Daikin Altherma 3 air-to-water heat pumps dominate the European residential heat pump market, particularly the R-series (Altherma 3 R, underfloor heating) and H HT series (high-temperature for radiator retrofits). Connecting Altherma to KNX provides: real-time COP and energy monitoring, weather-compensated setpoint control from KNX room thermostats, and SG Ready integration for solar surplus and cheap-tariff heating. The DKN Cloud EN gateway (Daikin BRP069A61 or BRP069C4x) is the hardware interface.

DKN Cloud EN gateway: Modbus TCP path

The DKN Cloud EN gateway (BRP069A61) is a WiFi/LAN adapter that mounts inside the indoor unit casing and connects to the Altherma 3 control board via the proprietary S21 or P1P2 connector. Once installed, the gateway provides: Daikin cloud access (for smartphone app), a local REST API (ONECTA API), and Modbus TCP on port 502. The Modbus TCP interface is the path for KNX integration.

Default Modbus TCP configuration: gateway IP = assigned by DHCP, port 502, slave address 1. The KNX-Modbus gateway (Weinzierl KNX ENO 634, or Intesis IBOX-KNX-MBS) connects to the same LAN as the DKN gateway and polls its Modbus registers. Key registers: Register 1 = operating mode (0=off, 1=heating, 2=cooling, 3=auto, 4=DHW, 5=emergency heat). Register 5 = leaving water temperature setpoint (°C, integer). Register 6 = actual leaving water temperature (°C, integer). Register 7 = outdoor air temperature (°C, signed, divided by 10). Register 10 = COP (actual, multiplied by 100, e.g., 350 = COP 3.5). Register 20 = daily heating energy (Wh, 32-bit). Register 21 = daily DHW energy (Wh, 32-bit).

KNX gateway configuration

In ETS6 for Weinzierl KNX ENO 634: add device to topology, configure Modbus connection: IP = DKN gateway IP, port 502, slave address 1, scan interval 60 seconds. Configure data objects: Object 1 = register 6 (leaving water temp), read holding register, 16-bit signed integer, DPT 9.001 (°C), KNX group address 3/5/1. Object 2 = register 10 (COP), read, 16-bit unsigned, scale ÷100, DPT 9.002, KNX group address 3/5/2. Object 3 = register 20 (daily energy), read, 32-bit unsigned (2 registers), DPT 14.019 (kWh ÷1000), KNX group address 5/5/1. Object 4 = register 5 (setpoint), read/write, 16-bit signed, DPT 9.001, KNX group address 3/5/0. After download: KNX room thermostat writes setpoint to 3/5/0 → gateway writes to Altherma register 5 → Altherma adjusts heating curve.

Weather compensation curve

Altherma's most efficient operating mode is weather-compensated (heating curve): outdoor temperature is automatically measured by the unit's outdoor sensor, and the leaving water temperature setpoint is derived from a linear heating curve (configurable: design outdoor temp / design flow temp). This is configured locally in the Altherma controller, not via Modbus. Modbus setpoint (register 5) overrides the weather curve if written — use with caution. Recommendation: let Altherma run the weather compensation curve autonomously; use Modbus only to apply a fixed offset (e.g., +2°C for comfort mode vs. setback -4°C for economy mode). Set the offset via KNX HVAC mode logic: comfort = write setpoint = heating curve nominal; economy = write setpoint = heating curve nominal -4°C.

SG Ready integration

Daikin Altherma 3 outdoor units have an SG Ready terminal block with 2 digital inputs (contact closure = active). Mode 2 (Normal) = both open. Mode 3 (Low tariff / Forced ON) = Input 1 closed. Mode 4 (PV surplus / Maximum) = both inputs closed. Mode 1 (Block) = Input 2 closed. KNX relay module (MDT SRA-0800.01, one channel per SG input): KNX binary output 1 → relay 1 → SG input 1 (volt-free). KNX binary output 2 → relay 2 → SG input 2. For solar surplus integration: HA monitors Fronius inverter surplus (via Modbus TCP) → when surplus > 2kW for 10 minutes → HA writes KNX group address (relay 1 + relay 2 close = Mode 4) → Altherma runs at maximum capacity, heating thermal buffer or DHW. When surplus < 0.5kW for 5 minutes → HA clears group addresses → Mode 2 (normal).

KNX weekly schedule for heat pump

KNX time-switch (MDT SCN-TU.01 or ETS6 inline timer logic): weekday schedule: 06:00 write "comfort mode" to HVAC mode GA (DPT 20.102, value 1=Comfort) → Weinzierl gateway writes Altherma to normal setpoint; 23:00 write "economy mode" (DPT 20.102, value 3=Economy) → gateway writes setpoint to -4°C lower. Weekend: comfort period 08:00-23:00. Holiday mode: manual KNX group address write to "protection" mode (DPT 20.102, value 4) → gateway writes minimum setpoint (frost protection 7°C). Astro clock link: in shoulder seasons (May, September), enable economy setpoint offset based on outdoor temperature KNX sensor reading via ETS6 comparison logic block.

Energy monitoring via KNX

Daily energy readings (register 20 = heating, register 21 = DHW) accumulate throughout the day (reset at midnight). The Weinzierl gateway reads these every 60 seconds. KNX group address 5/5/1 receives daily heating kWh. HA records this value, calculates: daily average COP = (heating energy kWh) / (electrical energy kWh from smart meter). Display on Gira X1 Smart Home app as a KNX sensor value: "Heat pump daily energy: 24.5 kWh". Weekly and monthly totals via HA energy dashboard (HA integrates KNX sensor entities into its native energy management).