Task 29
Task 29
SHC Task 29

Solar Crop Drying

Coffee Drying - Costa Rica

Early in the year an agreement to install a solar system on an existing coffee drying facility was reached with the cooperative Coopeldos in the western mountains of Costa Rica.  The coffee beans go through a primary drying phase (60% - 35% moisture content) in the vertical dryers and then a secondary drying (30% - 12% moisture content) in a series of guardiolas, rotating horizontal drums.  Based on the results of a feasibility study, 690 m2 of Solarwall collector were installed on the roof and the design air flow calculated to be 28 l/s/m2.  The collector efficiency was predicted to be 59% and the total system was predicted to deliver 1,993 gJ per year.  This performance will save over 300 tonnes of wood per year.

The system was monitored by Task experts during the 2004/05 drying season.  Early analysis indicated that there was significant air leakage in the furnace and ductwork.  Remedial measures were taken but there were still certain openings which were manually operated to control air flow.  It was recommended that automatic equipment be installed to increase efficiency but this was not implemented during the time frame of the Task.

Due to the air leakage and the plant operating below full capacity during periods in the season, the air flow through the collectors was much less than anticipated.  The collectors, however, did perform as predicted for the reduced air flow.  Over the season, the system displaced over 440 gJ of energy resulting in a saving of over 22,700 kg of wood.

Solar collectors on roof of drying facility
Solar collectors on roof of drying facility.

Duct from solar collector entering furnace
Duct from solar collector entering furnace.