Zehnder
ComfoAir Q HRV with Modbus Integration — Demand-Controlled KNX Ventilation
Zehnder Group (Gränichen, Switzerland, founded 1895) manufactures the ComfoAir Q heat recovery ventilation (HRV) range — the reference HRV unit for Passivhaus and low-energy buildings in Europe. ComfoAir Q integrates with KNX via ComfoConnect LAN C (Ethernet bridge, Modbus TCP) — fan speed, bypass mode, filter alarm, and CO2-linked demand-controlled ventilation as KNX group addresses.
Role in our panels
How we use Zehnder
ComfoAir Q hardware: ComfoAir Q350 (350 m³/h, 30Pa minimum SFP, heat recovery ≥92%, dual EC fans, integral bypass), Q450, Q600. ComfoConnect LAN C: Ethernet RJ45 bridge module that plugs into ComfoAir Q bus port — enables Modbus TCP (port 502) and Zehnder ComfoConnect API (REST). Modbus registers: 337=supply air speed 0-100%, 338=extract air speed, 341=operation mode (0=away, 1=low, 2=medium, 3=high, 4=boost), 209=bypass state (0=closed, 1=open), 211=filter dirty alarm (0/1), 221=supply temperature (°C×10). KNX integration chain: Intesis IN701KNX (Modbus TCP to KNX) → MAPS signal table: Register 341 (mode) → DPT 5.001 (scaled 0-100% = modes 0-4) → GA 8/0/0 (Ventilation Mode). Register 337 → DPT 5.001 → GA 8/0/1 (Supply Speed %). Register 209 → DPT 1.001 → GA 8/0/2 (Bypass Open). Register 211 → DPT 1.001 → GA 8/0/3 (Filter Alert). ETS6 demand-controlled ventilation logic: CO2 sensor GA 9/1/0 > 1000 ppm → send speed mode 3 (High) to GA 8/0/0. CO2 < 700 ppm for 15 minutes → send mode 1 (Low). Presence detector GA: if all rooms unoccupied → send mode 0 (Away) after 30-minute delay. Bypass mode and summer cooling: ComfoAir Q bypass opens automatically when outdoor air is cooler than indoor — free night cooling. KNX integration: force bypass via Modbus register write (341 = bypass mode 5 for manual override) → GA 8/0/4 (Bypass Force). Summer night cooling logic: if indoor temperature GA > 24°C AND outdoor temperature GA < 18°C AND time 22:00–06:00 → force bypass open → full outdoor air flushing. Reduces cooling load next day. EN 15251 compliance and commissioning: EN 15251 (indoor environment parameters) Category II: CO2 < 550 ppm above outdoor level (approximately 950 ppm total). ComfoAir Q in DCV mode maintains Category II compliance automatically. For BREEAM Hea 02 credit: log ventilation mode and CO2 levels via KNX group monitor or ARISTO database → demonstrate Category II maintained for 95% of occupied hours.
Modbus TCP integration via ComfoConnect LAN C — fan speed mode, bypass state, filter alarm, and supply temperature mapped to KNX GAs. CO2-linked demand-controlled ventilation logic in ETS6 for EN 15251 Category II indoor air quality compliance.
Used in these project types
Zehnder products
Key components we install
ComfoAir Q350 HRV
Residential and small commercial HRV unit, 350 m³/h maximum flow, ≥92% heat recovery efficiency, dual EC fans, integral enthalpy bypass, 30Pa minimum SFP. Accepts ComfoConnect LAN C module for Modbus TCP and REST API access. Used in Passivhaus and near-zero-energy buildings as the primary mechanical ventilation system integrated with KNX demand-controlled ventilation logic.
ComfoConnect LAN C
Ethernet RJ45 bridge module that plugs into ComfoAir Q bus port. Enables Modbus TCP (port 502) access to all ComfoAir Q registers and Zehnder ComfoConnect REST API. Required for KNX gateway integration (Intesis IN701KNX, MDT Modbus gateway). Also enables direct Home Assistant integration via the zehnder custom component without additional hardware.
ComfoAir Q450
HRV unit for larger residential properties and small commercial applications, 450 m³/h maximum flow. Same integration path as Q350 — ComfoConnect LAN C module for Modbus TCP and KNX gateway integration. Suitable for 5–8 bedroom homes or open-plan commercial spaces requiring higher ventilation rates.
ComfoCool Q600
Combined HRV and active cooling unit, 600 m³/h, for commercial applications requiring mechanical cooling alongside heat recovery. Modbus TCP via ComfoConnect LAN C — additional cooling mode register for KNX active cooling trigger. Used in office buildings and healthcare facilities with year-round ventilation and cooling requirements.
ComfoSense 7 Room Unit
Touchscreen room unit with CO2 sensor (NDIR, 0–2000 ppm), relative humidity sensor, temperature display, and manual ventilation mode override. Can be wired directly to ComfoAir Q or integrated into KNX via ComfoConnect — CO2 value readable via Modbus register for ETS6 demand-controlled ventilation logic.
Zehnder FAQ
Does ComfoConnect LAN C support Modbus TCP directly or only Zehnder API?
ComfoConnect LAN C supports both: Zehnder ComfoConnect API (REST, JSON) and Modbus TCP (port 502). Use Modbus TCP for KNX gateway integration (Intesis, MDT) as it is more standardised. Use ComfoConnect API for direct Home Assistant integration (HA zehnder integration reads all parameters).
Can KNX force ComfoAir Q into boost mode for kitchen extraction?
Yes — Modbus register 341, value 4 (Boost mode) via KNX/Modbus gateway write. Trigger from KNX binary input (kitchen boost button) or ETS6 logic (kitchen hob power > 0W → boost for 30 minutes). Ensure HRV ductwork sized for boost flow without excessive pressure.
What is the filter service interval for ComfoAir Q?
Zehnder recommends filter replacement every 12 months (ISO coarse 60%+ supply filter) or when filter dirty alarm triggers (Modbus register 211 = 1 → KNX GA 8/0/3 = 1). For dusty environments: check filter every 6 months. Log filter change dates in BMS for maintenance records.
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