## 6 Experimental Results and Discussion
### Variation of Height Above the Rooftop  
The height of the building integrated CAWT and the conventional straight-bladed VAWT were varied from \(Y=100\) to \(250\) mm above the gable rooftop of the building. Figure 12a-d compares the \(C_{\rm p}\) values between the building integrated CAWT and the conventional straight-bladed building integrated VAWT at turbine height \(Y=100\), \(150\), \(200\) and \(250\) mm. Results showing similar trend were obtained for Figure 12a-d. Figure 12a shows the coefficient of power against the tip speed ratio of the CAWT and the VAWT placed at \(100\) mm height above the rooftop of the building model. Based on the results obtained in Figure 12a, the CAWT can attain a maximum \(C_{\rm p}\) of \(0.1263\) at a TSR (\(\lambda\)) of \(1.1\). The maximum \(C_{\rm p}\) of the conventional straight-bladed VAWT integrated on the same rooftop of a building and subjected to similar experimental conditions is \(0.0345\) at a TSR (\(\lambda\)) of \(0.59\) (Figure 12a). The result shows that the \(C_{\rm p,max}\) for the CAWT increased by \(266\%\) compared to the straight-bladed VAWT for \(Y=100\) mm as shown in Table 3. Figure 12b compares the \(C_{\rm p}\) values between the CAWT and the straight-bladed VAWT placed at \(150\) mm height above the building model. The result showed that the maximum \(C_{\rm p}\) recorded by the CAWT at \(Y=150\) mm is \(0.1035\) at a TSR (\(\lambda\)) of \(1.16\) higher than the \(C_{\rm p,max}\) value recorded by the straight-bladed VAWT whose highest \(C_{p}\) value is \(0.0350\) at a TSR (\(\lambda\)) of \(0.60\). This shows that at \(150\) mm height above the gable rooftop, the CAWT outperformed the conventional straight-bladed VAWT by \(196\%\). This increase in \(C_{\rm p}\) values by the CAWT is attributed to the horizontal blades which serve as a horizontal axis wind turbine by interacting with the vertical airflow that is deflected from the building. Figure 12: Coefficient of power against tip speed ratio for CAWT and straight-bladed VAWT for height above the rooftop: (**a**) \(Y=100\) mm; (**b**) \(Y=150\) mm; (**c**) \(Y=200\) mm; and (**d**) \(Y=250\) mm. Figure 12c presents the \(C_{\rm p}\) value of the building integrated CAWT and the straight-bladed VAWT for \(Y=200\) mm. It can be observed that the CAWT outperformed the conventional straight-bladed VAWT. The results showed that the \(C_{\rm p}\) value attained by the CAWT is higher than that recorded by the VAWT. The maximum \(C_{\rm p}\) value recorded by the building integrated CAWT and VAWT are 0.0859 at a TSR (\(\lambda\)) of 1.08 and 0.0364 at a TSR (\(\lambda\)) of 0.51. In comparison, the maximum \(C_{p}\) value for the building integrated CAWT is 136% higher compared to the maximum \(C_{p}\) value of the building integrated VAWT. The improved performance of the building integrated CAWT is attributed to the horizontal blade which utilized the vertical wind deflected by the building and the pitch angles of the horizontal blades which expose the horizontal blades to an optimum angle of attack to the vertical wind. Similarly, the result presented in Figure 12d for \(Y=250\) mm indicates that the \(C_{p}\) value of the building integrated CAWT increases by 71% compared to the conventional straight-bladed VAWT under the same experimental conditions. The maximum \(C_{p}\) value recorded by the building integrated CAWT and VAWT at \(Y=250\) mm are 0.0765 at a TSR (\(\lambda\)), of 1.12, and 0.0448 at a TSR, (\(\lambda\)) of 0.66. The result were summarised in Table 3, and the \(C_{p}\) values were calculated using Equation (2). In general, the building integrated CAWT is shown to have better performance than the VAWT for all the configurations (100-250 mm). These significant improvements in the \(C_{\rm p}\) values of the building integrated CAWT is attributed to the cross axis orientation of the CAWT which enables it to operate with dual wind directions. The roof shape acts as an augmentation device to further increase the wind speed due to the accelerating effects of the roof.