Why does cooling a desert greenhouse cost water?

The practical cooling methods in this zone are evaporative: pad-and-fan and fogging both remove heat by turning water into vapour. The cooling capacity is real, and so is the consumption — in the place with the least water available.

Can a desert greenhouse be cooled without water?

Mechanical cooling avoids the water but spends a great deal of electricity instead, and in this zone the peak cooling demand coincides with the peak electrical demand of everything else. Most projects end up combining shading, evaporative cooling and water recovery rather than choosing one.

What happens to the water a desert greenhouse uses?

Whatever is not evaporated returns as drain water and is recovered. Reverse osmosis pre-treatment leaves a brine stream that has to be disposed of legally, and that disposal route is part of the project design rather than an afterthought.

Is a closed greenhouse better in a desert?

A more closed house holds cooled air and captures transpired moisture rather than venting it, which reduces water use per kilogram produced. It costs more to build and depends entirely on the cooling system working, so the trade is between capital cost and water consumption.

Greenhouses for Arid & Desert Climates

Everything that cools here spends water

Where: the Gulf states, Saudi Arabia, North Africa, Egypt, Iran, the American southwest, inland Australia, northern Mexico.

The problem is not that it is hot

It is that the two ways of getting heat out both come with a bill.

Vent it away and you are limited by how much cooler the outside air is — which at 45 degrees is not much. Evaporate water into the airstream and it works beautifully, because dry air has enormous capacity to absorb moisture. That is why adiabatic cooling, pad-and-fan and fogging dominate this climate.

And it is why the water question and the cooling question are the same question.

A greenhouse here competes with the crop for water

Evaporative cooling consumes water continuously through the hottest months, in a region where water is the scarcest input on site.

Source water is usually brackish groundwater, which means reverse osmosis at roughly 50 percent recovery — half of what you pump becomes permeate, half becomes brine you then have to do something with. And there is no rainfall worth collecting to dilute it.

So the design question is not “how do we cool it”. It is how much cooling can this site’s water budget actually afford, and the answer often reshapes the whole concept.

Light is the one thing in surplus

Everywhere else in this map, light is fought for. Here there is too much, and the surplus arrives as heat.

So the screen package inverts: shade and diffuse screens instead of energy screens, sized to shed radiation rather than to hold warmth. Diffusion earns its place twice over here — it spreads light deeper into the canopy and lowers leaf temperature peaks at the same time.

And the glass gets dirty

Dust is a permanent, quiet loss. A cover that transmits beautifully on handover transmits considerably less after a season of desert air, and cleaning becomes an operating cost rather than a maintenance afterthought.

Semi-closed concepts are worth genuine consideration here for the same reason — keeping the outside out reduces both the dust and the cooling load, at a capital cost that has to be earned back.

DutchGreenhouses® sizes the cooling strategy against your site’s water budget before anything else is chosen. Send us the location and a water analysis — that pair decides more here than the crop does.

From the knowledge base