## 5 Methods
### Experimental Set-Up  
For testing and comparing the performance of the CAWT with the conventional straight-bladed VAWT, the following configurations were considered:  
1. CAWT mounted on building mock-up rooftop;
2. Straight-bladed VAWT mounted on the same mock-up rooftop; and
3. Variation of height (CAWT and VAWT) above the rooftop.  
The experimental set-up for this study is presented in Figure 9. Figure 9a shows the experimental set-up, and Figure 9b shows the detail dimensions of the building model and the ventilation fans, used for the study respectively. The set-up consists of a building model with gable rooftop with 35\({}^{\circ}\) roof angle. The CAWT and the straight-bladed VAWT were mounted at heights of \(Y\) = 100 to 250 mm at 50 mm intervals above the rooftop of the building model as shown in Figure 9b. The wind speed measurements were taken downstream of the ventilation fans placed at a distance of 3500 mm away from the building model. The ventilation fans were arranged in an array in a 3 \(\times\) 3 configuration as shown in Figure 9a. An arrangement of 3 \(\times\) 3 equally spaced grid points which covers a cross-section of 1.0 m by 1.0 m downstream of the fan array was used for the measurement of the wind speed which was set at 4.5 \(\pm\) 0.2 m/s. The wind direction is set at 0\({}^{\circ}\) (i.e., perpendicular to the building model). Since the flow was not controlled, the blower was directed orthogonal to the test section area and the wind speed was measured at different lengths to conform spatial uniformity. The central axis of the turbine was taken as the center point, the wind speed measurements were taken at each measuring points by using a vane anemometer over a period of 5 min, repeatability and airflow uniformity were ensured by repeating the measurements for ten times at each point. To reduce the vortex flow createdby the blower, the wind speed error was reduced from \(U_{\infty}\) = 5.0 m/s \(\pm\) 0.8 (3.0 m) to 4.5 m/s \(\pm\) 0.2 (3.5 m), therefore creating a more uniform flow.  
The rotor of both the CAWT and the straight-bladed VAWT were in free-running conditions where only the inertial and bearing friction were applied. The measurement of the rotational speed (RPM) of both the turbines started immediately after switching on the ventilation fans until the stabilized RPM is achieved. The measurement was performed with a dynamometer controller system (Figure 10), which consists of a rectifier and resistive dump load. For current and voltage measurements, the alternating current (AC) voltage from the generator is rectified to direct current (DC). Frictional loss due to the generator is assumed to be negligible. The experiments were conducted for the above-mentioned configurations on the same building with the same roof shape under the same experimental conditions. The coefficient of power (\(C_{\mathrm{P}}\)) is calculated using Equation (2), and by rearranging Equation (2), the power extracted by the turbine can be calculated.  
Figure 9: (**a**) Experimental set-up of the CAWT; and (**b**) detailed dimensions of a building integrated with a CAWT and dimensions of the ventilation fans (all dimensions in mm).