How to document pumping efficiency and performance

OEM engineers who devise equipment that saves energy have it pretty good these days. They have the satisfaction of knowing that their work both saves their customers money and, on some level, helps the planet.

This is particularly true for engineers working on industrial projects that feature energy efficiency. Some utilities will give industrial customers financial incentives paying up to 70% of costs for efficiency projects (based on annual kilowatt-hour savings). Items covered under such policies typically include variable-speed drives (VSDs), controls, premium efficiency motors, and most other measures that can save electricity.

However, there is a catch. The utility expects to see verification of energy savings. Like all well-managed businesses, they (utilities) want to see the energy reductions before they cut checks. The end users, on the other hand, are looking at the bottom line (show me the money). While the concern is primarily energy savings, management looks at the big picture beyond energy savings. Upper managers typically want to make investments that increase productivity, reduce the costs of environmental compliance, lower production and waste-disposal costs, boost product quality and reliability, improve capacity, and make workers safer.

There is a benefit to this big picture methodology. In many cases, energy savings alone may be insufficient to justify a project. Though it should be understood that the primary objective is energy savings, management must look at what they are getting for the money. There are numerous cases where company management denied projects because the “energy specialist” failed to look beyond energy savings. And it is sometimes the case that the cost of downtime far outweighs the energy savings.

Centrifugal pumps are prime candidates for major energy savings, because their power use varies as the cube of the speed ratio (i.e., cut the speed in half and you reduce the power to one-eighth of the original value). They are the second most widely used type of mechanical equipment in the world, outnumbered only by the electric motor. The use of VSDs with centrifugal pumps, when properly applied, has a tremendous potential for cost and energy savings by reducing friction in the system.

In relative terms, pumps are efficient machines. Most typically operate near 75% efficiency (best efficiency point, or BEP). Because of this relatively high efficiency, it is easy to dismiss the potential energy savings available by optimizing pumping systems. But a pump is sensitive to how it is operated and it is the pumping system that has the greatest influence on pump energy use. Energy can account for as much as 75% of a pump’s total cost of ownership. A pump can be efficiently designed yet can be operated in an inefficient manner. As a result, many pumping systems operate at efficiencies far below their BEPs.