Electric motors are integral to HVAC systems, moving hot and cold air, pumping water, and operating compressors. When repairing and maintaining equipment, service technicians will encounter a variety of motors performing different tasks. To perform repairs as quickly and efficiently as possible, develop an understanding of common types of HVAC motors and how they work.
Electric Motors in HVAC
HVAC (Heating/Ventilation/Air-Conditioning) systems manage the heating, cooling, and circulation of air between indoor and outdoor environments in residential, commercial or industrial settings. Within these systems, electric motors perform critical duties operating fans, pumps, and compressors. They can range in size from small motors in domestic appliances such as fridges and air conditioners to large motors operating industrial furnaces.
The type of motor used in an HVAC system depends on the application. Blower HVAC motors driving fans have low starting torque requirements, while the compressor and pump motors require higher starting torque. Energy efficiency, reliability, and cost are also important factors, and each motor type comes with its own set of strengths and limitations.
Types of HVAC Motors
In the field, you'll find the following motor types operating in HVAC systems. Let's take a look at each of them in turn and cover the basics of how they work and how they compare with each other.
PSC (Permanent Split Capacitor) motors are a type of AC single-phase induction motor with mid-level characteristics that make them capable of handling many different tasks. They are characterized by having both a main winding and an auxiliary winding (the latter connected in series with a capacitor) permanently engaged in the motor circuit. The capacitor gives the motor moderate additional torque during startup and while running. Having both windings connected simultaneously provides an approximation of two-phase operation, which contributes to smoother, more efficient running and higher overall torque than a single-phase motor can typically provide.
Where energy efficiency is a primary concern, PSC motors are being displaced by ECM motors in many new products and installations.
PSC motors are cost-effective, versatile motors without being exceptional in any area, with outstanding reliability due to avoiding the necessity for a centrifugal switch that can wear out over time. This makes them easily the most common motors in HVAC systems, used for fans, pumps, and compressors in small to medium applications.
ECM motors (Electronically Commutated Motors), also known as brushless DC motors, offer standout performance characteristics compared to virtually every other electric motor type. Typically operating on AC power, they use a built-in inverter to convert the power to DC and feature a microprocessor that manages commutation, removing the need for brushes that can wear out over time. This technology enables them to maintain consistent speed in varying load conditions and reduces inefficiencies typically found in brushed commutation.
Although ECM motors are relatively expensive, they offer many advantages, including significant torque characteristics over the entire speed range and easier speed control capability. Their high efficiency, quietness, and compact size make them ideal for modern, high-tech air conditioning systems for homes and offices, providing exceptional performance while easily meeting energy efficiency regulations and guidelines.
Split Phase Motors
Split phase motors are a single-phase AC induction motor that features a main winding and a start winding that provides additional torque during startup. Once the motor reaches 70-80% of the rated speed, a centrifugal switch disengages the start winding, and the motor operates on the main winding alone.
Because capacitors aren't used in the design, split-phase motors are cost-effective, but they produce significantly less torque and have low energy efficiency. They provide good speed regulation during varying loads and are typically found in low-torque applications such as fans and blowers.
A CSIR (Capacitor-Start Induction-Run) motor is similar to the split-phase motor, with the addition of a capacitor on the start winding that boosts torque. These motors can produce up to 4 times the rated load torque at startup, enabling them to drive high-inertia loads. The main winding does not use a capacitor, which means that the motor's efficiency at speed is still relatively low.
CSIR motors are ideal for driving loads that require a lot of torque to get moving, such as compressors and pumps. While the lack of a run capacitor limits their efficiency once they get up to speed, it also makes them significantly more cost-effective than CSCR motors.
CSCR (Capacitor Start Capacitor Run) motors are similar to CSIR motors, with a second capacitor connected to the main winding. This gives them exceptional torque characteristics during both startup and normal operation.
Because they use two capacitors, CSCR motors are relatively expensive. Still, their significant performance characteristics make them ideal for all kinds of high-torque HVAC applications, especially in more extensive industrial settings where equivalent size ECM motors are either unavailable or cost-prohibitive.
Shaded Pole Motors
Shaded pole motors are a simple, low-cost type of single-phase AC induction motor. They use a single main winding and a 'shading' coil that creates a small starting torque to enable the motor to begin rotation. The shading coil consists of a simple copper ring that produces an opposing field to that of the main winding, resulting in a rudimentary approximation of a rotating magnetic field. Because the phase angle between the main winding and the shading coil is small, starting torque is limited, and both performance and efficiency are low overall compared to other motors.
Shaded pole motors are the most straightforward and economical HVAC motors on the market. Their relatively low torque, noisy operation, and low efficiency mean that they are typically limited to driving small fans in refrigerators and freezers.
Ordering Your HVAC Motor
At eMotors Direct, we've created a streamlined process to order an HVAC motor. We deliver to anywhere in Canada, giving you fast access to a large variety of motors.
Our Smart Search feature gives you the best tool for quickly solving all your HVAC motor needs. Find the motor specifications on the nameplate of the motor you're replacing. Input the motor specs into the search bar, and we'll bring up a list of options from our trusted brands in a matter of seconds. With our massive database of over 20,000 products, you can depend on finding a motor for your application.
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Once you've ordered, we'll deliver anywhere in Canada from one of our 30 manufacturer warehouses.
Whether you're an HVAC technician operating a small business or managing an industrial plant's daily operations, this fundamental knowledge of HVAC motors will help you find the best motor solution for your application.