Paying Attention To Power Factor

Looking to reduce energy use and emissions? Power factor correction helps facility management optimize power from the utility.

By Joy Silber

Facility managers cite energy efficiency as one of the top challenges they face each year. According to the U.S. EPA, the nearly five million buildings in the U.S. are responsible for nearly 20% of the nation’s energy use and greenhouse gas emissions. What’s worse, on average, 30% of the energy consumed in commercial buildings is wasted.

To reduce energy consumption and increase energy efficiency, many facility management executives are looking to renewable energy sources, such as solar or wind, to offset reliance on traditional electric power. Despite the growing prevalence of these solutions, there are drawbacks that can make alternative energy impractical for some, notably the significant upfront costs required to implement such a solution.

Another less expensive and more practical alternative is power factor correction, which makes existing utility electricity more efficient and delivers energy reductions of 10% or more. Power factor correction also offers significant environmental benefits on par with many renewable solutions. To understand how power factor correction works, first, let’s take a look at power factor.

A Primer On Power Factor

Power factor is a relatively dense topic, but essentially it is a measure of how efficiently electrical power is converted into useful work output. “Doesn’t all electrical power convert to perform work?” you might ask. Not exactly, and here’s why.

All inductive machines and devices that operate on AC systems, such as transformers, induction furnaces, and motors convert two kinds of energy: active energy, measured in killowatts (kW), to perform the actual mechanical work and heat, and reactive energy, measured in kilovolt-amperes-reactive (kVAR). The two types of energy together are referred to as apparent power, measured in kilovolt-amperes (kVA). To adequately power a load, the utility must supply enough energy to cover both the working and reactive currents.

To simplify this concept, consider a beer mug filled with your favorite brew. The mug capacity represents apparent power (kVA). The beer represents active power (kW). Don’t forget the foam, which represents reactive power (kVAR). Using this analogy, we can deduce the power factor by dividing the beer by the mug capacity, and it’s clear, you’re getting less beer than you’re paying for.

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Beer Analogy For Power Factor

The Downside Of Poor Power Factor

Obviously, the lower the power factor of a given piece of equipment, the less efficient it’s going to run. In the case of a data center, hospital, or manufacturing plant, there may be dozens of machines with poor power factor drawing excess energy every day, which not only costs money, but adds to carbon emissions.

Poor power factor can have significant economic and technical consequences for a facility. Consider that low power factor equipment has a high reactive power requirement. Therefore, that device requires a higher apparent power and thus a higher current. This results in increased energy consumption, higher utility costs, and potentially myriad additional costs associated with equipment, outages, and voltage drops. Consider also that utilities add a fee or penalty for reactive energy in excess of a set threshold for industrial or commercial customers.

Power Factor Correction

Power factor correction is a complex topic with clear benefits. Power factor correction helps bring the power factor closer to an optimal rating; thereby, reducing the amount of power an AC device must consume to generate its rated amount of power. Power factor correction effectively enables facilities to get more power out of the same amount of utility electricity.

Not surprisingly, there are numerous technical, economic, and environmental benefits associated with lower electricity consumption, particularly for large facilities.

  1. Energy reduction. A PFC system can reduce energy loss by up to 30 percent depending on the level of capacitive compensation.
  2. Energy efficiency. By optimizing power factor, facilities improve efficiency by increasing power quality to improve performance and reduce unplanned outages, while reducing harmonics stress and potential damage to your electrical network.
  3. Reduced equipment costs. Higher power factor allows for the use of smaller transformers, switchgear and cables and improves the reliability and lifespan of equipment.
  4. Lower carbon emissions. By reducing energy waste and overall consumption through PFC, facilities can significantly reduce the negative impact of carbon gas emissions. Power factor correction is calculated to generate potential savings in the European Union of about 48 terawatt hours (TWh) corresponding to 19 metric tons of CO2.

Solutions To Optimize Power Factor

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Capacitor bank (Photo: Schneider Electric)

To improve the power factor of an installation requires the use of a capacitor bank or energy compensator. These devices either supply or absorb reactive power to bring the power factor closer to its optimal rating. There are several factors to consider to optimize the performance of capacitor banks.

  1. Choose the optimum location. The actual location of a capacitor bank depends on the size and locations of the various loads. That said, to achieve the best results, the correction should be affected as close to the individual inductive items as possible.
  2. Decide the optimum level of compensation. This can be determined in two ways. The most common way is to review utility bills for the most heavily-loaded periods of the year — during the summer months, for example; then identify the highest fees enacted by the utility for reactive energy.
  3. Optimize power factor correction. The full potential of power factor correction can be enhanced by adopting certain measures:
  • Automatic capacitor banks provide the most economic benefit for low voltage loads
  • Installing automatic low voltage capacitor banks set to a power factor greater than the minimum to avoid reactive power fees, allows for full compensations without risk of overcompensation.
  • The use of capacitor banks even during periods when there is no charge for reactive energy can affect additional benefits in power factor correction systems.
  • To better manage large sites with multiple transformers, facility managers should consider devices for capacitor bank monitoring and control with built-in communications capabilities.

Power Factor Correction For Facility Management

Power factor correction has been in use for decades and is widely practiced in many countries as a method to reduce energy consumption and carbon emissions. While its potential to curb CO2 emissions is huge, lack of awareness has inhibited its use in some geographic areas. In the U.S., for example, renewable energy has gained more attention in recent years. However, the economic benefit of power factor correction for individual facilities is on par with renewable solutions and often generates a higher return on investment, while also minimizing waste and optimizing utility power.

power factorSilber is the senior manager, product management and business development of Power Solutions at Schneider Electric. With experience across multiple industries: food and beverage, mechanical, agriculture, and power transmission, she has held previous roles in national sales development, market segment management, marketing services management, and business development. Silber has a B.S. from North Carolina State University and is an active volunteer in her community.