Mitsubishi Automation delivers big savings for Irish food producer.

Progressive Irish mushroom producer Codd Mushrooms is one of the largest mushroom producers in Ireland, and achieved this position by integrating its focusing on produce quality, sustainability and production automation.

A recent initiative to save energy within its factory chilled water system, resulted in a PLC based control system using Mitsubishi Electric variable speed drives to control the various pumps and systems, and delivers savings of over 5400kWh a week, worth up to €40,000 per year in savings.

The company strives to supply the finest quality mushrooms, with a production and packing facility that is regarded as one of the most modern in Europe, and a vacuum cooling system that takes products from a field temperature of 20^°C down to 3^°C in just 20 minutes, and gives the produce two extra days of shelf life.

Chilled water system

Chilled water is constantly circulated throughout the plant. Water is cooled within an industrial chiller and then held at 5^°C in an insulated buffer tank. The water is then returned to the buffer tank considerably warmer than when it left. The returned water mixes with the cold water in the buffer tank and warms it up, so the chiller increases its cooling capacity to bring the temperature back down to 5^°C.

Local Mitsubishi Electric system integrator MPAC says: “Because the system didn’t have any way of knowing what the demand would be, it was always working at full capacity. In reality, demand at the plant is dynamic, and rarely needs the full capacity. Even at zero demand, the system would continue pumping the maximum volume of water through the factory.

Demand system

A thorough investigation of the chilled water system, looking at its inefficiencies and areas for possible improvement, and noting that it consumed 6115kWh of energy over a seven day monitoring period. It was not practicable to stop the chilled water on a regular basis, so MPAC developed a demand system with pumps under the control of Mitsubishi Electric FR-F740 variable speed drives linked to a Mitsubishi Electric MELSEC Q series PLC via CC-Link.

All process variables of pressure and temperature are measured by sensors, and all analogue and digital data is fed to the Q series PLC via Mitsubishi Electric STLite remote I/O unit. The PLC calculates the actual demand and calculates the appropriate response to meet the demand, sending control signals to the variable speed drives. By offering precise and appropriate control of the pumps, the volume of water moving through the primary and secondary circuits is always proportional to demand. Operator interaction and plant process visualisation is accomplished through a Mitsubishi Electric GOT series HMI.

Monitoring the energy consumption

Following the installation of the new control system, saw energy consumption reduced from 6115kWh using the original system running constantly at full speed, to just 664kWh using the new control method – a saving of 5451kWh.

Switching from DOL to VSDs has reduced electrical and mechanical stresses on the pump motors, and eliminated water hammer effects by removing the ‘shock’ of starting and stopping the pumps.  This has eased the operational stresses on the pumps and should improve bearing and seal life to further reduce maintenance requirements and repair costs.

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