Drives Bring Cold Produce to Ambient Temperature

Industrial inverter drives from Mitsubishi Electric are helping bring cold-stored fresh produce back to ambient temperature. Crop Systems, based in rural North Walsham, Norfolk, designs and installs potato- and crop-storage controllers and equipment for farmers, growers and produce suppliers. The basic concept Crop Systems has developed is a 14-bay batch-warming facility. Potatoes are transferred from storage to a bay, where a controller is set to provide gradual warming to a set point temperature over a specified period of time.

The target temperature varies between 4 and 10.5C, and the time is typically three to five days. This isn't a simple open-loop linear warming - parameters such as humidity and carbon-dioxide concentration are monitored and controlled throughout the process. 'We are using fans with inverter feeds so that their speeds can be varied, sensors around the bay or stores to monitor environmental conditions and a computer to read the sensors and adjust the inverters accordingly,' said Crop Systems' Ray Andrews.

'We developed our Evolution controller to give many varying levels of control through different types of sensors located around the store - from this we can adjust the fan speed according to the exact requirements. 'From here, it was a natural step to develop the warming bays along the same lines,' he added. The Evolution is designed with an automatic load cure programme, which keeps the fans running at an economical speed until the stock has settled down.

'We have also developed a automatic fogging programme so that we can better address the distribution of cleaning-in-place fog within the storage area and we have proven that stirring and re-circulating the air at reduced speeds helps give far better efficacy and extends the fogging intervals dramatically - this speeds the payback period to less than 18 months in some cases,' said Andrews. Central to these storage processes is the use of an F740 variable speed drive from Mitsubishi.

The F740 is the fan-rated version of the F700 range of drives and offers improved motor efficiency during constant-speed operation and acceleration periods, and optimum torque patterns that accurately match the power delivered to that required at any instant. The speed of optimisation is effectively instant, so the drive is always giving maximum performance and efficiency to the load. Its ease of commissioning, removable terminal block, on-board EMC filter, predictive maintenance monitor and tripless reliability, as well as its ability to optimise energy usage, made the F740 suitable for this fan drive application.

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