Quick answer: A shipping-container farm is a nearly sealed box, so almost all the water the plants take up comes back out as vapour that the climate system must remove. A good first estimate of the dehumidification load is daily water use minus what leaves in the harvest and the drains. For leafy greens that is close to the daily top-up of the nutrient tank. Size the dehumidifier for the lights-on period, when transpiration peaks, at the container's real temperature and RH. Then make sure the dried air reaches every rack level, because a single return-air sensor can read fine while the top shelf or the far end stays wet.
Quick answer
- Load ≈ water taken up by plants (sealed container).
- Size for lights-on, at the container's condition.
- Air must reach every rack level; measure at several positions.
Map the container
- Racks, levels, lights, doors, any outdoor-air openings.
- Supply and return air paths of the HVAC and dehumidifier.
- Water lines, tanks, drains, leaks.
- Service space around equipment.
A 40 ft high-cube container has about 67 m³ inside before racks. That small air volume saturates fast if moisture removal stops.
Worked example (illustrative)
- Leafy greens, nutrient tank top-up about 60 L/day, almost all transpired.
- Lights on 18 h/day; assume most transpiration then: 60 ÷ 18 ≈ 3.3 kg/h during lights-on (plus a little at night).
- Latent heat released when this condenses: 3.3 × 0.68 ≈ 2.3 kW. The air conditioning and dehumidification together must handle it, along with the lighting heat.
- Target, e.g. 22 °C / 65–70 % RH. The dehumidifier needs about 3.3 kg/h at that condition. Units rated at 30 °C / 80 % RH remove less at 22 °C / 65 %, so check the capacity curve.
Replace the top-up figure with your own records, and subtract water leaving in harvested plants and any drain-to-waste.
Lights-on vs lights-off
| Period | What happens | Risk |
|---|---|---|
| Lights on | High transpiration; heat from lights; AC runs | RH rises if AC alone can't remove enough latent load |
| Lights off | Transpiration falls; AC may stop; surfaces cool | Condensation on walls and racks if moisture control stops with the AC |
| Transitions | Rapid change | Short RH spikes |
Keep moisture control enabled independently of cooling. An AC that cycles off on temperature stops removing moisture. See can you run an AC and dehumidifier together.
Check airflow before adding capacity
- Measure RH and temperature at the top and bottom levels, and at both ends.
- Look for still pockets behind racks and near the doors.
- Add or redirect fans before adding dehumidifiers if one zone is wet and others are dry.
Diagnose wet surfaces
| Symptom | Likely cause |
|---|---|
| Wet walls at night | Wall below dew point (poor insulation, cold climate) with moisture control off |
| Water under racks | Leak or overflow, not humidity |
| Mould on top shelf | Poor air movement at the top level |
| Condensation near door | Outside air entering when the door opens |
Inquiry checklist
- Container size and insulation; climate outside
- Crop, rack layout, lighting hours and power
- Daily water use and drain-to-waste
- Target temperature and RH, day and night
- Current HVAC (capacity, controls)
- Power supply and drain point
- Space for equipment
Our indoor farming dehumidifiers include compact RYCM units rated 60–138 L/day (at stated conditions).
FAQ
Frequently asked questions
How big a dehumidifier does a container farm need?
About the plants' daily water uptake, removed mostly during lights-on, at the container's operating condition.
Can the air conditioner handle humidity in a container farm?
Partly; AC removes some moisture while cooling, but when it cycles off moisture builds up. A dedicated dehumidifier controls humidity separately.
Why is one shelf wetter than others?
Uneven airflow; check air movement at that level before adding capacity.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
