I have 16 vav boxes like the one showed in the pic mounted in stand alone ; i.e that there is no communication bus, each zone have a tc642 vav box control hooked up to a thermostat and controls a belimo 3 wire 24 vav actuator and only one output is used for the electric heat fan coil Relay. The rooftop unit hooked up to that system is controlled by an alerton tx653 controller; the inputs onthe main controller are return and supply temperature; pressure switch and main stat sensor and set point. The outputs are 2 stage cooling, one 0-10vac for SCR electric heat, one for by-pass damper and one for ventilation. I have four of those vav boxes pcb that are of different brands(prolon and staefa); as I said it is a stand alone pattern. I was thinking of finding four alerton vav box controllers(tc642) to replace the staefa and prolon controllers and link all the 16 boxes together with a bus comm all the way up to the main controller(tx653). I am thinking that the main controller would perform better with all the vav boxes communicating; by adding automatic changeover capabilities and better control of rooftop unit by controlling with an average demand instead of controlling only by return and supply temperature . Are there any real advantages to this and are those parts still available. Is the tc642 an alerton part or not? Alerton support is the worst I be seen and I am not sure but I think the box controllers are now model # tx-vav.... I am not a control specialist but i would like your input on this matter; thanks in advance!