Measuring pumping prices for electric irrigation pumps
by Brenna ShumbamhiniJune 10, 2022
If the wrong pump is chosen or is worn out, this will increase pumping costs and scale back productivity. In the second of a sequence of reality sheets, the NSW Department of Primary Industries describes a simple way to work out the pumping costs and vitality effectivity of your electrical pump.
Tests of irrigation pumps across New South Wales have discovered that many were not 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 contain costs, you should monitor your vitality usage, repair and keep the pump and work out what your pumping prices are.
When you have decided the working cost you can perform fast 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 determine when restore or substitute is cost-effective.
Measuring working costs
One method of monitoring pumping prices is to work out how a lot it costs to pump a megalitre of water. To do this, you should measure:
The power consumption fee in kilowatts (kW)
The circulate rate in litres per second (L/s).
Combining these measures with the value of electricity offers you the pumping cost.
Step 1: Measure the power used
You can measure the facility used by studying your electrical energy meter. Electronic meters are most commonly used however single and a quantity of meters proceed for use on many farms.
Electronic meters usually measure and report the electricity used for the main rate, shoulder fee and the off-peak rate in separate registers. The various charges are switched ‘on’ and ‘off’ by the inner clock on the applicable times.
Electronic meters report 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 determine identification quantity. For example, the current off-peak kilowatts may be given register number ‘126’. You ought to check with your native vitality authority what the display register numbers are for each of your charges.
The meter scrolls by way of every register at 4 to six second intervals.
The register number appears, typically in smaller numbers, on the LCD display screen (in the diagram, in the top left-hand corner) and may have a short description beneath (for instance: 126 = off-peak)
The usage in kilowatt-hours appears within the larger main display. It is often a six-figure quantity (for example: 1253.64).
When the time rate that is at present being measured is reached, the quantity may flash. Record this quantity. If none of the displays flash, document the readings from all of the shows.
Let the pump run for no less than quarter-hour before taking the subsequent studying.
In systems that consume massive amounts of electrical energy, 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 show may learn to a couple of decimal locations. If there is a multiplier, run the pump for a minimal of half-hour earlier than taking the second register reading.
If the second reading has not changed, you might be studying the mistaken register.
Reading an electronic meter
First studying (register 126) = 1253.64 kWh
Second reading (register 126) = 1254.sixteen kWh
Multiplier acknowledged on power invoice = forty
Power usage =
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 set up in an average place and working, 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 techniques that consume large quantities of electrical energy, the disc could additionally be geared down so it doesn’t run too quick. If so, you’ll notice a multiplier ‘M’ is marked on the meter.
M (multiplier as marked on meter) = 40
From this information you’ll be able to calculate the facility utilization in kilowatts.
Power usage =
In this instance, the pump makes use of 42kW.
Perform this check regularly, over a season or between seasons, to examine the pump’s power consumption. If you find that it takes less time for the same variety of disc revolutions than whenever you first tested the pump, the facility use is greater, and you’ll need to find out why.
This comparison is just possible when the irrigation is ready up in the identical position as the initial take a look at, with the identical number of sprinklers, and with the pumping water level roughly the identical.
Multiple disc meters
If there are three meters, for instance, one for every section of a three-phase energy provide, measure the three meters individually and add the kW figures together.
Measuring each meter individually offers an correct answer as hardly ever are three meters precisely the identical. If a very accurate result’s needed, you need to monitor the system over all of the irrigation positions for one full cycle.
In this case you should record the entire electrical energy used, the whole hours of use and the total quantity pumped over the period.
pressure gauge 10 bar : Measure the move price (Q)
The second measure wanted to calculate pumping price per megalitre is the flow fee of the system (Q).
The flow price is the amount (or quantity) of water pumped in a certain period of time, usually given in litres per second (L/s). It ought to be measured after the system has had sufficient time from startup to be working normally.
Measure the flow price by studying 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.one hundred forty five kL
Estimating flow price by discharge
If no water meter is fitted or it is dropping accuracy, the circulate fee of a spray irrigation system the place all of the sprinklers are the same model and size can be estimated by measuring the sprinkler discharge. Use several sprinklers: no much less than one initially of the line, one in the center and one at the end.
Record how long each 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 volume (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 circulate price of the system, multiply the typical by the number of sprinklers working.
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 = (1.11 + 1.25 + 1.43) ÷ three
There are 46 sprinklers operating, so the whole flow price is = 1.26 x 46 = 58L/s
Step three: Calculate the facility per megalitre pumped
From the facility utilization and the move fee, the kilowatt-hours per megalitre (kWh/ML) on your pump could be calculated.
This known as the ‘calibration’ worth (the value used where no water meter is put in and electrical energy meter readings are learn to infer the quantity of water used).
Pump calibration (kWh/ML)
= kW ÷ (Q x zero.0036)
= 42 ÷ (58 x zero.0036)
(Note: 0.0036 converts kilowatt-seconds per litre to kilowatt-hours per megalitre.)
Step four: Calculate the pumping price
Having calculated the facility used to pump a megalitre, if you know the price per kWh, you probably can calculate the worth of pumping.
The charges per kWh may be tough to work out exactly in case your supplier has different rates for day or night time, weekends, and so forth so you should contact your provider for help to work this out.
If supply 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 well the pump converts electrical energy into useful work to maneuver water.
The goal of careful pump choice and regular pump maintenance is to have the pump performing as efficiently as possible (ie shifting the most water for the least energy required). Efficient pump operation minimises operating prices per megalitre pumped.
Pump efficiency 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 figure under these means both 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 prices is to frequently monitor your power usage and verify on any vital change that suggests consideration is required.
To calculate pump effectivity, you want to know the flow rate (Q) and the pump pressure, or whole head (H or TH) of the system. The pressure and circulate that a pump is working at is called the duty or duty point. Pump effectivity varies over the range of attainable duties for any particular pump.
An adequate estimate of total dynamic head for floor methods is the vertical top in metres from supply water stage 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 stage to water level, plus the losses as a end result 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 working strain. This studying must be transformed to equal metres of head, that is additionally sometimes called Pressure Head.
New pumps normally have a strain gauge installed but they typically endure bodily damage rapidly. A better technique is to fit an entry point on the supply aspect of the pump where you possibly can quickly install a pressure gauge everytime you wish to take a studying. The gauge could be simply indifferent when not needed.
A change in the pump operating pressure via the season or across seasons, when irrigating the identical block or shift, immediately tells you one thing has modified.
A sudden reduction usually indicates a new leak or a blockage on the suction side; a gradual discount usually signifies put on of the impeller or sprinkler nozzles; and a rise normally suggests a blockage somewhere within the system downstream of the stress gauge.
Pressure could be considered equivalent to a pipe of water of a sure peak in metres. This is known as ‘head’ (H). At sea stage, the strain on the bottom of a pipe of water 10m high is about a hundred kilopascals (kPa).
If your strain 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 space between the centre line of the pump and the source water stage, 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 stage occur in the suction line, so guarantee every little thing right. Common problems include blocked inlet or foot-valve or strainer, pipe diameter too small, pipe damaged or crushed, suction height too great, or air trapped on the connection to the pump.
Turbine and axial circulate pumps should be submerged to function, in order that they normally wouldn’t have any suction head.
Pressure Head = 27.6m
Suction head = 4.0m
Total Head = 31.6m
Another useful determine that may now be calculated is the pumping cost per ML per metre of head. This permits a significant comparability between different pump stations.
Pumping cost per ML per metre head: = cost ($/ML) ÷ TH (m)
= $50.25/ML ÷ 31.6m
= $1.fifty nine / ML / m head
Step 6: Determine motor efficiency (Me)
Electric motors have an effectivity value. That is, they lose a few of the vitality going into them as heat. This energy loss changes with the scale of the motor. The table beneath is a tenet for motors operating at full load.
Submersible motors lose about four per cent more than air-cooled electric motors (for example, 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 may also be important 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 is a lack of vitality by way of 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 consists of the information 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
= fifty three.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 operate with a minimum of 85 per cent efficiency.
The pump in our instance is just about 54 per cent environment friendly, so how much can be saved by improving the effectivity from fifty four per cent to seventy five per cent?
Take this example:
If our pumping price is $50.25 per ML, the advance 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
If 900ML are pumped during a season, the total value saving is $14.07 × 900 = $12,663.
If impeller wear is the problem and the cost of replacement is $10,000, it would be paid for in less than one season. After that, the savings are all increased profit.
Notice that a reduction in the pump effectivity figure of 21 per cent (75 per cent to fifty four per cent) causes a rise in pumping price of 39 per cent ($36.18/ML to $50.25/ML).
Other factors that affect price and pump efficiency
There are two different variables have an result on value and pump effectivity: pump speed and impeller dimension.
You should know the pump pace so as to read the pump curves. The curves are usually prepared for specific pump speeds and impeller sizes.
If the pump is instantly coupled to the electric motor, the velocity 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 electric motors varies slightly, it will be good to check your motor pace 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 – ensure the pump is stopped earlier than measuring the pulleys).
A complication that can occur when figuring out the cost and effectivity revolves round Variable Speed Drives (VSD), also referred to as Variable Frequency Drives (VFD).
VSDs are becoming increasingly popular as their price reduces due to the advantages they provide. These models are added to electric motors and permit the speed to be altered by altering the frequency of the alternating current. They enable electrically driven pumps to have their velocity set at precisely what is required for the pump obligation and so they get rid of the need for throttling the irrigation system using valves.
Savings of 1 quarter of the standard power consumption are sometimes reported by irrigators, and may be as a lot 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 several times with the pump set at different typical speeds.
Impeller wear has the same impact as a reduction in impeller measurement so you should 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 discover out the dimensions by dismantling the pump and measuring it, or asking the one that made the change.
Sometimes an impeller is intentionally reduced in diameter to regulate the pump’s efficiency and acquire a specific responsibility.
To give a variety of duties, manufacturers could provide impellers of different diameters for a similar pump casing. Available impeller sizes are proven on the pump curves.
Power factor may considerably have an result on your running costs and maybe the operation of your pump as nicely.
Keeping track of your pump’s efficiency and prices isn’t difficult. It may save you a lot of money and maintain your irrigation system performing properly.
If you identify your pump is working beneath the acceptable minimum degree, check the internal condition for put on or upkeep and the suitability of the pump for its current obligation, or take steps to improve the drive or replace it with a VSD.