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The client’s engineers were limited in the types of changes they could implement. The system complexity increased the likelihood of equipment failure. It made troubleshooting difficult.

Two large, electrical enclosures were required to house the control panel components. These were costly and required an extensive amount of time to manufacture and install at the customer’s site. The client needed to reduce manufacturing costs and improve the reliability of the system. The client also wanted to increase the control system’s flexibility in order to meet their customers needs.

THE SOLUTION: REAL Controls met with the client’s engineers to evaluate their wants and needs for re-design. We developed a wish list of new features and capabilities and discussed other improvements. REAL Controls proposed several options to achieve the client’s goals. We reviewed the advantages, disadvantages and costs associated with each option. The option that best fit the client’s needs involved replacing the electro-mechanical based system with a Programmable Logic Controller (PLC). These devices have been used successfully in manufacturing process control applications for over 30 years and have been established as the standard. Although the PLC was not the least expensive option, it is a highly reliable, industrial quality device, which works very well to satisfy the client’s requirements for flexibility and expandability. The features of a PLC that were most attractive included: 

• Reliability: The PLC has an established track record for long life which cannot be matched by other systems such as those using personal computers. 

• Installation Simplicity: Installation and wiring is easier than electro-mechanical systems. Fewer components are needed and all of the PLC components are modular in design. 

• Easy Maintenance: Diagnosing a problem with a PLC card is fairly straightforward using the diagnostic features built into the PLC. The modular design of the PLC also allows field technicians to quickly replace damaged components returning the system to normal operation. 

• Flexibility: Customized programming changes can be made easily without shutting down the refrigeration equipment or rewiring the control panel. 

• Readily Available Spare Parts: All components of the PLC are commercially available from multiple vendors. Neither the client, nor their customers would have to rely upon a single source for replacement parts. 

In addition to the PLC upgrade, REAL Controls identified, and implemented, several other improvements to the equipment’s electrical system including: 

• Coordinating the overload protection devices for critical system components such as compressors and pumps. Should equipment failure occur, it ensures the least possible impact on operations. 

• Replacing the on/off field devices including the pressure, temperature and flow switches with analog devices which provide an accurate indication of actual operating conditions within the refrigeration system.

• Improving the regulation of the chiller discharge pressure by applying variable frequency motor drives (VFD) to regulate cooling fan speeds. 

• Incorporating Proportional-Integral-Derivative (PID) control methods, in place of conventional relay logic, to improve the overall control of temperatures, pressures and flow rates.

THE RESULTS: The client has realized significant manufacturing cost reductions as a result of the reduced number of components, reduced wire connections, and simplified panel design. The sensors, which replaced the mechanical switches, provide useful data that the engineers and field technicians use for troubleshooting and monitoring. The PLC provides expandability and flexibility enabling the client to customize the system for their customers’ needs. Overall, the system operates more efficiently which is evident in the reduced electrical utility bills.