Views: 1 Author: Site Editor Publish Time: 2025-11-19 Origin: Site
The grow room target relative humidity is 45–60%RH, depending on crop and stage (seedlings often higher; flowering usually lower). Aim for 50–55% as a safe general setpoint.
Track VPD (vapour pressure deficit) as the primary crop metric — maintain RH and temperature to hit the target VPD for your crop.
Keep the short-term dew-point below the canopy temperature to avoid condensation on leaves or equipment.
Evapotranspiration (ET) from plants (usually the biggest moisture source).
Make-up air/infiltration (outdoor air brings moisture).
Process moisture from irrigation, nutrient spraying, wet floors, post-harvest handling, drying rooms, or wash stations.
Temperature — dehumidification performance depends on air temp (refrigerant units lose efficiency at low temperatures; desiccant works better in cold).
Redundancy & control precision for continuous crop protection.
Refrigerant (compressor) dehumidifiers
The industrial refrigerant dehumidifier is best for warm, humid rooms (typical grow-room temps 18–30 °C).
Efficient at moderate-high temps; remove large volumes of water (tens to hundreds L/day).
They add sensible heat to the room (compressor heat + reheat from condenser) — can be helpful in cool climates, problematic if you need to avoid heating.
Desiccant dehumidifiers
Better at lower temperatures or when you need very low dew points.
Often used where air must be dried to very low RH or where freeze-risk exists.
Typically, higher energy use for the same water removed can require thermal regeneration (hot gas, steam, or electric).
Hybrid systems
Combine refrigerant + desiccant or integrate with HVAC heat-recovery to optimize efficiency across seasons/conditions.
Primary dehumidifier(s) sized to handle peak moisture load (ET + infiltration + process). Use modular units rather than one giant unit for redundancy.
Supply & return ducting to ensure even air distribution (consider mixing plenum or ducted units above/below racks).
Condensate management: gravity drain, floor trough + pump, or plumb to sewer — include float switches and alarms.
Controls & sensors: RH sensors (±2% accuracy), temp sensors, dew-point calculation, VPD setpoint logic, RH hysteresis, alarm thresholds. Integrate into BMS/PLC.
Filtration (pre-filter) to avoid biological fouling; consider UV or HEPA downstream if biosecurity is critical.
Air movement: fans for even distribution; avoid high-velocity air across leaves that increases transpiration stress.
Insulation & vapour barriers on walls/ceilings to avoid condensation in fabric/structure.
Primary control variable: Humidity (RH or dew point) tied to VPD calculations.
Setpoint logic: Use temperature + RH -> compute VPD -> actuate dehumidifier to maintain target VPD band.
Modulation: Use variable-speed fans/compressors or multistage units for smoother control and energy saving.
Interlocks: Lock out humidifiers when the grow room dehumidifier is running; interlock with irrigation cycles (pause irrigation or increase dehumidification after heavy irrigation events).
Alarms & notifications: High RH, low RH, condensate pump failure, sensor fault, door/open event. Remote monitoring and trending are essential.
Estimate plant ET (L/day). Typical ranges depend on crop & stage — from ~0.2–5 L/m²/day. Use crop data or measured ET.
Add process/moisture sources: wet floors, drying rooms, laundry, etc. (estimate L/day).
Calculate infiltration/moisture from outside: quantify air changes per hour (ACH) × outside absolute humidity difference → convert to L/day.
Sum all moisture inputs → Total L/day. Add safety margin (20–40%).
Select dehumidifier(s) with combined capacity ≥ required L/day at your operating temperature and entering air conditions (check manufacturer performance curves).
Distribute capacity across units to match zones and provide redundancy.
Worked example (clear step-by-step)
Assumptions:
Canopy area = 100 m².
Assumed ET = 1.0 L/m²/day (example crop & stage).
No other major process sources (conservative).
Safety margin = 30%.
Calculations:
Plant ET = 100 m² × 1.0 L/m²/day = 100 L/day.
Hourly rate = 100 L/day ÷ 24 hr/day = 4.1666667 L/hr (≈ 4.17 L/hr).
With a 30% safety margin, required capacity = 100 L/day × 1.30 = 130 L/day.
Recommendation from example:
Choose either a single ~130 L/day rated dehumidifier (capacity at your expected operating temperature), or better: two 70 L/day units for redundancy and easier maintenance (total 140 L/day).
Verify manufacturer performance curves at your room temperature and desired RH — advertised capacity is usually at 30°C/80% RH or similar; actual removal at your conditions may differ.
Place units so condensate drains straightforwardly; avoid sitting units directly on soil or near irrigation heads.
Use ducted in/return to balance humidity across vertical shelves — top/bottom tiers may differ in microclimate.
Ensure sufficient mixing: aim to avoid stagnant pockets where RH could be >5–10% above setpoint.
Refrigerant units release heat -> raises room temperature (useful if you need heat; bad if you want a cool room). Estimate sensible heat gain from unit specs and offset with cooling if necessary.
Desiccant units often require regeneration energy (electric or thermal) — factor energy cost.
Consider heat recovery: use dehumidifier condenser heat to preheat makeup air or to regenerate desiccant, improving system COP.
Keep condensate lines clean; stagnation can cause biological growth — use sloped, smooth piping and an auto-flush where possible.
Install pre-filters (MERV-rated) and clean/replace per schedule.
Keep the dehumidifier interior accessible for scheduled cleaning; document cleaning SOPs.
If you must combat spores/odours, consider UV-C downstream or activated carbon filters in the air path.
Design for N-1 redundancy for critical grow areas (i.e., if you need 130 L/day, install at least 2 units sized so that if one fails, the remaining unit(s) can keep humidity safe for a limited time, or install enough extra capacity).
Provide backup power or at least alarmed circuits for dehumidifiers and condensate pumps.
Commission with data logging (RH, temp, VPD, dehumidifier runtime, condensate flow) for 2–4 weeks before full crop load to tune setpoints.
Trend data to correlate irrigation events, heating/cooling cycles, and RH spikes.
Calibrate RH sensors every 3–6 months.
Weekly: empty/inspect condensate tray (if not plumbed), check drain pump, inspect filters.
Monthly: clean coils, check condensate lines, inspect sensors.
Quarterly: recalibrate RH sensors; check refrigerant charge or desiccant condition.
Annually: service compressor, check controls & alarms, replace major filters.
