Differences Between Multispeed & Variable Speed Air Handlers

Variable Speed Air Handler

• A variable speed are handler features an electric motor which operates at an infinite number of different RPM's. The motor is electronically controlled, and as a result works interactively with the thermostatic controls to not only turn on and off when required, but also adjust automatically to push the perfect amount of air through the system. The electronics in the variable speed motor directly control the motor's RPM's. This type of motor is more expensive than a single speed or multi-speed motor, but saves on energy costs over the long run

Multi-Speed Air Handler

• A multi-speed air handlers features a motor that operates at a fixed number of set speeds. Like a ceiling fan that has slow, medium and fast settings, the multi-speed air handler can operate at a few different speeds, and therefore air volume levels. This motor's RPM is controlled by the amount of voltage sent to the unit. The HVAC control center tells the motor whether to turn on in a slow, or higher RPM rate depending on the heating or cooling needs of the building.

Differences Between the Two

• Regarding costs, the multi-speed motor, and therefore the multi-speed air handler is generally less expensive than the variable speed unit. It simply costs less to design and build a multi-speed motor than a variable speed motor. The variable speed motor will also be more expensive to replace in the event of a part failure than a multi-speed motor.

Advantages and Disadvantages

• The biggest advantage of the variable speed over the multi-speed air handler is the ability of the variable speed unit to perfectly match the environmental needs in the building to the amount of heat and air pushed through the HVAC system. Variable speed motors are better suited to create multi-zone heating systems, because they can respond to the unique needs of different rooms in a building. A variable speed unit also has a "soft start" feature. When the unit turns on, it spins up to speed slowly instead of starting at a fixed speed. This means that for the building occupants, they will be less aware when the HVAC turns on, and turns off.