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The effect of Fresnel lens - solar absorber systems in greenhouses
- Chemisana, D., Lamnatou, C.H.R., Tripanagnostopoulos, Y.
- Acta horticulturae 2012 no.952 pp. 425-432
- ambient temperature, electricity, energy, fluid mechanics, greenhouses, heat transfer, infrared radiation, lighting, solar radiation, wind speed
- Fresnel lenses can be mounted stationary on the greenhouse roof combined with linear absorbers to receive and convert the concentrated solar radiation into heat, electricity or both. The linear Fresnel lenses can separate direct from diffuse solar radiation and this advantage makes them suitable for lighting and temperature control of the greenhouse interior space. The incident beam solar radiation is concentrated on the tracking PVT absorbers and can be taken away from the glazed space. In this way, lower illumination level is achieved while avoiding overheating of the interior space. Furthermore, in low intensity solar radiation, the absorbers can be out of focus leaving the light to come in the interior space and keep the irradiation at an acceptable level for the plants. The proposed system can cover a great part of greenhouse thermal as well as electrical load and seems to be a promising solution. Apart from the above mentioned contribution to greenhouse energy needs, Fresnel/PVT influence greenhouse interior space by the heated linear thermal absorbers, which are in higher temperature than the rest greenhouse components and plants. These absorbers work as linear “heat sources” of infrared radiation and influence mass and heat transfer (HT) as well as fluid flow (FF) phenomena in the greenhouse. In the frame of the present study, a greenhouse with Fresnel/PVT, operated under some defined conditions of solar radiation input and ratio beam to total, ambient temperature and wind speed, is considered. Regarding roof operation modes, configurations with and without roof openings are investigated and results for both cases are given. Computational Fluid Dynamics (CFD) methodology is used for the simulation of HT and FF phenomena involved in the above mentioned cases. Results such as FF fields and temperature contours are presented. In addition, some horticulture aspects provide a wider view of the studied issues by considering the effect of HT and FF patterns on plant processes.