Note on WEF pump ratings

[mas985]

I just updated the Hydraulics 101 sticky with the following paragraph as WEF seems to be getting some attention. Any feedback is welcome.

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Pump WEF Rating

DOE has adopted a metric for rating pumps for their relative efficiency called the Weight Efficient Factor (WEF) and unfortunately, it is not the best way to compare pumps. The reason is in the method of WEF calculation. First, the definition of energy factor:

Energy Factor = GPM * 60 / Watts

For single speed pumps, this is a not the worst way to compare pumps (e.g. THP is worse) but when comparing pumps that can operate at multiple speeds, the speed at which you compare the pumps can give wildly different results. This is why WEF was created but there is a fundamental flaw in the methodology. For a VS pump, EF can be calculated at any RPM and the lower the RPM, the higher the EF down to about 800 RPM and then it will start to climb again due to the drive electronics overhead energy use. So the lowest EF is at full speed which plays into the WEF calculation.

In order to calculate WEF of a VS pump, two measurements are combined with a weighting factor for each. One measurement is performed at 80% of full speed with a 20% weight while the second measurement is performed at a lower speed with a specific flow rate (e.g. 31.1 GPM for HHP > 0.75) and a 80% weight. So what this does in effect is to lower the WEF for the larger THP VS pumps when in fact the larger THP VS pump in a particular pump line may actually have better efficiency at a given flow rate than the lower THP VS pump. So the best way to choose a VS pump is to pick the largest THP pump in the product line of your favorite manufacture or compatible with your controller. Then when operating the pump, choose the lowest RPM for the given task and you will be operating efficiently.

 

[JamesW]

Weighted Energy Factor (WEF) is a standardized measurement of how much energy is required to move the water in terms of gallons per kWh of energy use.

A pump with a WEF of 7.847 means the pump is rated as being able to pump 7,847 gallons of water with one kWh of energy.

The problem with the WEF is that the gpm is not part of the equation.

You can move 7,847 gallons a lot more efficiently at 20 gpm than 40 gpm or 80 gpm through the same system.

So, unless you know that both pump's WEF numbers were measured at the same gpm, the WEF is not going to tell you the real information.

In my opinion, the WEF should be given at specific flow rates and on the exact same system curve.

In my opinion, giving the amount of water (gallons) moved for a specific amount of energy is a bogus term without specifying the flow rate and head loss.

In the case of the Superflo vs, it doesn't make sense that the pump would have any efficiency difference between a 115 volt supply and a 230 volt supply when moving the same gpm through the same system curve and the same head loss.

The pump affinity law shows that the power required to move water increases exponentially as the gpm increases.

For example, if the gpm is doubled, the power required is 6 to 8 times as much.

To move a set number of gallons, doing it twice as fast will take half the time. So, the energy used will still be 3 to 4 times as much.

For example, if you run at full speed and it's 2,000 watts for 8 hours, you will use 16 kilowatt hours.

If you run at half speed and it's 333 watts at 16 hours, it takes 5.333 kilowatt hours.

So, running at full speed takes 3 times as much energy to move the same number of gallons.

In my opinion, the WEF numbers are ridiculous and useless.

Trying to give a single number for the "efficiency" of a pool pump is stupid and worthless.

No one is going to use the number other than for marketing that exploits people's ignorance, like what happened with horsepower and service factor.

The only thing that the WEF does is incentivize the manufacturers to try to game the system to get better WEF numbers even when the changes are counterproductive.

99.9% of people don't know how to select the best pump anyway. Adding another metric will do nothing to make the situation better, especially because the metric is completely meaningless.

The WEF will make zero difference in anyone's ability to choose the best pump for their application.

In my opinion, the power usage in watts should given for specific operating points where the gpm and TDH are given.

Every manufacturer can produce a chart where the power, gpm and TDH are given for multiple points.

In addition, the manufacturer should be able to provide a calculator that can accept inputs such as rpm, TDH, gpm and power and provide the missing variables.

For example, if you input the tdh and gpm, the calculator will return the rpm and watts.

The calculator should even be able to tell you the best pump for your application based on your system requirements.

That way, you can compare one pump against another in a fair and accurate way.

Until the numbers are transparent about exactly what they are measuring, they should be ignored, in my opinion.

The important thing about efficiency is how much power a pump will use on your application, not on some theoretical system that is unlikely to match yours.

For every system, there are one or more flow rates that you will want or need to accomplish what you’re trying to do.

At each flow rate on your system, there will be a corresponding TDH (Total Dynamic Head), which is the amount of resistance produced by moving the water through the system.

What matters is how much power a pump will use for your unique application.

This would be relatively easy for manufacturers to measure with their current test equipment. They could produce charts and calculators that will output the power at any input THD and gpm. In fact, this is what Pentair has already done with the Intelliflo to allow it to calculate the flow on its variable flow models. The intelliflo calculates the TDH and the flow (GPM) from the RPM and the power usage.

Once you know the amount of power needed at each flow rate, you would multiply the power by the time needed for each flow rate and that will give you the amount of energy needed in kilowatt hours, which is what you pay for.

The people pushing WEF say it’s analogous to MPG for a car, but it’s a completely different situation.

The power usage of a pump changes exponentially by a cube factor. So, going from 30 gpm to 60 gpm uses 2^3 or 8 times as much power.

For a car, the amount of gas required does not increase by 8 times when going from 30 to 60 miles an hour. If that were true, the mileage would go from 40 mpg to 5 mpg when going from 30 to 60 miles per hour. In that case, what mpg rating should the car get? 5? 40? Somewhere in between? Depends a lot on how fast you're going to drive. Without knowing how fast you're going to drive, it's pointless to say what the mpg will be.

Interesting note. Pumps with three-phase motors are exempt from the WEF requirements. Variable speed pumps have three-phase motors. So, one could argue that they are exempt from the requirements.

 

[mas985]

The problem with the WEF is that the gpm is not part of the equation.

Actually, GPM is part of the equation as defined in this document: method of WEF calculation
In order to get to kgal/kwh, you need to use GPM and watts. The issue is at the high speed setting, it isn't same same GPM for every pump. I understand why they did that because they may not of been able to choose an upper GPM that was available to every pump. But just choosing one GPM would have been better.

But I agree with everything else.

For example, if you input the tdh and gpm, the calculator will return the rpm and watts.

The calculator should even be able to tell you the best pump for your application based on your system requirements.

That way, you can compare one pump against another in a fair and accurate way.

This is exactly what the "Energy Cost" spreadsheet in the "Pump Tools" workbook allows you to do.

 

[JamesW]

The problem with the WEF is that the gpm is not part of the equation.

I mean the customer's GPM and TDH are not part of the equation.

What is really needed, is a software calculator that will generate a system curve and find the best pump for a customer's specific needs based on their unique set of gpm and head loss specifics.

For example a customer might input:

Solar runs for 8 hours per day at 45 gpm and the TDH is 50 feet.
Skimming runs for 12 hours per day at 20 gpm and 18 feet of head.
Fountains run for 4 hours per day at 50 gpm and 45 feet of head.

What pump will best meet my needs?

In my opinion, WEF is totally useless and should be ignored.

 

[JamesW]

Most builders are completely clueless about these things as evidenced by the overwhelming number of WhisperFlo pumps being used for fountains and other water features.

WEF is not going to do anything to help anyone in any way.

Service Factor is being eliminated. So, that's a good thing.

 

[mas985]

What is really needed, is a software calculator that will generate a system curve and find the best pump for a customer's specific needs based on their unique set of gpm and head loss specifics.

For example a customer might input:

Solar runs for 8 hours per day at 45 gpm and the TDH is 50 feet.
Skimming runs for 12 hours per day at 20 gpm and 18 feet of head.
Fountains run for 4 hours per day at 50 gpm and 45 feet of head.

Again, you can do that with the "Energy Cost" worksheet. They would just be individual profiles. However, I don't think you need to go to that detail. In most cases, if you just choose the longest run time period, that will be good enough for comparison. If one pump is more efficient under one situation, it will be under the others as well. Getting the plumbing curve exactly correct is not all that critical either. Approximations are good enough (Curve-C or Curve-A).

But as I tell most people in the market for a VS, none of this is really going to make a large difference. All VS pumps are efficient. The difference in wattage are small especially at low GPM. The best advice is to go with the largest THP pump in the pump line and go with the manufacture that you have automation with or prefer. Keep it simple.

 

[JamesW]

The best advice is to go with the largest THP pump in the pump line and go with the manufacture that you have automation with or prefer. Keep it simple.

That's a good way to choose.

Manufacturers will push their pumps based on the WEF factor, as if it really mattered.

Hayward Pool Products currently adheres to WEF testing and has the highest WEF rated pumps in the pool industry.

Weighted Energy Factor for Pool Pumps: What You Need to Know - Hayward POOLSIDE Blog

The new weighted energy factor (WEF) regulations will make it easier for you to save energy and money when purchasing a pool pump.

blog.hayward-pool.com