【Daily Question 20101119】Does an inverter save electricity?

Of course, it saves electricity – by adjusting the speed via variable frequency, the power of the pump is adjusted indirectly, which results in energy savings.

Yes, we install frequency converters on certain fans and pumps here to save energy. It’s just that high-power frequency converters are a bit expensive.

This post was last edited by “Handsome to the extreme” on November 19, 2010, at 09:14. Variable frequency drives achieve energy savings by reducing voltage under light loads. When used in fan applications, when a lower air volume is required, the motor slows down, resulting in significant energy savings. In applications without speed control, the frequency converter does not save energy; it only improves the power factor.

If the equipment operates at full load all the time, then there is little room for saving electricity, as the frequency converter itself consumes about 5% of the power. If the equipment operates at low or partial load for extended periods, then using a frequency converter can be beneficial.

It is an undeniable fact that frequency converters can help save electricity; in some cases, they can reduce energy consumption by over 40%. However, in other situations, they may even result in more waste than operating without a frequency converter! Inverters achieve energy savings by reducing voltage under light load conditions. For torque-driven loads, since the speed does not change much, even a reduction in voltage has a minimal effect, resulting in only slight energy savings. However, this is different in the case of fans: when a lower volume of air is required, the motor slows down. We know that a fan’s energy consumption is proportional to the 1.7th power of its speed; therefore, the motor’s torque drops significantly, leading to notable energy savings. If we use it on oil wells, it will waste a lot of electrical energy by using brake resistors on the return trip, thus being even more energy-inefficient. Of course, if environmental requirements necessitate speed regulation, the energy-saving effect of frequency converters is quite significant. In applications without speed control, the frequency converter does not save energy; it only improves the power factor.

The energy savings provided by frequency converters are mainly reflected in the fact that the mechanical loads driven by the motors equipped with these converters, such as fans and water pumps, do not operate at full load all the time. When the system requires that these mechanical loads not operate at their rated load, the speed of the motors can be adjusted using a frequency converter, so that the power output by the motors meets the system’s requirements. This prevents the situation of using excessive power for a task that does not require it, thereby enabling energy savings. Furthermore, inverters can modify the reactive power loss of motors, improve starting conditions, and enhance the power factor; they can also reduce the active power loss caused by the transmission of reactive power, which is beneficial for energy conservation as well.

When the actual operating conditions do not match the designed conditions, using an inverter can help save electricity and conserve energy.

If used properly, it can definitely help save electricity. We didn’t use frequency converters before; in recent years, the motors of fans and gas stove burners have been gradually upgraded to those with frequency control, and the energy-saving effect is quite noticeable

In many materials and documents, frequency converters are described as control devices that help save electricity and energy, which leads people to think that they inherently contribute to energy conservation. However, this is actually a misconception; whether the use of frequency converters can indeed result in energy savings depends on the specific circumstances in which they are used. The reason why frequency converters can achieve energy savings in most cases is that they regulate the speed of motors. In reality, however, most speed control devices are capable of achieving this effect; therefore, it is clear that we cannot conclude that frequency converters are necessarily energy-saving products. The prerequisite for inverters to achieve energy savings is the speed-regulation characteristics of their loads. For those components whose speed has a significant impact on power consumption, such as centrifugal fans and centrifugal pumps, the regulation effect provided by inverters is significantly better than that achieved through conventional speed-control methods. Under these conditions, inverters can indeed help to save energy. If the spare parts handled by the frequency converter are constant-torque loads or even constant-power loads, then when the speed decreases, the drop in power is not significant or the power remains constant; as a result, the use of a frequency conversion speed controller does not achieve the same energy-saving effects as before, or it may not provide any energy savings at all. Whether there is a significant difference in the efficiency of variable-frequency speed controllers compared to that of digital DC speed controllers also needs to be considered in light of practical conditions. Under certain conditions, DC motors have higher power and a better power factor than AC motors; therefore, AC asynchronous motors together with variable-frequency speed controllers are not more energy-efficient than DC motors together with DC speed controllers. Source: Power Plant Chemistry Information Network