# Model-Based Assessment of Energy Efficiency in Industrial Pump Systems: A Case Study Approach
## 6 Results
### Simulation Results for Energy-Efficiency Indicators  
The simulation results for the energy-efficiency indicators of the five system variants are summarised in Table 6. The table also contains statistics for a drive that corresponds to the existing system and is listed in the penultimate column (258-IE1). The last column shows the indicators for the existing pump system calculated on the basis of the model obtained from the on-site measurements (as described in Section 2). All five system combinations show a saving of around 30% in energy consumption. However, the two variants with IMs are slightly less efficient, with variant 252-IE3 performing the worst with 26.15% savings. This is mainly due to the fact that the system is designed with a larger reserve, so that the pump operates with a lower relative load and consequently with a lower efficiency. The lower efficiency of IMs at lighter loads further exacerbates the problem. In contrast, SRMs perform significantly better with light loads than IMs, which leads to considerable energy savings. For example, the 237-IE5 achieves 2 percentage points more savings than the 237-IE3. The difference is even more pronounced when comparing the SRM-based 252-IE4 and 252-IE5 with the IM-based 252-IE3, with the SRMs achieving almost 7 percentage points higher savings. A comparison of the energy performance indicators between variant 258-IE1, which represents the simulation equivalent of the existing system, and the indicators obtained from measurements on the existing system shows very good agreement. In particular, the very small difference of 1.8% in electrical energy in favour of the measured value gives us a high degree of confidence in the accuracy of the simulation models and their results. If the simulated value for the electrical energy of the simulation equivalent were taken as a reference point, the estimated energy savings would be even slightly higher. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Energy-Efficiency Indicator** & **237-IE3** & **237-IE5** & **252-IE3** & **252-IE4** & **252-IE5** & **258-IE1** &
\begin{tabular}{c} **Exis.** \\ **System** \\ \end{tabular} \\ \hline \(\eta_{\text{sys}}\) average & (\%) & 48.33 & 50.67 & 45.46 & 49.68 & 50.94 & 32.29 & 34.22 \\ \(\eta_{\text{sys}}\) maximum & (\%) & 75.30 & 77.04 & 76.16 & 78.50 & 79.62 & 67.80 & 55.74 \\ \(P_{el}\) average & (kW) & 2.4814 & 2.3865 & 2.5886 & 2.4054 & 2.3527 & 3.5668 & 3.5052 \\ \(P_{el}\) maximum & (kW) & 13.125 & 12.766 & 12.882 & 12.497 & 12.322 & 14.554 & 17.615 \\ \(W_{el}\) & (MWh) & 20.997 & 20.194 & 21.904 & 20.354 & 19.908 & 30.182 & 29.66 \\ \hline
**Energy savings** & **(\%)** & **29.21** & **31.92** & **26.15** & **31.38** & **32.88** & \(\mathbf{-1.76}\)** & \(\mathbf{0}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of the energy-efficiency indicators of different pump–motor variants. The overlay of the annual dataset and the system efficiency maps with operating limits (Figures 15-17) provides a clear and comprehensive insight into the sizing of the pump system with respect to the operating requirements. As the maximum electrical power in the proposed pump systems is around 13 kW, there is some operating reserve even for the smaller 237 pump-based systems. This is shown by the fact that the annual dataset of operating points does not exceed the lower torque limit (unutilised TR, shown in red). The extent of the oversizing of the original pump system (shown here by the equivalent 258-IE1) is clearly visible in Figure 17b, where only the lower left part of the characteristics is utilised. As a result, the VSDP operates almost continuously at low efficiency. The dataset does not reach the maximum system efficiency range for any of the proposed VSDP variants, so there is a potential to further increase the energy savings by selecting even smaller system components. Interestingly, the moderately oversized, high-efficiency SRM-based 252-IE5 system delivers the best overall energy performance.