VFD Savings

[Dzboyce]

I installed a 300 hp Peerless lineshaft turbine Pump, a few years ago. It drew the 300 hp at its BEP which was 1,000 gpm and I don’t remember the TDH. But I to remember the hp draw at 0 gpm, or “deadhead”. It was 150 hp. So with this particular pump curve, the horsepower load was 150-300 hp across a flow of 0-1000 gpm.

 

[Dzboyce]

prv assembly https://www.cla-val.com/documents/pdf/E-90-01.pdf
valve https://www.cla-val.com/documents/pdf/E-100-01.pdf

At 1000 gpm flow there is only 3-4 psi friction loss thru a 6” cla-Val. Any additional pressure reduction is from the valve modulating the pressure.

 

[Besoeker]

yours is dismissed,

And yours remain:
"but if you can only slow the pump a few Hz to deliver the same Q and P it gets you zip"
If you think or even just speculate you can get by with 10hp that is a lot of energy savings compared with his throttling valves.
Note that "VFD savings" is the thread title.

 

[ptonsparky]

I am guessing that a removing the pressure reduction valves and putting VFD in would be part of the solution along with a pump more suited to speed changes. A 200 hp VFD we put in a few years ago only need something like 5 HZ increase to supply 2 pivots vs 1.

I will assume that when they need to use full flow for flushing they will want it and that 100 HP or at least the same GPM it produced better be there.

I do not know the pump curve nor any idea of the GPM they use.

Inlet to the pump is an 8" pipe directly to the supply tank. A 6" discharge splits and feeds the two pressure reduction valves which then combine again into a 12" line.

 

[Besoeker]

I am guessing that a removing the pressure reduction valves and putting VFD in would be part of the solution

Will save energy by reducing losses.

 

[kwired]

whrn you double the speed of the impeller;
you double the flow,
you square the pressure,
you cube the horsepower

That's why VFDs save money when running at reduced speed on centrifugal pump applications.
Yes, yet those simple points seem to be getting missed in favour of convoluted calculations mostly based on assumed operational parameters.

But if one only needed a 40 HP motor in the first place then there was a design flaw from the start, and probably could have used a lesser pump as well.

Now if they have a need for most of the 100 hp capacity at times that changes things, and looks like that is a possibility:

I am guessing that a removing the pressure reduction valves and putting VFD in would be part of the solution along with a pump more suited to speed changes. A 200 hp VFD we put in a few years ago only need something like 5 HZ increase to supply 2 pivots vs 1.

I will assume that when they need to use full flow for flushing they will want it and that 100 HP or at least the same GPM it produced better be there.

I do not know the pump curve nor any idea of the GPM they use.

Inlet to the pump is an 8" pipe directly to the supply tank. A 6" discharge splits and feeds the two pressure reduction valves which then combine again into a 12" line.

 

[Besoeker]

But if one only needed a 40 HP motor in the first place then there was a design flaw from the start, and probably could have used a lesser pump as well.

You'd still save energy by removing the throttling valves and using a VSD to get the same flow.

 

[kwired]

You'd still save energy by removing the throttling valves and using a VSD to get the same flow.

I don't disagree with that, just saying they could have spend less up front with a different pump and motor, maybe didn't need the valves, likey even could have used smaller piping, if 40 HP is the most ever needed.

 

[Besoeker]

I don't disagree with that, just saying they could have spend less up front with a different pump and motor, maybe didn't need the valves, likey even could have used smaller piping, if 40 HP is the most ever needed.

If there is a requirement to control flow or pressure, there isn't a lot of choice. You need either valves or a variable speed drive.

 

[kwired]

If there is a requirement to control flow or pressure, there isn't a lot of choice. You need either valves or a variable speed drive.

don't disagree with that either.

If this is for what I think it is for, probably not a requirement. I have been around some dairy farms and what they do is pump water from a lagoon into holding tank(s). This water is periodically released to "flush" manure off the floor and eventually finds it's way back to the lagoon it was pumped from. Simpler systems "flush" once the holding tank is full, others have timer on the flush gate. All that is needed from the pump is the ability to keep up with the demand. I think you see more that dump when tank is full - so the pump runs 24/7 and selecting proper flow rate is somewhat critical from the start, or else you may end up adding additional valves, or a VFD down the road, which may be ok of designing for future demands.

 

[Besoeker]

don't disagree with that either.

If this is for what I think it is for, probably not a requirement. I have been around some dairy farms and what they do is pump water from a lagoon into holding tank(s). This water is periodically released to "flush" manure off the floor and eventually finds it's way back to the lagoon it was pumped from. Simpler systems "flush" once the holding tank is full, others have timer on the flush gate. All that is needed from the pump is the ability to keep up with the demand. I think you see more that dump when tank is full - so the pump runs 24/7 and selecting proper flow rate is somewhat critical from the start, or else you may end up adding additional valves, or a VFD down the road, which may be ok of designing for future demands.

The OP does mentioned two pressure regulating valves.

 

[Ingenieur]

At 1000 gpm flow there is only 3-4 psi friction loss thru a 6” cla-Val. Any additional pressure reduction is from the valve modulating the pressure.

he has 43 psi drop
2800 gpm
the drop varies with flow/valve position
the chart is for a fully open valve at various flows

the valve Cv = 440
at 43 psi
gpm = 440 sqrt(43) = 2900 gpm
which means the valve is almost fully open

the hp for that drop ~ 2900 x 100 x 8.34 / (33000 0.7) ~ 100 hp per valve
he measured 40
something does not add up

 

[Ingenieur]

And yours remain:
"but if you can only slow the pump a few Hz to deliver the same Q and P it gets you zip"
If you think or even just speculate you can get by with 10hp that is a lot of energy savings compared with his throttling valves.
Note that "VFD savings" is the thread title.

the vfd is the worst option
new pump is the solution

100 hp pump
40 hp load , most of it wasted on valve drop

using a 100 hp vfd to drive a 100 hp pump at 10 hp is dumb

until we know
flow
system curve
pump curve
pump mfg/pn
system piping layout
control strategy, flow, press, etc

we know nothing
but with 40 psi drop and 40 out of 100 hp it is safe to say pump too big and valve too small
may be a simple as new motor and impeller, but unliely since we only need 10 hp or so
a vfd is layering bad engineering on top of bad engineering

 

[Besoeker]

100 hp pump
40 hp load , most of it wasted on valve drop

You just made my case watertight.

 

[Ingenieur]

You just made my case watertight.

nope
stated a fact
you ignored the rest
vfd = worst solution
pump with same Q at same head MINUS valve drop
cheaper, more reliable, easier to adjust (set prv), less losses than a vfd

100 hp vfd
100 hp motor
10 hp load after valve drop (40 total)

here's the post you cherry picked, disingenuously

the vfd is the worst option

new pump is the solution

100 hp pump
40 hp load , most of it wasted on valve drop

using a 100 hp vfd to drive a 100 hp pump at 10 hp is dumb

until we know
flow
system curve
pump curve
pump mfg/pn
system piping layout
control strategy, flow, press, etc

we know nothing
but with 40 psi drop and 40 out of 100 hp it is safe to say pump too big and valve too small
may be a simple as new motor and impeller, but unliely since we only need 10 hp or so
a vfd is layering bad engineering on top of bad engineering

 

[Ingenieur]

Customer with a 100 HP motor pumping from a large tank to two pressure regulating valves. Input pressure to the valves is 96 PSI. Output is 53 PSI on the load side of one of the valves. Assuming for the moment that they are both set the same.

The only restriction on the inlet side is the short pipe connecting the centrifugal pump to the tank.

The VFD savings calculator I found indicated payback was in less than 2 months by just changing the speed(s) for x amount of time for each. That would be a quick sell.

Seems to me that I would also need to know how much water is actually moving at that 53 PSI in the 6"? pipes leaving the PR valves. What other values do I need to make a better SEWAssumptiveG in cost savings for a customer?

how many pumps? you say 'a' pump, not 2, but then say 'speed(s)' implying 2?
if 2 does each pump feed 1 valve?
where was the press measued? at pump, valve, etc
how much pipe:
pump tp valve, length and dia
valve info, globe, angle, is it a self regulated prv?
if the drop is just across the valve is 43 psi (I doubt it) we know the flow
I suspect it includes piping losses

 

[Besoeker]

nope
stated a fact

Not so..
Your claim "40 hp load , most of it wasted on valve drop"
Remove the valves, remove that waste.
That's the logical conclusion from your claim.

 

[ptonsparky]

how many pumps? One you say 'a' pump, not 2, but then say 'speed(s)' implying 2? Means running the one pump at different speeds for different lengths of time.
if 2 does each pump feed 1 valve?
where was the Highpress measued? at pump, immediately prior to valves, etc
how much pipe:
pump tp valve, length and dia 6-8' and 6"
valve info, globe, angle, is it a self regulated prv? Self regulating would be my SEWAG. The valve is mounted horizontally and I would not call it a globe. I have no other info on it.
if the drop is just across the valve is 43 psi (I doubt it) we know the flow. Why would you doubt it? Granted we put in a $4 pressure gauge on the low side but it was new. The existing Hi press looks fairly new and of much better quality. I did not check for calibration
I suspect it includes piping losses

You are probably correct that there is piping losses, but how much in the maybe 10 feet from the line side of the PRV to the load side? The pressure gauge is on the load side of one valve but both pipes combine into the 12" within 10' or less. The building is 18' long and all that piping is inside it.

 

[Ingenieur]

Not so..
Your claim "40 hp load , most of it wasted on valve drop"
Remove the valves, remove that waste.
That's the logical conclusion from your claim.

you only cherry picked part of it, I've included it below
mods, I thought terms/conditions prevented editing posts
especially selectively and disingenuously?

but wrong anyways

can't remove the valves, they regulate the pressure
need to replace pump so inlet is a few pounds > outlet
so valve drop goes from 40 to 5 or less

100 hp vfd
100 hp pump
40 hp running
10 hp load

vfd is bad engineering on top of bad engineering

the vfd is the worst option
new pump is the solution

100 hp pump
40 hp load , most of it wasted on valve drop

using a 100 hp vfd to drive a 100 hp pump at 10 hp is dumb

until we know
flow
system curve
pump curve
pump mfg/pn
system piping layout
control strategy, flow, press, etc

we know nothing
but with 40 psi drop and 40 out of 100 hp it is safe to say pump too big and valve too small
may be a simple as new motor and impeller, but unliely since we only need 10 hp or so
a vfd is layering bad engineering on top of bad engineering

 

[Ingenieur]

You are probably correct that there is piping losses, but how much in the maybe 10 feet from the line side of the PRV to the load side? The pressure gauge is on the load side of one valve but both pipes combine into the 12" within 10' or less. The building is 18' long and all that piping is inside it.

6" piping losses 20 psi/100' at 2800 gpm, so moot
since you measured at the valve even less
of horizontal and a clay then a globe
the valve is linear so full open is 2900, valve is almost 100%

what is on the lo side 12"? how is the water discharged?
or does it always free flow

something doesn't add up
40 psi x 2800 gal ~ 100 hp, you measured 40 total

the idea would be a new pump with same flow at 35 psi less head