Fan Coil Unit Control with KNX
FCU integration with KNX building automation — 2-pipe and 4-pipe systems, fan speed, valve control and mode changeover. The standard for hotel and commercial office HVAC.
2-pipe vs 4-pipe fan coil systems
2-pipe system
- • Single pipe circuit: heating water OR cooling water (switched seasonally)
- • One water valve controls flow to the coil
- • Cannot simultaneously heat some rooms and cool others
- • Lower cost, simpler installation
- • Common in apartments and simpler office buildings
- • KNX valve: 1× 0-10V or on/off output
4-pipe system ✓ Preferred for hotels
- • Separate heating and cooling circuits always available
- • Two valves: hot water valve + chilled water valve
- • Simultaneous heating/cooling per zone possible
- • Higher comfort, flexible season changeover
- • Standard for 4-5 star hotels and premium offices
- • KNX valves: 2× 0-10V outputs (heating + cooling)
Fan speed control
Fan coil fans typically have 3 speed steps (Low/Medium/High) or variable speed (EC fan motor). KNX controls the fan via:
3-speed relay switching
3 relay outputs switch between Low/Medium/High fan motor taps. Simple but only 3 speeds. Some FCUs require a specific sequence (High first, then Medium/Low) — check FCU datasheet.
0-10V speed control
Single 0-10V output to EC fan motor speed controller. Provides continuous speed control (0–100%). Lower noise at intermediate speeds. Requires EC motor FCU.
PWM control
PWM signal (0–100%) to EC motor. Less common but used in premium FCU ranges. Same KNX object (DPT 5.001) as 0-10V.
The KNX fan coil actuator (Zennio KLIC-DD, MDT FAN module) handles fan speed logic internally — it receives the valve opening percentage and setpoint deviation from the KNX thermostat, then automatically selects the appropriate fan speed.
Zennio KLIC-DD — the standard KNX fan coil actuator
The KLIC-DD is configured in ETS as a complete fan coil controller. You set the valve opening speed, deadband, PI parameters, fan speed thresholds, and setpoint limits. The KNX thermostat (room controller) sends setpoint and measured temperature; the KLIC-DD drives the valves and fan. Multiple KLIC-DD units in a hotel are all configured identically from the same ETS product file.
Heating/cooling mode changeover
In a 4-pipe system, each FCU unit can switch between heating and cooling independently. The changeover is controlled by the KNX fan coil actuator based on:
In a 2-pipe system, mode changeover is a seasonal system-level operation — the building manager switches the plant from heating to cooling (typically spring/autumn). All FCUs follow the central system automatically.
Key KNX communication objects
| Object | DPT | Direction | Description |
|---|---|---|---|
| Setpoint | 9.001 (°C) | In | Temperature setpoint from room controller |
| Measured temp | 9.001 (°C) | In | Room temperature (from room sensor) |
| Valve position | 5.001 (%) | Out | Heating valve opening (0–100%) |
| Cooling valve | 5.001 (%) | Out | Cooling valve opening (4-pipe only) |
| Fan speed | 5.001 (%) | Out | Fan speed command to FC motor |
| Mode | 20.102 (HVAC) | In | Heating/Cooling/Fan/Off/Frost |
| On/Off | 1.001 | In | FCU on or off |
| Status | 1.001 | Out | Heating/cooling active status feedback |
Fan coil integration in your panel
We design KNX panels with Zennio KLIC-DD and MDT fan coil actuators pre-wired, tested, and ETS-programmed for your FCU specification.
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