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Motor & Variable Frequency Drives (VFDs)


Commercial buildings often have many more motors running in their HVAC systems than their owners are aware of. Too often these motors have a rated horsepower that is not suited to the load it is driving. This situation is a primary cause of energy inefficiency but also a simple opportunity to notably effect energy consumption.

Most induction motors that are used in air conditioning systems are effective and dependable. However, their efficiency declines when they run under partial load circumstances. Energy savings are realized when a mismatched motor is replaced with a motor that accurately pairs the horsepower to the load needs.

Another energy saving consideration is older motors. Improvements in motor designs have has given rise to a breed of motors that operate 2%-8% more effectively than older, typical motors. Combining new superior efficiency with a horsepower-to-load balance provides a relatively quick return on investment to owners.

Variable Frequency Drives

The Variable Frequency Drive (VFD) is the most beneficial cost savings device ever applied to HVAC systems. By combining system capacity to the actual load, significant savings in motor energy use can be realized.

In addition to saving energy, VFD’s also increase the lifespan of motors. Each time an induction motor starts, it draws an increased current, up to ten times higher than the maximum rated load for that motor. This power surge produces heat and attrition towards the motor’s winding. When motors start and stop frequently, they are subject to operational failure.

When a VFD is applied to an induction motor, the VFD lowers the voltage and frequency as the motor starts. The current progressively increases until a normal operating condition is reached. In this manner, the motor lifespan is significantly prolonged.

The installation of VFDs on fan and pump motors has proven to be successful in reducing operating expenses. Energy savings of 50 percent can be realized over traditional constant speed systems. The return on investment can often be accomplished within a 12 months.

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