Fan & Pad Evaporative Cooling

The standard way to cool a greenhouse in a hot dry climate — and a system whose performance is decided by pad face velocity and house length, not by fan size.

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  • 5equipment groups

WhatPulling air through a wet wall

Exhaust fans at one end of the house draw air through a wetted cellulose pad wall at the other. Water evaporating from the pad cools the incoming air, and the whole house air volume is replaced roughly once a minute. In a dry climate the drop across the pad is genuinely useful — commonly 6–12 °C.

WhoWho buys it

Commercial vegetable and flower growers in hot climates, greenhouse constructors delivering turnkey houses, and agricultural contractors retrofitting cooling into existing structures.

WhyWhy long houses cool unevenly

The air warms as it travels from pad to fan, picking up solar and plant heat along the way. In a long house the crop at the fan end can be several degrees hotter than at the pad end, which shows up as uneven growth and harvest timing. This is a design consequence, not a fault: beyond roughly 60 m the temperature rise becomes hard to accept, and the answer is to split the house rather than add fans.

HowSizing pads and fans together

Size fans for one complete air change per minute at the static pressure the pad wall imposes — not free-air. Set the pad area from face velocity: too fast and air leaves the pad still dry and carries water droplets; too slow and the house cannot make its air change. Match water flow so the pad is evenly wetted top to bottom, since dry patches short-circuit uncooled air straight through. Then add circulation fans as a separate system, because they must run when the vents are shut and the pad system is off.

Equipment this application needs

Axial Flow Fans Exhaust fan bank Axial Flow Fans752 Large-diameter units at the far end; rate them at pad-wall static pressure, never free-air. Air Coolers Pad systems & portable units Air Coolers264 Pad wall assemblies, and portable evaporative units for spot cooling and small houses. Exhaust Fans Night humidity purge Exhaust Fans134 Removing moisture at night is what prevents condensation dripping on the crop at dawn. Blowers Horizontal airflow Blowers416 Circulation between crop rows, running when the vents are shut and the pads are off. Ventilation Fan Parts Shutters, belts & pumps Ventilation Fan Parts261 Shutters that stick open in winter undo an entire season of heating.

What to check before you order

Corrosion Resistant 266
Permanent humidity plus fertiliser and pesticide spray.
IP55 / IP68 308
Motors sitting in a wet, sprayed environment.
Energy Saving 1,220
Fan banks run for thousands of hours a season.
380V 2,141
Three-phase for commercial-scale pad walls.
Solar Powered 175
Practical for remote houses and for keeping circulation running through outages.

Products for this application

Questions buyers ask

How much cooling does a fan and pad system deliver?
In a dry climate, commonly a 6–12 °C drop across the pad. The figure depends entirely on how much moisture the incoming air can still absorb, so the same equipment in a humid coastal climate may deliver 2–3 °C while pushing house humidity to levels the crop will not tolerate.
How long can a fan and pad greenhouse be?
Beyond roughly 60 m the temperature rise from pad end to fan end becomes hard to accept, because the air warms as it travels. Adding fans does not fix this — it is a consequence of the air path length. Long houses are normally split into shorter cooling zones instead.
Why do circulation fans need to be separate from the pad system?
Because they do a different job at a different time. Pad cooling exchanges house air with outside air on hot days; circulation keeps air moving inside the house when the vents are closed, on cold nights and in winter, to break up the humid layer at the leaf surface and prevent disease.

Related applications

Greenhouse & Horticulture Climate Control Fan-and-pad cooling, circulation fans, exhaust and heating for protected cropping — sized on air changes and on the crop's vapour pressure deficit,… Poultry & Livestock House Ventilation Tunnel and minimum-ventilation fans, evaporative cooling and house heating built for an ammonia-laden, washdown environment where a ventilation failure is measured in… Vertical Farm & Indoor Growing HVAC A sealed building where every watt of light becomes heat, and every litre the plants transpire has to be condensed back out…

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