Chronica Horticulturae volume 49 number 2 ... - Acta Horticulturae

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Figure 7. In the Netherlands about 1 billion m 3 natural gas is saved by the greenhouse industry using waste heat and CO 2 supply from Combined Heat and Power generators (CHP). world (e.g. Turkey, Germany) have geothermal potential that can be economically feasible for greenhouse heating. In 2007 the first geothermally heated greenhouse in The Netherlands was realized with a 7.25 ha tomato greenhouse being heated by a 5 MW geothermal source with water of 65°C from a depth of 1700 m. At this moment about 25 new projects are in the stage of feasibility study or first drilling (Fig. 8). New Designs of Energy Efficient Greenhouses Although development and implementation of individual energy saving components can result in energy savings, the only way to reach the ambitious targets on CO 2 emission, and steps to energy producing greenhouses, is by integrating energy conservative greenhouse systems including covering material, heating and ventilation/dehumidification, control algorithms and energy conversion systems. A theoretical solar greenhouse concept as developed by Bot et al. (2005) is a good example of an integral Figure 8. Geothermal energy as sustainable source is available in large regions of the world. energy efficient design where all components, including the energy conversion technologies and optimal control are incorporated. The objective of the solar greenhouse project was the development of a greenhouse system for high value crop production without the use of fossil fuels. The concept is a system that during the summer collects as much heat as possible to balance the minimized energy requirement during the winter. Such a system could be, combined with control algorithms for a dynamic control, resulting in a total realizable energy saving of over 60%. This enables a sustainable energy supply per ha greenhouse of only 600 kW that could be obtained through wind power or Photo Voltaic Panels. With completely and semi-closed greenhouses (Opdam et al., 2005) the next step in the design is to extract the total heat surplus during the summer and store the heat in the form of warm water at a temperature of 25-30ºC in a long term heat storage (aquifer): an isolated water containing sand layer usually at a depth of between 100-200 m. During the winter period, the heat is extracted from the aquifer using a heat pump and reused for heating the greenhouse itself and/or neighboring greenhouses or buildings, the so called “Energy Producing Greenhouse.” To achieve this, the performance of the greenhouse as a solar collector has to be maximized by further reduction of the heat loss and maximizing the heat collection by very efficient heat exchangers. The first trials in a commercial scale greenhouse with this system (Bakker et al., 2006), called “The Energy Producing Greenhouse” in Bergerden, The Netherlands, showed that a net energy surplus from the greenhouse was not reached since the output was limited by the grower’s temperature band widths and his frequent use of shading screens to minimize expected detrimental effects on his crop. A disadvantage of the heat producing systems is the low level of energy delivered by the system (water at 40°C), which requires modified heating systems and which has to be used in the direct neighborhood of the greenhouse. However, the heat delivery from greenhouses to the urban environment (greenhouse in energy grids) is a real option in the highly populated Westland area in The Netherlands. At least one commercial project is in a far stage of development and several improved designs of heat producing greenhouses are now being tested in the so called Innovation and Demonstration Centre for Energy Producing Greenhouses in Bleiswijk on the location of Wageningen UR Greenhouse Horticulture (Fig. 10). In an attempt to combine greenhouse production with electricity production instead of warm water production, Sonneveld et al. (2006) designed a system with a parabolic nearinfrared (NIR) reflecting greenhouse cover. This cover reflects and focuses the NIR radiation on a specific PV cell or solar collector to generate electricity (Fig. 11). The first results measured on an actual 100 m 2 prototype show that the Figure 9. In the so called “Energy Producing Greenhouse” the performance of the greenhouse as a solar collector has to be maximized by further reduction of the heat loss and maximizing the heat collection by very efficient heat exchangers. potential electric and thermal power generated by this system might be up to 15 kWh/m 2 electric and about 50 kWh/m 2 thermal energy. However, at the present time, due to the current price level of energy, the limited increase in crop production, and the complex and costly installations required, most systems and concepts of completely closed greenhouses are not economically competitive and could only be realized with specific support from local and national governments. For semi-arid regions in the world, some interesting designs have been realized for innovative and energy efficient greenhouses that incorporate high levels of technology and that intend to adapt the concept of closed or semi-closed greenhouse. In the Watergy project, a completely closed greenhouse was developed aiming at complete recirculation of water based on an innovative heat exchanger (Buchholz et al., 2005). The actual prototype showed promising results, but the economic feasibility of complete closed greenhouses still is the major bottleneck as in northern latitudes. Figure 10. Several improved designs of heat producing greenhouses are now being tested in the so-called Innovation and Demonstration Centre for Energy Producing Greenhouses in Bleiswijk on the location of Wageningen UR Greenhouse Horticulture. ISHS • 22
Figure 11. A prototype of the electricity producing greenhouse using reflected NIR for electricity production. semi-arid conditions, the primary steps are efficient natural ventilation, cooling, and reducing the solar energy flux into the greenhouse during the summer. For passive greenhouses, that use no fossil fuel for operational use at all, steps can be made by reducing the energy inputs for the greenhouse structure, irrigation, auxiliary equipments and inputs such as fertiliz- ers. Apart from the reduction of energy use, the use of various alternatives for fossil fuel such as waste heat and geothermal sources is a necessity to reach the ambitious goals on energy efficient producing greenhouses. However, practical application of all new designs depends on economic feasibility leading to different solutions in different areas of the world. REFERENCES The prevailing approach for developing energy efficient greenhouse systems for large areas in the world where heating may be convenient but is not essentially needed is still based on the development of passive greenhouses. Since in this situation, the energy input for climate conditioning is very limited, reduction of other processes responsible for CO 2 emission in the operation of passive greenhouses are taken into account. Life Cycle Analysis can be applied to the whole production process to identify which parts are more energy consuming. For unheated greenhouses, the greenhouse structure (foundations and perimeter walls) and auxiliary equipments (irrigation pipes, plastics for mulching, crop supporting members) account for 51% of the total gas emissions (Antón, 2004). New designs focus on the redesign of the foundation system and the use of recyclable concrete to reduce energy use. Since fertilizer production and use is another factor with strong influences on energy consumption of tomato production (about 36% of emissions) overall energy efficiency of the more passive greenhouses can be achieved by reduction in fertilization. CONCLUSION The design of more energy efficient greenhouses includes optimization of the greenhouse as a solar collector, improved production by a better control of the growth environment, and expanding the growth season. For moderate climates, promising routes are more airtight greenhouses with cooling, heat recovery and optimized environmental control. For more Adams, S.R., Woodward, G.C. and Valdes, V.M. 2002. The effects of leaf removal and of modifying temperature set-points with solar radiation on tomato. J. Hort.Sci. Biotech. 77:733-738. Antón, A. 2004. Utilización del análisis del ciclo de vida en la evaluación del impacto ambiental del cultivo bajo invernadero mediterráneo. Thesis Doctoral, Universitat Politécnica de Catalunya, Spain. Baeza, E.J. 2007. Optimización del diseño de los sistemas de ventilación en invernadero tipo parral. Tesis Doctoral, Universidad de Almería, Spain. Bailey, B.J. 1985. Wind dependent control of greenhouse temperature. Acta Hort. 174:381-386. Bakker, J.C., de Zwart, H.F. and Campen, J.B. 2006. Greenhouse cooling and heat recovery using fine wire heat exchangers in a closed pot plant greenhouse: design of an energy producing greenhouse. Acta Hort. 719:263-270. Bakker, J.C., Adams, S.R., Boulard, T. and Montero, J.I. 2008. Innovative technologies for an efficient use of energy. Acta Hort. 801:49-62. Bot, G.P.A., van de Braak, N.J., Challa, H., Hemming, S., Rieswijk, Th., van Straten, G. and Verlodt, I. 2005. The solar greenhouse: State of the art in energy saving and sustainable energy supply. Acta Hort. 691:501-508. Boulard, T. 2001. Solar energy for horticulture in France: Hopes and reality. Workshop on Renewable Energy in Agriculture, November 19th, 2001: Castello Utveggio – Palermo, EUROPEAN COMMIS- SION, Energy and Transport, Energy Framework programme 1998-2002. Buchholz, M., Jochum, P. and Zaragoza, G. 2005. Concept for water, heat and food supply from a closed greenhouse. The Watergy project. Acta Hort. 691:509-516. Campen, J.B. and Bot, G.P.A. 2002. Dehumidification in greenhouses by condensation on finned pipes. Biosyst. Eng. 82(2):177-185. Challa, H. and van de Vooren, J. 1980. A strategy for climate control in greenhouses in early winter production. Acta Hort. 106:159-164. ABOUT THE AUTHOR Dr. Sjaak Bakker has expertise in designing and developing energy conservative greenhouses and greenhouse environment - crop response interactions. At present he is Manager of the newly formed Business Unit Wageningen UR Greenhouse Horticulture. Within this new unit, the Greenhouse Technology Group, the former PPO Greenhouse Horticulture and the cropping systems department of Plant Research International are brought together with research facilities in both Wageningen and Bleiswijk. His address is Wageningen UR Glastuinbouw, Violierenweg 1, 2665 MV Bleiswijk, Post Box 20, 2665 ZG Bleiswijk, The Netherlands. Email: Sjaak.Bakker@wur.nl De Pascale, S. and Maggio, A. 2004. Sustainable protected cultivation at Mediterranean climate. Perspectives and challenges. Acta Hort. 691:29-42. Dieleman, A. and Kempkes, F. 2006. Energy screens in tomato: Determining the optimal opening strategy. Acta Hort. 718:599-606. Hamer, P.J.C., Bailey, B.J., Ford, M.G. and Virk, G.S. 2006. Novel methods of heating and cooling greenhouses: A feasibility study. Acta Hort. 719:223-230. Hemming, S. 2005. EFTE: A high transmission covermaterial (in German). Gärtnerbörse 105 (2005)6. Hemming, S., Kempkes, F., Van der Braak, N., Dueck, T. and Marissen, N. 2006. Filtering natural light at the greenhouse covering – Better greenhouse climate and higher production by filtering out NIR? Acta Hort. 711:411-416. Körner, O. 2003. Crop based climate regimes for energy saving in greenhouse cultivation. PhD Thesis, Wageningen Univ., The Netherlands. Langton, F.A. and Hamer, P.J.C. 2003. Energy efficient production of high quality ornamental species. Final Report to Defra, project HH1330. Lorenzo, P., García, M.L., Sanchez-Guerrero, M.C., Medrano, E., Caparrós, I. and Giménez, M. 2006. Influence of mobile shading on yield, crop transpiration and water use efficiency. Acta Hort. 719:471- 478. Montero, J.I. 2006. Evaporative cooling in greenhouses: Effects on microclimate, water use efficiency and plant response. Acta Hort. 719:373-383. Olofsson, T., Majabacka, A. and Engblom, S. 2006. Evaluation of energy performance for greenhouses based on multivariate analysis methodology. Acta Hort. 718:211-218. Opdam, J.J.G., Schoonderbeek, G.G., Heller, E.B.M. and de Gelder, A. 2005. Closed greenhouse: a starting point for sustainable entrepreneurship in horticulture. Acta Hort. 691:517-524. Sonneveld, P.J., Swinkels, G.L.A.M., Kempkes, F., Campen, J.B. and Bot, G.P.A. 2006. Greenhouse with integrated NIR filter and a solar cooling system. Acta Hort. 719:123-130. Sjaak Bakker CHRONICA HORTICULTURAE •VOL 49 • NUMBER 2 • 2009 • 23
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Page 3 and 4: NEWS & VIEWS FROM THE BOARD ISHS: S
Page 5 and 6: ISSUES Green Roofs and Living Walls
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Page 9 and 10: Figure 2. Flowering Rosa rubiginosa
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