PLC-TRRC PLC Industrial Process Control for TRRC

The objective of the Computer Controlled Refrigeration Unit with Refrigeration and Freezing Chamber "TRRC" designed by EDIBON is to introduce the student into the complex world of refrigeration systems, as well as to study and determine the characteristic operation parameters of the unit in function of the environmental demands (heat, temperature, refrigeration, etc.).

It is a unit designed to study a refrigeration system with two different chambers at different temperature. The refrigeration unit basically consists of a refrigeration circuit but, unlike usual circuits, it has two evaporators, one per chamber. Each evaporator has an evaporation pressure that enables to obtain different temperature conditions in the chambers.

Besides, this unit helps to acquire knowledge about design on purpose of the individual components.

This procedure performed by this unit consists of the following stages:

• Compression: This stage begins when the refrigerant enters the compressor. This refrigerant is compressed, increasing its pressure and temperature. The unit includes a pressure sensor, a manometer and a temperature sensor to measure those variables.
• Condensation: The refrigerant is driven to the condenser, where its temperature decreases, at constant pressure, and its state changes to liquid state. This change is explained because heat is given to the external air in the condenser. At the end of this stage, the pressure and temperature of the refrigerant are measured with a manometer and a temperature sensor. After leaving the condenser, the refrigerant goes to the accumulator, where it is stored to a greater or lesser extent in function of the chambers demand, and to a filter, to retain condensate particles. The flow is measured by a flow sensor. Before the expansion, it’s possible to cool the refrigerant in a heat exchanger to get down the temperature (supercooling process), to increase the efficiency of the process.
• Expansion: From that point, with two solenoid valves, the circuit branches in two paths covered simultaneously, one per chamber. After the valve that defines the path, the pressure and temperature of the refrigerant decreases in the expansion valve and its states becomes a mixture of liquid and vapor. At the end of this stage the pressure and temperature of the refrigerant is measured by a pressure sensor, a manometer and a temperature sensor. Solenoid valves enable the individual or parallel operation of the evaporators in the two chambers.
• Evaporation: Finally, the refrigerant enters the evaporator, where it is gradually transformed in gas due to the heat absorbed coming from the inside of the chamber. This process is carried out in the refrigeration chamber at a pressure and temperature higher than in the freezing chamber thanks to a valve that regulates the evaporation pressure, which enables to evaporate at higher pressures and temperatures. In the freezing chamber there is an electric heating element to remove any possible layer of frost after finishing the process. The pressure and temperature of the refrigerant are measured at the outlet of each chamber with a manometer and a temperature sensor and the effect of the evaporation pressure controller on the overall process is examined. The flows coming from both chambers are mixed at the end of this stage and then they pass through a liquid separator to retain liquid particles before entering the compressor again. The inlet conditions to the compressor are measured by a pressure sensor, a manometer and a temperature sensor. There is a pressure switch located between the inlet and outlet of the compressor that stops the process when hazardous pressures are reached.

All the components are arranged clearly in the unit and a signal lamp in the process schematic indicate the operating state of the selected components.

This Computer Controlled Unit is supplied with the EDIBON Computer Control System (SCADA), and includes: The unit itself + a Control Interface Box + a Data Acquisition Board + Computer Control, Data Acquisition and Data Management Software Packages, for controlling the process and all parameters involved in the process.