STULZ
Precision Air Conditioning for Data Centres and Critical Facilities
STULZ (Hamburg, Germany) manufactures precision air conditioning (PAC) for data centres, server rooms, telecom rooms, and critical facilities — CyberAir 3PRO DX and CW series are the European standard for server room cooling. Modbus RTU and optional BACnet/IP via the SPC controller enable KNX building management integration.
Role in our panels
How we use STULZ
CyberAir 3PRO DX (direct expansion, 10-57 kW): SPC (STULZ Precision Controller) provides RS485 Modbus RTU on terminals C+ / C- / GND. Modbus parameters: 19200 baud, 8N1, unit ID 1-247 (set via SPC keypad). Registers: 1 (unit status: 0=off, 1=cooling, 2=freecooling, 3=heating, 4=dehumidify, 9=alarm), 2 (supply air temperature, int16, 0.1°C), 3 (return air temperature, int16, 0.1°C), 4 (cooling capacity %, uint16), 5 (compressor speed %, uint16), 10 (high temp alarm active: 0/1), 11 (filter alarm active: 0/1), 12 (compressor alarm: 0/1). CyberAir 3PRO CW (chilled water): same SPC controller, additional registers for chilled water valve position (%) and water inlet/outlet temperatures. KNX integration: MDT Modbus Gateway polls SPC registers 1-12 every 30s. Unit status → KNX DPT 5.010, temperatures → DPT 9.001, alarms → DPT 1.005. KNX alarm telegram sent to building manager if high temp alarm (reg 10=1) or compressor alarm (reg 12=1). Critical interlock: KNX building fire alarm (from Bosch AVENAR via LOYTEC) activates KNX output → MDT relay actuator closes STULZ SPC remote shutdown contact (terminals RC1/RC2 on SPC) → precision air conditioning shuts down before CO2 suppression release (prevents pressurisation damage). N+1 redundancy: second STULZ unit Modbus address 2 — KNX monitors both, alerts if one unit fails (status=9 alarm) so engineer can be dispatched before the backup unit overloads.
STULZ SPC controller exposes Modbus RTU — KNX gateway monitors cooling unit status, supply/return temperatures, and alarm states. Critical facility interlock via KNX relay to SPC remote shutdown contact.
Used in these project types
STULZ products
Key components we install
CyberAir 3PRO DX 20 kW
20 kW DX precision air conditioning unit for server rooms. SPC controller with RS485 Modbus RTU (19200 baud, 8N1). Registers for unit status, supply/return air temperature, cooling capacity %, and alarm states. N+1 redundancy configurations with dual units on Modbus addresses 1 and 2.
CyberAir 3PRO CW chilled water
Chilled water precision air conditioning for data centres with central chiller plant. SPC controller same Modbus RTU register map as DX series plus additional registers for chilled water valve position (%) and water inlet/outlet temperatures. Used in larger data centres with central cooling infrastructure.
MiniSpace compact DX
Compact precision cooling for small server rooms (2-10 kW). SPC controller with Modbus RTU RS485 on same register map. Suitable for telecom equipment rooms, BTS cabinets, and UPS rooms where full CyberAir 3PRO is oversized.
WiboTec portable precision cooling
Portable precision air conditioning for temporary server room cooling during maintenance or emergency backup situations. SPC controller with Modbus RTU for integration with KNX building monitoring when deployed as temporary N+1 backup.
STULZ FAQ
What is the Modbus baud rate for STULZ SPC?
Default 19200 baud — different from the standard 9600 baud used by most Modbus RTU devices. Confirm on the SPC keypad: Settings → Communication → Modbus → Baud. If the baud rate is set incorrectly on the KNX Modbus gateway, the gateway will not receive valid responses from the SPC controller.
Can I trigger remote shutdown via Modbus?
No — Modbus cannot trigger emergency shutdown (safety design by STULZ). Use the SPC hardwire terminals RC1/RC2 for emergency/remote shutdown via dry contact. KNX relay actuator activates these terminals in critical interlock scenarios (e.g., fire alarm CO2 suppression pre-discharge). This is a deliberate safety limitation — Modbus is monitoring only.
Is BACnet/IP available as an alternative to Modbus RTU?
SPC Plus (optional upgrade module) adds BACnet/IP — enables direct integration with Metasys (Johnson Controls) or Distech BMS without a Modbus gateway. For KNX-only buildings, Modbus RTU via MDT or Weinzierl gateway remains the standard approach. Specify SPC Plus at order time — it cannot be retrofitted to standard SPC.
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