Irrigation Pump Efficiency Testing

Linda F. Benedict, Sheffield, Ron, Girouard, Ernest

Variability of operating costs per acre for 10 wells in southwest Louisiana.

Variability of potential cost savings per acre for 10 wells in southwest Louisiana.

Factors for estimating pumping efficiency

Nich Kenny, of Texas Agri-Life Extension, demonstrates how to install a torque cell on a diesel-powered irrigation pump.

Ron Sheffield and Ernest Girouard

Most agricultural producers who irrigate are using older diesel power units and old wells where upgrading to newer wells and diesel engines or electric motors needs to be technically and economically evaluated. Over the past several years we have seen tremendous swings in the cost of crude oil and diesel fuel. These higher fuel costs dramatically increased the cost of irrigating crops in Louisiana.
Irrigators need a mechanism by which to evaluate the condition of their pumping systems. With the current high diesel cost, this information is crucial in determining the profitability of switching to an electric motor or investigating the rebuilding of existing diesel power plants. Additionally, producers need such analyses when applying for federal grant funds from a Resource Conservation and Development program to assist electrical infrastructure or the Natural Resources Conservation Service to assist with well replacements.

In the spring of 2009, the AgCenter began working with the Natural Resources Conservation Service and Texas Agri-Life Extension to learn about hands-on irrigation well pumping-plant efficiency tests and evaluated several diesel and electric pumping plants in southwest and northeast Louisiana. These tests were used to estimate the average cost of operating irrigation systems and to evaluate the need to conduct further irrigation pumping-plant efficiency tests in Louisiana.

The initial tests found that diesel-powered pumping systems on southwest  Louisiana wells with water depths of 70 feet to 130 feet were found to have an average efficiency of about 16 percent with a 25 percent potential standard efficiency. The cost of irrigating an acre-inch of water (27,154 gallons) with a 3,000-gallon-per-minute pump and $2-per-gallon fuel, was found to be from $2.62 to $3.24 with an hourly cost ranging from $9.48 to $13.54 per pump southwesting unit. With proper operation, maintenance or replacement of system components, the cost per acre-inch could range from $0.95 to $1.51, and the cost over a typical 1,200-hour pumping season could range from $4,199 to $6,911. In a third of the units tested, farms could save nearly $16,000 per year by making appropriate changes to their irrigation pumping systems. With the price fluctuations seen during the summers of 2008 and 2011, the cost savings per pumping plant will only become more evident.

Electric pumping systems on wells in southwestern Louisiana were found to have an average efficiency of 39.7 percent to 40.5 percent with a potential standard efficiency of about 65 percent. The cost of irrigating, assuming $0.06 per kilowatt-hour, was found to range from $1.18 to $1.44 per acre-inch irrigated and an hourly cost range of $5.35 to $7.45 per pumping unit. It is estimated that through proper operation, maintenance or replacement of system components, a range of $1.38 to $1.66 per acre-inch irrigated or $2,155 to $4,025 over a typical 1,200-hour pumping season could be realized.

A pumping system’s efficiency is calculated by comparing the amount of fuel used with the amount of water pumped. This efficiency can change due to the depth of water being pulled from a well, the condition of an engine and the rate the motor is turning. The calculated performance is then compared with the performance of the motor under perfect, laboratory standards. Typically, electric pumping systems will have a 75 percent to 85 percent overall efficiency, and diesel-powered pumps will have between 18 percent and 35 percent efficiency, depending on the age and care of the engine.

To calculate a system’s pumping efficiency, several pieces of information are needed. If this information cannot be collected, assumptions can be made to estimate efficiency. However, great care needs to be taken to make appropriate assumptions to prevent a gross over- or under-estimation of the system’s performance.

Funds from the Louisiana Rice Research Board and the LSU AgCenter supported a trailer equipped with the necessary equipment to conduct further irrigation evaluations in southwest Louisiana. A grant from the U.S. Department of Agriculture and NRCS in 2011 will fund additional pumping-system evaluations in Louisiana over the next two years.

The goal of the Louisiana Irrigation Well Pump Efficiency Testing Program is to conduct irrigation pumping-plant efficiency tests and demonstrate their effectiveness to rice producers. To demonstrate this novel and specialized energy-focused conservation practice, 250 irrigation well pump efficiency tests will be conducted during 2012 in areas largely over the Chicot and Mississippi Alluvial aquifers in southwest Louisiana. Following each efficiency test, the irrigator will be provided with a set of technical evaluations and recommendations on changes that can be made to the operational settings of the pumping equipment to optimize energy, financial and water resources.

If the operational efficiency is found to be extremely low, specialized spreadsheets will identify the cost/return of rehabilitating the existing system compared with converting to a different power system, such as from a diesel to an electric pump. Field days for rice producers will demonstrate a pump test and present the general results and effects of well efficiency tests on water and energy conservation as well as on farm profitability.

The project also will develop a group of private, third-party auditors who will be trained to conduct irrigation pump efficiency tests in the future. To educate the auditors, the LSU AgCenter has joined with irrigation specialists from across the southern United States to develop a national Irrigation Pump Efficiency Testing Manual. The manual will be composed of how-to fact sheets and reference guides for specialized irrigation spreadsheets. These spreadsheets will be invaluable to auditors and producers for interpreting, comparing and summarizing the data collected during the on-farm pump efficiency tests so they can be easily understood and digested and their recommendations implemented.

Producers can then use this information when applying for federal grants or loans to convert from diesel to electric power units or when replacing a well. The AgCenter also will provide direct technical assistance through an interactive website and blog to assist auditors and conservation professionals as they encounter difficult situations and help them stay abreast of the latest news and technology related to energy and water conservation topics in Louisiana.

Ron Sheffield, Associate Professor, Department of Biological & Agricultural Engineering, Baton Rouge, La., and Ernest Girouard, Coordinator, Louisiana Master Farmer Program, W.A. Callegari Environmental Center, Baton Rouge, La.

(This article was published in the fall 2011 issue of Louisiana Agriculture magazine.)

11/30/2011 4:09:39 AM
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