Until now, governmental and market forces have tried to reduce electrical energy usage in industry primarily by targeting electric motors. While these “green” initiatives have often raised concerns for manufacturers, repair facilities and end users, they have also spurred innovation.
But the commercial and regulatory landscape continues to evolve, and the horizon coming into view includes a new focus on pumps and pump systems. Starting in January 2020, the U.S. Department of Energy (DOE) will begin implementing the first ever energy efficiency standards for freshwater rotodynamic (centrifugal and axial flow) pumps.1 These standards will directly affect pump manufacturers and, to a lesser extent, the pump repair market, while ultimately benefiting end users if the new focus can reduce their energy costs.
But pump efficiency opportunities go far beyond pump design. So, while the new standards are a step in the right direction, end users seeking to maximize savings will need to examine the design of the entire system.
Pump System Efficiency
Those helping the regulators write efficiency requirements for pumps understand that the system to which a pump is connected dictates its efficiency. Both the Hydraulic Institute (HI) and the CSA Group (formerly the Canadian Standards Association) have initiatives in progress to set standards for measuring and reporting pump system efficiency. This emerging interest in pump and pump system efficiency creates a demand for engineers and technicians who understand how the complex interaction between the two impacts efficiency. It is likely that independent service companies and pump vendors will fill that demand.
Examples to Consider
Consider the overall efficiency of a simple transfer system that pumps 2 million gallons [7,571 cubic meters (m3)] of water per day from a reservoir to a processing plant 200 feet (61 m) above (see Image 1). The actual hydraulic power required to lift the water would be 70 horsepower (hp), or 52 kilowatts (kW). Based on motor efficiency, an older National Electrical Manufacturers Association (NEMA) design motor would use 3,744 kilowatt hours (kWh) more than a NEMA premium efficiency model for 2,000 hours of operation, which at $0.12/kWh would amount to $450 in extra energy costs.
But because of hydraulic losses in the system (from pipes, valves, fittings, etc.) and the pump, 118 hp (88 kW) is required. Assuming the pump is 81 percent efficient, the efficiency loss (19 percent) would account for 33,437 kWhs for 2,000 hours of operation, costing about $4,000. The system accounts for 40 percent of the total energy usage, or 71,370 kWhs, which would cost about $8,564 annually.
While the example in Image 1 is for a properly sized pump on a typical system, pumps are often oversized for the application. But the “bigger is better” theory does not work for pumps. Throttling back an oversized pump to the desired flow rate can easily double or triple the energy losses in the system, making the energy saved by replacing a standard motor with a NEMA premium efficiency model seem trivial in comparison to the potential losses of a poorly designed pump and system.
Motors and pumps share some common characteristics. Volts and amps correlate with head and flow, for example, while electrical resistance in ohms is like feet of head loss in hydraulic systems. As industries look to improve efficiency in pumping systems, they need technicians and engineers to evaluate both their electrical and hydraulic requirements and propose options for improvement. Independent service centers can help those same end users take advantage of opportunities for energy savings.
The benefits are real, and the emphasis being placed on pump and system efficiency by the DOE, HI and CSA Group will continue to raise awareness. Trade organizations such as HI and EASA (the Electro-Mechanical Authority that supports independent service centers) are already training technicians for the task of evaluating efficiency improvement opportunities in pumps and pumping systems, so it is not too early to get started.
The first step in the process is to identify a qualified technical resource who can evaluate your pumping systems and recommend energy efficiency modifications where appropriate. Pump vendors may provide this service, or independent groups such as HI, Europump and EASA may provide referrals to independent technical resources.
1. Energy Conservation Standards for Pumps, 81 FR 4145 January 25, 2016.