KNX Hotel Room Controller: MDT SCN-RT55 Programming and PMS Integration
Hotel room automation requires precise coordination between presence detection, HVAC economy switching, DND/MUR signalling and PMS-triggered welcome scenes. The MDT SCN-RT55P provides a native KNX platform for all of these in a single room controller — but correct ETS6 group address structure and commissioning discipline are essential when scaling across 50 or more rooms.
Hotel room automation requirements
A hotel room KNX installation must satisfy a specific set of operational functions that differ from residential automation. The guest-facing functions — DND, MUR and welcome scene — must be reliable and intuitive. The energy-saving functions — HVAC economy mode and lights-off on absence — must operate automatically without guest interaction. The interface to the property management system (PMS) must be robust enough to survive network interruptions without leaving rooms locked in an unintended state.
Guest-facing functions
- DND (Do Not Disturb) button and door LED indicator
- MUR (Make Up Room) button and door LED indicator
- Welcome scene on card insert or PMS check-in
- Card slot presence detection (card in = occupied)
- Room display with temperature setpoint control
- Lighting scene selection (relax, reading, all off)
Energy and building management functions
- HVAC economy setpoint on absence (card removed)
- HVAC comfort setpoint on arrival (card inserted)
- All lights off scene on absence
- Blind position neutral on absence (50% for UV protection)
- DND/MUR status to housekeeping system
- Room energy metering per circuit (optional)
Eco mode during absence:hotel rooms account for a significant fraction of a hotel's total energy consumption. HVAC economy mode during guest absence — shifting the setpoint by 3°C from the comfort setpoint — typically reduces room HVAC energy use by 25–40%. At 100 rooms with 60% average occupancy, the cumulative saving is substantial. KNX card switch integration is the minimum viable presence detection; supplementing with PIR sensors significantly improves detection accuracy.
MDT SCN-RT55P room controller
The MDT SCN-RT55P is a 5.5-inch colour touchscreen room controller with native KNX TP bus connection. It is specifically designed for hotel room control applications and is programmable entirely in ETS6 without proprietary software. The panel-mount version fits into a standard 55mm wall box.
MDT SCN-RT55P specifications
Display: 5.5" TFT colour touchscreen, 480 × 272 px
Bus: Native KNX TP (no auxiliary power needed)
Inputs: 4 binary inputs (potential-free contacts)
— Input 1: Card switch (normally open)
— Input 2: DND button (momentary)
— Input 3: MUR button (momentary)
— Input 4: Spare / window contact
Outputs: 2 relay outputs (30V DC / 0.5A max)
— Output 1: DND LED indicator relay (12VDC)
— Output 2: MUR LED indicator relay (12VDC)
Thermostat: Integrated temperature sensor ±0.5°C
PI controller for HVAC setpoint output
Programming: ETS6 — full parameter access, scene storage
Housing: Flush-mount 55mm wall box (depth 42mm)Advantage: integrated bus power
The SCN-RT55P draws power directly from the KNX bus — no separate 230V supply to the room controller is needed. This simplifies cable routing: only the KNX YCYM 2×0.8mm² bus cable plus the low-voltage signal cables for inputs and LED outputs reach the controller position.
Current draw consideration
The SCN-RT55P draws approximately 12–15mA from the KNX bus. At 20 devices per line with one PS640 power supply (640mA), total current budget for other devices on the line is 640 − (20 × 14mA) = 360mA. Account for this when sizing binary inputs and actuators on the same line segment.
ETS6 group address structure
A consistent group address scheme is essential for hotel projects. With 50 or more rooms, any deviation from the schema makes commissioning errors difficult to trace. The recommended structure uses main group 10 for all hotel room functions, with sub-group equal to the room number and group address equal to the function index.
Group address schema — per room
Main group 10 = Hotel room functions Sub group = Room number (101–350) Group address = Function index GA 10/room/0 = Presence (DPT 1.002, 1=occupied, 0=vacant) GA 10/room/1 = DND status (DPT 1.001, 1=DND active) GA 10/room/2 = MUR status (DPT 1.001, 1=MUR active) GA 10/room/3 = Temperature actual (DPT 9.001, °C) GA 10/room/4 = HVAC setpoint (DPT 9.001, °C) GA 10/room/5 = Scene recall (DPT 18.001, scene number) GA 10/room/6 = Wake-up call trigger (DPT 1.001) GA 10/room/7 = Door lock status (DPT 1.002) Example for room 101: GA 10/101/0 Presence GA 10/101/1 DND GA 10/101/3 Temperature GA 10/101/5 Scene recall (1=Welcome, 2=Eco, 3=Sleep)
ETS6 template room:configure room 101 completely in ETS6, verify all functions, then use the ETS6 "Copy device" function to duplicate to rooms 102–150. Change only the individual address (1.1.102, 1.1.103, etc.) and the sub-group number in each group address. ETS6 supports batch group address offset during copy — select "Increment sub-group by 1 per copy" to automate the address scheme across all rooms.
Presence detection via card switch
The hotel card switch is a normally-open contact mounted in the wall holder near the room entrance. When the guest inserts their key card, the contact closes. This closure is wired to KNX binary input 1 on the SCN-RT55P, which converts the contact state to a KNX telegram on the presence group address.
Card switch ETS6 parameters
Input 1 — Card switch
Input type: Contact (not push-button)
Contact type: Normally open
Detection delay: 3 seconds (debounce — prevents
false absent signal during brief
card removal e.g. contactless use)
On activation (card in):
Send GA 10/room/0 = 1 (presence)
Trigger scene: Welcome (scene 1 via GA 10/room/5)
HVAC setpoint: send comfort value (21°C) to GA 10/room/4
On deactivation (card removed):
Hold-on delay: 180 seconds (3 minutes)
After delay, send GA 10/room/0 = 0 (absent)
Trigger scene: Eco (scene 2 — lights off, blinds 50%)
HVAC setpoint: send economy value to GA 10/room/4Card switch limitation
A guest may leave the room without removing their card, leaving presence = 1 even though the room is empty. HVAC will remain in comfort mode unnecessarily. Supplement with a PIR occupancy sensor using OR logic in ETS6: either card present or PIR active → HVAC comfort. Both absent for 5 minutes → HVAC economy.
180-second hold-on rationale
Guests frequently remove their card briefly — to use it at the minibar, to check its validity, or when returning late and fumbling at the door. A 3-minute hold prevents the HVAC from switching to economy and the lights from going off during these brief interruptions. This is a standard hotel KNX parameter — do not reduce below 60 seconds.
DND and MUR button logic
DND (Do Not Disturb) and MUR (Make Up Room) are mutually exclusive states — only one can be active at a time. Activating one must automatically clear the other. The door LED indicators provide visual confirmation to housekeeping staff without requiring them to knock or use a room phone.
DND/MUR ETS6 logic
DND button press (Input 2, momentary):
→ Toggle GA 10/room/1 (DND status)
If DND = 1:
→ Clear GA 10/room/2 = 0 (MUR cleared)
→ Relay Output 1 ON (DND LED illuminated — red)
→ Relay Output 2 OFF (MUR LED off)
→ Send DND telegram to housekeeping BMS GA
If DND = 0 (second press, DND off):
→ Relay Output 1 OFF (DND LED off)
MUR button press (Input 3, momentary):
→ Toggle GA 10/room/2 (MUR status)
If MUR = 1:
→ Clear GA 10/room/1 = 0 (DND cleared)
→ Relay Output 2 ON (MUR LED illuminated — green)
→ Relay Output 1 OFF (DND LED off)
→ Send MUR telegram to housekeeping BMS GA
If MUR = 0 (second press, MUR off):
→ Relay Output 2 OFF
Check-out (PMS event or card removed > 30 min):
→ GA 10/room/1 = 0 (DND cleared)
→ GA 10/room/2 = 0 (MUR cleared)
→ Both LED outputs OFFWelcome scene on check-in
The welcome scene activates when the guest first inserts their card after PMS check-in. It sets the room to a comfortable, welcoming state — avoiding the guest arriving to a dark room at minimum temperature. The scene is triggered via the KNX scene group address, either from the card switch input (local trigger) or from the PMS integration middleware (remote trigger via KNX IP gateway).
Welcome scene — DPT 18.001 scene 1
Scene 1: Welcome (triggered on first card insert or PMS check-in)
Lighting: Scene recall → 70% warm white throughout room
Blinds: Position 50% (half open — natural light welcome)
HVAC: Comfort setpoint 21°C sent to GA 10/room/4
TV: Standby power on (via KNX switch actuator)
Room display: Show welcome message with guest name
(if PMS integration active)
Scene 2: Eco (triggered on card removal after hold-on delay)
Lighting: All off
Blinds: Position 50% (UV protection, neutral position)
HVAC: Economy setpoint (comfort − 3°C)
TV: Off
Scene 3: Sleep
Lighting: Bedside only at 10%
Blinds: Fully closed (100%)
HVAC: Reduced comfort (−1°C from comfort setpoint)
TV: Off with timerHVAC zone control via KNX gateway
Hotel rooms typically have a standalone fan coil unit (FCU) with its own thermostat and fan controller. To integrate FCU control with KNX, a protocol gateway translates between the KNX setpoint telegram and the FCU control interface.
| FCU interface | KNX gateway | Notes |
|---|---|---|
| 0–10V analogue | KNX/0-10V converter (e.g., MDT AKI-0816.01) | Simple; setpoint as 0–10V voltage; limited feedback |
| Modbus RTU | Zennio KLIC-DD (KNX-Modbus gateway) | Full setpoint, mode, actual temperature feedback; recommended |
| Proprietary (BACnet/IP) | Loytec L-INX or LVIS gateway | For premium FCU brands with BACnet; most comprehensive |
| Conventional room stat | Replace with KNX thermostat actuator | Remove existing thermostat; KNX output to FCU on/off relay |
HVAC economy setpoints
Comfort setpoint (room occupied): 21°C (guest-adjustable ±2°C) Economy setpoint — winter absence: 18°C (frost protection + comfort on return) Economy setpoint — summer absence: 26°C (prevent excessive cooling of empty room) Setpoint switching: Card inserted → comfort setpoint sent immediately Card removed → hold-on 180s → economy setpoint sent PMS check-out → economy setpoint sent (overrides card state) Setpoint limits (ETS6 SCN-RT55P parameter): Guest minimum: 18°C (cannot set below this) Guest maximum: 26°C (cannot set above this) Absolute limits enforced by gateway — not by room controller
Multi-room commissioning strategy
A 50-room hotel floor requires systematic ETS6 project structure to avoid errors during commissioning. The key principle is to verify one complete room end-to-end before replicating the configuration across all rooms.
ETS6 multi-room commissioning workflow
Step 1: Configure and verify room 101 completely — All inputs (card, DND, MUR) verified on bus monitor — All GAs correct, DPT verified — HVAC gateway responds to setpoint changes — Welcome scene functional — PMS integration test (simulate check-in webhook) Step 2: Copy device in ETS6 — Right-click SCN-RT55 (room 101) → Copy — Paste 49 times (rooms 102–150) — ETS6 prompts for new individual address per copy — Assign 1.1.102, 1.1.103 … 1.1.150 Step 3: Batch group address update — ETS6 "Replace group addresses" function — Increment sub-group by 1 per room copy — Verify GA 10/102/0 … 10/150/7 assigned correctly Step 4: Download and commission — Download all 50 devices (batch download via ETS6) — Verify each room on site with bus monitor — Test DND/MUR indicators at room doors — Log commissioning record per room Individual address scheme (one KNX line per floor): Floor 1 (rooms 101–120): 1.1.101–1.1.120 Floor 2 (rooms 201–220): 1.2.101–1.2.120 Line coupler at each floor distribution board
KNX line topology for hotel floors
Hotel floors have a consistent room layout that maps well to KNX line topology. Each KNX TP line segment supports up to 64 devices and one power supply (PS640). For a typical hotel floor with 20 rooms, this is comfortably within the limit — allowing room for binary inputs, switch actuators and other devices alongside the room controllers.
Devices per room (typical)
- 1× MDT SCN-RT55P (room controller) — 14mA
- 1× KNX binary input 4-channel (card + DND + MUR + spare) — 7mA
- 1× KNX switch actuator 4-channel (DND LED, MUR LED, lock, spare) — 8mA
- 1× KNX dimmer actuator (lighting) — 10mA
- 1× KNX blind actuator (if motorised blinds) — 10mA
- Total per room: ~49mA bus current
Line sizing example — 12 rooms/line
- 12 rooms × 49mA = 588mA bus current
- PS640 capacity: 640mA
- Margin: 52mA (sufficient for line coupler)
- Device count: 12 × 5 = 60 devices (within 64 limit)
- Recommendation: 10–12 rooms per line for headroom
- KNX line coupler at floor distribution board
200-room hotel scale: 200 rooms ÷ 10 rooms per line = 20 KNX lines. 20 line couplers (e.g., ABB LK/S 4.2) connect to the backbone line via a KNX backbone coupler at the main distribution board. Group addresses: 200 rooms × 8 GAs per room = 1,600 group addresses — well within ETS6 limits. The entire project fits in a single ETS6 project file with structured building/floor/room hierarchy for navigation.
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