VFD design with pump + booster pump

[EE_Rancher_Farmer]

Main well irrigation pump is 75HP, lifting about 800 ft.
There is also a 40HP booster pump.

Output can go either downhill (requiring no booster pump) to irrigate 40 acre pasture (wheel lines) or uphill to a 5-tower pivot (c. 1,000 ft radius sprinkler system). Water is delivered to base of pivot via a 1,600 ft. pipeline. A portion of the area covered by the pivot is level, but the remainder has the 5th tower uphill from the center...requiring more pressure to operate those sprinklers at the end. At level area of the pivot, pressure at the base of the pivot reads 35psi with no booster pump running. When 40HP booster is also running, that pressure rises to about 90 psi. (too high) so some water is bled off into a pond (not ideal). So when level, pressure at base of pivot should be around 45psi; when end is uphill, about 75psi would probably be best pressure at base of pivot. A possible solution here might be a pressure sensor at the end of the pivot to feed back (wirelessly?) to the VFD...?... This might be expensive...?... Thoughts?

When water goes downhill from the well, there may be too much pressure built up by the time it gets down to the 40 acre pasture. Possibly slowing down the main (75HP) pump would be warranted so resulting pressure in pasture would be due mainly to altitude difference (and not additional pressure from excessive flow).

Additionally, there are plans to extend the main pipeline, up past the pivot about 1,200 ft (quite a distance, but uphill only slightly) in order to deliver water to a previously non-irrigated field.

Thinking I may be able to get away with one VFD for booster pump motor only, but maybe situation warrants one on each pump motor...? Budget is of concern, but if power savings could be significant by having both, then that direction will probably be taken.

Your thoughts on the above would be most appreciated.

 

[Cow]

I would have your local irrigation pivot dealer and pump company both pay a visit to your place, preferably at the same time and see what they recommend.

 

[Sahib]

When variable water flow and variable PSi is required, a VFD may be economically used but in OP case no frequent variation appears to exist and so manual pressure regulating valves instead of VFD's sufficient IMHO.

 

[ptonsparky]

You really do need to talk to your pivot rep.

You're a lucky fellow if you get to start irrigating previously non irrigated ground. Even in water rich NE, expanding irrigation is regulated.

 

[kwired]

Seems as though the booster pump is needed somewhere in the middle of the center pivot machine, possibly still with a VFD to vary output as needed. Put it before the supply end and it is boosting pressure in the entire system when the boost is only needed beyond a certain point. At the same time the further out in the system it is, the less HP it may need to be, as it is no longer pumping the volume of the entire system.

 

[Dzboyce]

What brand circle do you have? Do you already have an end gun booster pump on it? Is yourbexisting centrifugal booster pump at the well or at the pivot?

without knowing any more details, I would say yes a wireless pressure transducer at the end of the pivot controlling the booster pump is what you need. Any Valley or Zimmatic dealer can take care of this for you.

 

[Dzboyce]

I'm not involved with the center pivot end of the business anymore. But yes the best way to control pressure on sloping ground is with a wireless transducer controlling a VFD on the pump.

A simple on/of has been done for years with switches at the collector ring of the pivot. That's how the end gun is turned on and off on a non-computerized pivot control panel. Those switchs can be roller switches that are activated by ramps, or magnetic non-contact switches that close in proximity to magnetic tape.

 

[ptonsparky]

I'm not involved with the center pivot end of the business anymore. But yes the best way to control pressure on sloping ground is with a wireless transducer controlling a VFD on the pump.

A simple on/of has been done for years with switches at the collector ring of the pivot. That's how the end gun is turned on and off on a non-computerized pivot control panel. Those switchs can be roller switches that are activated by ramps, or magnetic non-contact switches that close in proximity to magnetic tape.

Those could be used to ramp up a VFD if money is to tight for real control.

 

[kwired]

I'm not involved with the center pivot end of the business anymore. But yes the best way to control pressure on sloping ground is with a wireless transducer controlling a VFD on the pump.

A simple on/of has been done for years with switches at the collector ring of the pivot. That's how the end gun is turned on and off on a non-computerized pivot control panel. Those switchs can be roller switches that are activated by ramps, or magnetic non-contact switches that close in proximity to magnetic tape.

Modern systems use GPS to tell what position the system is at, and some have cellular modems so you can the status of each of your systems, start and stop them, change speed, direction, etc., will also notify you if the system has changed operating status, all from your smart phone.

 

[EE_Rancher_Farmer]

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Reply to all:

Wow. You guys are awesome! Really appreciate ALL your thoughtful replies.

Having pump and irrigation outfits on-site at same time is very smart and will no-doubt result in a solution being formulated right there.

Irrigating previously un-irrigated ground: Water rights show 181 acres (currently only 90 being irrigated), but since the shop and horse barn were built on prime soils, then acreage was reduced. Water master says OK to redraw map (move area being irrigated). However, I think some of this was irrigated long ago. Recent (previous) owners were more horse people than farmers/ranchers, so their priorities were elsewhere...

Booster in middle of pivot makes a LOT of sense (wish I had thought of that!)...just need to get enough power out there--if not there already...?...(power to tower wheels, end gun booster is there, but maybe not big enough wires).

Pivot is a Valley unit about 11 or 12 yrs. old. Pretty modern panel. No GPS or cell phone conoosnectivity, but my understanding is that a module can be added to control from cell phone (I recall it's about a $2K - $3K option).

End gun booster is 1HP as I recall...could be 1.5...?... It has on/off capability (pivot knows what angle it's at)...so easily programmed to go on at X degrees and off at Y degrees, etc. It also has a protection switch so if it doesn't have enough water pressure to it (at 5th (last) tower), then after a few minutes it will shut off the end gun booster pump.

Even though the pivot controller is capable, if I can't get an output from that controller (at a certain angle) telling the VFD when to ramp up the well booster pump, then I could certainly go back to older tech and put a few switches at the collector ring as feedback to the VFD. It seems to me that a wireless pressure transducer will be the most energy saving because it would allow the VFD to adjust continuously as pressure varies...How much they cost is, of course, another factor.

Any thoughts on sending the pressure or position feedback signal back to the well pump via the AC power lines (similar to X-10 units)? Again, I don't know the cost of wireless transducers and receivers yet...Thought this might be a viable option...?... I'm pretty sure the power for the pivot comes directly from the well house--That's the only 3 phase power on the property. There is a barn with 220V power much closer to the base of the pivot, but I believe the tower wheel motors are 3 phase...

Again, really appreciate all your insight!

 

[kwired]

Just how much rise in elevation are we talking about when this system needs some boost?

Thing with your sprinklers is they are selected to system needs and is assumed all are operating at same pressure, exception is end gun might be on a booster pump. If you increase pressure on entire system because a section of the end of the system needs more pressure, then all other sprinklers are now operating at more then their design pressure and are applying more water then was planned, messing up the efficiency of the entire system.

I don't think you want to increase pressure in general, but you may need to boost pressure on a certain portion of the system if change in elevation causes pressure drop. You would only want to boost it back to about where it was designed to operate though. This has to be a pretty significant rise in elevation to have a significant impact on performance I would think.

 

[EE_Rancher_Farmer]

Reply to kwired's post

Reply to kwired's post

Not sure of the altitude change from base of pivot to highest point. However, when running only the main well pump (75HP) all sprinklers and end gun appear to work fine when there is no to little rise. As the pivot rotates and the end climbs higher, the end gun stops working and last set of sprinklers (past the last (5th) tower) put out less water. Near the highest point, the last set of sprinklers stop outputting and auto drains start working. Also, sprinklers between towers 4 and 5 show some decrease in output.

I need to check the sprinkler nozzles all along the pivot to determine model numbers to see if they are pressure compensating and with what pressure range they are designed to work. Unit is about 11 years old, so hopefully they have pressure compensating sprinklers...

I completely agree about not increasing pressure (using booster pump) any more than is necessary. Currently, the 40HP booster pump in well house is all or nothing. When on (with the main pump), it produces too much pressure (my current opinion before I look up sprinkler specs), and I relieve that excess pressure by dropping some of the water into a pond (not an ideal situation). 1. That water, although maintaining the level of the pond for wildlife, is not irrigating crops...yet. {Future plan is to use water in pond to irrigate lower 40 acre hay field, if needed at same time as pivot is running.}. 2. The current power bill for this system is a lot more than I'd like it to be (of course, right?). 3. I really don't want to overpressure the pivot... Extra maintenance costs... I believe a VFD would at least help with all of the above.

 

[ptonsparky]

I'm beginning to think you don't have enough HP to start with.

 

[Jraef]

...
I need to check the sprinkler nozzles all along the pivot to determine model numbers to see if they are pressure compensating and with what pressure range they are designed to work. Unit is about 11 years old, so hopefully they have pressure compensating sprinklers...

Methinks most likely someone replaced heads with the wrong flow rate somewhere along the line and you are not balancing your pressure correctly, or it has NEVER worked right because the nozzles were selected based on the FLAT area, not the worst case.

And yes, a VFD on the booster would help your situation with having excess in some parts. Get one with a PID (or just PI) control built in, connect a pressure transducer out at the end as a feedback signal and let the VFD give you only as much boost as you need at any given moment to keep the pressure at the end of the pipe at the minimum it needs.

 

[kwired]

I'm beginning to think you don't have enough HP to start with.

Same here, or someone changed sprinkler package and the unit is demanding more water then it was originally designed for. That could also cause overloading of motor as it is loaded more by increased flow then it is by pressure changes.

 

[Dzboyce]

One of my responsibilities when I worked for a Zimmatic dealer was to design the sprinkler packages for the center pivots. We used a computer program from Nelson Irrigation. I probably did 100 or more sprinkler charts every year. Do you have impacts on top of the spans? These need 50-60 psi. Do you have rotators on drops? These will have 25 or 30 psi pressure regulators for each rotator. Or you might have spinners with 20 psi regulators. Rotators or spinners on drops will save you 15-20% of your water from less evaporation and wind drift. If I converted a circle from impacts to drops I would drop from 1000-1200 gpm to about 850 gpm.

You should have a sprinkler chart for your pivot. It's usually in the pivot panel. It will tell you how many gpm the pivot is nozzled for and what the pressure needs to be at the pivot for enough pressure at the end of the machine, on level ground. It will also tell you tower by tower how much water you are using. The single last sprinkler will use more water than the entire first tower.