Choose greenhouse cooling from the site’s temperature and moisture conditions, the crop’s limits and the airflow the installed system can deliver. Evaporative cooling has a wet-bulb limit. A fan rating, covering material or greenhouse height alone cannot guarantee the temperature throughout a commercial crop.
What can a fan-and-pad system achieve in your climate?
The University of Florida’s fan-and-pad guide relates pad-outlet temperature to outdoor dry-bulb temperature, outdoor wet-bulb temperature and system efficiency:
Pad-outlet temperature = outdoor dry-bulb temperature − efficiency × (dry-bulb temperature − wet-bulb temperature).
Use efficiency as a fraction. The calculation describes air leaving the pad, not the temperature at every plant. Air can warm as it crosses the greenhouse. These distinctions rule out a universal cooling reduction for all tropical sites.
The following is an arithmetic illustration with hypothetical inputs. It is not measured weather, a CFGET test, an equipment specification or a promised result.
| Assumed input or calculated output | Lower-moisture case | Higher-moisture case |
|---|---|---|
| Outdoor dry-bulb temperature | 35°C | 35°C |
| Outdoor wet-bulb temperature | 24°C | 31°C |
| Assumed efficiency for this comparison only | 0.70 | 0.70 |
| Calculated pad-outlet temperature | 27.3°C | 32.2°C |
| Calculated temperature reduction at the pad | 7.7°C | 2.8°C |
The practical question is whether a proposal still meets the crop brief when the wet-bulb temperature is high. Ask the designer to replace every assumption with a stated weather source, equipment basis and operating condition. Require a separate prediction and acceptance plan for the crop zone.
For an existing house, record conditions outside, just after the pad and at representative crop positions. Note the measurement time, instrument, fan stage, vent position and whether the pads are wet uniformly. A single thermometer beside the pad cannot represent the warmest crop location. Use repeatable observations to decide what needs investigation, rather than buying a larger pump from one hot reading.
How should covering materials be compared?
Request data for the exact film, glass or polycarbonate product, including light transmission, light diffusion where specified, thermal properties, installed configuration and maintenance requirements. Do not substitute a generic material name for a product specification.
A useful comparison keeps the crop light requirement and climate duty unchanged. Ask which model inputs change when the covering changes, and which result comes from the calculation. A claimed energy saving needs an identified baseline, weather period, operating settings and method. It should not appear as an automatic percentage attached to polycarbonate or glass.
Record practical constraints too: replacement access, available panel or film sizes, cleaning, damage repair, spare availability and the structure designed to carry that covering. These affect operation even when two products have similar headline optical values.
Will the structure deliver the required airflow?
UConn’s natural-ventilation guidance explains the roles of wind and thermal buoyancy. Height is part of a design, not proof of a fixed cooling-load reduction. Ask for the vent arrangement, opening limits, screen resistance and the treatment of calm weather.
The University of Arizona’s ventilation and screening material also shows why restrictions belong in a fan-system assessment. A free-air fan rating cannot establish installed crop-zone airflow.
Keep natural-ventilation and fan-and-pad operating modes distinct. Ask the controls supplier to document which openings are commanded in each mode, how equipment responds to faults, and what the operator can verify. For screen selection, use the insect-screen ventilation guide and the actual resistance data for the proposed product.
What water and operating information belongs in the decision?
Separate crop irrigation from water used by cooling equipment. For each, record source quality, available flow, treatment, storage, maintenance and the response to an interruption. Do not set emitter flow, filter grade, pump power or pad area from a generic tropical specification.
The commercial irrigation comparison addresses crop delivery. Review cooling-water requirements with the selected equipment supplier. Ask who will inspect the system, what observations trigger service and which parts are kept on site.
Before committing funds, request one dated design case with its weather inputs, crop limits, predicted crop-zone conditions, utility requirements and unresolved assumptions. Price that scope, including local installation and operating responsibilities. If the modeled conditions miss the crop target, reconsider the system or production plan before accepting the equipment list.
Send the site weather basis, crop calendar, existing layout and measurement record through the CFGET contact page. The useful next step is a project-specific review of the remaining uncertainty.
