Fabrication and Evaluation of Polyhouse Type Solar Dryer for Drying Wet Coffee and Hot Pepper

One of the crucial post-harvest processes that contribute to the unique color, flavor, and taste of a coffee drink is drying technique. Solar drying refers to a technique that utilizes incident solar radiation to convert it into thermal energy required for drying purposes. A polyhouse solar dryer is a unique and cost-efficient method of drying agricultural products on a small as well as commercial scale. The fabricated dryer has three major units: a solar collector unit, a drying unit, and chimney unit components. The aim of this study was to manufacture and evaluate a 5-meter length and 2-meter width half-circled tunnel polyhouse type solar dryer using parchment coffee and hot pepper. The experimental results showed that the developed dryer has the capacity to dry averagely about 150 kg of hot pepper and 50 kg of wet coffee per batch. The obtained data were analyzed using software such as simple descriptive statistics and Origin Pro 2019 according to their suitability. Hot pepper was dried from an initial moisture content of about 82.95% to 10.42% in a polyhouse-type solar dryer within 6 days, while conventional sun drying took around 9 days. Using hot pepper, the average temperature inside the dryer was 53.90 °C to 62.57 °C in the full load condition, which was greater than the ambient temperature in all six days of the experiment. While the ambient relative humidity varies between 34.5% and 43.5%, the dryer's relative humidity using hot pepper was altered between 21.07% and 24.69%. In all six days of the experimental period, the relative humidity of the dryer was found to be less than that of ambient relative humidity due to the polyhouse effect. The wet coffee bean was dried from an initial moisture content of about 51.89% to 11.10% in a polyhouse-type solar dryer within 3 days, while by open-sun drying it took around 6 days. Using wet coffee, the temperature inside the dryer chamber were 50.08 °C to 54.08 °C at full load condition, which was greater than the ambient temperature in all three days of a tests. Whereas the ambient humidity in the air ranges from 39.77% to 42.22%, the dryer's relative humidity using wet coffee ranged between 22.22% and 23.46%. The average dryer thermal efficiencies of a polyhouse dryer use wet coffee beans and hot pepper were 64.48% and 86.87%, respectively.