MEI Index: This is the value listed in centrifugal pump catalogs that indicates the minimum efficiency requirement mandated by regulations for certain categories of clean-water pumps.
Table of Contents
Why You’ll Find the MEI in the Pump Catalog Today
In recent years, the European Commission has taken steps to establish mandatory minimum efficiency levels for certain product groups sold within the European Union. This initiative also includes clean water pumps, to which these standards have been applied since January 1, 2013.
The key point for anyone reading a technical catalog is that the value listed (MEI) is not merely “additional information”: it is an indicator linked to efficiency requirements that affect the product’s marketability within the European Union.
ErP Directive and Regulation 547/2012 (Lot 11): The Context
The European Commission has issued (in the text) the ErP Directive 2009/125/EC, which establishes the legislative framework governing the energy consumption of energy-using products. In the same context, it is noted that, for many years now, attention has been focused on mandatory minimum efficiency levels for certain categories, including:
- Electric Motors
- Wet-Rotor Circulators
For pumps, the document resulting from the ErP Directive is Regulation 547/2012 (Lot 11), which introducesthe MEI index for specific Pump Types.
What Does MEI (Minimum Efficiency Index) Mean, and Why Is It Important?
MEI = Minimum Efficiency Index. In practical terms, the MEI corresponds to a minimum threshold: products that fall below this threshold cannot be placed on the market.
The value listed in the catalog, therefore, serves to clarify the pump’s performance relative to this minimum efficiency requirement. And this is a point that directly impacts compliance: the text specifies that, since the MEI is one of the parameters that must be met in order to affix the CE marking to the product, pumps that do not meet the required efficiency levels cannot legally be placed on the European Union market.
To which categories of pumps does the MEI index apply?
Regulation 547/2012 (Lot 11) introduces the MEI index for the following categories of pumps (as listed):
- Standardized single-impeller horizontal pumps with a base (ESOB)
- Vertical Multistage Pumps (MS-V)
- Single-impeller Monobloc Pumps (ESCC)
- 4” and 6” Multistage Submersible Pumps (MSS)
- In-line Monoblock Pumps (ESCCi)
The text also includes a brief key to the abbreviations:
- ESOB End-Suction Self-Supporting Bearing Pump
- ESCC End-Suction Close-Coupled Pump
- ESCC Inline End-Suction Close-Coupled Pump
- MS Multistage Pump
- MSS Submersible Multistage Pump
This classification is useful because the efficiency requirement (and the related verification) begins with identifying the pump within the specified Pump Types.
Effective dates and MEI values listed
The text lists two operational deadlines along with their corresponding values:
- Effective January 1, 2013: MEI = 0.1
- Effective January 1, 2015: MEI = 0.4
These dates are intended to provide a framework for when the required levels take effect, serving as a timeline for the application of the regulation to the affected pumps.
The MEI Index and Efficiency: What It Really Measures (and What It Excludes)
Here is a point that often causes confusion:the MEI index is presented as a measure of a pump’s quality in terms of its efficiency, but it is specified that it refers tothe pump’s HYDRAULIC efficiency.
The text also clarifies what is not included in the MEI: the engine is not part of this discussion in any way. Engine efficiency is referred to as “another matter,” distinct from the issue of hydraulic efficiency as assessed by the MEI index.
How to Determine the Minimum Required Efficiency: Algorithm and Parameters
The minimum required hydraulic efficiency is determined using an algorithm that takes into account:
- prevalence
- Flow rate
- speed
- a constant directly related to the Pump Type being evaluated
In other words, the requirement is not a “single” number that is the same for all pumps: it depends on the performance parameters and the pump family (ESOB, ESCC, MS-V, MSS, ESCCi).
Compliance Check: The 3 Points—BEP, PL, and OL
The minimum hydraulic efficiency is verified by calculating the efficiency at three points within the pump’s performance range:
- BEP (Best Efficiency Point): the point at which the pump operates with maximum hydraulic efficiency
- PL (Part Load): where the pump operates at 75% of the flow rate measured at BEP
- OL (Over Load): when the pump operates at 110% of the flow rate measured at BEP
The pump is certified when the efficiency calculated at these three points falls within the limits set by the Regulation.
Conclusion
The MEI index value listed in the catalog tells you whether (and how) a pump meets the minimum efficiency requirements introduced by Regulation 547/2012 (Lot 11) under the ErP Directive. It is an indicator related tothe pump’s hydraulic efficiency, not the motor’s efficiency, and is measured at three points (BEP, PL, OL) across the performance range.
