Power Savings with VSD

http://en.wikipedia.org/wiki/Adjustable-speed_drive

According to this you save as much as you reduce the speed.

So the savings will have to be found in comparison to the loads in the system and the old way of regulating the flow from the pumps compared to the VSD system.

I agree.

gee..me too!

Hey, Thats for you reply, How did you work out the exact percentage

1 - 0.8^3 = 0.488

if the load is steady, but what if it varies?

so basically At the minute i have 2 single phase pumps at 1.56kw Each Running in Parallel, I need to move about 120L Litres a minute with only 5 meters of head.

(This is bit of a side issue related to pump size. To a web site I found that might just answer ALL my questions)

I used the formula

P= kW of Pump

G= Gravity 9.81

D= Density 1000kgm^3 (Water)

Q= Flow rate in m^3 second - 120/1000*60 = .0016

H= Head - 5 Meters

np= Pump efficiency 84% - Generic Figures

nm= Motor efficiency 92% - Generic Figures

p=9.81*1000*.0016*5 / 1000*.84*.92

Sorry I can't use the Correct symbols for some of the above.

Any way I tried the example and it worked fine, When I input my numbers i get A really low number like

0.1057

Surly That can't be correct.

Actually just forget all that. I just need to be able to work out what amount of water a 2.2kW pump will move when running at 80% 90%, With a head of 5 meters.

You may need to show us a set of pump curves at various rpm's. Some manufacturers have this readily available; others maybe not. Depending on the pump rpm and impeller diameter, there will be a certain minimum rpm required to produce 5m of head.

Thanks,

Sorry If i seem a bit all over the place.

basically I'm trying to work out what pumps i will need. Ill jump on and see if I can find any graphs from manufactures for us.

I need about 120L/ Min with 5 meters of head. Currently there are 2 x 1.56kW Single phase motors there, Is a bit of overkill, So I thought upgrading to a single bigger motor on a VSD thats why I'm here too, Trying to sort out the most efficient option.

For "backup" (its pretty critical that there is always a flow of water) Run 2 1.56kW motors off the same VSD and if one fails make it ramp up and go flat out.

Any input?

Still trying to get a few ideas sorted out.

What's going on here? Three posts ago, these were 2.2kW pumps. Please quit shuffling nameplates, and pick out a correct number.

Its the right answer to the question that was asked the wrong way around.

Basically you will always need as much power as work has to be done plus losses in the system. By using the correctly sized equipment and motors not much more power saving can be achieved.

It is what it is.

Using an oversized pump for small flow rates will incur lots of losses where basically a VSD might be the answer but only within the limits of the pump capabilities.

OP needs to do more homework!

Just be aware that whilst operating a pump at less than full power will certainly cut your hourly power bill, you will have to run the pump for longer to move the same amount of product.

If there is significant lift or viscosity involved, then you may end up using considerably more power to move the same amount if you run the pump more slowly.

This, or course, may not be relevant to your particular needs, and speed control of the pump may be advantageous

I had a situation recently where a large local swimming centre had been convinced that they could save costs by running their filter pumps via a VSD. Two problems which arose were that - firstly the filter had to operate for a lot longer to maintain the pool, and secondly that there was a smaller solar heating pump downstream of the filter pump which relied on said filter pump for its water supply, some of which it then diverted to the solar collectors. Running the filter pump on low power caused the heating pump to cavitate thus resulting in poor heating performance and possible damage to the pump impeller had it been allowed to continue unabated.

VSDs on pumps are not always a good idea unless flow control is an issue.