Solar thermal collectors for greenhouse heating

The paper presents the preliminary results of a research finalized to use solar thermal collectors to supply a greenhouse heating system. Aim of the research was to assess the potential of the system in terms of energy production, storage and use. A surface of 12 m2 of solar thermal flat plate collectors, a thermal insulated tank for the storage of the hot water, circulators and heating plastic pipes, an electronic control unit were used in the experiment. The test was realized at the experimental farm of the University of Bari, Southern Italy, in an arched roof steel greenhouse covered with a plastic film where a soil-less tomato cultivation was carried out. Solar radiation incident on the solar thermal collectors, air temperature above the heated cultivated surface, growing media temperature, water temperature inside the storage tank were measured and recorded continuously by a system composed of data logger and sensors. Results of the experiment showed that the use of the solar thermal collectors must be integrated with auxiliary heat sources, such as burners or heat pumps. The test showed that about 40% of the incident solar radiation was transferred as heat to the cultivation, obtaining an increase of 28% of the total yield.