When Do You Need an IO Module vs a New DDC Controller?

The Founder's Explanation (Teach Exactly This Way)

"When family grows, sometimes we add one room, sometimes we build a new house. If the new space needs its own kitchen, own water, own everything — then new house. Just for sleeping, add a room. IO module is adding a room. DDC controller is a new house with its own kitchen. Ask first: does this need its own brain?"

Teaching the Concept

Add a Room, or Build a New House? A growing family that just needs sleeping space adds a room to the existing house. But if the new space needs its own kitchen, water and independence, they build a separate house. The cost and the effort follow that one decision — and so does a BMS expansion. An IO module is a room; a new controller is a house with its own kitchen. Decide by Where the Logic Lives ``` NEED CHOOSE More points near a controller ..... IO MODULE that still has spare program Local logic / standalone control ... DDC CONTROLLER New zone / new plant Points far from any controller ..... DDC (or remote IO) ``` The Economics Follow the Same Logic ``` IO MODULE low cost, no new program, rides the bus DDC CONTROLLER higher cost, own program, own node, but runs on its own if the head-end is lost ``` Expansion is not about adding hardware — it is about deciding where the thinking happens.

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Related Topics

• What is a BMS DDC controller? — the programmable brain that runs the logic
• What is an IO list in BMS? — the master list of every input and output point
• Browse all Controllers topics — more from this section of the EnSmart BMS Library