As far as your concerns of VS blower in a dry climate.. It depends on the load calculation of what your sensible and latent needs are.. If you don't need much latent removal then the blower can be set up to higher cfm to remove more sensible heat and less latent..
You need a contractor that is familiar with Manual J(load calculation), Manual S(System selection) and Manual D(duct design). This type of contractor should be able to help you select the correct system and set that system up properly for your needs whether it will have a VS or PSC motor is up to you..
A VS blower on a "properly designed duct system" will be cheaper to run than a PSC blower and also will be quieter..
Make sure your contractor is taking the right steps to provide you with the comfort you are paying him for.. If he is using rules of thumb, time to find a true pro..
I am presently working on the house envelope and learning. My system is 20 years old so the time is coming. When it comes, I will definitely get a Manual J done as I don't see how I could proceed without one. I am assuming that it will come back guiding us toward the removal of a high sensible load vs latent. We are not as dry as more westerly parts of Texas but our issue is not humidity. It is day after day dryer hot heat in the summer.
So you would think that single speed with ramped up CFM would be good. On the other hand, being all-electic with strips right now, a heat pump seems the way to go, so having that single speed blower ramped up while using a heat pump in winter seems to be a recipe for cold blow deluxe. So, if my ductwork is okay or can be made okay, to handle the capabilities of the new system, maybe that's best. What do you think?
Quite honestly, the ductwork issue is what concerns me most. How much inadequacy in ductwork capability can be "overcome" by vs technology and do contractors rely a little too much on variable speed instead of recommending reworking or replacement of the ducts. I hope that's not a improper question.
The only way to know the cfm your ducts can handle is to test them.. TESP can be taken from your current system.. Based on a load calculation and system selection it will tell you the amount of airflow needed for the application.. If you have electric heat airhandler, you can also verify how much airflow you have by taking amps measurement, temp rise, voltage to element to determine the amount of airflow.. Knowing the amount of airflow you currently have at a particular TESP will tell how much airflow your ducts will handle..
Yes, I have seen some instances where a VS was used as a cure to a poor duct system instead of correcting the duct system.. To some extents it may help but without testing the contractor is just guessing(hoping) it will help..