Greenhouse dehumidification design starts with project data, not with a model number. Crop water use, night temperature, screens, ventilation, CO2 strategy and airflow layout can change the required moisture-removal capacity by a large margin.
Key Takeaways - Floor area alone is not enough for greenhouse dehumidifier sizing. - The supplier needs moisture source data, operating conditions and air-distribution constraints. - Day, night and transition periods should be separated because the peak risk may not match the daily average. - A good RFQ states assumptions clearly so the equipment recommendation can be checked.
The Minimum Data Set
A useful greenhouse RFQ should describe the crop, the room and the control objective.
| Input | Example format | Why it matters |
| Greenhouse layout | Area, height, bay count, compartments and screen zones. | Defines the controlled volume and zoning. |
| Crop and stage | Tomato, strawberry, leafy greens, propagation or mixed crop. | Changes transpiration and disease-risk profile. |
| Water use | Daily water consumption, irrigation volume or condensate estimate. | Helps estimate moisture released into the air. |
| Day and night conditions | Temperature, RH, dew point or VPD targets by period. | Separates plant response from condensation risk. |
| Ventilation strategy | Natural vents, exhaust fans, CO2 retention limits. | Determines whether ventilation can remove moisture. |
| Screen schedule | Thermal screen, blackout curtain or shade schedule. | Screens can trap moisture and change heat transfer. |
| Airflow layout | HAF fans, ducts, air tubes, aisles and crop height. | Determines whether dry air reaches the canopy. |
| Controls | Greenhouse computer, Modbus, relay, analog signal or standalone controller. | Affects staging and alarm integration. |
ASHRAE's HVAC design pathway lists psychrometrics, moist air properties and air distribution as core design concepts (ASHRAE). Greenhouse projects add another layer: the crop itself is a changing moisture source.
Separate the Operating Periods
Greenhouse load is rarely flat across 24 hours. A single daily average can hide the period that actually sizes the equipment.
| Period | Common design question |
| Daytime | Is ventilation enough when solar load, crop transpiration and CO2 strategy interact? |
| Dusk transition | Does RH spike when air cools and screens close? |
| Night | Can the crop stay dry without wasting heat through ventilation? |
| Blackout or screen closure | Is moisture trapped below the screen or curtain? |
| Irrigation or misting event | How long do leaves, fruit or trays remain wet? |
For greenhouse operators, trend data is more useful than a single snapshot. If available, send 7 to 14 days of temperature, RH, dew point, ventilation position, screen status and irrigation timing.
Convert Water Use Into a Load Assumption
In recirculating greenhouse systems, net water consumption can provide a practical starting point for transpiration load. The calculation still needs project review because drainage, leaks, evaporation from media and crop stage can change the balance.
Use a clear assumption format:
| Value | Example |
| Net water use | Liters per day or kg per day. |
| Active moisture period | Day, night, post-irrigation or screen-closed period. |
| Peak factor | Stated engineering assumption, not hidden in the final model. |
| Ventilation credit | Only when outdoor air is drier in absolute terms and venting is allowed. |
| Safety margin | Explained separately from missing data. |
For a worked example, see how many dehumidifiers a 5-hectare greenhouse may need. For calculator inputs, use the commercial dehumidifier sizing calculator guide.
Air Distribution Is Part of the Design Data
Capacity does not solve a greenhouse humidity problem if the dry air does not reach the crop zone. Include drawings or photos that show:
- crop rows, benches or tiers,
- aisles and service corridors,
- fan positions,
- duct or air-tube routes,
- screen or curtain movement,
- possible equipment locations,
- drainage route and service access.
If the project has an existing greenhouse computer, include the control interface and the signals available for dehumidifier staging.
RFQ Checklist
Before sending an inquiry, prepare this package:
| File or note | Purpose |
| Plan drawing or dimensions | Defines area, height and compartments. |
| Crop information | Explains moisture source and disease risk. |
| Operating targets | Defines day, night and transition conditions. |
| Water-use estimate | Gives a load basis. |
| Weather or outdoor design condition | Helps compare ventilation and dehumidification. |
| Control description | Shows how equipment should communicate. |
| Installation photos | Reveals hanging limits, ducts, drains and access. |
| Project stage and quantity | Separates concept review from final selection. |
Then decide whether the project needs ventilation strategy, refrigerant dehumidifiers, desiccant equipment or a hybrid approach. The agriculture dehumidification overview is the correct application entry point.
FAQ
Frequently Asked Questions
What is the most important input for greenhouse dehumidifier sizing?
The most important input is the moisture load by operating period. Area helps describe the greenhouse, but crop water use, night cooling, screen closure and ventilation limits usually explain the real load.
Can I size a greenhouse dehumidifier by square meters?
No. Square meters can be a rough context value, but they do not describe crop transpiration, outdoor air, temperature, dew point, curtain operation or airflow.
What if I do not have water-use data?
Send the best available project information and label the unknowns. A supplier can make a preliminary estimate, but the uncertainty should remain visible until measured data or a final design basis is available.
