I haven’t installed a whole house fan yet, but I had the builder rough out an opening when the house was built 2 years ago, and I’ve done quite a bit of research on this.
There’s no easy solution for automating a whole house fan beyond on/off. For on/off, any of the regular z-wave switches will do the job (GE, Zooz, etc.) but the hi/lo switch will need to stay.
See this discussion for more.