Editor's Note: This is the conclusion of a series based on Optimizing Pumping Systems: A Guide to Improved Energy Efficiency, Reliability, and Profitability, written by pump systems experts. This new guidebook continues the mission of Pump Systems Matter and the Hydraulic Institute to advance knowledge on pumping systems.
Click here for Part One, Part Two, Part Three, Part Four and Part Five.
In United States industrial plants, more than 40 million electric motors convert electricity into useful work. These motors consume about 60 percent of the electricity used in the industry. Increasing the energy efficiency of these existing motor systems can lead to dramatic energy savings nationwide. Pump system optimization is one of the most important ways to affect improvement.
Many installed pumping systems operate below best efficiency. Slight improvements in component efficiency will yield slight minor decreases in energy costs, whereas entire pumping system optimization can reduce energy costs by more than 20 percent.
Installed pumping systems operating below best efficiency often experience above average failure rates. Between 1991 and 1994, the Finnish Maintenance Society studied 20 plants and the performance of 1690 pumps. The pump malfunctions that were observed were categorized into 34 individual fault types under eight representative headings (see Table 1).
Economic justification of a pumping system improvement is critical to management's decision to advance or abandon the project. Development of a successful system optimization LCC program can help make the project more attractive.
Potential Energy Savings
Motor winding insulation eventually breaks down, even among motors that have been properly maintained during their life. If a motor's winding temperatures exceed the rated values for long periods, its insulation tends to break down more quickly. In motor applications below 37-kW (50-hp), the most common option is simply to replace the existing motor with an equivalent one. High efficiency motors should be considered in such cases since they are typically 3 to 8 percent more efficient than standard motors.
In larger applications, it may be more economical to rewind an existing motor. However, it is important to note that the rewinding process may decrease the motor efficiency. Note that in high-use applications, the efficiency advantage of high efficiency motors often provides an attractive payback period.
The Energy Policy Act (EPAct) of 1992 set minimum efficiency standards that went into effect in 1997 for most general-purpose motors from 1- to 200-hp. In addition, the National Electrical Manufacturers Association's NEMA PremiumTM energy efficiency motors program describes premium efficiency motors as those with even higher efficiencies than the levels established by EPAct. Premium efficiency motors can be cost-effective for pumps with many hours of operation.
Pumps directly support the production processes in many industrial plants and run as often as, or longer, than any other equipment in the facility. Energy consumption by long running pump systems can result in a substantial addition to a plant's annual operating costs. About 25 percent of all the energy consumed by motor driven equipment in United States manufacturing facilities is used to operate pumps (see Table 2). This makes pumping systems critical in the reduction of energy consumption in motor driven systems.
Component Approach
Plants are usually assembled as components or part of a process/component. The components are typically supplied by manufacturers that specialize in that field. When the engineering, procurement and construction (EPC) organization sends out bid packages for a plant, the package typically only contains the specifications related to the individual bidder's products. This practice prevents the respective component suppliers from fully understanding how their product will be applied. This practice also results in misapplied, inefficient equipment installations, specifically pumps and motors.
Similar to the way that a predictive maintenance (PM) schedule minimizes expensive repairs, a well-designed system can avoid higher-than necessary operating costs. Using a life cycle cost perspective during initial system design, or while planning system upgrades and modifications, can reduce operating costs and improve system reliability.
Overly Conservative or Improper Pump Selection
Improper pump selection is typically due to the lack of a systems approach as well as failure to model the pumping system. Again, this is due to use of the component approach when designing a plant. Conservative engineering practices often result in the specification, purchase and installation of pumps that exceed process requirements. Engineers often decide to include a margin of safety in sizing pumps to compensate for uncertainties in the design process. Anticipated expansions in system capacity and potential fouling effects add to the tendency to source pumps that are "one size up" from those that meet system requirements.
Unfortunately, oversizing pumps adds to system operating costs in terms of both energy and maintenance requirements. These costs are often overlooked during the system specification process. Because many of these operating and maintenance costs are avoidable, correcting an oversized pump can be a cost-effective system improvement.
Installation and Operation
Initial installation of a pumping system, particularly sub-base preparation, is critical to the life cycle cost. Structurally loose machinery will experience higher levels of vibration leading directly to increased wear.
Pumps are often used to maintain fluid levels in tanks by draining or filling them as necessary. Many systems rely on a level control system to activate the pumps automatically. This practice can lead to unreliable pump operation, especially in large pumps. Large pumps have high starting currents, and therefore generate higher friction losses during operation. Repeatedly stopping and restarting a pump can also accelerate seal wear. The mechanical seals in many pumps rely on a lubricating film of system fluid that develops within the first two revolutions. Investigate pump/motor applications designed to handle repeated starting and stopping.
Maintenance
Problems such as cavitation, frequent energizing and de-energizing of a pump motor and valve seat leakage can increase maintenance requirements and decrease the length of time between repairs. Seal and bearing manufacturers often provide a mean time between failure (MTBF) for a particular product. If the actual time to failure is much less than the manufacturer's recommended interval, the cause of the failure should be assessed. Predictive maintenance techniques determine the rate at which a problem is developing and allow operators to plan for equipment repairs. Some predictive maintenance techniques and their advantages are listed in Table 3.
Making a Business Case
Many energy efficient projects provide additional benefits that may not be immediately apparent to plant and corporate managers. These benefits include:
- Increased productivity
- Lower maintenance costs
- Reduced costs of environmental compliance
- Lower production costs
- Reduced waste disposal costs
- Improved product quality
- Improved capacity utilization
- Improved reliability
- Improved worker safety
Decreased energy costs coupled with these benefits should be a strong incentive for implementing a pumping system project. However, some corporate managers may need to be reminded of the benefits of energy cost savings. The investment that improves pump system efficiency will yield annual savings via reduced energy costs, and may therefore be viewed as a new source for capital income to the corporation. Additionally, increased pumping system efficiency may capture shareholder value.
The financial analysis of a pumping system investment should include the time value of money and be represented in one of the following ways:
- Net present value
- Internal rate of return
- Life cycle costs
- True cost of energy
Life Cycle Costing
A payback period is the time required for the net benefits of an investment to accrue to the point where they equal the cost of the initial outlay. For a project that returns benefits in consistent annual increments, the simple payback is equal to the initial investment divided by the annual benefit. The simplicity of simple payback makes it an ideal measure of project economics for use by plant and corporate managers in quick decisions. It is important to note that simple payback is an approximation and does not take into account the time value of money. More sophisticated analyses that take into account factors such as discount rates, tax impacts and the cost of capital include net present value and internal rate of return.
Analyzing from an Integrated System Perspective
Many organizations consider only the initial purchase and installation costs of a system. However, plant designers and managers will benefit from evaluating the LCC of different solutions before installing major new equipment or carrying out a major overhaul.
Conclusion
A proposal for a pumping system improvement project can be made attractive to corporate decision makers if the facility manager does the following:
- Identifies opportunities for improving pumping system efficiency
- Determines the life cycle cost of attaining each option
- Identifies the option(s) with the greatest net benefits
- Collaborates with financial staff to identify current corporate priorities
- Generates a proposal that demonstrates how the benefits of the pumping system project will directly respond to current corporate needs
Developing successful energy projects begins with laying the groundwork to support the project. Ideally, it starts with a facility reward program for cost-saving capital equipment projects and appropriately recognizes employees for their efforts. However, most of the time, the groundwork is done by a motivated individual who takes pride in the job and is inspired by what other facilities have done.
References:
- Optimizing Pumping Systems: A Guide for Improved Energy Efficiency, Reliability and Profitability (available at www.pumps.org)
- Comprehensive ANSI/HI Pump Standards covering definitions, nomenclature, application, installation, operation, maintenance guidelines and testing of pumps (available at www.pumps.org)
- Pump Life Cycle Cost: A Guide to LCC Analysis for Pumping Systems (available at www.pumps.org)
- Variable Speed Pumping: A Guide to Successful Applications (available at www.pumps.org)
- Mechanical Seals for Pumps: Application Guidelines (available at www.pumps.org)
- Pump Systems Matter website, www.pumpsystemsmatter.org, contains a matrix of available systems analysis tools, Pump Systems Improvement Modeling (PSIM) tool, case studies, articles and other resources
Pumps & Systems, November 2008
