## 3 Measurements  
In Table 1, it can be seen how the work between the different compressors of the same circuit is quite distributed. This fact, together with the number of annual working hours that is limited since the facility works two shifts and not three, conditions the return on investment for a general speed variation solution. Figure 6 graphically shows the operating profile obtained from the different groups of compressors in a typical summer week, during a few days of the first week of July. In the same way, more detailed measurements were made for a typical winter day during the month of February (Figure 7). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Paspiration** & **Pondensation** \\ \hline Circuit NH\({}_{3}-40\)\({}^{\circ}\)C & 0.61 bar & 12.40 bar \\ Circuit NH\({}_{3}-33\)\({}^{\circ}\)C & 1.20 bar & 12.60 bar \\ Circuit NH\({}_{3}-15\)\({}^{\circ}\)C & 2.35 bar & 12.20 bar \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average operating pressure values of the refrigeration circuits. Figure 6: Operation profile of the different groups of compressors in the summer period. The data in Figures 6 and 7 obtained from the operation measurements of the factory facilities control system help to visualize the operation mode and the average capacity level of the facility. With the capacity analysis, it was possible to measure the percentage of time (in a period of 30 days) for a certain level of capacity for each of the three refrigeration circuits (Figure 8). A greater detail of the independent capacity analysis for each of the lines shows the results for each of the lines: the line for the \(-40\)\({}^{\circ}\)C circuit formed by three compressors (A1, A2 and A9) (Figure 9); the line for the \(-33\)\({}^{\circ}\)C circuit formed by two compressors (A3  
Figure 8: Capacity analysis for refrigeration circuits. Figure 7: Operation profile for a typical day in February. and A4) (Figure 10); the line for the \(-15\)\({}^{\circ}\)C circuit formed by four compressors (A5, A6, A7 and A8) (Figure 11). In Figure 9, the red columns indicate the percentage of time it is at a certain percentage (of capacity) over the nominal revolutions of the compressor, unlike the rest of the columns that the joint capacity axis indicates the average position in which the slide is located and therefore the average load percentage of the compressor. Based on the results obtained, it is easy to see how only compressor A9 presents an opportunity in terms of capacity regulation through speed variation (VSD), since the rest of compressors, including compressor A1 which already has VSDs, are practically above  
Figure 10: Capacity analysis for the \(-33\)\({}^{\circ}\)C circuit. Figure 9: Capacity analysis for the \(-40\)\({}^{\circ}\)C circuit. 90% all the time or stopped, which greatly limits the return on the investment of a solution of this type from the energy point of view. It should be noted that during the analysis, it is seen that the capacity regulation in compressor A1 is carried out mainly by slide. As can be seen in Figure 9, the capacity regulation by speed variation (red column) occurs in very punctually and in short periods of time, with the result being that 95% of the time, the compressor is stopped or above 90% of the nominal revolutions of the compressor. In the capacity analysis of the circuit at \(-33\)\({}^{\circ}\)C (Figure 10) formed by two compressors (A3 and A4), more than 20% of the time, the compressors in this circuit are at partial load, which means that almost 60% of the time they are unemployed, which is why the capacity regulation solution by speed variation is not economically viable from the point of view of strictly energy saving. Despite this, there may be other technical reasons and reliability that do justify it.