermal energy storage for CSP tower plants

This paper is aimed at analyzing the behavior of a packed bed latent heat thermal energy storage system in concentrating solar power (CSP). One way of improving the performance of a latent thermal energy storage system is by implementing the multiple phase change materials (PCMs) design. The behavior of a packed bed latent heat thermal energy storage system at different cases is numerically analyzed. The molten salt is considered for the heat transfer fluid (HTF) with phase change material (PCM) capsules as the filler. In this design, spherical capsules filled with PCMs of different thermo-physical properties are used. The capsules are packed in the bed at different sections based on the PCM melting temperature. The model developed using the Concentric-Dispersion (C-D) equations. The governing equations are solved in MATLAB, and the results obtained are validated against experimental data from the literature. The performance of the systems is calculated. The results show that the three-stage PCMs system with different melting point exhibited the highest energy and exergy efficiency during a charging discharging cycle. Moreover, results show that the three-stage PCMs unit can improve the heat transfer rate greatly and shorten the heat storage time effectively.

Using of phase change materials to enhance the thermal performance of micro channel heat sink

In this paper using of the phase change materials (PCMs) in a micro-channel heat sink (MCHS) is numerically investigated. The air is first used in heat sink and then four phase change materials (paraffin wax, n-eicosane, p116 and RT41) have been used as cooling mediums in different types and different configurations at different ambient temperatures. Constant heat flux is applied on the base of heat sink and mixed (convection and radiation) boundary condition is applied at the top surfaces of heat sink.The results showed that, using of the phase change materials in micro-channels heat sink with different configurations lead to enhance the cooling performance of micro heat sink. The phase change material should be selected according to its melting temperature according to the certain application as different phase change martials caused different values of reduction in heat sink temperature in range of ambient temperature due to difference in melting temperatures of PCMs. The cost of materials depends on the classification of the PCM (organic and inorganic) and quantity of PCMs used in a certain application.

Optimization of solar photovoltaic system integrated with phase change material

The rise in the temperature of photovoltaic (PV) leads to decrease in the solar to electricity conversion efficiency. This paper presents a simulated study to investigate the thermal management of the PV panel using phase change material (PCM). It is found that once the PCM is fully melted, the rate of heat extraction by PCM decreases and, thus, the PV temperature starts increasing rapidly. In literature, the studies related to the performance analysis of the PV-PCM system are available. However, the optimization of the PCM quantity to cool the PV in various operating conditions and solar radiation levels is not available. Thus, it has been carried out in the presented work. The effects of the operating conditions (wind azimuth angle i.e. wind direction, wind velocity, melting temperature of PCM and ambient temperature) on the optimum depth of the PCM container have been analysed. The results show that as wind azimuth angle increases from 0° to 90°, the optimum depth of the PCM container (to maintain the PV at lower temperature) increases from 3.9 cm to 5.3 cm for ∑IT = 5 kWh/m2/day and from 2.4 cm to 3.2 cm for ∑IT = 3 kWh/m2/day for the chosen parameters.

Study of the Thermal Properties and the Fire Performance of Flame Retardant-Organic PCM in Bulk Form.

The implementation of organic phase change materials (PCMs) in several applications such as heating and cooling or building comfort is an important target in thermal energy storage (TES). However, one of the major drawbacks of organic PCMs implementation is flammability. The addition of flame retardants to PCMs or shape-stabilized PCMs is one of the approaches to address this problem and improve their final deployment in the building material sector. In this study, the most common organic PCM, Paraffin RT-21, and fatty acids mixtures of capric acid (CA), myristic acid (MA), and palmitic acid (PA) in bulk, were tested to improve their fire reaction. Several flame retardants, such as ammonium phosphate, melamine phosphate, hydromagnesite, magnesium hydroxide, and aluminum hydroxide, were tested. The properties of the improved PCM with flame retardants were characterized by thermogravimetric analyses (TGA), the dripping test, and differential scanning calorimetry (DSC). The results for the dripping test show that fire retardancy was considerably enhanced by the addition of hydromagnesite (50 wt %) and magnesium hydroxide (50 wt %) in fatty acids mixtures. This will help the final implementation of these enhanced PCMs in building sector. The influence of the addition of flame retardants on the melting enthalpy and temperatures of PCMs has been evaluated.

Mechanical properties of concrete containing beeswax/dammar gum as phase change material for thermal energy storage

This study aims to investigate the mechanical properties of concrete containing phase change materials (PCM). This research begins with the investigation of melting temperature, enthalpy, the thermal conductivity of the phase change materials using the T-history method, followed by preparation of concrete containing PCM, and finally testing of mechanical properties of concrete through compressive strength test. This study used beeswax, tallow, and dammar gum as PCM mixture. From the results of the PCM properties test, shows that the latent heat energy content from beeswax and tallow exhibit an excellent potential to be used as PCM, while dammar gum is benefited in increasing the thermal conductivity of concrete containing PCM. From concrete specimen test containing 10%, 20% and 30% PCM with 7 days and 28 days aged, the results exhibit that the mechanical properties of the concrete decreased along with the increasing of PCM content. The same test also conducted at the PCM melting temperature. Therefore, the concrete compressive strength test conducted at 45 oC. From the test results, the concrete compressive strength decreased about 3–24% of PCM-0% concrete compressive strength. Drastic compressive strength reduction tends to occur in PCM-Tallow concrete mixture. This study concluded that the PCM is potentially useful as a heat energy absorber material in buildings and lightweight concrete rather than construction structures.

Probing the cooling effectiveness of phase change materials on lithium-ion battery thermal response under overcharge condition

Usage of phase change materials (PCM) can help reduce the safety risk during LIB operation. This work investigates the cooling effectiveness of PCM on lithium ion battery operation under overcharge scenario. Combined with adiabatic overcharge tests at 0.1, 0.2, 0.5, 1, 2 current rates (C-rate), the relationship of cell thermal performance and cooling efficacy with C-rates, thermal contact resistance, amount and melting temperature of PCM are analyzed by lumped model. Results indicate steep decline of cooling effectiveness with C-rate increase. Temperature difference between cell and PCM is stable below 1C, however, abrupt hikes are observed at higher C-rates. Effectiveness increase with PCM thickness is also seen up to a critical thickness of 3 mm beyond which minimal change is observed while thermal contact resistance is found to enlarge the temperature difference between cell and PCM during the melting process causing wide variability in cooling effectiveness magnitude. For similar latent heat and density material, low melting temperature PCM exhibits superior cooling characteristics as compared to its high temperature counterpart. The results contribute to enhanced understanding of the thermal performance of PCM and LIB during overcharge process under varying conditions.

An optimal two-bout strategy with phase change material cooling vests to improve comfort in hot environment

Cooling vests incorporating phase change material (PCM) packets are used to improve comfort of workers in hot environments. This work aims to investigate by modeling and experimentation the effect of dividing the working duration into two bouts, where different PCM melting temperatures are used in each bout. An integrated bio-heat and fabric-PCM model predictions of physiological and subjective votes are validated via active human subject testing at hot conditions. A parametric study is performed to select, at two conditions (40°C and 45°C), the optimal PCM melting temperatures of the two bouts that would result with similar thermal comfort and sensation to the optimal single-bout case. The optimal case achieves most reductions in energy use for PCM regeneration, PCM carried weight and material cost.The results of the parametric study showed that heat storage is reduced in the second bout due to wearing the second vest with lower PCM melting temperature, thus thermal comfort and sensation are significantly improved. The optimal case at the 40°C environment uses a vest with 21°C PCMs in the first bout and a vest with 21°C PCMs in the second bout (V21→V21). At 45°C, the optimal case is V18→V10 with significant PCM weight reductions from the reference single bout case by a minimum of 47%. Thus, the issue of extra carried weight that affect metabolism and ease of movement when applying continuous cooling during work have been mitigated by using the two-bout strategy.