Solar kilns : feasibility of utilizing solar energy for drying lumber in developing countries

FOREST PRODUCTS LABORATORY AT MADISON, WISCONSIN, TESTED THE FEASIBILITY OF USING SOLAR ENERGY TO IMPROVE LUMBER DRYING BY SMALL-TO MEDIUM-SCALE OPERATORS IN LDCS. THE LITERATURE REVIEW OF SOLAR LUMBER DRYING THROUGHOUT THE WORLD CONFIRMS THE POTENTIAL OF SOLAR DRYING AND POINTS OUT THE SUCCESS OR FAILURE OF SOME DESIGN FEATURES, CONSTRUCTION DETAILS, AND APPLICATIONS OF SOLAR DRYERS. FEASIBILITY ESTIMATES SHOW THAT SOLAR DRYING IS PRACTICAL IF A DRYER MEETS PRODUCTION AND COST REQUIREMENTS. TWO SOLAR DRYER DESIGNS, A GREENHOUSE TYPE AND AN EXTERNAL COLLECTOR TYPE, HAVE GOOD POTENTIAL TO PROVIDE LOW COST KILN CAPACITY. PRODUCTION CAPACITY IS ESTIMATED BY A MATERIAL AND ENERGY BALANCE ANALYSIS, AND CONSTRUCTION COSTS ARE ESTIMATED. SOME ALTERNATIVES FOR SOLAR KILNS ARE DISCUSSED -- THE CONVENTIONAL STEAM HEATED OR DIRECT FIRED DRY KILNS AND THE LOW COST, CONCRETE BLOCK FURNACE KILN. THE LIMITATIONS TO THESE TYPES ARE THE POOR AIR CIRCULATION, LACK OF HUMIDIFICATION, AND THE SENSTIVITY OF THE AVAILABILITY OF WOOD WASTE. ANOTHER ALTERNATIVE IS A SOLAR KILN WITH A BACK-UP HEATING SYSTEM FOR NIGHT OR CLOUDY DAY OPERATION. A LARGE SECTION OF THIS REPORT IS DEVOTED TO SOLAR DRY KILN DESIGN OPTIMIZATION BY COMPUTER MODELING. THE INITIAL ENGINEERING STUDY RESULTED IN A COMPUTER PROGRAM CAPABLE OF EXPLORING THE MERITS OF SUPPLEMENTAL SOLAR DRYING, WHICH IS A COMBINATION OF SOLAR AND CONVENTIONAL FUELS AS AN ENERGY SOURCE. THIS COMPUTER MODEL ESTIMATED THE FEASIBILITY OF SUPPLEMENTAL SOLAR ENERGY AS A POSSIBLE WAY TO REDUCE DRYING FUEL COSTS.