Vaillant aroTHERM plus is the leading heat pump in the German-speaking market (DE, AT, CH) and widely installed across Northern Europe. The R290 (propane) refrigerant variant delivers high efficiency even at -20°C outdoor temperature. Integration with KNX provides: Modbus TCP monitoring of COP and energy production, weather-compensated setpoint adjustment from KNX room controllers, and SG Ready contact control for solar surplus and cheap-tariff charging.

VWZ AI interface adapter

The Vaillant VWZ AI (article number 0020261780) is a Modbus RTU/TCP interface adapter that connects to the aroTHERM plus indoor module (aroCOLLECT or auroSYSTEM). The adapter mounts on DIN-rail and connects to the indoor module via the eBUS2 service port (RJ12 connector). VWZ AI provides: Modbus RTU on RS-485 (for legacy gateways), Modbus TCP on RJ45 Ethernet (port 502, slave address 1). Power: 24V DC from panel or from eBUS2 bus. The VWZ AI register map is available from Vaillant technical support (free download with dealer account) — approximately 80 registers covering all system parameters.

Key Modbus registers

Register 1: System operation mode (0=off, 1=heating, 2=cooling, 3=DHW, 4=tank heating, 5=defrost). Read-write: write to change mode. Register 5: Desired flow temperature (°C × 10, signed, e.g., 350 = 35.0°C). Read-write: write to override weather compensation curve. Register 6: Actual flow temperature sensor reading (°C × 10, signed). Read-only. Register 7: Outdoor air temperature (°C × 10, signed). Read-only. Register 8: Return temperature (°C × 10). Read-only. Register 9: DHW temperature (°C × 10). Read-only. Register 10: Calculated COP (× 100, e.g., 400 = COP 4.0). Read-only. Register 20: Daily heating energy (Wh, 32-bit, two 16-bit registers). Register 21: Daily DHW energy (Wh, 32-bit). Register 50: Compressor frequency (Hz). Register 51: Fan speed (RPM). Register 60: SG Ready mode status (0-3, read-only, reflects current SG input state).

Weinzierl KNX ENO 634 gateway configuration

In ETS6: add Weinzierl ENO 634 to topology. Configure Modbus connection: IP = VWZ AI IP (from DHCP or static assignment on router), port 502, slave address 1, polling interval 60 seconds. Data point configuration: DP1 = register 6 (flow temp), function code 03, 16-bit signed, ÷10 scaling, DPT 9.001, KNX GA 3/5/0 (read only). DP2 = register 10 (COP), 16-bit unsigned, ÷100, DPT 9.002, KNX GA 3/5/2. DP3 = register 20 (daily energy, 32-bit), function code 03, 2 registers, DPT 14.019 (kWh ÷1000), KNX GA 5/5/0. DP4 = register 5 (setpoint), read/write, 16-bit signed, ×10 for write, DPT 9.001, KNX GA 3/5/1. For KNX economy setback: HA or ETS6 logic block: when KNX HVAC mode = economy → write setpoint -4°C to GA 3/5/1 → gateway writes to aroTHERM register 5.

SG Ready control via KNX relay

Vaillant aroTHERM plus outdoor unit has SG Ready terminal block (SG1, SG2, PE). These are digital inputs — voltage-free contact closure activates: SG1 closed = Mode 3 (low tariff, increased setpoint), SG1+SG2 closed = Mode 4 (PV surplus, maximum operation), SG2 closed only = Mode 1 (grid block). KNX relay actuator (MDT SRA-0800.01, 8-channel relay 16A): configure channel 1 for SG1, channel 2 for SG2. Wire: MDT SRA relay output (NO contact) → SG1 terminal on aroTHERM. The relay output is volt-free — no additional voltage source needed at the SG Ready terminals.

KNX group addresses for SG Ready: GA 8/5/0 (SG Ready Mode 3 = low tariff, DPT 1.001 → MDT SRA channel 1 close). GA 8/5/1 (SG Ready Mode 4 = PV surplus, DPT 1.001 → MDT SRA channel 2 close). For Mode 4: both channels must be closed simultaneously → automate via ETS6 logic: GA 8/5/1 = 1 → also trigger GA 8/5/0 = 1.

Solar surplus charging automation

Solar PV + aroTHERM SG Ready integration via Home Assistant: HA reads Fronius inverter surplus power (Modbus TCP → HA sensor). Automation logic: when solar surplus > 2kW for 5 minutes → set aroTHERM SG Mode 4 (write GA 8/5/0 = 1, GA 8/5/1 = 1) → aroTHERM increases compressor to maximum, charges thermal buffer tank. When surplus < 500W for 5 minutes → set Mode 2 (write GA 8/5/0 = 0, GA 8/5/1 = 0). Buffer tank (Vaillant uniSTOR VIH R 300 L) stores 300L of thermal energy. At COP 3.5 and 3kW surplus: 10.5kW thermal charging rate → 1 hour of charging = 10.5kWh thermal storage → covers evening heating without grid draw.

Cheap-tariff scheduling

For buildings on time-of-use electricity tariffs (Octopus Agile, Tibber, etc.): HA reads current tariff price via API → when price < threshold (e.g., < 15p/kWh) → trigger SG Ready Mode 3 → aroTHERM runs at elevated setpoint, pre-heating the buffer tank. When tariff is expensive → Mode 2 (normal). This dynamic tariff response requires HA as the logic layer — KNX time-switches alone cannot access real-time tariff data. The KNX relay module provides the physical SG Ready contact closure that Vaillant requires; HA provides the intelligence that decides when to activate it.