EFFICIENT ENERGY USE KEY
Many potato store operators are missing out on the chance to make significant savings in energy costs because they don’t have enough information on their energy usage to make informed decisions.
Yet using some simple technology – as either original or retro-fit – would enable them to make the right move, says Ray Andrews, from Crop Systems Limited:
“I don’t think many operators realise how much energy prices vary, or how frequently in any 24 hour period they change. Bear in mind that peak energy prices are often three times higher than off-peak rates.
“And these things are not fixed. I am sure many people don’t know how frequently suppliers change their pricing structures and timings. What represents the best deal today might not represent the best deal next week.
“Unless you keep a constant eye on everything – or use a store controller that does that job – you risk missing out on the best prices and the lowest available storage cost.
“This was one of the priorities we set in developing the SmartStor control system”, says Ray.
“This allows you monitor and manage your store 24-hours a day, even when you are away from it. That includes enabling you to monitor the best energy prices and store fan/fridge running times.
“I have great sympathy with farmers as they try to find the most competitive energy supplier. You might assume that your local farmer co-operative would give you the best price, but we have worked with farmers paying 13.5% less by dealing direct with the energy company.
“Our advice would be to look beyond the headline ‘unit cost’ and work out the cost including things like the capacity charge, renewal obligation, feed-in-tariff, reactive power charge, forecast charge, operational charge, data collection charge, administration, and climate levy.
“Having that day-to-day control is now imperative, and via SmartStor we can tell you your costs to the nearest penny minute by minute, calculate how the multiple tariffs charged can best be exploited to your advantage and give you complete control over your store”.
While the controller is key, it is also important to make sure the parts of the store equipment that consume energy are working efficiently:
“Let’s start with the fans, which are crucial to move the air through the crop and the store.
“Fans come in all shapes and sizes and generally push out a set quantity of air for every kw of power used – that is great if they are the correct size for the job in hand; but bad news if they are not correctly sized.
“In our experience, grain fans used in potato stores can consume 35% – 40% more energy than correctly sized fans that are designed for the job. And always remember than new fans are likely to be far more efficient than old ones.
“They also need to be correctly matched to the ducts and laterals used in a bulk store, or the pressure in them may rise to above the fans’ characteristics.
“While you need high capacity fans to dry and cure crops – or to blast them if they come in wet – the key to efficient energy use is to know how far you can slow them down at other times of the year.
“If fans are run at 80% of their capacity they use half the energy the do when running at full speed. The savings reduce when they run at lower speeds – but at that stage it is more important to ensure you are achieving the required airflow to maintain efficiency”.
Recirculation is essential to maintain performance, he adds. If airflow is insufficient then the air will not move through the crop effectively, while too much movement risks wasting energy and may also risk increasing dehydration.
Most operators are now using CO2 purging to counter conditions like Blackheart, but they need to be sensible about the levels they use. If they try to reduce it to 1,500ppm it consumes a huge amount of energy. Even moving from higher levels – 3,500ppm to 4,500ppm – makes a huge difference.
Similar issues affect fridges, with poorly performing units often using double the energy of efficient ones, while still struggling to achieve the same effect.
If the coil temperature is too low it can trigger a succession of problems – starting with fans having to run longer than ideal; the potential for premature icing which may restrict airflow; air short circuits and expansion valves shutting.
Once problems start they can build up rapidly, and de-frosting simply puts in-wanted heat back into the store and uses more energy. Installing as control system that enables you to keep a constant eye on problems like this – and which also sends you an alarm message as soon as the problem is detected – makes good sense, both in terms of keeping your stored crop in best condition and in terms of controlling storage costs.
Another key asset is being able to harness humidity with adiabatic cooling, which while it has limitations can have a serious impact on reducing energy usage.
Mr Andrews recently led an Innovate UK funded industry project examining the efficiency of box stores which showed that suction chambers can help improve air flows by up to 65%. Even greater improvements were achieved by the addition of other features such as plenum walls and side/top sheets.