Throughout the United States, water production and distribution costs are rising. Lower water levels coupled with growing population drive ever-increasing pumping costs as agricultural users and water providers struggle to meet consumer demand. Seasonal operations, lack of benchmarking data, and the first-cost orientation of pump operators result in functional, yet sub-optimal water system operations.
The efficiency of a pump may differ considerably from the installed efficiency for two main reasons.
Significant energy savings (typically 25-30%) in water pumping and distribution systems is possible. More specifically, the overall pumping system efficiency depends on motor efficiency, pump selection, piping layout and operational and maintenance conditions. Main factors contributing to pump efficiency include:
“The great aim of education is not knowledge but, action.” – Herbert Spencer
A pump test or an energy audit will assist you in:
Based on the experience on more than 15,000 pumps throughout the Western States, customers are typically saving as much as 30% on their pumping energy costs while taking advantage of thousands of dollars’ worth of utility energy-efficiency rebates.
The three well-known main pump types that are applied fora variety of uses include:
Centrifugal pumps are used in low head applications such as pumping from reservoirs, lakes, streams, and shallow wells. They are also used as boosters in water distribution and irrigation pipelines. Centrifugal pumps should be completely filled with water or “primed” before they can operate. The suction line including the pump should be filled with water and free of air, thereby making the airtight joints and connections very important components on the suction line. The suction lift of centrifugal pumps is limited to within 20 vertical feet of the water surface. The repair decisions for centrifugal pumps vary by application and typically performed when the flow rate declines to a level where other factors cannot be adjusted in the field.
Deep well turbine pumps are typically used in cased wells or where the water surface is below the practical limits of a centrifugal pump. Turbine pumps are also used with surface water systems. Since the intake for the turbine pump is continuously under water, priming is not a concern. The efficiency of these pumps is comparable or higher than most centrifugal pumps. They are usually more expensive than centrifugal pumps and comparatively more difficult to inspect and repair. Turbine pumps are generally repaired when the overall plant efficiency (OPE) reached 45% range.
The following table lists typical losses at major parts and compares the losses in efficient and inefficient pumping plants in turbine well pump.
|Types & Location of Losses||Efficient Plant||Inefficient Plant|
|Motor Bearing and Electrical Loss||9 %||9 %|
|Column & Shaft Loss||4 %||5 %|
|Pump Loss||14 %||31 %|
|Total Losses||27 %||45 %|
Submersible pumps can be selected to provide a wide range of flow rate and head combinations. A submersible pump is a turbine pump close-coupled to a submersible electric motor. Both pump and motor are suspended and submersed in the water. Similar to turbine pumps, submersible pumps are typically repaired when they reach 45% range. These pumps can be expensive due to the pump located down hole. This means installation and maintenance will be more difficult and may involve a lot more equipment. A submersible pumps prevents cavitation because it pulls the fluid rather than pushing the fluid by converting rotary energy into kinetic energy into pressure energy. Since the pump is submerged in water, a submersible pump is usually very efficient because they don’t have to spend a lot of energy moving water into the pump. Water pressure pushes the water into a submersible pump, thus saving a lot of energy.
Extending a pump’s life can be easily increased with the right maintenance plan. The effective useful life of a pump can change depending on the pump type and application. Under normal conditions, water pumps can last as long as 15 years without needing to be replaced. A list of maintenance plans are shown below3 :
Although there are many approaches to maintain and extend a pump’s useful life, we strongly recommend using both Predictive Maintenance and Machinery History for the best results while keeping the plan within budget. Performing a pump test, at least once every two years, under normal conditions, is recommended for continuing a Predictive Maintenance log and comparing results to your machinery’s history. It is also recommended to regularly check the following parameters for any of the recommended maintenance programs:
Visual inspections should also be performed regularly to find and troubleshoot wear, corrosion, discoloration, evidence of rubbing, damage, clogging, and for missing or additional parts.
If you have had a pump test performed and the results show that the Overall Pump Efficiency (OPE) is below 55%, you might want consider having a pump overhaul. The pump overhaul measure is a general term for work done to the pump system, which may include extensive maintenance such as rewinding the pump’s motor, rebuilding the pump’s bowl, painting, sand blasting, impeller trimming, drilling wells deeper, and more. Pump overhauls may also include part replacements such as installing new motors, pump bowl and pipe replacements, etc. Depending on the utility provider that you are using to apply for rebates, there are multiple methodologies for estimating and quantifying energy savings due to pump overhauls. The level of accuracy and verification needed may change depending on your utility provider, but in general, the best methodology for estimating and verifying pump overhaul energy savings is as follows:
If you have a variable load system, the installation of a VFD will most likely be very beneficial. For a pump, a variable load system is any system in which the end use of the water is not constant. For example, if your irrigation needs to change throughout the season, through a range of acre feet of water delivered, then you have a variable load system. In pumping terms, if you need 10,000 GPM for half of the year, and 5,000 GPM for the other half, you also have a variable load system. There are a multitude ways these variable load systems are typically controlled including throttling valves, bypass and control valves, and modulation of multiple pumps. Although these control methods to get the job done and provide the water demand are needed, they also waste huge amounts of energy, water, and operating costs. Using a VFD to control the pump’s speed can provide more accurate water supply while cutting down operating and maintenance costs. Please see below for a picture of a VFD on centrifugal booster pumps.
N = Speed (RPM or Hz if referring to VFD’s frequency)
F = Flow (GPM, CFM)
P = Power (Horsepower or Watts)
H = Head (Feet, pounds per square foot, inches of water, etc)
Real-world pump systems do not meet all these criteria but the Affinity Law can still be applied if modified to better represent the situation. A common method is to reduce the variable, N, is by changing the exponent from 2 to 2.4, or somewhere in between. The geometry of the system will determine what the number will be. This modifies the affinity law’s power equation to:(This modifies the affinity law’s power equation to: )
Please Contact us for more details on finding the energy savings you can achieve with a VFD installation.
If you have multiple pumps serving one end use water demand, you might want to consider a pump sequencing analysis. This analysis will look at the parameters governing your current control sequence and proposes a more efficient operating control scheme. Sequencing the pumps correctly can result in energy savings by utilizing the more efficient pump first or by staging the pumps correctly so that the least amount of energy is used to pump the same amount of water. There are many ways to estimate the proper way to sequence multiple pumps in a pump system. One way is to find the energy intensity of each pump. The energy intensity is the energy per unit volume of water that is pumped (kWh/acre-feet or kWh/MG). Using this metric, we can determine if multiple well pumps can serve a single end use water demand. The pumps should be sequenced such that the pumps with the smallest kWh/MG are operated first with additional water supply needs met by operating the other pumps with greater kWh/MG. Note that the feasibility of this measure can also depend on the elevation level of the well pumps, as well as any blending requirements for the water supplied.
When creating your pump system there are two elements that will help determine what pump to use. One is the system curve of your entire pump system. The second is the pump curve of the pump you intend to use. The system curve describes how the relationship of all components in your system will have when producing your well. This includes the well characteristics, piping, and components attached to the system. The system curve will change if the process changes, if the system is closed or open, or the well characteristics change. Changing the pump will not change the system curve.
The other element is the pump curve. A pump curve is a graph that describes the characteristics of the pump operation. Pump performance curves describe the relationship between the head, power, efficiency, and the flow rate for the pump. Usually the flow rate will be the constant to which all other components are compared to. By understanding these two curves, you can properly determine the point at which your pump will operate the most efficient.
If you have any questions on how to determine what pump is right for your system, please Contact us.
Pump tests are very important for determining the current operating performance of the individual equipment or system. These tests will help you realize the right time for action. The typical Pump Efficiency Tests measure the following parameters:
Depending on the type of pump, the following parameters might be measured as well:
From these above listed parameters, the following can be calculated:
The end result of overall pump efficiency is calculated by dividing the output energy “water horsepower” by the total energy input to the pump. The equation for calculating the water horsepower (WHP) is given below:
The unit is then converted to kilowatts (kW) and divided by the measured power consumption to get the efficiency.
Pump Testing will also provide added benefits including:
Depending on type of pump, location of pump, and its accessibility, there are many ways to perform a pump test. Please consult with the pump tester on how to properly prepare for your test. Some testers may use flow measurement equipment that requires an access hole on the pump’s discharge pipe which may require that the pump be turned off to drill the small hole and insert the measurement device. Other measurement devices do not require these same provisions. The pump must be on and running under normal conditions during the pump test. If the pump is a well pump, the tester may need to run the pump for as long as 30-45 minutes to stabilize the pumping water level.
The pump tester will also need key information regarding the pump’s design parameters to make a complete analysis. The tester may ask for the following information:
If a well pump is running when the tester arrives, they might need to shut it off after the test measurements are taken in order to measure the “recovered water level” of the well. This usually takes 15 minutes and indicates valuable information about the current well performance.
Pumps can also be operating with a wide variety of flow and pressure outputs that are normal for their application. In this case, a multi-condition pump test will be needed to accurately measure the pump’s various conditions. A multi-condition test consists of taking the required measurements at several different flow rates and discharge pressures. This is useful in situations where the pump design is unknown or where aquifer or discharge conditions have changed substantially. It may also lead to a decision to install a variable frequency drives (VFD) to more efficiently control the pump.
There are only a few simple steps needed to schedule a pump test. First, you’ll need to contact one of the approved participating pump test companies near your facility. Please visit our Pump Tester Locator or contact us for help finding the right company for you.
Next, you’ll need to call the pump tester to schedule test during normal hours of operation as the pump will have to be running during the test. You might need a site access agreement form signed before the test is performed to certify that the test company had a legal right to access the pump.
To find out if you meet the requirements to receive a free pump test, please contact us for qualification. If you do, the pump test company will be paid directly through the program and all paper work will be handled for you. If you do not meet the requirement for complimentary pump test, you may have to pay for the full cost of the test.
Depending on how the water is used, there can be significant wasted energy for each unit of water lost. For example, if the water is being pumped from a boiler, there is wasted heating and pumping energy. As this suggests, wasted water can bring about multitudes of wasted operating costs. The energy savings for reducing water leaks depends on your graphical region and application. For example, the average energy intensity of water used in Southern California is much higher than in Northern California. This is due to the fact that Southern California imports about 50% of its water from the Colorado River and the State Water Project (SWP), which is more energy intensive than any source of water supply used in Northern California. Shown below is a graph comparing the energy intensities of different water uses in both Southern and Northern California.
For example, by reducing leaks to save 100 Million Gallons (MG) per year at a wastewater treatment plant, that could add up to save up to 250,000 kWh, at $0.10 / kWh, that equals potentially $25,000 a year in savings. For a typical 10 MGD wastewater treatment plant, this would mean only reducing their water consumption by 2.7% which can easily be done by repairing common leaks. In many cases, a pump overhaul will reduce leakage and increase the pump’s overall efficiency.
Water systems are dynamic systems in which any change in a particular portion of a system can affect other portions of the system. Hydraulic modeling allows for the accounting of interactive effects between the different components and parts of the system. Similar to the energy use and efficiency simulation modeling for buildings, water systems (especially with multiple zones with varying elevations), should be modeled to understand the overall opportunities and make recommendations for capital and operational investments. It is not only less time-consuming, but also more cost-effective to investigate how changing the system’s configurations will affect the system as a whole. The models enable water system operators and engineers to update and maintain their systems as they grow, and to further investigate the feasibility of potential water and energy efficiency opportunities. The models can simulate system pressure between different zones and can be used to visualize and control pressure, sequencing and valve selection, as well as monitor energy consumption to optimize operational performance of water systems. A water agency can more accurately and cost-effectively decide which improvements will be most effective, where to place storage tanks, and how to sequence them based on an on-going water systems model. In certain cases, depending on current system issues, a hydraulic system model can identify as much as a 50% reduction in energy use.
In short, hydraulic models allow for different “scenarios” to be simulated before physical changes are made to the system. Hydraulic models that are updated and maintained on a regular basis can serve as an excellent tool for monitoring the energy consumption of different pumps in order to optimize the performance of water systems. If you have a significant number of pumps and an extensive water system, you are a good candidate for developing a hydraulic model. Data from any data acquisition system, as well as measured data, allows for proper calibration of a hydraulic model to accurately represent the actual water system.
Energy savings can usually be found with new developments in technology. Pumps and motors are always being redesigned and improved to make them more cost effective. Even old technology might become more feasible for customers to purchase due to new material innovations and market changes. It is our goal to stay updated on new technologies that may benefit pumping systems and to keep customers informed of the new technologies. Please see the catalog below for recent updates.
PMMs also require feedback control to align the stator’s field with the magnetic poles of the rotor. The phase of stator windings is switched, or commutated, which requires more sophisticated controls. A PMM driven pump requires a VSD with closed loop vector control capabilities. The cost for permanent magnets and the VSD with proper control capabilities increases the cost of a PMM by 15-20% compared to a standard IM driven ESP/PCP with VSD control.
The figure above on the left shows the results of laboratory tests [IEEE Paper No. PCIC-2012-39] conducted to compare efficiency of a PMM over an IM (10HP per rotor) for the same motor size (240 HP). PMM showed about 10% increase in motor efficiency compared to an IM at different speeds. The figure on the right shows the difference in kW consumption at various production rates. At 3,000 barrels/day the difference in power is 42.4 kW, which at the energy costs of $0.15/kWh, will result in $4,580 in energy cost savings per month for a pump that operates 24/7.
If your ESP or PCP pump is due for replacement, or if you are planning to install new down-hole pump equipment, we recommend installing a PMM drive instead of a conventional IM drive. Given the substantial savings potential and possible incentives, choosing a PMM is preferred and will result in reduced energy costs per barrel of oil production.
Contact us for help determining if a PMM drive is the best option for you.