**3.1 Indoor and outdoor thermal conditions**

The indoor and outdoor thermal condition measurement deals with the air temperature and relative humidity in both environments. Therefore, HMP60 temperature and relative humidity probe were used to measure the indoor as well as the outdoor air temperature and relative humidity of all zones in the house. The HMP60 probe uses a platinum resistance temperature (PRT) detector to measure air temperature, while air relative humidity is measured by capacitive relative humidity sensor [23, 24]. The measurement specifications of HMP60 probe temperature and relative humidity sensor are given in **Table 1** [25].

Three sets of HMP60 probes were used to measure the indoor air temperature and relative humidity. In each zone, one HMP60 probe was suspended at the height of 0.8 m to ensure that the measured air temperature is nearest to the temperature felt by the occupants. At the same time, the probe does not obstruct the activities of the occupants. The locations of the HMP60 probe in the house and a set outdoor weather station are indicated in **Figure 4**.

As shown in **Figure 4(b)**, the outdoor air temperature and relative humidity measuring probe was housed in a 6-plate naturally aspirated radiation shield. The white painted radiation shield enables it to reflect solar radiation. At the same time, the louvre allows natural free flow of air through the shield, thereby keeping the probe as close as possible to the ambient air temperature (eliminating solar effect) and water vapour [26].

#### **3.2 Solar radiation measurements**

In this study, solar radiation measurements cover ambient global horizontal irradiance (GHI) and global irradiance at the four perimeter walls of the house. Due to atmospheric interference, the sum of direct and diffuse solar radiation reaching the earth surface, excluding albedo, is called global radiation, and it can be observed on vertical and horizontal surfaces. Thus measured global radiation on a horizontal plane is called global horizontal irradiance [27, 28].

At the right-hand side of the outdoor weather monitoring setup in **Figure 4(b)**, the horizontally levelled Kipp and Zonen CMP-11 pyranometer was used to monitor the global horizontal irradiance (GHI). The pyranometer uses a 32-junction thermopile to measure solar radiation with a sensitivity of 8 μV m<sup>−</sup><sup>2</sup> and a spectral range of 285–2800 nm. Its response time is less than 1.7 s (63%) and 5 s (95%) [29]. The outdoor weather setup was elevated by 1 m above the roof, to ensure an unobstructed space for the radiometer. The pyranometer's dome was also cleaned twice per week to keep the dome clear of dew, dust,


**Table 1.**

*HPM60 temperature and relative humidity sensor specification.*

frost, birds' excreta, and any substance that may obstruct transmission of solar radiation.

Due to the daily sun movement, the solar irradiance at the elevations of a house varies. This, however, influences the thermal impact of the windows at various elevations. Thus, four Li-Cor 200R pyranometers with one pyranometer at each of the house elevation were used to monitor the global irradiance at the various elevations. **Figure 5** shows a Li-Cor 200R pyranometer measuring the global irradiance in one of the house's elevations.

As illustrated in **Figure 5**, the pyranometers were mounted vertically on the outer surface of each of the perimeter wall. They were mounted at an even height of 1.8 m. By so doing, the solar radiation falling on the walls was measured. Li-Cor pyranometer uses a silicon photovoltaic sensor mounted in a cosine-corrected head to measure solar irradiance. Together, a variable shunt resistor circuit in the cable is used to convert the measured current to a voltage signal [30].

#### **Figure 4.**

*(a) Floor layout of the house indicating the location of the indoor thermal sensor and (b) setup outdoor weather station.*

**Figure 5.** *Li-Cor 200R pyranometer for monitoring global vertical irradiance on the east elevation of the passive solar house.*

**213**

**Figure 6.**

*irradiance chart.*

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

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

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 measure-

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

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

observed in June, July, and August, whereas the rest of the months had an average

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

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

. Due to data loss and sky formation, an irregular distribution of solar

and the maximum irradiance of 996.0 W/m2

, where periods with the sun absent pro-

was logged in February

was

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

**4.1 Ambient solar radiation analysis**

excluded in the data analysis going forward.

**Figure 4(a)** ranges from 0 to 996.0 W/m2

**4. Results and discussions**

ment period.

duce 0 W/m2

of 192.8 W/m2

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