Remeha Quinta Ace 115 kW cascade system

The Remeha Quinta Ace is a floor-standing condensing gas boiler in 55–115 kW variants, designed for cascade configurations in commercial buildings. A three-boiler cascade (3 × 115 kW = 345 kW total) is typical for schools, hospitals, and office complexes. Cascade wiring: each boiler's eBUS port (2-wire, 9.6V DC idle, 9600 baud half-duplex) is daisy-chained with jumper-configured addresses (boiler 1 = address 1, boiler 2 = address 2, boiler 3 = address 3). The lead boiler (address 1) manages the cascade protocol internally — follower boilers respond to lead boiler commands and are not individually externally accessible.

The Remeha eBUS protocol is proprietary to BDR Thermea group products (Remeha, Baxi, de Dietrich). External control of Quinta Ace requires the Remeha eBUS-Modbus RTU adapter (accessory part number available from Remeha technical support). This adapter plugs into the lead boiler's eBUS port and presents a Modbus RTU slave interface on RS-485, Modbus slave ID 1.

eBUS-Modbus adapter register map

Critical Modbus holding registers via the Remeha eBUS-Modbus adapter: Register 1 = flow temperature setpoint (read/write, °C × 10; write 700 for 70°C). Register 2 = operating status (read-only: 0=standby, 1=CH heating active, 2=DHW active, 3=summer mode, 4=frost protection). Register 3 = actual flow temperature (read-only, °C × 10). Register 4 = return temperature (read-only, °C × 10). Register 100 = fault code (read-only: 0=no fault). Register 101 = lockout code (read-only: non-zero = boiler lockout requiring manual reset). Register 200 = cumulative gas energy today (read-only, kWh × 10). Register 201 = cumulative starts today (count). Register 202 = cumulative operating hours today (minutes).

Cascade-specific registers: Register 50 = number of active boilers in cascade (read-only, 1–3). Register 51 = cascade modulation level (% × 10, overall cascade output percentage). These provide KNX access to cascade performance without needing to poll individual boilers.

Modbus RTU to TCP conversion and KNX gateway

Wire the eBUS-Modbus adapter RS-485 port to a Moxa NPort 5110A RS-485-to-TCP converter. Configure the Moxa NPort: baud rate 9600, parity none, data bits 8, stop bit 1, Modbus RTU-over-TCP mode (RFC2217 not needed; use TCP raw transparent). The Moxa NPort presents the Modbus RTU slave on TCP port 502 at its assigned LAN IP.

Configure the Intesis IN701KNX gateway (Modbus TCP master mode) in Intesis MAPS software: slave IP = Moxa NPort IP, port 502, slave ID 1, polling interval 15 seconds (Remeha eBUS protocol can be slow — avoid polling below 10 seconds to prevent bus saturation). Map registers to KNX group addresses: Register 1 (flow setpoint) → DPT 9.001 (÷10) → GA 8/0/0 bidirectional. Register 2 (status) → DPT 5.001 → GA 8/0/1 read-only. Register 100 (fault) → DPT 1.005 → GA 8/0/2 read-only. Register 200 (gas energy today) → DPT 13.013 (×100 for Wh) → GA 8/0/3 read-only cyclic every 15 min. Register 50 (active boilers) → DPT 5.001 → GA 8/0/6 read-only. Register 51 (cascade modulation) → DPT 5.001 → GA 8/0/7 read-only.

Lead-lag rotation logic

Operating all boilers at equal run hours maximises cascade life expectancy and maintenance interval synchronisation. A KNX logic function (or IP-Symcon script) implements weekly lead rotation: every Monday at 00:00 KNX time, the active lead boiler designation rotates. In practical terms, this means the Modbus setpoint and on/off commands are sent to a different eBUS-Modbus adapter (each boiler gets its own Moxa NPort and Intesis gateway instance). A KNX GA 8/0/8 (DPT 5.001) tracks current lead boiler number (1, 2, or 3). Automation logic uses a multiplexer function: write setpoint only to the gateway corresponding to the current lead boiler GA value.

Remeha Control Online cloud complement

Remeha Control Online (app.remeha.com) provides a cloud API for the Remeha ISense or etwist controllers, offering historical gas consumption graphs and fault history not available via Modbus. For BREEAM Ene 02 sub-metering, export monthly gas consumption data from Control Online and cross-reference with KNX Modbus cumulative gas energy (Register 200) for validation. If values diverge by more than 5%, investigate polling failures or eBUS communication errors in the Moxa NPort diagnostic log.

Weather compensation and commissioning

KNX outdoor temperature sensor on GA 0/0/0 (DPT 9.001) drives a weather-compensated flow setpoint curve via KNX logic: T_outdoor -10°C → setpoint 80°C; T_outdoor 15°C → setpoint 40°C. Linear: setpoint = 80 − ((T_outdoor + 10) / 25) × 40. Result written to GA 8/0/0 → Intesis gateway → Modbus Register 1. This replaces fixed setpoint control and improves boiler efficiency by reducing flow temperature during mild weather, keeping the boiler in condensing mode longer.

Commissioning: write value 600 (60.0°C) to GA 8/0/0 in ETS6 Group Monitor and confirm Remeha controller display shows 60°C flow setpoint within 20 seconds. Read GA 8/0/6 and verify the active boiler count matches the cascade status displayed on the lead boiler controller. Simulate a fault by disconnecting the lead boiler outdoor sensor and verify GA 8/0/2 = 1 within one polling cycle (15 seconds).