**4. Numerical results**

## **4.1 Validation of the numerical model**

This section is devoted to the obtained experimental results and their comparison with experimental data. The validation of the numerical model used in this study was performed by following the temperature changes inside the PCM wall and the melting front states during the charging process. The numerical results were compared with the experimental temperature data recorded in the laboratory during the same period between February 25 and March 13, 2016. **Figure 6** shows the temperature evolution in the vertical plane x = L/2 vs. local time for the low position (a) (y = 1 cm) and the high position (b) (y = 7.5 cm) of the PCM wall. **Figure 6a** shows that the numerical results are quite similar to the experimental measurement. Indeed, the difference between the simulated and the measured values of the temperature at the bottom of PCM is about 0–4°C. It is also seen that in a higher position of PCM wall (**Figure 6b**) the experimental and numerical results of

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*

#### **Figure 6.**

cell temperature, and *hPCM-27* (W/m<sup>2</sup>

*Thermodynamics and Energy Engineering*

Energy input during charging is given by:

PCM-27.

PCM wall area.

where *I* (W/m<sup>2</sup>

processes are given by:

°C) is the heat transfer coefficient of

*Eic* ¼ *I:APCM wall* (17)

) is the

(18)

(19)

(20)

(21)

) is the irradiance intensity of the lamp and *APCM wall* (m<sup>2</sup>

• The energy efficiency of the PCM wall during the charging and the discharging

and *<sup>η</sup><sup>d</sup>* <sup>¼</sup> *ES*

*E*0

<sup>þ</sup> *MPCM*�<sup>27</sup>*:L:* <sup>1</sup> � *Ta*

*Ts* 

*EX*<sup>0</sup>

*Ts* 

*<sup>η</sup><sup>c</sup>* <sup>¼</sup> *<sup>E</sup>*<sup>0</sup> *Eic*

• The overall exergy transferred to the PCM wall is given by [29, 30]:

*T f Ti* 

where *Ta(K)* is the ambient temperature and *Ts(K)* is the temperature of sun.

*EXic* <sup>¼</sup> *<sup>I</sup>:APCM wall:* <sup>1</sup> � *Ta*

• Exergy efficiency of the PCM wall during the thermal storage and the thermal

This section is devoted to the obtained experimental results and their comparison with experimental data. The validation of the numerical model used in this study was performed by following the temperature changes inside the PCM wall and the melting front states during the charging process. The numerical results were compared with the experimental temperature data recorded in the laboratory during the same period between February 25 and March 13, 2016. **Figure 6** shows the temperature evolution in the vertical plane x = L/2 vs. local time for the low position (a) (y = 1 cm) and the high position (b) (y = 7.5 cm) of the PCM wall. **Figure 6a** shows that the numerical results are quite similar to the experimental measurement. Indeed, the difference between the simulated and the measured values of the temperature at the bottom of PCM is about 0–4°C. It is also seen that in a higher position of PCM wall (**Figure 6b**) the experimental and numerical results of

and <sup>Ψ</sup>*<sup>d</sup>* <sup>¼</sup> *ESX*

where E0 is the energy transferred to the PCM wall.

*EX*<sup>0</sup> ¼ *MPCM*�<sup>27</sup>*:CPCM*�<sup>27</sup>*: T <sup>f</sup>* � *Ti*

� *MPCM*�<sup>27</sup>*:Ta:Cp:* ln

discharging are respectively given by:

**4.1 Validation of the numerical model**

**4. Numerical results**

**154**

• Exergy input during the thermal storage is given by [30]:

<sup>Ψ</sup>*<sup>c</sup>* <sup>¼</sup> *EX*<sup>0</sup> *EXic*

*The simulated and the experimental temperature profile inside the PCM wall for two different times: (a) 4000 and (b) 6000 s.*

temperature obtained show an acceptable agreement, of about 0–5°C. It is concluded that the numerical model permits the simulation of the PCM wall thermal behavior with an acceptable accuracy.

#### **4.2 Exploitation of the numerical model**

**Figure 7** shows the variation of the energy and the exergy stored in the PCM wall during storage process. It is found that the recovered energy incessantly increases vs. charging time. It ranges between 95 and 780 W. This variation takes roughly 130 min and then the energy stored reaches a maximum, which value is due to the fact that the test cell temperature also fluctuates that is in the range of 22–24°C (**Figure 7**). On the other hand, it is found that the exergy stored grows with the charging time. However, it is seen that the exergy is lesser than the stored energy. It varies between 50 and 460 W.

**Figure 8** shows the variation of the energy and exergy efficiencies of PCM wall during the charging process. It is seen that the PCM wall performance increases gradually from 10 to 95%. **Figure 9** shows the variation of the energy and exergy efficiencies of PCM wall during the discharging process. It is seen that the PCM wall performance decreases regularly from 100 to 10%. It is found that the energy and exergy efficiencies are more important than the charging process. It is also seen that

**Figure 7.** *Thermal energy and exergy changes during the charging process.*

**Figure 8.**

*Thermal energy and exergy efficiency changes during the storage stage.*

the exergy efficiency is always found to be lower than the energy efficiency, which is due to the consideration of the losses/irreversibility during exergy analysis, which ultimately gives the information about the quality of energy or available energy. On the other hand, the energy efficiency is all about the quantity of energy rather than quality as it does not consider the losses/irreversibility in the analysis. Both the efficiencies are found to be decreasing with increasing loads. This is due to the fact that backup time is inversely proportional to the increase of the heating load.

heated side of the PCM wall acquires heat, causing the temperature increases of the PCM-27. Consequently, a decrease of PCM-27 density was noted, which ascends along the heated PCM wall. At the top of the test cell, the velocity of the fluid is very

*Evolution of the melting front and the velocity fields inside the PCM wall for two different instances ((a) 4000*

important, so the liquid descends along the solid-liquid interface. During its descent, it loses its heat to the cold interface. At the bottom of the interface, the fluid is cold, and the temperature of the melting rate gradients is low. A blocking of the thermal transfers leading to the slowdown of the interface movement occurs in the latter region. In the liquid phase, PCM-27, which is at the top of the field, has a slightly higher temperature than the bottom of the cavity temperature. It is noted that the interface movement forms a contour from the bottom of the cavity, along the heated side to descend on the other side of the PCM wall. It is seen that as convection increases, the melting rate increases in the upper part of the PCM wall.

**Figure 9.**

**Figure 10.**

**157**

*and (b) 6000 s).*

*Thermal energy and exergy efficiency changes during the discharging phase.*

*DOI: http://dx.doi.org/10.5772/intechopen.92557*

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective*

In **Figure 10**, the evolution of the melting front inside the vertical enclosure for two different instances (4000 and 6000 s) is represented. At the beginning of the heating process, the PCM-27 inside the vertical enclosure was in solid phase. Then, we detected the presence of two distinct phases: a liquid phase and a solid phase separated by melting front. It was seen that the ending of the melting process was observed after 6000 s. It is also seen that the liquid in the vicinity of the directly

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*

the exergy efficiency is always found to be lower than the energy efficiency, which is due to the consideration of the losses/irreversibility during exergy analysis, which ultimately gives the information about the quality of energy or available energy. On the other hand, the energy efficiency is all about the quantity of energy rather than quality as it does not consider the losses/irreversibility in the analysis. Both the efficiencies are found to be decreasing with increasing loads. This is due to the fact that backup time is inversely proportional to the increase of the heating load.

**Figure 7.**

**Figure 8.**

**156**

*Thermal energy and exergy changes during the charging process.*

*Thermodynamics and Energy Engineering*

*Thermal energy and exergy efficiency changes during the storage stage.*

In **Figure 10**, the evolution of the melting front inside the vertical enclosure for two different instances (4000 and 6000 s) is represented. At the beginning of the heating process, the PCM-27 inside the vertical enclosure was in solid phase. Then, we detected the presence of two distinct phases: a liquid phase and a solid phase separated by melting front. It was seen that the ending of the melting process was observed after 6000 s. It is also seen that the liquid in the vicinity of the directly

*Evolution of the melting front and the velocity fields inside the PCM wall for two different instances ((a) 4000 and (b) 6000 s).*

heated side of the PCM wall acquires heat, causing the temperature increases of the PCM-27. Consequently, a decrease of PCM-27 density was noted, which ascends along the heated PCM wall. At the top of the test cell, the velocity of the fluid is very important, so the liquid descends along the solid-liquid interface. During its descent, it loses its heat to the cold interface. At the bottom of the interface, the fluid is cold, and the temperature of the melting rate gradients is low. A blocking of the thermal transfers leading to the slowdown of the interface movement occurs in the latter region. In the liquid phase, PCM-27, which is at the top of the field, has a slightly higher temperature than the bottom of the cavity temperature. It is noted that the interface movement forms a contour from the bottom of the cavity, along the heated side to descend on the other side of the PCM wall. It is seen that as convection increases, the melting rate increases in the upper part of the PCM wall.

processes. It acquires the output signals from the thermocouples, digitizes, treats them and then saves the results. Data are directly collected with the help of an interface network between the measurement station and a computer equipped with application software. Storing data is performed with a regular pitch, equal to 60 s, in the form of text file. **Figure 12** shows the entire device and framework. Thirteen T-type copper-constantan thermocouples firstly calibrated with a measurement inaccuracy of 0.2°C were incorporated to PCM wall at the front surface, inside PCM, the back surface and inside the test chamber as shown in **Figure 10**. Between the exchanging plates, thermocouples (T-type) are inserted on both sides of the sample to measure the temperature fields on each side of the PCM wall. The thermocouples were fixed at the front and back surface with strong white tape and

1.05 0.58 1.42 2.22 1530 1710 172.42 300.15

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective*

**Enthalpy of fusion (kJ/kg)**

**Melting temperature (K)**

The experimental investigation was conducted for 14 consecutive days in September 2015 (from 23/09/2015 to 07/10/2015) to evaluate PCM wall performance. The temperature was measured at front surfaces of PCM wall, at back surfaces of PCM wall, inside the PCM and inside the test cell. The method adopted in the investigation consisted of imposing heating flux (lamp of 120 W) on the exposed PCM wall of the test cell. Simultaneous measurements of the temperature variations and heat flux exchanged during charging and discharging processes were accomplished to evaluate the PCM wall thermophysical properties [29, 30]. The experimental test conducted in the laboratory aims to determine the PCM characteristics during the storage phase. The test starts at 9:00 am and continues until the total melting of PCM-27. PCM is initially in the solid state at the ambient temperature of the room, which is about 22°C. Then, the right side of the PCM wall was heated by using a special lamp with a thermal power of about 120 W. The lamp was held at a distance of 10 10<sup>2</sup> m to guarantee the uniformity of heat over the entire PCM wall area. By using the data acquisition system, the temperature variation at the interior of PCM wall during the storage stage was followed. To evaluate the heat

were shielded from direct irradiation.

**Thermal conductivity (W/mK)**

**Table 1.**

**Figure 12.**

**159**

*Experimental device and framework.*

**Heat capacity (kJ/kgK)**

*DOI: http://dx.doi.org/10.5772/intechopen.92557*

**Solid Liquid Solid Liquid Solid Liquid**

*Thermophysical properties PCM-27 [30].*

**Density (kg/m<sup>3</sup> )**

**Figure 11.** *Isothermal and current lines inside the PCM wall for two different instances ((a) 4000 and (b) 6000 s).*

This is explained by the fact that the paraffin in the vicinity of the PCM wall heated side acquires heat, which causes the climb of the upper part with a high speed and then the liquid paraffin descends along the solid-liquid interface.

**Figure 11** shows the thermal and the dynamic behavior of the PCM-27 for two different instances (4000 and 6000 s). It was seen that at the beginning of the melting process, the interface is almost vertical, indicating the predominance of heat transfer by conduction mode. Isotherms remain vertical and parallel. Gradually as the convection increases, the melting rate increases in the upper portion of the interface. Therefore, the PCM-27 in the upper area has a higher temperature than the bottom of the cavity and the isotherms do not remain parallel. It is noted also that these movements are not made of the plate toward the solid–liquid interface. They form an outline by gravity from the bottom of the cavity, along the plate to descend on the other side on the solid-liquid interface.

### **5. Experimental investigation according to Tunisian scenario**

An experimental framework and procedure were accomplished in the laboratory in order to evaluate the PCM wall thermal performances, in particular its capacity to store the heat and to moderate internal test cell temperature. The experimental framework considered for the investigation of the thermal performances of the PCM wall comprises essentially a test cell with the dimensions 0.5 0.5 0.5 m<sup>3</sup> and managed to imitate a test room. Each sides of the test cell have the dimensions: 0.22 m length, 0.22 m width and 0.026 m thickness. One side of the conceived test cell is fixed with a Plexiglas parallelepiped-shaped container with a size of 22 <sup>22</sup> 2.6 mm<sup>3</sup> . The sides of the PCM wall are fixed with the epoxy resin to form a strong bond. Then, the Plexiglas container was field with paraffin-27, which melts at 27°C with a high latent heat storage capacity (about 110 J/g). Upon PCM solidification, a 7 10<sup>2</sup> m free space was left from the top of Plexiglas container to accommodate volume changes and release trapped air during successive melting and solidification phases. A 120-W incandescent lamp is used for heating the exposed side of the PCM wall. The thermophysical properties of the PCM-27 are given in **Table 1**.

Data acquisition is achieved by an autonomous acquisition device controlled by a Lab VIEW program adapted to measure temperature fluctuations during melting

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*


**Table 1.**

This is explained by the fact that the paraffin in the vicinity of the PCM wall heated side acquires heat, which causes the climb of the upper part with a high speed and

*Isothermal and current lines inside the PCM wall for two different instances ((a) 4000 and (b) 6000 s).*

**Figure 11** shows the thermal and the dynamic behavior of the PCM-27 for two different instances (4000 and 6000 s). It was seen that at the beginning of the melting process, the interface is almost vertical, indicating the predominance of heat transfer by conduction mode. Isotherms remain vertical and parallel. Gradually as the convection increases, the melting rate increases in the upper portion of the interface. Therefore, the PCM-27 in the upper area has a higher temperature than the bottom of the cavity and the isotherms do not remain parallel. It is noted also that these movements are not made of the plate toward the solid–liquid interface. They form an outline by gravity from the bottom of the cavity, along the plate to

then the liquid paraffin descends along the solid-liquid interface.

descend on the other side on the solid-liquid interface.

size of 22 <sup>22</sup> 2.6 mm<sup>3</sup>

given in **Table 1**.

**158**

**Figure 11.**

*Thermodynamics and Energy Engineering*

**5. Experimental investigation according to Tunisian scenario**

An experimental framework and procedure were accomplished in the laboratory in order to evaluate the PCM wall thermal performances, in particular its capacity to store the heat and to moderate internal test cell temperature. The experimental framework considered for the investigation of the thermal performances of the PCM wall comprises essentially a test cell with the dimensions 0.5 0.5 0.5 m<sup>3</sup> and managed to imitate a test room. Each sides of the test cell have the dimensions: 0.22 m length, 0.22 m width and 0.026 m thickness. One side of the conceived test cell is fixed with a Plexiglas parallelepiped-shaped container with a

to form a strong bond. Then, the Plexiglas container was field with paraffin-27, which melts at 27°C with a high latent heat storage capacity (about 110 J/g). Upon PCM solidification, a 7 10<sup>2</sup> m free space was left from the top of Plexiglas container to accommodate volume changes and release trapped air during successive melting and solidification phases. A 120-W incandescent lamp is used for heating the exposed side of the PCM wall. The thermophysical properties of the PCM-27 are

Data acquisition is achieved by an autonomous acquisition device controlled by a Lab VIEW program adapted to measure temperature fluctuations during melting

. The sides of the PCM wall are fixed with the epoxy resin

*Thermophysical properties PCM-27 [30].*

processes. It acquires the output signals from the thermocouples, digitizes, treats them and then saves the results. Data are directly collected with the help of an interface network between the measurement station and a computer equipped with application software. Storing data is performed with a regular pitch, equal to 60 s, in the form of text file. **Figure 12** shows the entire device and framework. Thirteen T-type copper-constantan thermocouples firstly calibrated with a measurement inaccuracy of 0.2°C were incorporated to PCM wall at the front surface, inside PCM, the back surface and inside the test chamber as shown in **Figure 10**. Between the exchanging plates, thermocouples (T-type) are inserted on both sides of the sample to measure the temperature fields on each side of the PCM wall. The thermocouples were fixed at the front and back surface with strong white tape and were shielded from direct irradiation.

The experimental investigation was conducted for 14 consecutive days in September 2015 (from 23/09/2015 to 07/10/2015) to evaluate PCM wall performance. The temperature was measured at front surfaces of PCM wall, at back surfaces of PCM wall, inside the PCM and inside the test cell. The method adopted in the investigation consisted of imposing heating flux (lamp of 120 W) on the exposed PCM wall of the test cell. Simultaneous measurements of the temperature variations and heat flux exchanged during charging and discharging processes were accomplished to evaluate the PCM wall thermophysical properties [29, 30]. The experimental test conducted in the laboratory aims to determine the PCM characteristics during the storage phase. The test starts at 9:00 am and continues until the total melting of PCM-27. PCM is initially in the solid state at the ambient temperature of the room, which is about 22°C. Then, the right side of the PCM wall was heated by using a special lamp with a thermal power of about 120 W. The lamp was held at a distance of 10 10<sup>2</sup> m to guarantee the uniformity of heat over the entire PCM wall area. By using the data acquisition system, the temperature variation at the interior of PCM wall during the storage stage was followed. To evaluate the heat

**Figure 12.** *Experimental device and framework.*

exchanged through the PCM wall during the discharge process, the lamp was omitted and then the PCM temperature fields were tracked.

The result of the experimental tests permits the characterization of the PCM wall and the description of the test cell thermal behavior. **Figure 13** shows the temperature evolution of PCM-27 inside the wall during the charging and discharging processes along the vertical axis (x = 10<sup>2</sup> m) (T1, T2, T3 and T4) and along the horizontal axis (y = 7.5 10<sup>2</sup> m) (T5, T6, T7, T8 and T9). It is found that the PCM solidification process during the discharging phase takes more time than the storage stage. This is explained by the formation of a solid layer of paraffin in contact with the PCM wall sides, which make a thermal isolation and consequently slow down the crystallization in the other parts of the wall. It is seen that by the launch of the melting process all temperature profiles grow linearly up to 27°C. This phase corresponds to sensible heat storage in the solid PCM. Then, it is noted that during about 20 min of heating process with the lamp of 120 W all positions confess symmetrical temperature profiles, around 27°C. It is noted that PCM-27 temperature rises rapidly especially in the first 20 min of the melting process, which corresponds to the sensible storage process inside the PCM wall. Then, the PCM-27 temperature varies slowly between 27 and 29°C during the latent heat storage process. After about 40 min of heating by the lamp, the PCM-27 temperature increases to reach 50°C. **Figure 13** shows also that the temperature of thermocouples that are close to the heated side increases rapidly than those of the other sides. During this phase, the storage of heat is achieved by sensible process inside the melt PCM. After the melting process, it is noted that the different vertical positions inside the PCM wall (y = 2, 8, 12 and 18 10<sup>3</sup> m) presented a dissimilarity in the measured temperature. This delay is explained by the trajectory of the melting front of the solid–liquid interface, which merges firstly from the positions located above the PCM wall to the bottom. The duration of this phase varies between 110 and 40 minutes from one position to another according to the thermocouple on-axis position (x = 10<sup>2</sup> m).

found that once the PCM wall is replaced by simple wooden wall the internal

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective*

**Figure 15** shows the temperature variation of the air inside the test cell with and without PCM wall during the discharging phase (cooling). As can be seen, the air temperature inside the test cell is stabilized around 21°C, which represents the ambient temperature, whereas with PCM wall, the air temperature inside the test cell decreases continuously with respect to time from 27 to 22°C. It is also noted that the temperature of the test cell with PCM is always higher than the temperature of the test cell without PCM. This shows the significance of using PCM inside the room and the temperature in the thermal comfort range can be maintained for a long time even with the heating load. Consequently, intruding of the PCM wall in the test cell

To generalize the investigation, a simple room (kid's room) inside a typical modern house (**Figure 16**) in Tunis, Tunisia, is considered. The building is com-

selected room are presented in **Table 2**. This scenario is archived by considering a

. The technical specifications of the

temperature of the test cell grows seriously from 29 to 40°C.

*Evolution of the temperature inside the test cell during the storage phase.*

*DOI: http://dx.doi.org/10.5772/intechopen.92557*

**Figure 14.**

**Figure 15.**

**161**

presents a good potential to be applied for space conditioning.

*Evolution of the temperature inside the test cell during the discharging phase.*

posed of five rooms with a floor area of 128 m<sup>2</sup>

**Figure 14** shows the variation of test cell air temperatures with and without PCM-27. The test was accomplished by exposing the PCM wall to the lamp of 120 W used as a heating load source. It is seen that during the charging phase the temperature profile inside the test cell with PCM wall is almost stable at 29°C. Indeed, the PCM wall permits the storage of the excess of heat supplied by the lamp. It is also

**Figure 13.** *Evolution of PCM temperature during charging and discharging phases.*

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*

#### **Figure 14.**

exchanged through the PCM wall during the discharge process, the lamp was

The result of the experimental tests permits the characterization of the PCM wall and the description of the test cell thermal behavior. **Figure 13** shows the temperature evolution of PCM-27 inside the wall during the charging and discharging processes along the vertical axis (x = 10<sup>2</sup> m) (T1, T2, T3 and T4) and along the horizontal axis (y = 7.5 10<sup>2</sup> m) (T5, T6, T7, T8 and T9). It is found that the PCM solidification process during the discharging phase takes more time than the storage stage. This is explained by the formation of a solid layer of paraffin in contact with the PCM wall sides, which make a thermal isolation and consequently slow down the crystallization in the other parts of the wall. It is seen that by the launch of the melting process all temperature profiles grow linearly up to 27°C. This phase corresponds to sensible heat storage in the solid PCM. Then, it is noted that during about 20 min of heating process with the lamp of 120 W all positions confess symmetrical temperature profiles, around 27°C. It is noted that PCM-27 temperature rises rapidly especially in the first 20 min of the melting process, which corresponds to the sensible storage process inside the PCM wall. Then, the PCM-27 temperature varies slowly between 27 and 29°C during the latent heat storage process. After about 40 min of heating by the lamp, the PCM-27 temperature increases to reach 50°C. **Figure 13** shows also that the temperature of thermocouples that are close to the heated side increases rapidly than those of the other sides. During this phase, the storage of heat is achieved by sensible process inside the melt PCM. After the melting process, it is noted that the different vertical positions inside the PCM wall (y = 2, 8, 12 and 18 10<sup>3</sup> m) presented a dissimilarity in the measured temperature. This delay is explained by the trajectory of the melting front of the solid–liquid interface, which merges firstly from the positions located above the PCM wall to the bottom. The duration of this phase varies between 110 and 40 minutes from one position to another according to the thermocouple on-axis position (x = 10<sup>2</sup> m). **Figure 14** shows the variation of test cell air temperatures with and without PCM-27. The test was accomplished by exposing the PCM wall to the lamp of 120 W used as a heating load source. It is seen that during the charging phase the temperature profile inside the test cell with PCM wall is almost stable at 29°C. Indeed, the PCM wall permits the storage of the excess of heat supplied by the lamp. It is also

omitted and then the PCM temperature fields were tracked.

*Thermodynamics and Energy Engineering*

**Figure 13.**

**160**

*Evolution of PCM temperature during charging and discharging phases.*

*Evolution of the temperature inside the test cell during the storage phase.*

found that once the PCM wall is replaced by simple wooden wall the internal temperature of the test cell grows seriously from 29 to 40°C.

**Figure 15** shows the temperature variation of the air inside the test cell with and without PCM wall during the discharging phase (cooling). As can be seen, the air temperature inside the test cell is stabilized around 21°C, which represents the ambient temperature, whereas with PCM wall, the air temperature inside the test cell decreases continuously with respect to time from 27 to 22°C. It is also noted that the temperature of the test cell with PCM is always higher than the temperature of the test cell without PCM. This shows the significance of using PCM inside the room and the temperature in the thermal comfort range can be maintained for a long time even with the heating load. Consequently, intruding of the PCM wall in the test cell presents a good potential to be applied for space conditioning.

To generalize the investigation, a simple room (kid's room) inside a typical modern house (**Figure 16**) in Tunis, Tunisia, is considered. The building is composed of five rooms with a floor area of 128 m<sup>2</sup> . The technical specifications of the selected room are presented in **Table 2**. This scenario is archived by considering a

**Figure 15.** *Evolution of the temperature inside the test cell during the discharging phase.*

**Figure 16.** *The typical house plan used in this study.*


#### **Table 2.**

*Structure and physical properties of the building structure.*

TRNSYS program. The component of the TRNSYS model is the flat-plate solar collector (type73) used as a heat source, storage tank (type4c) and the building (type 56a). In this section, the integration of the PCM wall in the envelope of a typical Tunisian building is simulated by using TRNSYS. The main TRNSYS component used is Type 399, which models a PCM wall. Type 399 is designed to interact with Type 56a and can simulate a PCM wall located in any position within the tested room. It should be also noted that a new Type 399 models a pure PCM-27 that is assumed to go through its freeze/thaw process at constant temperature, to have a constant specific heat in the liquid phase and to have a constant specific heat in the solid phase. The basic architectural specification of the selected room used in Tunisian scenario is given in **Table 2**.

2015. The outside temperature and the solar irradiation were also evaluated during the same period. During the hottest period of the day, the temperature of the tested room with PCM wall achieves 25°C, while that without PCM wall exceeds 27°C. During the night, the temperature of the tested room, with PCM wall, decreases in the value of 20°C. During the night, the temperatures for the system using the PCM wall become more marked, more of 1°C compared with that of the system without PCM wall. It is seen that the PCM wall performs its function of thermal shock

*Evolution of the ambient temperature inside the kid's room with and without PCM wall application.*

*Evolution of the energy stored in the PCM wall during the discharging phase.*

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective*

*DOI: http://dx.doi.org/10.5772/intechopen.92557*

The objective of this chapter is to show the importance of using PCM as storage material in buildings and to study the thermal potential offered by the integration of a PCM wall to enhance the thermal comfort of the occupant by reducing the thermal fluctuation and by improving the thermal inertia of the buildings' envelop.

Accordingly, an experimental prototype represented by a small-scale home

absorber.

**163**

**Figure 18.**

**Figure 17.**

**6. Conclusion**

**Figure 17** illustrates the evolution of the energy stored and destocked during four days, from January 1 to 4, 2015. During the day, the PCM wall stores a rate of heat brought by the solar collector, and this phase of storage is characterized by positive values of the energy. The latter forms a peak dependent on the period of sunshine and that can reach 1200 kJ m<sup>2</sup> . The heat accumulated during the day by the PCM wall will be restored to be used at the end of the day and during the night.

**Figure 18** illustrates the variation of the temperature inside the selected room with and without integration of PCM wall during the period from January 1 to 4,

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*

#### **Figure 17.**

*Evolution of the energy stored in the PCM wall during the discharging phase.*

**Figure 18.** *Evolution of the ambient temperature inside the kid's room with and without PCM wall application.*

2015. The outside temperature and the solar irradiation were also evaluated during the same period. During the hottest period of the day, the temperature of the tested room with PCM wall achieves 25°C, while that without PCM wall exceeds 27°C. During the night, the temperature of the tested room, with PCM wall, decreases in the value of 20°C. During the night, the temperatures for the system using the PCM wall become more marked, more of 1°C compared with that of the system without PCM wall. It is seen that the PCM wall performs its function of thermal shock absorber.

### **6. Conclusion**

The objective of this chapter is to show the importance of using PCM as storage material in buildings and to study the thermal potential offered by the integration of a PCM wall to enhance the thermal comfort of the occupant by reducing the thermal fluctuation and by improving the thermal inertia of the buildings' envelop. Accordingly, an experimental prototype represented by a small-scale home

TRNSYS program. The component of the TRNSYS model is the flat-plate solar collector (type73) used as a heat source, storage tank (type4c) and the building (type 56a). In this section, the integration of the PCM wall in the envelope of a typical Tunisian building is simulated by using TRNSYS. The main TRNSYS component used is Type 399, which models a PCM wall. Type 399 is designed to interact with Type 56a and can simulate a PCM wall located in any position within the tested room. It should be also noted that a new Type 399 models a pure PCM-27 that is assumed to go through its freeze/thaw process at constant temperature, to have a constant specific heat in the liquid phase and to have a constant specific heat in the solid phase. The basic architectural specification of the selected room used in Tuni-

Roof Concrete 0.24 7.56 2400 0.8

**Conductivity (kJ/(h m K))**

> 3.2 7.56 0.75

4.06 0.15

**Density (kg/m<sup>3</sup> )**

> 1800 2400 1200

> 1400 40

**Specific heat (kJ/kg K)**

> 1 0.8 1

> 1 0.8

**Figure 17** illustrates the evolution of the energy stored and destocked during four days, from January 1 to 4, 2015. During the day, the PCM wall stores a rate of heat brought by the solar collector, and this phase of storage is characterized by positive values of the energy. The latter forms a peak dependent on the period of

the PCM wall will be restored to be used at the end of the day and during the night. **Figure 18** illustrates the variation of the temperature inside the selected room with and without integration of PCM wall during the period from January 1 to 4,

. The heat accumulated during the day by

sian scenario is given in **Table 2**.

**Figure 16.**

**Table 2.**

**162**

*The typical house plan used in this study.*

*Thermodynamics and Energy Engineering*

Wall Brick

Ground Concretes

**Type Layer Thickness**

Concrete Gypsum

Insulation

*Structure and physical properties of the building structure.*

**(m)**

0.15 0.15 0.05

0.06 0.05

sunshine and that can reach 1200 kJ m<sup>2</sup>

(0.5 0.5 0.5 m3) was conceived in our laboratory. The test cell was equipped with a PCM-27 vertical enclosure placed at one side of the test cell. Several tests were carried out with an experimental setup designed for testing the viability of using PCM wall integrated in building structure. The experimental study was carried out by measuring temperature through the PCM wall. The test cell indoor temperature was also evaluated to appraise the thermal inertia of the wall envelope. During the heating 22 phase, the temperature inside PCM shelter appears constant at about 28°C. But it varied between 29 and 40°C inside the test room without PCM wall.

*T* temperature (K)

*DOI: http://dx.doi.org/10.5772/intechopen.92557*

*h* Enthalpy *t* Time (s)

**Greek symbols**

**Indices**

L cavity width

*ρ* density (kg/m3

s Solid l Liquid fus Fusion eq Equivalent

**Author details**

Majdi Hazami1

**165**

ν kinematic viscosity (m<sup>2</sup>

\*, Farah Mehdaoui<sup>1</sup>

Renato Lazzarin<sup>3</sup> and AmenAllah Guizani<sup>1</sup>

provided the original work is properly cited.

Technopole Borj Cedria, Tunisia

*Ti* inside air temperature (K) *To* outside air temperature (K) *Twi* inside wall temperature (K) *Two* outside wall temperature (K)

(*x, y*) Cartesian coordinates (m)

(u, v) velocity components (m/ss1)

*B* coefficient of thermal expansion μ dynamic viscosity (kg/m sm<sup>1</sup> s1) α Thermal diffusivity coefficient

)

*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective*

/s)

, Hichem Taghouti<sup>2</sup>

1 Laboratory of Thermal Processes, Research Center for Energy Technologies,

2 Department of Electrical Engineering, Laboratory of Analysis, Design and

3 Department of Management and Engineering, University of Padua, Vicenza, Italy

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Systems Control, National Engineering School of Tunis, Tunisia

\*Address all correspondence to: hazamdi321@yahoo.fr

, Marco Noro<sup>3</sup>

,

A numerical simulation based on FORTRAN program was also carried out to interpret the experimental data. The numerical simulation was achieved to solve the energy and the exergy mathematic relations to evaluate the PCM wall performances by determining the melting phase proprieties during the charging and the discharging processes. The numerical study constitutes a preliminary step before construction of cells equipped with such wallboards in order to obtain a certain indoor passive air conditioning and especially to avoid overheating of buildings during summer. The test of the numerical model shows that there is a good agreement between experimental and numerical results. The numerical model was then exploited to evaluate the PCM wall thermal behavior. It was found that the following of the evolution of the melting front, the velocity fields, the isothermal and the current lines shows that the paraffin-27 melting process is more significant in the upper part of the PCM wall.

To generalize the investigation for a typical modern house composed of five rooms with a floor area of 128 m<sup>2</sup> , a TRNSYS program simulation was proposed by considering the Tunisian scenario. The results were presented for a single room equipped with PCM wall. It was seen that during the day, the PCM wall stores a rate of heat that can reach 1200 kJ m<sup>2</sup> . It was found that during the hottest period of the day the temperature of the tested room with PCM wall achieves 25°C, while that without PCM wall exceeds 27°C. During the night, the temperature of the tested room, with PCM wall, is about 20°C. It is seen that the PCM wall performs its function of thermal shock absorber. The investigation showed that the efficiency of PCM wall is remarkable in the control and the reduction of the indoor temperature amplitude in the building.

The results obtained by this investigation are exploited in another new experimental work, which is in progress to optimize the geometric and the physical parameters of the PCM wall according to Tunisian buildings'specificity.

### **Acknowledgements**

The authors would like to thank the Laboratoire des Procédés Thermiques (LPT) and the Centre de Recherches et des Technologies de l'Energie (CRTEn), Tunis, Tunisia, for financially supporting the project and for supplying useful data.

### **Nomenclature**


*Energy Storage in PCM Wall Used in Buildings' Application: Opportunity and Perspective DOI: http://dx.doi.org/10.5772/intechopen.92557*

