- May 3, 2007
- 17,824
- Pool Size
- 20000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
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.
---------------------------------------------------------------------------------
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.
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