VS vs dual-speed pumps

[mjc123]

Hey all,

I'm in the market for a new pump (separate thread: So.... my pump is dead. Replacement recommendations?).

As part of the process, I've emailed virtually every pool supplier I can find both locally and nationally (who ship pumps). A number of responses back so far suggest a VS pump because it is "more energy efficient" than a dual or single speed pump. I get that it is better than single speed, but I can't figure out why a VS pump would be significantly cheaper to operate than a dual-speed that runs the majority of the time in low speed. Isn't a VS essentially a dual speed that can run anywhere in between high and low? The quotes I've received for VS pumps so far are like... $1299+tax, which is more than double what I can find a 2-speed for. It's hard to fathom I could possibly save $600 in energy costs over the life of the pump compared to the dual speed. Am I missing something here?

 

[Jimrahbe]

123,

A 2-speed pump will save you almost as much as a VS pump. VS pumps do not operate the same way as a single speed or 2-speed pumps so they are more energy efficient, but not all that much. And, they cost a lot more.

VS pumps are best when you have a spa or a number of water features, and you want to run at different RPMs throughout the day.. For a standard pool owner, a 2-Speed pump will work just fine.

Thanks,

Jim R.

 

[Texas Splash]

I have a relatively simple set-up. My 2-speed is on low 24/7. I only crank it up on high to vacuum or help with skimmer action when I'm brushing. Minimal energy cost. Welcome to TFP!

 

[mas985]

Just a few generalized data points:

A two speed on high speed will use the same energy as a single speed pump if both are producing the same flow rate.

A two speed on low speed will use about 1/4th the energy as high speed (i.e. 75% in energy).

A VS pump at the same flow rate as a single speed will save about 5%-15% in energy. Depends on which two pumps you are comparing.

A VS pump at the same flow rate as a two speed on low speed will save about 35%-50% in energy. Depends on which two pumps you are comparing.

However, the extra energy savings of the VS may not actually pay for itself over the lifetime of the pump. That depends on the pump cost, $/kwh and runtime.

 

[markayash]

Seems like a lot, my 1.65 VS form Inyo was $650 but I noticed they are out of them now

 

[Texas Splash]

A VS pump at the same flow rate as a single speed will save about 5%-15% in energy. Depends on which two pumps you are comparing.

A VS pump at the same flow rate as a two speed on low speed will save about 35%-50% in energy. Depends on which two pumps you are comparing.

Mark, can you confirm? Seems like those should be the other way around. Because a 1-speed is such an energy hog, I would think there would be more (%) savings from a 1-speed versus a 2-speed on low (more efficient). No? Maybe it's just me?

 

[mas985]

I am not entirely sure what you are getting at with your question but the two quotes you have shown relate a VS to a single speed at exactly the same flow rate and a VS to a two speed on low speed at exactly the same flow rate and not a single speed vs two speed on low which have different flow rates. The efficiency differences are small because you are comparing the two pumps at exactly the same flow rates. However, when you compare a full speed to low speed of a two speed, they are not at the same flow rate so the savings is much more (i.e. 75% savings). This is similar to comparing a VS at it most efficiency speed 1000 RPM to a single speed pump, the savings are huge (~90%) but so is the difference in flow rate (>3:1). So it depends on how you are comparing the pumps.

Forgot to mention that a single speed pump motor has efficiencies of 60%-85%, depending on HP ratings while a VS pump motor has an efficiency of close to 90% at full speed. So full speed to full speed, they are not that much different.

 

[mjc123]

Seems like a lot, my 1.65 VS form Inyo was $650 but I noticed they are out of them now

Yep, that's because you're in the US. A) *everything* is much cheaper to begin with, and B) at current FX, $650 USD ~= $950 CAD


Thanks to everyone else as well - much of what you have told me confirms my suspicions. If I could get a VS pump for, maybe 125% the cost of dual-speed, it would probably make sense, but 200+% doesn't seem to even just estimating the numbers in my head. FTR, I'm comparing using a VS pump on low speed most of the time to using a dual-speed pump at low speed most of the time. The usage/flow rates would likely be fairly similar, so we're looking at relatively marginal differences in efficiency. at $0.25/kWh or whatever I'm paying (forget the exact number), it would take a lot of runtime hours to offset a 200+% increase in price over the lifetime of the motor

 

[Mayorb]

Just want to throw in my two cents....
Two speed motors have been on the market for decades.
They're "bullet proof" compared to VS (which have the electronics on top of the motor)
and are immensely simpler to operate.
I just don't see enough ""up side" to justify the added expense and complexity (and probable earlier failure) of a motor that delivers only marginal savings versus the 2-speed motor.