The optimal allocation of the PCM within a composite wall for surface temperature and heat flux reduction: An experimental Approach

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The optimal allocation of the pcm within a composite wall for surface temperature and heat flux reduction: an...

Article in Applied Thermal Engineering · September 2017

DOI: 10.1016/j.applthermaleng.2017.08.168

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Research Paper

The optimal allocation of the PCM within a composite wall for surface temperature and heat flux reduction: An experimental Approach

Ayoub Gounni ^⇑ , Mustapha El Alami

LPMMAT Lab, Faculty of Sciences Aïn Chock, Hassan II University of Casablanca, Morocco

h i g h l i g h t s

The thermal performance of a PCM layer is studied using cavity at reduced scale.

The PCM layer produced a time delay in heat transfer.

The PCM layer close to the heat source produced lower heat fluxes through cavity walls.

The optimal allocation of the PCM inside the wall is determined experimentally.

a r t i c l e i n f o

Article history:

Received 18 February 2017 Revised 3 August 2017 Accepted 31 August 2017 Available online 1 September 2017

Keywords:

Reduced scale cavity Experimental study PCM allocation Lightweight building

a b s t r a c t

In the objective to enhance the thermal inertia of the light envelopes based on the lightweight materials such as the wood, the integration of the phase change materials in these envelopes is suggested.

However, the critical design challenge is the allocation of the PCM within building walls. In this work, a reduced scale cavity has been built and monitored. Its thermal performance is evaluated in four possible PCM allocations. The cavities at reduced scale provide the flexibility to test most kinds of wall construc- tions in real time and allows for the faster installation and dismantling of the test walls. The use of the cavity at reduced scale concept is demonstrated by evaluating the thermal performance of a thin phase change material (PCM) layer and its allocation inside the wall. The optimal allocation is studied based on the wall surface heat flux and surface temperature reduction. The results show that, first of all, the loca- tion of PCM layer close to the heat source reduces the surface temperature by 2°C and no effect is observed when the PCM layer is placed far from the heat source. Indeed, the allocation PCM/Wood/

PCM/Wood was be selected to be the optimal allocation for its great impact on the surface temperature and heat flux. In this configuration, the maximum surface temperature and peak heat flux are 19,502°C and 37.093 W/m².

Ó2017 Elsevier Ltd. All rights reserved.

1. Introduction

Carbon dioxide is a primary greenhouse gas that contribute to climate change, making it the most factor raising menace to the stability of the world’s economy and lifestyle

[1]. Energy consump-

tion presents the most source of greenhouse gas production; its contribution presents 69% of the total activities that produce greenhouse gases

[2]. In the worldwide scale, the building sector

is the largest contributor to the energy consumption. In morocco, the building sector consumption is projected to be 36% of total energy spending

[3]. In order to reduce the energy demand, the

thermal insulation is proposed for its capacity to increase the total

thermal resistance of walls. However, the wall thickness limitation and the lack of sufficient heat capacity of some insulation materials cannot achieve the desired reduction on the energy consumption

[4]. Indeed, in modern architecture buildings tend to be designed

by using lightweight materials. This kind of construction have a lack of thermal mass which may leads to low comfort and energy efficiency levels

[5].

For this reason, many researchers around the world suggest to integrate phase change material (PCM) into building envelop for its capacity to store the energy coming from exterior environment for later use

[6]. In literature, many papers reviewed the thermal

performance of the PCM incorporated into building envelop. In general, the most previous studies have found that the PCM improves the thermal performance of the building envelop by reducing the peak heat flux, time delay and indoor air temperature fluctuations

[7–11]. Siddiqui et al. [12]

have investigated the

http://dx.doi.org/10.1016/j.applthermaleng.2017.08.168

1359-4311/Ó2017 Elsevier Ltd. All rights reserved.

⇑Corresponding author.

E-mail addresses:[email protected](A. Gounni),[email protected] (M. El Alami).

Contents lists available atScienceDirect

Applied Thermal Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / a p t h e r m e n g

thermal performance of house with two commercially available solid-to-liquid PCM (Micronal) and solid to-solid PCM (DalHSM- 1) and then their thermal performance are compared with com- monly available forms of thermal mass (concrete slab). The novel PCM, 30% DalHSM-1, performs comparably with 20% Micronal for the heating season due to the slightly lower latent heat but showed performance inferior to Micronal PCM for the cooling season.

Indeed, it is seen that the performance of 20% Micronal PCM is comparable to that of a 4-in. concrete slab. Using a simple sol-gel technique, Deng and Yang

[13]

prepared a kind of PEG 8000 hydro- gels as shape-stabilized phase change materials (SSPCMs), and its thermal characteristics are investigated under the modified mass ratio of PEG and water. According to their results, the self- obtained PEG hydrogel displayed an excellent apparent melting temperature of 77

°

C and could remove excess liquid water at high temperature of 70

°

C.

Unfortunately, the most critical design challenge when the PCM is integrated in the building envelop is the incorporation method.

Some authors are highlight the various promising approach to incorporate the PCM into building construction. In the updated review, Zhou et al.

[10]

summarize the techniques on how the PCM is integrated into building envelop. The first one started from traditional methods in which the PCM can be integrated by direct incorporation, immersion or macro-encapsulation. These methods are easy to manipulate. However, the leakage phenomenon is the biggest problem, which is not good for long-term use. Using this method, Wang et al.

[14]

have incorporated a kind of shape- stabilized PCMs into cement mortar to prepare PCMs-brick and then testing the innovative composite-PCM wall in a medium scale thermal chamber under different testing cases. Using the thermal chamber test, their innovative PCM wall proved an excellent heat storage capacity, about 12.7% and 61% higher than that of the com- mon wall in the temperature range of 15–30

°

C and 18–24

°

C respectively. However, after just one month of monitoring, the leakage of paraffin wax is observed which affects the long time thermal performance of this kind of composite PCM wall. To pre- vent the flow and the leakage of the liquid PCM, Chang et al.

[15]

are prepared a macro-packed PCM (MPPCM) containing n- octadecane and then its thermal properties are characterized using a TCi thermal conductivity analyzer and a differential scanning calorimeter (DSC). Furthermore, the hygrothermal performance of the wood-frame structures applied the MPPCM is evaluated using the WUFI (Wäme und Feuchte instationär) program. Their results show that the phase transitions of n-octadecane occurred at 29.76

°

C during heating, their latent heats are 256.5 J/g and the thermal conductivity of the MPPCM was three times higher than that of the unpacked PCM. The hygrothermal analysis shows that the hygrothermal performance of the wood-frame structures applied the MPPCM, which replaced the use of the vapor retarder, is improved. Another incorporation method is the micro- encapsulation, which is the most suitable for thermal energy stor- age of buildings. In fact, this approach provides a valuable solution to overcome the problem of the leaking of the PCM from the sur- face and it is most suitable for PCMs integration in surface layers of building. One problem can be present when the PCM is microen- capsulated, the partial phase change (melting or solidification). To fully melt and solidify the PCM, a proposed method consists to con- tain the PCM in sheets laminated with aluminum, which can be placed longitudinally within the walls; this method is referred as to thermal shield

[11].

When the PCM is microencapsulated in sheets laminated with aluminum the challenge that can be presented is the location of the PCM inside the wall. Without prior study, the researchers place the PCM next to the interior environment within the wall or next to exterior environment. However, the location of the PCM layer can affects its total melting which translate to heat flux reduction.

Recently, the optimal PCM location inside the wall is studied experimentally by Lee et al.

[11]

using two identical test houses.

Their results indicated that, the optimal PCM location is 2.54 cm and 1.27 cm from the wallboard, respectively, for the south and west wall. At these locations, the peak heat flux reductions were 51.3% and 29.7% for the south and the west wall, respectively. Jin et al.

[16]

achieve a reduction of 11% in term of peak heat flux when the PCM is placed in the inward most location next to the internal face of the gypsum wallboard within the wall and there is no impact when the PCM is placed next to the internal face of the outer most layer of the wall. In order to confirm their results, the same authors

[17]

have built a mathematical model of a frame wall outfitted with a PCM layer and successfully validated by the experimental data. The numerical model is used to study the effect of the thickness of PCM layer, its melting temperature, its heat of fusion and the interior surface temperature of the wall on the opti- mal location of the thin PCM layer in the wall for six typical PCM layer locations. It is found that the optimal locations of PCM layer are 1/16 L, 2/16 L, 3/16 L, and 3/16 L when the thicknesses of PCM layer were 1 mm, 2 mm, 5 mm and 7 mm and the relative peak heat flux reductions are 9.48%, 35.91%, 53.99% and 56.11% respec- tively. This occurred because a large PCM layer thickness could absorb more latent heat, and then should be closer to the heat source in order to absorb more heat. The optimal PCM locations are 0/16 L, 3/16 L and 5/16 L and the relative peak heat flux are 31.84%, 53.99% and 53.41% when the melting temperatures of PCM are 25

°

C, 27

°

C and 29

°

C, respectively. This is because when increasing the melting temperature of PCM, its temperature in thermal cycle should also be increased in order to reach its melting transition temperature, therefore, the PCM should be closer to the outdoors (heat source). It is also observed that when increasing the heat of fusion, the optimal PCM location should be closer to the exterior surface of the wall in order to absorb more heat. The opti- mal locations are 1/16 L, 2/16 L and 3/16 L when the heat of fusion was 80 kJ/kg, 179 kJ/kg and 320 kJ/kg, respectively. The effect of the environmental conditions shows that the optimal locations are 4/16 L, 3/16 L and 1/16 L when the interior surface tempera- tures of the wall were 22

°

C, 24

°

C and 26

°

C, respectively. This means that the optimal location of a PCM layer should be closer to the interior surface of the wall in order to release latent heat when the interior surface temperature of the wall increased. To sum up, the optimal PCM location supposed to be close to the exte- rior environment when its specific latent heat, melting tempera- ture and the thickness of PCM layer are increased; however, it is supposed to be close to the interior environment when the interior surface temperature of the wall is increased.

Experiments are generally the most precise studies and have the most conclusive power. However, in the field of building research, the experiments are often more expensive. Moreover, to study the thermal performance of buildings integrated PCM layer, two buildings test are required, one to be used as a reference build- ing (without PCM) and the other for use as a retrofit building (with PCM). In this case, a calibration test prior to any retrofit is needed in order to assure the thermal performance similarities between the two buildings. However, the level of similarities of the thermal performance is difficult to establish in the building at real scale.

Recently, the experimental study of the thermal performance of

an enhanced PCM wall at reduced scale has taken great interest

by the researchers instead of those at real scale. The studies using

cavity at reduced scale have the advantage to (i) create a specific

weather conditions depending on winter or summer season with

different period heating/cooling depending on duration of day

and night; (ii) Using several kind of constructions with different

thicknesses and locations of PCM layer inside the wall without

need to reconstruct the walls; and (iii) it is easy to build and not

expensive compared to the cavities at real scale.

Despite the studies about building PCM walls, there is no study devoted to the best allocation of the PCM fraction with total thick- ness constraint. In this work, the thermal performance of a reduced scale cavity is performed using walls with or without PCM submit- ted to laboratory conditions. To be in accordance with the conclu- sions drawn from the literature review, the PCM used in this study is encapsulated in sheets laminated with aluminum and placed longitudinally within the walls of a reduced scale cavity and then its thermal performance is studied using cavity at reduced scale thermally controlled. The reduced scale cavity allowed us to build two configurations without need to reconstruct the whole build- ing, because its walls are removable and exchangeable. The exper- imental test is performed as follows:

(i) Calibration test of the vertical walls without PCM layer in order to assure the identical thermal performance. This test is approved based on the inside and outside surface walls temperatures.

(ii) Thermal performance of the PCM wall when the layers are inverted: three walls of the cavity are used. The aim is to study the thermal performance of the wall when the PCM and wood layers are inverted. This conclusion leads us to study the optimal PCM allocation inside the wall.

(iii) Thermal performances of the PCM wall under four possible PCM allocation. The comparison is made based on the sur- face temperature and heat flux reduction.

2. Experimental device

A cavity at reduced scale is used to investigate the effects of the PCM on the thermal performance of the cavity walls. The presenta- tion of the PCM layer and its thermal properties are shown in Sec- tion

2.1. The design of the test cell and its characteristics are

described for two configurations and to assure similarities of the thermal behavior of its vertical walls a calibration test of the cavity walls is proposed in Section

2.2. In addition, the operative condi-

tions, namely the imposed inside and outside air cavity tempera- ture are presented in Section

2.3.

2.1. PCM layer

The product used in this work is an organic paraffin and it is composed by copolymer (polyethylene, 40%) and paraffin (60%).

The final form of the composite PCM is a flexible sheet of 5 mm thickness as shown in the

Fig. 1.Table 1

gives the PCM thermal properties.

2.2. Test cell and measurement devices

In this work, the experimental tests are performed using cavity at reduced scale termed here as ‘‘test cell” (Fig. 2). It is composed of removable and exchangeable walls to discuss several configura- tions with or without PCM. The test cell dimensions are 0.4 m 0.4 m 0.4 m.

An incandescent bulb mounted in a black window protection, placed at the center of the test cell equidistant from each wall sur- face, is used as heat source. This later is connected to regulator that is programmed to fix the indoor air temperature in order to simu- late the heat load forced on external wall surfaces exposed to out- door environment in a real scale. The test cell is located in a conditioned laboratory which its temperature is kept at approxi- mately 15–17

°

C. Based on this condition, the interior of the test cell simulates the outdoor environment of the building. However the exterior of the test cell simulates the indoor environment of the building.

The all configurations presented in this study have walls with the same layers number in order to have the same contact number and then the same thermal contact resistance. In addition, the total thickness of the walls is kept constant. In this work, two configura- tions are built:

Configuration 1: The objective of this construction is to study the thermal performance of a wall outfitted with PCM layer compared to a control wall without PCM layer, also, to study the thermal performance of wall when the PCM and wood lay- ers are inverted.

Configuration 2: Four possible allocations of PCM layer inside the walls are constructed.

2.2.1. Construction of the configuration 1

Three walls of the cavity with or without PCM layer are used.

The wall without PCM layer is termed here as control wall, which consists of two wood layers with total thickness of 1.5 cm. The two

Fig. 1.PCM Panel used in this study.

Table 1

Thermal properties of PCM.

Melting temperature 21.7°C–31°C

Latent heat of fusion (0°C–30°C) 70 kJ/kg

Total heat storage capacity (Temperature range 0°C–30°C) 140 kJ/kg

Thermal conductivity (solid phase) 0.18 W/(mK)

Thermal conductivity (liquid phase) /(mK)

Fig. 2.Cavity placed in a controlled local temperature.

walls outfitted with the PCM is termed as PCM walls. The first PCM wall termed as ‘‘PCM1 wall” is consists of 1 cm wood layer and 0.5 cm PCM layer from inside to outside of the test cell. The second PCM wall is referred to as ‘‘PCM2 wall”. In the ‘‘PCM2 wall”, the lay- ers of the ‘‘PCM1 wall” are inverted. It consists of PCM layer fol- lowed by wood layer from inside to outside of the test cell (Fig. 3). The thermal performance comparison of the three walls is conducted based on the outside surface temperature.

2.2.2. Construction of the configuration 2

In this configuration, the four vertical walls are used. We keep the total thickness of the wall constant, and we address the behav- ior of the wall regarding allocation of the total thickness of the

PCM. The PCM layers used in this configuration have 0.5 cm thick- ness and the wood layers have 1 cm thickness. We consider 4 cases presented as shown in

Fig. 4.

2.2.3. Measurement devices

For each wall, the thermocouples are installed on the interior and exterior surfaces and between the wall layers using K-type thermocouples (2/10 mm) with an error of 0.1

°

C. In addition, eight fluxmeters with diameter of 2.54 cm, an accuracy of ±3% and a 0.3 s as response time are installed on the interior and exterior sur- faces to measure the heat fluxes across each wall.

2.2.4. Calibration test of the cavity walls

To assure the identical thermal performance of the four walls without PCM layers, a calibration test of the four walls, each con- sisting of two wood layers, is conducted. As shown in the

Fig. 5,

the inside and outside surface temperatures of the walls without PCM layers are almost identical with a sweet deviation. This agree- ment between the thermal performance of the walls without PCM means that any significant change in the thermal performance of the walls is the result of the PCM layers and its allocation in the walls.

2.3. Operative conditions

The tests were carried out during an one-cycle period in which the heat source inside the test cell is switched ‘‘on” for 12 h and its setpoint is 38

°

C, then switched off for 12 h. To create a tempera- ture difference between the outdoor and indoor environments of the test cell, the outdoor air temperature is kept constant at a low air temperature between 15–17

°

C.

Fig. 6

shows the imposed indoor and outdoor air temperature.

3. Results and discussion

Under the conditions presented in Section

2.3, the two configu-

rations described in the Section

2.2

are studied qualitatively and

Fig. 3.Construction of the walls.

Fig. 4.Allocations studied in this work.

Fig. 5.Exterior and interior surface temperature of the vertical walls with only wood layers during the calibration test.

quantitatively based on the surface temperature and heat flux den- sities across the four walls.

3.1. Thermal performance of the PCM wall when the layers are inverted

In this section, the thermal performance of three walls with or without PCM layer is performed to study the thermal response of wall outfitted with PCM layer compared to wall without PCM layer, also, to study the impact of two PCM locations on surface temper- ature. The composition of the walls was provided in

Fig. 3

above in Section

2.2.1.

Fig. 7

shows the outside surface temperature of the three walls.

First of all, it is observed that the walls outfitted with PCM layer (i.e. ‘PCM1 wall’ and ‘PCM2 wall’) affect the time delay compared to the control wall. This later achieved its peak temperature before the PCM walls. It is also observed that the outside surface temper- ature of the control wall have the similar trend as the ‘PCM1 wall’

in which the PCM layer is placed at the outer surface. At those

walls, the maximum outside surface temperature is about 22.9

°

C as shown in

Table 2. This means that at this location the PCM is

not reached its total melting. However, the ‘PCM2 wall’ in which the PCM layer is close to the heat source reduces, significantly, the outside surface temperature, which is 20.7

°

C (Table 2). This occurred because the PCM layer is in contact with the indoor hot air for which the temperature is around 36

°

C and therefore the PCM occurs a total melting which translates to the outside surface temperature reduction. In fact, the PCM layer occurs a fully melt, when it is placed next to the heat source because, in the heating period, the inside air temperature (i.e. 36

°

C) is almost higher than the interval phase transition temperature (i.e. 21.7

°

C–31

°

C).

Therefore, placing PCM close to the inside environment would increase the PCM temperature in the thermal cycles. In this case, the PCM would reach its interval phase transition temperature, which translates to total PCM melting. However, when the PCM layer is placed far from the heat source, its temperature in the ther- mal cycles does not reach the interval phase transition tempera- ture (i.e. 21.7

°

C–31

°

C) which translates to a partially melt.

Recalling that, in this work, the PCM location where the wall outside surface temperature, caused by the total PCM melting, is at lowest value is referred to as the optimal PCM location. There- fore, the optimal PCM layer could be affected by the phase transi- tion temperature of the PCM and the imposed temperature of the heat source inside the cavity.

Based on this finding, the thermal behavior of the two ‘‘PCM walls” is not the same when the layers are inverted. In the specific conditions of the study, the PCM layer should be placed next to the heat source for more optimal release of the latent heat. It is also concluded that the optimal location of the PCM could be affected by the phase transition temperature and the heat source tempera- ture. Our conclusions are in agreement with the studies done by Jin et al.

[16,17], which have found that the optimal location for the

PCM layer should be closer to the heat source. In their first publi- cation

[16], it is found that the location of the PCM layer near to

the heat source reduces the peak heat flux especially when the imposed maximum surface temperature was at its highest value and no effect when it is placed next to the internal face of the outermost layer of the wall. Under these conclusions, when it is placed close to the heat source, the PCM layer reaches its phase transition temperature and then occurs a fully melt which trans- lates to more reduction on peak heat flux and wall surface temper- ature. In their numerical study

[17], as explained in the

introduction, they concluded that the optimal location of a thin PCM layer in the wall is affected by the thermal properties of PCM and the environmental conditions.

As studied above, the effect on the surface temperature was higher when the PCM layer was placed next to the interior environ- ment. The obtained results encourage us to study the optimal allo- cation of the wall layers containing a PCM sheet. In the next section, four possible allocations with two PCM layers and two wood layers are studied in terms of outside surface temperature and heat flux reduction.

3.2. Optimal PCM allocation

A comparison between four possible allocations of PCM layer is investigated in terms of outside surface temperature and heat flux

Fig. 6.The imposed indoor and outdoor air temperature.

Fig. 7.Temperatures of the external faces, Inversion layers.

Table 2

Maximum outside surface temperature of the control wall and the two PCM walls.

Walls Control wall PCM1 wall PCM2 wall

Maximum outside surface temperature (°C)

22.990 22.932 20.734

reduction. The composition of the vertical walls was provided in

Fig. 4

above in Section

2.2.2.

3.2.1. Outside surface temperature

In order to compare the thermal performance of the four alloca- tions, we evaluate, for a one-cycle period, the outside surface tem- perature. It is shown from

Fig. 8

that the Allocation1 and Allocation3 reduce the outside surface temperatures compared to the other allocations. Their maximum outside surface tempera- tures are 19,502

°

C and 20,401

°

C, respectively, related to the Allo- cation1 and Allocation3 (Table 3). In those allocations, the PCM is next to the heat source and then would melt, totally, as a function of indoor air temperature. Indeed, the Allocation1 reduces about 1

°

C the outside surface temperature compared to the Allocation3.

This occurred because, the PCM, in the Allocation1, is distributed in such a way that it is both close to the heat source and to the out- side environment.

However, when the PCM is placed far from the heat source (i.e.

Allocation2 and Allocation4), it is found that its impact in reducing the outside surface temperature is less. In those allocations, the maximum outside surface temperatures are 21,894

°

C and 22,253

°

C, respectively, related to the Allocation2 and Allocation4 (Table 3). This is because when the PCM layers are in the middle of the wall, the temperature of the PCM is below its melting tem- perature interval during most of the time. This forced the PCM to partially melt which translate to the higher outside surface tem- perature. On the other hand, the Allocation2 reduces approxi- mately 0.4

°

C the outside surface temperature compared to the Allocation4 (Table 3). This is because, in the Allocation2, the PCM layer is near to the heat source. At this location, the PCM reaches a part of its melting temperature interval. The amount of PCM that occurs a melting is higher than that of the Allocation4.

As stated above, when the PCM layer is placed close to the heat source, its impact on the outside surface temperature is higher;

this is the case for the Allocation1 and Allocation3. Indeed, when we compare the allocations in which the PCM layers is distributed and the allocations in which the PCM layers are placed next to each other (i.e. Allocation1 vs Allocation3 and Allocation2 vs Alloca- tion4), it is shown that the allocations in which the PCM is dis- tributed (i.e. Allocation1 and Allocation2) reduce the outside surface temperature compared to the allocations in which the PCM layers are placed next to each other (i.e. Allocation3 and Allo-

cation4). Under those conclusions, the optimal PCM allocation is the allocation in which the PCM layer is close to the heat source and distributed in the wall, this is the case of the Allocation1.

3.2.2. Heat flux reduction

To have a comprehensive understanding about the thermal per- formance of the four allocations, we present in this section, a quan- titative study based on the heat flux across the studied allocations.

Fig. 9

shows the heat flux across the vertical walls. It is clearly seen that when the PCM is placed close to the heat source (i.e. Allo- cation1 and Allocation3), the peak heat flux is reduced. In these Allocations, the PCM layer close to the heat source reaches its melt- ing interval and then melt as a function of temperature. Indeed, the Allocation1 reduces the peak heat flux compared to the Alloca- tion3. Results of the peak heat flux measurements are shown in

Table 4. It is clearly seen that the peak heat flux is reduced the

most in the Allocation1. In this allocation the peak heat flux reaches 37.093 W/m

²

. In the Allocation2 and Allocation4, the peak heat flux is at its highest value about 61,360 W/m

²

and 62,494 W/

m

²

, respectively. These results confirm the thermal profile of the outside surface temperature shown in the

Fig. 8, and then, the opti-

mal PCM allocation is the allocation in which the PCM layer is close to the heat source and distributed in the wall, this is the case of the Allocation1.

Fig. 8.Temperatures of the external faces, Allocation.

Table 3

Peak outside surface temperature of the studied allocations.

Allocations Allocation1 Allocation2 Allocation3 Allocation4 Maximum outside

surface temperature (°C)

19,502 21,894 20,401 22,253

Fig. 9.Heat fluxes across the walls.

Table 4

Peak heat flux of the four allocations.

Allocations Allocation1 Allocation2 Allocation3 Allocation4 Peak heat flux

(W/m²)

37.093 61,360 46,381 62,494

4. Conclusion

The concept of using cavity at reduced scale is introduced via the evaluation of the thermal performance of walls outfitted with a thin PCM layer, encapsulated in sheets laminated with aluminum and placed longitudinally within the walls. Thanks to the walls of the cavity, which are removable and exchangeable, we studied two configurations without need to reconstruct the whole build- ing. Indeed this novel method for testing walls in a reduced scale cavity allowed us to create a cycle of heating on/off which simu- lates the external environment of a real building. In the first part of the paper, it is concluded that the PCM layer affects the time delay compared to the control wall. Indeed, it is observed that the thermal performance of the wall is not the same, when the wood and PCM layers are inverted. The PCM layer reduces the out- side surface temperature by 2

°

C when it is placed close to the heat source compared to when it is placed far from the heat source. It is concluded that, the impact of the PCM layer close to the heat source on the surface temperature reduction is greater. In the sec- ond part of the paper, four allocations of the PCM is studied. It is observed that, for a greater reduction of surface temperature and heat flux, the allocation of the PCM should be as PCM/Wood/

PCM/Wood from the internal to external side for which the PCM layer is close to heat source and distributed in the wall. In this con- figuration, the maximum surface temperature and peak heat flux are 19,502

°

C and 37.093 W/m

²

. The most conclusions of this research paper can be summarized as:

When the PCM was placed next to the interior environment, its impact on the surface temperature was greater and no effect when the PCM layer was placed on the external face of the wall.

It is also concluded that, the optimal PCM location could be affected by the PCM phase transition temperature and the imposed heat source temperature. This conclusion was in agreement with the previous studies of Jin et al.

[16,17].

For more peak heat flux reduction, it is recommended to place the PCM close to the heat source and distributed in the wall, this is the case of the Allocation1 (PCM/Wood/PCM/Wood).

Finally, the optimal allocation for a PCM could be affected by the PCM properties, wall structure and setpoint temperature inside the cavity. As a result, further studies are needed to have a compre- hensive understanding about the optimal allocation of the PCM inside the wall with different PCM properties and set point temper- ature together with different wall structures.

Acknowledgment

Authors acknowledge the financial support provided by IRESEN

‘‘Institut de Recherche en Energie Solaire et Energies Nouvelles”

Morocco.

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