Measuring pumping prices for electric irrigation pumps


Measuring pumping prices for electrical irrigation pumps

by Brenna ShumbamhiniJune 10, 2022


If the incorrect pump is chosen or is worn out, this could enhance pumping prices and scale back productiveness. In the second of a series of fact sheets, the NSW Department of Primary Industries describes a easy method to work out the pumping costs and vitality efficiency of your electric pump.
Tests of irrigation pumps throughout New South Wales have discovered that many weren’t performing efficiently, either because the mistaken pump had been chosen for the job, or as a end result of the pump was worn.
To comprise costs, you should monitor your vitality usage, restore and keep the pump and work out what your pumping prices are.
When you have determined the working cost you can perform quick checks to detect any change, and when you might have decided the pump efficiency, you’ll have the ability to examine it to the manufacturer’s figures to resolve when repair or alternative is cost-effective.
Measuring operating costs

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

The flow fee in litres per second (L/s).
Combining these measures with the value of electricity gives you the pumping price.
Step 1: Measure the power used

You can measure the power used by reading your electrical energy meter. Electronic meters are most commonly used however single and multiple meters proceed to be used on many farms.
Electronic meters

Electronic meters usually measure and document the electricity used for the main rate, shoulder price and the off-peak fee in separate registers. The varied charges are switched ‘on’ and ‘off’ by the inner clock at the applicable occasions.
Electronic meters report 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 3 determine identification quantity. For instance, the current off-peak kilowatts could also be given register number ‘126’. You ought to check with your native power authority what the display register numbers are for every of your charges.
The meter scrolls by way of each register at 4 to six second intervals.
The register quantity seems, often in smaller numbers, on the LCD screen (in the diagram, in the top left-hand corner) and may have a brief description beneath (for instance: 126 = off-peak)

The usage in kilowatt-hours appears in the larger major display. It is normally a six-figure quantity (for example: 1253.64).
When เกจวัดแรงดันลมคือ that is at present being measured is reached, the quantity might flash. Record this quantity. If not one of the displays flash, report the readings from all the shows.
Let the pump run for at least quarter-hour earlier than taking the subsequent reading.
In methods that eat giant amounts of electricity, there may be a multiplier programmed into the electronics.
If so, it goes to be famous on the electricity supplier’s bill for this meter as ‘Mult’ or ‘M’ and the show might learn to a couple of decimal locations. If there’s a multiplier, run the pump for a minimal of half-hour before taking the second register reading.
If the second reading has not changed, you would possibly be studying the mistaken register.
Reading an digital meter

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

Second reading (register 126) = 1254.16 kWh

Multiplier acknowledged on energy invoice = forty

Power usage =

Reading a disc meter

Note the score figure, 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 an average position and running, 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 techniques that consume massive quantities of electricity, the disc could also be geared down so it doesn’t run too fast. If so, you will discover a multiplier ‘M’ is marked on the meter.
M (multiplier as marked on meter) = forty

From this knowledge you presumably can calculate the power utilization in kilowatts.
Power utilization =

In this instance, the pump makes use of 42kW.
Perform this take a look at frequently, over a season or between seasons, to examine the pump’s energy consumption. If you discover that it takes much less time for the same variety of disc revolutions than if you first examined the pump, the facility use is greater, and you’ll need to find out why.
This comparison is just potential when the irrigation is set up in the same position as the initial take a look at, 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 energy supply, measure the three meters individually and add the kW figures collectively.
Measuring every meter individually offers an correct reply as not often are three meters precisely the same. If a very accurate result’s needed, you need to monitor the system over all the irrigation positions for one complete cycle.
In this case you need to report the whole electrical energy used, the entire hours of use and the total quantity pumped over the interval.
Step 2: Measure the flow fee (Q)

The second measure needed to calculate pumping price per megalitre is the move price of the system (Q).
The circulate 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 operating normally.
Measure the circulate fee by studying your water meter on the pump for ideally the whole irrigation cycle or no much less than 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.a hundred forty five kL

Q =

Estimating circulate rate by discharge

If no water meter is fitted or it is losing accuracy, the move price of a sprig irrigation system the place all the sprinklers are the same model and dimension could be estimated by measuring the sprinkler discharge. Use several sprinklers: at least one at the start of the line, one in the center and one at the finish.
Record how long each sprinkler takes to fill a container (for example, a 10L bucket or a 20L drum). To find the circulate rate of every sprinkler in litres, divide the container volume (in litres) by the point required to fill it (in seconds).
You can then find the average for the sprinklers you measured. To calculate the whole move rate of the system, multiply the typical by the variety of sprinklers operating.
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 move = (1.eleven + 1.25 + 1.43) ÷ 3

= 1.26L/s

There are forty six sprinklers operating, so the whole flow rate is = 1.26 x forty six = 58L/s

Step three: Calculate the facility per megalitre pumped

From the facility utilization and the flow fee, the kilowatt-hours per megalitre (kWh/ML) for your pump may be calculated.
This known as the ‘calibration’ worth (the worth used the place no water meter is installed and electricity meter readings are learn to deduce the amount of water used).
Pump calibration (kWh/ML)

= kW ÷ (Q x 0.0036)

= forty two ÷ (58 x zero.0036)

= 201.1kWh/ML

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

Step four: Calculate the pumping value

Having calculated the facility used to pump a megalitre, if you know the cost per kWh, you’ll be able to calculate the cost of pumping.
The charges per kWh may be troublesome to work out exactly if your provider has completely different rates for day or night time, weekends, and so forth so you must contact your supplier for assist to work this out.
Pumping costs

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

= $50.25 per ML

Measuring pump efficiency

Irrigation pump efficiency is a measure of how properly the pump converts electrical energy into helpful work to move water.
The goal of careful pump selection and common pump upkeep is to have the pump performing as effectively as potential (ie transferring probably the most water for the least power required). Efficient pump operation minimises working prices per megalitre pumped.
Pump efficiency of 70 per cent to 85 per cent ought to be achievable in most circumstances. An acceptable minimum for a centrifugal irrigation pump is sixty five per cent, and 75 per cent for a turbine pump.
An efficiency figure below these means either the mistaken pump was chosen for the job, the pump is worn and wishes repair or maintenance is needed.
The key to containing your pumping costs is to frequently monitor your vitality utilization and verify on any vital change that means attention is needed.
To calculate pump effectivity, you should know the circulate fee (Q) and the pump stress, or total head (H or TH) of the system. The pressure and circulate that a pump is working at known as the responsibility or duty point. Pump efficiency varies over the range of potential duties for any specific pump.
An enough estimate of whole dynamic head for surface techniques 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 peak of the water above the discharge, that is, water stage to water level, plus the losses as a result of friction in 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 operating stress. This reading must be converted to equal metres of head, this is additionally generally referred to as Pressure Head.
New pumps usually have a stress gauge put in but they often endure physical injury quickly. A better technique is to fit an access level on the delivery aspect of the pump where you presumably can briefly install a pressure gauge everytime you wish to take a studying. The gauge can be simply indifferent when not wanted.
A change within the pump operating strain via the season or across seasons, when irrigating the same block or shift, instantly tells you one thing has modified.
A sudden discount normally signifies a new leak or a blockage on the suction aspect; a gradual reduction usually indicates put on of the impeller or sprinkler nozzles; and a rise usually suggests a blockage somewhere within the system downstream of the strain gauge.
Pressure may be regarded as equivalent to a pipe of water of a sure peak in metres. This is known 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 pressure gauge reads solely in psi, convert to kPa by multiplying by 6.9.
For instance: 40 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 supply water degree, 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 5 metres.
Most problems with pumps positioned above the water level occur in the suction line, so ensure every thing correct. Common problems embrace blocked inlet or foot-valve or strainer, pipe diameter too small, pipe damaged or crushed, suction peak too nice, or air trapped on the connection to the pump.
Turbine and axial circulate pumps have to be submerged to operate, in order that they usually do not have any suction head.
For instance:
Pressure Head = 27.6m

Suction head = four.0m

Total Head = 31.6m

Another useful figure that can now be calculated is the pumping cost per ML per metre of head. This permits a meaningful comparability between totally 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 efficiency (Me)

Electric motors have an effectivity worth. That is, they lose a few of the power going into them as heat. This energy loss modifications with the dimensions of the motor. The desk under is a suggestion for motors operating at full load.
Submersible motors lose about 4 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 through lengthy electrical cables can also be important so this should be checked with an electrical engineer.
Step 7: Determine transmission losses (Df)

If the engine is not directly coupled to the pump, there’s a loss of power by way of the transmission. This loss is taken into consideration by what is termed the drive issue (Df).
Step 8: Calculate pump efficiency (Pe)

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

This instance contains the info 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 × 0.9)

= 1832.8 ÷ 34.02

= 53.9 per cent

Step 9: Calculating potential financial savings

Most centrifugal pumps are designed to operate with no less than seventy five per cent efficiency, and most turbine pumps are designed to function with a minimal of eighty five per cent efficiency.
The pump in our example is only about 54 per cent environment friendly, so how a lot can be saved by enhancing the effectivity from 54 per cent to 75 per cent?

Take this example:
If our pumping price 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 0.72)

= $50.25 – 36.18

= $14.07

If 900ML are pumped during a season, the whole cost saving is $14.07 × 900 = $12,663.
If impeller wear is the problem and the value of replacement is $10,000, it might be paid for in lower than one season. After that, the savings are all increased revenue.
Notice that a reduction within the pump effectivity figure of 21 per cent (75 per cent to 54 per cent) causes an increase in pumping value of 39 per cent ($36.18/ML to $50.25/ML).
Other components that have an effect on price and pump effectivity

There are two different variables affect value and pump efficiency: pump pace and impeller dimension.
Pump pace

You must know the pump velocity in order 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 electrical motor, the velocity 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 end result of the pace of electrical motors varies a little, it might be good to examine your motor velocity with a rev counter.
If the motor just isn’t immediately coupled to the pump, the velocity is altered by the gearing ratio of the transmission. Gear drives usually 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 certain the pump is stopped earlier than measuring the pulleys).
A complication that can happen when figuring out the fee and effectivity revolves around Variable Speed Drives (VSD), also referred to as Variable Frequency Drives (VFD).
VSDs have gotten increasingly well-liked as their worth reduces because of the benefits they offer. These items are added to electrical motors and permit the speed to be altered by changing the frequency of the alternating present. They allow electrically pushed pumps to have their speed set at exactly what is required for the pump duty and they remove the necessity for throttling the irrigation system using valves.
Savings of one quarter of the same old power consumption are sometimes reported by irrigators, and could also be as much as half relying on the situation. For determining the price and effectivity of a pump, the measurements outlined in this article must be made several instances with the pump set at totally different typical speeds.
Impeller measurement

Impeller put on has the same effect as a discount in impeller measurement so you have to know the dimensions 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 discover out the scale by dismantling the pump and measuring it, or asking the person who made the change.
Sometimes an impeller is deliberately decreased in diameter to adjust the pump’s performance and acquire a particular responsibility.
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 issue

Power factor may also considerably affect your working costs and maybe the operation of your pump as nicely.
Measuring performance

Keeping track of your pump’s efficiency and costs is not troublesome. It could save you some huge cash and keep your irrigation system performing properly.
If you establish your pump is working beneath the appropriate minimal degree, check the inner condition for wear or upkeep and the suitability of the pump for its present duty, or take steps to improve the drive or replace it with a VSD.

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