Combination of film and glass on the same greenhouse

Glass has been placed on the 2SaveEnergy greenhouse. This greenhouse will be built on the Innovative Demo Centre on territory of Wageningen UR Greenhouse in Bleiswijk, the Netherlands. Afterwards, in about two weeks, EFTE film will be placed underneath the glass. EFTE is a strong material and it will last more than 20 years. Project manager Frank Kempers from the Wageningen UR Greenhouse discusses the choices for EFTE film in combination with glass, for which an achievability research has been conducted previously.

The combination of EFTE film with glass has several advantages compared to using two layers of EFTE film or two layers of glass. Firstly, it is less expensive than using two layers of glass. Secondly, the Netherlands is considered as a “glass country”. Therefore it is expected that the Dutch growers will not be interested in foil greenhouses. Thirdly, glass transmits a smaller amount of infrared then EFTE. Therefore, the greenhouse will cool down less quickly at night, which is an advantage. However, due to the coatings on the glass, the same amount of sunlight (and therefore warmth) as the EFTE will be transmitted. Finally, dirt may prevent the transmission of sunlight, but this is not a problem for EFTE it repels dirt.

The opening between glass and EFTE foil will be left open. Therefore, the greenhouse air can flow between the two layers. This is important when snow lies on top of the greenhouse. Then, the ‘warm’ greenhouse air can be blown through the opening. If the space between the two layers will be isolated, the snow will stay longer on top of the greenhouse. They have learned this from a previous project.

The used EFTE-foil is diffuse and the glass is clear. This choice has been made because of the unknown condensation behaviour of diffuse glass as second layer. The transmission of light by diffuse EFTE film is less than the transparent, which is sufficient according to the project leader. The Japanese supplier is currently improving the transmission of light by diffuse film. If this succeeds, the film can be easily replaced by the improved one. This is one of the interesting innovations of this greenhouse.

In order to test the technique, the 2SaveEngergy greenhouse will probably be used for crops with a short growing process. Next year, the greenhouse will be tested by growing tomatoes.

Source: Energiek2020