Motorised Window Drives for KNX Automatic Ventilation
Motorised chain and spindle actuators allow KNX to open windows automatically for night cooling, CO2-triggered fresh air, and smoke ventilation — but safety priorities, rain protection logic, and EN 12101 compliance for smoke venting require careful system architecture.
Use cases — when KNX opens windows
| Use case | Trigger condition | Open position | Close condition | Safety override |
|---|---|---|---|---|
| Night cooling | 23:00–06:00 AND outdoor temp < 18°C | 100% (full open) | 06:45 before occupancy, or outdoor temp > 18°C | Rain close, wind close above 60 km/h |
| CO2 ventilation | CO2 > 1,000 ppm (MDT SCA-CO2 sensor) | 30% (ventilation gap) | CO2 < 800 ppm for 15 min | Rain close immediately |
| Smoke ventilation | Fire alarm relay activation | 100% full open — immediate | Fire brigade reset only | Not closeable during alarm |
| Rain close | Elsner P04 rain signal = 1 | Close — 0% (immediate command) | Rain signal = 0 for 5 min | Overrides all other sources |
Product overview — KNX window drive options
Geze E 300 N
Chain actuator — 300 N push/pull force
- • Supply: 230V AC, 50 Hz
- • Force: 300 N (suitable for heavy tilt/turn windows)
- • Stroke: 200 mm, 400 mm or 600 mm versions
- • Limit switches: integrated (no external sensor needed)
- • KNX: via Geze KNX Gateway adapter (GEZE IO 420)
- • Position control: travel time via gateway, not encoder
Geze E 250 N
Chain actuator — 250 N push/pull force
- • Supply: 230V AC, 50 Hz
- • Force: 250 N (light-to-medium windows)
- • Stroke: 200 mm, 400 mm versions
- • Limit switches: integrated
- • KNX: via Geze IO 420 gateway
- • Suitable for top-hung ventilation sashes
Siegenia Aeromat VT
Ventilation tilt drive
- • Supply: 24V DC
- • Designed for tilt-before-turn window ventilation position
- • Built-in position sensor for precise 80mm ventilation gap
- • KNX: via Siegenia DRIVE aeroControl KNX module
- • Suitable for Passivhaus window fittings (tilt hardware)
Windowmaster WCC 102
KNX-native chain actuator
- • Supply: 24V DC (from KNX panel PSU)
- • KNX: native bus device — no gateway required
- • Position control: DPT 5.001 (0–100%) with encoder feedback
- • Force: up to 200 N (single actuator)
- • Chain stroke: 300 mm or 500 mm
- • Most flexible for precision position KNX control
KNX integration options
Option 1 — KNX-native window actuator (Windowmaster WCC 102)
Advantages
Encoder feedback, exact position DPT 5.001, no gateway, 24V DC from panel PSU
Limitations
Higher per-unit cost (€180–250 per actuator), 24V DC supply requires separate circuit from 230V motors
Best for
Premium projects with precise ventilation setpoints, mixed with 230V blinds motors
Option 2 — Standard KNX blinds actuator + dumb chain actuator + travel time
Advantages
Cost-effective (€30–60 per chain actuator), reuses existing blinds actuator channels, familiar ETS6 setup
Limitations
Position accuracy ±5% (travel-time only), no encoder feedback, motor must be 230V AC
Best for
Simple open/close ventilation where exact position is not critical (night cooling, full open smoke vent)
Option 3 — KNX analog 0–10V output → drive controller
Advantages
Precise position via 0–10V setpoint, compatible with many industrial window drives
Limitations
Requires 0–10V output module (e.g. MDT AKD-0401.02), drive controller with 0–10V input (not all drives have this)
Best for
Commercial facades with Geze or Roto drive controllers that accept 0–10V position setpoint
Rain protection — immediate close logic
Rain close is the highest-priority automation command after smoke ventilation. An open window during rain causes water ingress, building damage, and liability. The logic must be fail-safe: if KNX fails, the window must still close.
KNX rain signal — Elsner P04
Elsner P04 rain sensor sends DPT 1.001 = 1 on first rain detection (heated sensor, no false positives from condensation). Link this GA to the 'Rain alarm' input of the window actuator. Actuator immediately closes all open windows.
Hold time — wait for dry
After rain stops (sensor = 0), wait 5 minutes before allowing re-opening. This prevents rapid open/close cycling from intermittent drizzle. Configure in ETS6 parameter 'Rain alarm hold time'.
Standalone rain sensor on drive controller
Do NOT rely solely on KNX for rain close. If the KNX bus fails, open windows must still close. Many chain actuators (Geze E 300 N via IO 420 gateway) support a direct 24V hardwired rain sensor input that closes the window independently of KNX bus state. Always wire this.
Power-off position
If mains power fails (actuator unpowered), the drive controller should default to closed position. Geze and Windowmaster drives can be configured for power-fail position = closed. Verify this in product documentation — not all drives have this feature.
CO2 ventilation — MDT SCA-CO2 integration
CO2-triggered window opening is one of the most effective KNX ventilation features — it directly improves indoor air quality without user intervention and reduces sick building syndrome complaints in offices and classrooms.
CO2 ventilation KNX logic — ETS pseudocode
// CO2-triggered window ventilation // MDT SCA-CO2 sensor → KNX → window actuator // Group addresses: // GA 5/0/1 — CO2 ppm value (DPT 9.008, from MDT SCA-CO2) // GA 5/0/2 — CO2 alarm (DPT 1.001, > 1000 ppm = 1) // GA 4/2/1 — Window position (DPT 5.001, to Windowmaster WCC 102) // GA 4/2/2 — Window status (DPT 5.001, from WCC 102 feedback) // GA 6/0/3 — Rain alarm (DPT 1.001, from Elsner P04) // ETS Logic block / Gira X1 rule: IF GA 5/0/2 == 1 // CO2 above 1000 ppm AND GA 6/0/3 == 0 // No rain (rain = closed, higher priority) THEN: SEND GA 4/2/1 = 30 // Open window to 30% (30% of travel time) // 30% = approx 90mm gap for ventilation // Stays at 30% while CO2 remains high IF GA 5/0/2 == 0 // CO2 below threshold for hysteresis period THEN: SEND GA 4/2/1 = 0 // Close window IF GA 6/0/3 == 1 // Rain detected — override CO2 logic THEN: SEND GA 4/2/1 = 0 // Immediate close — rain priority // This fires regardless of CO2 level
The 30% position (approx 90mm gap for a 300mm stroke actuator) provides adequate ventilation airflow while limiting heat loss and minimising noise ingress. For classrooms, a combined approach opening windows to 30% and simultaneously increasing HVAC fresh air flow via KNX HVAC setpoint override achieves better CO2 reduction than either method alone.
Night cooling sequence
Night cooling — opening windows overnight to flush thermal mass with cool outside air — can reduce the next-day peak room temperature by 3–5°C in heavyweight construction, avoiding air conditioning activation in moderate climates.
Night cooling logic conditions — KNX
// Night cooling — conditions for window opening
// All conditions must be true simultaneously
CONDITIONS (AND logic):
time >= 23:00 AND time <= 06:00 // Night hours only
outdoor_temp < 18°C // Elsner P04 temperature sensor
// (GA 6/0/7, DPT 9.001)
indoor_temp > outdoor_temp + 2°C // Cooling worthwhile
// (room temp sensor DPT 9.001)
rain == 0 // No rain (Elsner P04, GA 6/0/3)
wind_speed < 10 m/s // Moderate wind — not storm
// (Elsner P04, GA 6/0/1)
occupancy == 0 // Room unoccupied
// (PIR sensor, GA 1/3/x)
ACTION IF ALL CONDITIONS TRUE:
SEND window_position = 100% // Full open for max airflow
LOG "Night cooling: windows open"
CLOSE CONDITIONS (any one sufficient):
time >= 06:45 // Close before occupancy
outdoor_temp >= 18°C // Too warm — no benefit
rain == 1 // Rain — immediate close
wind_speed >= 10 m/s // Wind alarm approaching
// Safety: wind alarm threshold (15 m/s) fires regardless of scheduleClose at 06:45 (15 minutes before the 07:00 occupancy timer) ensures windows are closed and the space has returned to normal conditions before occupants arrive. If wind speed increases during the night, the wind alarm at 15 m/s fires the standard blinds/window retraction — the night cooling timer is bypassed and windows close immediately.
Smoke vent actuators — EN 12101 requirements
Smoke ventilation actuators are a legally separate category from comfort ventilation drives. They must comply with EN 12101-2 (natural smoke and heat exhaustors) and EN 12101-4 (power supplies). Using a standard chain actuator for smoke venting is a building code violation and creates insurance liability.
Dedicated 24V DC power supply — mandatory
EN 12101-4 requires a dedicated fire-classified power supply for smoke vent actuators (not the standard KNX 29V bus PSU). Typically a 24V DC UPS-backed supply with battery backup for minimum 72 hours. Brands: Belimo, Siemens, Systemair fire-rated PSU range.
Fail-safe spring return — mandatory
On power loss, the smoke vent actuator must automatically open the vent to the full-open position via a pre-loaded spring mechanism. This is the opposite of comfort ventilation (which defaults closed). Do not specify spring-return-to-closed drives for smoke vents.
Compliance testing — CE marking required
Smoke vent systems must be EN 12101-2 compliant. The actuator and vent sash together form a certified system — both components must carry the same certification number. Document this in the fire safety dossier.
KNX connection to smoke vent system
KNX can signal the smoke vent control panel (opening command via clean dry contact from KNX relay output), but the smoke vent control panel itself (e.g. D+H RZN 4404 or Colt Smoke Control Panel) must be an independent fire-classified system. KNX sends the trigger — the smoke vent panel executes the action with its own certified power supply.
Never use standard chain actuators for smoke venting
A Geze E 300 N, Windowmaster WCC 102, or any 230V AC comfort ventilation actuator must not be used for smoke venting — they lack spring return, fire-rated power supply compatibility, and EN 12101 certification. This is non-negotiable regardless of project budget.
Safety — full priority and limit requirements
Rain close — highest automation priority
Rain signal from Elsner P04 must immediately close all open comfort ventilation windows. No delay, no hold time, no override by CO2 or night cooling. Wire rain signal to both KNX actuator rain input and direct hardwired input on drive controller.
Child-lock — ventilation gap limit
In occupied spaces with children (schools, nurseries, residential), windows must not open beyond 80mm (ventilation gap only). Configure maximum open position in ETS6 to 80mm equivalent travel time percentage. Physical stop fitting on window hardware is also recommended as a backup.
Wind threshold close
Above 60 km/h wind (Elsner P04), all open windows must close immediately. This is separate from the blinds wind alarm (typically 45 km/h) — windows require a higher threshold because they are more structurally robust, but still not rated for storm-force wind when open.
Power-off position
Configure all window drive controllers for power-fail position = closed. Verify this setting in the drive controller setup tool — do not assume default. Test by disconnecting mains power during commissioning and confirming window closes.
Solar shading in your KNX panel
We wire blinds actuator modules with factory-calibrated motor groups, wind alarm inputs pre-connected to the Elsner sensor bus, and surge protection on all outdoor circuit feeds.
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