Measuring pumping prices for electric irrigation pumps


Measuring pumping prices for electrical irrigation pumps

by Brenna ShumbamhiniJune 10, 2022


If the wrong pump is chosen or is worn out, this will enhance pumping prices and scale back productiveness. In the second of a series of reality sheets, the NSW Department of Primary Industries describes a simple approach to work out the pumping costs and vitality efficiency of your electrical pump.
Tests of irrigation pumps across New South Wales have discovered that many weren’t performing efficiently, both because the incorrect pump had been chosen for the job, or because the pump was worn.
To include costs, you have to monitor your power usage, restore and preserve the pump and work out what your pumping costs are.
When you could have decided the operating price you probably can carry out quick checks to detect any change, and when you’ve determined the pump effectivity, you’ll have the ability to examine it to the manufacturer’s figures to decide when restore or replacement is cost-effective.
Measuring working prices

One means of tracking pumping prices is to work out how a lot it prices to pump a megalitre of water. To do that, you have to measure:
The power consumption rate in kilowatts (kW)

The circulate fee in litres per second (L/s).
Combining these measures with the price of electrical energy provides you the pumping price.
Step 1: Measure the power used

You can measure the facility used by reading your electricity meter. Electronic meters are mostly used but single and multiple meters proceed to be used on many farms.
Electronic meters

Electronic meters normally measure and document the electrical energy used for the principle fee, shoulder rate and the off-peak fee in separate registers. The varied rates are switched ‘on’ and ‘off’ by the inner clock at the appropriate instances.
Electronic meters record your electrical energy consumption in a time-of-use format. They can also have registers for the date, the time and for testing the display.
Each register has a 3 figure identification quantity. For example, the present off-peak kilowatts may be given register number ‘126’. You ought to verify along with your native power authority what the show register numbers are for each of your rates.
The meter scrolls through every register at 4 to six second intervals.
The register number seems, typically in smaller numbers, on the LCD screen (in the diagram, within the high left-hand corner) and should have a brief description beneath (for example: 126 = off-peak)

The utilization in kilowatt-hours appears in the larger main display. It is usually a six-figure number (for example: 1253.64).
When the time fee that’s presently being measured is reached, the quantity may flash. Record this number. If not certainly one of the displays flash, record the readings from all the displays.
Let the pump run for a minimal of 15 minutes earlier than taking the following reading.
In methods that devour giant quantities of electricity, there may be a multiplier programmed into the electronics.
If so, will in all probability be noted on the electrical energy supplier’s bill for this meter as ‘Mult’ or ‘M’ and the display might read to a few decimal places. If there’s a multiplier, run the pump for no less than 30 minutes earlier than taking the second register reading.
If the second studying has not modified, you’re studying the mistaken register.
Reading an electronic meter

First reading (register 126) = 1253.64 kWh

Second reading (register 126) = 1254.16 kWh

Multiplier acknowledged on power invoice = 40

Power usage =

Reading a disc meter

Note the score figure, the revolutions per kilowatt hour (r/kWh), marked on the electricity meter.
R (r/kWh as marked on meter) = 266.6

Next, with the irrigation system arrange in a mean position and running, time the spinning horizontal disc on the ability meter for a minimum of 10 per cent of R (In this instance, R is 266.6, so 10 per cent is about 30 revs).
N (number of disc revolutions) = 30 T (time of test) = 386 seconds

In techniques that consume giant amounts of electrical energy, the disc could also be geared down so it doesn’t run too quick. If so, you will notice a multiplier ‘M’ is marked on the meter.
M (multiplier as marked on meter) = forty

From this information you’ll have the ability to calculate the ability utilization in kilowatts.
Power utilization =

In this example, the pump uses 42kW.
Perform this test regularly, over a season or between seasons, to check the pump’s energy consumption. If you find that it takes less time for a similar variety of disc revolutions than if you first tested the pump, the power use is greater, and you’ll need to search out out why.
This comparison is just possible when the irrigation is about up in the same position because the preliminary test, with the same number of sprinklers, and with the pumping water degree roughly the same.
Multiple disc meters

If there are three meters, for instance, one for every phase of a three-phase power supply, measure the three meters individually and add the kW figures collectively.
Measuring each meter separately gives an correct answer as hardly ever are three meters precisely the identical. If a very accurate result’s wanted, you need to monitor the system over all the irrigation positions for one full cycle.
In this case you need to document the entire electrical energy used, the whole hours of use and the total quantity pumped over the period.
Step 2: Measure the move fee (Q)

The second measure wanted to calculate pumping price per megalitre is the flow fee of the system (Q).
The circulate fee is the quantity (or quantity) of water pumped in a sure amount of time, often given in litres per second (L/s). It ought to be measured after the system has had adequate time from startup to be running normally.
Measure the flow rate by studying your water meter at the pump for preferably the entire irrigation cycle or a minimal of half an hour and dividing the litres pumped by the point in seconds.
Water meter reading at begin: 1108.345 kL

Water meter reading after 35 minutes: hundred forty five kL

Q =

Estimating circulate rate by discharge

If no water meter is fitted or it is losing accuracy, the flow price of a twig irrigation system where all the sprinklers are the same mannequin and size could be estimated by measuring the sprinkler discharge. Use several sprinklers: no less than one at the start of the road, one in the middle and one at the end.
เกจวัดแรงดัน4นิ้วราคา how lengthy every sprinkler takes to fill a container (for example, a 10L bucket or a 20L drum). To find the circulate rate of each sprinkler in litres, divide the container quantity (in litres) by the point required to fill it (in seconds).
You can then find the typical for the sprinklers you measured. To calculate the entire flow rate of the system, multiply the typical by the variety of sprinklers working.
For example:
First sprinkler takes nine seconds to fill a 10L bucket = 10 ÷ 9 = 1.11L/s

Middle sprinkler takes eight seconds to fill a 10L bucket = 10 ÷ 8 = 1.25L/s

End sprinkler takes seven seconds to fill a 10L bucket = 10 ÷ 7 = 1.43L/s

Average flow = (1.11 + 1.25 + 1.43) ÷ three

= 1.26L/s

There are 46 sprinklers working, so the whole move rate is = 1.26 x forty six = 58L/s

Step 3: Calculate the facility per megalitre pumped

From the ability usage and the circulate rate, the kilowatt-hours per megalitre (kWh/ML) on your pump may be calculated.
This is called the ‘calibration’ worth (the worth used where no water meter is installed and electricity meter readings are read to infer the quantity of water used).
Pump calibration (kWh/ML)

= kW ÷ (Q x zero.0036)

= forty two ÷ (58 x zero.0036)

= 201.1kWh/ML

(Note: zero.0036 converts kilowatt-seconds per litre to kilowatt-hours per megalitre.)

Step four: Calculate the pumping cost

Having calculated the ability used to pump a megalitre, if you understand the fee per kWh, you probably can calculate the cost of pumping.
The costs per kWh may be difficult to work out precisely in case your supplier has totally different charges for day or night time, weekends, and so forth so you must contact your supplier for help to work this out.
Pumping prices

If provide prices 25 cents per kWh then:
Pumping value = 201 kWh/ML x $0.25

= $50.25 per ML

Measuring pump effectivity

Irrigation pump effectivity is a measure of how nicely the pump converts electrical energy into helpful work to maneuver water.
The goal of cautious pump selection and regular pump upkeep is to have the pump performing as effectively as attainable (ie shifting probably the most water for the least energy required). Efficient pump operation minimises running prices per megalitre pumped.
Pump effectivity of 70 per cent to 85 per cent should be achievable in most circumstances. An acceptable minimal for a centrifugal irrigation pump is 65 per cent, and seventy five per cent for a turbine pump.
An efficiency figure beneath these means either the mistaken pump was chosen for the job, the pump is worn and desires repair or maintenance is needed.
The key to containing your pumping prices is to frequently monitor your power utilization and verify on any significant change that implies consideration is needed.
To calculate pump efficiency, you should know the move fee (Q) and the pump stress, or total head (H or TH) of the system. The stress and circulate that a pump is working at is known as the obligation or responsibility level. Pump effectivity varies over the vary of possible duties for any particular pump.
An enough estimate of whole dynamic head for surface methods is the vertical top in metres from source water degree to the tip of the discharge pipe, or, if the discharge is submerged, to the peak of the water above the discharge, that is, water degree to water degree, plus the losses as a outcome of friction within the suction pipe.
Measure the discharge (or delivery) head

This is the strain learn from the gauge fitted at the pump when the system is at full operating strain. This reading needs to be converted to equivalent metres of head, that is also sometimes known as Pressure Head.
New pumps usually have a pressure gauge installed however they typically suffer bodily harm quickly. A higher method is to suit an entry level on the delivery side of the pump where you’ll find a way to temporarily install a pressure gauge everytime you wish to take a studying. The gauge could be easily indifferent when not needed.
A change within the pump working stress by way of the season or across seasons, when irrigating the identical block or shift, instantly tells you one thing has modified.
A sudden discount often indicates a brand new leak or a blockage on the suction side; a gradual reduction usually indicates wear of the impeller or sprinkler nozzles; and a rise normally suggests a blockage somewhere within the system downstream of the stress gauge.
Pressure may be thought of as equal to a pipe of water of a sure peak in metres. This is known as ‘head’ (H). At sea stage, the strain on the backside of a pipe of water 10m excessive is about one hundred kilopascals (kPa).
If your stress gauge reads solely in psi, convert to kPa by multiplying by 6.9.
For instance: 40 psi = forty × 6.9 = 276k Pa = 27.6 m head

Determine the suction head

Suction head is the distance between the centre line of the pump and the supply water degree, plus losses in the suction pipe if the pump is positioned above the water stage. Typical suction head figures for centrifugal pumps are three to 5 metres.
Most problems with pumps positioned above the water degree occur within the suction line, so guarantee every little thing right. Common problems include blocked inlet or foot-valve or strainer, pipe diameter too small, pipe broken or crushed, suction top too great, or air trapped at the connection to the pump.
Turbine and axial flow pumps have to be submerged to operate, so that they usually don’t have any suction head.
For example:
Pressure Head = 27.6m

Suction head = four.0m

Total Head = 31.6m

Another helpful figure that can now be calculated is the pumping price per ML per metre of head. This allows a significant comparability between different pump stations.
Pumping cost per ML per metre head: = value ($/ML) ÷ TH (m)

= $50.25/ML ÷ 31.6m

= $1.fifty nine / ML / m head

Step 6: Determine motor effectivity (Me)

Electric motors have an efficiency value. That is, they lose some of the power going into them as warmth. This vitality loss changes with the size of the motor. The table under is a guideline for motors working at full load.
Submersible motors lose about 4 per cent greater than air-cooled electric motors (for instance, the place Me is 88 per cent for an air-cooled motor it will be eighty four per cent for a submersible). Voltage losses through lengthy electrical cables can also be important so this must be checked with an electrical engineer.
Step 7: Determine transmission losses (Df)

If the engine just isn’t immediately coupled to the pump, there’s a loss of vitality by way of the transmission. This loss is taken into consideration by what’s termed the drive factor (Df).
Step eight: Calculate pump effectivity (Pe)

Pe = (Q × H) ÷ (power consumed × Me × Df)

This instance contains the data from the earlier steps discussed. The drive from the motor to the pump is a V-belt on this case.
Pe (87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf) = (Q × H) ÷ (power × Me × Df)

= (58 × 31.6) ÷ (42 × 0.9 × zero.9)

= 1832.8 ÷ 34.02

= 53.9 per cent

Step 9: Calculating potential savings

Most centrifugal pumps are designed to function with at least seventy five per cent effectivity, and most turbine pumps are designed to function with a minimal of eighty five per cent effectivity.
The pump in our example is simply about fifty four per cent environment friendly, so how much would be saved by improving the efficiency from fifty four per cent to 75 per cent?

Take this instance:
If our pumping cost is $50.25 per ML, the improvement is calculated as follows:
Cost saving per ML:
= $50.25 – (50.25 x (54 ÷ 75))

= $50.25 – (50.25 x zero.72)

= $50.25 – 36.18

= $14.07

If 900ML are pumped during a season, the entire value saving is $14.07 × 900 = $12,663.
If impeller put on is the issue and the worth of replacement is $10,000, it would be paid for in lower than one season. After that, the financial savings are all increased profit.
Notice that a discount within the pump effectivity figure of 21 per cent (75 per cent to 54 per cent) causes an increase in pumping value of 39 per cent ($36.18/ML to $50.25/ML).
Other components that have an effect on value and pump effectivity

There are two other variables affect price and pump efficiency: pump velocity and impeller dimension.
Pump velocity

You should know the pump speed so as to learn the pump curves. The curves are normally ready for specific pump speeds and impeller sizes.
If the pump is instantly coupled to the electrical motor, the speed is mounted by the velocity of the motor: two-pole motors run at 2,900 rev/min and four-pole motors run at 1,440 rev/min. However, as a end result of the velocity of electrical motors varies a little, it might be good to examine your motor speed with a rev counter.
If the motor just isn’t instantly coupled to the pump, the velocity is altered by the gearing ratio of the transmission. Gear drives usually have the ratio stamped on the identification plate.
The ratio for a V-belt and pulley drive could be calculated from the diameter of the pulleys on the motor and the pump (see the diagram beneath – make positive the pump is stopped earlier than measuring the pulleys).
A complication that can occur when understanding the fee and effectivity revolves round Variable Speed Drives (VSD), also referred to as Variable Frequency Drives (VFD).
VSDs are becoming increasingly in style as their worth reduces because of the advantages they provide. These units are added to electrical motors and allow the pace to be altered by altering the frequency of the alternating current. They permit electrically pushed pumps to have their pace set at exactly what’s required for the pump obligation they usually get rid of the need for throttling the irrigation system using valves.
Savings of one quarter of the standard power consumption are often reported by irrigators, and could additionally be as a lot as half depending on the state of affairs. For figuring out the cost and efficiency of a pump, the measurements outlined in this article must be made several occasions with the pump set at different typical speeds.
Impeller size

Impeller put on has the identical effect as a reduction in impeller dimension so you have to know the size of impeller fitted to your pump to work out which performance curve applies to your pump.
Sometimes the impeller measurement is stamped on the pump’s ID plate. If not, you want to find out the dimensions by dismantling the pump and measuring it, or asking the one that made the change.
Sometimes an impeller is deliberately decreased in diameter to adjust the pump’s efficiency and acquire a selected duty.
To give a spread of duties, manufacturers might offer impellers of different diameters for a similar pump casing. Available impeller sizes are proven on the pump curves.
Power factor

Power issue may substantially affect your operating prices and perhaps the operation of your pump as well.
Measuring performance

Keeping track of your pump’s performance and prices isn’t tough. It might save you a lot of money and hold your irrigation system performing properly.
If you establish your pump is operating beneath the suitable minimal level, verify the inner situation for wear or upkeep and the suitability of the pump for its present obligation, or take steps to enhance the drive or exchange it with a VSD.

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