Exchanged air control for maximum solar energy utilization in tobacco curing

Abstract

ABSTRACT TOBACCO was cured in three one-fifth scale (30 rack) units loaded on a MWF schedule each week for four weeks. A single-glazed flat plate collector and rock storage system raised the ambient temperature an average of 24.5 C during the day and 20.2 C at night to supply 37 percent of the required heat energy. The mean supplemental heat requirement was 12.7 MJ/kg of cured tobacco solids. Expressions for each term in an energy balance model are presented, and evaluated hourly in a simulation. Error in closure of the energy balance ranged for -6.8 percent to -0.1 percent with a mean of -3 per-cent for the 12 cures. The exchanged air rate was increased during the day to maximize usage of the solar system. The energy balance model was used to compare this strategy with a constant ventilation rate for each day du-ing the cure, equal to the time average rate for that period measured during the experiments. Increasing the rate during the day resulted in a 2 to 10 percent increase in the solar contribution with a mean of 5 percent for the 12 cures. Actual cure energy for the exchanged air schedules ranged from 21 to 37 percent more than the theoretical minimum calculated with the energy balance model. As a general guideline, the exchanged air schedule should be 20, 35, 50, 70, 40, and 20 air changed per hour for days 1 through 6 respectively. For a 5-day cure a general guideline is 30, 30, 50, 40, and 25 air changes per hour.