Design of a solar cooling system for greenhouse conditioning in a Mediterranean area

Monitoring and controlling environmental parameters inside a greenhouse are required to reach high yields and low environmental impacts. Ventilation, shading, evaporative cooling and refrigeration are methods of controlling air temperature and relative humidity in Mediterranean greenhouses. Nevertheless ventilation and shading are often not sufficient to remove the excess heat, refrigeration is generally expensive and evaporative cooling is based on the exploitation of high quality water, a resource to be preserved in the Mediterranean areas. In order to enhance the sustainability levels of the greenhouse sector, renewable energy sources can be exploited with the application of solar absorption systems for greenhouse cooling in areas with high outdoor temperatures. These systems take advantage of the simultaneity between the solar energy availability and the greenhouse cooling demand allowing the reduction of conventional electricity. This paper presents the simulation and optimization of a solar cooling system designed for a Mediterranean greenhouse, having a surface of 300 m2, using 68 m2 of evacuated tube solar collectors, a LiBr absorption unit with a cooling capacity of 17.6 kW and a pilot distribution system providing the cooling power for the volume surrounding the crop. The simulation study, predicting the performance of the unit, was based on the experimental data collected at the experimental centre of the University of Bari, Southern Italy. The results of the simulation indicated that the system is seasonally in phase with the climatic data; the delivered yearly cooling capacity for the greenhouse was 113 GJ, the required solar energy 157 GJ and the available solar energy on the 68 m2 capturing surface, with a slope of 30°, was 265 GJ. The simulation can be used as a forecasting tool of the effects of the changes on the parameters of the system before applying them on the greenhouse system.