When a greenhouse operates with its normal ventilation closed, crop moisture still enters the air. Recirculating that air can improve distribution, but it does not remove water by itself. A credible closed-mode humidity plan therefore names the water-removal device, its operating condition, the route by which collected water leaves, and the crop zones that receive treated air. It also states when the greenhouse is allowed to switch to an outside-air mode.
“Sealed greenhouse” is a description to test, not a zero-leakage specification. Some projects stay closed through an entire operating period; others close only at night or mix recirculated and outside air in a semi-closed mode. Write the actual mode schedule and air paths before selecting dehumidification equipment. The conceptual header image is AI-created; it is not a Yakeclimate installation or a finished system design.
Define the closed interval and its air boundary
Start with a named period such as a night with roof vents closed, a high-solar-load period with mechanical cooling, or a controlled CO₂ period. Record the vent, intake, exhaust, door and screen states for that period. Include deliberate purge or safety ventilation and a justified leakage assumption. A vent command of “closed” does not prove zero outside exchange or prove that the air below a screen mixes with the air above it.
| Operating description | Where moisture can leave | Equipment question |
|---|---|---|
| Closed mode with no planned outside-air drying | Condensate at an operating cooling or dehumidifying device, or moisture discharged by an applicable regeneration process | Can the selected equipment remove the relevant moisture load at the actual inlet condition throughout this interval? |
| Semi-closed mode with controlled outside-air mixing | The verified outside-air exchange and any mechanical removal | What share of each route is available under the weather, heat and CO₂ constraints? |
| Night-closed, day-ventilated greenhouse | A different route in each period | Which period determines equipment duty, and what happens at the transition? |
The greenhouse ventilation-versus-dehumidification guide owns the broader route-choice question. This guide starts after a closed or low-exchange mode has been proposed and asks whether its moisture route can actually carry the load. A research review of semi-closed greenhouses distinguishes recirculated, outside and mixed-air treatment modes; its examples are not a universal design for every greenhouse.
Account for water over the same operating period
Define the controlled volume and time window before comparing water sources with removal. Crop transpiration, wet substrate or floors, irrigation events and outdoor-air leakage may contribute. Planned ventilation can remove or add water depending on the outdoor and indoor air states, but it cannot be counted as a removal route in a period when that route is unavailable. Existing cooling coils may remove latent load only while their actual condition and runtime support condensation.
For an initial review, keep a period-by-period record:
| Record | What to confirm | Common mistake |
|---|---|---|
| Moisture entering the crop-zone air | Crop and growth stage, irrigation and drainage records, representative temperature/RH trend, wet surfaces and justified outside-air exchange | Treating total irrigation or a daily average as the hourly crop-air load |
| Intentional water removal | Device condensate or regeneration discharge, actual operating hours and the air volume the device treats | Counting a catalog rating obtained at a different inlet condition |
| Other changes in water storage | Surface condensation, wet materials or a changing air state that needs investigation | Calling water on glazing or leaves successful humidity control |
The first and last rows are not interchangeable: unwanted condensation can lower water vapor in the air while leaving a crop or structure wet. It is evidence of an unresolved local condition, not a designed water sink. The greenhouse project-data checklist gives the wider input set for estimating a design load. Do not convert an incomplete water balance into a machine count.
Use the demanding periods, not only a daily total. During a day-to-night transition, temperature, screen position, cooling runtime and crop moisture release can change together. State the permissible excursion and recovery time for each mode with the crop and controls owners. If the load cannot yet be bounded from records or justified assumptions, mark the duty open and gather the missing data; a generic safety factor does not repair an unidentified moisture source.
Match removal duty and the heat path
Compare required removal and available device removal on the same time basis, normally a named operating period with a stated inlet air temperature, humidity and airflow. For a proposed unit, request a capacity basis applicable to that condition and record defrost, permitted runtime, staging and service availability where they matter. If existing cooling equipment is claimed to carry part of the latent load, separate its measured or supported condensate duty from its sensible cooling duty. Do not assume that every air conditioner removes enough moisture merely because it runs.
The water and heat paths must be reviewed together. A self-contained dehumidifier that returns condenser heat to the greenhouse can add heat to its treated space. An air-treatment unit with an external heat sink, cooling coil or regeneration exhaust has a different heat balance. Specify where the heat goes, how condensate drains or regeneration moisture exits, and whether the same equipment can meet temperature and humidity duties simultaneously. Dalhousie University’s semi-closed greenhouse research summary frames simultaneous cooling and dehumidification as a balance against heat and moisture present at the time; it does not establish a Yakeclimate unit rating or an expected savings figure.
If outdoor-air exchange is a permitted fallback, define its weather and crop conditions separately. It may change heating, cooling and CO₂ duties as well as moisture removal. A closed-mode equipment review should not quietly take credit for venting that the chosen operating sequence prohibits.
Deliver treated air to the intended crop zone
The equipment can collect water at its own coil while a distant crop zone remains humid. Draw the return-air location, treatment device, supply path, screens, partitions, crop rows and drains. Identify where air could bypass the canopy or remain above a closed screen. Ask how each compartment is served, which sensors represent it, and what happens when a screen or door changes position.
Research on semi-closed greenhouse air treatment describes both corridor-and-duct and distributed-unit arrangements. A Wageningen University thesis abstract notes that the condition around crops varies spatially. A later Wageningen Plant Research report abstract finds that air-distribution effects depend on greenhouse design, crop and screen use. These sources support measuring the actual zones; they do not make one fan or duct layout correct for every site.
Use the existing greenhouse air-distribution guide for duct and tube details, and the sensor-placement guide for representative measurements. This page’s decision is narrower: a closed-mode removal claim is incomplete unless treated air reaches the zones named in the brief.
Specify the equipment interface without transferring system ownership
The greenhouse controls designer should define the mode and crop objective. The equipment supplier should state the unit’s supported operating envelope, command interface, run feedback, alarms, protective limits and condensate requirements. The two sides then agree which signals cross the boundary. An RH setpoint appearing on a controller screen does not by itself prove that the device received a command or ran at its expected duty.
| Interface item | Record for the closed-mode test |
|---|---|
| Command and authority | Which controller requests the unit, which modes permit it, and whether local protection can reject a request |
| Run and capacity proof | Actual run feedback, stage or speed state, inlet and outlet condition where available, and collected-water evidence appropriate to the device |
| Failure response | Sensor or communication fault, full drain, protective trip, power recovery, alarm owner and permitted restart |
| Mode transition | What changes when vents open, screens move, cooling leads, or an emergency purge is required |
The automated greenhouse humidity-control guide covers broader staging and sensor logic. This interface list is a handoff for a proposed closed operating mode; it is not a complete greenhouse PLC sequence. Confirm each item from the selected equipment and approved controls documents. No universal protocol, fail state or timer is assumed.
Verify the closed period before calling it controlled
Commissioning should follow the actual approved project sequence. First save the intended mode, crop-zone target and allowed excursion. Confirm vent and screen states, inspect the drain or regeneration path, and verify sensor IDs and clock alignment. Then trend a representative closed period with indoor and outdoor temperature/moisture conditions, crop-zone measurements, controller requests, real unit run feedback, alarms, condensate where applicable, and other active cooling or heating. Check that the removed-water evidence and the crop-zone response are consistent with the proposed duty.
If an emergency vent, door event or fault changed the boundary, mark that interval separately instead of presenting the trace as an uninterrupted sealed-mode result. If the equipment ran but a crop zone remained wet, review airflow and measurement position before simply increasing capacity. If RH fell while condensate was not observed, examine temperature changes, unintended ventilation, sensor behavior and moisture storage before crediting the device. A single acceptable controller reading is not a full-zone acceptance test.
The greenhouse humidity commissioning checklist covers the broader handover. Keep the closed-mode evidence attached to that record: defined air boundary, time window, load assumptions, selected capacity basis, treated-air route, command and run proof, alarm behavior, crop-zone response, unresolved deviations and named decision owners.
Prepare a reviewable equipment brief
Send the equipment reviewer a plan with compartments and screens; crop and stage; planned closed, semi-closed and ventilated periods; target temperature and moisture conditions with tolerances from the crop owner; indoor and outdoor time-series data; irrigation and drainage records; justified leakage and any permitted purge; existing cooling or dehumidification evidence; air-distribution layout; electrical and drainage limits; and the control points available. Label each item measured, assumed or open.
Yakeclimate designs and manufactures industrial dehumidification equipment for complex climate applications. It can review an application-specific moisture-removal duty, equipment operating conditions and interfaces against that brief. The grower and greenhouse controls designer remain responsible for crop targets and the complete climate sequence. Selection stays open where load, capacity or system constraints are unverified.
FAQ
Frequently asked questions
Does a sealed greenhouse need dehumidification?
It needs a defined route for the water entering the air during each closed period. That route may include operating cooling coils or dedicated dehumidification, depending on the project. Recirculation alone does not remove water; verify actual moisture-removal duty before deciding the equipment arrangement.
Can outside air be counted in a sealed-mode moisture balance?
Only the exchange actually permitted and justified for that period belongs in the balance. A semi-closed mode with controlled outside air is a different operating state from a closed mode with no planned ventilation. Record leakage and any safety purge, but do not quietly treat them as dependable drying capacity.
Is collected condensate enough to prove the crop zone is controlled?
No. Condensate shows that water was collected at a device. Check the unit’s operating condition, treated-air delivery, representative crop-zone temperature and moisture, and wet-surface risk during the same period.
What information should be confirmed before selecting a unit?
Confirm the closed-mode time window and air boundary, moisture load by period, allowed crop-zone condition, selected unit capacity at the actual inlet condition, heat and water discharge paths, air delivery, controls interface, drainage, power and service constraints. Missing items remain open questions rather than estimated machine quantities.
Technical sources
- Sapounas et al., Design, Control, and Performance Aspects of Semi-Closed Greenhouses — research review of recirculated, outside and mixed-air treatment modes, layouts and measurements.
- Wageningen University & Research, Dehumidification of greenhouses — thesis abstract on greenhouse humidity distribution and controlled air delivery.
- Wageningen Plant Research, Effect of air movement on greenhouse climate during dehumidification — report abstract on design, crop and screen dependence of distribution.
- Dalhousie University, semi-closed organic tomato greenhouse cooling and dehumidification project — simultaneous heat and moisture-duty context; its project outcomes are not used as equipment claims here.
