New glass coatings for high insulating greenhouses without light losses - energy saving, crop production and economic potentials

More than 90% of Dutch greenhouse area is covered with single glass. Energy losses through the covering are high during heating period (winter) but energy requirements are also high during cooling period (summer) in the case of semiclosed greenhouses. Until now, light losses of insulating coverings prevented growers from using double glass or plastic film. However, increasing energy prices allow new developments. Wageningen UR Greenhouse Horticulture studied the possibilities to use modern glass coatings to increase light transmission and save energy. Several glass types (standard glass, 90+ glass, low-iron glass) were covered with different anti-reflection coatings from different producers. Double glasses were produced; their optical properties were determined. It was possible to produce double glasses with new coatings having a higher light transmission than traditional single greenhouse glass (83-85% for hemispherical light, compared to 82-83% for traditional single glass) and a k-value of 3.6 Wm-2K-1 (compared to 7.6 Wm-2K-1 of a traditional single glass). Other double glasses were produced using a combination of anti-reflection and modern low-emission coatings, reaching an even lower k-value of ˜2.4 Wm-2K-1, however, showing a slight light loss (78.5% for hemispherical light). Calculations of greenhouse climate (temperature, humidity, CO2) and energy consumptions year-round were carried out with a validated dynamic climate model. Additionally the effects on tomato production (dry matter) were calculated for the different prototypes of coated and insulated glass. Double materials show the highest energy saving with 25-33%, depending on the composition but also low-emission coatings on single glass decrease the energy use with 15-20%. Economic calculations with current tomato and energy prices showed that single and double glasses with anti-reflection coating currently have the highest potential

New glass coatings for high insulating greenhouses without light losses - energy saving crop production and economic potentials

More than 90% of the Dutch greenhouse area is covered with single glass. Energy losses through the covering are high during the heating period (winter) but energy requirements are also high during the cooling period (summer) in the case of semi-closed greenhouses. Until now, light losses of insulating coverings prevented growers from using double glass or plastic film. However, increasing energy prices allow new developments. Wageningen UR Greenhouse Horticulture studied the possibilities to use modern glass coatings to increase light transmission and save energy. Several glass types (standard glass, 90+ glass, low-iron glass) were covered with different anti-reflection coatings from different producers. Double glasses were produced; their optical properties were determined. It was possible to produce double glasses with new coatings having a higher light transmission than traditional single greenhouse glass (83-85% for hemispherical (diffuse) light, compared to 82-83% for traditional single glass) and a k-value of 3.6 W m-2 K-1 (compared to7.6 W m-2 K-1 of a traditional single glass). Other double glasses were produced using a combination of anti-reflection and modern low-emission coatings, reaching an even lower k-value of ˜2.4 W m-2 K-1, however, showing a slight light loss (78.5% for hemispherical (diffuse) light). Calculations of greenhouse climate (temperature, humidity, CO2) and energy consumptions year-round were carried out with a validated dynamic climate model. Additionally the effects on tomato production (dry matter) were calculated for the different prototypes of coated and insulated glass. Double materials show the highest energy saving with 25-33%, depending on the composition but also low-emission coatings on single glass decrease the energy use with 15-20%. Economic calculations with current tomato and energy prices showed that single and double glasses with anti-reflection coating currently have the highest potential

The place of Zeno’s paradox

This paper begins by examining the recent history of interpretations of one of Zeno’s paradoxes of motion, the paradox of dichotomy. It then returns to the record of antiquity to ask how Aristotle ‘solved’ the paradox and what decisions about place and motion were assumed in that solution. After appealing to Heidegger’s readings of the Aristotelian text, the paper then proceeds to offer an entirely original interpretation of Zeno’s paradox of dichotomy, which has important implications for a contemporary understanding of motion and place (rather than space). Instead, the paradox is read as a provocation to ‘see’ something which Zeno, it would appear, believed was ‘missing’, or had been forgotten and had disappeared, and to review all over again what Parmenides might have meant in his claim that being is one, singular, and indivisible

The Influence of Colour on Radiometric Performances of Agricultural Nets

The whole construction parameters of the net, combined with the shape of the structure, the position of the sun and the sky conditions affect the radiometric performance of the permeable covering system. The radiometric properties of the permeable membrane influence the quality of the agricultural production and the aesthetic characteristics of the netting system. Moreover, the colour of the material and the light reflection- especially of the wavelengths visible for the human eye (VIS, 380-760nm)- is an interesting criterion to determine the aesthetic value of the net structure and its environmental impact. In order to investigate the influence of the threads colour on the radiometric properties of the net, a set of field tests were performed by means of a spectroradiometer in combination with an experimental setup 120x120x50cm covered with membranes formed by threads with different colour. A second set of experiments were performed, on the same kind of nets, in laboratory by means of a combination of a large integrating sphere and a small one: the transmissivity from a direct (tauDIR) and diffuse ((tauDIF) source and the reflectivity from diffuse source (¿) of 50x50cm samples were measured in the PAR range. The evaluation of the transmissivity values shows that the colour of a net influence spectral distribution of the radiation passing through the net absorbing their complementary colours. The transmissivity of black nets is almost constant in the visible range and the reduction of the incoming radiation is proportional to the solidity of the net. In the PAR range transparent and black nets doesn¿t cause an alteration of the spectrum of solar radiation and transmittance is almost constant with a slight growth in nets having lower porosity

Energy saving: From engineering to crop management

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 CO2 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 CO2 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

Options for Greenhouse Horticulture in Malaysia : trip report March 2008

Protected greenhouse horticulture is a growing activity in Malaysia that has been prioritized by the Malaysian government as an area of cooperation with The Netherlands. Also, the private sector sees business opportunities and initiates modernization. Traditional horticultural production takes place in the highlands, where land is scarce and production competes with tropical rainforest. However, there are opportunities in the lowlands. For example, in Terengganu, greenhouses that are modern to Malaysian standards have been successfully realized in 2007. Most relevant crops are currently cucumber, chillies, sweet pepper and tomato. Consumer’s demand or export opportunities may lead to the introduction of other crops. It is desired that these first developments are taken further, also for the highland regions where the majority of horticultural production is located