Recirculating the air from the attic as a pre-renovation control strategy in a greenhouse-type solar dryer

Recently, the study of greenhouse-type solar dryers has gained popularity, mainly due to using renewable energy as the primary energy source and the ability to control the greenhouse environment to adjust it to the desired air temperature for drying. However, control policies still need to be investigated to achieve a suitable environment to improve water removal. The objectives of this study were: 1) model a greenhouse-type solar dryer using computational fluid dynamics, and 2) evaluate alternative air distribution systems to improve internal conditions before air extraction. The greenhouse is located at the Universidad Autónoma Chapingo, Mexico. Measurements were made inside the greenhouse at different heights and compared with the CFD model. During the validation stage, it was found that the model adequately represents the system with only a difference of ±3°C between the computational model and the measurements. These differences can be explained if it is considered that the tables or other solids in the greenhouse were not taken into account for the computational model, as well as the precision of the sensors. Using the CFD model, two air recirculation systems were evaluated. The systems take the air in the greenhouse attic and force it to flow under the drying tables. The results found were a more homogeneous temperature in the greenhouse volume with a higher temperature at the height of the drying tables and an increased airspeed, which could improve drying and reduce the time needed to complete the process.