Annual Thermal Performance of an Industrial Hybrid Direct–Indirect Solar Air Heating System for Drying Applications in Morelos-México

Abstract

A theoretical–experimental annual analysis of a hybrid industrial direct–indirect solar air heating system performance for drying was conducted considering temperatures, useful energy Qu, efficiency η, and solar fraction SF. The direct solar air heating system located in Morelos, México, has flat-plate solar air collectors, and the indirect system has flat-plate solar water collectors, a thermal storage tank, a cross-flow fin, and a tube heat exchanger. A validated TRNSYS program modeled the process; the validation was carried out by comparing each component outlet temperature and useful energy with the respective experimental field data. The analysis considered annual usage over seven days a week, nine hours a day (from 09:00 to 18:00 h), and three operation modes. For the direct, indirect, and hybrid operation modes, the Qu values were 31.60, 55.19, and 75.18 MWh/yr; the annual η values were 0.44, 0.41, and 0.42; and the annual SF values were 0.45, and 0.73 for the indirect and hybrid mode, respectively. The hybridization of the direct–indirect solar air heating system increased annual performance by up to 58% in Qu and 42% in SF. The parametric analysis showed that a characteristic working nomogram of the hybrid system could be achieved, correlating the useful energy, efficiency, solar fraction, and operation temperature at a specified mass flow rate, and working temperature.