AGRICULTURE
Measuring pumping costs for electric irrigation pumps
by Brenna ShumbamhiniJune 10, 2022
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If the mistaken pump is chosen or is worn out, this could enhance pumping costs and cut back productivity. In the second of a sequence of fact sheets, the NSW Department of Primary Industries describes a simple way to work out the pumping prices and energy efficiency of your electrical pump.
Tests of irrigation pumps throughout New South Wales have found that many weren’t performing effectively, both because the wrong pump had been chosen for the job, or because the pump was worn.
To comprise costs, you have to monitor your vitality usage, restore and keep the pump and work out what your pumping costs are.
When you’ve decided the working cost you can carry out quick checks to detect any change, and when you might have decided the pump efficiency, you can examine it to the manufacturer’s figures to determine when repair or replacement is cost-effective.
Measuring working costs
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 price in kilowatts (kW)
The circulate rate in litres per second (L/s).
Combining เครื่องมือวัดpressure with the value of electrical energy offers you the pumping cost.
Step 1: Measure the facility used
You can measure the ability used 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 normally measure and record the electricity used for the primary fee, shoulder price and the off-peak fee in separate registers. The numerous rates are switched ‘on’ and ‘off’ by the internal clock on the applicable instances.
Electronic meters document your electrical energy 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 3 determine identification number. For instance, the current off-peak kilowatts may be given register quantity ‘126’. You ought to verify with your native power authority what the show register numbers are for every of your charges.
The meter scrolls via every register at 4 to six second intervals.
The register number appears, usually in smaller numbers, on the LCD screen (in the diagram, in the top left-hand corner) and will have a brief description beneath (for instance: 126 = off-peak)
The usage in kilowatt-hours appears within the bigger major display. It is often a six-figure quantity (for instance: 1253.64).
When the time rate that’s currently being measured is reached, the quantity could flash. Record this quantity. If none of the shows flash, document the readings from all the shows.
Let the pump run for no much less than quarter-hour before taking the next reading.
In techniques that eat large quantities of electricity, there may be a multiplier programmed into the electronics.
If so, it will be noted on the electricity supplier’s invoice for this meter as ‘Mult’ or ‘M’ and the show may learn to a few decimal places. If there’s a multiplier, run the pump for no less than 30 minutes before taking the second register studying.
If the second studying has not modified, you might be studying the mistaken register.
Reading an digital meter
First studying (register 126) = 1253.sixty four kWh
Second studying (register 126) = 1254.sixteen kWh
Multiplier said on power invoice = 40
Power utilization =
Reading a disc meter
Note the rating 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 arrange in a median place and operating, time the spinning horizontal disc on the ability meter for no less than 10 per cent of R (In this example, 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 eat large amounts of electrical energy, the disc may 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 probably can calculate the facility utilization in kilowatts.
Power utilization =
In this instance, the pump uses 42kW.
Perform this check often, over a season or between seasons, to examine the pump’s power consumption. If you find that it takes much less time for a similar variety of disc revolutions than whenever you first examined the pump, the facility use is larger, and you will need to find out why.
This comparability is simply possible when the irrigation is ready up in the same place as the initial take a look at, with the identical number of sprinklers, and with the pumping water level roughly the same.
Multiple disc meters
If there are three meters, for instance, one for each part of a three-phase energy supply, measure the three meters individually and add the kW figures collectively.
Measuring every meter individually provides an correct reply as rarely are three meters exactly the identical. If a very accurate result is wanted, you have to monitor the system over all of the irrigation positions for one complete cycle.
In this case you should report the whole electrical energy used, the total hours of use and the total quantity pumped over the period.
Step 2: Measure the move fee (Q)
The second measure needed to calculate pumping cost per megalitre is the flow rate of the system (Q).
The flow price is the quantity (or quantity) of water pumped in a certain amount of time, normally given in litres per second (L/s). It should be measured after the system has had sufficient time from startup to be working normally.
Measure the flow fee by reading your water meter at the pump for ideally the entire irrigation cycle or at least half an hour and dividing the litres pumped by the time in seconds.
Water meter reading at begin: 1108.345 kL
Water meter reading after 35 minutes: 1230.one hundred forty five kL
Q =
Estimating move fee by discharge
If no water meter is fitted or it is losing accuracy, the flow rate of a spray irrigation system the place all the sprinklers are the same model and size can be estimated by measuring the sprinkler discharge. Use several sprinklers: a minimal of one firstly of the line, 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 circulate fee of each sprinkler in litres, divide the container volume (in litres) by the point required to fill it (in seconds).
You can then find the common for the sprinklers you measured. To calculate the whole circulate price of the system, multiply the typical by the number of sprinklers working.
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 ÷ 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) ÷ three
= 1.26L/s
There are forty six sprinklers working, so the total circulate price is = 1.26 x forty six = 58L/s
Step 3: Calculate the facility per megalitre pumped
From the ability usage and the flow rate, the kilowatt-hours per megalitre (kWh/ML) in your pump may be calculated.
This is called the ‘calibration’ worth (the value used the place no water meter is put in and electricity meter readings are read to deduce the quantity of water used).
Pump calibration (kWh/ML)
= kW ÷ (Q x zero.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 value
Having calculated the facility used to pump a megalitre, if you know the cost per kWh, you presumably can calculate the worth of pumping.
The costs per kWh may be difficult to work out exactly in case your provider has completely different rates for day or evening, weekends, and so on so you should contact your supplier for help to work this out.
Pumping costs
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 efficiency is a measure of how properly the pump converts electrical power into helpful work to move water.
The purpose of careful pump selection and regular pump upkeep is to have the pump performing as efficiently as potential (ie shifting the most water for the least power required). Efficient pump operation minimises running costs per megalitre pumped.
Pump effectivity of 70 per cent to eighty five per cent must be achievable in most circumstances. An acceptable minimal for a centrifugal irrigation pump is 65 per cent, and 75 per cent for a turbine pump.
An efficiency determine below these means both the incorrect pump was chosen for the job, the pump is worn and desires repair or upkeep is needed.
The key to containing your pumping costs is to often monitor your vitality usage and verify on any important change that suggests attention is needed.
To calculate pump efficiency, you have to know the move price (Q) and the pump strain, or total head (H or TH) of the system. The pressure and move that a pump is working at known as the obligation or duty level. Pump effectivity varies over the vary of potential duties for any particular pump.
An enough estimate of whole dynamic head for surface techniques is the vertical height in metres from supply water degree to the top 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 stress read from the gauge fitted at the pump when the system is at full working stress. This studying must be transformed to equivalent metres of head, that is additionally sometimes referred to as Pressure Head.
New pumps often have a stress gauge put in however they usually suffer physical damage rapidly. A better method is to fit an entry point on the delivery facet of the pump where you can quickly set up a strain gauge everytime you wish to take a studying. The gauge may be simply detached when not wanted.
A change in the pump operating strain by way of the season or throughout seasons, when irrigating the same block or shift, instantly tells you one thing has changed.
A sudden discount normally signifies a new leak or a blockage on the suction aspect; a gradual reduction often indicates wear of the impeller or sprinkler nozzles; and a rise usually suggests a blockage someplace in the system downstream of the stress gauge.
Pressure can be thought of as equivalent to a pipe of water of a certain top in metres. This is known as ‘head’ (H). At sea level, the stress on the backside of a pipe of water 10m excessive is about 100 kilopascals (kPa).
If your strain gauge reads only in psi, convert to kPa by multiplying by 6.9.
For instance: 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 level, plus losses in the suction pipe if the pump is positioned above the water degree. Typical suction head figures for centrifugal pumps are three to five metres.
Most issues with pumps positioned above the water level happen in the suction line, so guarantee every thing correct. Common problems embody blocked inlet or foot-valve or strainer, pipe diameter too small, pipe broken or crushed, suction peak too nice, or air trapped at the connection to the pump.
Turbine and axial circulate pumps must be submerged to function, so that they normally do not have any suction head.
For instance:
Pressure Head = 27.6m
Suction head = four.0m
Total Head = 31.6m
Another helpful determine that can now be calculated is the pumping value per ML per metre of head. This permits a meaningful comparability between totally different pump stations.
Pumping cost per ML per metre head: = price ($/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 worth. That is, they lose some of the vitality going into them as heat. This vitality loss modifications with the dimensions of the motor. The table below is a tenet for motors operating at full load.
Submersible motors lose about four per cent greater than air-cooled electrical motors (for example, where Me is 88 per cent for an air-cooled motor it would be eighty four per cent for a submersible). Voltage losses through lengthy electrical cables can also be vital so this ought to be checked with an electrical engineer.
Step 7: Determine transmission losses (Df)
If the engine is not immediately coupled to the pump, there’s a loss of energy through the transmission. This loss is taken into consideration by what’s termed the drive factor (Df).
Step 8: Calculate pump effectivity (Pe)
Pe = (Q × H) ÷ (power consumed × Me × Df)
This instance contains the data 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 × zero.9 × 0.9)
= 1832.eight ÷ 34.02
= fifty three.9 per cent
Step 9: Calculating potential savings
Most centrifugal pumps are designed to operate with at least seventy five per cent efficiency, and most turbine pumps are designed to operate with a minimal of 85 per cent effectivity.
The pump in our instance is only about fifty four per cent environment friendly, so how much would be saved by enhancing the efficiency from fifty four per cent to seventy five per cent?
Take this example:
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 throughout a season, the entire cost saving is $14.07 × 900 = $12,663.
If impeller wear is the problem and the price of alternative is $10,000, it might be paid for in less than one season. After that, the savings are all increased profit.
Notice that a discount in the pump efficiency figure of 21 per cent (75 per cent to 54 per cent) causes a rise in pumping cost of 39 per cent ($36.18/ML to $50.25/ML).
Other factors that affect price and pump effectivity
There are two different variables affect price and pump effectivity: pump speed and impeller dimension.
Pump velocity
You should know the pump velocity in order to read the pump curves. The curves are usually ready for specific pump speeds and impeller sizes.
If the pump is directly coupled to the electrical motor, the velocity is fastened by the speed of the motor: two-pole motors run at 2,900 rev/min and four-pole motors run at 1,440 rev/min. However, because the pace of electrical motors varies a little, it will be good to verify your motor pace with a rev counter.
If the motor isn’t immediately 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 can be calculated from the diameter of the pulleys on the motor and the pump (see the diagram below – make positive the pump is stopped earlier than measuring the pulleys).
A complication that can occur when figuring out the fee and effectivity revolves round Variable Speed Drives (VSD), also called Variable Frequency Drives (VFD).
VSDs have gotten increasingly popular as their value reduces due to the benefits they provide. These units 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 precisely what is required for the pump duty they usually eliminate the necessity for throttling the irrigation system using valves.
Savings of one quarter of the identical old power consumption are sometimes reported by irrigators, and could also be as much as half depending on the state of affairs. For determining the fee and efficiency of a pump, the measurements outlined in this article must be made a number of times with the pump set at completely different typical speeds.
Impeller measurement
Impeller wear has the identical effect as a reduction in impeller dimension so you want 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 have to find out the scale by dismantling the pump and measuring it, or asking the one who made the change.
Sometimes an impeller is intentionally decreased in diameter to adjust the pump’s performance and procure a specific obligation.
To give a spread of duties, producers might supply impellers of different diameters for a similar pump casing. Available impeller sizes are shown on the pump curves.
Power factor
Power issue may considerably affect your operating prices and perhaps the operation of your pump as nicely.
Measuring performance
Keeping track of your pump’s performance and costs isn’t tough. It may prevent a lot of money and keep your irrigation system performing properly.
If you identify your pump is operating below the appropriate minimal level, verify the interior condition for wear or maintenance and the suitability of the pump for its current duty, or take steps to improve the drive or substitute it with a VSD.
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