How to balance power quality and energy efficiency
Commercial and residential buildings use 40% of our energy and 70% of electricity in the U.S., while the industrial sector consumes about 30% of the energy share. Any wasted electricity not only contributes to U.S. greenhouse gas emissions and places added stress on the grid, it’s a major financial cost to businesses.
Fortunately, as energy efficient technologies have evolved, the business and environmental case for upgrading projects has been steadily gaining traction across industries. Over the past few decades, there has been a general migration toward power electronics that provide better control, lower maintenance costs and much higher efficiencies.
These include variable speed drives to replace standard motors, LEDs to replace incandescent/fluorescent lights and switched-mode power supplies to replace conventional power supplies. However, what most people don’t realize is that energy-efficiency projects can cause power quality to deteriorate significantly, which can cause significant problems in facility operations.
Power quality and reliability issues cost the U.S. economy at least $119 billion each year. Because approximately 80% of all power quality problems originate from the customer’s side of the meter, it’s up to facility owners, managers, designers and high-tech equipment users to better understand and manage power quality issues.
Consulting engineers play a big role here; systematically planning for power quality monitoring and mitigation ahead of time is key to overcoming these challenges. Energy-efficiency equipment can provide benefits in one area while adversely influencing another.
The impact of power quality on energy efficiency
A piece of equipment, process or system that operates inefficiently can still have great power quality. Motors once used gearboxes and belts to control the speed of a driven load. This approach is extremely energy inefficient and maintenance heavy, but the impact on power quality is negligible. The momentum toward more energy-efficient solutions has increased the pace of replacement of inefficient motors and gearboxes with VSDs. They are also advantageous from both the perspectives of initial capital expense and the ongoing operations and maintenance costs perspective.
Unfortunately, VSDs and other power electronics like LEDs and uninterruptible power supplies can create serious waveform distortion and impact power quality where legacy technologies like motors and gearboxes did not. By leveraging the newer and more efficient technology, power quality issues may be created where there previously were none. For example, harmonics (a form of waveform distortion) may be introduced, creating opportunities for equipment malfunctioning and reduced operating life.
Conversely, poor power quality/reliability often leads to reduced energy efficiency. Overvoltages, undervoltages and phase imbalances can adversely impact both a facility’s production quality and the equipment used to make the product.
For example, a voltage transient can damage a motor’s stator winding insulation, requiring the motor to be rewound reducing its efficiency up to 5%. Because motors are significant energy consumers, this incremental difference can add up to significant energy consumption and costs over the life of the motor.
As another example, a voltage sag may cause a process to trip, causing products to be scrapped, resulting in wasted material (and the energy used to make the scrapped product). Not to mention that restarting a facility after an outage or incident is a serious proposition, involving lots of wasted energy and loss of productivity.
Overcoming the Catch-22
The negative impacts of the symbiotic relationship between efficiency equipment and power quality can be drastically minimized if systems are properly designed and fortified with connected technologies to help organizations manage their power distribution better. But this doesn’t always happen, at least not at the right time.
To illustrate, let’s say a facility is going through a large-scale energy-efficiency project to replace old drives with variable frequency drives. The proposal outlines the projected cost savings from the upgrades, but power quality problems are unforeseen at that point and are not factored in. It’s very possible that years later, unexplained outages and other strange electrical conditions will arise. This prompts the facility owner to have power quality mitigation equipment installed to correct the issues after the fact, but this is a far more expensive solution.
If local power quality monitoring and correction equipment was included in the proposal from the start, the budget may go up 5% to 10% but it dramatically reduces the risk of serious unplanned costs incurred down the road. The same is true for other energy-efficiency projects like LED retrofits. Assess what the cost would be and see if you could live with the consequences if power quality doesn’t get factored into original design.
Although it’s undoubtedly important for buildings to take advantage of the latest efficiency and sustainability upgrades, especially in today’s Industrie 4.0 environments, ignore power quality at your peril. The two-way street between efficiency and power quality requires a holistic approach to design and operation. Consultants and engineers need to be “PQ-ready,” as opposed to focusing on after-the-fact mitigation.