I'm at a loss as to what heat load could give you the heat profile you're targeting.
Are these VFD's already installed and running?
As to the stair step increases in power... why not a linear run-up?
Carbon Monoxide monitor...? Are you exhausting air from some confined diesel-electric set?
I'd throw the whole problem over to an engineer.
For such a costly system, any PLC expense will be dwarfed by the design effort.
