Variable refrigerant flow (VRF) systems from Toshiba — specifically the SMMS-e series — are a common choice for medium to large commercial buildings where multiple zones require individual temperature control with high efficiency. Unlike split units that have proprietary IR or simple on/off interfaces, the SMMS-e system supports a centralised BACnet/IP gateway that exposes each indoor unit as a fully addressable BACnet device. Combined with a LOYTEC LGATE-952 KNX/BACnet bridge, this creates a clean per-room KNX control architecture that ETS6 engineers can commission without deep BACnet expertise.

Toshiba SMMS-e VRF and BACnet gateway overview

The Toshiba SMMS-e VRF system supports 1 to 30 indoor units per outdoor unit pair, with indoor unit types spanning cassettes, ducted, wall-mounted, and ceiling-suspended. Each indoor unit communicates with the outdoor unit via the Toshiba AB proprietary bus. The Toshiba TCB-PCNT30TLE BACnet gateway connects to the Toshiba central control network via a dedicated RS-485 bus port (maximum 30 indoor units per gateway). The gateway presents each indoor unit as an individual BACnet device on the BACnet/IP network (UDP port 47808). Each BACnet device exposes the following BACnet objects: Analog Output AO0 — setpoint temperature (°C, 16.0–30.0); Binary Output BO0 — on/off command; Multi-State Output MSO0 — operating mode (1=Cool, 2=Heat, 3=Fan Only, 4=Auto, 5=Dry); Analog Output AO1 — fan speed (0=Auto, 1=Low, 2=Medium, 3=High); Analog Input AI0 — room temperature sensor reading; Binary Input BI0 — unit fault status. Gateway IP configuration: static IP on BMS LAN, subnet must be routable to LOYTEC LGATE.

LOYTEC LGATE-952 KNX/BACnet bridge configuration

The LOYTEC LGATE-952 acts as a BACnet client and KNX master simultaneously. Configuration via L-STUDIO software: create a BACnet/IP network connection (gateway IP, port 47808) → scan for BACnet devices → all TCB-PCNT30TLE registered indoor units appear as device list. For each indoor unit, bind BACnet objects to KNX data points: AO0 (setpoint) → KNX send group address with DPT 9.001; AI0 (room temp) → KNX send GA DPT 9.001; BO0 (on/off) → KNX send/receive GA DPT 1.001; MSO0 (mode) → KNX send/receive GA DPT 20.105 (HVAC mode: 0=Auto, 1=Comfort, 2=Standby, 3=Economy, 4=Protection — map to Toshiba modes accordingly); AO1 (fan speed) → KNX send/receive GA DPT 5.001.

Per-room KNX group address scheme

For a 12-room office building with 12 Toshiba indoor units, the KNX GA scheme follows a per-room structure under main group 9: GA 9/[room]/0 — On/Off DPT 1.001. GA 9/[room]/1 — Setpoint (°C) DPT 9.001. GA 9/[room]/2 — Actual room temperature DPT 9.001 (read from AI0). GA 9/[room]/3 — Operating mode DPT 20.105. GA 9/[room]/4 — Fan speed DPT 5.001. GA 9/[room]/5 — Fault status DPT 1.005. Where [room] = 1 through 12. This scheme allows individual room thermostats (e.g., MDT SCN-RT4.01 or Gira room controller) to directly address each VRF unit without intermediate logic. The LOYTEC LGATE handles all BACnet-to-KNX translation transparently.

Occupancy setback and group control

A PIR occupancy sensor (KNX, e.g., Jung 3360 WW) sends DPT 1.001 to GA 9/[room]/6 (occupancy). A KNX logic block implements setback: when occupancy = 0 (unoccupied) and HVAC mode is Comfort heating, setpoint GA 9/[room]/1 receives (current setpoint − 3°C); when mode is Comfort cooling, setpoint receives (current setpoint + 3°C). When room re-occupies, setpoint returns to scheduled comfort value. For group control of open-plan areas with multiple units, a KNX scene or group address fan-out sends identical setpoint/mode writes to all units in the zone simultaneously. VRF total power consumption monitoring: the Toshiba SMMS-e outdoor unit exposes a BACnet Analog Input for total system power (kW) — map this to GA 9/0/0 DPT 9.024 (kW) for energy dashboard display. Commissioning: verify each room by writing setpoint and confirming BACnet AI0 temperature reading stabilises; check fault bit BI0 with forced fault simulation if test mode available in service menu.