Efficiency Effect

October 28, 2011 11:16 AM

By Loretta Sorensen

Running irrigation pumps at lower efficiency will drain your money 

Inefficient irrigation negates the purpose of irrigating in the first place. For example, in Nebraska, a diesel-powered pumping plant operating at 70% efficiency can require $50 more per acre to pump water than if it was operating at 100% efficiency. That’s $5,000 for every 100 acres.
More than 30 years of studies have found it’s not uncommon for three-quarters of pumps to be operating at 77% efficiency. That’s a lot of precious water and money down the drain.

How can irrigators determine if their pumping plant is inefficient? Bill Kranz, University of Nebraska irrigation specialist, says optimizing pumping plant performance begins with record keeping.

"Track the amount and cost of energy used, so you know what your system takes to deliver each acre-inch of water," Kranz says. "You need to know your pumping lift [including drawdown when the pump starts], discharge pressure, field size and how many gallons of water were pumped during the growing season. Use that information to calculate the cost-per-gallon to pump the water. Compare your information to industry pumping standards. If it seems your system is using extra fuel or not operating closely to standards, a detailed test can reveal what needs to be corrected."

In approximately 30 minutes, a trained pumping station tester can use tools to bring an irrigation pump to optimum pressure, measure the pumping lift, and evaluate the pump pressure, flow rate and energy units used to help identify malfunctions. Some states offer a testing service through a university or Extension office.

Stay current. Irrigation pumping plants are made to operate at peak performance under a given set of conditions. If conditions change, pump performance changes too. Inadequate plumbing, changes to pipelines and an inefficient power unit are among the elements that will affect pumping station performance.

"Installing a lower-pressure sprinkling package could alter pump impeller performance," Kranz says. "Exact loss in operating efficiency depends on the impeller. Over time, the cost adds up."

If a pumping plant does need to be fixed, it’s fairly simple to calculate whether the repair costs can be recouped within an acceptable time frame, such as five years. If an irrigator finds he’s spending an extra $50 per acre to pump water on 1,000 acres, he knows he can save $50,000 a year by improving pumping plant efficiency. During a five-year period, the irrigator can invest up to $250,000 to pay for repairs and still recover the costs.

Right way to power up. Allen Thompson, associate professor in the Biological Engineering Department at the University of Missouri, says using the proper power source is important to overall efficiency.

"Collaborate with utility companies to manage power demand," he says. "Your power company can also help evaluate the benefits of a three-phase power source compared to internal combustion engines. If the power company has to install new transmission lines to accommodate a three-phase motor that might cost too much for the irrigator. It all depends on the time frame used to pay for the lines and the lifespan of the irrigation system."

The best-choice energy source for powering irrigation engines depends on the long-term relative price of one energy source compared to another. An Extension irrigation specialist can assist in comparing the costs of various energy sources.

Little tweaks. If testing reveals an inefficiency, the entire irrigation system should be evaluated to determine if a sprinkler package change or any other element of the pivot system is part of the problem.

"If the end gun on a pivot system isn’t equipped with a booster pump, the main pump pressure may change to pressurize the entire system," Kranz explains. "Power output of the engine or electric motor should also be measured.

All the data collected in an evaluation should be recorded and maintained. It serves as a valuable resource for future analysis."

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