Расчет тепловыделения и вентиляции щита

Расчет естественной конвекции — упрощенная модель по IEC 61439-1 Приложение D

Cooling capacity (W) ≈ 3 × A_eff × delta_T

Where:
  A_eff   = effective cooling surface area (m²)
  delta_T = permitted internal temperature rise above ambient (°C)

Example — small enclosed steel panel 600mm × 400mm × 200mm:
  A_eff ≈ 0.5m² (walls + partial top and bottom)
  For delta_T = 10°C:
    Capacity = 3 × 0.5 × 10 = 15W

  For 50W internal dissipation:
    Required delta_T = 50 / (3 × 0.5) = 33°C
    → Internal temp 35°C ambient + 33°C = 68°C  ✗  (exceeds 55°C component limit)

Conclusion: natural convection is inadequate for panels
above approximately 30W in a small enclosure.
Solution: ventilation louvres, fan-filter kit, or larger enclosure.

Расчет воздухообмена принудительной вентиляции

Required airflow:
  Q (m³/hr) = P_loss (W) / (0.34 × delta_T_allowed)

Where:
  0.34 = rho × Cp in SI units at standard conditions
         (air density × specific heat, simplified for m³/hr and W)
  delta_T_allowed = maximum permitted temperature rise (°C)

Example — 80W loss, 15°C temperature rise allowed:
  Q = 80 / (0.34 × 15) = 15.7 m³/hr

Select fan with rated flow above 20 m³/hr (1.3× safety factor).

Fan noise — axial fans at 20 m³/hr:
  Typical: 35–45 dBA
  Acceptable: plant rooms, electrical rooms
  Avoid in: living spaces, home cinemas (use centrifugal fan — slower,
  quieter, but larger; suitable for AV equipment panels)

Обязательное содержание документа теплового расчета

1. Component schedule with individual power losses (W)
2. Total internal power loss (W)
3. Enclosure type, dimensions, and surface area (m²)
4. Assumed ambient temperature (°C) — design case
5. Calculated internal temperature rise (°C)
6. Conclusion: natural convection adequate / forced ventilation required
7. Ventilation solution specified (louvre size or fan model and flow)

This document is required for:
  - IEC 61439-1 compliance (custom assemblies)
  - Insurance purposes for commercial panels
  - CE marking of the panel assembly

Инвентаризация потерь компонентов

6× MDT AKD-0802.01 relay actuators @ 2W each    =  12W
2× MDT AKD-0816.02 dimmer actuators @ 8W each   =  16W
1× WAGO 750-893 Modbus gateway                  =   3W
1× MDT STV-0640.01 KNX PSU                      =   6W
1× Weinzierl 770 KNX IP Router                  =   2W
20× MCB 16A @ 50% load → 0.4W each              =   8W
4× MCB 32A @ 50% load → 0.6W each               =   2.4W
2× 63A RCD @ 2.5W each                          =   5W
                                              ─────────
Total internal dissipation                       ≈  54W

Natural convection check (IEC 61439-1 Annex D):
  Capacity at 20°C rise = 3 × 1.5 × 20 = 90W
  54W < 90W → natural convection is adequate in this example.

However, louvres are still recommended because the simplified
model assumes free air circulation on all surfaces — an enclosure
in a packed services room has reduced effective surface area.
Conservative approach: specify fan-filter kit with 35°C thermostat.