How is a commercial greenhouse cooled?

In stages, chosen by climate. Roof ventilation and shading remove heat at almost no running cost and handle most of the year in temperate regions. Evaporative systems and mechanical cooling are added only where the local climate genuinely defeats the cheaper measures.

When does evaporative cooling stop working?

When the outside air is already too wet to take up more moisture. The usable limit is a dewpoint of roughly twenty-six degrees by day and twenty-two at night. Above that, pad-and-fan and fogging have no headroom, whatever their rated capacity.

Can a greenhouse be cooled below the outside temperature?

Only through evaporation. Ventilation alone approaches the outside temperature and cannot beat it. A healthy transpiring crop and dry incoming air can push the air below the inlet temperature, because the crop itself acts as an evaporative cooler.

Why do Dutch greenhouses not use pad-and-fan cooling?

Dutch summer air is too humid for evaporation to gain much, and a Venlo is built around a fifth of its floor area in openable roof vents. Pad-and-fan needs a sealed house with forced ventilation, which is the opposite structure.

Greenhouse Cooling Systems - DutchGreenhouses

Cooling is a ladder — you climb only as high as your climate requires

The single biggest mistake in hot-climate greenhouse projects is over-specifying cooling — paying for expensive mechanical systems where cheaper measures would have done the job. The right way to think about greenhouse cooling is as a ladder, where each rung removes more heat but costs more to install and run than the one below. Good design climbs only as high as the local climate actually demands, and no higher.

The bottom rungs are essentially free. Roof ventilation exchanges hot inside air for cooler outside air using nothing but wind and buoyancy, and shading or diffuse screens cut the incoming radiation load before it becomes heat inside the house. In temperate climates these passive measures alone keep the crop comfortable for most of the year, which is exactly why they are always the first line of defence.

The next rung up is adiabatic — evaporative — cooling, which exploits the fact that evaporating water absorbs heat. Pad-and-fan systems draw air through a wetted pad so it enters the greenhouse cooler, and high-pressure fogging sprays a fine mist that evaporates in the air itself, dropping temperature while raising humidity. These systems are highly effective in hot, dry climates, where the air has plenty of capacity to take up moisture; in already-humid regions their benefit shrinks because the air cannot evaporate much more water. HortiCoolers sit here too, delivering active, homogeneous cooling with dehumidification.

The top rung is full mechanical cooling — effectively air-conditioning the greenhouse — which can hold any target temperature but carries the highest capital and energy cost by a wide margin. It is reserved for extreme climates or high-value crops where nothing less will do. The whole point of the ladder is that the site's climate profile — how hot, how humid, how often — tells us precisely which rung is the economical choice, so you invest in exactly the cooling you need. DutchGreenhouses® designs the cooling strategy from your climate data. Get in touch to find your rung.

From the knowledge base