of the blower. For example, to calculate the fan rpm with a motor rpm of 1725, a 3” diameter motor pulley and a 7″ diameter fan pulley, use the following formula: Fan rpm = (diameter of motor pulley) (diameter of fan pulley) Fan rpm = 3/7 x 1725 Fan rpm = .4286 x 1725 Fan rpm = 739 These types of belt drive blowers (Figure 5a) were commonly used in older heating-only and commercial systems. Direct blowers (Figure 5b) have the blower wheel mounted directly on the motor shaft. The blower speed is adjusted electrically by chang- 6 National Oilheat Research Alliance ing the blower motor terminals or changing the settings of the motor speed selection switches on a related motor control board. Most residential equipment uses multi-speed direct drive blowers. This enables the speed of the motor to be adjusted to match the requirements of the heating and cooling system. ECM Blowers Electronically Commutated Motors (ECMs) are a combination of two components, a motor control and a three phase motor with a permanent magnet rotor. The motor control is designed to operate the motor from a single phase AC power supply for residential and light commercial applications. Internally, the motor control rectifies single phase AC power to DC power, which operates the microprocessor and powers the frequency drive. The microprocessor determines the operation of the motor by controlling the output of the frequency drive. The frequency drive delivers three-phase alternating current to the motor. This design improves efficiency and range of operation compared to Permanent Split Capacitor (PSC) motors, while providing precise programming of speed, torque or airflow in HVAC/R systems. ECMs are built in multi-speed designs with simple speed taps or communicate with an OEM control board which controls the inputs of the motor control (microprocessor). PSC motors are not only less efficient than ECMs, they suffer efficiency loss when operated at less than their rated speed. For example, x motor rpm Figure 5a Figure 5b 37 ECM blowers
NORA Advanced Air Flow
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