Semi-closed greenhouse.

The vent is the only tool most greenhouses have

A conventional greenhouse controls temperature by opening the roof

It works. It also throws away everything else in the air at the same time.

The CO₂ that was dosed into the house leaves through the same opening. So does the humidity that was being managed, and so does the exclusion the insect netting was built for. One lever, and every climate problem has to be solved by pulling it.

In a mild Dutch summer that is an acceptable compromise. In a hot climate it stops being one. At the peak of summer the outside air is not cool enough to help, so the vents stand wide open achieving very little — while the CO₂ enrichment is being paid for and vented in the same hour.

A semi-closed greenhouse conditions the air in place

Instead of trading inside air for outside air, the air is cooled, heated and dried where it stands.

DutchGreenhouses® does this with air handling units along the sides of the house, with HortiCoolers, or with both. Each carries a water-fed heat exchanger: cold water through it cools and dehumidifies, warm water through the same exchanger heats. The vents stay shut for far more hours of the year than they otherwise would.

The word that matters is semi. The house is not sealed. Vents remain, and they are used whenever the outside air is actually useful — which in most climates is a large part of spring and autumn. A fully closed greenhouse is a different and considerably more expensive machine.

The gain is not really the cooling

Cooling is what the equipment does. The reason to buy it is what stops leaving.

With the roof shut, a CO₂ concentration above ambient can be held rather than continuously replaced — and CO₂ is the raw material the crop is built from. Humidity can be set independently of temperature instead of being whatever the vent position leaves behind. Screens can stay drawn longer, because the house no longer depends on the roof opening to shed heat. Pest pressure falls, because the openings pests use are closed.

Those effects compound, and together they are the argument. Nobody buys cooling capacity. They buy the yield that a stable, CO₂-rich climate produces.

Where the air goes is the whole design

A semi-closed house with poor air distribution performs worse than a well-ventilated one. This is where these projects are won or lost.

Conditioned air has to reach the canopy evenly. Cold spots stall a crop and warm spots run it too fast, and a house with both is harder to steer than a house with neither. HortiCoolers are built around that problem: air is thrown upward as far as sixteen metres and descends in a circular pattern, entering the crop from above the way outside air would rather than being blown across it. The engineering follows the same logic — an oval-tube exchanger cuts air-side pressure drop by around 35%, which raises output by 15–20%.

Placement, throw and unit count are calculated per house against the site’s solar load and the crop’s target climate. They are not catalogue quantities.

And it runs backwards

The same units heat. Warm — or even luke-warm — water through the same exchangers turns the cooling system into a heating system, which matters in two places.

In a continental climate that swings hard between seasons, one set of equipment covers both extremes. And in any project with access to low-value heat, a residual industrial stream or a geothermal source that never reaches boiler temperature, the exchanger can use it — because it does not need water as hot as a pipe rail does.

What it costs

Capital, and electricity. This is a bigger machine than a vented house, and it runs on power a naturally ventilated greenhouse never spends.

That trade is worth making where ventilation genuinely fails: arid and desert climates, and humid tropical ones where venting removes almost no moisture because the outside air is already saturated. It is worth much less in a temperate maritime climate, where the vents already work for most of the year.

DutchGreenhouses® sizes the units against the site’s climate profile and the crop’s target climate, and settles the structure, the screens and the CO₂ strategy around them at the same time. Get in touch with the location and the crop — the first question, whether a semi-closed house is the right machine at all, deserves an honest answer before anything is specified.