Choosing a Fan Motor
The fan motor in your air conditioner moves hot air out of the condenser. It can also move cool air through ductwork and into rooms.
Nidec offers a broad range of fan motors based on our advanced technology. The core of these products is a brushless DC motor-based drive.
Choosing a Fan
Whether you’re cooling your home, mitigating heat in your garage or workshop, or moving air in commercial/industrial settings, choosing the right fan can make all the difference in comfort and efficiency. In order to understand which fan will best meet your needs, look at several key specifications.
For indoor/outdoor fans, you’ll want to consider the blade material and style (rounded or straight) as well as how easy it is to change the settings with a traditional pull chain or a remote control. You may also be interested in a built-in timer and/or programmable schedule.
Axial fans, with their propeller shape, are able to move a large volume of air with little increase in pressure between upstream and downstream. They are typically reserved for applications with low pressure drops and short circuits, but can be used in other applications as well.
Commercial/industrial fans are designed with versatility in mind, and can be used for a variety of tasks. They are often heavier and more durable than household fans, and come in a variety of designs to match your decor. Many have more than one fan speed setting, and are rated by their airflow rate in Cubic Feet Per Minute, or CFM. Look for a CFM rating when comparing fan options to find the one that will best suit your needs.
Motor Size
The first consideration when selecting a new Fan Motor fan motor is the size of the motor. This is typically determined by the specifications on the fan blades. The diameter, angle, and number of fan blades will determine the correct horsepower needed for the replacement fan motor.
For example, a four-blade 18” fan with an angle of 27 degrees and an RPM of 1140 would need a 3/4 HP fan motor. However, if the design airflow increased by 10% the brake horsepower would need to increase by 33%. This increase is more than the maximum capacity of a 3/4 HP motor, so a 1 HP motor is needed.
While it is important to consider the specifications on the fan blades, it is equally important to determine how the fan will be powered (belt-driven or direct drive). The power usage of a motor is not simply determined by its specified brake horsepower; it is also dependent upon how the fan is loaded.
For example, a 1-HP fan motor will use approximately 746 watts of electricity when connected to the specified fan. The amount of power it uses can be significantly more or less than this depending on how the fan is loaded. Electrical motors are not 100 percent efficient – they suffer from power losses due to resistance in the windings and friction in the bearings, etc.
Motor Design
The motor is the heart of your air conditioner, it moves the blades to blow cool air throughout your home. It is the most important part of your air conditioner, as it helps to maintain a consistent flow of air, which allows for a more efficient cooling process. A well-maintained fan motor will also prolong the lifespan of your air conditioning unit.
Most fan motors are basic sleeve bearing types. This design consists of the motor shaft supported by a porous sleeve filled with lubricant. This is fine for smaller high speed units where the radial and thrust loads remain relatively low Fan Motor and the rotational speeds are not too high. In such applications, sleeve bearings can be lubricated with pressurized air, which reduces the frictional power losses.
However, the disadvantage of using air as a lubricant is that it does not stay in place and can be forced out of the bearing by gravity. This causes the sleeve to wear out and produce additional noise and rotor wobble.
A newer method of lubricating sleeve bearings is to use magnetic fluid. This eliminates the need for contact lubrication and produces very little frictional loss. However, it is quite expensive and requires more sophisticated and costly electrical systems and controls to operate.
Motor Efficiency
When choosing a fan motor, energy efficiency should be one of the highest selection criteria. But don’t confuse “motor efficiency” with the overall efficiencies of a fan, drive and speed control.
How much power a motor uses depends less on the size of its engine (i.e. its rated horsepower) than it does on the work demanded of it to spin the prop at a particular speed. For example, increasing the speed of a 52-inch fan with a 2-HP motor from 540 to 593rpm nearly doubles its power usage (1,492 vs. 1,046 watts).
A high motor efficiency will cut power consumption and associated operating costs. Unfortunately, it’s not always possible to obtain accurate data on a motor’s efficiency because nameplate full-load performance values apply only to rated voltage conditions. Therefore, root mean square (RMS) current measurements must be corrected to account for supply-voltage variations.
It’s also important to note that motor efficiency is a combined measure of fan and motor performance under standard air conditions. Consequently, the DOE has adopted a new metric called fan efficiency index that accounts for both motor and control losses. This is a big improvement over the peak-based metrics previously used for rating system performance. Details of this metric are documented in an AMCA white paper downloadable from their website. As a result of this development, designers are now able to consider both the overall fan and motor efficiency of a system, allowing them to make more cost-effective choices in selecting fans and motors.