PSC vs. ECM Motors: Know Their Differences

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PSC vs. ECM Motors: Know Their Differences

Posted On: October 19, 2016

PSC vs. ECM Motors: Know Their Differences

The heating, ventilation and air conditioning (HVAC) industry uses a variety of motor technologies in its equipment. Historically, the two predominant motor types have been permanent split capacitor (PSC) single speed motors and electronically commutated motors (ECM) with variable-speed capability. HVAC professionals understand the key differences between these motor types. This article aims to share those differences to you today. 

PSC Motors 

For many years, PSC single-speed motor technology has been the standard in the HVAC industry. It represents the highest installed base. 

PSC motors are considered single-speed (speed refers to rate of rotational motion) because they have no internal controls that can be programmed automatically to vary the rotation of the motor over an operating range. In order to make PSC motors more flexible for various applications, speed taps are included to allow the mechanical contractor to manipulate the motor’s speed to ensure that the correct amount of airflow is delivered. There is, of course, a limit to the amount of static pressure the motor can handle, so it is important to keep in mind the optimal performance and safety. As static pressure increases, a PSC motor’s performance tends to drop off because it cannot adjust torque or speed. 

Because of its design, there are some disadvantages intrinsic in PSC motors. They are less efficient than other motors because they consume more watts. They are not ideal for continuous fan operation because since they run close to full speed, they use more energy than what the function requires. This also makes them less attractive for other continuous filtration applications. They are also the least quiet among the motor technologies. They do not offer customized airflow patterns that are often critical when it comes to managing humidity. 
 


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ECM Motors 

ECM variable speed motor technology is highly variable and is ideal for various advanced applications. 

ECM technology is based on a direct current (DC) design that is more efficient and it runs cooler than AC PSC motors. They are, in fact, approximately 80% efficient compared to the 60% efficiency rating of PSC designs. ECM motors are programmable. In the case of a failure, the control or the motor can be replaced without having to replace the entire unit. They are also designed to run over a wide range of speeds, making them ideal for delivering airflow in a multitude of system designs. They also draw the least amount of watts, making them the most efficient motor technology. They are also the quietest among the motor technologies since they have the ability to ramp up and down slowly, making them ideal for certain applications with noise concerns. 

When it comes to disadvantages, ECM variable-speed motors come at a premium cost. 

To see the difference in performance between the two types of motors, check out this chart:


 


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*Chart data courtesy of: Biemayer, P., Lutz, J., & Lekov, A. (2004). Measurement of airflow in residential furnaces*




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The term excellent or incredible does not seem high enough praise for the Twintech Heating and cooling company that recently replaced our 15 year old furnace. To start with, the response from Dave at Twintech to our original pricing request was the quickest and most professional of the 5 prices we received which included two of the primary natural gas providers. The Twintech pricing was the most competitive by a considerable margin.
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I didn't hesitate to call Twintech in for a 2nd time as they did an outstanding job installing my new furnace last year. This time my 18 year old air conditioner was on its last legs. Greg and the team are top notch, highly skilled technicians. The job was executed in a timely and professional manner. Greg was extremely thorough and went the extra mile to make sure everything was operating efficiently. Lastly, Dave is a true gentleman and really made the customer experience pleasurable and worry free. Always remember that good work ain't cheap and cheap work ain't good.

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