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Saving energy through better pump control

25 September 2016

Find out how an Irish mushroom producer made energy savings of over 5400kWh a week by automating control of its chilled water system. 

The production and packing facility of Codd Mushrooms is said to be one of the most modern in Europe. The vacuum cooling system takes products from a field temperature of 20°C down to 3°C in just 20 minutes – a process which ensures two days extra shelf life.

The company’s commitment to sustainability has already seen it adopt renewable energy generation, and it is always looking for ways to make further energy savings.

The company maintains a clear focus on the benefits of automation, as Raymond Codd, director at Codd Mushrooms, explains: “Through progressive automation, we have been able to advance our production as the business has grown.”

The company was keen to investigate whether energy savings could be made in the factory chilled water system, and at the same time increase reliability. The chilled water system serves the requirements of various production areas, which all work independently and need varying amounts of heating or cooling depending on the environmental conditions and the point in the production cycle. Water is initially cooled to 5°C, stored and pumped through heat exchangers in the production areas. It is then returned to the chiller for recooling and reuse.

To investigate the possibilities for energy savings, Codd Mushrooms called in local Mitsubishi Electric system integrator MPAC. Matt Pender, director at MPAC takes up the story: “Because the system didn’t have any way of knowing what the demand would be, it was always working at full capacity. As such, it was only ever working efficiently when demand was equal to 100% of capacity.”

“In reality, demand at the plant is dynamic. It rarely needs the full capacity, and even if it does it still won’t be a constant demand. The system demand varies hour by hour and day by day, with a number of different influencing factors, including the number of production rooms calling for cooling, the stage of the cycle the rooms are in and the external ambient temperature dictated by the local weather and the humidity.”

Even at zero demand, the old system would continue pumping the maximum volume of water and, even it wouldn’t be drawn through the heat exchangers, it would still warm up en-route. 

MPAC performed an investigation of the chilled water system, looking at areas for improvement. It was noted that the system consumed 6115kWh of energy over a seven day monitoring period. 

Although a theoretical maximum efficiency could be achieved by stopping the system when there was no demand, this would lose the ability to detect when demand increased again. “If we didn’t keep some sort of buffer of chilled water, it would result in a  ‘laggy’ system that was slow to respond when a given production area called for cooling,” said Pender.

The solution developed by MPAC lay in between, with a calculated demand system. The various pumps in the system – including the primary pump that circulates water between the chiller and buffer tank, the secondary pump feeding the lower side of the factory, and the twinset pump feeding the upper side – were all fitted with Mitsubishi Electric FR-F740 variable speed drives. These were linked to a Mitsubishi Electric MELSEC Q series PLC via a CC-Link communication protocol.

All process variables are measured by sensors and data is fed to the PLC via remote I/O units. The PLC calculates the actual demand and appropriate response, adjusting the drives accordingly. By controlling the pumps, the flow of water is always proportional to demand. Process visualisation is via a GOT series HMI.

“With this system, the pumps are operating more efficiently, and the amount of warm water returning to the buffer is significantly reduced,” said Pender. 

Monitoring consumption
Following installation of the new control system, MPAC monitored demand over a second seven day period, and saw energy consumption reduced from 6115kWh to just 664kWh – a saving of 5451kWh.

Furthermore, the drives have reduced electrical and mechanical stresses on the pump and motors and eliminated water hammer, so should reduce maintenance and repair costs.

Summing up, Codd said: “MPAC has helped us to automate our processes which has increased our productivity and overall efficiency.”

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