I just purchased a 2 speed Master Flow 24" Whole House Fan (WHFS24M). Is it possible to wire the fan so that I can eliminate the pull chain and use a wall switch or a variable speed wall switch?

Hi, I've done a fair amount of traditional (110/220) wiring so when I visited my sister several months ago, I volunteered to replace several of her bathroom fan switches. I've ordered & received the switches (made by Venmar) - the instructions are woefully inadequate (they just describe how to cut a hole in the wall for the switches, nothing on wiring). I took apart one of her switches when I visited her - they are low voltage and have 3 wires coming in. When I visit her in a couple of weeks the wiring should be simple since I'm replacing the same switch. I've never dealt with low voltage wiring and have a few questions: There are 5 switches to replace - they run a central exhaust fan. I'd guess that the wiring for all comes from a single circuit, would this be correct? And since this is all low voltage, would there be a transformer somewhere that steps the voltage down? Would most electricians put such a transformer near the main box and would it look like a transformer you'd see for common appliances? Finally, do I need to power that circuit/transformer down when I do this work? I guess that is the first question, if I don't then I don't need to find the transformer. Thanks! Bob