David Loureiro, Maria Joao Martins, Jose Antonio Santos, Antonio Nogueira,
Jorge Cruz Costa, Luis Pestana, Edgar Atai’de

INETI, Department of Renewable Energies, Campus do Lumiar, 1649-038 Lisbon, Portugal

E-mail: david. loureiro@ineti. pt

Abstract

The aim of this work is to contribute to the discussion of the methodology that leads to a better systematization of the knowledge on solar drying. Based on a case study for the lumber industry, the options and solutions adopted will be reported, along with their evaluation criteria and existing or developed tools. The kilns have 50 m3 interior capacities and proved the capability to dry maritime pine 27 mm thick, from green to 12% moisture content in about 33 days. The performance of the drying process has a significant seasonal and weather dependence, so an interactive control system is essential in order to profit as much as possible from the favorable exterior conditions.

1 Introduction

The use of solar energy for drying purposes is in general meant to save drying costs, primary energy and to reduce CO2 emissions. For these reasons over the last few decades, several solar drying systems have been described for agriculture and forest products, many of them reported in Europe [1,2] where the performance of the drying process has a significant seasonal dependence. This trend has been triggered by the promotion of rational energy use and renewable energies sources by European Union next to industrial manufactures.

Although several innovative versions and applications have been reported, there is an important lack of reliable information on the energy efficiency of solar energy based driers which is essential to gather in order to establish such driers as an acceptable industrial alternative when compared with traditional types based on fossil sources of energy.

The aim of this paper is to contribute to a discussion on the methodology that leads to a better systematization of the knowledge about the solar drying area, namely on the energy efficiency, wood quality, drying duration and drying costs. Based on a case study for the lumber industry, the options and solutions adopted will be discussed, along with their evaluation criteria and existing or developed tools.