3.1. Thermal Performance and Energy Consumption between Construction Types
In this section, we present the simulation results for the four proposed building types built with local materials, and their performance for each of Morocco’s six climatic zones is assessed. The first type of construction (#1) is brick, which is the reference type, the second (#2) is brick with double-walled exterior walls, the third (#3) is clay, and the fourth (#4) is clay with double-walled clay exterior walls. The comparison of the simulation results is presented for the coldest winter week and the warmest summer week during the year for each city (
Table 6). The selection of these weeks is based on the average ambient temperature value per week in every city.
Figure 7 shows the outdoor and indoor temperatures for the four building types during the hottest days of summer and the coldest days of winter for the six cities representing the six climate zones. The figure shows that Rabat and Tangier cities are characterized by a steady ambient temperature with a small amplitude of variation throughout the week. Still, there is a slight temperature rise in Tangier during summer. The other cities show almost the same temperature profile, except for Ifran and Meknes, where the maximum temperature is around 35 °C, while the temperature for Marrakech and Er-Rachidia can reach values higher than 40 °C.
Indeed, as can be noticed from
Figure 7, the indoor air temperatures for the construction type cases #2, #3, and #4 are lower in comparison to the ones for type #1 during the warmest weeks. This decrease, which depends on the weather and the construction material, reaches its maximum during the afternoon. In addition, we can see that the thermal insulation of the exterior walls (type #2) leads to the lowest indoor air temperature in the afternoon and the highest at night and in the morning. Thus, the thermal insulation prevents heat from entering the house while keeping the indoor air warm at night, which shows that the temperature variation per day for type #1 is higher than the one for type #2.
By comparing the air temperature inside the type #3 and #4 buildings to that of type #1, we can notice that the effect of the clay construction is directly observable, especially in the daily peak temperatures. Moreover, for most days, the maximum temperatures recorded in types #3 and #4 remain below those of type #1 and are in the same range as the ones of type #2. From a quantitative point of view, it is observed that the house’s interior temperature for the clay construction for types #3 and #4 is lower compared to the brick construction during hot weeks. This decrease can reach 1.75 °C, 2.32 °C, 2.19 °C, 3.34 °C, 1.84 °C and 2.04 °C for the cities of Rabat, Tangier, Meknes, Ifran, Marrakech and Er-Rachidia, respectively.
Although types #2, #3, and #4 have very similar daytime maximum indoor temperatures, type #2 has a lower temperature than the other two at night, showing that the daily average temperature of this type is lower than the ones of types #3 and #4.
In the same context, we observe that the indoor temperatures for the coastal cities and of the four models are higher than the outdoor temperatures due to the humidity, which is high in these cities. Humidity also plays a significant role in indoor temperature variation because building materials are susceptible to water saturation since thermal conductivity increases with the rate of water saturation [
59].
According to
Table 7, for each investigated site and the winter’s coldest days, the outdoor temperature varies between 6 °C and 17 °C for the two coastal cities, Rabat and Tangier, and in the range of 2 °C to 15 °C, −1 °C to 13 °C, 2 °C to 20 °C and −3 °C to 13 °C for the cities of Meknes, Ifran, Marrakech and Er-Rachidia, respectively (
Figure 7). This variation affects the temperature inside the buildings, where we observe that the amplitude of the variation in the interior temperature in the cities of Rabat, Tangier, Meknes, and Marrakech is between 10 °C and 16 °C. By contrast, in the two coldest cities, Ifran and Er-Rachidia, the temperature inside the buildings can decrease by up to 4 °C.
According to
Figure 7, we can notice that the presence of a material with a high thermal capacity reduces the temperature variations. Indeed, throughout the two weeks, the interior temperature increases and decreases less rapidly (lower slope) in the two types #3 and #4, which contain clay, compared to type #1. This is due to the fact that clay has a heat capacity of about 1042 J/(kg·K), which is higher than that of brick (794 J/(kg·K)). This characteristic is very beneficial during the winter season. In another way, the air added to the building envelope improves the thermal performance of the brick building while reducing the daily thermal amplitude from 6 °C to 2.5 °C. The low thermal conductivity of the air prevents heat from penetrating inside in summer and outside in winter.
To support our findings, a study conducted by Dlimi et al. revealed that adding thermal insulation to a building’s external walls enhances its heat storage capacity and improves its resistance to thermal changes. The building’s high thermal inertia enables it to use and retain solar and internal heat. In contrast, the increased thermal resistance reduces the heat loss, resulting in a rise in temperature and a reduction in energy consumption, particularly in winter [
60].
In this section, the PMV index was proposed to evaluate the human thermal comfort in the building. As discussed above, the thermal sensations experienced by the operating personnel were described with the PMV index according to the requirements of ISO 7730. Based on the measured and calculated environmental data and human factors, the PMV index was determined, and the calculation results are presented in
Figure 8.
Figure 8 shows that the PMV indicator amplitude varies according to the construction type. As can be noticed, the PMV and the internal temperature of the buildings with construction types #3 and #4 are the same in summer, demonstrating a relationship between the two parameters. In fact, since the PMV is an indicator of the thermal sensation of the house’s occupants, if the temperature increases, the environment overheats and people feel more warmth. In other words, the PMV index increases. During the hottest week, the PMV indicator was between 1.1 and 1.8 for building types #2, #3, and #4 in the city of Er-Rachidia. This means the PMV = 2 value, corresponding to the feeling of harmful heat, was not exceeded in the analyzed points. Therefore, the microclimate of the room can be classified as moderate. Yet, for construction type #1, the PMV increases by 2, which means that the indoor climate is warmer. This figure also shows the PMV variation during the coldest period. The PMV values during this period are lower than −1 in all the evaluated cities and for all the proposed construction types, except for the city of Ifran, where they are lower than −2, which means freezing temperatures and high energy consumption for heating in this city.
Figure 9 shows the graphs of the annual energy consumption needed to maintain an ambient temperature in the thermal comfort range, i.e., above 20 °C in winter and below 26 °C in summer. From this figure, we can notice that building type #1 has the highest overall thermal load, which exceeds 194 kWh/m
2/year in Ifran (cold climate) and Er-Rachidia (desert climate), while it is about 160 kWh/m
2/year for Meknes and 120 kWh/m
2/year in Marrakech and Tangier. In contrast, it is nearly 109 kWh/m
2/year in Rabat.
In addition, we can also observe that type #2 requires a remarkably lower thermal load in all climates than type #1. Note that double-wall bricks for exterior walls significantly impact the total annual energy demand due to reducing it by over 20% in comparison with building type #1. Building type #4 reduces as well the energy demand by over 15%. In addition, building type #3 has a slight demand reduction of less than 10% for all the cities.
The effect of the climate on the total energy consumption of the building was clear for the city of Ifran, which is characterized by a short, dry and hot summer and a long, cold winter. This shows the high total energy consumption of this city, especially for heating. Indeed, the total energy needed in type #2 is 169.83 kWh/m2/year, and the energy consumption for heating, which is 146.18 kWh/m2/year, represents 86% of the total consumption. Moreover, for the desert city of Er-Rachidia, which has mild winters and scorching and sunny summers, the total energy consumed by type #2 is 146.94 kWh/m2/year, and the proportion of heating consumption does not exceed 78%, with consumption equal to 115.19 kWh/m2/year. On the other hand, the two coastal cities with a Mediterranean climate represent low energy consumption.
To evaluate the overall energy requirements for heating and cooling in a building, a total degree days (TDD) coefficient is assessed. The TDD is a comprehensive measure that combines both the heating degree days (HDD) and cooling degree days (CDD), taking into account the temperature variations throughout a specific period. Additionally, the high HDD value of 1630 for Ifran indicates a substantial proportion of its heating consumption. Er-Rachidia ranks second with a TDD value of 2161, accompanied by a high HDD (1241) and CDD (920), indicating a considerable heating consumption percentage. On the other hand, Rabat and Tangier represent the minimum TDD values of 1347 and 1524, respectively.
Based on the above results, the construction material (especially type #2) has a remarkable influence on decreasing the energy consumption by increasing the heat insolation and, thus, the thermal comfort for all the regions. The U-value of this type complies with the requirements of the Réglementation Thermique Marocaine des Constructions (RTCM) for all of Morocco’s climatic zones [
45]. Reducing energy consumption also reduces emissions of carbon dioxide (CO
2) and other gases responsible for global warming. Nevertheless, the energy consumption is still considerable and it should be optimized. For this reason, we have assessed the impact of adding inclined roofs to the proposed building configurations on decreasing the energy consumption and increasing the thermal comfort for the Moroccan climatic zones.
3.2. The Impact of the Roof Incline
Many passive and active methods can be used to improve these buildings’ thermal and energy efficiency. In our study, we will evaluate the impact of a building’s roof pitch on the energy demand and thermal discomfort hours. For this reason, three roof inclination angles, 15°, 30°, and 45° and south directed, are selected for the type #2 construction since it is the one that demonstrates the best performance in the six climate zones studied. In what follows, we will compare the results of these three configurations with those obtained with the horizontal roof. The results show that the temperature inside the building increases with the roof pitch for all the building types studied and in all the six cities. This increase is advantageous in winter because it decreases the heating loads, although it is disadvantageous in summer because it increases the energy consumption of air conditioning. In addition, the temperature increase varies according to the type of building and the time of year. In fact, for the type #2 building, this increase does not exceed 1.2 °C in summer for the three inclination angles. However, in winter, the temperature increases by more than 1 °C for the 30° and 45° tilt angles.
Figure 10 and
Figure 11 represent the temperature variations inside this building during the coldest and warmest weeks and for the different slope angles. As the inclination angle increased, the temperature inside the building increased proportionally. This temperature increase can reach 10% in winter for the coastal cities, 16% for Meknes and Marrakech, and 19% and 22% for Ifran and Er-Rachidia for an inclination angle of 45°. This is mainly due to the concentrated solar flux amount received by the roof in winter. However, this increase does not exceed 5% for all the cities in summer.
Figure 12 shows the influence of the roof pitch angle variation on the total annual energy consumption, which is the sum of the two energy expenditures for heating and cooling in the six studied cities. As can be noticed, building type #2 has the lowest annual energy consumption for all the studied angles in the different cities. In addition, it is clear that the 30° tilt angle represents the most significant reduction in the energy consumption. This reduction differs according to the climate zone. Indeed, the energy consumption values for Rabat city vary between 77.28 kWh/m
2/year and 109.34 kWh/m
2/year, which represents the lowest consumption in comparison to the other climatic areas. When this value is compared to the base case (horizontal roof), it can be seen that the energy performance is improved by 9.25% with construction type #2 and an inclination angle equal to 30°.
To better analyze the results, we can observe that the heating load ratio to the total energy intensity is 87.64%. While comparing this ratio to the reference case (horizontal roof), the heating load ratio decreases by 13.73%. Similarly, the cooling load ratio increases by 4.5%. Although the heating and cooling load ratio in the overall consumption has the opposite effect, the values of the total energy consumption decreased in comparison to the reference case, in which the energy consumption increased from 0.26 kWh/m2/year to 8.31 kWh/m2/year in terms of cooling, while it decreased from 6.57 kWh/m2/year to 17.45 kWh/m2/year for heating. For Tangier city, we find that the values of the total energy consumption vary between 121.06 kWh/m2/year and 131.15 kWh/m2/year, while for the cities of Meknes, Ifran, Marrakech, and Er-Rachidia, this parameter varies respectively between 110.61 and 153.9 kWh/m2/year; 155.29 and 218.17 kWh/m2/year; 86.61 and 127.33 kWh/m2/year and between 137.04 and 194.67 kWh/m2/year, for the cities mentioned above. Based on these results, the best energy performance—for the reference case—increased by 2.80% with a building with type #2 construction and an inclination angle equal to 15° for the city of Tangier. On the other hand, the energy performance enhancement was obtained for the other cities with an inclination angle equal to 30°. This enhancement is around 8.98%, 8.56%, 9.93%, and 6.73% for the cities of Meknes, Ifran, Marrakech, and Er-Rachidia, respectively.
Regarding the cooling load rate, this parameter increases in all the studied cities, while the heating load decreases as the roof pitch increases, rising the discomfort hours in summer versus a decrease during winter (
Table 8). Indeed, based on the simulation results, we found that the maximum number of hours of discomfort due to cold is recorded in the Ifran city, with several hours between 4279 and 4843 h for the different types of constructions. This represents more than 48% of the total hours in the year and highlights the critical energy consumption for this climate zone due to heating. For Meknes, the number of hours of discomfort is between 3973 h and 4537 h for the different building configurations, as it is between 3494 h and 4059 h for Er-Rachidia. Although Meknes has a high number of hours of discomfort compared to Er-Rachidia, this total number of hours over the year represents more than 28% for Er-Rachidia and it does not exceed 21% for Meknes. This is mainly due to the difference in temperature between day and night, as well as the long days of high temperature for Er-Rachidia, which is characterized by a semi-arid climate. Regarding Rabat, the number of cold discomfort hours is between 3345 and 4047 h, representing more than 38% of the year. As for Tangier and Marrakech, they have the lowest number of hours of discomfort due to cold, which is between 2938 h and 3719 h, a percentage lower than 42% for both cities. This leads to a similar result in the total energy consumption of these two cities. This is quite reasonable since Tangier is characterized by a humid climate (due to its proximity to the sea), especially in winter, which leads to a relatively warm and temperate winter and autumn, so no heating is needed. As for Marrakech, this city is characterized by a semi-desert climate known for a mild winter.
This variation impacts the temperature inside the building, which rises when the roof’s tilt angle increases, resulting in a decrease in the winter heating demand and an increase in the summer cooling demand. Therefore, the amounts of the energy variations (drop and increase) vary depending on the tilt angle. For example, building type #2 in Rabat city can save 6580 Wh/m2/year in heating energy with the 15° tilt angle. This value increases to 11,700 Wh/m2/year with the 30° angle and remains the same with the 45° angle. On the other hand, the cooling demand increases by 1380 Wh/m2/year, 3830 Wh/m2/year, and 6010 Wh/m2/year for the 15°, 30°, and 45° tilt angles, respectively, due to the rise in solar radiation captured by the roof and the increase in solar gains, which increase the indoor temperature. On the other hand, the total energy decreased by 5190 Wh/m2/year for a 15° angle, 7870 Wh/m2/year for a 30° angle, and 5510 Wh/m2/year for a 45° angle. We can see the same remarks for all the building types in all the studied cities, where the roof angle of 30° represents the low heating energy consumption.
In addition, to optimize the total consumption of the building, a southern orientation with a 30° angle of inclination is the ideal configuration in Morocco. This configuration will reduce the annual energy consumption of the buildings. The same results were obtained in a previous study on different roof pitch values ranging from 0° to 45° construction in the town of Er-Rachidia, where the 30° pitch presents the best results for construction in the town of Er-Rachidia [
14].
3.3. Generalization of the Study to the Moroccan Region
In order to present a clear configuration and ensure the visibility of our study results and to generalize our building configuration founding (Type #2) for all of Morocco,
Figure 13 presents the spatial distribution of the annual thermal energy demand across Morocco for an apartment of type #2 with a horizontal roof and another one with a roof inclined with 30° and oriented to the south. The two maps show that the Atlantic and Mediterranean regions, known for their temperate winters, represent the lowest energy consumption in Morocco, while the regions with the coldest winters, such as the city of Ifran and the desert region, represent the highest energy consumption. All the cities also have reduced energy consumption when the roof is inclined. However, this reduction varies from one climatic zone to another depending on their geographical location and climate characterizations. According to the simulation results, the maximum annual thermal energy demand for the type #2 building with a horizontal roof is recorded in Figuig with 188.65 kWh/m
2/year, followed by Ifran with 169.35 kWh/m
2/year and Laanaceur with 142.9 kWh/m
2/year. Conversely, the minimum annual thermal energy demand is found in Sidi Ifni at 12.47 kWh/m
2/year, followed by Tan-Tan at 18 kWh/m
2/year and Agadir at 38.61 kWh/m
2/year. The common point between the above-mentioned cities is their location in climate zone 1.
The construction with a roof slope of 30° toward the south gives very interesting results concerning the cities with latitudes lower than 30° N. We observe an increase in the energy consumption, for example, in the cities of Tan-Tan and Dakhla. At latitude a of 28.26° N and 23° N, the energy demand in these two cities increases, respectively, by 4% and 8%. On the other hand, the cities whose latitude is higher than 30° N experience a decrease in the annual energy demand, and this decrease has a maximum value equal to 20% in the city Sidi-Ifni, whose latitude is close to 30° N.