PHOTO: The performance curves of the Grundfos SL/SE22.214.171.124.4.52H wastewater pump, including the total efficiency curve (Eta 1). The Eta 2 curve shows the hydraulic efficiency.
As it is impossible to claim that a wastewater pump which contains an integral motor is IE2 or IE3 compliant, Grundfos offers a solution which they consider addresses the subject of pump and motor efficiency. Grundfos SE1/SEV and SL1/SLV wastewater pumps now incorporate the electrical internals, i.e. the rotor and stator, of the IE3 motor in the pump housing.
“What make the wastewater pump motor differ from the conventional IE3 motor are the bearings, mechanical seals and the absence of fan cooling as described above,” explains Robert Bork Hansen. “In wet installations, cooling is provided by the fluid in which the pump is submerged. The rotors and the stators from the Grundfos IE3 motor are type test certified in accordance with the TEFC motor standard and supported by measurement reports, so to all intents and purposes it is an IE3 compliant motor. However, by changing the bearings, adding a mechanical shaft seal and method of cooling, IE3 motor compliancy is negated.”
The main reason why an efficiency standard has not been introduced to date for wastewater pumps could be due to the fact that manufacturers, legislation and standard makers see wastewater pump motors as a separate unit and not as a unit integrated in the pump, and therefore they are having difficulties in defining the motor friction losses and efficiency.
Pump manufacturers who claim that their wastewater pumps are IE3 compliant are guilty of misleading consultants and end users. If a tender document specifies that wastewater pumps must comply with IE3, then it is impossible for any manufacturer to supply such a pump since there is no applicable standard available regarding the efficiency definitions for wastewater pumps with integrated motors.
Using the electrical components from an IE3 motor and installing them in a wastewater pump does provide some information about the efficiency level of the entire motor unit. What it does not provide is any specific value because the friction losses in a wastewater pump are different from those present in a standard pump and these losses are not taken into account. Nor does it tell anything about the hydraulics side, which is where the greater possibilities for efficiency gains exist.
“To attain the highest level of efficiency in the pump system, the pump selected must have a BEP (Best Efficiency Point) that best matches the duty point,” says Mikael Nedergaard. “The BEP is largely dependent on the characteristics of the pump, these being power, flow and head and it is the point on the pump curve that gives the most efficient operation. It must be remembered that pump efficiency will decline substantially if the pump operates away from the designed BEP.”
Grundfos believes that rather than concentrating exclusively on motor efficiency, manufacturers, consultants and end users need to address total pump efficiency defined in the ISO 9906:2012 ‘Performance acceptance test for rotodynamic pumps’ standard, or ANSI/HI 11.6.2012 ‘Performance acceptance test for rotodynamic submersible pumps’ standard when discussing wastewater and submersible motor pumps. Of equal importance to motor efficiency are pump hydraulics, as the possibilities for improving pump efficiency are far greater. In the absence of an appropriate energy efficiency standard for the pump, it is inevitable the manufacturers and vendors are going to highlight the IE3 connection. This situation is starting to change and Europump is discussing proposals for an appropriate pump standard. The drive towards establishing a suitable standard cannot come exclusively from pump manufacturers, but has also to be driven by politicians and regulatory bodies.
“In recent years an energy standard has been produced for small circulator pumps where, like wastewater and submersible pumps, the motor and shaft are contained in a single housing and cannot be tested separately,” comments Mikael Nedergaard. “Endorsed by the EU, the standard drawn up by Europump, the pump manufacturers’ trade association and pump manufacturers, consists of seven classifications of energy-saving. The energy efficiency index (EEI) of the pump is calculated according to an annual load profile and the pump is labelled according to its energy efficiency. By introducing energy labelling, the end user can compare products and specify the most appropriate pump, or pumps, for the installation.”
If this can be achieved for circulator pumps, then it follows that an internationally recognised energy standard can also be produced for wastewater pumps. As the wastewater treatment industry is gradually moving to larger and more efficient treatment plants that require larger pumps, energy costs are going to become far more important. The pump industry and regulatory bodies will have to respond accordingly and invest in a testing regime that gives the end users the information that they require.
Story by Bryan Orchard
Grundfos Facts on Pumps and Energy
Grundfos Blueflux® Energy Label background
International Electrotechnical Commission
TC2 Rotating Machinery Work Programme (14) publications
National Electrical Manufacturers Association (NEMA)
Europump’s Pump Efficiency for Single stage Centrifugal Pumps Guide
Europump Guideline on the application of the Regulation 640/2009/EC on Electric Motor Efficiency – May 2011
Ecodesign Preparatory Studies on pumps (ENER Lot 28: Wastewater pumps)