Search

The application of new cultivation techniques (Het Nieuwe Telen) in Dutch greenhouses heavily relies on using one or more movable screens. Screens also affect the control of the greenhouse climate by radiation exchanges and air and humidity exchanges between the lower and upper part of the screens. This directly influences energy saving. The objectives of the project were the quantification of the screen properties by standardised measurements: thermal properties such as emissivity, aerodynamic properties such as air permeability and humidity transport characteristics. From the measured properties the overall potential energy saving can then be calculated under defined conditions for an objective comparison of the performance of different screen materials in dry and wet conditions. This helps growers to understand more about screen properties and allows them to make an informed choice of investment and practical usage. The results show that screens low permeability and low emissivity give highest energy saving. De toepassing van Het Nieuwe Telen in Nederlandse kassen is sterk afhankelijk van het gebruik van één of meerdere beweegbare schermen. Schermen beïnvloeden ook de beheersing van het kasklimaat door effecten op uitstraling en lucht- en vochtuitwisseling onder en boven het scherm. Dit heeft direct invloed op de energiebesparing. De doelstellingen van het project waren het kwantificeren van de schermeigenschappen door gestandaardiseerde metingen: thermische eigenschappen zoals emissie, aerodynamische eigenschappen zoals luchtdoorlatendheid en vochttransport. Uit de gemeten schermeigenschappen kan vervolgens de totale potentiële energiebesparing worden berekend onder vooraf gedefinieerde omstandigheden. Hiermee wordt een objectieve vergelijking van schermmaterialen onder droge en natte omstandigheden mogelijk. Hierdoor krijgen telers meer inzicht in schermeigenschappen en kunnen ze een weloverwogen keuze maken voor hun investeringen en gebruik in de praktijk. De resultaten laten zien dat schermen met een lage permeabiliteit en een lage emissie de grootste energiebesparing opleveren.

Anthurium and Scheffl era are high-value ornamental crops requiring low sunlight levels, preferably of diffuse nature. This is achieved by shading screens, temporary coatings and combinations of both. Electrochromic glass able to regulate light transmission or diffusion could allow higher light sum than traditional shading without exceeding light damage thresholds, leading to improved crop growth. Two small-scale experiments were conducted simultaneously to evaluate the possibilities of EC Glass to be used as greenhouse cover for these crops. Two types of electrochromic glass where used: a darkening EC glass for anthurium; a diffusing EC glass for Scheffl era. The EC Glasses were compared to a reference fl oat glass with a temporary coating. Darkening EC Glass gave very good control of the light conditions: higher light sum by more constant light, less peaks on sunny days and more light on clouded days. However, this did not translate in faster growth, more fl owers or better plant quality. The achieved light advantage by the glass was counteracted by high leaf temperatures that lead to stomata closure and lower photosynthesis effi ciency during sunny periods. Diffusing EC Glass gave also good control of the light conditions as programmed: diffuse light whenever the set threshold was reached. The diffusive state lead to a slightly lower light sum than the reference coated glass. However, the changing diffusion conditions did not result in faster growth, nor better plant quality: the plants from the Diffusing Glass treatments remained shorter and had a lower leaf area than the constantly diffuse reference. Anthurium en Scheffl era zijn hoogwaardige sierteeltgewassen die geteeld worden met laag, bij voorkeur diffuus licht. Dit wordt bereikt door schermdoeken, tijdelijke coatings en combinaties van beide. Met elektrochroom glas dat in staat is om de lichttransmissie of -diffusie te reguleren, kan een hogere lichtsom worden behaald dan met traditionele afscherming, zonder de drempels voor lichtschade te overschrijden. Dit kan teeltversnelling geven. Twee kleinschalige experimenten zijn simultaan uitgevoerd om de mogelijkheden van EC Glass als kasdek voor deze gewassen te evalueren. Twee soorten elektrochroom glas zijn gebruikt: tintbaar EC Glas voor anthurium; helder-diffuus EC glas voor Scheffl era. De EC-glazen werden vergeleken met een referentie van fl oatglas met een tijdelijke coating. Tintbaar EC Glass gaf een zeer goede controle over de lichtomstandigheden: hogere lichtsom door constanter licht, minder pieken op zonnige dagen en meer licht op bewolkte dagen. Dit vertaalde zich echter niet in een snellere groei, meer bloemen of een betere plantkwaliteit. Het bereikte lichtvoordeel van het glas werd teniet gedaan door hoge bladtemperaturen die leidden tot huidmondjessluiting en een lagere fotosyntheseeffi ciëntie. Diffuus EC Glass gaf ook een goede licht controle zoals geprogrammeerd: diffuus licht wanneer de ingestelde drempel werd bereikt. De diffuse toestand leidt tot een iets lagere lichtsom dan het referentieglas. De veranderende diffusiecondities leidden echter niet tot snellere groei, noch tot betere plantkwaliteit: de planten uit de diffusieglasbehandelingen bleven korter en hadden een lager bladoppervlak dan de continu diffuse referentie.

Experiments done in the past have shown a clear advantage for many crops of receiving more diffuse light in relation to direct light. However, in these experiments, extremely high light scattering levels were never tested, and therefore, we do not know whether such results could be extrapolated, and how. The scattering is quantifi ed by means of the Hortiscatter (0-100%) parameter as defi ned in norm NEN2675. In this trial an innovative material in the form of rectangular lamellae has been used, that when positioned vertically above the crop and below the source of light, can generate a very high Hortiscatter (>90%). These highly diffusive vertical lamellae were tested in three trials in a climate chamber using young tomato plants, with both direct light and a conventional Hortiscatter (50%) as reference treatments. Light interception, leaf photosynthetic capacity of different layers and dry matter (and other related production values) were compared. Despite the efforts in optimizing the set up, it was not possible to maintain a homogeneous horizontal PAR intensity distribution. However, results indicate that, regardless of the light intensity, young tomato plants under a very high Hortiscatter intercepted more PAR light in the three trials. On the other hand, both top and bottom leaves under this treatment did not show a higher photosynthetic capacity than under a direct light treatment. Finally, results indicate a trend to higher total dry matter production under the very high Hortiscatter. However, more research, if possible under sunlight conditions and trying to minimize the sources of variation are needed in the future.

Some high-value ornamental crops, such as Anthurium sp. and Phalenopsis sp., are shade loving crops which are grown under relatively low sunlight levels. In summer, these are achieved by different shading techniques such as shading screens, temporary coatings and combinations of both. However, these options are not optimal because screens do not allow to regulate light smoothly (slow reaction to changing light conditions) and coatings take also light in days with low radiation. Glass in which the transmission can be modulated (i.e. electrochromic glasses) could overcome these problems bringing a more stable climate in the greenhouse and possibly a higher light sum. This could all lead to improved and faster growth of these crops. A small-scale experiment was conducted with the shade plant pot-anthurium as crop example for a fi rst evaluation of the possibilities of EC Glass to be used as greenhouse cover. The questions we wanted to answer were if it controls light intensity as programmed, and if it improves crop growth and time to market. Five shading treatments were compared: 1. Float glass (no shade); 2. EC Glass managed at a fi xed level; 3. EC glass managed as a screen; 4. Coating; 5. Diffuse glass (no shade). The light levels were well controlled under both EC glass panes, but damage was induced to plants on very hot days due to overheating of the glass panes in dark state and consequent overheating of ambient air. There was a trend to shorter plants and smaller leaves & fl owers compared to the reference in a greenhouse. More research is required to evaluate the potential of smart glasses to become greenhouse covers for these high value crops.