I think he may be overstating the figures a little. By using variable speed, AC or DC, you can match the motor speed to the air flow requirements. If a low air volume is needed, the motor speed can be reduced, and the energy it draws is reduced. The energy reduction is by the cube of the speed, so at 1/2 speed, the energy required is 1/2 x 1/2 x 1/2, or 1/8th. This is all very real and can be proven by looking up the "affinity laws" for more details.
BUT... (and this is a big butt),
When running at full speed, there is NO energy savings, in fact the Variable Speed Drive drive will actually consume MORE energy than just running the motor. So the claim he makes, while true for a portion of the operating time, is not to be confused with the overall cost of running a HVAC system.
The real savings come from circulating the air continuously, which evens out the overall temperature and maintains a better comfort level for the occupants. In the old system, you would heat up the place and while the blower was running, the air felt warm. But when the t-stat was satisfied, the blower shuts down and the air stratifies, leaving your feet feeling colder even though the air at the t-stat level is warm. That makes you either suffer with cold feet, or, like most people, turn up the t-stat. What a continuous circulating system does is let you feel better with a lower setting, and the heating can cycle on and off less often.
Now if you ran a blower motor full speed 24/7, the electricity would cost you a lot. But by using low speed from a VSD blower for circulation and only turning it up when the burner is on, you save energy comparatively to running full speed. The overall savings compared to a non-continuous system is what you really need to investigate, and that's a little more nebulous.
The AC vs DC issue is just a technology preference. You can do it either way, but typically a DC motor was more trouble because of wear parts like brushes, or was more expensive because it needs to use permanent magnets (PMDC). The GE ECM motor is a PMDC motor with a built-in VSD, produced n high enough volume to make it competitive to standard motors (or rather, less uncompetitive). It is also a bottom-up redesign to achieve very high efficiency compared to a similar 1 phase AC PSC motor, the kind you would need if you wanted to use a VFD on a 1 phase motor. So that, coupled with variable speed capability, makes a nice package for energy efficient HVAC systems.
What they don't show you on their literature however is how it would compare to a 3 phase motor, which is what a lot of their competitors use. I have heard that if you use a 240V 1 phase supply to a VFD, then use a 240V 3 phase motor, it achieves even higher efficiency than the ECM. But if you have to have the voltage doubler on the line side of the VFD to accept 120V input, they are about the same. So GE has essentially conceded this product to be valuable only to the North American marketplace. Still, there are a lot of HVAC systems here...
