Single speed pump vs. Variable speed pump

JamesW

TFP Expert
Mar 2, 2011
18,590
And if you get with the flow restriction valve and cut the power consumption in half, as I was able to do with my system, you get.
Ball valve:$12.65
Savings per month $30
Break even: 13 days
Total saving over 120 months: $3600

Savings are there for those that, for whatever reason, have a single speed pump.
In my opinion, using a valve to restrict the flow is not a good choice.

I don't think that you could get the power to half without cutting the flow to basically zero.

Going to a smaller impeller would be a much better option to reduce power and flow.

You can go to a two speed pump or variable speed.
 

Darin

Member
May 29, 2015
22
Muscatine/IA
I actually did a write up on the savings of variable speed by utilizing a vfd. It can be found here. VFD, Real World Results.
Just remember that the pump affinity law is theoretical, there is heat and noise losses, thus using an amp clamp will give your "real" results. Still using a variable speed, whether a conventional 3 phase or mag motor will give quick payback. Now is it worth it to you to just throttle your single or two speed motor? Well that is up to you as you will save money, just not as much. If you have the ability to save money now, then buy a VS system, if you do not then throttle your present pump after all you will save money. Whenever it does die replace it with a VS.
 
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mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,252
Pleasanton, CA
Just remember that the pump affinity law is theoretical, there is heat and noise losses, thus using an amp clamp will give your "real" results.
Technically, affinity laws only apply to pump wet ends and not motors & drives. Unfortunately, too many have used the affinity equations to estimate motor power savings which is a misuse of the affinity equations. This is because motor efficiency changes with RPM so the affinity equation cannot be used unless the efficiency is known as well which in most cases it is not. However, the affinity equations do fairly accurately represent hydraulic power, head and GPM for which they were originally intended.
 

JamesW

TFP Expert
Mar 2, 2011
18,590
if you do not then throttle your present pump after all you will save money.
In my opinion, throttling is almost never going to be a good choice.

If you want to reduce the power, replace the impeller with a smaller impeller.
 

Jcciaschi

New member
May 31, 2020
1
23231
I have a variable speed Hayward and I'll chime in here with some numbers.

Most variable speed motors will take 120v or 240v, alter it into DC, and then kick it back out as 3 phase. Why? 3 phase motors are more efficient than motors that run on single phase so immediately you gain efficiency. But there is more.

My pump allows me to set 3 speeds and I can choose RPM's anywhere from 100-3000 in increments of 20. I have the high speed set at 3000, the middle speed at 2000, and slow speed at 1000. The 3000 was easy as it is the fastest the motor will go. The 2000 is the speed where pressure will register about 1lb. I chose this speed due to back pressure and resistance. The more resistance the pump encounters the more amperage it will draw thus the lower the pressure the lower the amperage. At 1lb I know the pump is at its most efficient state of moving water. The slow speed is 1000 rpm. This was chosen as it works for my setup. I found I could run at 800 rpm when the filter was sparkling clean but if it got a little dirty the pump wasn't moving enough water to overcome the additional resistance and would airlock. So how much amperage do these speed draw?

The top of the pump had a display that shows speed, time, and amperage draw.
At 1000 rpm it draw about 76 watts
At 2000 rpm it draws around 320
At 3000 rpm it draws about 970 watts

As you can see, doubling the speed does not double the amperage so I use this to my advantage.

I have the pump set to run at 1000 rpm 20 hours a day. In the morning around 11 it runs at 2000 rpm for 2 hours and in the evening it runs at 3000 for about 2 hours. The 2000 rpm time was chosen as it is sunny on the pool at that time so it move around the water to take advantage of solar gain. The 3000 rpm time was chosen as that is when we usually swim and stir up the pool. I also went further and looked up the flow characteristics to ensure I was turning over the water enough with this plan. Thus far it has worked.

There is an added benefit of my current setup. I have found the pump running 24/7 just seems to keep the water clearer. I had a pool before with a single speed motor that would run for 8 hours a day and always had issues. Granted that was years ago in a different state, and many other variables so I could be wrong but I like the idea of water moving 24/7.

So how much does this pump cost to run? Simple math. We pay about .11/kw of power. 1000w = 1kw
970 watts x 2 hours = 1940
320 watts x 2 hours = 640
76 watts x 20 hours = 1520

Thus a 24 hour period uses 4100 watts or 4.1kw or .45 cents a day or roughly $13/month

A single speed running 8 hours a day (assuming the same wattage but again VS pumps are more efficient) would use:
970 x 8 = 7760 watts or 7.76kw or .85 cents a day or roughly $25/month

Hope this sheds some light on a variable speed VS a 2 speed VS a single speed.
 
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