Measuring pumping prices for electrical irrigation pumps


Measuring pumping pressure gauge octa for electrical irrigation pumps

by Brenna ShumbamhiniJune 10, 2022


If the incorrect pump is chosen or is worn out, this could increase pumping costs and scale back productivity. In the second of a collection of fact sheets, the NSW Department of Primary Industries describes a easy method to work out the pumping prices and energy efficiency of your electric pump.
Tests of irrigation pumps across New South Wales have found that many weren’t performing efficiently, either because the incorrect pump had been chosen for the job, or because the pump was worn.
To comprise prices, you need to monitor your energy utilization, restore and keep the pump and work out what your pumping costs are.
When you’ve determined the working value you can carry out fast checks to detect any change, and when you’ve decided the pump efficiency, you probably can evaluate it to the manufacturer’s figures to resolve when restore or substitute is cost-effective.
Measuring working prices

One way of monitoring pumping prices is to work out how much it prices to pump a megalitre of water. To do that, you need to measure:
The power consumption fee in kilowatts (kW)

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

You can measure the ability used by studying your electrical energy meter. Electronic meters are mostly used but single and a number of meters continue for use on many farms.
Electronic meters

Electronic meters usually measure and record the electrical energy used for the main fee, shoulder rate and the off-peak price in separate registers. The numerous charges are switched ‘on’ and ‘off’ by the interior clock on the acceptable instances.
Electronic meters report your electrical energy consumption in a time-of-use format. They may also have registers for the date, the time and for testing the display.
Each register has a three determine identification number. For example, the present off-peak kilowatts may be given register number ‘126’. You should verify with your local energy authority what the show register numbers are for every of your rates.
The meter scrolls through each register at four to 6 second intervals.
The register number appears, usually in smaller numbers, on the LCD screen (in the diagram, within the prime left-hand corner) and may have a short description underneath (for instance: 126 = off-peak)

The usage in kilowatt-hours seems within the larger main display. It is usually a six-figure quantity (for instance: 1253.64).
When the time rate that’s presently being measured is reached, the number may flash. Record this number. If none of the displays flash, document the readings from all the displays.
Let the pump run for a minimum of quarter-hour earlier than taking the next reading.
In techniques that devour large quantities of electrical energy, there could also be a multiplier programmed into the electronics.
If so, will probably be famous on the electrical energy supplier’s bill for this meter as ‘Mult’ or ‘M’ and the show may learn to a couple of decimal locations. If there’s a multiplier, run the pump for a minimal of 30 minutes before taking the second register reading.
If the second studying has not modified, you’re reading the incorrect register.
Reading an digital meter

First studying (register 126) = 1253.sixty four kWh

Second studying (register 126) = 1254.16 kWh

Multiplier acknowledged on energy bill = 40

Power utilization =

Reading a disc meter

Note the rating determine, the revolutions per kilowatt hour (r/kWh), marked on the electrical energy meter.
R (r/kWh as marked on meter) = 266.6

Next, with the irrigation system set up in a mean place and working, time the spinning horizontal disc on the power meter for at least 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 systems that eat large amounts of electrical energy, the disc could additionally be geared down so it doesn’t run too quick. If so, you will discover a multiplier ‘M’ is marked on the meter.
M (multiplier as marked on meter) = forty

From this information you probably can calculate the ability utilization in kilowatts.
Power utilization =

In this example, the pump uses 42kW.
Perform this test frequently, over a season or between seasons, to verify the pump’s power consumption. If you find that it takes less time for a similar number of disc revolutions than if you first tested the pump, the ability use is larger, and you will need to seek out out why.
This comparison is only attainable when the irrigation is set up in the same position as the preliminary check, with the identical variety of sprinklers, and with the pumping water degree roughly the same.
Multiple disc meters

If there are three meters, for example, one for every section of a three-phase power provide, measure the three meters individually and add the kW figures collectively.
Measuring every meter individually gives an accurate reply as not often are three meters precisely the identical. If a really accurate result is wanted, you should monitor the system over all of the irrigation positions for one full cycle.
In this case you have to report the total electricity used, the entire hours of use and the whole quantity pumped over the period.
Step 2: Measure the circulate fee (Q)

The second measure needed to calculate pumping value per megalitre is the flow price of the system (Q).
The move fee is the amount (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 operating usually.
Measure the move fee by studying your water meter on the pump for preferably the entire irrigation cycle or no less than 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: 1230.a hundred forty five kL

Q =

Estimating circulate rate by discharge

If no water meter is fitted or it’s shedding accuracy, the move fee of a sprig irrigation system where all the sprinklers are the same mannequin and size can be estimated by measuring the sprinkler discharge. Use a number of sprinklers: a minimal of one initially of the road, one within the center and one on the end.
Record how long each sprinkler takes to fill a container (for example, a 10L bucket or a 20L drum). To discover the move price of each sprinkler in litres, divide the container quantity (in litres) by the time required to fill it (in seconds).
You can then discover the typical for the sprinklers you measured. To calculate the total move price of the system, multiply the common by the variety of sprinklers operating.
For instance:
First sprinkler takes 9 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 move = (1.11 + 1.25 + 1.43) ÷ 3

= 1.26L/s

There are 46 sprinklers working, so the total circulate fee is = 1.26 x forty six = 58L/s

Step three: Calculate the facility per megalitre pumped

From the facility usage and the flow fee, the kilowatt-hours per megalitre (kWh/ML) for your pump could be calculated.
This is called the ‘calibration’ value (the worth used where no water meter is installed and electrical energy meter readings are learn to deduce the quantity of water used).
Pump calibration (kWh/ML)

= kW ÷ (Q x 0.0036)

= forty two ÷ (58 x 0.0036)

= 201.1kWh/ML

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

Step 4: Calculate the pumping price

Having calculated the facility used to pump a megalitre, if you realize the cost per kWh, you presumably can calculate the price of pumping.
The costs per kWh may be tough to work out exactly in case your provider has totally different rates for day or evening, weekends, and so on so you should contact your provider for assist to work this out.
Pumping prices

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

= $50.25 per ML

Measuring pump effectivity

Irrigation pump efficiency is a measure of how well the pump converts electrical power into useful work to move water.
The purpose of careful pump selection and common pump maintenance is to have the pump performing as effectively as attainable (ie transferring essentially the most water for the least vitality required). Efficient pump operation minimises running prices per megalitre pumped.
เพรสเชอร์เกจ of 70 per cent to 85 per cent ought to be achievable in most circumstances. An acceptable minimal for a centrifugal irrigation pump is sixty five per cent, and 75 per cent for a turbine pump.
An efficiency determine below these means both the wrong pump was chosen for the job, the pump is worn and wishes repair or maintenance is needed.
The key to containing your pumping prices is to frequently monitor your energy usage and examine on any important change that means consideration is needed.
To calculate pump effectivity, you need to know the move rate (Q) and the pump stress, or whole head (H or TH) of the system. The strain and flow that a pump is working at is called the obligation or responsibility point. Pump efficiency varies over the range of possible duties for any specific pump.
An adequate estimate of total dynamic head for surface systems is the vertical peak in metres from source water level to the end of the discharge pipe, or, if the discharge is submerged, to the height of the water above the discharge, that’s, water level to water degree, plus the losses due to friction within the suction pipe.
Measure the discharge (or delivery) head

This is the pressure learn from the gauge fitted at the pump when the system is at full working strain. This studying must be converted to equal metres of head, this is additionally generally referred to as Pressure Head.
New pumps normally have a strain gauge put in but they often suffer physical injury shortly. A better technique is to suit an entry level on the supply aspect of the pump where you possibly can briefly install a pressure gauge everytime you want to take a studying. The gauge may be simply indifferent when not wanted.
A change within the pump working strain through the season or across seasons, when irrigating the same block or shift, instantly tells you something has modified.
A sudden reduction usually signifies a new leak or a blockage on the suction side; a gradual discount normally signifies wear of the impeller or sprinkler nozzles; and a rise usually suggests a blockage someplace in the system downstream of the stress gauge.
Pressure could be considered equivalent to a pipe of water of a sure height in metres. This is referred to as ‘head’ (H). At sea degree, the stress at the backside of a pipe of water 10m high is about one hundred kilopascals (kPa).
If your pressure gauge reads only in psi, convert to kPa by multiplying by 6.9.
For example: 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 level. Typical suction head figures for centrifugal pumps are three to five metres.
Most problems with pumps positioned above the water stage happen within the suction line, so guarantee every little thing right. Common issues include blocked inlet or foot-valve or strainer, pipe diameter too small, pipe damaged or crushed, suction top too nice, or air trapped on the connection to the pump.
Turbine and axial circulate pumps should be submerged to operate, in order that they often do not have any suction head.
For instance:
Pressure Head = 27.6m

Suction head = four.0m

Total Head = 31.6m

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

= $50.25/ML ÷ 31.6m

= $1.fifty nine / ML / m head

Step 6: Determine motor effectivity (Me)

Electric motors have an effectivity value. That is, they lose a variety of the power going into them as heat. This power loss modifications with the size of the motor. The desk under is a suggestion for motors working at full load.
Submersible motors lose about four per cent more than air-cooled electrical motors (for instance, where Me is 88 per cent for an air-cooled motor it will be eighty four per cent for a submersible). Voltage losses by way of long electrical cables may also be important so this must be checked with an electrical engineer.
Step 7: Determine transmission losses (Df)

If the engine is not instantly coupled to the pump, there is a lack of energy via the transmission. This loss is taken under consideration by what’s termed the drive factor (Df).
Step 8: Calculate pump efficiency (Pe)

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

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

= (58 × 31.6) ÷ (42 × 0.9 × 0.9)

= 1832.8 ÷ 34.02

= 53.9 per cent

Step 9: Calculating potential savings

Most centrifugal pumps are designed to operate with at least 75 per cent effectivity, and most turbine pumps are designed to function with no much less than 85 per cent effectivity.
The pump in our example is just about 54 per cent efficient, so how much could be saved by improving the efficiency from 54 per cent to 75 per cent?

Take this example:
If our pumping value 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 wear is the issue and the price of substitute is $10,000, it will be paid for in lower than one season. After that, the savings are all increased revenue.
Notice that a discount in the pump effectivity determine of 21 per cent (75 per cent to 54 per cent) causes a rise in pumping value of 39 per cent ($36.18/ML to $50.25/ML).
Other elements that affect price and pump effectivity

There are two other variables have an effect on price and pump efficiency: pump pace and impeller dimension.
Pump velocity

You should know the pump speed to have the ability to learn the pump curves. The curves are often 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 outcome of the speed of electrical motors varies slightly, it will be good to examine your motor velocity with a rev counter.
If the motor isn’t immediately coupled to the pump, the pace is altered by the gearing ratio of the transmission. Gear drives normally have the ratio stamped on the identification plate.
The ratio for a V-belt and pulley drive can be calculated from the diameter of the pulleys on the motor and the pump (see the diagram beneath – make certain the pump is stopped before measuring the pulleys).
A complication that can happen when working out the price and effectivity revolves round Variable Speed Drives (VSD), also referred to as Variable Frequency Drives (VFD).
VSDs have gotten increasingly in style as their value reduces due to the benefits they provide. These models are added to electrical motors and allow the pace to be altered by altering the frequency of the alternating present. They permit electrically driven pumps to have their velocity set at exactly what is required for the pump responsibility they usually eliminate the necessity for throttling the irrigation system using valves.
Savings of 1 quarter of the usual power consumption are often reported by irrigators, and could also be as a lot as half relying on the state of affairs. For determining the fee and efficiency of a pump, the measurements outlined on this article should be made a number of times with the pump set at completely different typical speeds.
Impeller measurement

Impeller wear has the same impact as a discount in impeller dimension so you have to know the size of impeller fitted to your pump to work out which efficiency curve applies to your pump.
Sometimes the impeller dimension is stamped on the pump’s ID plate. If not, you have to find out the size by dismantling the pump and measuring it, or asking the one that made the change.
Sometimes an impeller is intentionally lowered in diameter to adjust the pump’s performance and acquire a selected duty.
To give a variety of duties, manufacturers could supply impellers of various diameters for a similar pump casing. Available impeller sizes are proven on the pump curves.
Power factor

Power issue may substantially have an result on your working costs and maybe the operation of your pump as nicely.
Measuring efficiency

Keeping monitor of your pump’s performance and costs just isn’t troublesome. It might prevent a lot of money and keep your irrigation system performing correctly.
If you determine your pump is operating below the suitable minimum stage, examine the interior condition for wear or maintenance and the suitability of the pump for its current responsibility, or take steps to enhance the drive or substitute it with a VSD.

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