Quick answer: A "sealed" electrical or battery enclosure still takes in moisture, through four routes: leakage through gaskets, glands and joints; thermal breathing as the air expands and contracts each day; service door openings, which swap much of the internal air at once; and ventilation, where fitted. Each route's moisture load is roughly airflow × air density × (outdoor g/kg − target g/kg). For a tight cabinet, breathing adds very little. Leakage and door openings usually dominate, and a fan-filter ventilation path can add far more than both. An IP rating is not a leakage rate: use a test, manufacturer data or a stated assumption.
Quick answer
- Load = air entering × 1.16 kg/m³ × Δx (g/kg).
- Leakage and door events usually dominate in sealed cabinets; ventilation dominates where fitted.
- An IP rating doesn't give an air-change rate.
Define the air boundary
One cabinet, a multi-compartment battery cabinet, connected cabinets, a BESS container, or a room of cabinets: the boundary sets the volume, the leakage paths and the door events.
Four ways air enters
| Route | Driver | How to estimate |
|---|---|---|
| Leakage | Wind, fans, stack effect, pressure from HVAC | Test (decay or pressure), manufacturer data, or assumption |
| Thermal breathing | Air volume changes with temperature | Volume × ΔT ÷ absolute temperature, per cycle |
| Service doors | Mixing when doors open | Fraction of volume replaced per visit |
| Ventilation | Fans, filtered vents, safety ventilation | Design airflow |
Worked comparison (illustrative)
Cabinet free volume 1 m³; outdoor 30 °C / 80 % RH (21.6 g/kg); target 25 °C / 40 % RH (7.9 g/kg); Δx ≈ 13.7 g/kg.
| Route | Assumption | Moisture |
|---|---|---|
| Thermal breathing | 20 K daily swing | about 1 g/day |
| Door opening | Replaces one free volume | about 16 g per visit |
| Leakage | 0.5 air changes per hour | about 190 g/day |
| Fan-filter ventilation | 100 m³/h | about 38 kg/day |
(Calculated; actual leakage must come from data or tests.) Breathing adds very little; leakage adds hundreds of grams a day; a ventilated cabinet adds tens of kilograms, which a small cabinet dehumidifier can't remove. See fan-filter vs sealed cooling.
For a 40 m³ BESS container the same method gives litres per day; see BESS container sizing.
Internal moisture
- Water trapped during assembly or construction.
- Wet cables, packaging and materials brought in.
- Condensate from HVAC that isn't drained out.
The initial dry-down after commissioning can be larger than the steady load.
Inspect and classify each path
| Path | Check |
|---|---|
| Door and panel gaskets | Compression, damage, gaps |
| Cable glands and entries | Sealed, sized, unused entries plugged |
| Drains | Traps, check valves, open outlets |
| Vents and pressure-equalisation devices | Type; membrane or open |
| Joints between modules | Sealant continuity |
| Site penetrations | Finished and sealed |
Recovery time is an acceptance requirement
Agree how fast the enclosure must return to target after a door event, for example within 2 hours after a 15-minute visit. The dehumidifier must remove the door-event moisture in that time, on top of the steady load.
Control coordination
- Keep moisture control running when HVAC cycles off.
- Use a door switch to start drying immediately after a service visit.
- Alarm if recovery takes longer than agreed.
Our electrical cabinet dehumidifiers range from 0.5 L/day Peltier to 10 L/day compressor units.
FAQ
Frequently asked questions
Does a sealed IP-rated enclosure need a dehumidifier?
It can: leakage, door openings and trapped moisture still bring water in; an IP rating doesn't stop air exchange.
How much moisture does opening a cabinet door add?
About one free volume of outdoor air per visit; for 1 m³ at 30 °C / 80 % RH vs 25 °C / 40 %, roughly 16 g.
Is breathing a big moisture source?
For a tight cabinet, no: about a gram a day in the example; leakage and doors matter more.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics; Ventilation and infiltration.
- IEC 60529, Degrees of protection provided by enclosures (IP code).
