**1.1 Short historical overview on the related researches**

For several decades until this time in Japan, the researches on a solar lumber drying apparatus are mainly as follows: (1) Firstly, a small sized semi passive-type solar lumber dryer made by hand was experimented by Hokkaido Forest Research Institute (Norota, T., et al., 1983) and some products were practically used over northern area in Hokkaido. (2) Second, a large scale solar lumber drying house, an active-type, was developed by a big company, as a national project (Miyoshi, M., Sep., 1987), (Kanayama, K., Baba, H., 2004), and was examined for three years. (3) Third, as a result of the above task, a larger one, using the same type of apparatus was constructed by technical transfer to overseas. In Indonesia, a much bigger size active-type solar lumber drying system was constructed for drying a broadleaf wood, like lauan, during several year (Yamada, M., 1998).

However, in this research aimed at solar lumber drying by improving an agricultural vinyl house, an active-passive type was examined (Kanayama, K., et al., 2006), adopting the new concept as above, and "a fully passive-type solar lumber drying" was ultimately created by our project team (Kanayama, K., et al., 2007), (Kanayama, K., et al., 2008), (Baba, H., et al., 2008). This technical article (Kanayama, K., et al., 2009), (Baba, H., et al. 2009), firstly deals with an optical-thermal mechanism of volumetric solar radiation (S. R.) incidence and a capability of volumetric solar heat collected into "a fully passive-type solar lumber drying house" covered by a composite film, consisting of a triple transparent film and a CF-sheet. The outside view of "a fully passive-type solar lumber drying house" looks like non-transparent from the outside, so it might be called an opaque house. An insulated cylinder (chimney) with a damper duct is set on the outside of the opaque house to make it fully passive function. Subsequently, the opaque house was carefully designed and actually constructed at the main site for the proving test; Ashoro (43°14.5'N, 143°33.5'E) and the sub-site for the proving test, Asahikawa (43°46'N, 142°22'E) in the eastern and northern parts of Hokkaido respectively. A proving performance test of the opaque house and the analysis of the results were successfully carried out by our project team for two and a half years. The capability of the solar lumber drying of the opaque house could be verified experimentally (Kanayama, et al., Aug., 2008), (Baba. et al., Oct., 2008), (Koga, et al., Oct., 2008).
