AGRICULTURE
Measuring pumping prices for electrical irrigation pumps
by Brenna ShumbamhiniJune 10, 2022
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If the incorrect pump is chosen or is worn out, this will enhance pumping costs and scale back productivity. In the second of a collection of truth sheets, the NSW Department of Primary Industries describes a easy method to work out the pumping costs and energy effectivity of your electric pump.
Tests of irrigation pumps across New South Wales have found that many weren’t performing effectively, both as a outcome of the wrong pump had been chosen for the job, or as a result of the pump was worn.
To include prices, you should monitor your power usage, repair and preserve the pump and work out what your pumping prices are.
When you’ve determined the working cost you can perform fast checks to detect any change, and when you have determined the pump effectivity, you can examine it to the manufacturer’s figures to decide when repair or substitute is cost-effective.
Measuring operating เกจวัดแรงดัน of monitoring pumping costs is to work out how much it prices to pump a megalitre of water. To do that, you need to measure:
The power consumption price in kilowatts (kW)
The move fee in litres per second (L/s).
Combining these measures with the value of electrical energy provides you the pumping price.
Step 1: Measure the ability used
You can measure the ability utilized by studying your electricity meter. Electronic meters are mostly used however single and multiple meters proceed to be used on many farms.
Electronic meters
Electronic meters usually measure and report the electrical energy used for the main rate, shoulder rate and the off-peak fee in separate registers. The varied rates are switched ‘on’ and ‘off’ by the inner clock at the acceptable times.
Electronic meters document your electricity consumption in a time-of-use format. They may have registers for the date, the time and for testing the display.
Each register has a three figure identification quantity. For example, the current off-peak kilowatts could also be given register number ‘126’. You ought to verify with your native vitality authority what the show register numbers are for each of your charges.
The meter scrolls by way of every register at four to 6 second intervals.
The register number appears, often in smaller numbers, on the LCD display (in the diagram, in the prime left-hand corner) and should have a short description underneath (for example: 126 = off-peak)
The utilization in kilowatt-hours seems in the bigger primary show. It is often a six-figure number (for example: 1253.64).
When the time rate that’s currently being measured is reached, the number might flash. Record this quantity. If not one of the displays flash, record the readings from all the displays.
Let the pump run for no much less than quarter-hour before taking the next reading.
In methods that devour large quantities of electrical energy, there may be a multiplier programmed into the electronics.
If so, it goes to be noted on the electricity supplier’s bill for this meter as ‘Mult’ or ‘M’ and the show may read to a couple of decimal places. If there’s a multiplier, run the pump for no much less than half-hour before taking the second register reading.
If the second studying has not changed, you’re studying the incorrect register.
Reading an electronic meter
First studying (register 126) = 1253.64 kWh
Second reading (register 126) = 1254.16 kWh
Multiplier stated on power invoice = forty
Power utilization =
Reading a disc meter
Note the score figure, 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 median position and running, time the spinning horizontal disc on the facility 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 methods that devour large quantities of electricity, the disc could additionally be geared down so it doesn’t run too fast. If so, you’ll discover a multiplier ‘M’ is marked on the meter.
M (multiplier as marked on meter) = forty
From this data you can calculate the facility utilization in kilowatts.
Power utilization =
In this example, the pump uses 42kW.
Perform this take a look at often, over a season or between seasons, to examine the pump’s power consumption. If you discover that it takes much less time for the same number of disc revolutions than if you first tested the pump, the ability use is higher, and you will need to search out out why.
This comparison is only potential when the irrigation is set up in the same place because the initial take a look at, with the same variety of sprinklers, and with the pumping water degree roughly the same.
Multiple disc meters
If there are three meters, for example, one for each part of a three-phase power provide, measure the three meters individually and add the kW figures collectively.
Measuring every meter individually offers an correct answer as rarely are three meters precisely the same. If a very correct result’s wanted, you have to monitor the system over all the irrigation positions for one full cycle.
In this case you want to report the entire electrical energy used, the entire hours of use and the total quantity pumped over the interval.
Step 2: Measure the circulate rate (Q)
The second measure needed to calculate pumping price per megalitre is the circulate rate of the system (Q).
The circulate price is the amount (or quantity) of water pumped in a certain period of time, normally given in litres per second (L/s). It ought to be measured after the system has had sufficient time from startup to be operating usually.
Measure the circulate rate by reading your water meter at the pump for ideally the entire irrigation cycle or a minimal of half an hour and dividing the litres pumped by the point in seconds.
Water meter studying at begin: 1108.345 kL
Water meter studying after 35 minutes: 1230.one hundred forty five kL
Q =
Estimating circulate fee by discharge
If no water meter is fitted or it is dropping accuracy, the move price of a spray irrigation system where all the sprinklers are the same mannequin and dimension may be estimated by measuring the sprinkler discharge. Use several sprinklers: at least one firstly of the road, one in the center and one at the finish.
Record how lengthy every sprinkler takes to fill a container (for instance, a 10L bucket or a 20L drum). To discover the circulate price of each sprinkler in litres, divide the container quantity (in litres) by the time required to fill it (in seconds).
You can then find the average for the sprinklers you measured. To calculate the whole flow fee of the system, multiply the typical by the number of sprinklers working.
For instance:
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 ÷ eight = 1.25L/s
End sprinkler takes seven seconds to fill a 10L bucket = 10 ÷ 7 = 1.43L/s
Average flow = (1.eleven + 1.25 + 1.43) ÷ 3
= 1.26L/s
There are forty six sprinklers operating, so the whole move price is = 1.26 x forty six = 58L/s
Step three: Calculate the facility per megalitre pumped
From the facility utilization and the flow price, the kilowatt-hours per megalitre (kWh/ML) for your pump can be calculated.
This known as the ‘calibration’ value (the worth used the place no water meter is installed and electrical energy meter readings are learn to deduce the amount of water used).
Pump calibration (kWh/ML)
= kW ÷ (Q x 0.0036)
= 42 ÷ (58 x zero.0036)
= 201.1kWh/ML
(Note: 0.0036 converts kilowatt-seconds per litre to kilowatt-hours per megalitre.)
Step 4: Calculate the pumping cost
Having calculated the facility used to pump a megalitre, if you understand the fee per kWh, you presumably can calculate the value of pumping.
The expenses per kWh may be tough to work out precisely in case your supplier has different charges for day or night, weekends, and so on so you should contact your provider for help to work this out.
Pumping prices
If provide costs 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 useful work to maneuver water.
The goal of careful pump choice and regular pump upkeep is to have the pump performing as efficiently as potential (ie transferring probably the most water for the least energy required). Efficient pump operation minimises operating costs per megalitre pumped.
Pump efficiency of 70 per cent to eighty five per cent must be achievable in most circumstances. An acceptable minimum for a centrifugal irrigation pump is 65 per cent, and 75 per cent for a turbine pump.
An effectivity determine below these means both the mistaken pump was chosen for the job, the pump is worn and desires repair or maintenance is required.
The key to containing your pumping costs is to regularly monitor your vitality utilization and verify on any significant change that means attention is needed.
To calculate pump efficiency, you have to know the flow rate (Q) and the pump stress, or complete head (H or TH) of the system. The pressure and circulate that a pump is working at known as the duty or obligation level. Pump effectivity varies over the vary of attainable duties for any specific pump.
An sufficient estimate of whole dynamic head for floor systems is the vertical top in metres from source water stage to the end of the discharge pipe, or, if the discharge is submerged, to the height of the water above the discharge, that is, water degree to water stage, plus the losses as a result of friction in the suction pipe.
Measure the discharge (or delivery) head
This is the strain read from the gauge fitted at the pump when the system is at full operating strain. This reading must be transformed to equal metres of head, this is also generally known as Pressure Head.
New pumps often have a stress gauge installed but they usually endure bodily damage shortly. A higher method is to fit an entry point on the supply side of the pump the place you probably can temporarily set up a stress gauge everytime you wish to take a studying. The gauge could be easily detached when not wanted.
A change in the pump working stress via the season or across seasons, when irrigating the identical block or shift, instantly tells you one thing has changed.
A sudden discount often signifies a model new leak or a blockage on the suction facet; a gradual reduction normally signifies put on of the impeller or sprinkler nozzles; and an increase often suggests a blockage somewhere in the system downstream of the pressure gauge.
Pressure could be considered equal to a pipe of water of a certain height in metres. This is referred to as ‘head’ (H). At sea stage, the strain on the bottom of a pipe of water 10m excessive is about one hundred kilopascals (kPa).
If your pressure gauge reads only in psi, convert to kPa by multiplying by 6.9.
For example: forty psi = 40 × 6.9 = 276k Pa = 27.6 m head
Determine the suction head
Suction head is the gap between the centre line of the pump and the source water degree, plus losses within 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 in the suction line, so guarantee every little thing right. Common problems embody 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 circulate pumps should be submerged to operate, so that they usually do not have any suction head.
For instance:
Pressure Head = 27.6m
Suction head = 4.0m
Total Head = 31.6m
Another helpful figure that can now be calculated is the pumping value per ML per metre of head. This allows a significant comparison between different pump stations.
Pumping price per ML per metre head: = price ($/ML) ÷ TH (m)
= $50.25/ML ÷ 31.6m
= $1.59 / ML / m head
Step 6: Determine motor efficiency (Me)
Electric motors have an efficiency value. That is, they lose a few of the vitality going into them as heat. This vitality loss adjustments with the dimensions of the motor. The desk under is a guideline for motors working at full load.
Submersible motors lose about 4 per cent more than air-cooled electrical motors (for instance, the place Me is 88 per cent for an air-cooled motor it would be eighty four per cent for a submersible). Voltage losses by way of 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 directly coupled to the pump, there is a loss of vitality via the transmission. This loss is taken into account by what’s termed the drive factor (Df).
Step eight: Calculate pump effectivity (Pe)
Pe = (Q × H) ÷ (power consumed × Me × Df)
This example consists of the information from the earlier steps mentioned. 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 × zero.9 × zero.9)
= 1832.8 ÷ 34.02
= fifty three.9 per cent
Step 9: Calculating potential savings
Most centrifugal pumps are designed to function with no less than seventy five per cent efficiency, and most turbine pumps are designed to operate with at least eighty five per cent effectivity.
The pump in our example is just about 54 per cent efficient, so how a lot can be saved by enhancing the effectivity from fifty four per cent to 75 per cent?
Take this instance:
If our pumping price is $50.25 per ML, the development 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 throughout a season, the total price saving is $14.07 × 900 = $12,663.
If impeller put on is the issue and the cost of substitute is $10,000, it would be paid for in lower than one season. After that, the financial savings are all elevated revenue.
Notice that a reduction within the pump efficiency figure of 21 per cent (75 per cent to 54 per cent) causes an increase in pumping cost of 39 per cent ($36.18/ML to $50.25/ML).
Other elements that have an result on price and pump efficiency
There are two different variables have an effect on value and pump effectivity: pump pace and impeller measurement.
Pump pace
You must know the pump speed so as to learn the pump curves. The curves are normally ready for particular pump speeds and impeller sizes.
If the pump is directly coupled to the electric motor, the pace is fastened by the pace 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 velocity of electric motors varies somewhat, it will be good to examine your motor pace with a rev counter.
If the motor just isn’t directly coupled to the pump, the speed 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 may be calculated from the diameter of the pulleys on the motor and the pump (see the diagram under – make sure the pump is stopped earlier than measuring the pulleys).
A complication that can happen when understanding the cost and efficiency revolves round Variable Speed Drives (VSD), also recognized as Variable Frequency Drives (VFD).
VSDs are becoming increasingly in style as their value reduces because of the benefits they offer. These items are added to electric motors and permit the speed to be altered by changing the frequency of the alternating present. They enable electrically pushed pumps to have their velocity set at exactly what’s required for the pump obligation and they remove the need for throttling the irrigation system utilizing valves.
Savings of 1 quarter of the similar old power consumption are sometimes 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 in this article must be made several occasions with the pump set at totally different typical speeds.
digital pressure gauge put on has the identical effect as a reduction in impeller dimension so you have to know the scale 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 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 regulate the pump’s efficiency and procure a particular responsibility.
To give a range of duties, manufacturers may supply impellers of various diameters for the same pump casing. Available impeller sizes are shown on the pump curves.
Power issue
Power factor can also substantially have an result on your operating prices and perhaps the operation of your pump as properly.
Measuring efficiency
Keeping observe of your pump’s efficiency and prices just isn’t troublesome. It could prevent some huge cash and maintain your irrigation system performing correctly.
If you identify your pump is working under the acceptable minimum degree, check the inner condition for wear or maintenance and the suitability of the pump for its present responsibility, or take steps to enhance the drive or replace it with a VSD.
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