## 3 Results and Discussion
### Analysis in an Industrial Refrigeration System
#### 3.2.1 Electric Power Consumed by the Condenser  
The initial condensation conditions existing in the industry unit investigated are the operation of the evaporative condenser with a nominal mass flow rate of air during all operating times of the refrigeration system. It is worth mentioning that the conditions found in the present study are normally the same in all other plants in the industrial refrigeration field. This situation represents the highest consumption of electricity by evaporative condenser fans, regardless of the variations that can occur during the thermodynamic process. When the condensation pressure was used as the operation parameter, the electric currents of the motors were found to generate the necessary mass flow rate of air to attend the refrigeration cycle and achieve the best overall energy efficiency of the plant. Table 2 shows the results of electrical current reduction as a function of nominal operation of the mass flow rate of air in the EC in an industrial refrigeration system. In that table, \(I_{\rm n}\) represents the nominal electrical current (electrical current with fan drive motor at 60 Hz), while \(I_{\rm r}\) refers to the electrical current of the fan drive motor at the frequency imputed by the pressure control system.  
The results showed that when the refrigeration system operated with a reduced mass flow rate of the air in the EC, the decrease in the electric energy consumption by EC could reach a magnitude of 86.89%. Thus, it is possible to notice that, when the refrigeration system allowed a reduction in the magnitude of the mass flow rate of air in the EC to values lower than the nominal magnitudes, it was also possible to reduce the electricity consumption. Therefore, the use of modeling to control the pressure head in the EC proved  
Figure 4: Variation of condensation temperature as a function of the mass flow rate of air.  
to be an important strategy to save energy in real refrigeration plants, leading to a large economic savings each day.  
Considering that other electrical parameters did not suffer from significant variation, an analysis could be performed in terms of the electric current consumed. Figure 5 demonstrates the variation in the electric current demanded by the EC fans as a function of the change in the mass flow rate of air. The change in electrical current caused by the variations in the mass flow rate ratio obtained here was in accordance with the expected behavior predicted by the fan laws. The results indicated that the increase in the mass flow rate of air also led to an increase in the electric current demanded by the EC fans, explaining the increase in the consumption of electric energy.  
It is worth mentioning that the refrigeration system is a liquid overfeed system, the expansion valve is a low-pressure float valve, and it is placed at the inlet of the low pressure receiver (vertical separator). The expansion valve covers a large range of liquid flow rate, in general, until 1.5 times the nominal liquid flow rate. The condensation pressure of those valves also operates in a large range of magnitudes. Thus, the condensation pressure variations promoted by the FHPTC do not provide a significant change in the operation of the expansion valve.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(\dot{m}_{\text{air}}\)/\(\dot{m}_{\text{total}}\) & \(P_{n}\) (kW) & \(P_{m}\) (kW) & **Difference (\%)** \\ \hline
1.00 & 1.89 & 1.89 & 0.00 \\
0.92 & 1.89 & 1.51 & 20.88 \\
0.85 & 1.89 & 1.16 & 38.98 \\
0.73 & 1.89 & 0.92 & 51.86 \\
0.66 & 1.89 & 0.69 & 63.81 \\
0.58 & 1.89 & 0.52 & 72.51 \\
0.48 & 1.89 & 0.40 & 79.00 \\
0.39 & 1.89 & 0.29 & 84.22 \\
0.31 & 1.89 & 0.24 & 86.89 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Current electric reduction with modification of the air mass flow.  
Figure 5: Variation of the electric current demand by the fan motor of the evaporative condenser as a function of modification of operating rotation.