The ideal greenhouse humidity is a crop- and stage-specific operating band paired with temperature, time of day and representative canopy measurements. A broad reference such as 60–80% RH cannot serve as the setpoint for every greenhouse. Start with an applicable crop protocol, check what conditions it assumes, and translate it into a documented target that the crop and controls teams can review.
This guide shows that process with a published lettuce-production reference and a transparent calculation example. Once the target and remaining moisture load are defined, review greenhouse dehumidifier equipment or submit the operating conditions through the project requirements form.
Understand what the reference actually says
Three useful sources answer different questions. The humidity section of Sustainable Greenhouse Systems, hosted by the University of Arizona, describes 60–80% RH as a general greenhouse guide. It also discusses temperature, leaf temperature, vapour pressure deficit and condensation. It does not validate that band for every cultivar, growth stage or night-time condition.
The peer-reviewed greenhouse environmental measurement guidelines discuss how to measure and report conditions around plants. Their broad statement that many crops perform well at 50–80% RH is not a specific crop-control schedule. The measurement method and location matter when applying any target.
The Wageningen process-based humidity-control research models a reference cut-chrysanthemum crop under defined temperature regimes. It supports examining changing crop and climate processes. Its simulated energy outcomes are not measured savings for another greenhouse or for Yakeclimate equipment.
Use each source for its actual purpose: background, measurement method or a defined research case. For an operating target, obtain crop-specific advice and record the relevant version and section.
A crop-specific example: greenhouse hydroponic lettuce
The Cornell CEA Hydroponic Lettuce Handbook, 2013, section 3.3, lists 24°C day / 19°C night air setpoints and an RH range of 50–70% for its described production system. Its early germination sequence uses humidity covers, so those production references should not be applied automatically to covered germinating seed.
For an illustrative post-transplant lettuce review, use those published conditions as the source reference, then select 65% RH as an example calculation input within that range. Cornell does not prescribe that midpoint as a universal optimum. The local crop adviser must decide whether the production reference is suitable for the actual cultivar, stage and facility. Cornell handbook.
| Illustrative air condition | Calculated air VPD | Calculated dew point | What the comparison shows |
|---|---|---|---|
| Day example: 24°C / 65% RH | About 1.04 kPa | About 17.0°C | A local surface near or below the dew point needs investigation |
| Night example: 19°C / 65% RH | About 0.77 kPa | About 12.3°C | The same RH percentage produces a different VPD and dew point |
These are calculated examples, not greenhouse measurements or Yakeclimate test results. Air VPD uses saturation vapour pressure at the stated air temperature; it is not leaf VPD unless the leaf and air temperatures are equal. Values use the saturation-vapour-pressure relationship in FAO Irrigation and Drainage Paper 56, with dew point obtained by inverting that relationship over liquid water.
Reproduce the comparison with the VPD calculator and dew-point calculator. Small differences can result from the formula and rounding used. A real condensation decision also needs simultaneous local surface temperature and measurement uncertainty; a calculated dew point alone does not prove that a leaf became wet.
Turn the source into a reviewable target record
The example below shows a completed desk-study record with explicit open decisions. It does not claim a site trial or a crop specialist's approval. Replace the illustrative entries with your project information before issuing an operating instruction.
| Field | Example entry | Responsible review |
|---|---|---|
| Crop and stage | Hydroponic lettuce after transplant; cultivar to be supplied | Crop adviser checks applicability |
| Source and scope | Cornell CEA handbook, 2013, section 3.3; described lettuce-production system | Crop adviser records the accepted source and any local adjustment |
| Period and temperature | Day 24°C; night 19°C, used here as reference conditions | Grower confirms the intended temperature programme |
| Candidate RH band | Published 50–70% reference; 65% used only for the calculations above | Crop adviser approves or changes the project band |
| Measurement plan | Representative canopy air plus the reported cold or wet location, with time-aligned temperature and RH | Instrumentation owner records location, method and uncertainty |
| Controller and alarm | Action bounds, delay and alarm duration remain unset in this desk example | Controls owner proposes settings against the approved crop band |
| Approval status | Demonstration only; no site measurements or named human approval | Record reviewer, date, observations and decision after the site review |
The useful outcome is an approved crop-stage-period target and a way to check it. An unsigned worksheet can organize the decision, but it cannot replace the decision. If the crop source does not state temperature, stage or intended period, resolve those gaps with the crop adviser before treating its RH value as a control instruction.
Keep the operating band separate from the controller
The crop operating band describes conditions wanted in the relevant growing zone. The controller uses its sensor and programmed logic to request heating, ventilation or moisture removal. An alarm asks someone to investigate. These functions need related settings, but they are not interchangeable.
For example, a controller in a warm return-air location may report a different RH from the canopy. Copying the crop's upper boundary into that controller does not prove that the canopy stays within the band. First compare the measurement locations; then record why the action bounds differ from the crop limits, including response time and uncertainty.
Use the greenhouse control deadband guide for the control sequence after the crop band is chosen. Use the sensor placement and monitoring guide for representative measurements. Neither a new controller offset nor a lower setpoint should be used merely to hide disagreement between sensors.
Test the target during the period that matters
Record the crop zone through the operating period that motivated the concern: irrigation, screen closure, the transition into night, the coolest hours or recovery after vent changes. Keep crop stage, vent positions, heating, circulation and moisture-removal operation attached to the readings.
Check the affected location as well as the control sensor. If a leaf or frame becomes wet while the house average looks acceptable, investigate its local temperature and water path. If plant symptoms occur without a clear moisture mechanism, retain other possible explanations for the crop specialist. A single RH value does not diagnose disease or establish a yield response.
The night-time humidity and dew-point guide develops the event-based check. Repeat the review when crop stage, screen practice, season, sensor arrangement or ventilation changes materially. Record what was changed and why.
Translate the approved target into an equipment requirement
The greenhouse moisture-balance guide explains how ventilation, heating, moisture generation and mechanical removal interact. Establish the remaining removal duty before selecting equipment; the chosen RH percentage does not determine capacity by itself.
As a product-rating example, Yakeclimate's RYDZ-90DM is listed at 90 L/24h at 30°C / 80% RH. That catalogue condition differs from the illustrative lettuce conditions above. It does not establish removal at 24°C / 65% RH or 19°C / 65% RH. A proposal needs performance information at the actual inlet conditions, with air distribution, power, drainage and controls reviewed. RYDZ-90DM product data.
Send the approved crop band, operating periods, measurements, water-load estimate and installation constraints with your greenhouse equipment enquiry. For application-specific equipment or interfaces, use the engineering requirements form. The crop team owns the horticultural target; Yakeclimate reviews the defined dehumidification-equipment duty.
FAQ
Frequently asked questions
Is 60–80% RH ideal for every greenhouse?
No. That is a general reference in a greenhouse systems review. Select a crop- and stage-specific band with temperature, operating period and a suitable source or crop adviser.
Should day and night use the same RH setting?
Not automatically. The worked example shows that the same 65% RH at 24°C and 19°C produces different air VPD and dew point. The crop programme and actual measurements determine whether one setting is suitable.
Is the lettuce example a tested Yakeclimate growing recipe?
No. It combines a published Cornell production reference with explicitly illustrative calculations. It has no site validation or named crop-review approval.
Does the target tell me which dehumidifier to buy?
No. Equipment selection also needs moisture load, actual inlet conditions, air distribution, drainage, power and control requirements.
