Comparative study of conventional and solar heating systems under tunnel Tunisian greenhouses: Thermal performance and economic analysis

To keep the optimum growing environment, greenhouses should be low energy consumers. In order to reduce the energy consumption in agricultural greenhouses at night, two tunnel greenhouses, with 100 m(2) of area, are constructed and installed in the CRTEn (Research and Technologies Centre of Energy) of Tunisia. The first is equipped with a buried and suspended heat exchanger and the second one is devoid of a heating system. Two heating sources have been used in order to increase the nocturnal air temperature under greenhouse: an Electrical Heating System (EHS) and a Solar Heating System (SHS). We propose in this study to compare the two heating systems. The efficiency of the solar collector is determined and the effectiveness of the evacuated tube solar collector with a water storage tank is also examined. The average value of energy efficiencies of the evacuated tube solar water heater is about 46%. The EHS allows an increase of inside air temperature of 4 degrees C while the use the SHS permits temperature rise of 2 degrees C. An economic analysis shows that the use of a system of 3 evacuated tube solar collectors for greenhouse heating is rentable since the payback period of the solar system is 3 years. (C) 2015 Elsevier Ltd. All rights reserved.