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HVAC control logic
Controllers coordinate heating, cooling, ventilation, pumps, valves and other building functions using measured values and operating schedules.
The control layer connects building needs to equipment behaviour
At the automation level, controllers read sensors and commands, calculate outputs and coordinate devices. Control sequences may cover air handling, heating and cooling substations, pumps, heat recovery, room temperature, lighting and shading. Controllers must be selected for the specific application, I/O capacity, network compatibility and long-term maintenance requirements.
Communication protocols – choosing the right one
| Protocol | Typical role | Engineering consideration |
|---|---|---|
| BACnet | Building automation and supervisory integration | Object support, device identifiers, IP routing and cybersecurity |
| KNX | Room control, lighting, shading and selected HVAC functions | ETS project, group-address design and gateways |
| Modbus | Controllers, drives, meters and industrial equipment | Register maps, data types, scaling and write permissions |
| DALI | Addressable digital lighting systems | Gateway, group and scene design; emergency-lighting requirements |
| M-Bus | Heat, water and other utility meters | Meter addressing, master capacity and telegram interpretation |
| LonWorks | Legacy and specialised building systems | Available interface support and replacement strategy |
Typical controller families
Siemens Climatix is widely used in OEM HVAC equipment, including air-handling units and heating or cooling equipment. Desigo PXC addresses building automation and integration tasks. SIMATIC S7-1200/S7-1500 offers PLC capabilities for industrial and selected technical-process applications. The choice depends on requirements, not on a universal ranking.
Room automation and total building control
Room-level control can coordinate temperature, air quality, light and blinds. Larger systems require additional consideration of shared energy generation, load prioritisation, alarm handling and interaction between rooms and central equipment. A controller should behave predictably if a supervisory workstation or network link becomes unavailable.
Commissioning requirements
Verify all I/O, sensor calibration, valve direction, communications, interlocks, manual overrides, safe states and trend data. Record test results and document the installed controller program and configuration. Particular care is required when replacing equipment in a live building.