In some parts of the country, we have just come through one of the hottest summers on record. Air conditioners were going crazy and the power draw approached critical “brown-out” levels.
For many thinking people, it brought yet another reminder of how dependent we all are on the use of power. After all, high temperatures and high humidity may be lovely when you’re on vacation, but it gets a little uncomfortable when you’re working in it. How long is it going to be when we are consuming more energy that we’re producing? After all, it takes about 10 years or more to put a power station on line from the date of it’s inception. While we’re waiting, we’re going to have to start conserving this precious commodity.
So the question is, can you save some energy in your plant?
Let’s take a look at how we size our pumps for a simple transfer pumping system where we take from one tank and move the liquid to another. Normal procedures would have us select the pump so that the Design Conditions are close to the Best Efficiency Point. The Design Flow usually represents the average flow needed to transfer the liquid in the time required, while the Design Head includes either the maximum or minimum Static Head.
If it includes the Minimum Static Head, that means that the system curve is going to move to the left from the B.E.P. on the pump curve. This means that the pump will be moving into lower areas of Flow and Efficiency, resulting in a higher Power Draw for the total operation.
If it includes the Maximum Static Head, the pump will still start against the Minimum Static Head which means that the system curve is going to move to the left towards the B.E.P. from a higher flow rate on the pump curve. Under these conditions the pump will be starting at a much higher Flow, but again in lower areas of Efficiency. This too will result in a higher Power Draw for the total operation.
The most efficient pump selection will be where the design conditions move from the right of the Best Efficiency Point back to the left side and stays in the range of high efficiency at all times. This will save power and money.
Author of “The Practical Pumping Handbook” and a specialistr in Pumping Reliability, Ross Mackay can be reached at www.practicalpumping.com or at 1-800-465-6260