The pump is operating outside of its pump curve efficiency range.
The pump is worn or not of a proper design.
The flow of water is restricted or throttled on the suction (and/or) discharge side.
The electrical control system, i.e., VFD is not designed for the application. This is common in high head pumping systems where a VFD controls the whole flow in just a small band if Hz. VFDs are not always efficient in these cases.
The Distribution System is not routing and controlling the flow of pumped water properly to its destination, i.e., re-pumping or short circuiting, faulty PRVs, etc. (see System Modeling Efficiencies.)
Other Distribution System Problems, i.e., storage issues, leaks, corrosion, pipe age and quality, under sizing, etc.
Pump station pipe materials and fittings are corroded or tuberculated, increasing the friction coefficients.
The electrical Load Factor is too low and the head losses on the distribution system are excessive. Load Factor (LF) is a fractional number or percentage indicating the average amount of time per day a motor or pump runs, i.e., a Load Factor of 0.25 or 25% means the pump runs on average six hours per day.
The electrical system Power Factor (PF) is not efficient or too low.
The water system Peaking Factor is too high (above 2.0).
The pumping systems are not cooled properly.
Metering issues, such as old worn meters, no master metering strategy, and no leak detection. etc.
Pump curves and pump performance should be regularly reviewed and tested. Test each pump on at least four points on the curve. Have a VFD curve available if the pump is on a VFD and test at several speed points.
If you use the most economic utility power rate for your pumping systems, significant money can be saved.
If you pump during the designated off peak periods of the electrical utility, you can also save money by completely eliminating or reducing the Power Demand Charge. Adequate storage capacity is essential to follow this strategy.
If you use Variable Frequency Drives (VFDs) to increase your Load Factor, or use jockey type pumps, you reduce your costs by reducing your demand and energy charge.
If you have a high head loss on a pump plant, a VFD can reduce your energy cost by reducing the total dynamic pumping head.
If you are charged a power factor penalty, you can eliminate that charge by implementing power factor correction strategies.
Pump cycles and operation should always be selected for efficiency, yet be prepared for any emergency operation scenario.
Always match the VFD to the proper pump and pump curve.
Never use a restrictor valve to control the flow rate of a pump.
Run pumps more often (prioritize) based on their costs per unit of water pumped, also referred to Specific Energy. If possible, choose the most efficient pumps first in a system for pumping.
Carefully develop effective multiple pump rotation and lockout strategies.
Provide for pump back-up strategies.
Carefully review the necessity for pump trimming when using a VFD. Often the VFD acts as the pump trim.
Evaluate multiple and smaller pump designs, vs. one or two large pumps in a pumping plant.
Review well and pump designs to evaluate if a line drive pump is more efficient than a submersible pump system. Submersible motors are typically less efficient.
Implement SCADA and control system lockouts to prevent operators from running multiple pumps when not needed, or bumping pumps unnecessarily during an on- peak pumping period.
Provide engineered pressure and surge protection systems to better protect distribution infrastructure and pumps from wear, breaks, leaks, etc.
Provide or specify motor shaft grounding brushes to protect bearings on VFD operated pumps.
Typically small jockey type pumps should run first and as long as possible to extend the load factors as much as possible. A load factor above 80 % is not unrealistic, in fact it is preferred.
Regularly evaluate for service or replacement any old and worn pumping equipment.
Use high performance lubricants on motors for extended performance and lower operating temperatures, and maintain levels.
Well “pump to waste” cycles typically run pumps at their highest energy and power demands. Provide a back pressure or pressure sustaining valve in line with the pump control valve, or add a sustaining pilot on the pump control valve, to hold waste discharge pressures closer to the efficiency point on the curve. Ensure that these valves are not oversized. They should provide a significant back pressure simply as a function of their size. An alternative for a VFD controlled pump would be to run the waste cycle at a lower speed.
Evaluate your pump exercise and water testing strategies. Avoid running a pump for a short period just to exercise it. If a pumping system needs this, evaluate running it in an off-peak period or on a generator regularly. The same applies to running well pumps for a simple water test, when they would normally be idle for a month or more.
Ensure that your well and well pump performance matches its design characteristics and pump curve. Also monitor well static and dynamic drawdown and specific capacity over time. If there are irregularities—the pump may be worn, or the pumping column may be leaking into the well annular space. When changing or servicing well pumps, perform a video inspection to ensure that the well casing is in good condition. A corroded or malfunctioning casing and screen system will restrict flow into the well casing and lower drawdown levels, thus increasing energy and power requirements.
In summary, implement water pumping and operational management strategies similar to the following:
Reduce energy usage on pumping facilities by ensuring that pumps are not running at a level or in a configuration which increases head losses in the pumping or piping systems.
Eliminating a possible return flow loop or leak in a pumping station through relief/surge anticipator valves or emergency fire flow PRVs.
Review pump curves to better limit Variable Frequency Drives (VFD) to their optimum frequency range settings.
Avoid “across the line” starters for motors where possible. Reduced Voltage Soft Starters (RVSS) and VFD’s are usually better, depending on the application, and offer far better motor protection strategies.
Monitor temperatures and environmental variables better in all pumping and other remote facilities to get better controlled energy use for heating and/or cooling. Use motion detectors for lighting controls and install more efficient fluorescent (T5 or T8) or LED lighting.
Evaluate and implement better and more efficient cooling systems for the
larger pumping facilities, to not only save energy but extend pump life.
Improve the efficiency and reliability of larger HVAC heating and cooling systems by, monitoring air pressures, humidity, and other parameters. And to better control operation in the winter months, using the heating systems only when needed. Integrate HVAC controls into PLCs and integrate with system SCADA equipment. Investigate using the water itself for cooling and heating (i.e., Water Furnace technology).
Ensure where feasible, that pumps controlled by Variable Frequency Drives (VFDs) do not have their impellers trimmed, thus allowing for a wider range of operational flows and pressures.
Large pump motors should be wound with RTDs (temperature sensors), and associated motor protection relays, to better monitor motor winding conditions.
Establish power quality meters on larger facilities with daily SCADA logging capabilities.
The pump is operating outside of its pump curve efficiency range.
Pump curves and pump performance should be regularly reviewed and tested. Test each pump on at least four points on the curve. Have a VFD curve available if the pump is on a VFD and test at several speed points.
If you are charged a power factor penalty, you can eliminate that charge by implementing power factor correction strategies.
