Energy, Thermal, and Economic Benefits of Aerogel Glazing Systems for Educational Buildings in Hot Arid Climates

Abstract

The high cost of air conditioning during the summer makes it crucial to develop strategies to reduce energy use in buildings, especially in hot arid climates. Nanomaterial-based external window insulation is considered an effective method for achieving this goal. This research examines the effectiveness of using aerogel-based glazing systems combined with passive design techniques to improve energy efficiency in buildings in hot arid regions. This study presents various scenarios, including building orientation and aspect ratio, utilizing field measurements and energy simulations with aerogel-filled windows. This study is two-phased. The first phase compares two rooms with aerogel and conventional glazing in Aswan. The new glazing system made the room 0.3–1.9 °C cooler. The second phase simulated the Egyptian Japanese School in Aswan to assess the effects of aerogel glazing systems and altering the enclosed semi-open courtyard’s building orientation and aspect ratio. Results show that using aerogel glazing systems and altering the building orientation and aspect ratio can significantly reduce energy consumption and improve indoor thermal comfort. The results reveal that Scenario 1, which represents using aerogel glazing in the northern façade, could reduce the average air temperature between 0.30 and 1.49 °C below the base case (BC). Scenario 3, which used aerogel glazing on the southern facade, reduced annual energy consumption by 26.3% compared to the BC. Meanwhile, Scenario 5, a semi-open courtyard with an aerogel glazing system and an aspect ratio of 2.40, could save 25.7% more energy than Scenario 1. The economic viability of the scenarios was also analyzed using a simple payback period analysis, with Scenario 3 having the second-shortest payback period of 4.13 years. By insulating the exterior panes of windows, this study proposes that adopting aerogel glazing systems can make windows more cost-effective and ecologically sustainable.

1. Introduction

School buildings consume a significant amount of energy all over the world. For instance, the numerous educational institutions in the United Kingdom contribute significantly to the country’s overall high energy consumption among non-industrial energy users [1]. In Egypt, there are around 57,749 existing school buildings, accommodating approximately 24.4 million students, which makes them an essential element of the country’s public building stock [2]. Regarding temperature control and energy efficiency in schools, the classroom is the most fundamental and crucial element. Most children’s daily lives are spent in school, where they may give their full attention to their education. Classrooms are one-of-a-kind and unlike any other built environment because of their increased density. Students generate a lot of sensible and latent heat in the classroom, which must be countered during the warmer months but could help cut costs during the colder months [3]. In a study of 3766 children at 27 schools, researchers found that seven critical design elements accounted for 16% of the difference in students’ academic development [4]. These parameters included comfortable temperatures, enough lighting, low humidity, and high levels of clean air.

On the other side, Egypt’s electricity production has risen from 57.2 billion kilowatt hours in the year 2000 to 183.5 billion kilowatt hours in 2020 [5]. Improved building design, the implementation of energy-efficient technologies, and the enhancement of operations and maintenance are predicted to reduce school energy costs by 20%, according to the United States Department of Energy [6]. Energy efficiency must be taken into account early on in the design process to accurately determine the actual energy balance of educational buildings, improve the quality of the design of ventilation, lighting, and window systems, and choose the best possible parameters for windows in classrooms [7]. Therefore, there is a strong motivation for the education sector to pursue energy efficiency, as schools have more standardized energy consumption and must offer specific high standards of environmental comfort [8]. The cost of heating and cooling a building is directly related to the efficiency of its building envelope [9,10,11,12]. To create buildings that use energy efficiently, it is necessary to properly insulate several different types of contemporary building envelopes. To achieve this goal, it is essential to develop a marketable product [13]. One of the most effective methods for achieving thermal comfort in buildings is using thin insulating materials that allow extensive retrofits to the existing building. This method is less expensive than installing extensive cooling systems or high-tech systems with electro-microsensors to regulate the amount of light, the intensity of the sun’s glare, and the temperature within the building [6].

Regarding energy balance, windows can affect a building’s energy consumption through the amount of heat they gain from the sun or lose through conduction [14]. Researchers have suggested using new insulation materials with low thermal conductivity values to improve a window’s thermal resistance [15]. One promising material for highly energy-efficient windows is aerogel, which has a very low conductivity of around 0.015 W/m² K compared to other insulation materials. Its application in the window and glazing industries has increased the thermal resistance of these elements and has significant potential [16,17,18,19].

Several studies investigate the effect of insulation materials based on nanomaterials to illustrate their impact on the energy demand for lighting, cooling, and heating purposes. Aerogel is a substance with exceptional thermal characteristics; it has traditionally been used as insulating blankets in buildings. It is now also included in window glass systems and other conventional building materials like concretes and plasters. Creating new energy-efficient materials is of the highest priority for the construction technology industry. Products with added aerogels are promising materials for enhancing the thermal resistance of building envelopes [20].

Buratti et al. conducted a study to assess the impact of insulation and different types of glazing on solar gain and cooling load in Iranian schools in hot climates, both humid and dry. They found that using the aerogel glazing system significantly reduced solar gain by 73% and cooling loads by approximately 33% compared to a simple glazed window [21]. Compared to a standard double-glazing window, the aerogel glazing system still resulted in substantial reductions of around 56% and 16%, respectively, for solar gain and cooling consumption.

Other researchers looked at how aerogel glazing, with its significantly lower thermal conductivity, affected energy efficiency. Nanoporous silica aerogel (20–100 nm) materials have various unique properties, including low density (100 kg/m³) and thermal conductivity (0.010–0.023 W/m·K) [22]. They have been successfully integrated into recently introduced aerogel-based insulating products such as flexible blankets [23,24,25]. Aerogels are so called because they are made from gels. Aerogels, despite their name, are not soft and sticky like a gel but rather hard and dry. Their structure is highly porous and transparent [26]. In recent years, three distinct categories of aerogel insulation for buildings have emerged [22]:

• Insulation products that rely solely on the outstanding thermal performance of silica aerogels;
• Monolithic aerogel and translucent or transparent insulating materials based on granular aerogel.

Silica aerogel, whose properties are mentioned and proven in various studies [27,28], has a pore diameter of 1–100 nm (∼20 on average), a tensile strength of 16 kPa, a primary particle diameter of 2–4 nm, and a porosity of about 85–99.9 (typically ∼95). The most often used aerogel for construction, due to its low thermal conductivity (about 0.018–0.020 W/m·K for translucent granular aerogel), low density (around 80 kg/m³), and good optical transparency, aerogel window glazing has been seen as having the most significant potential for improving the thermal performance and daylighting in window glazing systems [27,29,30]. In-field experiments by Franco et al. assessed the thermal and illumination performance of novel glazing systems, including aerogel. According to their research, aerogel can reduce heating energy use by as much as 50% during the winter. It has already been proven to maintain the thermal zone warmer for many days after the heating system has been turned off. Visual tests revealed that the granule reduced the average daily brightness by 10% on clear days [31].

Interspace glazing systems can be used with monolithic or granular aerogels for better thermal resistance and light transmission. Researchers have tried to reduce the thermal conductivity of aerogel down to below 0.010 W/(m·K) by applying different levels of compression on a bed of aerogel with a density of 68 kg/m³ and thermal conductivity of 0.0024 W/(m·K), as described in a study by Neugebauer et al. [32].

Umberto Berardi believes that aerogels will soon dominate building exterior treatments due to manufacturers’ efforts to lower costs. Berardi’s research demonstrated that adding aerogels caused a linear reduction in the thermal conductivity and mechanical strength of concrete and plaster mix. Their study also revealed that incorporating thin aerogel-enhanced products in opaque and transparent envelopes could result in significantly high thermal resistance values, leading to a potential overall energy savings of up to 34% in buildings [20]. As the production costs of aerogels are projected to decrease due to manufacturers’ efforts, the interest in aerogel is expected to grow in the building refurbishment sector in the near future.

Cannavale et al. [33] developed a novel aerogel-based “thermal break” for window frames, compared the performance of this new frame with that of currently used and obsolete frames, and discovered a significantly reduced conductance in the frames and a 27% energy use reduction.

Similarly, Abdelrady et al. [34] evaluated the impact of nanogel glazing and nano-VIPs on the energy performance of a building by comparing several scenarios, including various walls and glass windows in New Aswan City (PS insulation, double glazing, nano-VIPs, and nano-gel glazing). The simulation results for the walls demonstrated that using insulation based on polystyrene foam and nano-VIPs reduces annual energy consumption by 23%. The simulation results for the windows indicated that the best results were achieved when the window glazing system was combined with two layers, one of nanogel and the other of argon, between two layers of transparent glass thickness of 6 mm, saving approximately 26% of energy consumption.

Researchers Yu Huang and Jian-lei Niu analyzed a first-generation silica aerogel window sample. The sample was 25 × 25 cm. After analyzing the sample’s thermal and optical properties, they found that the transmittance of the window sample dropped from 0.8 to around 0.45 after silica aerogel was incorporated. As a bonus, reflectance increased, albeit only a little. U-values of 2.8 W/m² K for the silica aerogel glazing and 3.2 W/m² K for the reference glazing were recorded. This meant that compared to a standard double-layer glazing system, the silica aerogel glazing sample performed better in terms of thermal efficiency [35,36].

Recently published research focused on improving building insulation by using polycarbonate windows with nanogel, resulting in a 14.3% reduction in annual energy consumption in a hot arid climate [37]. According to the authors, the utilization of nanogel, which has a low U-value, was responsible for achieving greater energy savings than double-paned polycarbonate windows. Their study discovered that incorporating a nanogel layer between two argon layers and two polycarbonate panes led to a significant reduction of 29% in annual energy consumption. Furthermore, using the nanogel layer between two argon layers and two single polycarbonate panes resulted in the lowest CO₂ emissions, with a notable improvement of approximately 22.23%.

On the other hand, T. Nguyen et al. [28] created a silica aerogel water-based paste by combining water with ground silica aerogel and certain surfactants. The result of combining this powder with a CaCO₃/TiO₂ paste and an acrylic resin was to create thermal insulation paint. The thermal insulation of silicon aerogel particles added to water-based paint has been enhanced by roughly 1.2 °C. Berardi discusses the lighting and energy simulations on a school building in Massachusetts (US) with the contemporary glazing systems developed using monolithic panels or granular aerogel. The simulations used in the study were based on different window configurations, each featuring monolithic aerogel panels in the cavity. Aerogel windows can be replaced at 40%, 60%, 80%, or 100%. Aerogel was an effective solution in this retrofitting model, with a 40% aerogel case successfully reducing the overly bright sunshine effect and significantly increasing the resistance value [38].

Using a cardboard model of a house, Gaoa et al. compared the performance of traditional clear glass glazing such as specular double-glazing units (DGUs) and diffuse aerogel glazing units (AGUs) for daylight management in the cold climate of Oslo, Norway. To determine AGUs’ viability in energy-efficient construction, they investigated their energy performance, physical attributes, process economics, and environmental impact. According to their findings, these things are valid [24]:

• Promising glazing technology (AGUs) might cut heat loss by up to 58%, translating to a 21% reduction in total energy use (heating, cooling, and lighting);
• For user comfort, AGUs must be able to provide high-quality diffuse light and achieve the best homogenous dispersion of the sun’s glare.

Two different thicknesses of aerogel (10 and 0 mm) were evaluated in windows made of transparent twin-wall polycarbonate sheets filled with granular aerogel and a control panel without aerogel. The results were verified using steady-state calculations performed by M. Dowson et al. The tests revealed that the 10 and 6 mm aerogel panels reduced heat loss by 80% and 74% without obstructing any beneficial sunlight [39]. With the help of a homogenizer, Kim et al. combined silica aerogel with pressure-sensitive adhesives in four distinct silica masses (10, 15, and 20 mass%). The thermal conductivity of a film can be decreased by combining adhesives with silica aerogels adhered to the film. Once silica aerogel (20 mass%) is added, thermal conductivity drops by roughly 32% [40].

Even though nanomaterial-based insulating glazing has been explored in earlier studies, this study presents a novel notion of how to use a technical solution, an advanced nanomaterial-based glazing system, along with various passive climatic solutions such as building orientations and aspect ratios.

This research investigates the potential of using aerogel-based glazing systems in combination with passive design techniques, such as building orientation and aspect ratio, to improve energy efficiency in buildings. The novelty of this research lies in implementing several potential scenarios, categorized into two main categories: building orientation and aspect ratio. Four alternative scenarios (Sc1, Sc2, Sc3, and Sc4) were tested for the north, east, south, and west orientations. Additionally, two scenarios (Sc5 and Sc6) were tested for the aspect ratio of the inside semi-open courtyard. All scenarios were tested using 6 mm thick double-paned windows filled with aerogel granules. In contrast, the base-case scenario (BC) used a single pane of transparent glass 3 mm thick, which is typical for Egyptian schools. This study offers insight into the potential of aerogel-based glazing systems and passive design techniques to reduce energy consumption and improve thermal comfort in buildings.

2. Materials and Methods

There were two significant steps in this study. The first step, as shown in Figure 1, was evaluating the field in two similar rooms with the same geometry built on top of Aswan University buildings. Then, just one room’s window was prepared for aerogel glazing on the construction site. This step aimed to find a low-cost experimental model that can be used to test how aerogel glazing affects the temperature indoors. In the second step, Design-Builder software was used to model and simulate the effect of aerogel glazing on the temperature inside the Egyptian Japanese schools in Aswan city and the amount of energy needed to cool the schools. The main building case study is that of the Egyptian Japanese schools. However, in the first step of this study, the focus is on a room at Aswan University that is being studied, because it costs less to install aerogel glazing on a small scale. Finally, an economic analysis was held to investigate the effect of installing these aerogel glazing systems in the case study model (Egyptian Japanese school), which was simulated in the same step.

2.1. Case Study Area

According to the Köppen–Geiger classification (Köppen-Geiger, 2022), Egypt has a desert hot arid climate, meaning the weather is mostly hot and dry. Aswan is a governorate in the south of Egypt, between the coordinates 24°05′26″ N and 32°53′57″ E. Aswan city is 879 km from Cairo. It is 194 m above sea level and has a governorate area of 34,608 km². The climate in Aswan is hot during the summer and warm in the winter. It is characterized by a continental climate, with an increase in maximum and minimum temperature differences throughout 24 h, regardless of the season. The two places where the study investigation took place are shown in Figure 2. The first was at the Faculty of Engineering at Aswan University. The second phase took place as a case study building at the Egyptian Japanese School.

2.2. Weather Data File

According to the official website of the US Department of Energy, the simulation software incorporates the Aswan climate region’s 2002 Energy Plus Weather (epw) file. These (epw) files are content CSV files with hourly weather data for the study location for a year. A Hobo U30 weather station was put on the roof of the building for the college of engineering in Aswan, Egypt. To make the software work as it would in the real world, the software’s weather data file was replaced with an in situ (2221) weather data file from the weather station [11].

You can obtain the dry-bulb temperature and the relative humidity from the weather station. After changing these settings in a new CSV file, the new CSV file was exported to a new (epw) file and used as input data in the Design-Builder software according to the ASHRAE Guideline 14-2002. The Design-Builder software lets users determine parameters such as cooling energy, window heat gain, temperatures, illuminance, and the annual distribution of daylight in different zones.

2.3. Usage Material, LUMIRA TRANSLISENT LA1000

One of the manufacturers supplied a granular silica aerogel called LUMIRA TRANSLISENT LA1000. In terms of granule diameter, the samples have a particle size range of (0.7–4.0 mm), as displayed in the material datasheet [41], which demonstrates the low thermal conductivity (0.018–0.023 W/m·K), light transmission (>90% per cm), durability, light permeability, and hydrophobic nature of silica aerogel granules. Most prior field investigations were conducted in cold climates, so a window sample was produced to test the thermal and optical qualities of aerogel granules in Aswan City, which represents the hot arid desert regions.

Furthermore, in this section, the study presents experimental results evaluating the changes in interior conditions (including temperature, humidity, and natural lighting) brought about by the addition of granular aerogel between two panes of glass in a building’s exterior wall. Figure 3 depicts the experimental field model used in this study, which consists of two identical standard rooms with dimensions of 3 m in width, 3 m in width, and 3 m in height.

Each room was built from the same materials and oriented in the same direction; they both have a door on the south wall and a set of two-wing aluminum windows in the middle of the north wall.

Table 1. The main characteristics of the two experimental rooms.

Item	Specification
Type	Standard two rooms
Location	Faculty of engineering-Aswan-Egypt
Floor area (m2)	9
Floor height (m)	3
Window dimensions (m)	1.00 × 1.00
Door dimensions (m)	0.90 × 2.20
Wall layers (m)	Outer Cement plaster = 0.02 Inner Brickwork = 0.12
Ceiling (m)	Metal roofing sheet = 0.01 Foam sheet = 0.05 Cement plaster = 0.03

displays the characteristics of the building materials used in Rooms 1 and 2, except for the material used to fill the windows. Referring to Figure 4, the window in room 1 has a total thickness of 18.00 mm (6 mm glass + 6 mm air + 6 mm glass). Similar glazing can be found in Room 2, but 6 mm aerogel granules fill between panes. All other materials and components are identical. The two rooms have 0.12 m brick walls. Each room has one door 0.9 m wide and one double-glazed window 1.00 m wide. P1 and P2 in Figure 4 refer to the windows in Room 1 and Room 2, respectively. Air is the filling material for P1; aerogel granules are the filling material for P2.

Figure 5 shows the processes followed to produce a window sample consisting of a double-glazed window made of clear glass. The area between the panes of glass was then filled with aerogel granules. Using the datasheet for the silica aerogel granule sample, it was determined that its thermal conductivity is about 0.18 W/m K. As shown in Figure 6, the tested material displays very little transparency. This helped let in natural light and reduce glare in the testing room.

For several months and during several seasons of the year, thermal readings were obtained using a HOBO U12 data logger. The data logger is an instrument for recording environmental conditions such as temperature, humidity, and light intensity. Using a Testo 865—Thermal imager (160 × 120 pixels), the apparent surface temperature of the aerogel glazing window was monitored continuously throughout the day.

2.4. The Simulation Process Using Design-Builder

The simulation process was based on an existing educational building model (the Egyptian Japanese School building) in Aswan City in a residential district (El Akkad district). The building was created as a 2D model in AUTOCAD software, then exported for modeling in Design-Builder software licensed version (V.5.0.0.105). Different environmental indicators were obtained with Design-Builder software, represented in results (cooling, temperature, daylight, and illuminance distribution in the classroom) for the case study.

The school building has a ground floor plan and three typical floors and is categorized into two main blocks connected by an interior corridor; each block has two stairs and services. One of these blocks has about six classrooms, while the other includes laboratories, the library, and other service spaces. The simulation focused on one of these blocks: student classrooms.

2.5. Proposed Study Scenarios

Several potential scenarios for the building under study were implemented in the simulation. Two significant categories were employed to generate these concepts. The orientation of the classrooms is the first category. Figure 7 shows four alternative scenarios (Sc1, Sc2, Sc3, and Sc4) for the north, east, south, and west directions, respectively. The second category is the aspect ratio of the inside semi-open courtyard, which resulted in two distinct scenarios (Sc5 and Sc6). These scenarios were tested with 6 mm thick double-paned windows filled with aerogel granules. At the same time, the current base-case scenario (BC) is a single pane of transparent glass 3 mm thick, which is conventional for Egyptian schools. The specifications of the analyzed window scenarios are presented in

Table 2. Investigated scenarios in the simulation process.

	Building Orientation	Aspect Ratio	Glazing Type	U-Value	Light Transmission	Solar Heat Transmission (SHGC)
BC	North	1.2	Sgl Clr 3 mm	5.894	0.898	0.861
SC1	North	1.2	Dbl Clr 6 mm/6 mm Aerogel	2.320	0.671	0.616
SC2	East
SC3	South
SC4	West
SC5	North	2.4
SC6	North	0.6

.

While running simulations, Design-Builder was fed additional input data of alternative hypotheses.

Table 3. Specifications of the school building model.

	Material	Thickness [mm]	U-Value [W/(m2K)]	R-Value [(m2-K)/W]
External wall	- Cement plaster - Brickwork - Cement plaster	20 250 20	1.911	0.523
Internal wall	- Cement plaster - Brickwork - Cement plaster	20 120 20	2.386	0.419
Ceiling	Reinforced concrete slab	200	2.847	0.351

presents the specifications for these hypothetical situations, and

Table 4. Simulation hypothesis input.

Item	Specification
Latitude	23.97
Longitude	32.78
Elevation above sea level (m)	194
Maximum monthly outdoor dry-bulb temperature (°C)	34.82
Minimum monthly outdoor dry-bulb temperature (°C)	15.89
Type	Multi-story educational building
Floor area (m2)	1760
Floor height (m)	3.20
Occupancy (m2/person)	0.41
Open-plan office occupancy schedule	8:00–15:00
Windows	Double-glazed (DG) with aerogel granules filling
Lighting (lux)	300
HVAC	split air conditioner
Cooling setpoint (°C)	25
Heating setpoint (°C)	20
Aerogel granule thermal conductivity coefficient (mW/mK)	18
Aerogel specific heat coefficient (j/kg-k)	1320 [42]

shows the attributes of aerogel granules gleaned from the product datasheet.

3. Results and Discussion

3.1. Field Investigation Results

To compare the performance of the innovative aerogel glazing system with the conventional one, preliminary climatic data were collected in the experimental field room, one with aerogel granules window (case R1) and the other room without aerogel granules window (case R2) from September 2021, the beginning of the school season in Egypt, for eight months until April 2022. As previously stated, R1 and R2 were not environmentally treated and had thin brick walls and a metal roof; as a result, the temperatures inside these rooms were greater than expected under actual conditions. Tests were conducted without any ambient climate treatments to examine the thermal performance without any HVAC system and to emphasize the variations between various weather conditions (sunny and overcast days) in terms of interior air temperature (Temp) and relative humidity (RH). Similar construction in R1 and R2 resulted in the ability to compare test performance under controlled conditions (air temperature and relative humidity). In Figure 8a,b, the monitoring internal air temperatures (Temp) in R1 and R2 are compared on the 22nd of September, a hot, sunny day, and the 6th of December, a cold day. During the study hours of 10:00 a.m. to 5:00 p.m. on the 22nd of September, the interior air temperature in R1 was lower than in R2 by around 0.2 and 1.0 K. During the night, the air temperatures in the two rooms were comparable, with R1 being slightly warmer than R2 (differences between 0.3 and 1.9 K). By witnessing the cold day on the 6th of December, temperature readings for R1 and R2 were collected. During study hours (8:00 a.m. to 5:30 p.m.), temperatures in R1 increased and became warmer than those in R2. On the other hand, the relative humidity (RH) values observed for the 22nd of September in R1 were always greater than those in R2, as shown in Figure 8a. This result is more compatible with previous studies [9,34] and could be attributed to the effect of the granular aerogel’s moisture content. The most significant improvement rates were observed between 10:00 a.m. and 12:00 p.m. RH peak values with the greatest improvement difference were in R1 at 3:00 p.m. RH readings on the 6th of December in R1 were consistently higher than those in R2 in Figure 8b. RH improvement rates were greatest between 02:00 p.m. and 08:00 p.m. RH maximum improvement peak values in R1 were at 2:00 a.m. and 6:00 p.m.

The most significant observation is that the advanced aerogel glazing system could decrease the internal air temperature during warm seasons by reducing heat transfer from the building’s exterior to its interior. During cold seasons, it keeps the interior air temperature warmer than the outside. Considering that the same amount of water vapor results in higher relative humidity in cool air than in warm air, the cooler air temperature in Room 1 during the period between 2:00 a.m. and 6:00 p.m. in the hot seasons causes higher levels of relative humidity compared to the relative humidity in Room 2. During the winter seasons, however, the two investigated rooms’ air temperature dropped significantly due to the climatic conditions outside, resulting in a significant rise in relative humidity.

3.2. Simulation Results

This section contains the simulation results of the proposed cases in an educational building (the Egyptian Japanese School) divided into two categories: (i) thermal analysis and (ii) energy consumption for cooling.

3.2.1. Thermal Analysis

The environmental software (Climate consultant application) indicates that the thermal comfort zone for Aswan residents is between (19.5 °C and 26 °C). To attain thermal comfort and human health, buildings need to be cooled by air conditioning, increasing cooling energy consumption. This section contains the thermal results for building scenarios without air conditioning. The monthly mean air temperature for each scenario illustrated in Figure 9 is based on the simulation findings. The collected data indicate that the mean air temperature in Sc1 is lower than in the BC. The mean air temperature has decreased between 0.30 and 1.49 °C. In contrast, it was observed that the mean air temperature for Sc4 is greater than that of the BC from April to August, albeit by a small value (0.08 to 0.02 °C). Sc2 has a similarly modest impact, with a 0.06° to 0.19 °C monthly temperature increase (May to August).

When comparing the mean air temperature variations from each scenario during the summer, as in Figure 10, the Sc5 scenario with an aspect ratio of 2.4 is the best option compared to the BC. Sc6, which has an aspect ratio of 0.6, is the best scenario for wintertime warming. During the summer, Sc3 (to the south) and Sc1 (to the north) experience almost the same difference in mean air temperatures. Sc4 was the most suitable winter scenario (west orientation).

The findings demonstrate that thermal comfort in Aswan city during winter is achievable under all aerogel scenarios (the middle of October till the middle of March). Therefore, it plays a crucial role in lowering heating demands in the winter. Every potential scenario place Aswan, Egypt, outside its thermal comfort zone during the summer months; nonetheless, these scenarios all lower the building’s mean indoor temperature. For instance, the most significant monthly drop in temperature occurred in July, with readings averaging 5.38 °C cooler than usual. The mean air temperature dropped the most for the Sc5 aspect ratio (=2.4). Sc4, which indicates a westward orientation for classrooms, has the lowest efficiency among the investigated scenarios, reducing temperatures by only 5.38 °C. The other summer months show a similar pattern of behavior, albeit with smaller average decreases.

3.2.2. Energy Consumption for Cooling

This study investigates how different scenarios, including aerogel glazing, affect educational buildings’ energy consumption. The base case model (BC) had a double-glazed window without any thermal insulation in the building envelope. Then, aerogel granules were added in four building orientations (Sc1, Sc2, Sc3, and Sc4). The next step was to look at the effect of the two aspect ratios for the semi-open courtyard on the energy demand for cooling (Sc5 and Sc6).

To investigate their efficiency, six different scenarios were examined using data on cooling energy use. The monthly energy consumption for the cooling load, as presented in Figure 11 results in the school building for each simulated instance. In addition, there has been a discernible increase in the monthly energy requirement for cooling (from April to September).

All the scenarios follow a similar pattern, with findings that can be summarized as follows. Firstly, Figure 11 shows that all analyzed scenarios, except Sc2 and Sc4, significantly reduced annual cooling demand compared to the BC scenario during the summer. However, Sc2 and Sc4 consumed the most energy for cooling compared to the BC scenario, ranging from 980 kWh to 3990 kWh. Secondly, annual cooling consumption for Sc1 decreased by around 23.2%, while Sc3 and Sc5 reduced their annual cooling consumption by approximately 26.3% and 25.7%, respectively, compared to the BC scenario (Figure 12). Thirdly, Sc4 (west orientation) had the smallest impact of all the scenarios, increasing cooling efficiency by just 11.2%, while Sc2 had a cooling efficiency boost of around 13.2%. Fourthly, Sc3, which faced the south side of the building, resulted in the greatest cooling savings ratio and improved the building’s energy efficiency by 72,600 kWh. Finally, in September, Sc3 had the highest rate of improvement in cooling use among all the scenarios, at 8950 kWh.

Insulating nanogel glazing is composed of small silica nanoparticles in a polymer matrix. Nanogels prevent heat transmission due to their high porosity and low thermal conductivity. Nanogel glazing reduces solar radiation entering a building, lowering the demand for air conditioning.

Building orientation and aspect ratio affect nanogel glazing’s ability to reduce cooling energy in hot, arid regions. In a hot, dry climate, a south-facing building receives more solar radiation than a north-facing one. Hence, a south-facing building may benefit more from nanogel glazing than a north-facing one.

Sc3, representing the south-facing building orientation, greatly reduces cooling load and energy consumption in this investigation. Enhanced nanogel glazing lowers heat gain and saves energy in Sc3 due to the building occupancy schedule, which starts at 8:00 a.m. and finishes at 3:00 p.m., the sun path, and the ability to reduce irradiation via these windows in this building orientation. Therefore, installing nanogel glazing in south-facing buildings may save more energy.

These findings are consistent with previous studies that recommend the main glass surface of a building should face south to achieve maximum energy savings [34,43]. On the other hand, the aspect ratio may impact heat gain via windows in hot, dry environments. Buildings with a high aspect ratio (tall and narrow) have lower heat gain through the windows and use less energy (i.e., short and wide). As a result, Sc5 is generally more effective than Sc1 and Sc6.

3.3. The Cost Analysis of the Proposed Aerogel Glazing Scenarios

Multiple efficiency measures were investigated for the energy retrofit of the building. Mainly, the energy improvement intervention on the envelope was carried out, and replacing conventional windows with aerogel glazing windows was investigated for multiple scenarios (building orientations and aspect ratio of the semi-open courtyard), to determine the optimal scenario for energy savings and thermal comfort. According to the previous results, Sc3 is the best for reducing cooling demand, while Sc5 and Sc6 offer excellent thermal conditions. To determine the simple payback period (SPP) of aerogel glazing use versus the energy savings of the three scenarios, these three scenarios and the base case were investigated economically.

The cost of energy consumption for educational building, which falls within the commercial uses of the building sector, was estimated using Egyptian Pounds (EGP) at a rate set by the Egyptian Ministry of Electricity and Renewable Energy [44] for commercial sector buildings, the fifth bracket for the load category of more than 1000 (kWh) is EGP 1.6. The price of each energy category is gradually increased beginning in July of each year. Consequently, the purpose of this study was to evaluate the economic viability of the effect of the aerogel glazing window sample on the amount of cooling energy required by applying the most current electricity pricing.

Several methods were utilized to evaluate the economic viability of the aerogel samples. Some studies employed a simple payback period (SPP) to compare alternative solutions [23,34]. The SPP is a calculation that estimates the time required for a financial investment to be repaid entirely. This approach enables decision-makers to assess various investment opportunities and opt for the most lucrative option that generates maximum profits within the shortest period, assuming the criterion is not crucial.

Table 5. The monetary strategy for the educational building and energy costs and payback time.

	Wall Cost (EGP)	Window Cost (EGP)	Total Cost (EGP)	Additional Investment (EGP)	Energy Cost (EGP/year)	Annual Saving (EGP/year)	SPP (year)
BC	491,625	300,000	791,625	-	441,205.49	-	-
Sc3	491,625	780,000	1,271,625	480,000	325,048.34	116,157.16	4.13
Sc5	473,625	780,000	1,253,625	462,000	327,757.12	113,448.37	4.07
Sc6	527,625	780,000	1,307,625	516,000	356,132.71	85,072.78	6.07

reports the different energy efficiency measures with aerogel-glazing windows proposed in the best three scenarios. The costs of the interventions were based on the local Egyptian market, and the LUMIRA TRANSLISENT LA1000 billing was supplied from an online corporation, the world’s leading online source for aerogel materials. The cost of aerogel granules is USD 55/bottle. The window needs three bottles/m² to fill it.

The facade of the classrooms in the educational building was calculated, and the ratio of the glazing windows in this facade also amounted to 34% of the facade percentage. By comparing the energy-saving costs of the scenarios with the additional investment of the aerogel granules and the annual saving in EGP, the payback period for each scenario was obtained. Additional investment = Case scenario cost difference from the base case = (Sc cost-BC cost). This cost represents the cost of aerogel glazed in the building facade and the cost of the other default construction component (bricks, interior and exterior plastering). The annual energy savings is the difference between energy savings of the renovation scenarios and the energy consumption for the base case. Finally, the value of additional investment divided by annual energy saving is the payback period for each scenario obtained.

$$\mathrm{Payback} \mathrm{Period}=\frac{{\mathrm{Additional} }_{\mathrm{investment}}}{{\mathrm{Annual} }_{\mathrm{energy} \mathrm{saving}}}$$

(1)

Sc5 provides a shorter payback period and is the second-most successful scenario in terms of energy efficiency. It had an SPP of 4.07 years, less than Sc3 and Sc6. Sc3 was the second-most successful scenario in terms of SPP value, with a duration of 4.13 years, and the preferable scenario in terms of energy savings. The aspect ratio represented by Sc5 is 2.4. Compared to other possible scenarios, this scenario’s lower building costs result from the smaller building size that results from the narrower courtyard. The outcome is a dramatic increase in the additional investment and a corresponding reduction in the simple payback period (SPP).

Most resources, including the literature, manuals, and user guides on passive solar techniques, recommend the south-facing orientation of buildings [45]. This aligns with the review study conducted by R. Galatioto and colleagues [46], who concluded that orientation is the most crucial factor in passive solar building design and can lead to higher energy savings. Shaviv [47] also examined the orientation of a building’s glazing surface and found that the main glazing surface should face south to achieve maximum energy efficiency, especially in hot and humid climates. Without south-facing orientation, the structure should be oriented southeast to achieve optimal results.

Although this study identifies the south direction (Sc3) as the optimal scenario in terms of energy required for cooling and the time needed to recoup the initial investment, the north direction (sc1) is deemed the optimal option due to its substantial energy savings for cooling purposes (23.2%). It has the same time as the Sc3 payback period (4.13 years). As well as the advantages of daylight from the north, prior research suggests that the north sky delivers diffused light characterized by a high chromaticity and relatively low luminance [48]. Despite differences in sky conditions, the light source stays constant and uniform. The south sky is characterized by sun movement along a bright sky dome and a cooler color.

4. Conclusions

Aerogel granules have been one of the most promising materials in building thermal insulation in the last decades. In Egypt, educational buildings’ reliance on traditional glazing has made the classrooms extremely vulnerable to thermal conditions, which disturb students while they are studying. Aerogel granular glazing windows with adequate transparency and low thermal conductivity are an intriguing idea for classrooms in Aswan and other places with high temperatures.

This study has found that aerogel glazing offers significant energy savings compared to traditional glazing materials in six different scenarios. The most effective scenario for aerogel glazing was Sc3, where cooling energy consumption was reduced by 26.3% compared to the base case scenario, with a payback period of 4.13 years. Similarly, Sc5 showed that changing the aspect ratio of the semi-open courtyard to 2.4 and installing an aerogel glazing system could reduce cooling energy use by 25.7%, with a payback period of 4.07 years. On the other hand, Sc4, where classrooms were oriented towards the west direction, had the lowest energy conservation rate at 11.2%. The study also revealed that Sc5, with an aspect ratio of 2.4 for the semi-open courtyard, was the best thermal scenario for summer. In contrast, Sc6, with an aspect ratio of 0.6, was the ideal scenario for winter heating. Finally, the study found that Sc1 and Sc3, representing classrooms with a south and north orientation, respectively, have similar summer thermal conditions regarding monthly mean air temperature. Overall, these findings demonstrate that aerogel glazing is a highly effective alternative to traditional glazing materials when it comes to energy savings.

In conclusion, this study examines the impact of different scenarios, including aerogel glazing, building orientation, and aspect ratio, on the energy consumption of educational buildings in hot arid regions. The results demonstrate that nanogel glazing reduces cooling energy consumption by preventing heat transmission due to its high porosity and low thermal conductivity. The findings also indicate that building orientation and aspect ratio plays an important role in determining the effectiveness of nanogel glazing.

While the south direction (Sc3) has the lowest energy requirements and payback period, the north direction (Sc1) is deemed optimal due to its significant energy savings for cooling purposes and the advantages of diffused daylight.

In contrast, a high aspect ratio (Sc5) was more effective than short and wide buildings (Sc1 and Sc6) in reducing heat gain through windows. These findings support previous studies suggesting that the main glass surface of a building should face south to achieve maximum energy savings. Previous research has also indicated that the north sky delivers a constant and uniform light source with high chromaticity and low luminance [48]. In contrast, the south sky is characterized by sun movement and cooler color. Ultimately, the decision on orientation should take into account both energy efficiency and lighting quality. Overall, the study highlights the importance of considering building orientation and aspect ratio when implementing energy-efficient solutions in educational buildings in hot, arid regions.