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

**Figure 6(a)** shows the variation of daily solar radiation over time. A maximum solar radiation of 890 W/m<sup>2</sup> was reached between 11:00 am and 1:00 pm. Solar radiation creates a temperature 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

**Figure 6.** (a) The variation of daily solar radiation over to time. (b) The variation of different temperatures with time.

Validation was done for the numerical simulation with the experimental results. The detailed model for the numerical calculation was studied, including boundary condition, geometry and material physical properties [7]. Results of chimney air temperature, cooling tower inlet temperature and aluminum surface temperature with the help of the analytical model were found in good agreement with the corresponding experimental values. The experimental results tend to be higher than analytical model by about 2% and 2.5% in average. However, the airflow at the chimney is higher than analytical model by about 40%. This indicates that the presence of outdoor high wind speed and pressure coefficient on building surfaces and chimney outlets increases airflow rate of the stack effect with a negative effect of reverse flow that occurs in the chimney for some time and decreases performance of the evaporative pad

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Due to the buoyancy force, the outer hot air passed through the expanded paper with water droplet, and then the outdoor air temperature was reduced inside the wind tower after passing through the wet pad. A graph indicating a typical variation of indoor cooling using a cooling medium is shown in **Figure 9**. The air temperature inside the room increased gradually due to the presence of occupants inside the room and heat gained by the building. Also, the temperature inside chimney air cavity is decreased gradually due to the absence of thermal storage attaching to the aluminum plate when solar irradiation decreases gradually. Therefore, the air temperature increases in the chimney air cavity, corresponding to the increase of solar radiation.

**Figure 9.** (a) The variation between tower inlet temperature, room temperature and chimney inlet temperature based on

the cooling effect. (b) The temperature difference between chimney air cavity and outdoor temperature.

with an average difference of 6% for the indoor temperature.

**Figure 8.** The variation of glass surface temperatures in the solar chimney.

intensity of incident solar radiation in this period. Temperature was recorded in the middle of the aluminum plate. After midday, temperature started to decrease until 65°C at 3:30 pm, followed by a sharp drop of temperature due to decrease of solar intensity and high heat release without any thermal storage integrated with the aluminum plate. Also, glass surface temperature has the same pattern as aluminum temperature with 15°C higher than outdoor temperature. This affects air cavity temperature strongly. This finding is in agreement with [22].

**Figure 7** shows the temperature profile of outlet air inside the chimney cavity. It is clear that the temperature of the chimney cavity increases and reaches 48°C for the highest temperature at 12:00 pm with high solar radiation. The temperature of air cavity is higher than outdoor until 4:00 pm. Then, a strong reduction of air temperature inside the cavity was reached. This is due to the decrease of aluminum surface temperature and heat release from the absorber. **Figure 4** shows the thermal images of outside chimney glass plate with the highest three temperature points on its surface at 12 pm on 13/8/2015.

**Figure 8** shows the temperature distribution of three points on the upper side of the solar chimney (glass surface temperature) with an average temperature of 38°C and 36°C at 1:00 pm and 3:00 pm, respectively, due to high solar intensity. The thermal gradient of chimney surface temperature and aluminum surface temperature strongly affects the airflow through the chimney.

**Figure 7.** (a) Temperature profile of outlet air inside the chimney cavity from 10:00 am until 14:45 pm. (b) Temperature profile of outlet air inside the chimney cavity from 14:38 am until 18:30 pm.

**Figure 8.** The variation of glass surface temperatures in the solar chimney.

intensity of incident solar radiation in this period. Temperature was recorded in the middle of the aluminum plate. After midday, temperature started to decrease until 65°C at 3:30 pm, followed by a sharp drop of temperature due to decrease of solar intensity and high heat release without any thermal storage integrated with the aluminum plate. Also, glass surface temperature has the same pattern as aluminum temperature with 15°C higher than outdoor temperature. This affects air cavity temperature strongly. This finding is in agreement with [22]. **Figure 7** shows the temperature profile of outlet air inside the chimney cavity. It is clear that the temperature of the chimney cavity increases and reaches 48°C for the highest temperature at 12:00 pm with high solar radiation. The temperature of air cavity is higher than outdoor until 4:00 pm. Then, a strong reduction of air temperature inside the cavity was reached. This is due to the decrease of aluminum surface temperature and heat release from the absorber. **Figure 4** shows the thermal images of outside chimney glass plate with the highest three tem-

**Figure 6.** (a) The variation of daily solar radiation over to time. (b) The variation of different temperatures with time.

**Figure 8** shows the temperature distribution of three points on the upper side of the solar chimney (glass surface temperature) with an average temperature of 38°C and 36°C at 1:00 pm and 3:00 pm, respectively, due to high solar intensity. The thermal gradient of chimney surface temperature and aluminum surface temperature strongly affects the airflow through the chimney.

**Figure 7.** (a) Temperature profile of outlet air inside the chimney cavity from 10:00 am until 14:45 pm. (b) Temperature

perature points on its surface at 12 pm on 13/8/2015.

90 Energy Systems and Environment

profile of outlet air inside the chimney cavity from 14:38 am until 18:30 pm.

Validation was done for the numerical simulation with the experimental results. The detailed model for the numerical calculation was studied, including boundary condition, geometry and material physical properties [7]. Results of chimney air temperature, cooling tower inlet temperature and aluminum surface temperature with the help of the analytical model were found in good agreement with the corresponding experimental values. The experimental results tend to be higher than analytical model by about 2% and 2.5% in average. However, the airflow at the chimney is higher than analytical model by about 40%. This indicates that the presence of outdoor high wind speed and pressure coefficient on building surfaces and chimney outlets increases airflow rate of the stack effect with a negative effect of reverse flow that occurs in the chimney for some time and decreases performance of the evaporative pad with an average difference of 6% for the indoor temperature.

Due to the buoyancy force, the outer hot air passed through the expanded paper with water droplet, and then the outdoor air temperature was reduced inside the wind tower after passing through the wet pad. A graph indicating a typical variation of indoor cooling using a cooling medium is shown in **Figure 9**. The air temperature inside the room increased gradually due to the presence of occupants inside the room and heat gained by the building. Also, the temperature inside chimney air cavity is decreased gradually due to the absence of thermal storage attaching to the aluminum plate when solar irradiation decreases gradually. Therefore, the air temperature increases in the chimney air cavity, corresponding to the increase of solar radiation.

**Figure 9.** (a) The variation between tower inlet temperature, room temperature and chimney inlet temperature based on the cooling effect. (b) The temperature difference between chimney air cavity and outdoor temperature.

**Figure 10.** The variation of expanded paper surface temperatures (cooling pad).

**Figure 10** shows that the minimum surface temperature of the expanded paper (cooling pad), with water droplet, was 19.4°C at 3:00 pm with an average wet bulb temperature of 22°C. The decrease of surface temperature of cooling pad strongly affects airflow temperature and causes reduction of outdoor air temperature with constant enthalpy. This demonstrates the concept of evaporative cooling. The average water consumption is 16 l/ day. This is because the outdoor air that flows through the pads is cooled to a temperature close to the WBT. Then, the indoor air of the building, cooled by an evaporative cooling system, is further heated by about 1–3°C above the output air from the evaporative cooling system, depending on the airflow rate of evaporative cooling and indoor heat gained by the building. This finding is in agreement with [23, 24]. Energy consumption for this system is 18 W only.

room relative humidity is located within the acceptable range of relative humidity 20%~60%, according to ASHRAE Standard 2004 [19]. Arundel concluded that the optimum humidity level for minimizing adverse effects for health is between 40 and 60% [25]. Also, most of the investigated cases were very close to the summer comfort zone. This is because the air outside

**Figure 11.** Temperature profile for indoor environment with a cooling technique compared to outdoor condition on the

**Indoor temperature Range Mean ± SD Sample distribution**

550 ppm, with three occupants staying inside the room. The lower concentration inside the room

inside the experimental room is very low. The average concentration is

28.3–31.7 30.1 ± 0.86 −0.63 −1.01

**Skewness Kurtosis**

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is so dry, typically below 10% relative humidity during daytime.

**Figure 12.** Temperature and humidity conditions inside the room after using the SCPC system.

The concentration of CO<sup>2</sup>

90% acceptable range of adaptive comfort standard.

**Table 2.** The statistical analysis of indoor temperature.

#### **5. Thermal comfort and CO2 evaluation according to ASHRAE and ACS**

It is observed that most of the outlet air temperatures from the wind tower are below the upper limit of the 90% acceptable range, as shown in **Figure 11**. The temperature of the outside air that passes through the wet medium can be reduced significantly with a difference 6 K ~ 7 K. Only 10% of the measured data exceeded the upper limits. **Table 2** shows the statistical analysis for indoor temperatures with a statistically significant difference = 0.024 (p level < 0.05). Therefore, the supplied air is still considered suitable to enhance indoor thermal comfort. The maximum indoor temperature was reached at 6:00 pm with a long time lag between outdoor and indoor temperatures. This is due to the effect of indoor thermal mass that impacts room cooling. This is in agreement with [23]. Reducing indoor temperature is based on the amount of water that passes inside the wet pad and the number of nozzles in the water tube.

Humidity is strongly affected by cooling the wet medium. It is observed that indoor relative humidity after using passive cooling did not rise above 57% during daytime and most of the time was below 50%, indicating that further cooling is needed. **Figure 12** shows that

**Figure 11.** Temperature profile for indoor environment with a cooling technique compared to outdoor condition on the 90% acceptable range of adaptive comfort standard.


**Table 2.** The statistical analysis of indoor temperature.

**Figure 10** shows that the minimum surface temperature of the expanded paper (cooling pad), with water droplet, was 19.4°C at 3:00 pm with an average wet bulb temperature of 22°C. The decrease of surface temperature of cooling pad strongly affects airflow temperature and causes reduction of outdoor air temperature with constant enthalpy. This demonstrates the concept of evaporative cooling. The average water consumption is 16 l/ day. This is because the outdoor air that flows through the pads is cooled to a temperature close to the WBT. Then, the indoor air of the building, cooled by an evaporative cooling system, is further heated by about 1–3°C above the output air from the evaporative cooling system, depending on the airflow rate of evaporative cooling and indoor heat gained by the building. This finding is in agreement with [23, 24]. Energy consumption for this

**Figure 10.** The variation of expanded paper surface temperatures (cooling pad).

It is observed that most of the outlet air temperatures from the wind tower are below the upper limit of the 90% acceptable range, as shown in **Figure 11**. The temperature of the outside air that passes through the wet medium can be reduced significantly with a difference 6 K ~ 7 K. Only 10% of the measured data exceeded the upper limits. **Table 2** shows the statistical analysis for indoor temperatures with a statistically significant difference = 0.024 (p level < 0.05). Therefore, the supplied air is still considered suitable to enhance indoor thermal comfort. The maximum indoor temperature was reached at 6:00 pm with a long time lag between outdoor and indoor temperatures. This is due to the effect of indoor thermal mass that impacts room cooling. This is in agreement with [23]. Reducing indoor temperature is based on the amount of water that passes inside the wet pad and the number of nozzles in

Humidity is strongly affected by cooling the wet medium. It is observed that indoor relative humidity after using passive cooling did not rise above 57% during daytime and most of the time was below 50%, indicating that further cooling is needed. **Figure 12** shows that

 **evaluation according to ASHRAE and** 

system is 18 W only.

92 Energy Systems and Environment

**ACS**

the water tube.

**5. Thermal comfort and CO2**

room relative humidity is located within the acceptable range of relative humidity 20%~60%, according to ASHRAE Standard 2004 [19]. Arundel concluded that the optimum humidity level for minimizing adverse effects for health is between 40 and 60% [25]. Also, most of the investigated cases were very close to the summer comfort zone. This is because the air outside is so dry, typically below 10% relative humidity during daytime.

The concentration of CO<sup>2</sup> inside the experimental room is very low. The average concentration is 550 ppm, with three occupants staying inside the room. The lower concentration inside the room

**Figure 12.** Temperature and humidity conditions inside the room after using the SCPC system.

is due to high airflow rate in the chimney and wind speed to a maximum of 0.69 kg/s, which affects CO<sup>2</sup> concentration. This helps improve the indoor air quality and achieve a safe environment according to [22]. **Figure 13** shows the variation of indoor carbon dioxide concentration.

10255—National Challenges Program. The author gives special thanks to the engineers in the

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Department of Architecture, Faculty of Engineering, Assiut University, Assiut, Egypt

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**Author details**

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Amr Sayed Hassan Abdallah

**Figure 13.** Indoor CO<sup>2</sup> concentration inside the room with SCPC system.
