KNX Motor Actuators: Valve Drives, Damper Actuators and Feedback Signals
KNX motor actuators span a broad range: electrothermal valves for underfloor heating manifolds, modulating HVAC zone valves with position feedback, VAV damper blade actuators for variable air volume control, and motorised window drives for natural ventilation. Each type uses different DPT objects, mechanical specifications, and cable requirements.
KNX motor actuator types overview
The term "motor actuator" in a KNX context covers three distinct actuator categories, each governed by different KNX datapoint types and serving different building systems:
| Actuator type | KNX DPT objects | Typical application |
|---|---|---|
| Blind / shutter / jalousie actuators | DPT 1.008 (UP/DOWN), DPT 5.001 (position %) | Roller shutters, awnings, venetian blinds, motorised windows, skylights |
| KNX valve actuators (ON/OFF) | DPT 1.001 (open/close) | Underfloor heating manifold valves, zone radiator valves |
| KNX modulating valve actuators | DPT 5.001 (0–100% position) | HVAC 2-pipe and 4-pipe zone valves, chilled beam valves |
| KNX VAV damper actuators | DPT 5.001 (0–100% blade position) | VAV box damper blades, supply air diffuser actuators |
| KNX fan coil gateways | DPT 9.001 temp + DPT 5.001 fan % | Fan coil units with chilled/hot water coil and AC fan |
KNX valve actuators for underfloor heating
Underfloor heating manifolds typically have 4–12 zone circuits, each controlled by an electrothermal valve actuator. These are normally closed (NC) actuators: the coil is de-energised when closed, and opens when 24V AC is applied to the coil terminals. A KNX relay actuator switches the 24V AC supply to each valve coil.
Electrothermal valve actuators
- Danfoss TWA-A: 24V AC/DC, NC, 2.5N force, 3-min stroke time
- Honeywell V8043: 24V AC, NC, 2.8N force, suitable for M30×1.5 valve bodies
- Belimo TF24-ON: 24V AC/DC, NC, 100N force, 3-min stroke time
- Current draw: 0.5–1.2W holding (typically 24V × 50mA)
- KNX relay output: DPT 1.001 = 1 closes relay → valve opens
KNX relay actuator for valve control
- MDT SCN-8V63.01: 8-channel, 24V AC output, DIN-rail 4 modules
- Each channel: independent ON/OFF, 1A contact rating, LED status indicator
- ETS6: PI controller (MDT SCN-RT55P thermostat) sends DPT 1.001 telegrams
- PI control calculates ON/OFF ratio: e.g. at 50% demand → 15 min on, 15 min off per 30 min cycle
- Avoid rapid switching: minimum cycle time parameter 300s recommended for valve longevity
Pump interlock: the heating/cooling circuit pump should only run when at least one zone valve is open. In ETS6, use a logic function: if any valve actuator output = 1 (open) → pump enable = 1. This prevents the pump circulating against closed valves and extends pump motor life.
KNX modulating valve actuators
For precise HVAC zone control, modulating valve actuators with proportional positioning are used. The Belimo NV24A-KNX is the most common native KNX modulating valve actuator for HVAC zone applications.
Belimo NV24A-KNX — specifications
Valve body: DN15, Kv 1.0 m³/h (standard HVAC zone size) Connection: M30×1.5 thread, pairs with Belimo valve bodies Supply: 24V AC/DC from KNX PS640 auxiliary (NOT from bus) Bus current: 12mA from KNX TP bus (communication only) Force: 95N (adequate for 2-pipe zone valves to 1 bar ΔP) Running time: 75 seconds (0–100% stroke) Feedback: Actual valve position DPT 5.001 (sent on change + cyclic) KNX DPT objects: Object 1: Set position (DPT 5.001, 0–255 = 0–100%) Object 2: Actual position feedback (DPT 5.001) Object 3: Valve status (DPT 1.001, open/closed threshold) Object 4: Manual override (DPT 1.001, local button on actuator)
Advantages over ON/OFF valves
- Precise flow control: 30% open = 30% Kv flow rate
- No water hammer from rapid full-stroke switching
- Better room temperature stability in moderate-load conditions
- Position feedback enables fault detection in ETS6
24V auxiliary supply note
The Belimo NV24A-KNX requires a separate 24V AC/DC supply for the motor — this must NOT be drawn from the KNX bus. Use a dedicated 24V SMPS (e.g. MEAN WELL MDR-60-24) with sufficient current for all modulating valve actuators on the circuit. Calculate: 24V / 95N × number of actuators × 1.2 safety factor.
Zennio KLIC-DD fan coil unit gateway
Fan coil units (FCU) with their own internal controller — typically a proprietary thermostat — can be integrated into KNX using a dedicated gateway. The Zennio KLIC-DD interfaces the KNX bus with the FCU controller via 0–10V analogue signals and digital on/off contacts.
Zennio KLIC-DD integration architecture
KNX room temperature sensor (DPT 9.001) → KLIC-DD KNX object: room temperature → KLIC-DD PI algorithm (setpoint vs actual) → 0–10V output to FCU fan speed controller (0V = off, 10V = max) → Relay output: valve open/close contact to FCU water valve KLIC-DD KNX objects: Input: Room temperature DPT 9.001 (from KNX sensor) Input: Setpoint DPT 9.001 (from KNX thermostat GA) Input: Mode: heating/cooling/fan-only DPT 20.102 Output: Fan speed feedback DPT 5.001 (0–100%) Output: Valve status DPT 1.001 (open/closed) Wiring to FCU: 0–10V signal: KLIC-DD 0V and AO terminals → FCU speed control input Valve relay: KLIC-DD relay COM/NO → FCU valve coil or valve relay input 24V AC: FCU provides (or from panel 24V supply)
KNX damper actuators for VAV boxes
Variable air volume (VAV) boxes use a motorised damper blade to regulate the airflow into each zone. For KNX-integrated VAV control, the Belimo NM24A-KNX provides native KNX TP connectivity with proportional damper positioning.
Belimo NM24A-KNX specifications
- Torque: 10 N·m (for VAV box damper blades up to 1m²)
- Supply: 24V AC/DC auxiliary (not from KNX bus)
- Running time: 150 seconds (0–100% blade rotation)
- KNX DPT: set position DPT 5.001, feedback DPT 5.001
- Spring return option: blade returns to closed on power loss
VAV control via ETS6 logic
- CO2 sensor (MDT SCN-CO2W12.01) sends ppm via DPT 9.008
- ETS6 PI logic: CO2 actual vs setpoint (800 ppm) → damper position %
- Output DPT 5.001 → NM24A-KNX set position object
- Minimum position: 15% (fresh air minimum ventilation rate EN 16798)
- Maximum: 100% (high CO2 or fire mode flush)
KNX jalousie actuators for motorised windows
KNX jalousie actuators designed for blind and shutter control also drive motorised windows, skylights, and atrium louvres that use 230V AC motors with UP/DOWN/COMMON terminals. The MDT SCN-JAL1600.02 provides 16 independent channels, each rated at 600W for 230V AC motor loads.
MDT SCN-JAL1600.02 — KNX objects and travel time calibration
KNX objects per channel: Move UP/DOWN: DPT 1.008 (0 = UP, 1 = DOWN) Step UP/DOWN: DPT 3.008 (4-bit: direction + step %) Set position: DPT 5.001 (0 = fully closed, 255 = fully open) Slat angle: DPT 5.001 (for venetian blinds with slat control) Position status: DPT 5.001 (feedback, sent after movement completes) Travel time calibration (ETS6 parameter): Measure full UP and DOWN travel times physically (stopwatch) Enter in ETS6 parameter: travel_time_down = 45s, travel_time_up = 42s Actuator calculates intermediate positions as a fraction of travel time Example: position 50% → run motor DOWN for 50% × 45s = 22.5s Recalibrate if motor or window mechanics are changed Auto-reference run: MDT JAL actuator performs full DOWN then full UP on first power-up to synchronise internal position counter — do not skip this step
Feedback signals for fire and smoke dampers
Fire dampers and smoke extract dampers require position verification — the building control system must confirm that the actuator has actually reached the commanded position. This is a safety requirement under EN 15004 (gaseous suppression) and EN 12101-6 (smoke extract). KNX binary inputs connected to actuator end-position switches provide this feedback.
Fire damper feedback wiring and ETS6 logic
Actuator with end-position feedback (e.g. Belimo FSNF230-S):
Micro-switch closes when blade reaches fully open position
Micro-switch opens when blade is anywhere other than fully open
Wiring:
Micro-switch COM → 24V DC (from panel 24V auxiliary)
Micro-switch NO → MDT BE-0800.01 binary input terminal IN1
BE-0800.01 reference terminal → 0V (24V common)
ETS6 logic for safety verification:
Command: KNX output relay → fire damper actuator (open)
Feedback: MDT BE-0800.01 IN1 → DPT 1.001 GA "Damper 1 open confirmed"
ETS6 timer logic:
On command sent → start 90s timer
If feedback = 1 (open confirmed) within 90s → clear timer, log OK
If timer expires without feedback = 1 → send alarm telegram
→ Gira X1 alert: "Fire Damper 1 — Position Not Confirmed"
→ BMS alarm point via KNX group addressCable sizing for motor actuator circuits
Different actuator types require different cable specifications. Using undersized or inappropriate cable is a common cause of actuator failure and panel overheating.
| Actuator type | Voltage | Current | Cable specification |
|---|---|---|---|
| Electrothermal valve (ON/OFF) | 24V AC | 50mA | 2-core 0.5mm² from relay actuator to valve coil |
| Modulating valve (Belimo NV24A-KNX) | 24V AC | 250mA running | 2-core 1.0mm² from 24V SMPS to actuator (24V + 0V) |
| KNX TP bus connection (all actuators) | 29V SELV | Device bus current | YCYM 2×2×0.8mm² KNX TP bus cable |
| Motorised shutter / window (230V motor) | 230V AC | Up to 2.6A (600W) | 3-core 1.5mm² (UP/DOWN/COM) from JAL actuator to motor |
| VAV damper actuator (Belimo NM24A-KNX) | 24V AC | 200mA running | 2-core 1.0mm² from 24V SMPS; separate 0.8mm² YCYM for KNX TP |
| Binary input feedback cable | 24V DC | 20mA signal | 2-core 0.5mm² shielded from end-position switch to binary input |
Cable segregation: route 230V motor cables (shutter actuators, motorised windows) in separate cable ducts from KNX TP bus cables and 24V control cables. The magnetic field from 230V AC motor switching generates EMC noise that can cause errors on adjacent KNX TP cables if run in the same duct without shielding.
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