Behind the Scenes of Creating Automation Strategies

Automating refrigeration systems helps provide stable and energy-efficient refrigeration for pharmaceutical goods. Automated alarm processes help businesses ensure they protect their refrigerated stock from rising temperatures. We talked to refrigeration control and monitoring expert Adrian Westrup – Head of Sales UK Retail & EMEA at RDM – who provided tips about building redundancy into the system, sensor calibration, and monitoring specific parts about the refrigeration system such as defrost heaters.

Programmable Logic Controller (PLC) software is essential when it comes to creating automated control strategies for refrigeration systems. Can you tell us what PLC software is and give examples of the control possibilities it provides for refrigeration systems?

PLC software is used to program, monitor and control industrial automation systems, refrigeration plant is one example.

Using PLC software, engineers can create and implement bespoke, automated control strategies that meet the client’s exact specification whilst enhancing reliability and providing precise temperature control. The engineer can include a range of energy efficient solutions and alarm automation in this design.

Some example control possibilities include the implementation and control of redundancy/ backup systems, optimised evaporator fan speed control, enhanced defrost management and control, emergency response automation, preventative maintenance activities, energy management and reduction, as well as remote monitoring and control.

Catching rising refrigeration temperatures quickly is crucial in the pharmaceutical industry. What automated monitoring options are available for businesses to catch issues?

In the first instance, the accuracy and resolution of the sensors is critical. A good PLC device should monitor things like temperature and humidity as close to real-time as possible and allow for the calibration of these sensors.

Another enhancement is the generation of periodic reminders for the engineer to check and confirm accuracy of these sensors. The system should generate alarm notifications when sensors deviate from pre-determined limits to account for faulty sensors or genuine deterioration of the refrigeration plant or faults. Including redundant sensors allows for a failsafe but they can also provide a comparison to verify the primary sensor’s accuracy and performance.

With accurate sensor data, the system can highlight potential plant failures to allow engineers to rectify issues before they become a problem. But more importantly, the system provides a mechanism to protect product quality and maximise shelf life.

If problems occur, integration of the PLC to a Building Management System (BMS) is key for alarm monitoring. This is typically achieved using industry communication protocols such as XML, Modbus or BACnet. It can also be advantageous if the PLC can generate alarm notifications directly in the form of SMS text messages, local audible and visual indications, or email alerts.   

If there is an over-temperature alarm, it’s important that it is resolved as quickly as possible. How can automation software and other technology help?

Near to real time data monitoring is one way to allow systems to react as quickly as possible. PLC systems which utilise IP based networks, such as Ethernet/IP over CAT6 or CAT7 patch cables, Wi-Fi and fibre, have speed advantages over older legacy networks such as RS485. This enables BMS systems to be alerted to deviations from specification as quickly as possible. 

A comprehensive system will monitor both the refrigeration plant performance and product core temperature. If the refrigeration system starts to struggle, the refrigeration engineer will get advance notice should the system fail to achieve the required temperature. A high product core temperature, determined by either product simulation probes or insertion probes embedded in the product, allow the system to alert staff when it’s time to take action to preserve stock. The product probe can also form part of the business’s due diligence and temperature compliance records. 

Introducing data analytics and predictive maintenance software enables the PLC to highlight failures in advance, once the refrigeration equipment deviates from expected operation. Engineers can take action hours or sometimes days in advance of an actual breakdown, minimising the likelihood of a complete refrigeration failure. This would prevent stock loss or staff time lost to removing products from a faulty unit.

These solutions also allow engineers to perform plant comparisons between one system and another, providing a mechanism for identifying well or poorly performing equipment.

The use of additional sensors and system data can help generate a more robust monitoring solution and highlight issues in advance. One of the more common failures in the refrigeration cycle is a fault with the evaporator defrost heater. By introducing a Current Transformer (CT) an engineer can design an automation solution which monitors the current draw of the defrost heater when activated. If the current is too small it could indicate a fault with the heater or associated control wiring. This highlights failures as they occur and enables engineers to react quicker. 

Without this automation solution, the efficiency of the evaporator would drop over time and potentially result in the evaporator completely icing up. The engineer would only become aware of issues when the cold store/cabinet went over temperature. 

What automated alarm solutions are available to help businesses achieve stable refrigeration temperatures and energy efficient operations?

One solution revolves around the performance of a refrigeration pack’s condenser or gas cooler. This feature monitors the efficiency of a condenser or gas cooler to highlight energy wastage. Three probes are fitted to measure liquid return, discharge and ambient air temperature. The temperature difference across the condenser is calculated and monitored. If it drops below three predefined alarm limits, a notification is generated for each. This signals that the condenser is not operating efficiently, for example due to the condenser being blocked with debris or a fan failure. A second method would involve measuring and comparing the outlet temperature with the ambient air temperature.

Another feature would monitor the defrost cycle of an evaporator in a cold store or cabinet. The defrost warning feature will give a warning if a consecutive number of defrost cycles on a particular evaporator terminate on its time limit as opposed to the defrost temperature limit. If a defrost cycle terminates on time then it may indicate that the evaporator has not cleared all the ice which will affect efficiency and use more power. It may also be a pre-cursor that the associated defrost plant is failing.

A second related defrost feature would be one which utilises a defrost limit and produces an alarm if an evaporator has more than a pre-set amount of defrost cycles per day for its design specification. This would highlight human error during the configuration and setup of the refrigeration controllers or additional defrosts being implemented to mask a refrigeration fault. Both cases use energy unnecessarily.

The previously mentioned product simulation for alarm monitoring and temperature compliance can also highlight energy wastage. If product under temperature alarms are generated for refrigeration equipment, product quality is at risk and it also highlights energy wastage as the product is being overcooled.

If it’s not practical to install a physical probe, software can be used to calculate a product’s core temperature. This can be calculated using the evaporator air on and air off temperature probes before applying an algorithm which along with a settable time constant make it relevant to the cold store or case design and product to be monitored.