Ok guys, get ready to rip !!
I'm going to get blasted for this...but here goes !
Having any system that uses a variable speed motor without a subseguent reducal in BTU output. In other words, a two speed system may have a two speed blower & a two speed compressor for two different levels of cooling. And this is very efficient.
But, if you just have a variable speed blower without a two or more speed compressor, then you only save the difference in energy between the variable speed motor & the single or two speed motor.
By my calculations, you would save less than $10.00 / year for that differance in blowers, and yet that variable speed blower will cost you several hundred dollars more to install it and many hundreds more to replace it. To me that is 'no payback'.
And the only benefit that you would receive, is a little lower humidity level. So, do you have a problem with humidity ?? It may be worth the var. sp. Just realize that you are spending hundreds for a small comfort difference.
OK guys, I can take it !!! LOL