Diffuse Greenhouse Covering Materials - Material Technology, Measurements and Evaluation of Optical Properties

Self Cite

In greenhouse horticulture, energy costs form an increasingly larger part of the total production costs. Energy is primarily used for temperature control, reduction of air humidity, increase of light intensity and CO 2 supply. Use of fossil energy can be reduced by limiting the energy demand of the system and decreasing energy losses, by intelligent climate control, by increasing the energy efficiency of the crop and by replacing fossil energy sources by sustainable ones. Energy requirement of the greenhouse can be lowered up to 20-30% by using greenhouse covers with higher insulating values and the use of energy screens. A prerequisite is that these materials should not involve considerable light loss, since this would result in a loss of production. In energy efficient greenhouse concepts, durable energy sources should be included. In (semi-)closed greenhouses, the excess of solar energy in summer is collected and stored in aquifers to be reused in winter to heat the greenhouse. Ventilation windows are closed, with specific benefits to the crop: high CO 2 levels can be maintained, and temperature and humidity can be controlled to the needs of the crop. Development of new greenhouse concepts is ongoing. Current examples are greenhouse systems which convert natural energy sources such as solar energy into high-value energy such as electricity. Given a certain technical infrastructure of the greenhouse, energy consumption can be further reduced by energy efficient climate control and crop management. Essential elements are to allow fluctuating temperatures, lower crop transpiration, allow higher humidities, make efficient use of light and create fluent transitions in set points. Consequences for plant growth are related to rate of development, photosynthesis, assimilate distribution, transpiration and the occurrence of diseases or disorders. Since processes involved are complex, knowledge exchange between researchers and growers is essential to realize the goals set to reduce the energy consumption. INTRODUCTIONIn current greenhouse horticulture, next to high production levels, quality and timeliness of production are important. This can be reached by optimal control of greenhouse climate for which energy is of major importance. The need for (energy) cost reduction has become higher, since with increasing prices of natural gas in the last decade, energy forms a substantial fraction of the total production costs. The liberalisation of the energy market for growers since 2002 has increased the growers' awareness of the energy consumption of their cropping systems. This free market implies that growers do not pay a fixed price per unit of natural gas anymore, but that prices are greatly determined by the maximum supply capacity of the gas contract. Therefore, it is important to reduce peaks in energy use. In view of the Kyoto protocol several governments have set goals for energy use and CO 2 emission. In the Netherlands, the horticultural sector and government have agreed to improve the energy efficiency (p...

Section: Lightmentioning

confidence: 99%

Energy Saving: From Engineering to Crop Management

Dieleman¹,

Hemming²

2011

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“…This can be achieved by diffuse light. Light can be made diffuse by modern covering materials (Hemming et al, 2008b). Such materials contain pigments, macro-or microstructures, which are able to scatter a fraction of direct light over an almost flat distribution of incidence angles (that is into diffuse light).…”

Section: Introductionmentioning

confidence: 99%

“…Efficient structures make the light diffuse without a significant reduction in light transmission. During the past six years Wageningen UR Greenhouse Horticulture has investigated the potential of diffuse covering materials used in Dutch greenhouses (Hemming et al, 2005a(Hemming et al, , 2008b. The suitability of several greenhouse covering materials and their optical properties (PAR transmission: τ-direct and τ-diffuse, haze) was investigated in laboratories, desk studies, using models and simulations, as well as in practice.…”

Section: Introductionmentioning

confidence: 99%

Effect of Diffuse Glass on Climate and Plant Environment: First Results From an Experiment on Roses

Kempkes¹,

Stanghellini²,

Victoria³

et al. 2012

High energy use in rose cultivation at higher latitudes is caused by the need for artificial light to supplement scarce sun radiation. On the other hand, since too high radiation levels are known to reduce flower quality, shading is widely applied during spring and summer, either through movable screens or seasonal whitewash. In both cases damage to the crop is avoided at the cost of reducing potential assimilation by reduction of (PAR) light. Recent research on cucumber has shown that diffusing cover materials have the potential of improving the uniformity of vertical light distribution in a crop, therefore decreasing the energy load on the uppermost crop layer to the advantage of underlying crop layers. Light diffusion, however, usually implies a loss of overall transmission. This drawback can be avoided by antireflection coatings, so that most recently diffusive glass covers have become available with the same transmissivity of standard glass. The application of such a cover on roses could decrease the need for shading so that a desired radiation sum could be achieved with less need for artificial light. Such an experiment is in progress on a crop of roses (cv Red Naomi) at the research station of Wageningen UR Greenhouse Horticulture in Bleiswijk, NL, in two compartments. One is covered with diffuse glass with anti-reflection coating with a light transmission of 93% perpendicular and 83% hemispherical and haze factor of 72%. The reference compartment is covered with standard glass. This paper describes the effect of a diffusing cover on the greenhouse climate (air-and plant-temperature, humidity and ventilation requirement) and water balance compared to a greenhouse covered with standard glass. It's showed that the effect on greenhouse climate is limited but flower temperature is reduced in the diffuse compartment which has effect on flower quality. It seems therefore that the material has potential for reducing leaf burning and if the use of shade screens or whitewash can be reduced there is a potential increase of yield with the same energy input.

“…Modern greenhouse coverings are able to transform most of the light entering the greenhouse into diffuse light. A quantitative foundation for the potentials of diffuse light in Dutch greenhouses was given earlier by Hemming et al (2005Hemming et al ( , 2008a. It was shown in modelling and experimental studies that crops such as fruit vegetables with a high plant canopy as well as ornamentals with a small plant canopy can utilize diffuse light better than direct light.…”

Section: Diffuse Lightmentioning

confidence: 99%

Use of Natural and Artificial Light in Horticulture - Interaction of Plant and Technology

Hemming¹

2011

Self Cite

In intensive horticultural cultivation natural light levels often limit crop production during several periods. For an optimum plant production and product quality light intensity, spectrum and photoperiod have to be adapted to the needs of the crops at every moment. Light has to be optimised together with all other growth factors like temperature, humidity and CO 2 . For a sustainable greenhouse production the use of freely available sunlight has to be preferred. New transparent greenhouse covering materials, like ETFE, glass with new anti-reflection coatings or materials with micro-surface structures, transmit a very high amount of light into the greenhouse. Other new materials are able to scatter the incoming light and make it diffuse. Diffuse light penetrates deeper into the canopy, increases light interception by the crop, influences micro-climate and increases crop production by 6.5-9.2% in The Netherlands, the potential in lower latitudes is even higher. Other materials manipulate light spectrum. Photoselective nettings have been developed in different colours influencing morphogenesis and crop production. Fluorescent plastic films combine effects on morphogenesis with high light transmission, especially important for higher latitudes. When sunlight is optimized it can still be necessary to add artificial light to ensure a year-round supply of horticultural products. There is still room for improving the crop energy efficiency under artificial lighting by changing duration and intensity of lighting, different growing systems and plant densities. Since artificial lighting requires a high amount of energy, new artificial lighting systems have been developed, such as interlighting and light emitting diodes (LED). LED give the possibility for true light spectrum control in the future. The (partial) replacement of HPS lamps by LED systems is currently under investigation in Dutch greenhouses. Integration in current growing systems has full attention. In order to reach a high sustainable and economic beneficial production the factor light has to be integrated and optimized within the total horticultural system.