PLC/SCADA systems in automation control design for individual quick freezing process in cooling tunnels Goran Jagetić, Marko Habazin, Tomislav Špoljarić University of Applied Sciences - Department of Electrical Engineering, Zagreb, Croatia [email protected], [email protected], [email protected] ABSTRACT - Individual quick freezing process is a two periods of operation: refrigeration period and complex cooling process that takes place in cooling defrosting period. Refrigeration period is longer and tunnels and is used for dynamic thermal processing of in it refrigeration elements (compressor, condenser certain type of goods. Type of goods and temperature and evaporator fans) are switched according to room of goods that needs to be achieved over specific time in temperature probe/probes. Defrosting period is much cooling tunnel determine the complexity of cooling process. Complex cooling process is therefore divided shorter and in it defrosting elements (electrical into two types of regulation. Temperature regulation, heaters/hot gas valve) are switched according to the inferior type, is used for control of the cooling and evaporator temperature probe or by time (off- defrosting parts of the system according to predefined delayed timer function of a regulator). Fig. 1 shows room temperature. Superior time-cycle regulation is simplified block diagram of a small scale used to control various cycles of operation by defining refrigeration system operated by one-cycle its time frames. These cycles together form a period of regulation (refrigeration with defrost). time in which the cooling system is appropriately used for goods' freezing. This paper describes further development in automation control design for complex cooling process in cooling tunnels. This design includes selection of appropriate control devices (temperature/pressure Compressor regulators, PLC device, HMI/SCADA), definition of LADDER program solution for dynamic time-cycle control, connection and configuration of HMI/SCADA system used for defining the number/duration of time cycles of cooling and defrosting operations and Condenser (fans) monitoring the system conditions. I. INTRODUCTION probe Regulator . Simple cooling process [1] is thermal process used in refrigeration systems for maintaining room temperature via temperature regulator and at least one temperature probe. Temperature is achieved and Fans temp Evaporator Heaters maintained by correct switching of refrigeration probe . system elements – compressor, electromagnetic valve, evaporator fans and condenser fans. This EMvalve basic type of operation is not time-dependent and is most commonly used in small scale cooling systems Roomtemp with required temperature above 0°C. When required room temperature needs to be maintained below 0°C, refrigeration system needs Evaporator defrosting for evaporator section due to icing. This Cold room is done by switching the electrical heaters that need Figure 1. Block diagram of a simple cooling process to be inserted into the evaporator section or, when electrical defrost is not available, by defrosting with On a fig. 2 a time flow diagram of a simple hot gas. Defrosting element operation (heater or cooling process is shown with one cycle control valve) is done separately from other refrigeration design (refrigeration with defrost period). A system elements (compressor, fans, etc.). repeating time cycle duration is described with When defrost is needed, control design takes simple equation: form of one cycle regulation [1] thus making it time dependent. A repeating cycle of operation consists of 푇푐 = 푇푟 + 푇푑, (1) 1896 MIPRO 2015/SP where 푇푟 is a refrigeration period duration and 푇푑 is durations, and three defrost periods of same a defrost period duration. When refrigeration process duration. Processing time is defined with 푇푝: is active, temperature regulation according to room temperature probe is active. When defrost process is 푇푝 = 푇푟1 + 푇푟2 + 푇푟3 + 3 ∙ 푇푑, (2) active, temperature regulation according to evaporator temperature probe is active. on on process stateprocess off process state process off time T T T time d d r1 r2 r3 d Tr Td T T T Tc1 Tc2 Tc3 Tc Tc Tc Tp refrigeration process state refrigeration process state defrost process state defrost process state Figure 2. Time flow diagram of a simple cooling process Figure 3. Time flow diagram of a three-cycle complex cooling The complexity of a described control system process may increase in larger cooling systems by adding also the pressure control in suction line (for Processing time is a duration of a whole process sequential switching control of the compressors in a and it can be repeated. But in individual quick multiset) and discharge line (sequential switching freezing it is a duration of a freezing process of control of condenser fans). Most of today’s goods, therefore it is not repeated until the next temperature regulators have a two cycle control, goods’ exchange. which also increases the complexity by defining There is a possibility for defrost and durations of two different refrigeration periods, refrigeration elements of a system to act at the same while defrost duration is the same in each cycle, but time for a brief moment when system goes from one is also user defined. All these additions still make the state to another. That may be unwanted in larger cooling process simple. systems from perspective of rational electric energy consumption and unwanted protective elements’ II. COMPLEX COOLING PROCESS AND switching states. In that case pause periods are INDIVIDUAL QUICK FREEZING introduced. Pause periods maintain the system When defining complex cooling process, one inoperative for short period (about 5 to 10 seconds) needs to take into account that room temperature is in order the switching to be done properly. not the main parameter. Room temperature is With this in mind, processing time for 푛 intermediary parameter for achieving the main number of cycles can be generally described as: parameter - temperature of goods that needs to be 푛 achieved over time. This type of processing certain 푇푝 = ∑(푇푝푟,푖 + 푇푟,푖 + 푇푝푑,푖 + 푇푑,푖), (3) type of goods requires specific definition of time 푖=1 cycles involved in process [3]. By specific definition it is assumed that each cycle has its duration defined where for i-th cycle terms are: by end user. It means that each operation period, - 푇 – refrigeration period, whether it is refrigeration or defrost period, has also 푟,푖 its duration defined in each of the cycles. A number - 푇푑,푖 – defrost period, of cycles is also defined by end user. - 푇푝푟,푖 – pause period before refrigeration, Because there are a lot of types of goods that - 푇푝푑,푖 – pause period before defrost. can be cooled or frozen over time [5], control system Complex cooling process may be implemented design for one system needs to have a possibility for in control design of a small scale refrigeration end user to define number of operating cycles and system (temperature control only with switching of various durations of that cycles, thus making it compressors and fans), as well as in larger scale possible for one system to process different type of refrigeration systems’ control designs with pressure goods. This type of design makes the system time- and temperature control. One such design is dependent, which requires more than one control described in this paper. This proposed design is device to maintain the process on a desired level of implemented to work with large scale refrigeration efficiency. system in a freezing tunnel. Cooling process that On fig. 3 a time flow diagram of one such takes place in a tunnel is also known as individual complex cooling process is shown. This process quick freezing. consists of three refrigeration periods of different Individual quick freezing is a refrigeration process of a complex nature that manages predefined MIPRO 2015/SP 1897 type of goods. Generally, the term or its abbreviation probes inside the compressor, the pRack device IQF relates to fast freezing process of solid foods manages the switching of the compressor. such as various types of vegetables, meat, fish or Evaporator control with MPXpro® operates fruit while trying to preserve virtually most of the according to inlet and outlet temperature of the properties of the parent foodstuffs. A great and fast evaporator during refrigeration period. In defrost reduction in room/tunnel temperature reduces period electric heaters are switched according to rapidly the temperature of goods. This halts the evaporator temperature probe. MPXpro® controller activities of microorganisms that cause goods to manages also the opening of electromagnetic valve deteriorate and generate toxic substances. and sequential opening of the thermoexpansion Additionally, the enzymatic and biochemical valve. reactions of the digestive enzymes which are found in all living tissues and whose activities continue even after death are also greatly reduced. In goods Compressor 1 frozen with IQF process there is no clumping together and there aren’t any pieces of grains. Goods Compressor 2 remain individual separate pieces. Hence the term microcontroller device “individual” [6]. Compressor/condenser There are several types of individual quick freezing processes [4], and the one described in this paper is called individual quick freezing in air-blast freezing tunnels. The goods intended to be frozen are placed on trays. These trays are placed inside the tunnel, where freezing process takes place for a Condenser 1 fans