HVAC (Heating, Ventilating, and Air Conditioning) refers to systems that heat or cool a designated environment. HVAC systems are especially important when it comes to designing large office buildings or climate-controlled environments, such as some aquatic enclosures at the zoo. An HVAC system depends heavily upon the quick movement of air from one location to another to achieve heating or cooling. AC motors have been used in past applications to serve as the primary air driving force, but they are not always the most efficient choice because they run continuously at full power. Electronically Commutated Motors (ECMs) were developed to offer a greater range of operability choices, and to minimize noise. Simply put, they use electronic controls to vary their speed. This article explains what ECMs are and how they work.

ECM Basics

ECMs are a type of DC motor. They are also called DC fan motors, EEM fan motors, and variable speed fan motors. They function using a built-in inverter and a magnet rotor, and as a result, can achieve greater efficiency in air-flow systems than some kinds of AC motors. (Although an AC current is used for ECM, the ECM’s internal rectifier converts the current to DC voltage).  They use a microprocessor controller to sequentially energize and de-energize each winding of the stator with power that generates an electrical current.  The processor-based pulse control builds a magnetic field that causes the rotor inside this ring of magnets to turn. The microprocessor uses a closed-loop feedback mechanism to more precisely control the magnetic fields, minimizing the eddy currents and losses used by traditional mechanically commutated motors.  This also allows a brushless motor to be used, therefore reducing points of physical contact within the moving components of the motor and making them more durable.

Permanent split capacitor (PSC) motors, often used in conjunction with electronic SCR motors, are somewhat inefficient when used in air control systems. This is because the fan motor noise requires the motor to run at less than a full load. When turned down, PSC efficiency suffers and falls in the range of 12 to 45 percent. ECMs, on the other hand, maintain a high level (65 to 75 percent) of efficiency at a variety of speeds. As a result, ECMs are more energy-efficient and can reduce operating costs. Additionally, ECMs are not prone to overheating and do not require additional measures to offset the generation of heat, as PSCs often do.

ECMs are also relatively low-maintenance; the use of true ball bearings reduces the need for oiling, and varied start-up speeds reduce stress on mounting hardware. The operating range is significant enough to enable one ECM to replace two induction-style models, which simplifies the replacement, maintenance, and installation processes, and minimizes product choices. However, not all ECM motors run at variable speeds and selection depends heavily upon application specifications. The initial cost of an ECM can be high but is typically balanced by overall energy savings in the long run.

ECMs in HVAC Systems

When considering an ECM for application in an HVAC system, there are several factors to keep in mind. Although ECMs are often selected because many models run at variable speeds, in certain condenser applications it is preferable to select and ECM that runs at a fixed speed—an ECM running at a fixed speed s in a condenser unit still uses less energy than a typical PSC motor running at a fixed speed in a similar unit. As a result of increased energy savings, a condenser operating with an ECM will have a higher SEER (seasonal energy efficiency ratio) rating.

In other HVAC units, an ECM can run at variable speeds but depends on a controller that pre-programs speed, including the rate at which the motor ramps up. Typically, PSC motors start and almost immediately run at full capacity, while an ECM can start slowly and stop slowly, which helps reduce humidity in a room. Additionally, the control can be set to alter the amount of air an ECM motor drives through the system, which enables a greater range of possible air-flow rates.

A typical ECM operating in an HVAC system will go through several stages, as determined beforehand by a manufacturer or a preprogrammed controller. In its first stage, and ECM runs at a lower speed to remove humidity (this is especially important in a cooling system). Next, the ECM reaches its designated peak speed, as specified for the application, maintaining high efficiency despite any shifts in operating speed. When the ECM stops, it can be programmed to stop slowly, which is called a soft stop.

EC motors are used in applications where a small motor is needed, and a variable frequency drive (VFD) is not cost-effective.  They also work well when constant design flow is required because the motor design is more efficient. 

Source: Thomas Supplier Discovery Platform