KNX building energy management architecture

A KNX building energy management system (BEMS) integrates MID-certified electricity meters, thermal meters, and gas meters into the KNX bus network via Modbus gateways, providing real-time energy visibility, automated demand response, and the sub-metering data required for BREEAM Ene 02 certification. The architecture: individual energy meters (ABB B24 or Eastron SDM630 Modbus) on each load group → Modbus RTU/TCP → Intesis or Weinzierl Modbus-KNX gateway → KNX TP bus → ARISTO BewO energy management platform for dashboards, alerts, and report generation.

Meter placement follows BREEAM Ene 02 sub-metering requirements: one main incomer meter (total building energy), and separate sub-meters for HVAC (heating + cooling as a combined load, or separate for each), lighting (DALI bus with integrated power metering, or a separate DALI zone meter), domestic hot water, and transport (EV chargers). Each sub-meter has dedicated KNX GAs for power (kW), energy (kWh), and demand peak (kW peak in current 15-minute interval).

ABB B24 MID meter Modbus register map

The ABB B24 112-100 is a three-phase MID-certified energy analyser with RS-485 Modbus RTU (slave address configurable 1–247, baud 9600 default). Key holding registers: Register 0x0000 = Voltage L1-N (×0.1V, 16-bit), 0x0002 = Voltage L2-N, 0x0004 = Voltage L3-N. Register 0x0006 = Current L1 (×0.001A, 32-bit spanning 0x0006–0x0007). Register 0x000C = Active Power L1 (W, 32-bit signed). Register 0x0012 = Total Three-Phase Active Power (W, 32-bit signed — primary register for KNX power GA). Register 0x0156 = Total Active Energy Import (×0.01 kWh, 32-bit unsigned — primary register for KNX energy GA).

Map to KNX GAs via Intesis IN701KNX: Register 0x0012 (total power) → DPT 13.010 (4-byte signed, W) → GA 6/0/0 (building total power, read-only, send-on-change 500W, cyclic 60 seconds). Register 0x0156 (total energy) → DPT 13.013 (4-byte signed, Wh) → GA 6/0/1 (building total energy, read-only, cyclic 15 minutes). HVAC sub-meter → GA 6/1/0 (HVAC power), GA 6/1/1 (HVAC energy). Lighting sub-meter → GA 6/2/0, GA 6/2/1. Transport (EV charger) → GA 6/3/0, GA 6/3/1. DHW → GA 6/4/0, GA 6/4/1.

Time-of-use tariff scheduling

Smart electricity tariffs apply different rates at different times of day. A KNX weekly controller (or IP-Symcon script reading tariff schedule from an API) publishes the current tariff rate to GA 6/1/0 as DPT 9.001 (€/kWh). Typical three-period tariff: peak (07:00–22:00 weekdays, €0.28/kWh), off-peak (22:00–07:00 weekdays, €0.10/kWh), super off-peak (weekends and public holidays, €0.08/kWh).

ETS6 comparator logic monitors GA 6/1/0: when tariff > 0.25 €/kWh (peak) → shift flexible loads. This triggers: heat pump mode change → write SG Ready State 2 (normal heating only, no surplus operation) to GA 2/0/5 (DPT 5.001). EV charger 1 → write 0 to GA 6/5/0 (DPT 1.001 pause signal). Smart appliances with KNX-connected shelly or Sonoff relays (dishwasher, washing machine) → write 0 to GA 6/6/0 (defer start signal — device internal scheduler holds until permitted). When tariff < 0.12 €/kWh (super off-peak): heat pump SG Ready State 3 (enhanced operation, increase buffer tank temperature to store cheap energy). EV charger 1 resume (write 1 to GA 6/5/0). Appliance permit (write 1 to GA 6/6/0). Water heater boost (write 1 to GA 6/7/0 — activates electric boost element for DHW storage during cheap rate).

Peak demand limiting and demand response

Many commercial electricity tariffs apply a demand charge based on the peak 15-minute average kW demand recorded in the billing period. Exceeding a contracted demand limit incurs penalty charges. KNX demand response logic: monitor GA 6/0/0 (total building power, updated every 60 seconds). Calculate rolling 15-minute demand average in IP-Symcon or a KNX logic block. When rolling average > 80% of contracted limit (e.g., 80 kW for a 100 kW contract) → initiate load shedding cascade: priority 1 (shed immediately) — pause secondary EV charger (GA 6/5/1 = 0). Priority 2 (shed if still over limit after 2 minutes) — dim all DALI zones to 50% via scene GA 4/0/0. Priority 3 (shed if still over limit) — switch HVAC units to setback mode (raise cooling setpoint by 2°C, lower heating setpoint by 2°C via zone setpoint GAs). Restore loads in reverse priority order when power drops below 70% of contracted limit.

BREEAM sub-metering and CO2 reporting

BREEAM Ene 02 requires measured sub-metering data demonstrating that HVAC, lighting, and other significant loads are individually monitored. ARISTO BewO is configured with one energy widget per sub-meter GA pair (power GA + energy GA). BewO generates BREEAM-formatted reports: monthly energy table by category, peak demand graph, and operational carbon estimate. Operational carbon: total building energy GA 6/0/1 (kWh) × UK or EU grid carbon intensity factor (0.233 kgCO2/kWh for EU average grid, or location-specific factor from IEA data). BewO calculates daily CO2 emissions (kgCO2) and publishes to a KNX GA (GA 6/8/0, DPT 9.001) for display on the building lobby dashboard or tenant energy portal.

For buildings with on-site solar PV, an additional export meter (ABB B24 on PV output) feeds GA 6/9/0 (PV generation power) and GA 6/9/1 (PV generation energy). Net consumption = building import energy (GA 6/0/1) − PV export (GA 6/9/1). KNX self-consumption logic: when PV generation (GA 6/9/0) > 20 kW surplus (building load < PV output) → activate flexible loads (EV charger at maximum rate, heat pump SG Ready State 4, water heater boost) to maximise self-consumption and avoid export at low feed-in tariff rates.

Commissioning and verification

Meter commissioning: apply a known resistive load (e.g., a 3-phase 3 kW test heater) on the HVAC sub-meter circuit. Verify HVAC power GA 6/1/0 reads 3000 W (±2%) in ARISTO BewO and ETS6 Group Monitor. Run for 1 hour and verify HVAC energy GA 6/1/1 increments by approximately 3000 Wh. Test tariff scheduling: temporarily set the KNX weekly controller to peak tariff period and verify GA 6/1/0 transitions to peak rate, EV charger pauses, and heat pump changes to SG Ready State 2. Verify demand response by using a test load bank to push total building power above the 80 kW demand threshold and confirm DALI dimming and HVAC setback occur within the programmed delay times. Export ARISTO BewO BREEAM report and confirm all required sub-metering categories are present with 15-minute interval data.