Energy consumption pattern modification in greenhouses by a hybrid solar-geothermal heating system

Greenhouses play a key role in producing various crops in Bohemian climates and during the entire year. To provide the desired temperature within the greenhouse during the cold months of the year, diesel air heaters are generally employed, burning huge amount of fossil fuels. In this work, an innovative hybrid system including solar and geothermal heating units has been proposed to be used to reduce the heating duty of diesel air heaters in greenhouses. Taking ambient temperature in different seasons and the desired temperature in the greenhouse into account, three operational strategies are planned for the proposed system. Next, considering the defined operational strategies and economic issues, the solar and geothermal parts are accurately sized and designed. Finally, a hybrid system including a solar system with 430 flat plate collectors and a geothermal system consisting of 35 boreholes, with 150 m depth each, is found to be the most thermo-economically efficient system for the case study of this work. A comprehensive energy analysis on the designed configuration shows that a total annual of almost 256,000 and 192,000 m(3) fuel saving may be possible in the case study by the solar and geothermal systems, respectively. Finally, the proposed hybrid system performance is economically compared with previously proposed systems for the same objective by the internal rate of return (IRR) method, proving its superiority with an IRR of 0.115.