## 3 Experimental Setup
### Employed Testing Protocol  
The employed experimental protocol to measure the hydraulic performances of both the microturbine and the PAT is provided in Figure 5. First, all the instruments have been systematically calibrated and/or rechecked before the beginning of measurements. Considering the classical point-by-point method, the measurements on the microturbine have been performed for 11 different testing head values to build the full efficiency 3D hill-chart of the microturbine. Moreover, as resumed in Table 2, nine values of constant ratio \(\alpha\) between the runners' absolute rotational speed were systematically considered for each constant testing head. That makes a total of more than 1000 acquired operating points. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Measured Quantity** & **Sensor Type** & **Range** & **Accuracy** \\ \hline \multirow{2}{*}{Discharge (Q)} & \multirow{2}{*}{Danfoss MAGFLO MAG3100 Water} & \multirow{2}{*}{0.\(\pm\)100 [m\({}^{3}\)/h]} & \multirow{2}{*}{\(\pm\)0.5 [\%]} \\  & electromagnetic flowmeter & & \\ \hline \multirow{2}{*}{Head (H)} & \multirow{2}{*}{Endress and Hauser Deltabar  M PMD55} & \multirow{2}{*}{0.16 [bar]} & \multirow{2}{*}{\(\pm\)0.1 [\%]} \\  & differential pressure sensor & & \\ \hline \multirow{2}{*}{Setting level (H\({}_{\text{S}}\))} & \multirow{2}{*}{Fuji FCX-CII Series differential pressure sensor} & \multirow{2}{*}{0.5 [bar]} & \multirow{2}{*}{\(\pm\)0.2 [\%]} \\ \hline \multirow{2}{*}{Absolute static pressure (M\({}_{1,2,3,4}\))} & \multirow{2}{*}{Endress and Hauser Cerabar T PMC 131} & \multirow{2}{*}{0.10/20 [bar]} & \multirow{2}{*}{\(\pm\)0.05 [\%]} \\  & capacitive pressure transducer & & \\ \hline \multirow{2}{*}{Water Temperature (T)} & \multirow{2}{*}{Endress and Hauser Easytemp TMR 31 PT100} & \multirow{2}{*}{0.100 [\({}^{\circ}\)C]} & \multirow{2}{*}{\(\pm\)0.1 [\%]} \\  & transducer & & \\ \hline \multirow{2}{*}{Pumps’ rotational speed (Np\({}_{\text{p1,2,3}}\))} & \multirow{2}{*}{Sick VTF180-2P42417 photoelectric proximity sensor} & \multirow{2}{*}{0.1000 [Hz]} & \multirow{2}{*}{-} \\  & & & \\ \hline \multirow{2}{*}{Mechanical torque (T\({}_{\text{mec.A,B}}\))} & \multirow{2}{*}{NCTE 2200 torquemeter} & \multirow{2}{*}{0.\(\pm\)7.5 [Nm]} & \multirow{2}{*}{\(\pm\)1 [\%]} \\ \hline \multirow{2}{*}{Turbine rotational speed (N\({}_{\text{A,B}}\))} & \multirow{2}{*}{IED incremental encoder} & \multirow{2}{*}{0.7500 [min\({}^{-1}\)]} & \multirow{2}{*}{2048 [ppr]} \\  & & & \\ \hline \multirow{2}{*}{Electrical power (P\({}_{\text{elec}}\))} & \multirow{2}{*}{Zimmer LM5500 precision electrical} & \multirow{2}{*}{0.1000 [V\({}_{\text{rms}}\)]} & \multirow{2}{*}{\(\pm\)0.03 [\%]} \\  & multimeter & & \\ \hline \multirow{2}{*}{PAT rotational speed (N)} & \multirow{2}{*}{Incremental encoder} & \multirow{2}{*}{0.6000 [min\({}^{-1}\)]} & \multirow{2}{*}{4096 [ppr]} \\ \hline \multirow{2}{*}{**Data acquisition and control**} & \multirow{2}{*}{} & \multirow{2}{*}{} \\ \hline \multirow{2}{*}{NI CompactRIO 9074 controller} & \multirow{2}{*}{Dedicated to the control/monitoring of the test rig} & \multirow{2}{*}{} \\  & & & \\ \hline \multirow{2}{*}{NI cDNAQ-9174 digitizer} & \multirow{2}{*}{Dedicated to the control/monitoring of the testing model using the standard static measurements method} & \multirow{2}{*}{} \\  & & \\ \hline \multirow{2}{*}{NI cDNAQ-9174 digitizer} & \multirow{2}{*}{Dedicated to the control/monitoring of the testing model for the dynamic measurements} & \multirow{2}{*}{} \\  & & \\ \end{tabular}
\end{table} 
Table 1: Main characteristics of the employed instruments for performance measurements. Figure 5: Flowchart of the employed experimental protocol [32; 33]. In the case of the PAT, the measurements have been performed at 10 different constant rotational speed values of the recirculating pumps.