Quick answer: Fan-filter ventilation cools a cabinet with outside air, so every bit of moisture in that air comes inside. In a humid climate it brings in kilograms of water a day, and condensation forms on anything colder than the outdoor dew point. Sealed cooling keeps outside air out. An air-to-air heat exchanger removes heat without removing moisture. An air-to-water exchanger and a cabinet air conditioner have cold surfaces that condense water, so they need a condensate route. For lowest condensation risk in humid places, choose a sealed method, seal the cabinet, drain any cooling-coil condensate outside, and add dehumidification if the inside dew point can still reach cold surfaces.
Quick answer
- Fan-filter: outside moisture comes in with the cooling air.
- Sealed exchangers: keep outside air out; check internal moisture and cold surfaces.
- Air conditioners and water exchangers: condense water; plan the drain.
Four cooling arrangements
| Arrangement | Air boundary | Moisture effect | Condensation risk |
|---|---|---|---|
| Fan and filter | Outside air replaces cabinet air | Brings in outdoor moisture continuously | High in humid climates, on surfaces below outdoor dew point |
| Air-to-air exchanger | Internal and external air separate | No moisture removal; leakage still adds some | Low ingress, but trapped and door moisture stays |
| Air-to-water exchanger | Cabinet air cooled by water circuit | Removes moisture if coil is below dew point | Coil condenses; needs drain |
| Cabinet air conditioner | Internal air passes evaporator | Removes some moisture while cooling | Evaporator and cold discharge can condense; drain needed |
Sensible cooling leaves the humidity ratio unchanged; only a surface below the dew point condenses water (ASHRAE Handbook—Fundamentals, Psychrometrics).
How much water a fan-filter brings in
For 100 m³/h of outside air at 30 °C / 80 % RH, compared with 25 °C / 40 % inside, the cabinet takes in about 38 kg of water a day if nothing removes it (calculated; see air leakage and door moisture). Most passes through. But any surface below about 26 °C, the outdoor dew point, will collect water, and night cooling makes that likely.
Follow water separately from heat
- Where does the cooling air come from? Outside air carries outdoor moisture.
- Which surfaces get colder than the air's dew point? Coils, cold-water pipes, walls at night.
- Where does condensate go? Into a tray and out through a sealed drain, or onto equipment?
- What happens when cooling stops? The dew point may then reach surfaces that are now colder.
Choosing
| Site and need | Usually suitable |
|---|---|
| Dry climate, low heat load | Fan-filter can work |
| Humid or coastal climate | Sealed cooling plus moisture control |
| High heat load, sealed | Air conditioner or water exchanger with drain |
| Night temperature drops, outdoor installation | Sealed plus heater or dehumidifier |
See heater vs ventilation vs dehumidifier, BESS container condensation with air conditioning and our electrical cabinet dehumidifiers.
FAQ
Frequently asked questions
Do fan-filter units cause condensation?
They bring in outdoor moisture; condensation forms where cabinet surfaces fall below the outdoor dew point.
Does a cabinet air conditioner prevent condensation?
It lowers temperature and removes some moisture, but its cold surfaces condense water that must be drained, and humidity can rise when it cycles off.
Is an air-to-air heat exchanger better for humidity?
It keeps outdoor moisture out, but doesn't remove moisture already inside or brought in by doors.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
