What's the cheapest way to deliver 50% flow?
This example represents a bank of cooling towers with three fans. Motor speed control is used to regulate the cooling effect as demand varies. The question is, what is the most energy-efficient combination of motors and speeds to achieve 50% flow?
We start with one motor running at full speed and one at half speed: try different combinations
(hint: the optimum combination uses only 13% of full power)
% flow with
The reason for the dramatic result is that the power demand of the fan increases with the cube of speed. So halving the speed cuts the energy demand to one-eighth.
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