## 2 Methodology
### Modeling of the Logical Control  
Environmental conditions are constantly changing, which affects the refrigeration system operation. Therefore, any manual intervention in the system probably would not lead to any energy savings. Thus, the use of some autonomous strategy, such as logical modeling, allows the achievement of continuous decisions to ensure the operation of the refrigeration system in a more efficient way. The logical control modeling developed in this work consisted of the dynamic analysis of the variations suffered by the condensation pressure inside a refrigeration system. During a configurable period, taking the evaporative condenser pressure as a principal parameter, the model examined the possibility of modifying the rotation of the electric motors of the heat exchanger fans to increase or reduce the airflow rate in the device. The dynamic modulation applied to the fan produced variations in the electrical power demands of the condenser and compressor. This change could initially modify the heat transfer rate rejected in the condenser, requiring a modification of the condensation  
Figure 2: Divisions of the air intakes of the industrial refrigeration unit of the evaporative condenser for the measurements of the inlet velocity. pressure so that the thermal balance could be satisfied. These continuous modifications directly influenced the compression ratio pressure in which the compressor is operating. The flowchart illustrated in Figure 3 shows the main steps explaining the logical control modeling work. At any instant of time, various monitored physical quantities were acquired using the measuring instruments connected to the PLC, such as the head condensation pressure, the suction pressure, the \(T_{\text{DB}}\), the \(T_{\text{WB}}\) inverter frequency, and the electrical consumption. Next, these values were analyzed by the model and compared with the previously stored data from previous measurements. If the answer of the logical model was positive for modulation as a function of the previous air mass flow rate, the controller changed the frequency value to be transmitted to the electric motor of the fan. This new operating mass flow rate of air led the refrigeration system to a new thermodynamic equilibrium seeking to identify the point of the lowest electricity consumption. The programming was developed using structured block language and scripts. The flowchart of the algorithm consisted of the following logical process steps:  
1. Initially, it started the refrigeration facility with the airflow rate of the evaporative condenser (EC) at the maximum magnitude;
2. The model collected the operation data variables that were part of the process;
3. At this point, the condensation pressure value was changed. In this step, if the head pressure achieved a critical limit as previously established, logical control modeling improved the maximum mass flow rate of the air through the EC to reduce the pressure levels. At each pressure input, it was necessary to wait a required time interval for stabilization of the pressures and temperatures. The stabilization time is very important to the system to avoid impacts caused by the variation of the mass flow rate of the air. If the condensation pressure did not achieve a critical level, the logical  
Figure 3: Flowchart of the developed logical model of control. model read the instantaneous consumed power and, at the same time, evaluated the magnitudes of the other stored quantities (condensation pressure and temperatures);
4. In case a reduction in the electricity consumption has occurred, the algorithm examined the last item in the database and identified whether there was a reduction in the frequency operation of electric motors of the fans. If positive, the algorithm decided to reduce the operation frequency again. If negative, the algorithm increased the frequency.