A cellulose pad is one component of a greenhouse cooling system. It cannot compensate for insufficient fan capacity, air leaks, poor water distribution or a climate with little wet-bulb depression. The system should be designed by a qualified greenhouse or ventilation engineer for the crop, structure and local design weather.
How fan-and-pad cooling works
Exhaust fans create negative pressure inside the greenhouse. Warm outside air enters through the wet pad, some water evaporates and the air temperature falls while humidity rises. The cooled air then travels through the crop zone toward the fans.
The theoretical limit is related to the outdoor wet-bulb temperature. Hot, dry air has more evaporative potential than warm, humid air. This is why a pad should never be marketed with one guaranteed temperature drop for every country or season.
Information required before pad selection
- Greenhouse length, width, height and internal obstructions
- Crop and acceptable temperature and humidity range
- Local design dry-bulb and wet-bulb conditions
- Required ventilation rate and installed fan performance
- Proposed pad-face velocity and available wall area
- Water quality, tank, pump and distribution-header design
- Existing frame dimensions and replacement-pad sizes
An engineer uses these inputs to select fan duty, pad face area and water circulation. The pad manufacturer then needs thickness, height, length, flute design and any edge treatment or frame constraint.
5090 or 7090 for a greenhouse?
The labels refer to flute geometry, not a universal quality grade. Different geometries change contact area, airflow resistance and water behaviour. The appropriate choice depends on the system designer's airflow and pressure-drop target, dust load, water management and the manufacturer's tested product data. See our 5090 and 7090 comparison as a starting point, then confirm the project specification.
Water distribution is as important as the pad
The top header should wet the pad evenly without leaving dry stripes or sending unnecessary water into the airflow. The sump, pump, filters, valves and bleed-off arrangement must match water quality and circulation demand.
Mineral concentration rises as water evaporates. A water-treatment specialist may recommend bleed-off or other controls. Avoid unapproved cleaning chemicals because they can damage paper, resin, adhesive, plants or workers.
Common operating problems
| Symptom | Items to check |
|---|---|
| Warm zone near pad | Dry sections, bypass air, low water flow, blocked face |
| Warm zone near fans | Greenhouse length, heat load, airflow distribution, fan duty |
| Water droplets in air | Excess flow, damaged pad, wrong orientation, high face velocity |
| Uneven cooling | Header blockage, air leakage, dirty pad, fan staging |
| Rapid mineral build-up | Source-water quality, bleed-off, filtration, cleaning practice |
Maintenance that protects performance
Inspect wetting pattern, strainers, pump and sump routinely. Keep vegetation, cartons and equipment away from the pad face and airflow path. Follow the pad and system supplier's cleaning instructions, repair water leaks promptly and replace damaged sections that allow bypass air.
For local pad-manufacturing projects, repeatable flute geometry, bonding and final dimensions help the finished products fit greenhouse frames and wet consistently. Read our quality-control guide or review country-specific export planning before requesting machinery. Discuss a production-line requirement.