How much more electrical noise does an EC motor create compared to a standard PSC motor? Are EC motors as noisy as a VFD?
The way you are asking the questing is a bit like comparing apples and oranges. A PSC motor is not a variable speed motor by itself. So comparing it to an ECM may be a mismatch right there. But some fan suppliers in particular do offer fixed speed ECMs for the simple reason that they are about 20%
more efficient than PSC motors. So in THAT context, they can be compared. However then you throw in the VFD issue, which implies you ARE asking about variable speed. In that case, you then have to ask if you mean to compare an ECM to a PSC motor using a VFD? If so, then it gets more complicated.
The only reason to use a PSC motor is because you only have single phase power. PSC motors are ONLY used for single phase applications. ECMs are ALSO designed, for the most part, as single phase. But as mentioned, they are really BLDC motors that have a built-in converter, which, in the versions intended to REPLACE motors in applications typically done with PSC motors, will accept single phase input.
However, if you want to compare them in VARIABLE SPEED applications, then there is no point in using a single phase PSC motor any longer, as they are horribly inefficient (i.e. 60%). There are a few VFDs made for running single phase PSC motors, but they are for retrofit applications where the motor is too expensive to replace. You would be foolish to use one of those on a new design, the VFDs are specialized low volume products and are comparatively very expensive, plus the motor is still going to be inefficient. For variable speed applications being designed from the ground up, you would compare an ECM to a VFD that can accept 1 phase input + a standard
3 phase 230V motor.
In that only viable comparison then, the difference in electrical noise is virtually nil. The noise is for the most part a result of the converter sections being Switched Mode Power Supplies, and both of them are going to be identical. The only possible difference might be in any extra filtering that one or the other might include, which will vary by manufacturer. The ECM will win hands down however based on size and cost.
In comparing an ECM to a PSC motor in a
fixed speed application (without a VFD for the PSC motor), the PSC will have virtually no electrical noise, so ANY electrical noise generated by the ECM will cause it to lose in that comparison. The ECM would win on efficiency, but not if electrical noise is your only criteria. Audible noise is possibly the opposite by the way. ECM motors are designed for the most part to replace PSC in fans, so they must have the same audible noise standards. But when using variable speed, lowing the speed often results in less duct noise, meaning the ECM might win there.
Where ECM always loses is in the budget battle. 3-4X the price of a PSC motor in a fixed speed application. Might win against a VFD + 3 phase motor though.