Swegon GOLD series air handling units (RX, LP, PX, CX) include a built-in RS485 Modbus RTU interface on the GOLD Control Panel. KNX integration provides demand-controlled ventilation setpoint adjustment, CO2 and temperature telemetry, and filter alarm routing to building management.

RS485 Connection

GOLD Control Panel RS485 terminals: B+ (positive), B- (negative), GND. Use screened twisted pair (e.g. Belden 3105A or equivalent). MDT or Weinzierl Modbus gateway RS485 port, or LOYTEC LGATE-920 RS485 port.

Baud rate: 19200, data bits 8, parity none, stop bits 1 (8N1). Note: Swegon GOLD uses 8N1 — not the standard HVAC 8E1. This is a common source of integration failure. Unit ID: configured in GOLD Control Panel under Communication > Modbus > Slave address (default 1).

Register Map

Holding registers (FC3 and FC6 for writes): - Register 1: Unit on/off uint16 — 1=on, 0=off - Register 2: Operating mode uint16 — 0=off, 1=auto, 2=manual, 3=override/external - Register 4: Supply air temperature setpoint int16, degrees Cx10 (write with FC6) - Register 10: Supply air temperature actual int16, degrees Cx10 - Register 11: Extract air temperature int16, degrees Cx10 - Register 12: Outdoor air temperature int16, degrees Cx10 - Register 20: Supply fan speed percentage uint16, 0-100 - Register 21: Extract fan speed percentage uint16, 0-100 - Register 30: Heat recovery efficiency percentage uint16 - Register 40: CO2 sensor ppm uint16 (requires optional CO2 sensor on GOLD unit) - Register 50: Filter alarm uint16 — 0=OK, 1=filter service required

MDT Modbus Gateway Configuration

MDT SCN-MOD.02 RS485 port. Read task A: registers 10-12 (temperatures, 60s). Read task B: registers 20-21 and 30 (fan speeds + recovery, 120s). Read task C: registers 40 and 50 (CO2 and filter, 30s for CO2, 300s for filter). Write object for setpoint: FC6, register 4, scale input by 10.

KNX GAs: supply air temp -> DPT 9.001 GA 6/6/0. CO2 -> DPT 9.008 GA 6/6/3 (ppm). Filter alarm -> DPT 1.005 GA 6/6/5. Write setpoint -> DPT 9.001 GA 6/6/10 (write to register 4 x10).

Demand-Controlled Ventilation via KNX CO2

KNX logic controller logic: when CO2 (GA 6/6/3) > 900 ppm: write setpoint GA 6/6/10 = 18 (18 degrees C, i.e. write 180 to register 4 via gateway) AND write mode GA 6/6/11 = 2 (manual override). When CO2 < 700 ppm and occupancy GA 2/0/0 = 0 (unoccupied): write mode = 0 (off) to reduce energy. When occupancy = 1 (occupied): write mode = 1 (auto), let GOLD PID controller handle setpoint.

LOYTEC LGATE-920 Alternative

LOYTEC LGATE-920: dedicated Modbus-to-KNX gateway with auto-discovery. Connect GOLD RS485 to LGATE-920 RS485-1 port. In LGATE configuration (web UI at http://lgate-ip): add Modbus device 'Swegon GOLD' at unit ID 1, 19200/8N1. Import Modbus template or configure registers manually. LGATE auto-maps to KNX DPs — supply air temp to KNX 9.001, CO2 to KNX 9.008, filter alarm to KNX 1.005. Commissioning time: approximately 20 minutes for a single GOLD unit.

BACnet Option

GOLD RX with GOLD NET BACnet card: BACnet/IP on port 47808. Analogue Input AI-0 (supply temp), AI-1 (extract temp), AI-3 (CO2), Binary Input BI-0 (filter alarm), Analogue Output AO-0 (setpoint). LOYTEC LGATE-950 bridges BACnet/IP to KNX — no Modbus required.