As a rule of thumb, when rewinding costs exceed 60% of the costs of a new motor, purchasing the new motor may be a better choice . When rewinding a motor, it is important to choose a motor service center that follows best practice motor rewinding standards in order to minimize potential efficiency losses. An ANSI approved recommended best practice standard has been offered by the Electric Apparatus Service Association for the repair and rewinding of motors . When best rewinding practices are implemented, efficiency losses are typically less than 0.5% to 1% . However, poor quality rewinds may result in larger efficiency losses. It is therefore important to inquire whether the motor service center follows EASA best practice standards . Maintenance. Motor maintenance measures can be categorized as either preventative or predictive. Preventative measures, the purpose of which is to prevent unexpected downtime of motors, include electrical consideration, voltage imbalance minimization, load consideration, and motor ventilation, alignment, and lubrication. The purpose of predictive motor maintenance is to observe ongoing motor temperature, vibration, large round garden pots and other operating data to identify when it becomes necessary to overhaul or replace a motor before failure occurs .
The savings associated with an ongoing motor maintenance program are significant, and could range from 2% to 30% of total motor system energy use . Properly sized motors. Motors that are sized inappropriately result in unnecessary energy losses. Where peak loads on driven equipment can be reduced, motor size can also be reduced. Replacing oversized motors with properly sized motors saves, on average for U.S. industry, 1.2% of total motor system electricity consumption . Higher savings can often be realized for smaller motors and individual motor systems.To determine the proper motor size, the following data are needed: load on the motor, operating efficiency of the motor at that load point, the full-load speed of the motor to be replaced, and the full-load speed of the replacement motor. The U.S. DOE’s Best Practices program provides a fact sheet that can assist in decisions regarding replacement of oversized and under loaded motors . Additionally, software packages such as MotorMaster+ can aid in proper motor selection. Adjustable speed drives .21 Adjustable-speed drives better match speed to load requirements for motor operations, and therefore ensure that motor energy use is optimized to a given application. Adjustable-speed drive systems are offered by many suppliers and are available worldwide. Worrell et al. provide an overview of savings achieved with ASDs in a wide array of applications; typical energy savings are shown to vary between 7% and 60%. Energy audits carried out at seven fresh fruit and vegetable processing plants in California estimated simple payback periods for ASDs ranging from 0.8 to 2.8 years . Two published case studies on applications of ASDs in the U.S. fruit and vegetable processing industry report similar benefits.
At Odwalla Juice Company’s Dinuva, California, facility, an energy audit estimated that the installation of ASDs on the facility’s glycol pump motors would save the company $31,500 in electricity costs per year with a payback period of six months . In a three-year study of the application of ASDs to ventilation fans in storage units for potatoes, electricity savings of 40% were reported, with two companies citing payback periods of less than two years . Power factor correction. Inductive loads like transformers, electric motors, and HID lighting may cause a low power factor. A low power factor may result in increased power consumption, and hence increased electricity costs. The power factor can be corrected by minimizing idling of electric motors , replacing motors with premium-efficient motors , and installing capacitors in the AC circuit to reduce the magnitude of reactive power in the system. Minimizing voltage unbalances. A voltage unbalance degrades the performance and shortens the life of three-phase motors. A voltage unbalance causes a current unbalance, which will result in torque pulsations, increased vibration and mechanical stress, increased losses, and motor overheating, which can reduce the life of a motor’s winding insulation. Voltage unbalances may be caused by faulty operation of power factor correction equipment, an unbalanced transformer bank, or an open circuit. A rule of thumb is that the voltage unbalance at the motor terminals should not exceed 1%. Even a 1% unbalance will reduce motor efficiency at part load operation, while a 2.5% unbalance will reduce motor efficiency at full load operation.As with motors, it is important to take a systems approach when assessing pump energy efficiency improvement opportunities within a facility. For example, although an individual pump might be operating efficiently, it could be generating more flow than the system requires for a given application and therefore wasting energy. Thus, it is important to not only assess individual pump efficiencies, but also to assess how well the various end uses in a facility’s pump system are being served by its pumps .
It is also important to consider that the initial capital cost of a pump is typically only a small fraction of its total life cycle costs. In general, maintenance costs and energy costs represent by far the most significant fraction of a pump’s total life cycle costs. In some cases, energy costs can account for up to 90% of the total cost of owning a pump . Thus, the decision to make a capital investment in pumping equipment should be made based on projected energy and maintenance costs rather than on initial capital costs alone. The basic components in a pump system are pumps, drive motors, piping networks, valves, and system controls. Some of the most significant energy efficiency measures applicable to these components and to pump systems as a whole are described below.Pump demand reduction. An important component of the systems approach is to minimize pump demand by better matching pump requirements to end use loads. Two effective strategies for reducing pump demand are the use of holding tanks and the elimination of bypass loops. Holding tanks can be used to equalize pump flows over a production cycle, which can allow for more efficient operation of pumps at reduced speeds and lead to energy savings of 10% to 20% . Holding tanks and can also reduce the need to add pump capacity. The elimination of bypass loops and other unnecessary flows can also lead to energy savings of 10% to 20% . Other effective strategies for reducing pump demand include lowering process static pressures, minimizing elevation rises in the piping system, and lowering spray nozzle velocities. Controls. Control systems can increase the energy efficiency of a pump system by shutting off pumps automatically when demand is reduced, or, alternatively, by putting pumps on standby at reduced loads until demand increases. In 2000, Cisco Systems upgraded the controls on its fountain pumps so that pumps would be turned off automatically during periods of peak electrical system demand. A wireless control system was able to control all pumps simultaneously from one location. The project saved $32,000 and 400,000 kWh annually, representing a savings of 61.5% in the total energy consumption of the fountain pumps . With a total cost of $29,000, large round pots the simple payback period was 11 months. In addition to energy savings, the project reduced maintenance costs and increased the pump system’s equipment life. High-efficiency pumps. It has been estimated that up to 16% of pumps in use in U.S. industry are more than 20 years old . Considering that a pump’s efficiency may degrade by 10% to 25% over the course of its life, the replacement of aging pumps can lead to significant energy savings. The installation of newer, higher-efficiency pumps typically leads to pump system energy savings of 2% to 10% . A number of high-efficiency pumps are available for specific pressure head and flow rate capacity requirements. Choosing the right pump often saves both operating costs and capital costs. For a given duty, selecting a pump that runs at the highest speed suitable for the application will generally result in a more efficient selection as well as the lowest initial cost . Properly sized pumps. Pumps that are oversized for a particular application consume more energy than is truly necessary. Replacing oversized pumps with pumps that are properly sized can often reduce the electricity use of a pumping system by 15% to 25% . Where peak loads can be reduced through improvements to pump system design or operation , pump size can also be reduced. If a pump is dramatically oversized, often its speed can be reduced with gear or belt drives or a slower speed motor. The typical payback period for the above strategies can be less than one year . The Welches Point Pump Station replaced one of their system’s four identical pumps with a smaller model .
They found that the smaller pump could more efficiently handle typical system flows and the remaining three larger pumps could be reserved for peak flows. While the smaller pump needed to run longer to handle the same total volume, its slower pace and reduced pressure resulted in less friction-related losses and less wear and tear. Installing the smaller pump has reduced the pump system’s annual electricity use by more than 20%. Furthermore, it was estimated that using this approach at each of the city’s 36 stations would result in annual energy savings of over $100,000. In addition to the energy savings projected, less wear on the system was expected to result in less maintenance, less downtime, and longer life for the equipment. Additionally, the station noise was significantly reduced with the smaller pump. Multiple pumps for variable loads. The use of multiple pumps installed in parallel can be a cost-effective and energy-efficient solution for pump systems with variable loads. Parallel pumps offer redundancy and increased reliability, and can often reduce pump system electricity use by 10% to 50% for highly variable loads . Parallel pump arrangements often consist of a large pump, which operates during periods of peak demand, and a small pump , which operates under normal, more steady-state conditions . Because the pony pump is sized for normal system operation, this configuration operates more efficiently than a system that relies on a large pump to handle loads far below its optimum capacity. For example, one case study of a Finnish pulp and paper plant indicated that by installing a pony pump in parallel with an existing larger pump to circulate water from a paper machine into two tanks, electricity cost savings of $36,500 per year were realized with a simple payback period of just 6 months .Trimming an impeller is slightly less effective than buying a smaller impeller from the pump manufacturer, but can be useful when an impeller at the next smaller available size would be too small for the given pump load. The energy savings associated with impeller trimming are dependent upon pump power, system flow, and system head, but are roughly proportional to the cube of the diameter reduction . An additional benefit of impeller trimming is a decrease in pump operating and maintenance costs. To reduce energy consumption and improve the performance of its beer cooling process, the Stroh Brewery Company analyzed the glycol circulation system used for batch cooling of beer products at its G. Heileman Division brewing facility in La Crosse, Wisconsin. By simply trimming down the diameter of the pump impeller and fully opening the discharge gate valve, cooling circulation system energy use was reduced by 50%, resulting in savings of $19,000 in the first year. With a cost of $1,500, the simple payback period for this measure was about one month .Avoiding throttling valves. Throttling valves and bypass loops are indications of oversized pumps as well as the inability of the pump system design to accommodate load variations efficiently, and should always be avoided . Pump demand reduction, controls, impeller trimming, and multiple pump strategies should always be more energy-efficient flow management strategies than throttling valves. Replacement of belt drives. According to inventory data of U.S. industrial pumps, up to 4% of pumps are equipped with V-belt drives . Many of these V-belt drives can be replaced with direct couplings, which are estimated to lead to energy savings of around 1%. Proper pipe sizing. Pipes that are too small for the required flow velocity can significantly increase the amount of energy required for pumping, in much the same way that drinking a beverage through a small straw requires a greater amount of suction.