Resource Type: Open source

Pumping water for irrigation can be a major expense for irrigated farms. In 2003 more than 500,000 pumps were used for irrigation, and the total estimated energy cost nationwide was over 15.5 billion dollars. Improving the efficiency of irrigation pumps has many benefits, including improving the profitability of the irrigated farm.
When a single pump is required to operate over a range of flow rates and pressures, standard procedure is to design the pump to meet the greatest output demand of both flow and pressure. For this reason, pumps are often oversized and they will be operating inefficiently over a range of duties. This common situation presents an opportunity to reduce energy requirements by using control methods such as a variable speed drive.

Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial
facilities. Significant opportunities exist to reduce pumping system energy consumption through smart design, retrofitting, and operating practices. In particular,
the many pumping applications with variable-duty requirements offer great potential for savings. The savings often go well beyond energy, and may include improved performance, improved reliability, and reduced life cycle costs. Most existing systems requiring flow control make use of bypass lines, throttling valves, or pump speed adjustments. The most efficient of these is pump speed control. When a pump’s speed is reduced, less energy is imparted to the fluid and less energy needs to be throttled or bypassed. Speed can be controlled in a number of ways, with the most popular type of variable speed drive (VSD) being the variable frequency drive (VFD). Pump speed adjustment is not appropriate for all pumping systems, however. This overview provides highlights from Variable Speed Pumping — A Guide To Successful Applications, which has been developed by Europump and the Hydraulic Institute as a primer and tool to assist plant owners and designers as well as pump, motor, and drive manufacturers and distributors. When the requirements of a pump and system are understood, the user can consult this guide to help determine whether variable speed pumping is the correct choice. The guide is applicable for both new and retrofit installations and contains flowcharts to assist in the selection process.

A large proportion of the electricity produced around the world is used to raise, move or pressurize liquids and gases with machines such as pumps, fans and compressors.
Given the increasing importance of controlling energy consumption, special attention must be paid to the way these machines are operated and the energy savings that can be achieved through variable speed control. These different aspects will be dealt with in this Cahier Technique publication, both from the qualitative and quantitative standpoint. Variable speed drives are among the front-ranking solutions proposed by Schneider Electric to increase Energy efficiency.