Electrical panels are vital in all installations. Managing thermal dissipation ensures safety, efficiency, and equipment longevity.
This guide details thermal dissipation calculations, including formulas, tables, examples, and thorough parameter explanations.
Thermal Dissipation Calculator
Common Values for Thermal Dissipation in Electrical Panels
To design or evaluate thermal dissipation, engineers frequently rely on standardized or commonly observed values. Below is a table showcasing estimated power dissipation values by type of equipment and typical panel conditions. These values serve as guidance for thermal load estimation before conducting precise calculations.
Table 1: Common Power Dissipation Values by Component
| Component Type | Rated Power (kW) | Dissipation Factor (W) | Typical Efficiency (%) | Notes |
|---|---|---|---|---|
| Contactors | 0.2 – 1.0 | 2 – 10 | ~97% | Depends on coil size and switching freq. |
| Circuit Breakers | 0.5 – 2.5 | 4 – 15 | ~98% | Includes thermal-magnetic and MCCBs |
| Variable Frequency Drives | 1.5 – 75 | 50 – 2000 | 90 – 97% | Varies based on load and switching freq. |
| PLC Units | 0.1 – 0.5 | 1 – 5 | ~95% | Low power dissipation but sensitive |
| Transformers | 0.5 – 150 | 20 – 3000 | 92 – 98% | Consider core loss and copper loss |
| Industrial Power Supplies | 0.1 – 2.0 | 3 – 30 | 85 – 92% | Higher loss under full load |
| Lighting Ballasts | 0.1 – 1.0 | 1 – 10 | 90 – 95% | Applies to emergency lighting systems |
| HMI Panels / Touchscreens | 0.05 – 0.2 | 2 – 7 | 90 – 95% | Passive dissipation, but heat sensitive |
Table 2: Ambient Conditions vs. Allowable Heat Dissipation
| Ambient Temperature (°C) | Maximum Dissipation (W/m³) | Notes |
| 25 | 1000 | Standard reference condition |
| 30 | 800 | Requires moderate derating |
| 35 | 600 | Requires ventilation or forced cooling |
| 40 | 400 | Usually exceeds panel natural dissipation capacity |
| 45 | 250 | Forced air or AC required |
| 50 | 150 | Risk of component failure without active cooling |
Formulas for Thermal Dissipation Calculation
Several key formulas are used to calculate heat dissipation in electrical panels. These involve the electrical losses from devices and the thermal characteristics of the enclosure.
1. Basic Thermal Dissipation Formula
- Q = Power dissipation in watts (W)
- I = Current in amperes (A)
- R = Resistance in ohms (Ω)
Common Values:
- For copper busbars: R ≈ 0.0000175 Ω/m
- I varies from 10A to 1000A depending on load type
2. Power Loss in Equipment (General)
- P_loss = Power dissipated as heat (W)
- P_in = Input power (W)
- η = Efficiency (expressed as a decimal)
Example: For a 10 kW drive at 95% efficiency:
3. Thermal Power per Unit Volume
- q_v = Specific heat dissipation (W/m³)
- Q = Total dissipated power (W)
- V = Enclosure internal volume (m³)
Important for validating enclosure thermal limits.
4. Enclosure Surface Area Calculation
- A = Surface area in m²
- h, w, l = height, width, length of the panel in meters
5. Heat Transfer by Natural Convection
- h = Heat transfer coefficient (W/m²·K); natural convection ≈ 5–10 W/m²·K
- A = Enclosure surface area (m²)
- T_inside = Internal temperature (°C)
- T_ambient = External ambient temperature (°C)
Real-World Examples of Thermal Dissipation Calculations
Example 1: Medium-Sized Industrial Control Panel
Scenario: A control panel in a manufacturing facility houses a 15 kW variable frequency drive (VFD), three 10 A contactors, and a 500 VA transformer. The enclosure volume is 1.2 m³, ambient temperature is 35°C.
Step 1 – Estimate Heat Dissipation Per Component:
- VFD: 15,000 W × (1 – 0.95) = 750 W
- 3 Contactors: 3 × 5 W = 15 W
- Transformer: Assume 95% efficiency ⇒ 500 × (1 – 0.95) = 25 W
Total Power Dissipation (Q):
Step 2 – Thermal Power per Unit Volume:
Compare with Table 2: At 35°C, the max allowable is 600 W/m³ → Exceeds limit
Action Required:
- Add ventilation or forced air cooling
- Increase panel size or improve heat dissipation by relocating VFD
Example 2: Low-Voltage Distribution Board in Commercial Building
Scenario: A 0.8 m³ panel includes:
- 1 power supply unit: 1.5 kW, 90% efficiency
- 4 circuit breakers: Each dissipates 8 W
- PLC controller: 3 W
Step 1 – Heat Losses:
- PSU: 1500 × (1 – 0.90) = 150 W
- Circuit breakers: 4 × 8 = 32 W
- PLC: 3 W
Total Dissipation (Q):
Thermal Density (q_v):
At 25°C ambient (allowable 1000 W/m³), this is acceptable.
Final Assessment: No additional cooling required under current conditions.
Additional Guidelines and Considerations
- De-rating Factors: Most manufacturers publish de-rating curves depending on internal temperature rise. Always consult the datasheet.
- Hot Spots: Identify areas with poor air circulation and high concentration of heat-producing devices.
- Thermal Imaging: Use thermography to validate thermal models in real-world conditions.
- IEC and UL Standards: Ensure calculations align with IEC 61439 and UL 508A recommendations for panel builders.
- Heat Sink Integration: External heat sinks or thermal bridges can improve dissipation in dense layouts.