Thermal load trends in greenhouse electronics
LED panels, pump drivers, and fan controllers commonly dissipate 10–80 W as heat. Small sealed control boxes can run 5–12°C hotter than the surrounding aisle, especially when mounted near reflectors or irrigation lines. Using the hottest midday ambient prevents undersizing. A 10–20% margin usually covers dust, aging interfaces, and seasonal peaks during peak summer weeks often.
Temperature limits that protect crops and hardware
Many power devices remain stable below 85–105°C junction temperature, yet garden installations benefit from conservative targets to reduce failures and avoid heating nearby leaves. If ambient is 32°C and the limit is 90°C, ΔT is 58°C. At 35 W with a 15% margin, effective power becomes 40.25 W, lowering allowable total resistance to about 1.44°C/W.
Interpreting the thermal resistance network
Heat flow is modeled as resistances in series: RθJA = RθJC + RθCS + RθSA. Datasheets often list RθJC for the package; mounting materials add RθCS from pads, grease, and pressure. If RθJC is 1.6°C/W and RθCS is 0.4°C/W, then 2.0°C/W is consumed before the sink, so the remaining budget must be met by the heat sink and airflow.
Airflow, orientation, and altitude effects
Still air is approximated with h near 10 W/m²K, light airflow with about 25 W/m²K, and forced airflow near 50 W/m²K. Vertical fins typically perform 5–10% better than horizontal fins in natural convection because warm air rises cleanly through channels. At 1,000 m altitude, lower air density can reduce cooling roughly 6–7% in this simplified adjustment, so extra margin is recommended.
Selecting a practical heat sink from catalogs
Choose a catalog RθSA equal to or lower than the corrected target, then confirm footprint, fin height, and clearance from wiring and drip lines. Dark anodized surfaces can slightly improve radiation at higher temperatures, while copper bases can help spread heat for small contact areas. After installation, log case temperature for 30 minutes at steady load; if it exceeds plan, increase airflow, improve mounting, or select more surface area.