# Evaluation of phase change materials for a light-weight building in Morocco: Effect of building's volume, window orientation & infiltration

Imad Ait Laasri, Niima Es-Sakali, Abdelkader Outzourhit, Mohamed Oualid Mghazli

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## ► To cite this version:

Imad Ait Laasri, Niima Es-Sakali, Abdelkader Outzourhit, Mohamed Oualid Mghazli. Evaluation of phase change materials for a light-weight building in Morocco: Effect of building's volume, window orientation & infiltration. Energy and Built Environment, 2024, 5 (6), pp.863-877. 10.1016/j.enbenv.2023.06.013. hal-05010118

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Submitted on 28 Mar 2025

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# Evaluation of phase change materials for a light-weight building in Morocco: Effect of building's volume, window orientation & infiltration

Imad Ait Laasri<sup>a, c, *</sup>, Niima Es-sakali<sup>b, c</sup>, Abdelkader Outzourhit<sup>a</sup>, Mohamed Oualid Mghazli<sup>c, d</sup>

## ARTICLE INFO

### Keywords:

- Building energy efficiency
- Phase change materials
- Passive thermal regulation

## ABSTRACT

In this study, we will model a light-weight building made of phase change materials (PCMs) to analyze the impact of the building volume, window orientation, and air infiltration on the PCM performance. This is done by calculating the energy savings attained by the use of PCM across all of Morocco. We'll use the commercial Rubitherm panels with RT28HC as a phase change material in this work. Typically, the EnergyPlus simulation engine is chosen to perform the modeling. The impact of building volumes is also evaluated on the PCM activation for light-weight square buildings with different side lengths of 10 m, 9 m, 8 m, and 7 m. Also, we looked at how well the PCM performed in terms of energy savings and thermal regulation at different window orientation placements (south, north, west, and east) and various air infiltration rates (0.5, 1, 1.5, and 3 ACH). This paper's primary objective is to determine the energy savings for the PCM-enhanced building in Morocco, as well as the effect of building volume, window orientation, and infiltration on the PCM capabilities for stabilizing the indoor room temperature. The results show good indoor temperature stabilization during the summer, for the light-weight square building with a south-facing window and no air infiltration. This configuration was able to achieve a total fluctuation reduction of 1303.3 °C for the 10 m building in a semi-arid environment. Besides, a high energy savings percentage of 69.56% was achieved for the PCM-enhanced building with the south-oriented window and air infiltration of 0.5 air change per hour.

## 1. Introduction

Researchers in the past decades, have been very interested in phase change materials (PCMs) because they can provide a small storage volume while having a high energy density [1]. These PCMs help make thermal energy storage (TES) at a nearly constant temperature, which can help in improving indoor thermal comfort [2,3]. This enables the use of the charging and discharging cycles for passive thermal regulation and indoor air temperature stabilization in buildings [4], as well as a significant decrease in the energy usage of HVAC systems [5,6]. Therefore, the use of PCMs in buildings should be assessed to estimate how much energy consumption for cooling and heating is reduced. Even though, the need for cooling is quite more important in Morocco than heating [7]. Nevertheless, it is always important to investigate the effect of PCM on heating energy savings as well. Still, the use of PCMs in buildings requires an encapsulation solution to avoid any leakage. To stop any leakage during phase transition, researchers have put forth a variety of encapsulation techniques over the years such as Macro-encapsulated

PCM [8–12], Shape-stabilized PCMs [13,14], and Micro-encapsulated PCM [15,16], and.

Additionally, the use of macro-encapsulated PCM solutions in walls has been extensively tested and shown to be successful. When integrating PCMs into the interior side of the building's outer walls, the ideal location and placement for the PCM in the building must also be investigated. For a lightweight construction, Lagou et al. [17] conducted a numerical analysis to assess the effects of PCM in three positions: the outer surface, the middle, and the interior surface of the wall. The finite element method based on the software COMSOL Multiphysics was used to carry out this numerical research. The authors demonstrated through the visualization of the probability density function (PDF) for yearly temperatures, that a rather small temperature range distribution was attained for the PCM placed on the interior side of the wall. Although the authors only took into account the wall's conduction, the PCM installed on the interior surface has accomplished the highest room temperature stabilization. Another study in a humid subtropical region for a light-weight building enhanced with PCM that melts at 25 °C was evaluated

<footnote><sup>a</sup> Laboratory (LaMEE), Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakesh, Morocco</footnote>

<footnote><sup>b</sup> Laboratory (LMAID), Rabat National School of Mine, Rabat, Morocco</footnote>

<footnote><sup>c</sup> Green Energy Park (UM6P/IRESEN), km2 R206, Benguerir, Morocco</footnote>

<footnote><sup>d</sup> ENTPE, LTDS UMR CNRS 5513, Université de Lyon, Cedex, Vaulx-en-Velin, France</footnote>

<footnote>* Corresponding author at: Laboratory (LaMEE), Faculty of Sciences Semlalia, Cadi Ayyad University, Marrakesh, Morocco. E-mail addresses: imad.aitlaasri@ced.uca.ma, imadadaitlaasri@gmail.com (I.A. Laasri).</footnote>
## Nomenclature

### Latin symbols

* s: the side length of the square building (m)

* c<sub>p</sub>: specific heat capacity at constant pressure (J.kg<sup>-1</sup>.K<sup>-1</sup>)

* c: space discretization coefficient (-)

* k<sub>w</sub>: thermal conductivity of the interface between the nodes i and i + 1 (W.m<sup>-1</sup>.K<sup>-1</sup>)

* k<sub>E</sub>: thermal conductivity of the interface between the nodes i and i-1 (W.m<sup>-1</sup>.K<sup>-1</sup>)

* T: temperature (K)

* C: thermal mass (kJ.m<sup>-2</sup>.K<sup>-1</sup>)

* k: thermal conductivity (W.m<sup>-1</sup>.K<sup>-1</sup>)

* t: time (s)

* Δt: time step (s)

* Δx: space discretization (m)

### Greek symbols

* ρ: density (kg.m<sup>-3</sup>)

* α: thermal diffusivity (m<sup>2</sup>.s<sup>-1</sup>)

### Subscripts

* n: number of days

* i: space discretization node

* j: time step node

### Acronyms

* ACH: air changes per hour

* AHB: air heat balance

* CondFD: conduction finite difference

* CSM: compact storage modules

* HVAC: heating, ventilation, and air-conditioning

* OSB: oriented strand board

* PCM: phase change material

* PDF: probability density function

* TES: thermal energy storage

* TFR: temperature fluctuation reduction

by Sun et al. [18] for its thermal performance. The results show that the energy savings were impacted by the shift in humidity, indicating that the PCM implementation was highly dependent on humidity. Even so, the energy savings would be considerable and would have a short simple payback period of 16.4 years. Nevertheless, in previous research [19], we have studied the effect of PCM placed on the interior side of the exterior wall envelope for different building parameters. Investigations were conducted on three different building geometries with different external surfaces. These designs were chosen to determine whether adding more CSM panels to the outside wall will increase energy efficiency and stabilize room temperature. The various geometries were chosen while maintaining a constant building volume in each scenario. In addition, the evaluation of the impact of building construction was done simultaneously for light and heavy weight construction types and finally, the effect of different phase change temperatures (22 °C, 25 °C, and 28 °C) was assessed. The results revealed that the square building for a light-weight construction with a PCM that melts at 28 °C showed the highest indoor temperature fluctuation reductions as well as a great passive temperature regulation during summer. In addition, the results also showed that for each PCM with a different melting point, the highest energy savings were achieved with an HVAC setpoint that is equal to the phase change temperature of that PCM.

Nonetheless, there is a lack in the literature for a general-purpose study that evaluates the phase change material's passive thermal regulation and temperature fluctuation reduction depending on the building parameters, such as the assessment of phase change materials performance at different floors, different building volume, as well as the effect

of window orientation placement and building air infiltration. These parameters could affect positively or negatively the passive thermal regulation of PCMs. Many studies in the literature, do consider this, but not in a building with PCM. Hamdaoui et al. [20] evaluated the thermal performance of an office building with intermittent occupancy according to three different construction scenarios. TRNSYS software was used to simulate the six Moroccan cities which represent the country's typical climate zones. The authors have investigated the effects of envelope construction type, air infiltration, and glazing surface. Still, this study did not include phase change materials, thus, we can say that there is a need for studies that include phase change materials and assess their impact on different constructions, glazing, and air infiltration scenarios. Generally, in Morocco, the window-to-wall ratio (WWR) used is around 25% [21], whereas other studies have estimated for buildings located in Marrakech city a WWR range of 16 to 25% [22]. However, there are very few studies for the case of Morocco, that include phase change materials while studying the impact of window orientation placement with a typical window-to-wall ratio. This shows that it is necessary to know which window orientation is impacting positively or negatively the passive thermal regulation of phase change materials in buildings. Yet, the majority of building simulation studies overlook the effects of hysteresis when simulating PCMs [23]. Since the primary goal of this research is to investigate the impact of building volumes, window orientation, and air infiltration, it will also include the hysteresis effect in all the simulations. A hysteresis model for phase transition has already been calibrated for use in the EnergyPlus simulation engine [24]. Thus, to illustrate and assess the PCM's energy savings and passive temperature regulation. We'll utilize probability density function visualizations of indoor air temperature, annual temperature fluctuation reduction, and monthly energy savings.

Therefore, in this paper, we will simulate a 3-story light-weight square building, different scenarios for the building volumes, window orientation placements, and air infiltration rates. A 10 m, 9 m, 8 m, and 7 m light-weight square building with a respective floor height of 3 m, 2.7 m, 2.4 m, and 2.1 m are the four different building volumes that were selected. To preserve a length-to-height ratio all across the various square building volumes, the floor heights were carefully set. As for the window orientation, we will place a simple double-glazed window with WWR of 25% in one of the 4 different directions (south, north, west, and east), to assess the most beneficial orientation. This is done while also assessing the possibility of distributing the WWR on two or more orientations if they can impact positively the passive thermal regulation of phase change materials. Finally, we also study four different air infiltration rates, which are 0.5, 1, 1.5, and 3 ACH. These outdoor air flows are based on the requirements of ASHRAE 66.1 & 66.2. Still, the majority of standards are using 0.5 ACH as the minimum outdoor airflow [25]. Thus, the objective of this paper is to analyze and assess the temperature fluctuation reduction along with the passive thermal regulation of the PCM in all of these scenarios, while taking into consideration the energy savings for cooling and heating. Moreover, the final building configuration including the optimal building volume, window orientation, and infiltration will be simulated in the 12 regions of Morocco. This is done to evaluate the PCM energy savings for cooling and heating in the case of Morocco.

## 2. Methodology

### 2.1. Building, materials & site description

This study will involve a simple square building shown in Fig. 1 with three stories and no windows. This building was chosen because it was found to be the best configuration for a light-weight building with PCM that melts at 28 °C in our previous research [19]. Each building volume has a side length of 10 m, 9 m, 8 m, and 7 m with a respective floor height of 3 m, 2.7 m, 2.4 m, and 2.1 m as shown in Table 1. The resulting respective floor height of 2.1 m is indeed barely respecting the
<table><caption>**Table 1**
Building volumes configuration and properties.</caption><thead><tr><th></th><th>10 × 10 × 3</th><th>9 × 9 × 2.7</th><th>8 × 8 × 2.4</th><th>7 × 7 × 2.1</th></tr></thead><tbody><tr><td>Building inner wall surface area (m2)</td><td>360.00</td><td>291.60</td><td>230.40</td><td>176.40</td></tr><tr><td>Length to height ratio (-)</td><td>3.33</td><td>3.33</td><td>3.33</td><td>3.33</td></tr><tr><td>Mass of PCM (kg)</td><td>2666.67</td><td>2240.00</td><td>1848.89</td><td>1493.33</td></tr><tr><td>The volume of PCM (m3)</td><td>3.6</td><td>2.916</td><td>2.304</td><td>1.764</td></tr></tbody></table>

<table><caption>**Table 2**
Light-weight building construction thermophysical properties.</caption><thead><tr><th>Light-weight<br>Construction</th><th>Materials</th><th>Thickness<br>(m)</th><th>Density<br>(kg/m³)</th><th>Specific heat<br>capacity (J/kg.K)</th><th>Thermal<br>conductivity<br>(W/m.K)</th></tr></thead><tbody><tr><td rowspan="4">Walls<br>[U = 0.501 W/m².K<br>C = 88.4 kJ/m².K]</td><td>Plasterboard (outside)</td><td>0.02</td><td>700</td><td>1000</td><td>0.21</td></tr><tr><td>Mineral wool insulation</td><td>0.05</td><td>100</td><td>1030</td><td>0.04</td></tr><tr><td>OSB</td><td>0.05</td><td>650</td><td>1700</td><td>0.13</td></tr><tr><td>Plasterboard (inside)</td><td>0.02</td><td>700</td><td>1000</td><td>0.21</td></tr><tr><td rowspan="3">Floors, ceilings &amp; roof<br>[U = 0.42 W/m².K<br>C = 134.1 kJ/m².K]</td><td>OSB</td><td>0.06</td><td>650</td><td>1700</td><td>0.13</td></tr><tr><td>Styrofoam insulation</td><td>0.05</td><td>20</td><td>1500</td><td>0.04</td></tr><tr><td>OSB</td><td>0.06</td><td>650</td><td>1700</td><td>0.13</td></tr></tbody></table>

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** The 3D & 2D plan of the light-weight square building.</figcaption></figure>

<table><caption>**Table 3**
Phase change material's thermophysical properties.</caption><thead><tr><th></th><th>Rubitherm<br>PCM 28 [29]</th></tr></thead><tbody><tr><td>Melting temperature range (°C)</td><td>27–29</td></tr><tr><td>Solidification temperature range (°C)</td><td>29–27</td></tr><tr><td>Specific latent heat (kJ/kg)</td><td>250</td></tr><tr><td>Density, solid (kg/m³)</td><td>880</td></tr><tr><td>Density, liquid (kg/m³)</td><td>770</td></tr><tr><td>Specific heat capacity (J/kg.K)</td><td>2000</td></tr><tr><td>Thermal conductivity (W/m.K)</td><td>0.2</td></tr></tbody></table>

architectural standards, nevertheless, it was kept to evaluate the impact of the PCM even outside the box of architectural standards. Also, this is done to keep the length-to-height ratio similar, in order to fairly compare thermal regulation and energy performance, these story heights were altered.

Moreover, after studying the effect of building volume on PCM performance, we will add a double-glazed window with a 12 mm air gap between two 6 mm clear glasses that covers a window-to-wall ratio of 25%. This double-glazed window configuration was chosen as it is one of the most available window constructions in Morocco and it has been studied in the literature for light-weight buildings [26]. The thermal transmittance (U-value) of this window is 2.8 W/m².K with a solar heat gain coefficient of 0.75 and visible transmittance of 0.8. These values were extracted from the Moroccan construction database [27]. This window will be placed in four different orientations: South, North, West, and East. This is done to evaluate the PCM effect on indoor temperature fluctuation reduction, passive thermal regulation, and energy savings. Afterward, the optimal window orientation with the highest PCM activation will be selected for the assessment of air infiltration on the PCM performance. Four different infiltrations rate were chosen 0.5, 1, 1.5, and 3 ACH.

As for the light-weight construction details, the building is made up of two different construction sets, the same construction set is used for the floors, ceilings, and roof. The only construction set that differs is the wall. From the outside of the building to the inside of the building, the wall is made of plasterboard, mineral wool (insulating material), OSB, and plasterboard, each with a thickness of 20 mm, 50 mm, and 20 mm. In addition, OSB, Styrofoam, and OSB with thicknesses of 60 mm, 50 mm, and 60 mm are used to construct the flooring, ceilings, and roof. Table 2 lists the thermophysical characteristics of building con-

struction. Moreover, the U-value and thermal mass (C) are also shown and have been calculated using the equations from our previous work [19]. Besides, The PCM is installed on the inside surface of the building's external walls. This PCM is a paraffin wax (RT 28 HC) that has been enclosed in a Rubitherm commercial CSM panel [28], which has the following measurements: 0.3 m x 0.45 m x 0.015 m. Table 3 lists the thermophysical properties of the PCM used in the CSM panels.

Fig. 2 shows the summary of the effects that will be investigated in this study, besides, the commercial CSM panels are placed on the interior side of the building's exterior walls.

As for the weather data, they are extracted from a local weather station located in Benguerir city in Morocco, this city is within the 'Marrakech-Safi' region. Moreover, this weather station is inside the Green Energy Park research platform. Nevertheless, in this paper, we will conduct an evaluation study on the final selected PCM building with the optimal window orientation and the standard air infiltration in the 12 regions of Morocco shown in Fig. 3. The simulation was conducted for 13 different cities shown as red dots in Fig. 3, the weather data for all regions except 'Marrakech-Safi', were extracted from the software Meteonorm [30].

Fig. 3 demonstrates that only a single city in each region was simulated. Whereas, only in the 'Fes-Meknes' region, two cities were simulated. This is because we initially selected cities with the densest population. Yet, according to the Moroccan thermal regulation [31], there are six climatic zones shown in Table 4. So, we have one missing climatic zone that is not represented by any of the initially selected cities. Thus, we have added the representative city of that missing zone, which is 'Ifrane' located in the 'Fes-Meknes' region with an elevation of 1 665 m. So, we had to simulate two different cities in the same region as we have two different climatic zones in that specific region.
<figure><img src="image_5.png" /><figcaption>Fig. 2. The different effects investigated in this study.</figcaption></figure>

<table><caption>**Table 4**
The climatic zones of Morocco according to the Moroccan thermal regulation [31,32].</caption><thead><tr><th>Climatic Zone</th><th>Zone 1</th><th>Zone 2</th><th>Zone 3</th><th>Zone 4</th><th>Zone 5</th><th>Zone 6</th></tr></thead><tbody><tr><td>Representative City</td><td>Agadir</td><td>Tanger</td><td>Fes</td><td>Ifrane</td><td>Marrakech</td><td>Errachidia</td></tr><tr><td>Region</td><td>Souss-Massa</td><td>Tanger-Tetouan-Al Hoceima</td><td>Fes-Meknes</td><td>Fes-Meknes</td><td>Marrakech-Safi</td><td>Draa-Tafilalet</td></tr><tr><td>Climate Type</td><td>Atlantic</td><td>Mediterranean</td><td>Continental</td><td>Cold</td><td>Semi-arid</td><td>Desert</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Fig. 3. The twelve regions of Morocco and the cities simulated (red dots).</figcaption></figure>

## 2.2. Numerical procedure

The phase change model with hysteresis was applied using the conduction finite difference mode of the simulation program EnergyPlus v22.1. The following equations serve as a representation of PCM modeling in EnergyPlus:

$$c_p \rho \Delta x \frac{(T_{i}^{j+1} - T_{i}^{j})}{\Delta t} = k_{\omega} \frac{(T_{i+1}^{j+1} - T_{i}^{j+1})}{\Delta x} + k_E \frac{(T_{i-1}^{j+1} - T_{i}^{j+1})}{\Delta x} \quad (1)$$

$$k_{\omega} = \frac{(k_{i+1}^{j+1} - k_{i}^{j+1})}{2} \quad (2)$$

$$k_E = \frac{(k_{i-1}^{j+1} - k_{i}^{j+1})}{2} \quad (3)$$

$$\Delta x = \sqrt{c\alpha\Delta t} \quad (4)$$

Eq. (1) illustrates the EnergyPlus fully implicit scheme, which determines the thermal conductivity between nodes through linear interpolation. Eqs. (2) and (3) are used to compute the interpolation of heat conductivity between nodes in the interior and the exterior, respectively. Eq. (4) determines the space discretization in each construction layer, which is determined by the space discretization coefficient (c) and the time step (Δt). Furthermore, several presumptions are made by EnergyPlus’s Air Heat Balance (AHB) algorithm, including:

* Uniform interior air temperature, inner and outer surface temperatures for each thermal zone,

* Long and short radiation waves are equally distributed in space,

* One-dimensional heat transfer occurs through the building’s construction layers (Thermal bridges are neglected).

In this work, the internal heat gains, external shadings, and the reflective properties of CSM panels were not considered to further simplify the simulation of phase change materials in buildings. Furthermore, an Ideal HVAC system was used to obtain energy consumption for cooling and heating with a setpoint of 28 °C. This setpoint was chosen to evaluate the PCM energy savings at its melting temperature as it has shown in previous work that this approach shows the highest energy savings [19]. As for the numerical validation, the numerical model was configured according to the recommendation in the literature [33], with a small space discretization equal to 1 and a small time step equal to 1 min [19].

## 2.3. Key performance indicators for PCM analysis in buildings

Post-processing of the EnergyPlus outputs is done to analyze how well the improved PCM building performs in terms of temperature stabilization and energy savings. For further computations, the monthly energy consumption of the entire building and the annual room temperature on every floor are retrieved. The first factor considered is the
<figure><img src="image_7.png" /><figcaption>Fig. 4. Yearly temperature analysis of the building for different building volumes (a) Temperature fluctuation reduction in all floors; (b) probability density function for the third floor.</figcaption></figure>

annual temperature fluctuation reduction (TFR); to begin, we determine the daily TFR on every floor. This is done by determining the largest temperature variation for each day with and without PCM, then we compare the findings. To estimate the total TFR on every floor, we first acquire the daily TFR and then add it up over the whole year. The formulas used for calculating the total TFR are shown below.

$$TFR_n = (T_{max,n} - T_{min,n})_{Without PCM} - (T_{max,n} - T_{min,n})_{With PCM} \quad (5)$$

$$TFR_{total} = \sum_{1}^{n} TFR_{n} \quad (6)$$

Eq. (6) is used to obtain the annual TFR total, whereas Eq. (5) shows the daily TFR total. Second, we calculate the probability density function (PDF), this is accomplished by doing a statistical analysis of the temperature density for the room temperature in a specific building floor. The floor with the greatest TFR is typically the one we choose. This metric will help us get a comprehensive assessment of the performance of temperature stabilization for the entire year. For both the situation with and without PCM, it is also required to visualize the indoor room temperature during the warmest summer week and the coldest winter week. Finally, for the energy savings evaluation, we simply take the energy consumption for the case without PCM and subtract it from the case with PCM. The energy savings are further computed to give us the energy savings percentage, which is calculated by dividing the energy savings by the energy consumption for the case without PCM.

# 3. Results and discussion

## 3.1. Effect of building volume

### 3.1.1. Building temperature evaluation

The temperature fluctuation reduction (TFR) on each floor is illustrated in Fig. 4(a). The building with the largest TFR is 7 m × 7 m × 2.1 m. In addition, we can conclude that the third floor is always where the highest TFR is found. The interior air temperature variation is a little bit higher and closer to the PCM melting point on the third level since it is exposed to solar radiation. Although not considerable, the reduction in temperature fluctuations can be seen as being roughly the same for all the various building volumes. This is because more CSM panels are used as the building volume expands. As a result, there are more CSM panels available to store and release heat even when the volume is expanded. As a result, the annual variation in temperature is only marginally altered. However, if the CSM panels remained constant, it can be anticipated that the TFR will be maximum for the smallest building volume. It is obvious that the third floor always has the highest TFR, but as was already mentioned, this floor is exposed to more solar and wind energy from its boundaries than the second floor. Yet, the first floor has the lowest TFR, which is to be expected given that it is in contact with the ground and hence receives greater ground-based temperature stabilization. As a result, the temperature inside is slightly stabilized and moved away from the PCM melting point, which diminishes the effectiveness of the CSM panels. Furthermore, in Fig. 4(b) the probability density function on the third floor is presented. The PDF shows a great passive thermal regulation for the case with PCM 28 in all building volumes. However, it has
<figure><img src="image_8.png" /><figcaption>Fig. 5. Indoor air temperature of the third floor in winter for different building volumes.</figcaption></figure>

the same pattern in all the building cases is very similar. Meaning that the building volume has a very low impact on the passive thermal regulation as well as the temperature fluctuation reduction of phase change materials in buildings.

Figs. 5 and 6 display the third floor's interior air temperature for the coldest winter week and the warmest summer week. We notice that the PCM regulation is only effective during the summer, as the PCM melting point in the summer is near to the outdoor conditions compared to the winter period. The indoor air temperatures in winter for the cases with and without PCM are lower than the PCM melting point (28 °C), hence, the CSM panels are ineffective. In order to improve PCM activation all year long, we advise either changing the CSM panels periodically or installing cascaded CSM panels with different melting points. Meaning to place two or three different CSM panel types that contain PCM with various melting points. This will unquestionably have a favorable effect on raising PCM activation levels year-round, which will lead to improved passive temperature regulation. However, additional experimental work in this field is required if we are to create a continuous-active passive thermal regulation system using phase-change materials. Yet, the results with the PCM 28 throughout the summer are quite impressive. Moreover, there is less temperature fluctuation and better stability in the indoor air temperature. Due to the passive CSM panel installation, this is advantageous. As a result, we can use an HVAC system to even further regulate the room temperature with greater energy efficiency.

### 3.1.2. Building energy analysis

Fig. 7 shows the energy savings for cooling and heating in the case of an ideal HVAC system. It was discovered that, except a few months, the

<table><caption>Table 5
Yearly energy savings percentage for different building volumes.</caption><tr><td></td><td>10 × 10 × 3</td><td>9 × 9 × 2.7</td><td>8 × 8 × 2.4</td><td>7 × 7 × 2.1</td></tr><tr><td>Energy savings (%)</td><td>9.97%</td><td>10.05%</td><td>9.94%</td><td>10.11%</td></tr></table>

summertime sees a decrease in the need for cooling as well as heating. This may be caused by the indoor air temperature varying during these months at levels below the range of the PCM melting point. Also, when the building volume expands, more energy is saved. This is because a larger building volume allows for the installation of more CSM panels on the walls, which results in greater energy conservation.

Still, it is apparent in Table 5, that the yearly energy savings is nearly about 10% in all the building volumes. Therefore, we can conclude that the building volumes have nearly no effect on the PCM performance in buildings.

### 3.2. Effect of window orientation

#### 3.2.1. Building temperature evaluation

Fig. 8 shows the temperature fluctuation reduction on all floors and the probability density function on the first floor for all the window orientations. According to Fig. 8(a) the south-oriented window has the highest TFR, which reduces fluctuations by 1303.3 °C in the whole building during the entire year. As for the other orientation, the west-oriented window seems to be also advantageous. However, the north orientation is the worst case, whereas the east is only slightly better compared to the
<figure><img src="image_9.png" /><figcaption>Fig. 6. Indoor air temperature of the third floor in summer for different building volumes.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Fig. 7. Monthly energy savings for different building volumes in terms of (a) Cooling energy consumption; (b) Heating energy consumption.</figcaption></figure>

north. Nevertheless, compared to the previous section without windows, the addition of windows has changed the TFR distribution on different floors. When using windows, the building has the highest TFR on the first floor, and the lowest TFR on the third floor. This means that the TFR distribution has been reversed due to Windows. Since the window is increasing heat gain, the third floor had an advantage without windows because the heat gain was only through the roof, and helped to

shift the indoor temperature near the PCM melting point. However, in the south and west orientations even though the third floor has the lowest TFR, still when compared to the previous section, the temperature fluctuation reduction seems to have improved. On the other hand, the additional heat gain through windows has allowed for the first floor, to further stabilize the temperature. This reversed behavior is mainly due to the sun heating directly, the interior walls on the higher floors
<figure><img src="image_11.png" /><figcaption>**Fig. 8.** Yearly temperature analysis of the building for different window orientations (a) Temperature fluctuation reduction in all floors; (b) probability density function for the first floor.</figcaption></figure>

through the windows, reversely, on lower floors, the sun mainly heats the floor because of the sun's elevation angle. Furthermore, the probability density function in Fig. 8(b) shows that the north window orientation has nearly the same pattern compared to the previous section without windows, with only an increase in the density. However, the south orientation shows a very sharp and narrow thermal regulation.

Figs. 9 and 10 show the indoor temperature in winter's coldest week and in summer's hottest week, respectively. The PCM 28 has again no effect during the winter period, except for a small temperature increase in the south window orientation. However, the indoor air temperature variation has changed depending on the window orientation. Nevertheless, for the summer period, only the north and south orientations show good passive temperature regulations. This is because the north orientation has not affected the building that much, thus, the temperature regulation performance is nearly the same when compared to the previous section without windows. As for the south orientation, it has helped to capture heat gains during the winter period when the sun elevation angle is low, and advantageously in summer, the sun elevation angle is higher. Therefore, there is not a huge temperature regulation drawback. However, the fluctuations have lost a bit of stabilization as in the case with PCM for the south orientation, it is clear that there is a slight temperature fluctuation visible in the summer period compared to the north or the previous section without windows.

### 3.2.2. Building energy analysis

Fig. 11 shows the monthly energy savings in different window orientations for cooling and heating. The south orientation provides good energy savings for cooling but not during the summer months. This is

due to the south orientation having an increased heat gain throughout the whole year, which affects or negatively the cooling energy savings during summer months. As for the PCM energy savings, even though in the previous section the indoor temperature of the first floor only shows a small indoor temperature difference between the case with and without PCM. Nonetheless, the energy savings are evaluated at the whole building, including all three floors, and during the whole month. This implies that even though the PCM is not highly useful in the first week of January, still, when the indoor temperature rises after the coldest week, the PCM starts to activate, which generates energy savings. However, during the summer months, it has a negative impact on cooling energy. Still, the west orientation shows good energy savings for both cooling and heating. Nonetheless, during January, the heating energy savings is negatively impacted for both west and south orientations. This is due to the west direction during this month being more directed toward the sun compared to the south direction and because the building at this step is considered to be air-tight (no infiltration). Therefore, this causes a greenhouse effect which accumulates heat gains without a possible way of escaping the air-tight building. Still, it can be recommended to have buildings with a distributed window-to-wall ratio across the south, east, and even west directions, to take from each orientation its effectiveness on PCM activation. Nevertheless, in the next section air infiltration rate effect will be assessed using the south-oriented window, as it has shown very good results in terms of TFR and PDF. Moreover, the relationship between the negative energy savings and the building's air-tightness will be evaluated as well.

Yet, the results for yearly energy saving percentages in Table 6, show that the east and west orientations have the highest energy saving per-
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Indoor air temperature of the first floor in winter for different window orientations.</figcaption></figure>

<table><caption>**Table 6**

Yearly energy savings percentage for different window orientations.</caption><thead><tr><th></th><th>East</th><th>West</th><th>South</th><th>North</th></tr></thead><tbody><tr><th>Energy savings (%)</th><td>25.36%</td><td>24.66%</td><td>12.73%</td><td>12.52%</td></tr></tbody></table>

percentage of nearly 25%. Thus, it can be recommended to use a mix of east or west window orientation with the south window orientation, to take the positive effect of PCM thermal regulation as well as the PCM energy savings from each configuration.

### 3.3. Effect of building infiltration

#### 3.3.1. Building temperature evaluation

Fig. 12(a) shows the TFR for different air infiltration rates on different floors, based on that the air infiltration has reduced the TFR compared to the previous section. However, the air infiltration has made the TFR slightly constant for the different floors, except for an air infiltration of 1 ACH. The addition of air infiltration in the model will add heat losses or heat gains depending on the season, therefore a balance of heat gains and heat losses are created. Still, according to Fig. 12(b) the air infiltration impact negatively the passive thermal regulation, as the air infiltration increases, the temperature stabilization is lost. This can be seen for an air infiltration of 3 ACH, in which the case with and without PCM has nearly the same probability density function of the indoor air

<table><caption>**Table 7**

Yearly energy savings percentage for different building infiltration rates.</caption><thead><tr><th></th><th>0.5 ACH</th><th>1 ACH</th><th>1.5 ACH</th><th>3 ACH</th></tr></thead><tbody><tr><th>Energy savings (%)</th><td>20.28%</td><td>11.61%</td><td>7.74%</td><td>3.78%</td></tr></tbody></table>

temperature, with only a slight temperature shift, which is caused by the melting point of the PCM 28.

Figs. 13 and 14 show the indoor air temperature during the coldest week in winter and the hottest week in summer, respectively. We still get the same behavior in winter, with PCM 28 having a slight very small to no effect on the indoor air temperature. Nevertheless, during summer it is very clear that the air infiltration rate has a negative effect on indoor temperature fluctuation. Still, the PCM affects decreasing the indoor temperature, however, the temperature stabilization is decreased as the air infiltration increases.

#### 3.3.2. Building energy analysis

Fig. 15 shows the energy savings for different air infiltration rates for cooling and heating. The cooling energy savings are now always positive for all months, when the building has air infiltration, thus eliminating the greenhouse effect. Still, low air infiltration is always desirable, as it shows that energy savings is decreased at high air infiltration rates.

Moreover, in Table 7, we can see the yearly energy saving percentages for different building infiltrations. The highest energy saving per-
<figure><img src="image_13.png" /><figcaption>Fig. 10. Indoor air temperature of the first floor in summer for different window orientations.</figcaption></figure>

<figure><img src="image_14.png" /><figcaption>Fig. 11. Monthly energy savings for different window orientations in terms of (a) Cooling energy consumption; (b) Heating energy consumption.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Fig. 12.** Yearly temperature analysis of the building for different building infiltrations (a) Temperature fluctuation reduction in all floors; (b) probability density function for the second floor.</figcaption></figure>
<figure><img src="image_16.png" /><figcaption>Fig. 13. Indoor air temperature of the second floor in winter for different building infiltrations.</figcaption></figure>
<figure><img src="image_17.png" /><figcaption>Fig. 14. Indoor air temperature of the second floor in summer for different building infiltrations.</figcaption></figure>

<figure><img src="image_18.png" /><figcaption>Fig. 15. Monthly energy savings for different building infiltrations in terms of (a) Cooling energy consumption; (b) Heating energy consumption.</figcaption></figure>

percentage of nearly 20% is achieved by the 0.5 ACH case. This shows that the air infiltration of 0.5 ACH has increased the PCM energy savings when compared to the case without infiltration in the previous section. For that reason, we can say that low air infiltration is desirable for a PCM-enhanced building.

### 3.4. Evaluation of the energy savings for the PCM enhanced building

Fig. 16 shows the cooling energy savings for the 12 regions in Mo- rocco, based on that, the PCM-enhanced building has the lowest energy savings for cooling in Ifrane City (zone 4), which represents the cold
<figure><img src="image_19.png" /><figcaption>**Fig. 16.** Yearly cooling energy savings for the PCM-enhanced building in different regions in Morocco.</figcaption></figure>

<figure><img src="image_20.png" /><figcaption>**Fig. 17.** Yearly heating energy savings for the PCM-enhanced building in different regions in Morocco.</figcaption></figure>

climate. This is a logical pattern. Still, in terms of energy saving percentage, Ifrane City has nearly an energy efficiency of 55.89% when compared to the case without PCM. Moreover, the highest energy saving percentage of 69.56% is observed for the region 'Dakhla-Oued Ed-Dahab', which is represented by the Dakhla city located in the Atlantic climatic zone. Nevertheless, all the other regions have a great energy saving percentage except for the region 'Draa-Tafilalet', which shows a low energy saving percentage of 24.48%. This region is represented by Errachidia City, which is within the desert climatic zone.

Fig. 17 shows the heating energy savings for the 12 regions in Morocco, based on that the PCM-enhanced building has the lowest energy saving for heating in the 'Dakhla-Oued Ed-Dahab' region, which is within the Atlantic climatic zone. However, much higher heating energy savings are achieved for the region 'Souss-Massa'. The city selected for the simulation of this region is Agadir, which is the representative city of the Atlantic climate zone. Therefore, it is very advisable to study as many cities as possible in the same climatic zone. Moreover, the regions 'Fes-Meknes', 'L'Oriental' & 'Tanger-Tetouan-Al Hoceima' shows the best energy savings. Still, the energy savings percentage is very high in all regions except the regions located at the bottom of Morocco. The

accuracy of the spatial data in the regions located at the bottom of Morocco is lower compared to the regions. This is because the number of points covering the regions at the bottom is small, plus the cities selected for these regions are only located in one climatic zone and near the Atlantic Ocean. Nevertheless, the highest energy saving percentage of 15.63% was observed for the region 'Draa-Tafilalet', which is simulated in the city Errachidia that represents the desert climate. Therefore, we can conclude that PCM 28 has slightly good heating energy savings for all climatic zones. Yet, it is always recommended to simulate more cities to further evaluate the PCM heating performance, especially in the Atlantic and desert climate zones, as they have the lowest number of cities representing them. Nonetheless, the heating energy savings are low compared to the cooling energy savings for PCM 28. Thus, we can say that PCM 28 is good for cooling mode operation, nevertheless, the heating mode can be turned off or set at a lower setpoint temperature as it does not have that much heating energy savings percentage, which can imply that there is not much passive thermal regulation benefit in heating mode.

## 4. Conclusions

In this work, we have studied the effect of phase change materials on different building volumes, window orientations, and air infiltration rates for a lightweight square building in a semi-arid climate. This study has evaluated the energy savings, and temperature fluctuation reduction, which was up to 1303.3 °C for the 10 m building with a south window orientation and without air infiltration. Afterward, it was revealed that air infiltration can also be beneficial for the building in terms of energy savings, nonetheless, high infiltration rates can still decrease the PCM performance. Moreover, the final configuration of the building with a south window orientation and 0.5 ACH air infiltration has been used to assess the PCM energy savings in different climatic zones of Morocco. So, the following are the primary conclusions:

(1) The use of PCM on an air-tight building without windows shows great temperature regulation, still, the south orientation with a low infiltration rate can be recommended. Nevertheless, for future work, it is highly advised to study the effect of window-to-wall ratio as well as the thermal and optical properties of the window such as solar heat gain coefficient and visible transmittance on the PCM activation.

(2) The PCM 28 enhanced greatly the temperature stabilization, especially during summer for all the scenarios studied. However, future work should include different PCM with different melting points in different periods, to further enhance the PCM activation throughout the year.

(3) The building volume does not affect the PCM passive temperature regulation, as long as you can fill the increased volume with phase change materials.

(4) The window orientation has a very high effect on PCM passive temperature regulation, however, the implementation of PCM is always beneficial for all window orientations. Still, we recommend the use of a south orientation. Nevertheless, if the building can allow windows at different orientations, we highly suggest combining the south orientation with other orientations such as east or west.

(5) The air infiltration rate has a direct effect on the PCM thermal regulation as well as energy savings. A high air infiltration rate will result in decreased passive thermal regulation by the PCM.

(6) The PCM 28 energy savings for cooling is very high in all the climatic zones, except for desert climates. Nonetheless, heating energy savings are also slightly significant in all climatic zones, except some cities located in the bottom regions of Morocco in the Atlantic climate zone. Still, other cities within the Atlantic climate zone, show good PCM heating energy savings. Therefore, it is recommended for spatial data evaluation studies, to include many cities as possible in each climatic zone.
Moreover, it is also very suggested to study different heating and cooling setpoints instead of having the same setpoint for both heating and cooling, as this may prove to help to prioritize more on the energy savings for cooling or heating depending on the PCM melting point. Furthermore, it is also important to study in future research, the thermal energy storage aspect of PCM-enhanced buildings with a low heating setpoint and a high cooling setpoint.

## Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## CRediT authorship contribution statement

**Imad Ait Laasri:** Conceptualization, Methodology, Investigation, Software, Formal analysis, Data curation, Writing – original draft, Visualization. **Niima Es-sakali:** Investigation, Software, Formal analysis, Data curation, Writing – original draft, Visualization. **Abdelkader Outzourhit:** Writing – review & editing, Investigation, Resources, Supervision. **Mohamed Oualid Mghazli:** Investigation, Writing – review & editing, Resources, Project administration.

## Acknowledgments

The authors are thankful and appreciative of the financial support received from IRESEN (Research Institute for Solar Energy and New Energies, Morocco), CNRST (National Center for Scientific and Technical Research, Morocco), and MESRSI (Ministry of Higher Education, Scientific Research and Innovation, Morocco).

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