Wilo Stratos MAXO is Wilo's intelligent variable-speed circulator — the main competitor to the Grundfos MAGNA3 in European HVAC hydronic systems. Like MAGNA3, Stratos MAXO supports Modbus RTU or BACnet MS/TP via the IF-Module communication module, enabling pump speed, power consumption, and fault status to be monitored via KNX building automation. This guide covers IF-Module installation, Modbus RTU register map, MDT KNX/Modbus gateway configuration, and HVAC energy reporting.

Wilo Stratos MAXO specifications

Stratos MAXO-Z (heating/cooling variant, DN25–DN50, 0.04–1.5kW), Stratos MAXO-D (domestic hot water, DHW hygiene function). Both feature: IE5 permanent magnet ECM motor, built-in differential pressure sensor, integrated auto-adapt algorithm (AUTOADAPT equivalent — automatically adjusts pressure setpoint to system demand), 3.5-inch colour display (speed RPM, power W, differential pressure kPa, flow l/h, operating hours). ErP 2015 EEI < 0.20 compliant. AUTOADAPT mode: pump learns system curve over first 3-7 operating days and locks optimal setpoint — no manual pressure calibration. Manual mode: constant pressure (for constant-flow circuits) or constant differential pressure (for variable-flow).

IF-Module installation and configuration

Wilo IF-Module (separate order, slides into GENIBus-equivalent slot on Stratos MAXO): available in Modbus RTU (IF-Module Modbus), BACnet MS/TP, and LonWorks variants. Insertion: slide IF-Module into slot on pump body (rear, below display), secure with 2 screws. No tools for pump disassembly. Connections: RS-485 A, B, GND terminals on IF-Module. Modbus address: set via pump display (Menu > Communication > Modbus address, 1–247). Default baud rate: 9600, 8N1, half-duplex. Termination: if Stratos MAXO is the last device on RS-485 daisy chain → enable termination resistor switch on IF-Module. Multiple pumps on one RS-485 bus: daisy chain (A→A, B→B, GND→GND), each pump unique Modbus address.

Wilo Stratos MAXO Modbus register map

Key holding registers (function code 03, read; function code 06, write single register): Register 1 = Setpoint (0–100%, write to change speed reference in remote control mode). Register 3 = Actual speed (RPM, read-only, uint16). Register 5 = Motor power (W, read-only, uint16). Register 7 = Differential pressure (0.1 kPa resolution, read-only, int16). Register 9 = Flow rate (l/h, read-only, estimated). Register 11 = Fluid temperature (0.1°C resolution, read-only, int16). Register 100 = Alarm register (bit 0 = general fault, bit 1 = dry run, bit 2 = blocked rotor, bit 3 = overtemperature). Register 200 = Energy counter (kWh, read-only, uint32, accumulator). Enable remote Modbus control: pump display > Menu > Operating mode > Remote. Without this setting, writing to register 1 has no effect — pump runs on AUTOADAPT.

MDT KNX/Modbus gateway (SCN-MODBUS.01) signal table

MDT SCN-MODBUS.01 acts as Modbus RTU master on RS-485 and exposes registers as KNX group objects. ETS6 configuration (MDT ETS6 plug-in): Signal 1: Device address = pump Modbus address, Register = 5 (Power W), Data type = uint16, KNX DPT 7.001 (2-byte unsigned, W), GA 8/2/0 (Pump Power W). Signal 2: Register = 3 (Speed RPM) → DPT 7.001 → GA 8/2/1. Signal 3: Register = 7 (ΔP, 0.1 kPa) → DPT 9.024 (2-byte float, pressure kPa, scale ÷10) → GA 8/2/2. Signal 4: Register = 100 (Alarm) → DPT 1.001 (bit 0 extract) → GA 8/2/3 (Pump Fault). Signal 5: Register = 200 (kWh counter) → DPT 12.001 (4-byte unsigned, energy Wh, ×1000 for kWh→Wh conversion formula in MDT function) → GA 8/2/4. Poll interval: 30 seconds for monitoring, 10 seconds if active control. Download SCN-MODBUS.01 configuration.

Hydraulic circuit monitoring for BREEAM

For BREEAM Energy credit Ene 02 (sub-metering): pump energy (kWh counter register 200) serves as HVAC sub-metering data point. Install Stratos MAXO on: (1) chiller primary circuit pump (largest energy consumer), (2) heating secondary pump, (3) DHW circulation pump. Three pumps × 1 KNX energy counter each → separate GAs for energy management system. Daily total: ARISTO BewO script or IP-Symcon reads GA 8/2/4 at 23:59 → stores to database → generates weekly CSV report for BREEAM energy assessor. Combined with Eastron SDM630 electrical sub-meters → complete HVAC energy picture: pump + fan coil + chiller electrical consumption per floor.

Differential pressure monitoring and fault alerting

Advanced logic: monitor Stratos MAXO differential pressure (GA 8/2/2) to detect hydronic imbalance. Normal operating range for a 4-pipe HVAC circuit: ΔP 20–60 kPa depending on design setpoint. If ΔP drops below 5 kPa → possible pump dry run or pipe leak → trigger KNX alarm GA → notify facilities manager via ARISTO email alert. If ΔP rises above 90 kPa → possible closed motorised valve or blocked strainer → alarm. KNX logic (MDT Logic Module): GA 8/2/2 (ΔP value) → threshold comparator → if < 5kPa for 60 seconds → output GA 8/9/0 = 1 (Pump Low Pressure Alarm). ETS6 timer prevents false alarms during pump startup (ΔP rises from 0 to operating range in first 30 seconds). This predictive maintenance approach reduces HVAC downtime in commercial buildings.