Retrofit automation projects — where cable runs to switches are not possible without major disruption — require wireless control. Two established technologies serve KNX retrofit installations: KNX RF (EN 50090-3-3, 868MHz, bidirectional, battery or mains powered) and EnOcean (868MHz, energy harvesting, unidirectional by default but bidirectional in enhanced mode). Both integrate into KNX TP panels via dedicated coupler devices: KNX RF devices use KNX RF/S couplers, EnOcean devices use ENO 634 (Weinzierl) or EnOcean/KNX gateways. Choosing between them depends on battery preference, range requirement, and whether two-way communication (status feedback to switch) is needed.

KNX RF fundamentals

KNX RF (Radio Frequency) is part of the KNX standard — same DPT system, same ETS6 programming, same group addresses as KNX TP. KNX RF devices communicate at 868MHz (SRD band, 25mW max in Europe) in a star topology via an RF/S coupler (KNX TP device that decodes RF telegrams and forwards to KNX TP bus). Bidirectional: actuators can send status feedback to RF pushbuttons — LED on button confirms relay state. Battery life: KNX RF pushbuttons typically 2-5 years depending on usage (4× AA alkaline). KNX RF bidirectional mode: pushbutton can receive telegram from KNX bus — shows confirmation LED. ETS6: program KNX RF devices exactly as TP devices — same group address editor, same parameter pages. KNX RF repeater: optional to extend range in large buildings.

EnOcean fundamentals

EnOcean 868MHz uses energy harvesting: piezoelectric generators in pushbuttons (each button press generates power for one telegram) or solar cells for presence sensors. No battery replacement required — EnOcean switches self-power from ambient energy. Telegram structure: 8-byte data packet, no acknowledgement in standard mode (unidirectional). EEP (EnOcean Equipment Profile) defines telegram format: EEP F6-02-01 (rocker pushbutton), EEP D5-00-01 (1-channel contact sensor). EnOcean gateway to KNX: Weinzierl ENO 634 (DIN-rail, up to 254 EnOcean devices, ETS6 plug-in, maps EnOcean EEPs to KNX group addresses). Range: 30m indoors, 300m open field. In buildings: expect 15-25m through walls — reinforced concrete significantly reduces range.

Range comparison in practice

KNX RF: 868MHz 25mW typical range 30m indoors through 2-3 walls of standard construction. KNX RF can use repeaters (RF/RC) to extend reach to hard-to-reach areas. EnOcean: similar 868MHz range but often better wall penetration characteristics in practice due to lower frequency (compared to 2.4GHz WiFi/Zigbee). For multi-storey concrete buildings: both KNX RF and EnOcean struggle through ceiling slabs — consider additional coupler/repeater per floor. Practical rule: if direct line-of-sight or one-wall distance: both work reliably. Two or more concrete walls or floors: plan for repeaters or additional gateway per zone.

ETS6 programming differences

KNX RF: ETS6 programmes RF devices identically to TP devices — add RF/S coupler to topology, scan for RF devices (or enter device codes manually), assign physical addresses, configure group addresses. Same workflow as TP commissioning. EnOcean via Weinzierl ENO 634: ETS6 ENO 634 plug-in shows EnOcean device list. Each device added by: scan (requires button press on device to learn) or manual EEP + ID entry. Map EnOcean telegram to KNX group address: e.g. button A1 press → GA 1/1/0 value 1 (DPT 1.001). No bidirectional status feedback to EnOcean switch (standard mode) — no LED confirmation.

Project selection guide

Choose KNX RF when: budget allows battery replacement (2-5 year cycle), LED confirmation feedback on switch is required by client, maximum compatibility with ETS6 programming workflow is priority, or wall switch positions are known and fixed. Choose EnOcean when: zero maintenance (no batteries) is a hard requirement (listed buildings, hard-to-access switches), switches may be repositioned after installation (stick-on self-adhesive pushbuttons), or ambient light is available for solar harvesting presence sensors. For most UK and Northern Europe retrofit projects: EnOcean via Weinzierl ENO 634 gateway is the preferred choice — zero battery maintenance and the energy harvesting principle appeals to building owners.