Greenhouse Cooling by Nir-Reflection

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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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“…Heat-barrier or 'heat-blocking' films. Fluid-roof greenhouses filtering out the infrared wavelength bands of the solar spectrum (Van Bavel et al, 1985) paved the way towards the development of heat-barrier films (NIR-reflecting films; Hemming et al, 2006b). These films allow a substantial reduction of the greenhouse heat load (Abdel-Ghany et al, 2001;Sonneveld et al, 2006), and lower risks of conditions of heat stress.…”

Section: Disease and Pests Control ('Uv-blocking')mentioning

confidence: 99%

Innovation in Plant-Greenhouse Interactions and Crop Management

Heuvelink¹,

Gonzalez-Real²

2008

Abstract(Semi)-closed greenhouses allow for better control of climate conditions compared to conventional greenhouses. To make the high investments for such greenhouses economically feasible, substantial yield increases are necessary. In north-Europe supplementary assimilation light in greenhouse horticulture is increasingly used to improve yield and product quality to meet market demands for year-round production and to obtain a more regular labor demand throughout the year. Using inter-lighting instead of lights only on top of the crop, and Light Emitting Diodes (LEDs), could increase substantially light and energy efficiency. As soon as LEDs will reach high enough efficiency and feasible price, they are expected to replace high pressure sodium lamps in greenhouse horticulture. Another important issue is the choice of the greenhouse cover which should be optimized from the crop point of view. A cover with high transmission of light, but low transmission of NIR, results in a better climate during the warm season (reduced temperatures, less crop transpiration, higher CO 2 -concentration possible because of reduced ventilation demand). Increasing the diffusive power of the cover material could result in a better distribution of the radiation over the crop canopy, therefore leading to substantial increase in absorbed radiation (up to 20% for highly diffusive covers) and improving radiation use efficiency and yield. Under these new conditions (high CO 2 and high light levels) other genotypes than the present cultivars may be superior. However, the possible effect of breeding especially for these new conditions is still little investigated. Under improved crop management, maintaining leaf area index high enough and controlling source-sink balance is discussed. In conclusion, there are a lot of possibilities to further improve yield and quality of greenhouse produce, and meanwhile reduce the input of fossil fuel energy.

“…A desk study of Hemming (Hemming et al, 2007) found that permanent NIR filtering in the cover would increase energy consumption in the Dutch climate by 10%, and concluded that movable screens would be more suitable in such conditions. In the experiment whose preliminary results we present here, we compare the effect on the greenhouse climate and crop water use of a NIR reflecting material and a standard material with similar PAR transmission, both installed as movable screens.…”

Section: Introductionmentioning

confidence: 99%

Cover Materials Excluding Near Infrared Radiation: Effect on Greenhouse Climate and Plant Processes

Kempkes¹,

Stanghellini²,

Hemming³

et al. 2008

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Only about half of the energy that enters a greenhouse as sun radiation is in the wavelength range that is useful for photosynthesis (PAR, Photosynthetically Active Radiation). Nearly all the remaining energy fraction is in the Near InfraRed range (NIR) and warms the greenhouse and crop and does contribute to transpiration, none of which is necessarily always desirable. Materials or additives for greenhouse covers that reflect or absorb a part of the NIR radiation have recently become commercially available. Besides lowering greenhouse temperature (which is the primary aim), a NIR-excluding cover has quite a few side-effects, that may become relevant in the passive or semi-passive greenhouses typical of high-energy climates. For instance, the ratio of assimilation to transpiration (the water use efficiency) should increase. By lowering the ventilation requirement, such a cover may hinder in-flow of carbon dioxide, thereby limiting the photosynthesis rate. A previous desk study has shown that in cooler climates such as The Netherlands, a permanent NIR filter may increase year-round energy requirement up to 10%. In this work we present the first results of a rose crop glasshouse experiment with an internal movable, NIR-reflecting screen. We analyse the effect on greenhouse temperature, carbon dioxide management and humidity and on crop transpiration. We then discuss the most appropriate application of a NIR-selective filter, in view of the prevailing climate and the available ambient management option.