DC return pump efficiency and noise vs flow

[Randy Holmes-Farley]

Is it possible to make any generalizations about submersible dc return pump efficiency and noise vs flow?

In particular, whether a larger pump of the same brand and style at, say, 50% flow is more efficient or noisy than its smaller sibling at 100%, while attaining the same flow?

TIA

 

[Turtle_reef]

In general, a larger pump operating at 50% flow would likely be more efficient and quieter than a smaller pump operating at 100% flow to achieve the same overall flow rate.

The efficiency wity larger pumps often gave more efficent motor designs and can handle higher flow rates with less internal friction. That being said operating a larger pump at lower flow rate can reduce losses and improve efficiency.

larger pumps may have larger motor housings and better noise isolation, leading to lower noise levels but opperating at a lower flow rate can reduce the mechanical vibrations and noise associated with the impeller and motor. However should note that some manufacturers may optimize smaller pumps for specific flow ranges, resulting in comparable or even superior performance at certain operating points

 

[Miami Reef]

I think it’s akin to a human heart: Will a heart pushed to its max act similarly to a stronger heart that is pushed 50% as strong?

Anyway, the DC pumps these days are incredibly quiet. I have 2 that run together and they are extremely silent.

I use the Echotech Vectra M2. I run both about 70% strength.

 

[Pod_01]

I recall reading that DC pumps are most efficient when running at 80%, but I am going by memory.

From my experience the DC pumps seem to loose flow over time. I am not sure why that is or if all do it but there is decrease so larger pump is good idea. I start at 40/50% but later need to bump it up to 70/80% to get same flow.

I always found AC pumps noisy/ humming.

All of the pumps I use are DC and they are all silent, no hum or vibration. So far I used Vectra S1, Maxspect Jump DC 6K, Innovative marine Mighty Jet, Royal Exclusive pump for skimmer.
The Mighty Jet is used in 10gal tank that is located in my daughter room and it is dead silent, no hum or vibrations.

The negative, as mentioned they loose power and they do eventually stop working. My Vectra S1 and Tunze DC skimmer pump stopped working so the lifespan seems to be 4 to 5 years.
They do need one week to break in and be silent, time for the biofilm to build up.

 

[Fenral]

Randy,
Short form is no. Making that generalization is not a good idea - to many variables around design specifications. Most dc pumps are more electrically efficient then their ac counterparts . But absolute efficiency and noise are going to depend on all kinds of mechanical design characteristics. Even the same manufacture and model may perform very differently due to quality control, and nature of the fluid being moved…

 

[VintageReefer]

In my experience, the quietest and most efficient setup is a dc pump operating around 40-60%

This is an easy task for it and puts low strain/load on the internals.

My return pump is around 1000gph, I run at 40%, it’s silent, I can’t hear it at all. And it consumes 14 watts, extremely efficient for a return pump this size

 

[BeanAnimal]

Is it possible to make any generalizations about submersible dc return pump efficiency and noise vs flow?

In particular, whether a larger pump of the same brand and style at, say, 50% flow is more efficient or noisy than its smaller sibling at 100%, while attaining the same flow?

TIA

All centrifugal pumps will have what is called a BEP (best efficiency point) where the power to flow ratio is maximized. This depends on several variables and the only way to really make that comparison is by examining pump curves.

With DC variable speed pumps, each speed setting will have its own BEP based on head pressure, but this can't be determined without accurate pumps curves or a flow meter and power meter.

Unfortunately, very few DC return pump manufacturers provide pump curves. I assume because most wouldn't match their published flow claims.

In general - The larger pump running at a fraction of the rated speed will offer better efficiency.
1 - a pump running at 100% is typically running beyond its BEP
2 - a pump running at 100% will run hotter than a pump running at a fraction of its rated load. Electrical resistance rises with heat and efficiency drops.
3- the larger volute and impeller will have less frictional loss and turbulence in the volute due to pumping the same volume through a larger area.

Important Note:

DC pumps require electronics to operate (a driver circuit) In some (most) models, these components (the DC driver circuits and power mosfets) are potted into the pump body. This simplifies speed control connectivity and allows them to be "water cooled". If the driver was in the external controller, it would get hot and need active cooling and more complex cabling to the controller.

A DC pump being driven at 100% output is likely going to be very hard on the driver with regard to operating temperature compared to the same pump running at a lower power. Lower output means less heat and a longer life. So unlike an AC pump, you get longer life oversizing the pump and under driving it.

All in - always go with the larger size and under drive it.

Forgive typos and proof reading... on iPhone and don't have my old person glasses.

 

[BeanAnimal]

Related Bonus:

Dead Heading (closing off the outlet) of a centrifugal pump will not damage it (in theory). With a closed output, the pump is doing LESS work than it would if it were pumping water. The only issue is the buildup of heat in the volute due to the trapped water running in endless circles and now new flow to carry the heat away... So in practice, dead heading is fine for a short period, but if you forget to open the valve back up the water in the volute will heat and could cavitate.

 

[Randy Holmes-Farley]

This has been a great discussion. Thanks very much everyone!

 

[KStatefan]

Just an example of a pump performance chart with BEP

 

[Randy Holmes-Farley]

Just an example of a pump performance chart with BEP

Thanks.

300 horsepower. Pretty big pump. lol

 

[Fenral]

Thanks.

300 horsepower. Pretty big pump. lol

Must be a city mains pump

 

[BeanAnimal]

Must be a city mains pump

We had some monsters that we used underground in the mining industry.
That is a monster multistage wet end, no motor. Guessingby the size..1200 kW (so ~1600HP) or so would be needed to drive that at 300 meters of head.

Depending on the location of the mine, the amount of water we move underground (to prevent the mine from flooding) is sometimes insane.

but the pumps that were scary were the hydraulic pumps that ran the longwall equipment. 5K to 8K PSI with 2" supply lines. Insane volume and pressure.

Here is a pump car with (3) hydraulic pumps typically connected in a lead/lag setup that can spool up more volume to maintain pressure up (5000 - 8000 PSI) as flow is demanded.... Designed to supply 300 GPM to maybe 500 GPM at those pressures. A broken 1 1/4" hose would beat you to death whipping around and a smaller hose like 1/2" would slice you like a waterjet cutter... crazy stuff. That is a SMALL pump car below. Larger mines would have maybe 1 or 2 larger pumps per car. The sound they make is pretty wild also... Just standing next to them you know they are serious.

Those pumps power these (typically ~100 - 200 on a longwall face that is is 1000 to 1500 feet wide and a maybe a mile long). They are called "shields" and the hold up (literally) the world above them as we mine underneath... The entire 1000' x 5000' block of call, letting the world collapse behind us we move forward. All of the black hoses (under the curly hose protectors) are the hydraulics. 5000 PSI or more