This designer puts a 3D model of a building's HVAC equipment next to a live BACnet control schematic, so the mechanical system and its controls are visible at the same time. Click any device — an AHU, VAV box, DDC controller, chiller, boiler, or pump — and the tool cross-highlights it in both the 3D view and the schematic. It's a learning and design aid for HVAC and controls engineers, BAS technicians, and students connecting equipment to the DDC logic that runs it.
The view links physical equipment to the control network that operates it:
• 3D building model — AHUs, VAV terminal boxes, chiller, boiler, pumps, and ductwork in place. • BACnet schematic — the controllers and the data links that tie sensors, actuators, and equipment together. • Cross-highlighting — selecting a device lights it up in both panels so you can see hardware and controls as one system. • DDC points — the inputs (temperatures, pressures, status) and outputs (valve, damper, and fan commands) at each controller.
Each major piece of equipment has a DDC (direct digital control) controller that reads its sensors and drives its actuators to hold setpoints. Those controllers share data over a BACnet network — an open communication protocol — so an AHU controller can pass a duct-pressure or supply-temperature value to the VAV controllers, and a plant controller can stage chillers and pumps. The supervisory layer applies system-wide logic such as temperature and pressure resets, often based on standardized ASHRAE Guideline 36 sequences, while local controllers handle the fast loops.
1. Drag to orbit the 3D model, scroll to zoom, and pan to reposition. 2. Click a device in either panel — the 3D model or the schematic — to cross-highlight it in both. 3. Follow the BACnet links between controllers to see how an AHU coordinates with its downstream VAV boxes and the central plant.
BACnet (Building Automation and Control Networks) is an open, vendor-neutral communication protocol — standardized as ASHRAE Standard 135 — used by building automation devices to share data. It lets controllers, sensors, and equipment from different manufacturers interoperate on the same network, exchanging objects and properties such as temperatures, setpoints, and equipment status.
DDC is control performed by a microprocessor-based controller that reads digital and analog inputs (sensors) and computes outputs (commands to valves, dampers, and fans) in software. It replaced older pneumatic and electromechanical controls, enabling precise PID loops, programmable sequences, trending, alarming, and remote supervision through the building automation system.
An air-handling unit typically includes air filters, heating and cooling coils, supply and (often) return fans, and dampers — including outdoor-air, return-air, and exhaust dampers that form the economizer. Its DDC controller modulates the coil valves, fan speed, and dampers to deliver air at the target supply temperature and duct static pressure.
A VAV (variable air volume) terminal box throttles the volume of conditioned air delivered to a zone using a modulating damper, varying airflow to match the zone's load instead of changing the air temperature. Many boxes add a reheat coil to warm the air for zones that need heating, and each box's DDC controller reflects its airflow setpoint and damper position on the BACnet network.