**2. A new concept of a solar lumber drying technology**

### **2.1 Outline of the concept**

An opaque house is covered by a composite surface consisting of a triple transparent film with double air layers and a CF-sheet, among which are a few spaces held by a skeleton frame. In this case, solar radiation (S. R.) incident upon the house surface is absorbed by the CF-sheet effectively, and converted into solar heat (infrared radiation) and only few

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

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

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.,

An opaque house is covered by a composite surface consisting of a triple transparent film with double air layers and a CF-sheet, among which are a few spaces held by a skeleton frame. In this case, solar radiation (S. R.) incident upon the house surface is absorbed by the CF-sheet effectively, and converted into solar heat (infrared radiation) and only few

(chimney), (9) thermo siphon effect, and so on.

2008), (Koga, et al., Oct., 2008).

**2.1 Outline of the concept** 

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

broadleaf wood, like lauan, during several year (Yamada, M., 1998).

**2. A new concept of a solar lumber drying technology** 

part of the incidence is transmitted through the opaque house as solar ray ultimately. As shown in Fig.1, this optical and thermal mechanism is induced by a "transparent insulation/blackbody cavity effect" (Kanayama, K., et al., 2010), (Kanayama, K., et al., 2010). From this, an incident ray falls three-dimensionally into the cubical opaque house (=Volumetric S. R. incidence) and global S. R. from the sky is collected threedimensionally by the opaque house (=Volumetric solar heat collected) too. In this case solar heat can be collected passively by the opaque house and saved passively into the opaque house. Hence, any electric power is needless. On the other hand, a moist air produced when drying lumber in the opaque house can be sucked by the draft force through an insulated cylinder set on the outside of the opaque house (Fig.5). This is a thermo siphon phenomenon caused by density difference due to temperature difference between inside air and outside air of the opaque house. As above, the combination of the composite surface consisting of a triple transparent film and a CF-sheet, and an insulated cylinder with a damper duct, could successfully collect S. R. Besides, the inside air is taken out from, and the outside air is taken into, the opaque house in accompany of the phenomenon. In this case, electric power is needless, so this is the reason for the name: "a fully passive-type solar lumber drying house".

coverd by a composite surface, (Kanayama, K., et al., Jun.,2009) Fig. 1. "Transparent Insulation/Blackbody Cavity Effect" on the opaque house covered by a composite surface. (Kanayama, K. et al., Jun., 2009)

Fig.1 "Transparent Insulation/Blackbody Cavity effect" on the opaque house

#### **2.2 Explanation on the "transparent insulation/blackbody cavity effect"**

Referring to Fig.1 and Fig.2, when a unit of S. R., IoND (Normal direct radiation=1.0), was incident upon the opaque house covered by a composite surface, 0.804 of that is transmitted through triple transparent film, 0.85 of that is absorbed by the CF-sheet (=scattering medium with apparent absorptance 0.85), and 0.9 of that is passed through a skeleton frame, as discussed in the section 2.3 in detail. However, the CF-sheet inside the house absorbs 0.7, transmits 0.15, and the residual 0.15 is reflected toward the outside of the opaque house. Consequently, 0.615 (≡0.6) is trapped as solar heat (=infrared radiation) into the opaque house. Because the inside of the house is a closed space covered by the composite surface involving the CF-sheet, the solar heat under goes secondary reflection, absorption and re-emission as infrared ray in the cavity, so that a quasi-blackbody is realized or obtained with blackness of 0.85 or more, because that the transmitted ray of 0.15 is also incident on any body inside the house, and absorbed as heat.

A component transmitted outside from the inside of the house is very small due to triple transparent film, but mostly opaque for the infrared region. Heat (=near infrared and infrared radiation) of relatively high temperature inside the house is mostly, sometimes, shut out by the double air layers among the triple film, and due to a radiation property which is protective for infrared region, so that as a result, heat transfer loss is negligibly small. Thus, when S. R. is incident upon an opaque house it is mostly trapped within the opaque house as solar heat. Therefore, this phenomenon, because that the inside of the house is filled with infrared radiation beam, is called "transparent insulation/blackbody cavity effect".

#### **2.3 Component materials and efficiency of volumetric collection**

Fig.2 shows relation between radiation properties of the materials, consisting of composite surface, and intensity of direct S. R. incidence IoND in detail. On the radiation property of each material, assuming that a single transparent film's transmittance is τf=0.93, a triple transparent film's transmittance is τ<sup>f</sup> 3=0.804. If the CF-sheet's absorptance is αS=0.85, and the passing rate of the skeleton frame is τF=0.90, so the coefficient of transmittance-absorptance of the composite surface becomes (τ・α)CS=τ<sup>f</sup> <sup>3</sup>・αs・τF=0.804・0.85・0.90=0.614≡0.60. Fig.3 shows angular relation (θ, a) of solar colleting surfaces An and a house model, consisting of multi-surface An, n=1….n. If the solar radiation (S. R.) incident on the multi-surface, made up of a number of composite surfaces, from A1 to An, was known a intensity of I(d)tilt, on a tilt surface, by multiplying the I(d)tilt into the corresponding surfaces, A1 ~An, and summing up each product, the volumetric S. R. incidence, I(Q)VI, can be determined. Moreover, by multiplying coefficient of transmittance-absorptance (τ・α)CS 〔=0. 6]into I(Q)VI, the volumetric solar heat collected, QVC, is obtained. This is called as a conventional calculation method. Therefore, the efficiency of volumetric solar heat collected ηVC is defined as following Eq.(1):

$$\mathfrak{gl}\_{\rm VC} = \mathbf{I}(\mathbf{Q})\_{\rm Vl} / \mathbf{I}(\mathbf{Q})\_{\rm Pl} \times \left(\mathbf{\tau} \cdot \mathbf{a}\right)\_{\rm CS} = \mathfrak{gl}\_{\rm Vl} \times \left(\mathbf{\tau} \cdot \mathbf{a}\right)\_{\rm CS} \tag{1}$$

where I(Q)fl is S. R. incidence on the floor, ηVI is the efficiency of the volumetric S. R. incidence. In this case, I(d)tilt in the database database (NEDO's Report, (1997)) shown in Table 1 from AMeDAS is used as numerals at the experimental site; Ashoro (43°14.5'N, 143°33.5'E), Tokachi-pref., in Hokkaido.

Referring to Fig.1 and Fig.2, when a unit of S. R., IoND (Normal direct radiation=1.0), was incident upon the opaque house covered by a composite surface, 0.804 of that is transmitted through triple transparent film, 0.85 of that is absorbed by the CF-sheet (=scattering medium with apparent absorptance 0.85), and 0.9 of that is passed through a skeleton frame, as discussed in the section 2.3 in detail. However, the CF-sheet inside the house absorbs 0.7, transmits 0.15, and the residual 0.15 is reflected toward the outside of the opaque house. Consequently, 0.615 (≡0.6) is trapped as solar heat (=infrared radiation) into the opaque house. Because the inside of the house is a closed space covered by the composite surface involving the CF-sheet, the solar heat under goes secondary reflection, absorption and re-emission as infrared ray in the cavity, so that a quasi-blackbody is realized or obtained with blackness of 0.85 or more, because that the transmitted ray of

A component transmitted outside from the inside of the house is very small due to triple transparent film, but mostly opaque for the infrared region. Heat (=near infrared and infrared radiation) of relatively high temperature inside the house is mostly, sometimes, shut out by the double air layers among the triple film, and due to a radiation property which is protective for infrared region, so that as a result, heat transfer loss is negligibly small. Thus, when S. R. is incident upon an opaque house it is mostly trapped within the opaque house as solar heat. Therefore, this phenomenon, because that the inside of the house is filled with

Fig.2 shows relation between radiation properties of the materials, consisting of composite surface, and intensity of direct S. R. incidence IoND in detail. On the radiation property of each material, assuming that a single transparent film's transmittance is τf=0.93, a triple

passing rate of the skeleton frame is τF=0.90, so the coefficient of transmittance-absorptance

shows angular relation (θ, a) of solar colleting surfaces An and a house model, consisting of multi-surface An, n=1….n. If the solar radiation (S. R.) incident on the multi-surface, made up of a number of composite surfaces, from A1 to An, was known a intensity of I(d)tilt, on a tilt surface, by multiplying the I(d)tilt into the corresponding surfaces, A1 ~An, and summing up each product, the volumetric S. R. incidence, I(Q)VI, can be determined. Moreover, by multiplying coefficient of transmittance-absorptance (τ・α)CS 〔=0. 6]into I(Q)VI, the volumetric solar heat collected, QVC, is obtained. This is called as a conventional calculation method. Therefore, the efficiency of volumetric solar heat collected ηVC is defined as

 ηVC=I(Q)VI/I(Q)fl×(τ・α)CS=ηVI×(τ・α)CS (1) where I(Q)fl is S. R. incidence on the floor, ηVI is the efficiency of the volumetric S. R. incidence. In this case, I(d)tilt in the database database (NEDO's Report, (1997)) shown in Table 1 from AMeDAS is used as numerals at the experimental site; Ashoro (43°14.5'N,

3=0.804. If the CF-sheet's absorptance is αS=0.85, and the

<sup>3</sup>・αs・τF=0.804・0.85・0.90=0.614≡0.60. Fig.3

**2.2 Explanation on the "transparent insulation/blackbody cavity effect"** 

0.15 is also incident on any body inside the house, and absorbed as heat.

infrared radiation beam, is called "transparent insulation/blackbody cavity effect".

**2.3 Component materials and efficiency of volumetric collection** 

transparent film's transmittance is τ<sup>f</sup>

143°33.5'E), Tokachi-pref., in Hokkaido.

following Eq.(1):

of the composite surface becomes (τ・α)CS=τ<sup>f</sup>

Fig. 2. Radioactive property of materials consisting the house and a mutual relation between incident S. R. and collecting surface

Fig. 3. Angle relation on a solar collecting surface An and a house model consisting of multisurface An, n=1・・・n


Table 1. Solar Radiation (S. R.) Incidence on a Tilt Surfaces I(d)tilt at Experimental Site; Ashoro (4314.5'N, 14333.5'E) MJ/m2d (South-North model)
