By Marcelle Dibrell
When it comes to everyday circulation needs, less is best should be the motto.
This is because of the Pump Affinity Law, one of several affinity laws that expresses the relationship between head, flow rate, shaft speed, and power and are all involved in a pump’s performance.
There are three relationships given by the law that are relevant to the discussion of pumps. The first is that the shaft speed is proportional to the flow rate. The second is that the pressure or head is proportional to the square of the shaft speed. The third is that the power is proportional to the cube of the shaft speed.
So if the speed is reduced by half, the power is reduced by an eighth.
½ speed ≈ ½ x ½ x ½ power = 1/8 kW.
And if the speed is reduced by a third, the power is reduced by 1/27.
Operating pumps at high flow rates is an unnecessary waste of energy for everyday use.
And that’s the advantage of variable-speed pumps: they can be operated at the lowest flow rate that provides adequate filtration most of the time, and then amped up only when the situation calls for it. That equals substantial financial savings.
The initial price of a variable-speed pump is greater than traditional pumps but many manufacturers advertise that the money can be recouped in about three years. And plenty state utility companies offer rebates and incentives for converting to energy efficient variable-speed pumps. Nationwide, incentives range from around $100 to $600. Considering that an average variable speed pump’s price is roughly $1,000, the incentives make these pumps even more attractive.
The long and short of it is that the energy savings is real.
In this special edition of Service Industry News, we focus on the heart of the circulation process, the pump, and the means by which it redistributes the water to every corner of the pool.
It is a topic explained by a branch of science called hydraulics, and it involves a lot of math: we’re wading into the deep end for this issue.
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