## 4 Improvement of Energy Efficiency by Speed Regulation in Compressors A6 and A9. Results Obtained  
To calculate energy savings for the speed variation solution in compressor number 6, the histogram in Figure 11 is considered to determine the number of hours it operates at a certain degree of capacity as well as the COP values (Coefficient of Performance), for the same percentages of capacity, obtained from the manufacturer's data, the result of which can be seen in Table 3. The percentage of time is based on the maximum hours that can be worked per year (8760 h). The energy saving result for this compressor is 72,440 kWh (sum of all the savings obtained for each percentage of capacity). To estimate the total savings, we have obtained the savings by adding the savings of the rest of the compressors in the circuit, since it is assumed that the compressor with speed variation would remain in the queue, regulating the capacity of the circuit and the rest could be kept at 100% capacity levels, maximizing the COP of all compressors. In the same way, the savings analysis carried out for the rest of the \(-15\)\({}^{\circ}\)C line compressors is as follows: compressor A5: 62,865 kWh; compressor A6: 72,440 kWh; compressor A7: 45,804 kWh; compressor A8: 25,663 kWh. The total annual energy saving with the measurements carried out in the A6 compressor, regulating the capacity of the \(-15\)\({}^{\circ}\)C circuit, is 206,772 kWh. Although, as previously mentioned, the number of operating hours is a limiting factor, it is possible to keep a compressor operating for several hours to maximize energy savings. Based on the capacity analysis carried out, it was proposed to optimize the capacity management of the A6 compressor of the ammonia circuit at \(-15\)\({}^{\circ}\)C, integrating a speed variator and managing the slide regulation in conjunction with the speed variation as a function of the suction pressure (evaporation) so that the system can operate according to the graph in Figure 12 extracted from the characteristics provided by the manufacturer of the refrigeration compressors. As can be seen in the data in Figure 12, throughout the regulation range (100% to 44%), limits imposed by the working conditions of the motor/compressor (lubrication and ventilation) established by the manufacturer regarding the spin speed (2950 rpm to 1475 rpm), savings of up to 31% can be achieved. It is also worth noting that for the upper \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**COMP.A6** & \multirow{2}{*}{**Time**} & **Absorbed** & \multirow{2}{*}{**Refrigeration**} & **COP** & **Abs.** & **COP** & **Specific** & **Estimated** \\
**Capacity (\%)** & & & **Power (kW)** & **(no VSD)** & **Power** & **(VSD)** & **Saving** & **Saving** \\  & & **(kW)** & & & **VSD (kW)** & & **(kWh)** \\ \hline  
\hline
0–10 & 32.61\% & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Energy saving results due to speed variation in compressor No. 6.  
regulation range (100% to 80%), the capacity control by means of the slide acts in a similar way to the speed variation conditions, with the consequent reduction in energy saving opportunities. Another aspect to note is that with the speed variation option, the working range can be extended to reach the maximum rotation speed allowed by the manufacturer (mechanical considerations) of 3540 rpm, and in this way the compressors could expand their theoretical cooling capacity to 120% of the nominal. This possibility cannot be realized by means of mechanical slide control. The variable speed drives will be those appropriate to the power of the compressor motor. It will involve integrating input/output signals to regulate the electronics of the compressors, PLC (Programmable Logic Controller) programming integrating the control ramp, as well as a new electrical installation to integrate cabinets with variable speed drives and new electrical wiring with the required technical condition for this type of facility.