**1. Introduction**

Since old time, natural air drying technique had been utilized in several areas of the world before artificial drying methods for wood were developed. In Hokkaido, Japan, a research on the modified type, in place of the natural air dryer, was developed as a practical technology. For instance, the solar dryers of greenhouse-type and solar house-type were made by hand or constructed architecturally. After tested at the public institute, some of the apparatus were distributed to some areas of northern part of Hokkaido. For several decades, from just after the first energy crisis 1973 until the recent time, as an application of solar radiation in the field of forest industry, an active-type and a semi passive-type of solar wood dryers have been developed experimentally and constructed annually. For instance, a semi passive-type handmade solar lumber dryer was invented by the Hokkaido Forest Industry Product Institute, which occupied one era in a wide area as an auxiliary lumber dryer. Recently, in order to suppress the global warming, a policy to reduce emission of carbon dioxide was urgently required on the worldwide. For example, an artificial steamtype lumber drying emits a lot of carbon dioxide because it consumes a lot of fossil oil, i.e., about fifty liters per one cubic meters of wood.

In this chapter therefore, in drying process of wood materials in forest industry, by improving the greenhouse-type dryer or solar house-type dryer, several highly advanced models of solar lumber drying apparatus were provided and structured. A test of performance of one of them was carried out successfully at the experimental site in Hokkaido. In this case, practical use of solar radiation under a new concept of transparent insulation-blackbody cavity effect, two models of a fully passive-type solar lumber drying house were designed and constructed. One of which is a south-north model and the other is an east-west model. The measurement and analysis on the working performance of both models were carried out by our project team for several years under severe winter season. The results obtained from both models were fairly good and compared well with each other. Consequently, from the performance, both models of the fully passive solar lumber drying house developed, in this national project, were recognized to be good for drying laminar lumber, even under a sever cold season in Hokkaido.

This research is based on a new concept, therefore, a special feature involved in the article, will be expressed by a few technical keywords which will introduce the contents as follows: (1) transparent insulation/blackbody cavity effect, (2) composite surface, (3) CF-sheet, (4) coefficient of transmittance-absorptance, (5) volumetric S. R. incidence, (6) efficiency of volumetric solar heat collection, (7) volumetric solar heat collected, (8) insulated cylinder (chimney), (9) thermo siphon effect, and so on.
