smartconfiguration

Motor efficiency depends on power-factor correction, too

Richard Newell 

6/12/2009 8:52 AM EDT

Electric motor power efficiency has taken center stage. Individuals, corporations, and governments are increasingly interested in saving power, now that technology can make it possible and economy demands it. Advances in motor control algorithms and cost-effective electronic components for implementing motor drives are creating a revolution in virtually every electric motor market. Control of the power factor in an efficient manner also means less lost energy, both in the motor and drive electronics, and in the power grids supplying the electricity to the homes, offices, and factories where the motors are used. 

The potential energy savings are staggering. Over 40 million electric motors are used in the United States alone in manufacturing operations. Electric motors account for 65-70% of industrial electrical energy consumption and about 57% of all electrical consumption worldwide. Saving even a few percent of the world's estimated 16,000-plus terawatt-hours (TWh) annual consumption of electricity amounts to several hundreds of trillions of watt-hours per year. Currently, the average motor in use today has an efficiency of 88% in converting electrical into mechanical energy. Figures on the order of 96% conversion efficiency are technically feasible for larger motors. For more information on motor-control technology, check out the article "Stepping Motor Fundamentals." 

For comparison, the electrical generation capacity of photovoltaic solar cells in all of Europe, where both Germany and Spain currently lead the U.S. in installed base, is projected to be only 15 TWh/yr. in 2010. In the UK alone, with an annual total electrical consumption of approximately 350 TWh, the Institute of Engineering and Technology estimated that 5 TWh could be saved annually through the use of more efficient electric motors. Furthermore, many motors aren't used in an efficient manner. For example, the motor may be oversized for the job at hand, or much of its mechanical output power may be wasted, meaning that additional savings may come from how the motor is used, on top of the savings from the motor itself. In 1996, the U.S. Department of Energy speculated on savings of 5 TWh/yr. by 2000, and a 100 TWh/yr. savings potential by 2010, considering both motor and related system-level savings. 

The potential is there to make significant advances in the next few years as older motors and drives are replaced by newer more efficient ones. Because of the cost savings in electricity, many industries are voluntarily accelerating the turn-over of their installed motor base, even replacing motors before they wear out. This is because the payback for the newer, more efficient motors and drives can be realized in less than a year and usually less than two years. Great strides are already being made. In the UK, for instance, sales of the least efficient motors, grade Eff3, have dropped from 68% to 8% between 1997 and 2004. During the same period, sales of the most efficient grade (Eff1) have increased from 2% to 7%, and further jumped to 17% in 2006, with the middle grade (Eff2) making up the balance of sales. 

Regulatory Influences on Motor Efficiency

Governments around the world are providing regulatory pressure to use more efficient motors. Starting with the Environmental Protection Act of 1992, which mandated motor efficiency standards and took effect in 1997, the U.S. government has been steadily increasing regulations. There are other voluntary incentives as well, such as National Electrical Manufacturers Association's (NEMA) Premium efficiency labeling standard (2001). Australia implemented standards on motors ranging from 0.73 to 185 kW in 2001 and tightened efficiency requirements in 2006. Very recently (March 2009), the European Union passed mandatory Minimum Efficiency Performance Standards (MEPS), which will be phased in from 2011 to 2017. Brazil (2002) and China (starting in 2010) also have current or planned mandatory standards. Figure 1 shows a comparison of efficiency requirements for various-sized motors in several jurisdictions, including the voluntary NEMA and Consortium for Energy Efficiency (CEE) standards, versus the wide range of efficiencies of available motors. 

1. Several mandatory and voluntary world-wide motor efficiency standards (lines) compared to commercially available motors (highlighted area).

Electric motor savings are achieved in several ways. The first is in the motor design itself, through the use of better materials, design, and construction. Another is by optimizing the mechanical angle between the various rotating magnetic fields inside the motor. This is done using the newer family of motor control algorithms, generally referred to together as space vector control, flux vector control, or field-oriented control. By keeping the magnetic fields of the rotor and stator oriented with the optimal angles between them under various speed and torque conditions (typically near 90 degrees), the motor can always operate at peak efficiency. 

As a side benefit, other characteristics can also be optimized, such as fast and stable dynamic response to load changes, precise control of speed or torque, soft starting and braking, prevention of stalling at low speeds, high starting torques, and fault detection; often without sacrificing much in the way of overall energy efficiency. Some of these features were once obtainable only from a more expensive motor type, but can be achieved with the now ubiquitous, low-cost, and reliable ac induction motor, which comprises 90% of U.S. motor sales. One of the most significant advantages of the newer control algorithms is efficient variable speed operation. 

A large opportunity for system-level energy savings comes from using variable-speed motor drives. A well-designed pump or fan motor running at half speed consumes only one-eighth the energy compared to running at full speed. Many older pump and fan installations used fixed-speed motors connected directly to the power mains, and controlled the liquid or air flow using throttling valves or air dampers. The valves or dampers create a back pressure, reducing the flow, but at the expense of efficiency. This is probably how the HVAC forced-air system works in your office building; dampers control the airflow into each workspace while the central fan, which is sized for peak requirements, runs at full speed all the time—even if the combined airflow requirements of the building are currently very low. Replacing these motors with variable speed drives and eliminating or controlling the dampers more intelligently can save up to two-thirds their overall energy consumption. 

US study: Energy-efficient houses cut mortgage defaults by a third

The risk of defaulting on a mortgage is around a third lower if you live in an energy efficient home, according to the first study attempting to correlate such risks.

“This finding is robust, significant, and consistent across several model specifications,” says the report by the Chapel Hill Center for Community Capital at the University of North Carolina and the Washington-based Institute for Market Transformation (IMT).

“The lower risks associated with energy efficiency should be taken into consideration when underwriting mortgages,” the report’s authors propose.

According to the paper, reduced utility costs from energy saving measures provide home-buyers with enough capital to avoid repayment problems that often result in repossessions. Home foreclosures in the US have soared since the 2008 global financial crisis, whose ripple effects are still being felt in Europe today.

Investments in residential efficiency can often produce higher capital returns than interest rates or other investment opportunities. 

But mortgagees are often deterred from making them by the high upfront cost of home improvements such as roof insulation, heating/cooling upgrades, double glazing, and efficient water management systems. 

To offset this, the study advocates new financing mechanisms such as ‘energy efficiency mortgages’ to nudge first-time and moderate-income buyers towards energy savings measures. At present, these are small-scale are under-subscribed.

Dan Staniaszek, a senior expert at the Building Performance Institute Europe (BPIE) told EurActiv that efficiency improvements were “not exclusively a rich man's investment at the moment, but of course people with the money to invest are more likely to be able to do so.”

As well as energy efficient mortgages, the BPIE advocates preferential bank loans for building renovations, third party refinancing mechanisms such as Energy Service Company Obligations (ESCOs), and measures such as the UK’s Green Deal which allows investments to be partially offset against future energy bills.

Deeper renovation agenda

The danger of relatively cheap and easy renovations - such as the installation of wool insulation and upgrading heating systems – was that they could raise the price of best-value wholesale refurbishments, which were more expensive in the short term, Staniaszek said.

“We are keen to push a deeper renovation agenda where you look at the whole building holistically,” he said. “It requires a shift in mind-set to renovate with a view to achieving the highest possible performance and integrating other measures later on.”

“If you are upgrading a heating system or rewiring the electrics, you might factor in that at some point in the future you could have a solar heating system on the roof,” he added.

Passive solar heating – in which windows, walls and floors all collect, store and distribute solar energy – is widely seen as the ideal standard but it can initially add a few percentage points to a building’s cost.

Energy savings advocates hope that Europe-wide moves to incentivise these sorts of CO2-saving technologies will be spurred by legislation such as the EU’s Energy Efficiency Directive, which obliges member states to develop building renovation strategies.

The Energy Performance in Buildings Directive also requires that all new buildings in the EU be nearly-zero-emitting by 2021.