As we’ve covered the past two weeks, installing an adjustable speed drive on all motor-driven systems may not be your best investment.
In certain applications, a drive can reduce your motor-related energy costs by 10 – 60%, recouping your investment within 24 months.[i][ii][iii][iv] The three questions in the first post in this series will help you to identify these beneficial applications. On the other hand, the second post in this series will help you ferret out those situations where a drive is a poor or potentially harmful investment.
Though these two posts, you may have discovered that an adjustable speed drive will not be the energy savings panacea that you hoped it would be. Hence, to conclude our “Does every motor need a drive?” series, here’s four ways to redeem energy savings from your motor-driven systems without installing a drive:
1. Fix your power quality problems
As we discussed last week, power quality issues include voltage variations (sags, swells, and interruptions), transients, waveform distortion, frequency variations, amplitude fluctuations, phase imbalances, and low power factor.
Power quality issues cost you both energy and money: First, your electric utility may be charging you a fee for how your power quality affects their grid, such as if your facility operates at a low power factor. Second, these power quality issues cause your motors to operate less efficiently, meaning that they consume more energy and produce less work. Third, poor power quality generates more heat in your motor, accelerating the degradation of the motor’s bearings and windings. This accelerated degradation
- shortens the motor’s useful life, adding to your capital replacement expenses;
- increases the frequency and scope of your motors’ maintenance needs, escalating your maintenance expenses; and
- raises the probability that the motor will fail, decreasing your production availability and possibly creating scrap or rework.
2. Shift your operations off-peak
While this recommendation doesn’t save energy, it can greatly reduce your energy expenses. Many power utilities offer time-of-use (TOU) rates that vary by season (summer vs. winter) and time of day (peak vs. off-peak). TOU rates reflect utilities cost to produce power during these periods, meaning that power used during high-use “peak” periods costs slightly more than fixed-rate service and substantially more than during low-use “off-peak” periods. Peak periods generally include early mornings and evenings in the winter (e.g., 5:00 am to 9:00 am and 5:00 pm to 9:00 pm October through May) and afternoons in the summer (e.g., 1:00 pm to 6:00 pm June through September), although the exact blocking varies by utility and location. Compared to a fixed, or flat, rate structure that charges the same electric rate all year long, switching to a TOU rate and shifting your operations to off-peak hours where practicable can save you up to 15% on your annual energy costs.
3. Replace your older motors
Efficiency standards for industrial induction motors evolved significantly over the past 25 years. Because motors sold today are up to 7% more efficient than motors sold 25 years ago and up to 3% more efficient than motors sold just 5 years ago, you can often justify replacing these older motors simply based on energy cost savings. This calculation should consider, at a minimum, the change in efficiency, the motor’s load, annual run-hours, and your electric rate; but this calculation can become quite complicated for motors operating at variable speeds and loads on tiered rate structures. [Teensy sales plug: Let Motors@Work run this analysis for you — request your customized demo today.]
4. Reengineer your process
Whereas replacing your motor may gain you a few efficiency points, the US Department of Energy (DOE) estimates that process improvements can reduce facilities’ energy use by up to 50%.[v]
The DOE reports that process reengineering alone can decrease facilities’ energy consumption by up to 30%.[vi] For example, imagine a raw-water pump station that currently operates a 750 Hp motor on a variable-frequency drive; the influent raw water from this station feeds directly into the water treatment plant. Perhaps this system has limited finished water storage, or perhaps its operators try to minimize the age of their finished water due to comply with local regulations or achieve certain water quality standards. Either way, the operators modulate the drive’s frequency set point throughout the day to match the demand for finished water — operating this motor, on average, at less than 50% of its load. At this load, the motor’s efficiency is approximately half what’s listed on its nameplate.
A more efficient process may use multiple parallel pump motors — for example, three 250 Hp motors with one connected to a drive. This reengineered process allows the operator to ramp flow up and down using the drive-connected motor, turning on the other two motors sequentially each time the drive-connected motor reaches 100% load. In addition to improving efficiency today, such modular designs easily expand to meet growing demand.
To push your energy savings towards 50%, DOE writes, requires process reengineering plus “the integration of advanced sensors and controls [that] enable optimization of the entire [motor-driven] system.” Continuing our water utility example, AWWA recently demonstrated that real-time sensors and controls allow water utilities to lower their system pressure, decreasing leakage and thereby reducing the quantity of water requiring treatment and associated energy expenses.[vii] To learn more, check out this white paper about how Motors@Work’s patent-pending analytics provides you with the intelligence you need to optimize your motor-driven systems.
To find out whether it’s economical to replace your motors, to shift your organization to TOU rates, or to install a drive, or to learn how to reduce your motor-related energy expenses by up to 30%, visit www.motorsatwork.com or email me.
Nicole Dyess is the Director of Client Solutions for Motors@Work, which provides cloud-based energy management solutions for maintaining and operating motors and motor-driven systems at their peak efficiency and lowest lifecycle cost.
[i] Siemens, “Variable Frequency Drives and Energy Savings” (2010).
[ii] Honeywell, “VFD Energy Savings and Payback Calculator” accessed 2016.
[iii] Rockwell Automation, “Energy savings with variable frequency drives: Invest in energy management with intelligent motor control solutions,” (2007).
[iv] ABB, “Energy efficiency: Using drives to control motors can lead to big savings,” accessed 2016.
[v] US Department of Energy, “Technology Opportunities to Reduce US Greenhouse Gas Emissions,” (Oak Ridge National Laboratory, 1997) as cited in “Scenarios for a Clean Energy Future,” by the US Department of Energy Interlaboratory Working Group (2000): Chapter 8. Similar comments also appear in “Improving Motor and Drive System Performance: A sourcebook for Industry,” (2008).
[vi] US Department of Energy, “Technology Opportunities to Reduce US Greenhouse Gas Emissions,” (Oak Ridge National Laboratory, 1997) as cited in “Scenarios for a Clean Energy Future,” by the US Department of Energy Interlaboratory Working Group (2000): Chapter 8. Similar comments also appear in “Improving Motor and Drive System Performance: A sourcebook for Industry,” (2008).
[vii] American Water Works Association (AWWA) & the Partnership for Safe Water, “TECH TIP: Distribution System Pressure Monitoring,” (July 2015).