QwikSEER White Paper

in the pressure drop in the ductwork. The ideal flow rate also varies with environmental

conditions.

A PSC blower motor is less efficient than ECM or X-13 motor. They are also the least

expensive and most reliable motor due to their simplicity.

ECM Motor

An ECM motor is a brushless, direct current (DC) motor with an internal microprocessor that

manages commutation, resulting in synchronous operation over a range of speeds. In addition to

being more efficient than PSC motors, the variable-speed capability can be used on some

systems to either deliver a constant airflow over a wide range of pressure drops in duct work or

to provide a variable airflow based on environmental conditions (outdoor air temperature, return

air temperature, return air humidity). An ECM motor can be programmed to deliver a constant

airflow even while air filter configuration and cleanliness, or ducting geometries change.

Expensive and potentially unreliable electronics are required to maintain a constant airflow over

a wide range of possible duct work pressure drops. Additional electronics are required to account

for airflow optimization based on environmental conditions.

Constant Torque ECM Motor (AKA X-13 Motor)

The term X-13 motor originally referred to the high-efficiency motor developed by Regal-Beloit

(General Electric) to help meet the 13 SEER mandate, but the name has become somewhat of a

generic name for a class of less sophisticated ECM motors that provide constant torque (not

constant air flow). These motors are high-efficiency, brushless DC motors, controlled by a 24

volt signal. The X-13 motor delivers constant torque, meaning the airflow still decreases as the

pressure drop in the ductwork increases, but the change of air flow rate with pressure drop is far

less dramatic than for the PSC motor.

X-13 motor efficiency is similar to ECM motor efficiency, but the X-13 motor has a less

sophisticated electronic control and must be programmed with a torque value that provides

sufficient airflow at the worst case external static pressure. Therefore, although the efficiency of

the X-13 and ECM motors are similar, the X-13 motor will typically draw more energy than a

continuously variable speed ECM motor that optimizes airflow. Like a conventional PSC motor,

the X-13 motor usually moves more air than is required for certain environmental conditions.

This type of blower motor does not optimize airflow based on outdoor or indoor air conditions.

Analog and Digital Thermostats

Although a few high-end air conditioning systems have digital thermostats that communicate

with a digital data line and can control air handler airflow or compressor speed, conventional

analog thermostats simply provide a 24 VDC signal to the contactor that activates the air handler

or compressor.

Analog Thermostats

A conventional analog thermostat activates the G (green) wire so that 24 VAC between G and C

(common) activates the evaporator blower contactor, 24 VAC across Y (yellow) and C activates