AGRICULTURE
Measuring pumping costs 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 prices and reduce productiveness. In the second of a collection of fact sheets, the NSW Department of Primary Industries describes a simple way to work out the pumping costs and energy efficiency of your electric pump.
Tests of irrigation pumps throughout New South Wales have discovered that many weren’t performing effectively, either as a result of the mistaken pump had been chosen for the job, or as a result of the pump was worn.
To include costs, you want to monitor your energy utilization, repair and preserve the pump and work out what your pumping costs are.
When you have decided the working cost you’ll be able to perform quick checks to detect any change, and when you’ve decided the pump effectivity, you’ll have the ability to evaluate it to the manufacturer’s figures to resolve when repair or substitute is cost-effective.
Measuring working costs
One way of tracking pumping costs is to work out how much it costs to pump a megalitre of water. To do this, you want to measure:
The energy consumption rate in kilowatts (kW)
The move fee in litres per second (L/s).
Combining these measures with the value of electrical energy gives you the pumping price.
Step 1: Measure the power used
You can measure the ability utilized by studying your electrical energy meter. Electronic meters are most commonly used however single and a quantity of meters proceed to be used on many farms.
Electronic meters
Electronic meters usually measure and record the electricity used for the main fee, shoulder fee and the off-peak fee in separate registers. The varied charges are switched ‘on’ and ‘off’ by the inner clock on the applicable occasions.
Electronic meters document your electrical energy consumption in a time-of-use format. They may also have registers for the date, the time and for testing the show.
Each register has a 3 determine identification number. For instance, the current off-peak kilowatts could also be given register quantity ‘126’. You should check together with your native vitality authority what the display register numbers are for each of your rates.
The meter scrolls through each register at four to 6 second intervals.
The register number appears, often in smaller numbers, on the LCD display screen (in the diagram, within the top left-hand corner) and will have a brief description beneath (for example: 126 = off-peak)
The utilization in kilowatt-hours appears within the bigger main display. It is usually a six-figure quantity (for example: 1253.64).
When the time fee that’s currently being measured is reached, the number might flash. Record this number. If none of the displays flash, record the readings from all of the displays.
Let the pump run for a minimal of 15 minutes earlier than taking the following studying.
In techniques that eat massive amounts of electricity, there may be a multiplier programmed into the electronics.
If so, it will be noted on the electricity supplier’s bill for this meter as ‘Mult’ or ‘M’ and the display might learn to a couple of decimal locations. If there’s a multiplier, run the pump for at least half-hour before taking the second register studying.
If the second reading has not changed, you might be studying the mistaken register.
Reading an digital meter
First studying (register 126) = 1253.64 kWh
Second reading (register 126) = 1254.16 kWh
Multiplier stated on power bill = 40
Power utilization =
Reading a disc meter
Note the rating determine, 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 at least 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 techniques that eat massive quantities of electricity, 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) = 40
From this knowledge you’ll be able to calculate the ability usage in kilowatts.
Power utilization =
In this example, the pump makes use of 42kW.
Perform this check regularly, over a season or between seasons, to examine the pump’s energy consumption. If you discover that it takes less time for a similar variety of disc revolutions than whenever you first tested the pump, the power use is greater, and you will want to search out out why.
This comparability is simply attainable when the irrigation is ready up in the same position because the initial test, with the identical number of sprinklers, and with the pumping water stage roughly the same.
Multiple disc meters
If there are three meters, for instance, one for each part of a three-phase power provide, measure the three meters individually and add the kW figures collectively.
Measuring each meter individually gives an correct answer as hardly ever are three meters precisely the same. If a very accurate result’s needed, you have to monitor the system over all of the irrigation positions for one complete cycle.
In this case you should report the whole electricity used, the whole hours of use and the entire quantity pumped over the period.
Step 2: Measure the move price (Q)
The second measure wanted to calculate pumping price per megalitre is the flow fee of the system (Q).
The move rate is the quantity (or quantity) of water pumped in a sure period of time, normally given in litres per second (L/s). It must be measured after the system has had sufficient time from startup to be working usually.
Measure the circulate price by reading your water meter on the pump for ideally the entire irrigation cycle or no less than half an hour and dividing the litres pumped by the time in seconds.
Water meter studying at start: 1108.345 kL
Water meter studying after 35 minutes: 1230.145 kL
Q =
Estimating move price by discharge
If no water meter is fitted or it’s losing accuracy, the circulate price of a twig irrigation system where all of the sprinklers are the identical mannequin and measurement may be estimated by measuring the sprinkler discharge. Use a number of sprinklers: at least one initially of the road, one within the middle and one at the finish.
Record how lengthy each sprinkler takes to fill a container (for example, a 10L bucket or a 20L drum). To find the flow rate of every sprinkler in litres, divide the container quantity (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 move fee 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 ÷ 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 46 sprinklers working, so the total circulate rate is = 1.26 x forty six = 58L/s
Step three: Calculate the power per megalitre pumped
From the power utilization and the circulate fee, the kilowatt-hours per megalitre (kWh/ML) on your pump may be calculated.
This known as the ‘calibration’ value (the worth used where 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 0.0036)
= 42 ÷ (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 know the price per kWh, you possibly can calculate the value of pumping.
The expenses per kWh could also be difficult to work out precisely if your provider has completely different rates for day or night, weekends, and so forth so you want to 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 efficiency
Irrigation pump efficiency is a measure of how well the pump converts electrical vitality into useful work to move water.
The purpose of careful pump choice and common pump maintenance is to have the pump performing as efficiently as potential (ie transferring essentially the most water for the least energy required). Efficient pump operation minimises working prices per megalitre pumped.
Pump efficiency of 70 per cent to eighty five per cent ought to 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 efficiency determine beneath these means either the incorrect pump was chosen for the job, the pump is worn and desires restore or upkeep is required.
The key to containing your pumping costs is to often monitor your energy usage and verify on any important change that implies attention is required.
To calculate pump efficiency, you should know the circulate rate (Q) and the pump strain, or total head (H or TH) of the system. The strain and flow that a pump is working at is identified as the responsibility or obligation point. Pump effectivity varies over the vary of potential duties for any specific pump.
An enough estimate of whole dynamic head for surface methods is the vertical height in metres from source water degree to the tip of the discharge pipe, or, if the discharge is submerged, to the height of the water above the discharge, that is, water level to water degree, plus the losses due to friction in the suction pipe.
Measure the discharge (or delivery) head
This is the strain learn from the gauge fitted on the pump when the system is at full working strain. This reading needs to be transformed to equivalent metres of head, this is additionally typically referred to as Pressure Head.
New pumps often have a pressure gauge put in but they typically endure bodily damage quickly. A better methodology is to fit an entry level on the supply side of the pump the place you presumably can quickly install a pressure gauge whenever you want to take a studying. The gauge could be simply detached when not wanted.
A change in the pump working stress by way of the season or throughout seasons, when irrigating the same block or shift, immediately tells you one thing has changed.
A sudden reduction usually indicates a brand new leak or a blockage on the suction facet; a gradual reduction normally indicates put on of the impeller or sprinkler nozzles; and a rise normally suggests a blockage somewhere in the system downstream of the strain gauge.
Pressure can be thought of as equal to a pipe of water of a sure peak in metres. This is referred to as ‘head’ (H). At sea degree, the stress on the bottom of a pipe of water 10m high is about one hundred kilopascals (kPa).
If your stress gauge reads solely 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 space between the centre line of the pump and the supply water degree, plus losses within the suction pipe if the pump is positioned above the water level. Typical suction head figures for centrifugal pumps are three to 5 metres.
Most problems with pumps positioned above the water degree happen in the suction line, so ensure every little thing appropriate. Common issues embrace blocked inlet or foot-valve or strainer, pipe diameter too small, pipe broken or crushed, suction top too great, or air trapped on the connection to the pump.
Turbine and axial circulate pumps should be submerged to function, so they usually wouldn’t have any suction head.
For instance:
Pressure Head = 27.6m
Suction head = 4.0m
Total Head = 31.6m
Another helpful determine that may now be calculated is the pumping price per ML per metre of head. This permits a significant 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 efficiency (Me)
Electric motors have an efficiency worth. That is, they lose a few of the energy going into them as warmth. This power loss adjustments with the size of the motor. The table below is a guideline for motors operating at full load.
Submersible motors lose about 4 per cent more than air-cooled electric motors (for example, where Me is 88 per cent for an air-cooled motor it might be 84 per cent for a submersible). Voltage losses through 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 just isn’t instantly coupled to the pump, there’s a loss of power through the transmission. This loss is taken under consideration by what is termed the drive issue (Df).
Step eight: Calculate pump efficiency (Pe)
Pe = (Q × H) ÷ (power consumed × Me × Df)
This example contains the info from the previous steps discussed. The drive from the motor to the pump is a V-belt on this case.
ร้านซ่อมเครื่องวัดความดันโลหิต (87a03eb4327cd2ba79570dbcca4066c6d479b8f7279bafdb318e7183d82771cf) = (Q × H) ÷ (power × Me × Df)
= (58 × 31.6) ÷ (42 × zero.9 × 0.9)
= 1832.eight ÷ 34.02
= 53.9 per cent
Step 9: Calculating potential financial savings
Most centrifugal pumps are designed to function with at least seventy five per cent effectivity, and most turbine pumps are designed to operate with no less than 85 per cent efficiency.
The pump in our example is simply about 54 per cent efficient, so how a lot can be saved by improving the effectivity from fifty four per cent to seventy five per cent?
Take this example:
If our pumping value 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 during a season, the entire value saving is $14.07 × 900 = $12,663.
If impeller put on is the issue and the cost of replacement is $10,000, it might be paid for in lower than one season. After that, the savings are all increased profit.
Notice that a discount in the pump effectivity determine of 21 per cent (75 per cent to 54 per cent) causes an increase in pumping price of 39 per cent ($36.18/ML to $50.25/ML).
Other components that affect cost and pump efficiency
There are two other variables affect price and pump effectivity: pump speed and impeller measurement.
Pump speed
You should know the pump velocity so as to learn the pump curves. The curves are usually ready for specific pump speeds and impeller sizes.
If the pump is instantly coupled to the electric motor, the speed is fixed 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 result of the speed of electrical motors varies a little, it will be good to examine your motor velocity with a rev counter.
If the motor is not 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 may be calculated from the diameter of the pulleys on the motor and the pump (see the diagram below – make sure the pump is stopped earlier than measuring the pulleys).
A complication that can happen when understanding the cost and efficiency revolves around Variable Speed Drives (VSD), also recognized as Variable Frequency Drives (VFD).
VSDs have gotten more and more well-liked as their price reduces because of the advantages they offer. These items are added to electric motors and permit the velocity to be altered by altering the frequency of the alternating current. They enable electrically pushed pumps to have their speed set at exactly what’s required for the pump responsibility and they eliminate the need for throttling the irrigation system using valves.
Savings of one quarter of the standard power consumption are sometimes reported by irrigators, and may be as much as half relying on the situation. For figuring out the fee and effectivity of a pump, the measurements outlined on this article ought to be made a quantity of occasions with the pump set at different typical speeds.
Impeller measurement
Impeller put on has the identical effect as a discount in impeller size so you want to know the scale of impeller fitted to your pump to work out which performance curve applies to your pump.
Sometimes the impeller dimension is stamped on the pump’s ID plate. If not, you should find out the scale by dismantling the pump and measuring it, or asking the one that made the change.
Sometimes an impeller is deliberately lowered in diameter to adjust the pump’s performance and acquire a specific obligation.
To give a spread of duties, manufacturers might provide impellers of various diameters for a similar pump casing. Available impeller sizes are shown on the pump curves.
Power issue
Power factor may substantially have an effect on your operating prices and maybe the operation of your pump as properly.
Measuring efficiency
Keeping observe of your pump’s efficiency and costs isn’t troublesome. It might save you a lot of money and keep your irrigation system performing properly.
If you identify your pump is working under the suitable minimum level, examine the interior condition for wear or maintenance and the suitability of the pump for its current obligation, or take steps to enhance the drive or substitute it with a VSD.
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