**4.1 Ambient solar radiation analysis**

Thermal monitoring of the house which involves the global horizontal irradiance (GHI), resultant global irradiance at the various elevations, and indoor and ambient air temperature was initiated in September 2016 and continued until September 2017. Uncontrollably, 944 data entries were missed, amounting to 5% of missing data. The missing data occurs in November 2016, December 2016, February 2017, and March 2017. The periods with missing data in the affected months were excluded in the data analysis going forward.

The measured GHI and average irradiance profile are given in **Figure 6(a)**, while **Figure 6(b)** shows the monthly average GHI and total irradiation over the measurement period.

As seen in **Figure 6(a)**, due to the measurement period considered, the winter dip, represented by June, July, and August months, was obtained at the right-hand side of the profile. This, however, did not affect the measured irradiance during the entire period. In agreement with theory [31, 32], the measured GHI as seen in **Figure 4(a)** ranges from 0 to 996.0 W/m2 , where periods with the sun absent produce 0 W/m2 and the maximum irradiance of 996.0 W/m2 was logged in February 2017 at 12 h30. Furthermore, monthly average irradiance and total irradiation were developed to portray a typical sequential distribution of annual GHI at the southern hemisphere as shown in **Figure 6(b)**. Also, the solar irradiance and irradiation distribution were predicted using a Gaussian function. The trend of the chart tends to correspond with the solar radiation distribution in the southern hemisphere [33]. In other words, a relatively lower solar irradiance of an average of 140.5 W/m2 was observed in June, July, and August, whereas the rest of the months had an average of 192.8 W/m2 . Due to data loss and sky formation, an irregular distribution of solar irradiance was observed in January, February, November, and December. Hence, the red and blue band areas were used to indicate the period considered as summer and winter seasons, respectively, in the thermal performance evaluation of the house.

Solar irradiance across the north, east, south, and west elevations of a house varies due to daily movement of the sun. Consequently, heat transfer through the perimeter walls varies across the elevations [34]. The global irradiance at the various elevations was measured to depict the received solar irradiance and corresponding heat transfer through the windows. Daily summer and winter average global

#### **Figure 6.**

*(a) Measured and average global horizontal irradiance and (b) monthly average irradiance and total irradiance chart.*

irradiance at the north, east, south, and west elevations, as well as their corresponding irradiation, is given in **Figure 7**.

Practically, the sun travels daily from the east to the west through the north elevation in the southern hemisphere and the south elevation in the northern hemisphere [35, 36]. The measured solar irradiance at the building elevations in **Figure 7** concords with the above concept. Hence the north elevation receives a significant amount of solar radiation during the day, while the south elevation receives minimum daily solar radiation. Nevertheless, the solar irradiance at the north and south elevations peaked at approximately the same time (mid-day). Also, both irradiance (north and south elevations) followed the same trend as the GHI. The solar irradiance at the east and west elevations was also observed to peak at the early and late hours of the day, respectively.

The sharp dip in the west irradiance distribution was due to deciduous trees planted at the west side of the house. The trees were intended to shade the late afternoon sun and prevent cold winter wind. Further analysis of the solar radiation at the house elevations is given in **Table 2**.

As observed in **Figure 7** as well as **Table 1**, the daily average winter irradiance at the north elevation was higher than the average GHI by 106.27 W/m<sup>2</sup> . It was also observed to be higher than the north elevation average irradiance by 161.27 W/ m2 in the summer season. The relatively high north irradiance during the winter season which is due to the low-angle winter sun is the fundamental principle of passive solar design for heating concerning the ambient weather conditions. The north elevation outperformed the others regarding daily average and maximum

#### **Figure 7.**

*Measured solar global irradiance at the elevations of the house and corresponding heat energy on typical summer and typical winter days.*


**215**

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irradiance as well as the daily irradiation, comparing other elevations in **Table 1**. The solar irradiation in **Figure 7(a)** and **(b)** serves as the instantaneous (30 min interval) heat energy received from the sun at the respective elevation, whereas, **Table 1** gives the daily cumulative heat energy. Per day, the north elevation had the

Heat transfer through the windows of a house is the sum of conductive and radiative heat transfer. During the day (present of the sun), both means of heat transfer coincide. While at night, conductive heat transfer is dominant. Due to the indoor and ambient air temperature difference, conductive heat transfer transpires through the windows. Conductive heat transfer through the windows is

*Q <sup>c</sup>* = ∑*AU*(*Teo* − *Ti*) (1)

where *A* is the area of the window including the frame, *U* is the conductive heat

*I ho*

*ho* represents the surface (convective and radiative) heat transfer coefficient

correction to infrared radiation transfer between a surface and the environment, if

of the surface for solar radiation. Using Eq. (2) and **Figure 7**, the average summer and winter sol-air temperature at the various elevations of the passive solar house

assumed to be 0°C for the windows, considering that they are vertically inclined to the sunrays. Regarding solar absorption α of the surfaces, a dark-coloured surface of

of the windows were dark in colour. Comparing **Figures 9** and **7**, the sol-air temperature at each of the house elevation corresponds to their respective global irradiance. Both parameters (sol-air temperature and global irradiance) were observed to follow the same trend and peaks at the same time. However, during the absence of the sun, the sol-air temperature at the various elevations of the house was found to

The sun is solely responsible for radiative heat transfer. Hence, radiative heat transfer only occurs during the period the sun is present, and it is referred to as solar heat gain. Equation (1) must be positive to achieve solar heat gain. However, the instantaneous radiative or solar heat gain through a window can be evaluated by

K/W was assumed [36], since the perimeter walls and the wooden frame

K), while *I* is global solar irradiance at a given elevation (W/m<sup>2</sup>

In computing the sol-air temperature, longwave radiation factor (

<sup>−</sup> <sup>Δ</sup>*qir* \_\_\_\_ *ho*

(2)

). Δ*qir* is the

). Furthermore, α is the absorptance

\_\_\_\_ Δ*qir ho* ) was

temperature was replaced by *Teo* in Eq. (1). As indicated in **Table 1**, the daily irradiance varies across the house elevations; it is, however, not viable to quantify the conductive heat transfer through each window, assuming a uniform ambient air temperature. Thus, a parameter that incorporates the ambient air temperature and solar radiation was introduced to evaluate the heat transfer through the windows; this parameter is called as sol-air temperature *Teo*. Sol-air temperature also caters for convective and radiative heat transfer between the windows and ambient air film.

represents indoor air temperature. The ambient air

*DOI: http://dx.doi.org/10.5772/intechopen.85997*

maximum heat energy during the winter season.

**4.2 Windows heat transfer and solar heat gain**

given as [37]

(W/m<sup>2</sup>

0.053 m2

be approximately equal.

transfer coefficient, and *Ti*

Sol-air temperature is given by [38]:

*Teo* = *To* + \_\_

the sky temperature is different from *To* (W/m<sup>2</sup>

was computed and given in **Figure 8**.

#### **Table 2.**

*Typical summer day solar global radiation at the house elevations.*

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design DOI: http://dx.doi.org/10.5772/intechopen.85997*

irradiance as well as the daily irradiation, comparing other elevations in **Table 1**. The solar irradiation in **Figure 7(a)** and **(b)** serves as the instantaneous (30 min interval) heat energy received from the sun at the respective elevation, whereas, **Table 1** gives the daily cumulative heat energy. Per day, the north elevation had the maximum heat energy during the winter season.

#### **4.2 Windows heat transfer and solar heat gain**

*Wind Solar Hybrid Renewable Energy System*

ing irradiation, is given in **Figure 7**.

at the house elevations is given in **Table 2**.

irradiance at the north, east, south, and west elevations, as well as their correspond-

Practically, the sun travels daily from the east to the west through the north elevation in the southern hemisphere and the south elevation in the northern hemisphere [35, 36]. The measured solar irradiance at the building elevations in **Figure 7** concords with the above concept. Hence the north elevation receives a significant amount of solar radiation during the day, while the south elevation receives minimum daily solar radiation. Nevertheless, the solar irradiance at the north and south elevations peaked at approximately the same time (mid-day). Also, both irradiance (north and south elevations) followed the same trend as the GHI. The solar irradiance at the east and west elevations was also observed to peak at the early and late hours of the day, respectively. The sharp dip in the west irradiance distribution was due to deciduous trees planted at the west side of the house. The trees were intended to shade the late afternoon sun and prevent cold winter wind. Further analysis of the solar radiation

As observed in **Figure 7** as well as **Table 1**, the daily average winter irradiance

 in the summer season. The relatively high north irradiance during the winter season which is due to the low-angle winter sun is the fundamental principle of passive solar design for heating concerning the ambient weather conditions. The north elevation outperformed the others regarding daily average and maximum

**Summer season Winter season**

**Average (W/m2 )**

**Maximum (W/m2 )**

**Peak time**

**Daily irradiation (kWh/m2 )**

**Daily irradiation (kWh/m2 )**

*Measured solar global irradiance at the elevations of the house and corresponding heat energy on typical* 

North 215.1 472.4 12 h00 3.23 376.4 741.5 12 h30 4.71 East 188.4 510.7 09 h30 2.83 156.0 490.6 9 h30 1.95 West 123.4 349.6 14 h00 1.85 92.7 311.7 14 h00 1.16 South 76.6 126.7 11 h00 1.15 44.2 78.0 12 h00 0.55

observed to be higher than the north elevation average irradiance by 161.27 W/

. It was also

at the north elevation was higher than the average GHI by 106.27 W/m<sup>2</sup>

**214**

**Table 2.**

**Building elevation**

**Figure 7.**

**Average (W/m2 )**

*summer and typical winter days.*

**Maximum (W/m2 )**

*Typical summer day solar global radiation at the house elevations.*

**Peak time**

m2

Heat transfer through the windows of a house is the sum of conductive and radiative heat transfer. During the day (present of the sun), both means of heat transfer coincide. While at night, conductive heat transfer is dominant. Due to the indoor and ambient air temperature difference, conductive heat transfer transpires through the windows. Conductive heat transfer through the windows is given as [37]

$$Q\_{c\theta} = \Sigma AU \{T\_{co} - T\_i\} \tag{1}$$

where *A* is the area of the window including the frame, *U* is the conductive heat transfer coefficient, and *Ti* represents indoor air temperature. The ambient air temperature was replaced by *Teo* in Eq. (1). As indicated in **Table 1**, the daily irradiance varies across the house elevations; it is, however, not viable to quantify the conductive heat transfer through each window, assuming a uniform ambient air temperature. Thus, a parameter that incorporates the ambient air temperature and solar radiation was introduced to evaluate the heat transfer through the windows; this parameter is called as sol-air temperature *Teo*. Sol-air temperature also caters for convective and radiative heat transfer between the windows and ambient air film. Sol-air temperature is given by [38]:

$$T\_{co} = T\_o + \frac{aI}{h\_o} - \frac{\Delta qir}{h\_o} \tag{2}$$

*ho* represents the surface (convective and radiative) heat transfer coefficient (W/m<sup>2</sup> K), while *I* is global solar irradiance at a given elevation (W/m<sup>2</sup> ). Δ*qir* is the correction to infrared radiation transfer between a surface and the environment, if the sky temperature is different from *To* (W/m<sup>2</sup> ). Furthermore, α is the absorptance of the surface for solar radiation. Using Eq. (2) and **Figure 7**, the average summer and winter sol-air temperature at the various elevations of the passive solar house was computed and given in **Figure 8**.

In computing the sol-air temperature, longwave radiation factor ( \_\_\_\_ Δ*qir ho* ) was assumed to be 0°C for the windows, considering that they are vertically inclined to the sunrays. Regarding solar absorption α of the surfaces, a dark-coloured surface of 0.053 m2 K/W was assumed [36], since the perimeter walls and the wooden frame of the windows were dark in colour. Comparing **Figures 9** and **7**, the sol-air temperature at each of the house elevation corresponds to their respective global irradiance. Both parameters (sol-air temperature and global irradiance) were observed to follow the same trend and peaks at the same time. However, during the absence of the sun, the sol-air temperature at the various elevations of the house was found to be approximately equal.

The sun is solely responsible for radiative heat transfer. Hence, radiative heat transfer only occurs during the period the sun is present, and it is referred to as solar heat gain. Equation (1) must be positive to achieve solar heat gain. However, the instantaneous radiative or solar heat gain through a window can be evaluated by

$$Q\_{nl} = \mathcal{A} \times \text{SC} \times \text{SHGF} \tag{3}$$

where *SC* is the shading coefficient of the window. It varies with respect to the type of glazing and shading device (blind, drape, etc.). Depending on the reflection, absorption, and transmission of the glazing and shading device, a significant amount of solar heat gain is reduced or transferred through the window. An inverse function of the *SC* is the solar heat gain factor (*SHGF*). *SHGF* is the fraction of solar heat transmitted through a specific window. Hence, *SHGF* takes into consideration the geographical location of the window; time of the day, month, and year; as well as orientation of the window. The *SHGF* for windows in specific locations on the earth with respect to the parameters as mentioned above is given by ASHRAE [38]. However, a universal substitute for *SHGF* is the solar heat gain coefficient (*SHGC*). The relationship between both parameters are given as

$$\text{SHGF} = \text{SHGC} \times I \tag{4}$$

Therefore Eq. (3) can be rewritten as

$$Q\_{cal} = A \times \text{SC} \times \text{SHGC} \times I \tag{5}$$

Hence, the instantaneous heat transfer through the house windows at the various elevations was computed by combining Eqs. (1) and (5) together with **Figures 7** and **8**. The resultant summer and winter daily heat transfer through the house windows is given in **Figure 9(a)** and **(b)**, respectively.

The following assumptions were made to obtain the profile given in **Figure 10**. The SHGC and U-value of a timber frame window are 0.77 and 5.6 W/m2 K, respectively [18]. In all windows excluding the clerestory windows, semiopen weave and medium colour single drapes were used. Hence, the SC of the windows was 0.51. On the other hand, no drapes were used in the clerestory windows; thus the SC was 0.95 [39]. The area of the frame and thermal lag factor of the windows were ignored. In terms of operation, all windows were closed at all times.

In both figures, the north-facing windows had the maximum heat gain. This includes the clerestory and north perimeter windows. Heat gain through the clerestory windows was found to be maximum with 759 W at 14 h00 and 1356.50 W at 12 h30, in summer and winter, respectively. The daily average heat gain through the same windows was 507.72 W in summer and 896.51 W in winter. The north

**217**

kWh/m2

**Figure 10.**

**Figure 9.**

as well as 14.19 kWh/m2

with 0.45 kWh/m<sup>2</sup>

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design*

*Typical summer and winter daily heat transfer through the windows of a passive solar house.*

perimeter windows' heat transfer follows the same trend but 79 and 41% lesser in

The least heat gain was obtained at the south perimeter windows. Their daily average heat gain was 76.29 W in summer and 50.85 W in winter. Heat transfer through the south windows was 85% lesser than that of the clerestory windows in summer and 94% lower in the winter season. The clerestory windows also had the maximum heat loss. The daily average heat loss difference between the clerestory windows and the other perimeter windows was 15.62 and 14.42 W in summer and winter, respectively. Furthermore, the daily cumulative heat energy through the

/window in winter. This results in 9.30 and 18.60 kWh/m<sup>2</sup>

was obtained in all windows in summer. Also in winter, 0.52 kWh/m<sup>2</sup>

heat energy generated in the living room and south-facing bedroom in summer,

in the living room and 28.38 kWh/m<sup>2</sup>

bedroom in winter. Once again, the south perimeter windows were the most underperforming. The daily cumulative heat energy gain through the south windows was 82 and 94% lesser than that of the clerestory windows in summer and winter, respectively. An average daily cumulative heat energy loss of 0.48 kWh/m2

obtained. Besides, the east perimeter windows had the maximum heat energy loss

The clerestory windows show significant heat contribution to the inner space of the house. From the findings, it indicates that the clerestory windows were able to

/window in summer and 0.51 kWh/m2

/window in summer and 4.73

/window in winter.

daily cumulative

/window

/window was

in the south-facing

*DOI: http://dx.doi.org/10.5772/intechopen.85997*

summer and winter, respectively.

*Seasonal daily windows' cumulative heat energy.*

windows in summer and winter is given in **Figure 10**. The clerestory windows generate 3.10 kWh/m<sup>2</sup>

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design DOI: http://dx.doi.org/10.5772/intechopen.85997*

**Figure 9.**

*Wind Solar Hybrid Renewable Energy System*

relationship between both parameters are given as

Therefore Eq. (3) can be rewritten as

*Qsol* = *A* × *SC* × *SHGF* (3)

where *SC* is the shading coefficient of the window. It varies with respect to the type of glazing and shading device (blind, drape, etc.). Depending on the reflection, absorption, and transmission of the glazing and shading device, a significant amount of solar heat gain is reduced or transferred through the window. An inverse function of the *SC* is the solar heat gain factor (*SHGF*). *SHGF* is the fraction of solar heat transmitted through a specific window. Hence, *SHGF* takes into consideration the geographical location of the window; time of the day, month, and year; as well as orientation of the window. The *SHGF* for windows in specific locations on the earth with respect to the parameters as mentioned above is given by ASHRAE [38]. However, a universal substitute for *SHGF* is the solar heat gain coefficient (*SHGC*). The

*SHGF* = *SHGC* × *I* (4)

*Qsol* = *A* × *SC* × *SHGC* × *I* (5)

The following assumptions were made to obtain the profile given in **Figure 10**.

tively [18]. In all windows excluding the clerestory windows, semiopen weave and medium colour single drapes were used. Hence, the SC of the windows was 0.51. On the other hand, no drapes were used in the clerestory windows; thus the SC was 0.95 [39]. The area of the frame and thermal lag factor of the windows were ignored. In

In both figures, the north-facing windows had the maximum heat gain. This includes the clerestory and north perimeter windows. Heat gain through the

clerestory windows was found to be maximum with 759 W at 14 h00 and 1356.50 W at 12 h30, in summer and winter, respectively. The daily average heat gain through the same windows was 507.72 W in summer and 896.51 W in winter. The north

*Sol-air temperature at various elevations of a passive solar house on average summer and winter days.*

K, respec-

Hence, the instantaneous heat transfer through the house windows at the various elevations was computed by combining Eqs. (1) and (5) together with **Figures 7** and **8**. The resultant summer and winter daily heat transfer through the

house windows is given in **Figure 9(a)** and **(b)**, respectively.

terms of operation, all windows were closed at all times.

The SHGC and U-value of a timber frame window are 0.77 and 5.6 W/m2

**216**

**Figure 8.**

*Typical summer and winter daily heat transfer through the windows of a passive solar house.*

**Figure 10.** *Seasonal daily windows' cumulative heat energy.*

perimeter windows' heat transfer follows the same trend but 79 and 41% lesser in summer and winter, respectively.

The least heat gain was obtained at the south perimeter windows. Their daily average heat gain was 76.29 W in summer and 50.85 W in winter. Heat transfer through the south windows was 85% lesser than that of the clerestory windows in summer and 94% lower in the winter season. The clerestory windows also had the maximum heat loss. The daily average heat loss difference between the clerestory windows and the other perimeter windows was 15.62 and 14.42 W in summer and winter, respectively. Furthermore, the daily cumulative heat energy through the windows in summer and winter is given in **Figure 10**.

The clerestory windows generate 3.10 kWh/m<sup>2</sup> /window in summer and 4.73 kWh/m2 /window in winter. This results in 9.30 and 18.60 kWh/m<sup>2</sup> daily cumulative heat energy generated in the living room and south-facing bedroom in summer, as well as 14.19 kWh/m2 in the living room and 28.38 kWh/m<sup>2</sup> in the south-facing bedroom in winter. Once again, the south perimeter windows were the most underperforming. The daily cumulative heat energy gain through the south windows was 82 and 94% lesser than that of the clerestory windows in summer and winter, respectively. An average daily cumulative heat energy loss of 0.48 kWh/m2 /window was obtained in all windows in summer. Also in winter, 0.52 kWh/m<sup>2</sup> /window was obtained. Besides, the east perimeter windows had the maximum heat energy loss with 0.45 kWh/m<sup>2</sup> /window in summer and 0.51 kWh/m2 /window in winter.

The clerestory windows show significant heat contribution to the inner space of the house. From the findings, it indicates that the clerestory windows were able to

offset the underperforming south perimeter windows. Also, irrespective of size (glass surface area), the clerestory windows outperformed the other windows in both seasons in terms of heat gain. It can be said that the performance of the windows is a factor of the orientation of the house rather than the surface area of the windows (glass). Additionally, the solar heat gain through the windows was examined. The summer and winter daily average solar irradiation on the outer surface of the house windows and the resultant heat energy gain are given in **Figures 11** and **12**, respectively.

From **Figure 11**, the south perimeter windows had minimum heat energy transmission. It was found that 48%/window of solar irradiation was transmitted through the south perimeter windows. The clerestory windows, on the other hand, had the maximum heat energy transmission with 96%/window. Similar behaviour was observed in **Figure 12**. The south perimeter and clerestory windows heat energy transmission with respect to their solar irradiation were 52 and 101%/window, respectively. Detailed findings of the solar irradiation of the house windows and the resultant heat energy transmission are given in **Table 3**.

As stated earlier, the heat energy transmitted through the windows (glass area) is due to simultaneous conductive and radiative heat transfer. Although, the above comparative analysis only took into consideration the radiative heat energy generated on the windows' outer surface. Also, no shading device (drapes) was used in the clerestory windows. Hence, during the winter season, more than 100% of heat energy was transmitted through the clerestory windows.

#### **4.3 Indoor weather conditions analysis**

The indoor air temperature and relative humidity were the focus of the indoor weather conditions analysis. Thus, both parameters of each zone in the house were measured separately to establish the thermal influence of the various activities and orientation of the rooms (see **Figure 4**). The seasonal daily indoor air temperature and relative humidity profiles of the different zones in the house are given in **Figure 13**.

In **Figure 13**, the vertical bar charts below and above represent the air temperature and relative humidity percentage difference, respectively, of the three zones. A minimal summer day air temperature and relative humidity percentage difference were observed. However, zone 3 had the maximum air temperature and relative

**Figure 11.**

*Typical summer day solar heat gain of the house north, east, south, west, and clerestory windows.*

**219**

**Figure 13.**

**Figure 12.**

**Table 3.**

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design*

humidity percentage difference in both days. On a typical summer day, the air temperature percentage difference was 4% at 12 h00 and a corresponding relative humidity of 3% at 11 h00. The air temperature and relative humidity percentage differences were, respectively, 16% and 12% on a typical winter day. Further find-

*Typical winter day solar heat gain of the house north, east, south, west, and clerestory windows.*

**Windows Summer Winter**

**Transmitted heat energy (%/window)**

North 3.23 63 4.71 67 East 2.83 60 1.95 63 South 1.15 48 0.55 52 West 1.85 57 1.16 61 Clerestory 3.23 96 4.71 101

*Average summer and winter days' air temperature and relative humidity distribution in the various zone.*

**Solar irradiation (kWh/m2 )**

**Transmitted heat energy (%/window)**

*DOI: http://dx.doi.org/10.5772/intechopen.85997*

ings of **Figure 13** are summarised in **Table 4**.

**Solar irradiation (kWh/m2 )**

*Seasonal solar heat energy transmitted through the windows.*

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design DOI: http://dx.doi.org/10.5772/intechopen.85997*

humidity percentage difference in both days. On a typical summer day, the air temperature percentage difference was 4% at 12 h00 and a corresponding relative humidity of 3% at 11 h00. The air temperature and relative humidity percentage differences were, respectively, 16% and 12% on a typical winter day. Further findings of **Figure 13** are summarised in **Table 4**.

#### **Figure 12.**

*Wind Solar Hybrid Renewable Energy System*

offset the underperforming south perimeter windows. Also, irrespective of size (glass surface area), the clerestory windows outperformed the other windows in both seasons in terms of heat gain. It can be said that the performance of the windows is a factor of the orientation of the house rather than the surface area of the windows (glass). Additionally, the solar heat gain through the windows was examined. The summer and winter daily average solar irradiation on the outer surface of the house windows and the resultant heat energy gain are given in **Figures 11** and **12**, respectively. From **Figure 11**, the south perimeter windows had minimum heat energy transmission. It was found that 48%/window of solar irradiation was transmitted through the south perimeter windows. The clerestory windows, on the other hand, had the maximum heat energy transmission with 96%/window. Similar behaviour was observed in **Figure 12**. The south perimeter and clerestory windows heat energy transmission with respect to their solar irradiation were 52 and 101%/window, respectively. Detailed findings of the solar irradiation of the house windows

As stated earlier, the heat energy transmitted through the windows (glass area) is due to simultaneous conductive and radiative heat transfer. Although, the above comparative analysis only took into consideration the radiative heat energy generated on the windows' outer surface. Also, no shading device (drapes) was used in the clerestory windows. Hence, during the winter season, more than 100% of heat

The indoor air temperature and relative humidity were the focus of the indoor weather conditions analysis. Thus, both parameters of each zone in the house were measured separately to establish the thermal influence of the various activities and orientation of the rooms (see **Figure 4**). The seasonal daily indoor air temperature and relative humidity profiles of the different zones in the house are given in **Figure 13**. In **Figure 13**, the vertical bar charts below and above represent the air temperature and relative humidity percentage difference, respectively, of the three zones. A minimal summer day air temperature and relative humidity percentage difference were observed. However, zone 3 had the maximum air temperature and relative

*Typical summer day solar heat gain of the house north, east, south, west, and clerestory windows.*

and the resultant heat energy transmission are given in **Table 3**.

energy was transmitted through the clerestory windows.

**4.3 Indoor weather conditions analysis**

**218**

**Figure 11.**

*Typical winter day solar heat gain of the house north, east, south, west, and clerestory windows.*


#### **Table 3.**

*Seasonal solar heat energy transmitted through the windows.*

#### **Figure 13.**

*Average summer and winter days' air temperature and relative humidity distribution in the various zone.*

In **Tables 4** and **5**, the daily swing refers to the difference between the daily maximum and minimum air temperature and relative humidity. In **Table 4**, a fairly constant daily air temperature swing with an average of 5.6°C was observed, although the relative humidity swing in each zone varies. This was expected given that the presence and activities of occupants in a room are an influencing factor of relative humidity.

Furthermore, varying air temperature and relative humidity were observed in each zone during the typical winter day. This implies that a relatively high diurnal temperature variation was experienced during the winter season. In addition, zone 3 had the maximum daily air temperature swing of 9.6°C. This was as a result of the northfacing clerestory windows. Recall that the house was designed to optimise even air temperature indoors. Hence, the clerestory windows were installed to distribute solar radiation to the south floor area of the house. The blue dash circles in **Figure 13** indicate air temperature increase in zone 3 (south-facing room) due to penetrated solar radiation, consequently increasing the day and night air temperature differences in the zone. Zone 3 air temperature tends to increase more in winter due to the low-angled sun experienced during the season, regarding the blue circled area in both figures.

However, the average indoor air temperature and relative humidity in all zones were obtained and used to illustrate the indoor air temperature and relative humidity distribution within the thermal comfort zone. The average air temperature of all zones was represented by the whole building air temperature, while whole building relative humidity served as the average relative humidity of the three zones. Summer season frequency distribution of the whole building and ambient air temperature, as well as their corresponding relative humidity, are shown in **Figure 14**.


**Table 4.**

*Typical summer day indoor air temperature and relative humidity variation in the house zones.*


**221**

**Figure 14.**

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design*

A total of 12,607 data entries were used to develop the summer whole building and ambient air temperature and relative humidity distribution profile. As seen in **Figure 14**, the whole building and ambient air temperature distributions were divided into nine classes of 4.9°C width, and the air relative humidity frequency distribution curve is made of 11 classes of 9.99% width. Statistically, the whole building and ambient air temperature were not normally distributed. The whole building temperature skewness was 0.20 with a standard error (S.E) of 0.02, whereas a skewness of 0.41 (S.E 0.02) was obtained for the ambient temperature. Although both whole building and ambient air relative humidity in **Figure 14** were also not normally distributed, an opposite skewness was obtained. The whole building and ambient relative humidity had a skewness of −23.32 and − 23.68,

This implies that the measured air temperature and relative humidity deviate away from their mean towards the positive and negative side, respectively, where the whole building and ambient mean values are indicated by the blue broken (24°C) and solid (19°C) lines in their respective classes. The broken red line (47%) is used to identify the mean value of the whole building relative humidity, while the

Thermally in **Figure 14**, the solid grey line and band indicate the indoor air temperature (20 and 24°C) and relative humidity (30 and 60%) comfort zones, respectively [40]. In this regard, 49% of the whole building air temperature and approximately 85% of its corresponding relative humidity were found within the thermal comfort, whereas only 21 and 28% of the ambient air temperature and

In the winter season, a total of 4386 data entries were used to develop the whole building thermal condition, ambient air temperature, and relative humidity distribution profile. Nonetheless, a similar behaviour of the whole building, ambient air temperature, and relative humidity were observed. **Figure 15** shows the measured ambient and whole building air temperature as well as the resultant relative humid-

From **Figure 15**, the whole building temperature and relative humidity skewness were 0.22 and −0.21, respectively, with a S.E of 0.04. Meanwhile, a skewness of 0.22 was observed for the ambient air temperature, while the relative humidity skewness was −0.15, both with a S.E of 0.04. Hence, the whole building, ambient air temperature, and relative humidity curves are asymmetric. In other words, the mean of the whole building air temperature drifts away from the thermal comfort zone, leaving only 23% of the whole building temperature distribution in the

solid red line signifies the mean ambient relative humidity of 68%.

relative humidity, respectively, were in the thermal comfort zone.

*Whole building and ambient air temperature and relative humidity summer season profile.*

*DOI: http://dx.doi.org/10.5772/intechopen.85997*

respectively, both with a S.E of 0.02.

ity during the winter season.

#### **Table 5.**

*Typical winter day indoor air temperature and relative humidity variation in the house zones.*

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design DOI: http://dx.doi.org/10.5772/intechopen.85997*

A total of 12,607 data entries were used to develop the summer whole building and ambient air temperature and relative humidity distribution profile. As seen in **Figure 14**, the whole building and ambient air temperature distributions were divided into nine classes of 4.9°C width, and the air relative humidity frequency distribution curve is made of 11 classes of 9.99% width. Statistically, the whole building and ambient air temperature were not normally distributed. The whole building temperature skewness was 0.20 with a standard error (S.E) of 0.02, whereas a skewness of 0.41 (S.E 0.02) was obtained for the ambient temperature. Although both whole building and ambient air relative humidity in **Figure 14** were also not normally distributed, an opposite skewness was obtained. The whole building and ambient relative humidity had a skewness of −23.32 and − 23.68, respectively, both with a S.E of 0.02.

This implies that the measured air temperature and relative humidity deviate away from their mean towards the positive and negative side, respectively, where the whole building and ambient mean values are indicated by the blue broken (24°C) and solid (19°C) lines in their respective classes. The broken red line (47%) is used to identify the mean value of the whole building relative humidity, while the solid red line signifies the mean ambient relative humidity of 68%.

Thermally in **Figure 14**, the solid grey line and band indicate the indoor air temperature (20 and 24°C) and relative humidity (30 and 60%) comfort zones, respectively [40]. In this regard, 49% of the whole building air temperature and approximately 85% of its corresponding relative humidity were found within the thermal comfort, whereas only 21 and 28% of the ambient air temperature and relative humidity, respectively, were in the thermal comfort zone.

In the winter season, a total of 4386 data entries were used to develop the whole building thermal condition, ambient air temperature, and relative humidity distribution profile. Nonetheless, a similar behaviour of the whole building, ambient air temperature, and relative humidity were observed. **Figure 15** shows the measured ambient and whole building air temperature as well as the resultant relative humidity during the winter season.

From **Figure 15**, the whole building temperature and relative humidity skewness were 0.22 and −0.21, respectively, with a S.E of 0.04. Meanwhile, a skewness of 0.22 was observed for the ambient air temperature, while the relative humidity skewness was −0.15, both with a S.E of 0.04. Hence, the whole building, ambient air temperature, and relative humidity curves are asymmetric. In other words, the mean of the whole building air temperature drifts away from the thermal comfort zone, leaving only 23% of the whole building temperature distribution in the

**Figure 14.** *Whole building and ambient air temperature and relative humidity summer season profile.*

*Wind Solar Hybrid Renewable Energy System*

relative humidity.

In **Tables 4** and **5**, the daily swing refers to the difference between the daily maximum and minimum air temperature and relative humidity. In **Table 4**,

a fairly constant daily air temperature swing with an average of 5.6°C was observed, although the relative humidity swing in each zone varies. This was expected given that the presence and activities of occupants in a room are an influencing factor of

Furthermore, varying air temperature and relative humidity were observed in each

zone during the typical winter day. This implies that a relatively high diurnal temperature variation was experienced during the winter season. In addition, zone 3 had the maximum daily air temperature swing of 9.6°C. This was as a result of the northfacing clerestory windows. Recall that the house was designed to optimise even air temperature indoors. Hence, the clerestory windows were installed to distribute solar radiation to the south floor area of the house. The blue dash circles in **Figure 13** indicate air temperature increase in zone 3 (south-facing room) due to penetrated solar radiation, consequently increasing the day and night air temperature differences in the zone. Zone 3 air temperature tends to increase more in winter due to the low-angled sun experienced during the season, regarding the blue circled area in both figures. However, the average indoor air temperature and relative humidity in all zones were obtained and used to illustrate the indoor air temperature and relative humidity distribution within the thermal comfort zone. The average air temperature of all zones was represented by the whole building air temperature, while whole building relative humidity served as the average relative humidity of the three zones. Summer season frequency distribution of the whole building and ambient air temperature, as

well as their corresponding relative humidity, are shown in **Figure 14**.

**Temp. (°C)**

4 (0.9°C)

2 (0.4°C)

**Zone 1 2 3**

2.9 (1.3%)

0.9 (0.4%)

**RH (%) Temp.** 

Daily swing 5.4 14.4 5.8 16.1 5.7 13.5

Peak time 12 h00 18 h30 16 h00 18 h30 11 h00 11 h00

**(°C)**

2 (0.5°C)

1 (0.2°C)

**Zone 1 2 3**

*Typical summer day indoor air temperature and relative humidity variation in the house zones.*

6.5 (2.2%)

3.1 (1.3%)

*Typical winter day indoor air temperature and relative humidity variation in the house zones.*

**RH (%) Temp.** 

Daily swing 6.1 16.3 6.7 20.0 9.6 22.2

Peak time 12 h00 12 h00 11 h00 12 h00 12 h00 12 h00

**(°C)**

4.8 (0.9°C)

2.3 (0.4°C) **RH (%) Temp.** 

**RH (%) Temp.** 

2.7 (1.2%)

1.7 (0.8%) **(°C)**

4 (1.1°C)

1 (0.3°C)

5.7 (1.9%)

2.5 (1.0%) **(°C)**

16.2 (3.4°C)

3.9 (0.7°C) **RH (%)**

**RH (%)**

3.1 (1.3%)

1.1 (0.5%)

12.2 (4.1%)

3.6 (1.5%)

**Temp. (°C)**

11.6 (2.4°C)

2.2 (0.4°C)

**220**

**Table 5.**

**Table 4.**

**Indoor weather parameter**

**Indoor weather parameter**

Max. per. diff. (%) (equiv. temp.)

Average per. diff. (%) (equiv. temp.)

Max. per. diff. (%) (equiv. temp.)

Average per. diff. (%) (equiv. temp.)

**Figure 15.** *Whole building and ambient air temperature and relative humidity winter season profile.*

thermal comfort zone. However, the percentage of the ambient air temperature in the thermal comfort zone deviates by 10%, whereas approximately 78 and 29% of the whole building and ambient air relative humidity, respectively, were inside the thermal comfort zone.

Based on the findings, it could be said that the whole building air temperature to a certain degree is influenced by the ambient air temperature given that both distributions follow the same trend in both seasons. Nevertheless, the same cannot be said for the whole building and ambient air relative humidity. In both seasons, the whole building relative humidity distribution tends to follow the whole building air temperature.

Theoretically, relative humidity is a measure in percentage of the amount of water vapour in the air compared to the amount of water vapour the air can hold at a given temperature. Considering that the amount of water vapour the air can hold mainly depends on the air temperature, an increase in air temperature increases the capacity of water vapour the air can hold. At a fixed amount of water vapour, an increase in air temperature results in a decrease of the air relative humidity and vice versa. Therefore, the measured air temperature and relative humidity in **Figures 14** and **15** are in line with theory.

## **5. Conclusion**

The aim of this study is to analyse the thermal performance of a prototype low-cost energy-efficient house in South Africa. A passive solar house in SolarWatt Park, Alice, was used in the study. The indoor and ambient weather conditions of the house were monitored. Indoor and outdoor air temperature, relative humidity, as well as global horizontal irradiance and global irradiance at the various elevations of the house constitute the weather conditions.

It was found that strategic locating of the windows provides significant daylighting and heating for the inner space of the house. Also, the heat contribution of the windows was found to be dependent on the house orientation and shading materials (blind and drape). The performance of the north-facing clerestory and south-facing windows supports this claim. The daily cumulative heat contribution of the clerestory windows with no shading material was higher than that of the south-facing windows by 1.08 kWh/m2 /windows in summer and 4.45 kWh/m<sup>2</sup> / windows in winter. Due to conductive and radiative heat transfer which co-occurs in the windows, the clerestory windows were found to transmit more than 100% of the solar radiative energy generated on the outer surface in winter. The performance

**223**

**Author details**

provided the original work is properly cited.

Ochuko K. Overen\*, Edson L. Meyer and Golden Makaka

\*Address all correspondence to: ooveren@ufh.ac.za

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

University of Fort Hare, Fort Hare Institute of Technology, Alice, South Africa

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design*

of the clerestory windows as shown in the findings made it an essential component

It was also observed that the generated heat from the windows does not constitute overheating indoor. In summer, 49% of the whole building air temperature and approximately 85% of its corresponding relative humidity were found within the thermal comfort. Only 23% temperature and 78% relative humidity distributions of

the whole building were in the thermal comfort zone in the winter season.

This work was based on the research supported in part by the National Research Foundation of South Africa (Grant number 116763). We also acknowledge the Department of Science and Technology and Govan Mbeki Research and

The authors declared no conflicts of interest regarding the authorship of this

*DOI: http://dx.doi.org/10.5772/intechopen.85997*

**Acknowledgements**

**Conflict of interest**

publication.

of direct solar heat gain strategy in passive solar design.

Development Centre for supporting this research.

*Towards Sustainable Rural Development in South Africa through Passive Solar Housing Design DOI: http://dx.doi.org/10.5772/intechopen.85997*

of the clerestory windows as shown in the findings made it an essential component of direct solar heat gain strategy in passive solar design.

It was also observed that the generated heat from the windows does not constitute overheating indoor. In summer, 49% of the whole building air temperature and approximately 85% of its corresponding relative humidity were found within the thermal comfort. Only 23% temperature and 78% relative humidity distributions of the whole building were in the thermal comfort zone in the winter season.
