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Pump and fan motors offer the best opportunity for energy savings through the installation of variable Speed Drives.
A 10% reduction in the speed of a pump or fan will give a 25% reduction in energy consumption.
A 20% speed reduction will give a 50% reduction in energy consumption.
The greater the speed reduction, the greater the savings.
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The greatest savings are often found in applications involving centrifugal pumps, because the energy savings made by slowing down a pump are determined by the "Cube Law", reducing speed by 10% could reduce energy consumption by 25%, 20% less speed could mean a 50% reduction. You might think this sounds wrong, surely a 10% reduction in speed should be a 10% reduction in energy usage. A little bit of background into how a pump works makes this more understandable. A pump speeds up water flow, the faster it works the faster the water travels, both into and out of the pump, as the water flow rate increases so does the dynamic head or pressure that the pump has to overcome. Inside the pump is a set of vanes (called an impellor) these accelerate the water from the centre of the impellor to the circumference increasing both the flow rate and pressure. By slowing down a pump not only does the impellor slow down but so does the pressure against which it has to work. The combination of these factors leads to the energy saving being related to the cube of the reduction in input speed.
(saving = reduction x reduction x reduction).
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