Irrigation pump

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dmagyar

dmagyar

Senior Member
Location
Rocklin, Ca.
I've got a prospective client wanting to reduce his electric bill and I noticed he has a 5 hp 240 volt single phase irrigation pump setup. What would you consider to be a good way to check the sizing of this pump to the work it was doing? I've checked nameplate FLC amperage noted at 23 amps, and while running this motor is drawing only 18.5 amps. I'm thinking its not too loaded for a reading like this. I've got the motor torque curve for the existing motor and a 3 hp that may be sufficient for this application but wasn't sure of my logic. Any suggestions appreciated.
 
kwired

kwired

Electron manager
Location
NE Nebraska
Load on the pump will increase if flow is increased. Does the flow ever increase or is it at max flow rate when you checked amps? Does the flow rate ever drop even lower?

Variable speed controller is one way to use less energy if the amount of flow varies, may have a hard time finding one to use with 5 hp

Is this a submersible pump? I know Franklin makes a variable speed drive for up to 2 hp single phase submersibles but am not sure if they go any larger than that. These drives also make the pump last longer from soft starting it.
 
dmagyar

dmagyar

Senior Member
Location
Rocklin, Ca.
Flow steady

Flow steady

As far as I can determine the existing flow is relatively constant with several different zones, each with about 6 - 7 large sprinkler heads. Inlet pipe and outlet are both 2" PVC, which changes at some unknown point to 1" which continues to respective sprinkler heads. Pump is ground mounted centrifugal irrigation pump. He's irrigating about 1.25 acres from a large pond adjacent to the property, no lift to speak of (about 3-4').
 
kwired

kwired

Electron manager
Location
NE Nebraska
If you use the 3HP motor you will be running at or near its full load current or even into its service factor.

Any energy saved will be probably be minimal enough that you will spend it on replacement motor sooner than you would with the 5hp because you are running it near its design limits and it will operate at a higher temperature especially if only 1.0 service factor.
 
dmagyar

dmagyar

Senior Member
Location
Rocklin, Ca.
Not such a good idea

Not such a good idea

Part of this exploration was that I wanted to figure out if it was possible and made sense to change out the motor to achieve greater efficiency, but as you pointed out even if the motor performs in a satisfactory fashion, which at it's peak hp probably won't; & that the cost of changing this existing set up wouldn't make any kind of financial sense. I know if I was installing a new motor or motor pump combination for myself that I would like something other than just a good feeling that: it was going to work; and second that in the end I could see some degree of savings.

This made me appreciate several things: living in town & being able to water the lawn just by turning on the tap. Even though I'm just paying for the water which is cheap compared to running a five hp pump for every minute of watering time. I don't have an acre either and that's fine with me, because sooner or later if you water it, you're going to have to cut it.
 
kwired

kwired

Electron manager
Location
NE Nebraska
dmagyar said:
Part of this exploration was that I wanted to figure out if it was possible and made sense to change out the motor to achieve greater efficiency, but as you pointed out even if the motor performs in a satisfactory fashion, which at it's peak hp probably won't; & that the cost of changing this existing set up wouldn't make any kind of financial sense. I know if I was installing a new motor or motor pump combination for myself that I would like something other than just a good feeling that: it was going to work; and second that in the end I could see some degree of savings.

This made me appreciate several things: living in town & being able to water the lawn just by turning on the tap. Even though I'm just paying for the water which is cheap compared to running a five hp pump for every minute of watering time. I don't have an acre either and that's fine with me, because sooner or later if you water it, you're going to have to cut it.
Click to expand...

You also have to remember that if you are watering an acre with municipal water you will use much more water than you would to water just a couple thousand square feet or even ten thousand. The pump is cheaper in a city near me than city water, many people have shallow wells there for lawn watering because city water is too expensive for lawn watering.
 
O

One-eyed Jack

Senior Member
Location
Scotland Neck, NC
dmagyar said:
Part of this exploration was that I wanted to figure out if it was possible and made sense to change out the motor to achieve greater efficiency, but as you pointed out even if the motor performs in a satisfactory fashion, which at it's peak hp probably won't; & that the cost of changing this existing set up wouldn't make any kind of financial sense. I know if I was installing a new motor or motor pump combination for myself that I would like something other than just a good feeling that: it was going to work; and second that in the end I could see some degree of savings.

This made me appreciate several things: living in town & being able to water the lawn just by turning on the tap. Even though I'm just paying for the water which is cheap compared to running a five hp pump for every minute of watering time. I don't have an acre either and that's fine with me, because sooner or later if you water it, you're going to have to cut it.
Click to expand...
You could not begin to buy water as cheap as you can pump it. At 4.00 per thousand gallons in my area. That 5hp pump will pump 24.00 worth of public water in one hr.vs .75 for electricity at .15kwh.
 
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