HVAC dehumidifer on multiple systems


New Member
I've asked my HVAC guys to set up my Aprilaire 1700 whole house dehumidifier to work on three areas and they are having trouble figuring out how it can work.

The whole house dehumidifier is ducted to three areas using controllable dampers: the main floor system, the basement system, and the unfinished basement area. The Aprilaire natively supports one system plus the local area (in this case the unfinished basement). I do not want to buy another 1700, so the trick is to get it to work for three areas as follows:

If system A (main floor hvac) is energized, then the damper for it opens and the dampers for the system B (lower level) and local area are closed (even if system B gets a call to energize).

If system B is energized and system A is not, then System B damper opens and system A and the local area close.

If neither system A nor B are energized, then the local area damper is open and system A and B dampers are closed.

They HVAC guys have been unable to find relays or whatever to make this work. I was wondering if this could be solved with an intelligent controller and scripting (like the RCS CommStar 308 or similar). Any ideas?
how 'bout this . . . both relays are normally open, shown energized . . .


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