Inverter drive systems save faster than expected

Dairy Crest is helping to offset the problem of high energy costs with the installation of four turnkey energy saving systems at its Maelor site near Wrexham.

Dairy Crest is helping to offset the problem of high energy costs with the installation of four turnkey energy saving systems at its Maelor site near Wrexham.

Designed, manufactured and installed by Wyko Electronic Services, the systems are fitted to cooling towers and an effluent pump at the Maelor site.

Although costing in excess of GBP 14,000 in total, the systems are well on track to achieve their original calculated payback of just one year.

In fact especially so, as the original payback figure was calculated based on GBP 0.025/kWh; today this figure has risen sharply to GBP 0.046/kWh, providing the potential for a much faster payback.

Dairy Crest's site at Maelor is split in to two independent factories.

Maelor Pre-Pack is a cheese packing facility and Maelor SDI (specialist dairy ingredients) is a whey processing plant.

SDI takes in tankers of whey and whey concentrate from cheese manufacturing sites and produces lactose powder and DeLactose whey concentrate.

Central to the production processes at the SDI site are three cooling towers with fans driven by 18.5kW motors, and an effluent pump driven by an 11kW motor.

What all these drive motors had in common until recently was that they were all running at high speed most of the time, including weekends.

Chris Dale, who is Engineering Manager at the SDI site, was aware that this type of running was inefficient and was keen to do something about it.

Helpfully, Dairy Crest is very proactive in energy saving and energy management, so his representations regarding the cooling tower fans and effluent pump were well received.

Dairy Crest has been a participant in the negotiated Climate Change Energy Agreement since 2000, and has identified and invested in many energy saving projects at its UK plants.

The starting point for the SDI project was to invite suitable companies to visit the site, survey the equipment and provide a specification and a price for providing systems for the three fan motors and the pump motor.

One of the companies contacted was Wyko Electronic Services, a company that specialises in providing turnkey automation packages to industry.

Engineers from the company visited the site and assessed the motors, noting the hours that they were run, their rated speed and current and duty cycle.

In addition, the Wyko team was asked to include temperature sensing of the ponds at the base of the cooling towers.

This meant that, with the installation of inverter drive systems, there was a facility for interactive control between the temperature of the pond and the speed of the cooling fans; hence, the fans would not be running at full speed for most of the time.

The result of the motor survey was a series of energy saving calculations.

These were based on the use of four, turnkey control systems employing Omron-Yaskawa E7 inverters.

Designed for energy saving applications, the inverters have an advanced Level-2 tuning feature that de fluxes motors for enhanced energy efficiency.

The total cost of the systems was just over GBP 14,000, a figure that included project design, all peripheral equipment and also installation and commissioning.

Based on energy costs of GBP 0.025/kWh, Wyko calculated a payback on this investment of one year; this included all claims for ECAs.

Wyko's quote and payback calculations were submitted in a competitive tendering process to Dairy Crest management.

Subsequently, Wyko was awarded the project, not only on the basis on of their payback figures, but also because the company assumed full project responsibility for installation and commissioning.

Installation of the energy saving systems took place over a weekend during one of Dairy Crest's shutdowns; this avoided any costly downtime.

As part of its installation, Wyko set-up PID control loops on each of the three cooling tower ponds.

A standard feature on the Omron Yaskawa invertors, the PID loops are linked to temperature sensors in the ponds.

This arrangement enables continuous and optimised control of the pond temperature to ensure maximum efficiency from the cooling tower fans.

"The VSD installations have delivered the predicted benefits in line with the project plan", said Chris Dale.

"The specific energy savings are difficult to verify as the performance depends on variables such as ambient temperature for the cooling towers, and tank level for the effluent pump".

"However, when the cooling towers were switched to the VSD supply there was a step change in electricity usage that indicates energy savings in line with Wyko's calculations".

Commenting on the application, Vic Harris of Wyko Electronic Services said: "The rationale for investing in energy saving projects was strong, when hourly kilowatt-hourly rates were at GBP 0.025".

"Now that these rates have increased substantially, the imperative for industry in general to invest and reduce its energy costs has become compelling".

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