There’s more to PEI than meets the eye

Energy efficiency is the biggest design challenge you face as energy costs rise and environmental concerns grow. In 2015, the Department of Energy (DOE) created the Pump Energy Index (PEI) to recognize the role pumps play in overall system efficiency. Effective by 2020, this mandate will make it easier to achieve efficiency … IF you understand how it works.

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Learn the Truth Behind These Common PEI Myths

Myth: PEI rates all pumps.

Truth: No. For now, only clean water pumps that fall within a limited scope will be rated.

The DOE working group evaluated data from more than 20 manufacturers and 3,000 pump models to develop a set of initial parameters for pumps, which will act as a baseline for the Pump Energy Index (PEI) ratings. Five pump types were decided on, as well as a set of specific scope parameters based on performance data. The limited scope for these ratings is likely to expand in the future to accommodate new, more efficient technologies or designs. Explore the drop-downs to find out what’s currently included and what isn’t.

  • Pump Parameters
    • Basic Model BEP Requirements (At BEP, does the pump meet…)
      • Power input: 1–200 HP
      • Flow rate: 25 gpm or greater
      • Total dynamic head: less than 460′
    • Operating Requirements (Can the pump operate within…)
      • Temperature range: 14–248°F
      • Operating speed range (+/- 20%):*
        • 1,440–2,160 rpm
        • 2,880–4,320 rpm
    • *If the operating speed at BEP is outside the defined speed range, the pumps will be derated to fall within the speed range, and then be checked for the BEP requirements and given a score, if applicable.
  • Included Categories
    • End-suction close-coupled (ESCC) pumps
    • End-suction frame-mounted (ESFM) pumps
    • Inline (IL) pumps
    • Radially split, multistage, vertical (RSV) inline casing diffuser pumps
    • Vertical-turbine submersible (VTS) pumps
  • Excluded Categories
    • Fire pumps
    • Self-priming pumps
    • Prime assist pumps
    • Magnet-driven pumps
    • Nuclear-controlled pumps
    • Submersible turbines with more than 6″ discharge
    • Circulators

Myth: Lower PEI always means the most efficient pump.

Truth: No — it’s not always this easy.

Lower PEI scores are meant to indicate lower power consumption, but there are other important factors to consider, like your operating location on the curve and your load profile. Because PEI is based on a specific load profile, the most efficient pump for your application may not always have the lowest PEI rating. To achieve the highest efficiency for your system, you will want to factor in the actual operating point as well as your system’s load profile. Here’s an example:

Pump A

400 gpm @ 75″ TDH
Brake Horsepower: 11.09 BHP
Mechanical Efficiency: 76.98%
PEI: 0.95

This pump has a better PEI than Pump B, but it is actually less efficient and has a higher power consumption than Pump B due to the operating point on the curve.

Pump B

400 gpm @ 75″ TDH
Brake Horsepower: 10.75 BHP
Mechanical Efficiency: 79.15%
PEI: 0.98

This pump’s PEI score is not as good. But it has a lower BHP and a higher mechanical efficiency because it is operating closer to its best efficiency point (BEP) than pump A, making it the more efficient pump.

Myth: Low pump PEI guarantees high system efficiency.

Truth: It doesn’t. Pump PEI does not equal system PEI, and there are many other factors to consider. Here are a few to think about:

Load Profile

PEI is based on specific load profiles. The constant load rating is measured at 75%, 100% and 110% of best efficiency point (BEP) by throttling a valve. The variable load rating is measured at 25, 50, 75 and 100% of BEP using a variable speed control curve. The horsepower measurements taken at each point are then weighted evenly. PEI should be a good indicator of pump efficiency for systems with load profiles similar to those tested. For different load profiles, check the actual pump efficiency instead of relying on PEI.

Pump Controls

Advanced control logic for variable load applications can deliver extra efficiency that PEI doesn’t measure. Proportional pressure controls, packaged systems and parallel pumping arrangements can all add efficiency that doesn’t factor into PEI.

Pump Selection

Where you’re operating on the pump curve matters more to your system efficiency than PEI. If you choose a pump with a low PEI, but you’re operating significantly left of BEP, a pump with a higher PEI might actually provide better overall system performance because it’s operating near the best efficiency point. You can see a good example of pump curves like this in the “Lower PEI always means the most efficient pump” misconception.

Other System Components

It’s possible to have efficient pumps powering an inefficient system. Make sure that the other mechanical components of your system are also built for efficiency.

Myth: If I spec a PEI of below 1, I’m covered.

Truth: Yes and no. It is true that as of 2020, pumps with a PEI higher than 1 may no longer be sold or installed. However, specifying ONLY based on PEI can eliminate your best options. Consider the Grundfos TPE3:

The horsepower of the first model is outside the PEI tested range (1–200) at best efficiency point (BEP). The speeds of the last three models are also outside the PEI range.

But if you specified pumps only based on PEI, you’d be eliminating those pumps and the exceptional energy efficiency they can deliver.

PEI Rates All Pumps

Lower PEI Always Means the Most Efficient Pump

Low Pump PEI Guarantees System Efficiency

If I Spec a PEI of Below 1, I’m Covered

Understand What PEI Means For You

Learn Where HI Energy Ratings Fit In

The Hydraulic Institute Energy Rating (ER) predicts the power savings of any pump that meets PEI’s baseline standard. The HI Energy Rating was designed to be a more user-friendly rating that makes it easier to understand the value your pump is providing.

While lower numbers equate to better PEI scores, it’s higher numbers you want for ER scores. You can see how it works on this sample label, which displays PEI and the corresponding ER score. Here’s the math:

ER = (1 - PEIrating) x 100
Label showing a PEI of 0.35 and an Energy Rating of 65

Put it All Together to Specify the Right Pumps

The first step to consistently delivering energy efficiency is fully understanding your system and/or application requirements. Pump selection should most importantly be based off of load profile and part load efficiencies. Once you have this data, your pump’s actual energy consumption can be determined.

If your specified pump is within the DOE’s scope, be sure to know and understand where the potential pitfalls are, and choose a manufacturer you can trust to deliver the efficiency you need.

Click here to download a helpful e-book covering these regulations in more detail, and be sure to reference the “What to Watch For” section starting on page 16.

For more information contact your Grundfos representative. 

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