**2. Test room and SCPC system description**

performance of solar chimneys using different configurations has been experimentally investigated by different researchers. The concept of metallic solar wall (MSW) on a full-scale model was studied for a single-room house under tropical climatic conditions in Thailand. It was shown that a MSW with 2 m height and 0.145 m air gap (cavity between glass and aluminum) can produce a mass flow rate up to 0.02 kg/s for a house with a base area of 11.55 m<sup>2</sup>

height of 2.68 m and optimum natural ventilation. Such low-cost solar chimney construction can significantly reduce heat gain in the house by creating adequate flow rate to improve thermal comfort [2]. The thermal performance of a solar chimney was investigated on a full-scale model under Mediterranean daylight and night-time conditions for natural ventilation. A 4.5 m high, 1.0 m wide and 0.15 m thick reinforced concrete wall was used as a solar absorber, whose southern surface was painted matte black with insulation on the side and back surfaces. The absorber wall was covered by glass of 0.1 m thickness to reduce the convection heat. With

 occurring at around 13:00 h. Discharge coefficient was experimentally determined to carry out volumetric flow rate calculation. It was concluded that the airflow rate through a solar chimney system is greatly affected by the pressure difference between openings caused by thermal gradients and by wind velocity [3]. An experiment of solar-induced ventilation strategy was conducted. The experiment consisted of two parts, namely, a roof solar collector and a vertical stack. The purpose of the roof solar collector was to capture as much solar radiation as possible, thus maximizing the air temperature inside the channel of the roof solar collector. The heated air inside the channel rose and flowed into the vertical stack due to the pressure difference between the two zones. Meanwhile, the vertical stack was important in providing significant height for sufficient stack pressure. The walls of vertical stack were insulated to minimize the heat loss to the environment. The findings indicated that the proposed strategy was able to enhance the stack ventilation, both in semi-clear sky and overcast sky conditions. The highest air temperature difference between the air inside the stack and the ambient air was achieved in the semi-clear sky condition, which was about 9.9°C (45.8–35.9°C). Besides, in the overcast sky condition, the highest air temperature difference was 6.2°C (39.3–33.1°C) [4]. Also, an experimental study of a vertical channel simulating a solar chimney and a Trombe wall was conducted. The vertical channel had a transparent cover and an absorber plate, painted matte black. The vertical channel was open at both ends, and its dimensions were 1.025 m high, 0.925 m wide and 0.02 m–0.11 m variable depth. Heat input to the absorber plate was supplied by electrical means (200–1000 W) in steps of 200 W. Air temperature and velocity measurements inside the channel were obtained. The results showed that air temperature was increased continuously along the channel height, while the cover and the absorber plate temperatures were not. The cover temperature, as well as the absorber plate temperature, increased continuously to the middle height and then began to decrease. The authors concluded that the mass flow rate is a function of the heat input as well as on the channel depth,

this configuration, a maximum flow rate of 374 m<sup>3</sup>

while the efficiency of the system is a function of the heat input only [5].

It was concluded that a serious problem of discomfort exists inside houses in projects of new Assiut city based on natural ventilation strategy only [6–9]. Traditional passive techniques were used in ancient architectures to achieve the desired summer comfort without the need

m2

84 Energy Systems and Environment

and a

/h was reported at a solar intensity of 604 W/

A single room was built in Assiut University (El-Gorib site) in Assiut, Egypt. Room dimensions are 3.8 x 3.8 x 2.8 m (L × W × H) based on the previous numerical model of solar chimneys integrated with passive cooling [7, 8]. It is located at a latitude of 27°3'N and a longitude of 31°15′ E. In terms of climatic characteristics, Assiut is located in southern Upper Egypt zone. It is characterized by hot dry summers with a maximum outdoor temperature that ranges from 41–46°C and a minimum temperature that ranges from 16–21°C in the summer months. This zone has a global radiation range of 1000 to 1125 W/m<sup>2</sup> in the summer and 650 to 800 W/m<sup>2</sup> in the winter. Outdoor climate analysis was done based on field measurements at 2-minute time interval to analyze 1-year data (2015). **Figure 1** shows the temperature and humidity patterns of 2015. Selecting 2 months for monitoring (August and September) was done to test indoor environment using passive air conditions. These periods were selected to

**Figure 1.** Temperature and humidity pattern of outdoor condition during the year of 2015.

investigate the effect of different patterns of (high/low) outdoor conditions. Also, solar radiation was measured for outdoor conditions, with a maximum solar radiation of 890 W/m<sup>2</sup> reached between 11:00 am and 1:00 pm. Solar radiation creates a temperature gradient inside the chimney air cavity that causes the driving force of air inside the chimney under the effect of stack effect.

door opening towards the north. **Figure 2** shows the outer view of the room with the SCPC

The walls of the building are made from hollow clay bricks 0.1 m thick and covered with

ceiling is made from 0.12 m thick concrete and covered with 0.01 m thick cement on the inner side. The ceiling is covered by insulation and concrete cover with thicknesses 0.15 and 0.07 m,

K) for the wall. The

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cement from both sides with thicknesses 0.02 m and a U-value of 2.6 (W/m<sup>2</sup>

**Figure 2.** The outer view of the room with SCPC system fixed on its roof.

system on its roof.

respectively, as shown in **Figure 3**.

**Figure 3.** The description of roof layers and their thicknesses.

The average solar brightness in Assiut was 12.125 h/day [16]. This encourages applying the SCPC system in this area. The overall heat transfer coefficient of the building part is calculated based on the physical properties of materials available in the local market with the same properties as the materials used in the numerical model. **Table 1** shows the characteristics of building materials. The overall heat transfer coefficients of walls, floors and roofs are 2.60, 0.797 and 0.443, respectively. The window opening is oriented towards the south and the


**Table 1.** Description of building materials used.

**Figure 2.** The outer view of the room with SCPC system fixed on its roof.

investigate the effect of different patterns of (high/low) outdoor conditions. Also, solar radiation was measured for outdoor conditions, with a maximum solar radiation of 890 W/m<sup>2</sup> reached between 11:00 am and 1:00 pm. Solar radiation creates a temperature gradient inside the chimney air cavity that causes the driving force of air inside the chimney under the effect

**Figure 1.** Temperature and humidity pattern of outdoor condition during the year of 2015.

The average solar brightness in Assiut was 12.125 h/day [16]. This encourages applying the SCPC system in this area. The overall heat transfer coefficient of the building part is calculated based on the physical properties of materials available in the local market with the same properties as the materials used in the numerical model. **Table 1** shows the characteristics of building materials. The overall heat transfer coefficients of walls, floors and roofs are 2.60, 0.797 and 0.443, respectively. The window opening is oriented towards the south and the

**Building part Material Conductivity (kJ/h m K) U-Value (W/m2 K) Thickness (m)**

Brick 3.60 0.10

Concrete slab 4.2 0.12 Cement plaster (coating) 4.50 0.01

Insulation 0.2 0.02 Concrete 4.2 0.10

1.26 2.60 0.02

1.26 0.02

Glass windows Single glass — 5.68 0.004

Roof Insulation 0.2 0.443 0.05

Ground Floor — 0.797 0.10

of stack effect.

86 Energy Systems and Environment

External walls Common plaster + cement (coating)

(coating)

**Table 1.** Description of building materials used.

Common plaster + cement

door opening towards the north. **Figure 2** shows the outer view of the room with the SCPC system on its roof.

The walls of the building are made from hollow clay bricks 0.1 m thick and covered with cement from both sides with thicknesses 0.02 m and a U-value of 2.6 (W/m<sup>2</sup> K) for the wall. The ceiling is made from 0.12 m thick concrete and covered with 0.01 m thick cement on the inner side. The ceiling is covered by insulation and concrete cover with thicknesses 0.15 and 0.07 m, respectively, as shown in **Figure 3**.

**Figure 3.** The description of roof layers and their thicknesses.

The passive cooling technique was integrated inside the short wind tower with the opening facing north. The method applied in this study will depend on cooling the interior space envelope using cheap and local cooling materials without consuming much energy. The tower was built with dimensions 1 m x 1 m x 1 m (L × W × H). The wet pad in wind tower is made from 0.1-m thick expanded paper. A water tube was installed on the top of the expanded paper with small nozzles. A water pump is used to recirculate water from the water reservoir in the bottom of the pad. Water is supplied from the water tank to the bottom water reservoir using a concentric floating valve. It opens when the level of water in the bottom reservoir decreases

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In order to understand the actual indoor environment after using the passive cooling system,

Comfort ventilation is the important factor that deals directly with the human body and depends on the strategy used. It is based on the theory that high airspeed around the human body accelerates the skin's evaporation rate and, accordingly, improves the heat dissipation from the human body. This in turn shifts up the comfort upper level by providing such direct physiological cooling effect and decreases human discomfort due to skin wetness and the high humidity level [20]. In comfort ventilation strategy, two different impacts of the air velocity of the human body were determined: first, the heat exchange of the body that happens with convection; second, the evaporative capacity of the air. According to ASHRAE Standard 55 for naturally ventilated buildings, the acceptable thermal environment of indoor operative temperature ranges between 22°C and 28°C, and the comfort indoor air velocity of 1.6 m/s can be beneficial for improving comfort at higher temperatures [19]. So, new residence must have the acceptable thermal environment for all occupants. According to ASHRAE Standard 62–2001, ventilation rates depend upon the floor area, whereas the minimum ACH was 0.35, but no less than 15 CFM/person [21]. Also, passive natural ventilation standards require a minimum of three air changes for residential buildings. Finally, the comfort ventilation can

**Figure 6(a)** shows the variation of daily solar radiation over time. A maximum solar radiation

gradient inside the chimney air cavity, and the warm air is less dense than cool air so it rises and creates a difference in pressure which in turn induces air movement, causing the driving force of air inside the chimney under the effect of stack effect. The main component of the solar chimney is the absorber plate, which was made of an aluminum plate painted black with 0.95 emissivity. A wind-driven protection was used at the top in order to avoid reverse flow. It is clear that the maximum surface temperature of aluminum was 86°C at 1:30 pm due to high

was reached between 11:00 am and 1:00 pm. Solar radiation creates a temperature

a sample data will be presented from 2-month data monitoring as an example.

easily be enhanced by appropriate building design and the system used.

**4. Solar radiation and surface temperature analysis**

as shown in **Figure 5**.

**3. Comfort ventilation**

of 890 W/m<sup>2</sup>

**Figure 4.** Cross section of the solar chimney cross section.

A thermal insulation, 0.1 m thick, is installed inside the floor layer to examine the performance of the integrated SCPC system for indoor thermal comfort while excluding heat effect from the ground. The SCPC system consists of two components: the solar chimney and the short wind tower. The solar chimney was fixed on the roof of the room facing south. The SCPC system is made from widely available and conventional materials in the Egyptian market. The solar chimney is made from black aluminum with emissivity 0.95 and glass with transmissivity 0.84 and thicknesses of 0.002 m and 0.1 m, respectively, as shown in **Figure 4**. Performance of the solar chimney was examined in the first phase. The maximum airflow rate in the chimney was 0.69 kg/s during a high solar radiation of 890 W/m<sup>2</sup> [17, 18].

**Figure 5.** The description of evaporative technique in the wind tower made from expanded paper with water droplet from upper side.

The passive cooling technique was integrated inside the short wind tower with the opening facing north. The method applied in this study will depend on cooling the interior space envelope using cheap and local cooling materials without consuming much energy. The tower was built with dimensions 1 m x 1 m x 1 m (L × W × H). The wet pad in wind tower is made from 0.1-m thick expanded paper. A water tube was installed on the top of the expanded paper with small nozzles. A water pump is used to recirculate water from the water reservoir in the bottom of the pad. Water is supplied from the water tank to the bottom water reservoir using a concentric floating valve. It opens when the level of water in the bottom reservoir decreases as shown in **Figure 5**.

In order to understand the actual indoor environment after using the passive cooling system, a sample data will be presented from 2-month data monitoring as an example.
