Stiebel Eltron
WPL heat pumps with SG Ready and ISG web Modbus TCP for KNX PV self-consumption
Germany's leading heat pump manufacturer, supplying WPL air-source and WPF ground-source heat pumps to over 100,000 residential installations annually. SG Ready standard compliance makes Stiebel Eltron heat pumps ideal for KNX-integrated PV self-consumption projects.
Role in our panels
How we use Stiebel Eltron
SG Ready S1/S2 terminal wiring to MDT relay actuator provides the most straightforward KNX integration path. Two dry-contact relay outputs from an MDT BJ65-AB08.01 relay actuator connect directly to terminals 31 (S1) and 32 (S2) on the WPL control PCB, enabling States 2, 3, and 4 from KNX PV surplus logic. State 2 (S1 closed) enables the heat pump at reduced setpoint; State 3 (S2 closed) activates DHW boost; State 4 (S1+S2 closed) runs at maximum capacity for peak PV absorption. The optional ISG web module exposes the full Modbus TCP register map over port 502. Key registers: flow setpoint (Reg 1, DPT 9.001), operating mode (Reg 100, DPT 5.001), COP reading (Reg 4, value × 0.1, DPT 9.002), and DHW setpoint (Reg 10, DPT 9.001). An Intesis IN701KNX gateway maps these registers to KNX group addresses, enabling full setpoint and mode control from any KNX logic controller. KNX PV surplus logic driving SG Ready states is the primary use case in new-build German residential projects. An MDT PV surplus logic controller or LOYTEC LVIS-ME3 monitors the SMA or Fronius inverter Modbus feed for export power; when export exceeds 2 kW, the KNX relay actuator closes S2 for DHW boost. When export exceeds 4 kW, both S1 and S2 close for maximum heat pump capacity. The hysteresis timer (configurable in KNX logic: minimum 30 minutes per SG Ready cycle) prevents rapid cycling. DHW boost scheduling from KNX time controller integrates with the ISG web Modbus register 10 for setpoint override. A KNX Theben TR 648 time controller writes the DHW setpoint to GA linked to Intesis Modbus output at 06:00 (raise to 55°C for Legionella prevention weekly) and resets to 50°C at 08:00. Fault monitoring via Modbus register 200 (fault code) mapped to KNX DPT 1.005 triggers a KNX notification via Gira HomeServer email function or MDT Glastaster II push notification.
Stiebel Eltron WPL heat pumps integrate with KNX via two methods: (1) SG Ready relay wiring — two MDT BJ65-AB08.01 relay channels connect to S1 (terminal 31) and S2 (terminal 32) on the WPL control PCB, enabling States 2/3/4 from KNX PV surplus logic. (2) ISG web Modbus TCP — the optional Internet Service Gateway module exposes flow setpoint (Reg 1), mode (Reg 100), COP (Reg 4), and DHW setpoint (Reg 10) via Modbus TCP port 502. Intesis IN701KNX maps these to KNX GAs: setpoint DPT 9.001, mode DPT 5.001, COP DPT 9.002.
Used in these project types
Stiebel Eltron products
Key components we install
WPL 17 ACS
17 kW air-source heat pump with SG Ready S1/S2 terminal input. Monovalent operation to -25°C (bivalent point at -15°C for most German climates). Integral heat pump manager HMP controls defrost, DHW priority, and SG Ready state transitions. Modbus TCP available with optional ISG web module. A++ rated. Connects to 200L SHM-Plus buffer store for hydraulic separation. Typical installation: DIN rail panel with MDT relay actuator for SG Ready wiring, Intesis IN701KNX for ISG web Modbus TCP integration.
WPF 7 S
7 kW ground-source heat pump for brine/water operation. Higher COP (up to 5.1 at B0/W35) compared to air-source WPL. SG Ready S1/S2 terminals at PCB (same wiring as WPL). Requires ground loop (horizontal collectors or vertical boreholes). Optimal for passive house projects where heating demand is low and COP maximisation is the priority. ISG web Modbus TCP integration identical to WPL range.
ISG web
Internet Service Gateway — plug-in module for WPL and WPF heat pumps providing Modbus TCP server on port 502. Full register map: flow setpoint (Reg 1), return temp (Reg 2), outdoor temp (Reg 3), COP × 10 (Reg 4), operating mode (Reg 100), fault code (Reg 200), DHW setpoint (Reg 10), DHW current temp (Reg 11). Also provides manufacturer cloud access for warranty monitoring. Required for any KNX project using Modbus TCP integration rather than SG Ready relay-only approach.
SHM-Plus
300L thermal buffer store providing hydraulic separation between heat pump primary circuit and heating distribution secondary circuit. Allows heat pump to run at higher efficiency by decoupling from zone valve cycling. Installed between WPL/WPF and underfloor heating manifold or fan coil unit secondary circuit. DIN rail panel wiring includes WPL control cable, SHM temperature sensor (PT1000), and zone valve actuators from same panel. Essential for multi-zone projects with UFH zones controlled by KNX Theben or Danfoss actuators.
FE7 Remote
Remote room control with eBUS interface for WPL/WPF heat pumps. Displays flow temp, DHW temp, room temp setpoint, and operating mode. eBUS 2-wire connection (same cable as Vaillant/Dimplex eBUS) runs to heat pump PCB. Can be used alongside KNX integration — eBUS room control provides local override while KNX provides energy management automation. Flush-mount to standard 55mm wall box. Not required when full ISG web Modbus TCP KNX integration is deployed.
Stiebel Eltron FAQ
Does Stiebel Eltron WPL support KNX natively?
No — Stiebel Eltron heat pumps do not have a native KNX bus interface. Integration uses two methods: (1) SG Ready relay wiring — two dry-contact outputs from a KNX relay actuator (e.g. MDT BJ65-AB08.01) connect to S1 (terminal 31) and S2 (terminal 32) on the WPL control PCB, enabling 4 operating states from KNX PV surplus logic; (2) ISG web Modbus TCP — the optional Internet Service Gateway module exposes full Modbus TCP register map on port 502, bridged to KNX via Intesis IN701KNX or Weinzierl KNX-Modbus gateway.
What is SG Ready and how does KNX control it?
SG Ready (Smart Grid Ready) is a German heat pump association standard defining four operating states via two dry-contact relay inputs (S1, S2): State 1 (S1+S2 closed) = blocked/off; State 2 (S1 closed only) = reduced setpoint, economy mode; State 3 (neither closed) = normal operation; State 4 (S2 closed only) = DHW boost/maximum capacity. KNX controls SG Ready states by writing to two KNX relay actuator outputs — one connected to S1, one to S2 on the heat pump PCB. A KNX PV surplus logic function block monitors inverter export power and activates the appropriate relay combination.
Can I monitor COP via KNX?
Yes — with the optional ISG web Modbus TCP module installed, Modbus register 4 contains the current COP value multiplied by 10 (e.g. register value 42 = COP 4.2). The Intesis IN701KNX gateway reads this register and maps it to a KNX group address with DPT 9.002 (2-byte float). This enables KNX energy monitoring dashboards (Gira HomeServer, LOYTEC LVIS) to display real-time COP and log daily average COP for BREEAM or BEG subsidy reporting.
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