Overview

STULZ CyberAir 3PRO DX (10-57 kW direct expansion) and CW (chilled water) are the standard precision air conditioning units for European data centres and server rooms. SPC (STULZ Precision Controller) provides Modbus RTU RS485 on terminals labelled C+, C-, GND (on SPC circuit board, accessible after removing front panel).

RS485 Communication Parameters

Parameters: 19200 baud, 8N1, unit ID 1-247 (set via SPC keypad: Settings > Communication > Modbus > Unit Address). Important: default baud rate is 19200, not the standard 9600. Configure KNX Modbus gateway (MDT SCN-MIG.01 or Weinzierl 5013) to 19200 baud to match.

Register Map

All holding registers (FC3): 1 (unit status: 0=off, 1=cooling, 2=freecooling, 3=heating, 4=dehumidify, 9=alarm stop), 2 (supply air temperature, int16, 0.1 degrees C), 3 (return air temperature, int16, 0.1 degrees C), 4 (cooling capacity, uint16, %), 5 (compressor speed, uint16, %), 10 (high temp alarm: 0=normal, 1=alarm), 11 (filter alarm: 0=normal, 1=clogged), 12 (compressor alarm: 0=normal, 1=fault).

MDT Gateway Read Tasks

Poll all 12 registers every 30s. KNX mapping: reg 1 (unit status) to DPT 5.010, regs 2-3 (temperatures) to DPT 9.001, regs 10-12 (alarms) to DPT 1.005 alarm bit.

KNX Alarm Notifications

When reg 10=1 (high temp alarm): KNX GA 9/0/1 ON triggers Gira X1 push notification to facility manager. When reg 12=1 (compressor fault): GA 9/0/2 ON triggers email notification (Gira HomeServer email action).

Critical Facility Interlock

Fire suppression coordination: when KNX building fire alarm activates (Bosch AVENAR via LOYTEC -> KNX binary input), KNX logic executes: write Modbus register 100 via MDT gateway = 1 to STULZ SPC remote shutdown (note: shutdown via RS232 hardwire contact RC1/RC2 on SPC is more reliable — connect KNX relay actuator MDT AKD channel 5 to RC1/RC2 terminals). After KNX delay 30s: activate suppression release interlock.

N+1 Redundancy Monitoring

Second STULZ unit at unit ID 2. KNX monitors both units. If unit 1 alarm (reg 9=1): notify maintenance AND switch to unit 2 via KNX changeover relay.