## 6 Experimental Results and Discussion
### Variation of Height Above the Rooftop
The increased wind speed which is deflected from the roof of the building is utilized by the horizontal blades to increase the torque output of the CAWT by having a larger area for the oncoming wind to interact with the turbine. Furthermore, the horizontal blades of the CAWT create aerodynamic lift force that contributes in improving the self-starting characteristics of the CAWT. The presence of the horizontal blades as the supporting struts of the CAWT can lead to double advantage to minimize the parasitic drag contribution during the revolution and to produce some positive torque [49]. Furthermore, due to the performance improvement in the CAWT due to the skewed flow effect can also lead to a reduction of the minimum cut-in speed, thus extending the operating range of the rotor and increasing the energy harvesting for the low-wind conditions. The case is not the same for the VAWT since the arms (supporting struts) of the vertical blade is not an airfoil and thus does not utilize the deflected airflow from the accelerating effect of the roof. The low \(C_{\rm p}\) output of the conventional straight-bladed VAWT is attributed to the radial arms (supporting struts) of the VAWT. The supporting struts of the VAWT inevitably affect the power output of the turbine by adding additional drag (parasitic drag) on the turbine, thereby affecting the overall performance of the VAWT [10; 44; 50]. The results are summarized in Table 3.  
Figure 13a-d compares the rotational speed of the free running CAWT and the straight-bladed VAWT placed at 100 to 250 mm height above the gabl \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Height (mm)** & **Parameter** & **CAWT** & **Straight-Bladed VAWT** & **Percentage of Improvement (\%)** \\ \hline \multirow{3}{*}{\(Y=100\)} & RPM & 554 & 179 & 209 \\  & C\({}_{\rm p,max}\) & 0.1263 & 0.0345 & 266 \\  & TSR for \(C_{\rm p,max}\) & 1.1 & 0.59 & 86 \\ \hline \multirow{3}{*}{\(Y=150\)} & RPM & 512 & 189 & 171 \\  & C\({}_{\rm p,max}\) & 0.1035 & 0.0350 & 196 \\  & TSR for \(C_{\rm p,max}\) & 1.16 & 0.60 & 93 \\ \hline \multirow{3}{*}{\(Y=200\)} & RPM & 474 & 212 & 123 \\  & C\({}_{\rm p,max}\) & 0.0859 & 0.0364 & 136 \\  & TSR for \(C_{\rm p,max}\) & 1.08 & 0.51 & 112 \\ \hline \multirow{3}{*}{\(Y=250\)} & RPM & 449 & 233 & 93 \\  & C\({}_{\rm p,max}\) & 0.0765 & 0.0448 & 71 \\ \cline{1-1}  & TSR for \(C_{\rm p,max}\) & 1.12 & 0.66 & 70 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Summary of the experimental results for the CAWT and the VAWT. The time recording is started immediately after switching on the ventilation fans. Figure 13a shows the rotational speed for CAWT and the one for VAWT at \(Y=100\) mm. The RPM for both turbines increases with time until it reaches maximum values of 554 and 179 RPM at \(t=178\) and \(t=249\) s, respectively. The rotational speed becomes constant (stabilize) after that. The maximum RPM recorded by the CAWT is 209% higher than the one for the VAWT under the same experimental conditions. Furthermore, the figure shows that the CAWT started to rotate earlier than the VAWT. At \(Y=150\) mm, the results shown in Figure 13b indicate that the rotational speed recorded by the building integrated CAWT is 171% higher than the one recorded by the building integrated VAWT (Table 3). Similarly, Figure 13c,d presents the RPM of the building integrated CAWT and the VAWT for \(Y=200\) and 250 mm height above the rooftop of the building. It can be observed from the figure that the CAWT integrated onto the building with gable rooftop outperformed the VAWT. The result showed that the RPM increases by 123% and 93%, respectively, compared to the straight-bladed VAWT mounted at the same height and subjected to similar experimental conditions. The improved performance of the building integrated CAWT is attributed to the cross axis orientation of the CAWT where the horizontal blades, which is also the supporting struts of the CAWT, utilized the vertical airflow that is deflected from the building thereby improving the overall performance of the CAWT.