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Sawtooth roof not better during winter time

A sawtooth greenhouse with diffused glass doesn't allow more light to enter than a standard venlo-roof. This is the outcome of a new research project from Wageningen UR Greenhouse Horticulture. The project analyses the need to increase the amount of light during the winter. The validation of a simulation model was the main objective.

During the winter period, the prices of the greenhouse product are usually high; but simultaneously during this period, the available amount of light is the limiting factor for winter production. Hence, its is important to utilise the available light as much as possible for crop production. Important factors are the structure of the greenhouse (construction elements, orientation, the slope, symmetrical or asymmetrical rooftop) and the material used for the rooftop (basic material, coating(s), diffused or clear glass).

In the first phase of the project a simulation model was used in order to obtain a number of promising new concepts. A combination of these concepts was integrated in a prototype Winterlight Greenhouse, of which a demonstration greenhouse will be built at the the IDC Energy project. Read more here about this project.

Condensation and precipitation
To validate the simulation model, an experiment was conducted with 3 scale models of which the amount of light transmission through the roof during the winter was measured. On average there was a good match between the measurements and the calculation.

There is also evidence that an asymmetrical top (sawtooth roof) in combination with diffuse glass provides no significant greater amount of light. Therefore the prototype will be build with a venlo-roof.

From the tests it is evident that condensation and precipitation have a major effect on the measured light transmission. In this project rain decreased the transmission by 5%. Diffuse or coated glass behaves differently in this than standard glass. However there is no uniform measurement protocol on how to measure wet materials. This will be developed in a new project.

This project is financed by the program Kas als Energiebron, industry research body LTO Glaskracht Nederland and the Dutch ministry of Economic Affairs.

By Dennis Medema, Kas als Energiebron

The final report is available and can be found at Kas als Energiebron.
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