# Thermal Characteristics and Parametric Analysis of an Improved Solar Wall
## 3 Thermal Characteristics Analysis of the Improved Solar Wall
### Effect of Solar Walls on the Indoor Thermal Environment and Energy Consumption  
To analyze the heating and cooling effect of solar walls under extremely climate weather, the monitoring data of three hottest days in summer (from 29 August to 31 August) and coldest days (from 24 January to 27 January) in winter were selected. The indoor air temperature of different rooms is shown in Figure 6. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Monitored Parameters** & **Instrument Name** & **Accuracy** & **Photos** \\ \hline \multirow{4}{*}{Surface temperature and heat flow} & JTNT-B & \(\pm\)0.1 \({}^{\circ}\)C \\  & Temperature & \(\pm\)0.01 W/m\({}^{2}\) \\  & test system & \\ \cline{1-1}  & & \\ Air temperature and relative & TR-72U Temperature and & \(\pm\)0.1 \({}^{\circ}\)C \\ humidity & humidity recorder & \(\pm\)1\% \\ \cline{1-1}  & & \\ Solar irradiance & E-log & \(\pm\)1 W/m\({}^{2}\) \\ Air temperature and relative & Outdoor weather station & \(\pm\)0.01 m/s \\ humidity & & \(\pm\)0.1 \({}^{\circ}\)C \\ \cline{1-1}  & & \\ Air velocity & KANOMAX-6004 & \(\pm\)0.01 m/s \\  & Hot-wire anemometer & \\ \cline{1-1} temperature field & FLIR T440 & \(\pm\)1 \({}^{\circ}\)C \\ Infrared thermal imager & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Monitored data and technical specification of measuring instruments. Figure 6: Variation of indoor air temperature in the passive solar house. As shown in Figure 6a, during the winter, the indoor air temperature was above 10 \({}^{\circ}\)C because of the passive heating of the solar wall. While the outdoor temperature fluctuated between \(-5.9\)\({}^{\circ}\)C and \(6.6\)\({}^{\circ}\)C, the indoor air temperature of living room and bedrooms was nearly the same under the heating effect of solar walls, which fluctuated between 9.2 \({}^{\circ}\)C and 15.3 \({}^{\circ}\)C. Due to the less direct heat gain, the temperature of the corridor was much lower than the south room, in the range of 7.1-9.8 \({}^{\circ}\)C.  
During the summer, the color of the absorber board changed to white and dampers were closed to prevent heat transfer between the air channel and indoor air. As shown in Figure 6b, the outdoor air temperature fluctuated between 20.5 \({}^{\circ}\)C and 31.2 \({}^{\circ}\)C during the testing period. Under the passive cooling, the air temperature of the rooms facing south (living room and two bedrooms) was in the range of 25-26.6 \({}^{\circ}\)C. By contrast, the air temperature of the corridor was lower, varying from 23.9 to 26.9 \({}^{\circ}\)C.  
The solar wall has an obvious effect on increasing indoor temperature and reducing energy consumption in winter. Experiments were carried out to determine the winter heating effect of the color-changing solar wall under clear weather. The color-changing solar wall belongs to a type of flat solar air collector. The thermal efficiency (\(\eta\)) can be obtained as the ratio of the useful energy (heat gained) by the flowing air to the amount of total solar energy incident on the absorber surface area at any time as presented as follows:  
\[\eta=\frac{mc_{p}(T_{out}-T_{in})}{A\cdot G} \tag{1}\]  
The air mass flowrate m at the end of the hot air passage duct can be determined as:  
\[m=\rho A_{f}u \tag{2}\]  
The measured outlet air temperature and air velocity of the collector are shown in Figure 7a. Based on the experimental data and equations, the heat supplied by solar walls is shown in Figure 7b, the average daily heat output of the color-changing solar wall is 1.08 MJ per unit floor area on clear days in winter. The average thermal efficiency of the solar wall is 56.8%. The application of solar walls is mainly reflected in reducing the annual energy consumption of buildings. Taking the experimental solar house in Dalian as an example, the application effect of solar walls is quantitatively analyzed. According to the climate data of Dalian and the thermal parameters of the reference building, the annual heating demand of the solar house is 466.5 MJ.