Misura dell'energia con KNX: Eastron SDM630, Carlo Gavazzi EM340 e certificazione MID

Classi di precisione MID per contatori elettrici

MID Annex V — Active electrical energy meters:

  Class A: ±2% accuracy (basic residential, rarely used for sub-metering)
  Class B: ±1% accuracy (minimum for commercial billing sub-metering)
  Class C: ±0.5% accuracy (high-precision billing, revenue metering)

  Eastron SDM630 MCT: MID Class B approved
    → suitable for commercial tenant billing sub-metering
  Carlo Gavazzi EM340 MID: MID Class 1 (= Class B equivalent)
    → DIN-rail, European certification, strong local support

  Non-MID meters (e.g. Eastron SDM120, SDM72D standard):
    → monitoring only — cannot be used for legal billing
    → acceptable for BREEAM energy monitoring (not billing)
    → acceptable for KNX self-consumption tracking

Specifica e cablaggio dei TA

CT accuracy class:
  Class 0.5: required for MID billing sub-metering
  Class 1.0: acceptable for non-billing energy monitoring
  Class 3.0: basic monitoring only, insufficient for MID

Split-core CTs (Eastron SCT-013-100, 100A / 33mV output):
  → clip around existing conductors — no disconnection required
  → suitable for retrofits where shutdown is not possible
  → mV output connects to SDM72D-M (voltage input CT meter)

Solid-core CTs (Chauvin Arnoux C series, 100A/5A output):
  → higher accuracy, better for MID Class 0.5 applications
  → installed at initial wiring stage (conductor must pass through)
  → 5A output → SDM630 MCT (CT/5A input version)

CT wiring:
  Secondary leads S1/S2 in pairs (twisted)
  Polarity: P1 mark (K) facing supply side of conductor
  Short-circuit CT secondary before disconnecting from meter
  — open-circuit CT secondary at load produces dangerous HV

Tabella segnali MDT SCN-MODBUS.01 — sotto-misurazione per piano

SDM630 address 1 (Floor 1 total):
  Register 0x0034 (Total Power, W)
    → DPT 13.010 (4-byte signed W)
    → GA 9/3/0 — Floor 1 Total Power W
    → Poll interval: 60 seconds

  Register 0x0046 (kWh import, accumulated)
    → DPT 12.001 (4-byte unsigned, ×1000 = Wh)
    → GA 9/3/1 — Floor 1 kWh Import
    → Poll interval: 60 seconds

SDM630 address 2 (Floor 1 Lighting circuit):
  Register 0x0034 → GA 9/3/2 — Lighting Power W
  Register 0x0046 → GA 9/3/3 — Lighting kWh

SDM630 address 3 (Floor 1 HVAC):
  Register 0x0034 → GA 9/3/4 — HVAC Power W
  Register 0x0046 → GA 9/3/5 — HVAC kWh

Note: DPT 12.001 is uint32 (0–4,294,967,295 Wh = ~4.3 GWh)
  — sufficient for any building-level accumulation without rollover

Architettura di misurazione BREEAM Hea 05

Five mandatory end-use categories (buildings > 1,000m²):
  1. Lighting          → separate MCB group, separate SDM630
  2. Small power       → office equipment, desks, sockets
  3. HVAC              → fan coils, pumps, AHU, refrigeration
  4. IT equipment      → server room, comms rooms
  5. Catering          → kitchen, dishwasher, vending

Per floor:
  → 1× RS-485 bus segment
  → 5× SDM630 (one per end-use, addresses 1–5)
  → 1× MDT SCN-MODBUS.01 gateway per floor
  → Gateway connects to KNX TP line for that floor

Building total: KNX IP-Symcon or ARISTO BewO:
  → Sum GA values per end-use across all floors
  → Daily trending at 1-minute resolution
  → CSV export for BREEAM assessor at project completion

BREEAM documentation required:
  → Meter schedule showing meter ID, end-use, floor, MID approval
  → Wiring diagram showing CT position and polarity
  → 30-day trending data export from commissioning period

Sequenza di verifica del sottocontatore in messa in servizio

Step 1 — Modbus communications check:
  Use Modbus Poll PC software or MDT gateway diagnostic
  Read holding register 0x0034 (Total Power) from each meter
  Confirm response received within 500ms timeout
  Confirm device address matches meter DIP switch setting

Step 2 — CT direction (polarity) check:
  Apply a known resistive load on the metered circuit
  (electric panel heater, known wattage, power factor = 1)
  Read GA for power in ETS6 Group Monitor
  Positive value = correct CT polarity (consumption direction)
  Negative value = swap CT secondary leads S1 and S2

Step 3 — Accuracy verification (MID meters):
  Connect calibrated reference power meter in parallel
  Apply load for 30-minute test period
  Compare accumulated kWh: SDM630 vs reference
  Acceptable tolerance: ± 1% for Class B MID meter
  Record results in commissioning documentation for BREEAM