Patent Publication Number: US-10323861-B2

Title: Building accessory structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of and claims the priority benefit of U.S. patent application Ser. No. 14/846,823, filed on Sep. 6, 2015, now pending, which claims the priority benefit of China patent application serial no. 201410647808.9, filed on Nov. 13, 2014. The entirety of each of the above-mentioned patent applications is hereby incorporated by reference herein and made a part of this specification. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a building-integrated energy collector and an accessory structure of a building. Specifically, the invention relates to a building-integrated solar thermal collector and a building accessory structure using the solar thermal collector. 
     Description of Related Art 
     With the rising awareness of environmental conservation, the public is paying more attention to the concepts of energy saving and reducing carbon emissions. The technologies of utilizing renewable energy have gained worldwide attention. In terms of renewable energy, solar energy is widely available. Unlike other energy sources, such as fossil energy or nuclear energy, solar energy does not cause carbon emissions or radiative pollution. Therefore, solar thermal collectors that convert sunlight into thermal energy have been applied in many fields and the production of solar thermal collectors has become an important industry. 
     A solar thermal collector with a large solar-receiving area can generate a relatively large amount of thermal energy for use. Many manufacturers in this field are putting efforts into integrating the concept of “green building” with the solar thermal collector, that is, to install solar thermal collectors on parts of a building that receive the most sunlight, so as to use the thermal energy generated by the solar thermal collectors to compensate for the thermal energy consumed in the building (e.g., supply of hot water or heating). However, the structures of current solar thermal collectors usually are not rigid and the installation requires attaching the collectors to existing building exterior structures, rather than become part of the building exterior structure. In addition, the bulky size and thickness of current solar thermal collectors limits the applicability and design flexibility of the solar thermal collector in the field of building integrated solar thermal (BIST). 
     SUMMARY OF THE INVENTION 
     The disclosure provides a solar thermal collector and a building accessory structure. When compared with conventional solar thermal collectors, the provided solar thermal collector has more rigid structure and better design flexibility. It also has less overall thickness and thus less wind resistance. As a result, the provided solar thermal collector is advantageous to be applied to a building as an accessory structure of the building. 
     The solar thermal collector of the disclosure includes at least one heat absorbing plate and at least one heat insulating plate. Each of the heat absorbing plates includes at least one first slab and a plurality of first engaging parts connected with the first slab. Each of the heat insulating plate includes at least one second slab and a plurality of second engaging parts connected with the second slab. The first engaging parts are respectively engaged with the second engaging parts, and a gap is maintained between the first slab and the second slab to form a heat collecting channel, through which a heat transfer medium can flow between the heat absorbing plate and the heat insulating plate. A heat conductivity of the heat absorbing plate is at least 30 times greater than a heat conductivity of the heat insulating plate. 
     In an embodiment of the invention, the solar thermal collector further includes a plurality of connecting pipes, which are connected to the edges of the heat collecting channels. 
     In an embodiment of the invention, the connecting pipe further includes a plurality of openings to allow the heat transfer medium to flow in and out of the heat collecting channels through the connecting pipe. 
     In an embodiment of the invention, each of the second engaging parts includes an extending groove and a hook groove, while each of the first engaging parts includes an extending section and a hook section. Each extending section is engaged with the corresponding extending groove, and each hook section is engaged with the corresponding hook groove in order to attach the heat absorbing plate to the heat insulating plate. 
     In an embodiment of the invention, the hood groove further includes a filler to be filled in the hook groove where the hook section is engaged. 
     In an embodiment of the invention, the filler includes a wedge, a curable adhesive, or a sealant. 
     In an embodiment of the invention, each of the first slabs and each of the second slabs are curved slabs, and each of the first slabs and the corresponding second slab are curved in the same direction. 
     In an embodiment of the invention, the solar thermal collector further includes a solar selective absorption coating that covers a solar-receiving surface of the heat absorbing plate. 
     The building accessory structure of the disclosure includes at least one frame and the frame connects to a plurality of the solar thermal collectors mentioned above. The proposed building accessory structure is suitable to be applied to an external area of a building. The frame is configured to hold the solar thermal collectors and the collectors are placed in parallel to each other in the frame. 
     In an embodiment of the invention, the frame includes at least one light-transmissive front cover placed on the side facing the heat absorbing plates. The frame also includes at least one light-transmissive back cover placed on the side facing the heat insulating plates. 
     In another embodiment of the invention, the frame includes at least one light-transmissive sleeve tube to hold the solar thermal collector. In addition, the light-transmissive sleeve is formed in one piece. 
     In an embodiment of the invention, the light-transmissive sleeve tube is made of non-glass materials. 
     In an embodiment of the invention, the light-transmissive sleeve tube is made of plastic materials. 
     In an embodiment of the invention, the external area includes a balcony or a terrace of the building. 
     In an embodiment of the invention, the building accessory structure is adapted to be a railing or barrier to be applied to the balcony or the terrace. 
     In an embodiment of the invention, the external area includes a rooftop, a window, a patio, or an open space adjacent to the building. 
     In an embodiment of the invention, the building accessory structure is adapted to be a shading structure or a covering structure to be applied to, the rooftop, the window, the patio, or the open space adjacent to the building. 
     Based on the above, the provided solar thermal collector allows the heat transfer medium to directly contact and flow through the heat absorbing plate, which means the solar thermal collector of the disclosure has a much larger heat exchange area than conventional collectors. Moreover, in the provided solar thermal collector, the heat conductivity of the heat absorbing plate is more than 30 times greater than the heat conductivity of the heat insulating plate. With such configuration, the thermal energy of sunlight can be efficiently transferred to the heat transfer medium through a large contact area of the heat absorbing plate, which has high heat conductivity. Meanwhile, the heat insulating plate providing favorable thermal insulation can effectively reduce heat loss of the provided solar thermal collector. In addition, the heat insulating plate of the disclosure is made of composite material that is light in weight, strong in structural strength and low in heat loss rate. Therefore, the thickness of the solar thermal collector profile and the collector frame can be effectively reduced without sacrificing the structural strength and the thermal insulation performance. Furthermore, due to the reduction of the solar thermal collector&#39;s overall thickness, the wind resistance is lowered to improve the applicability and design flexibility when the solar thermal collector is integrated with the building. 
     In addition, different from conventional collectors that can only be installed on rooftops, the solar thermal collector of the disclosure can be framed as building accessory structures that can be applied to building external areas, such as a balcony, window, or patio, to serve as railings, louvers, or patio shade structures. Therefore, the design flexibility can significantly improve the applicability when the solar thermal collector is integrated with the building. 
     In order to make the aforementioned and other features and advantages of the invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of a solar thermal collector according to an embodiment of the invention. 
         FIG. 2  is a schematic cross-sectional view of the solar thermal collector of  FIG. 1  along the line A-A′. 
         FIG. 3  is a schematic view showing a stress distribution of the solar thermal collector of  FIG. 2  applied with internal pressure. 
         FIG. 4  is a schematic partially enlarged view of the solar thermal collector of  FIG. 1 . 
         FIG. 5  is a schematic cross-sectional view of the solar thermal collector of FIG.  4  along the line B-B′. 
         FIG. 6  is a schematic partially enlarged cross-sectional view of a heat absorbing plate according to an embodiment of the invention. 
         FIG. 7  is a schematic view of a building accessory structure according to an embodiment of the invention. 
         FIG. 8A  to  FIG. 8C  are schematic exploded views and assembled view of a light-transmissive sleeve tube and a solar thermal collector according to an embodiment of the invention. 
         FIG. 9  to  FIG. 11  are schematic views showing uses of a building accessory structure according to different embodiments of the invention. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     It is to be understood that the foregoing and other technical contents, features, and advantages are intended to be described more comprehensively by providing embodiments accompanied with figures hereinafter. In the following embodiments, wording used to indicate directions, such as “up,” “down,” “front,” “back,” “left,” and “right,” merely refers to directions in the accompanying figures. Therefore, the directional wording is used to illustrate rather than limit the invention. Moreover, the same or similar reference numerals represent the same or similar elements in the following embodiments. 
       FIG. 1  is a schematic view of a solar thermal collector according to an embodiment of the invention.  FIG. 2  is a schematic cross-sectional view of the solar thermal collector of  FIG. 1  along the line A-A′. With reference to  FIG. 1  and  FIG. 2 , in this embodiment, a solar thermal collector  100  includes at least one heat absorbing plate  110  and at least one heat insulating plate  120 . The heat absorbing plate  110  includes at least one first slab  112  and a plurality of first engaging parts  114  connected with the first slab  112 . The heat insulating plate  120  includes at least one second slab  122  and a plurality of second engaging parts  124  connected with the second slab  122 . The first engaging parts  114  are respectively engaged with the second engaging parts  124 , and a gap G 1  is maintained between the first slab  112  and the second slab  122  to define a heat collecting channel CH, through which a heat transfer medium flows in a longitudinal direction D 1  of the first slab  112 . 
     In this embodiment, a heat conductivity of the heat absorbing plate  110  is substantially 30 times or more greater than a heat conductivity of the heat insulating plate  120 . More specifically, both the heat absorbing plate  110  and the heat insulating plate  120  may be formed integrally. The heat absorbing plate  110  may be formed integrally by stamping or rolling process, for example. A material of the heat absorbing plate  110  may be stainless steel and the heat conductivity of the heat absorbing plate  110  is about 12-30 W/(m° C). A material of the heat insulating plate  120  may be a composite material, such as fiber reinforced plastics (FRP), and the heat conductivity of the heat insulating plate  120  may be about 0.23-0.35 W/(m° C.). The fiber reinforced plastics include thermosetting resin or thermoplastic resin, and glass fiber or carbon fiber, for example. More specifically, the fiber reinforced plastics are composite materials mainly formed by mixing thermosetting resin or thermoplastic resin with glass fiber or carbon fiber, and function as reinforced concrete. Generally speaking, the fiber reinforced plastics have great strength per unit weight. That is, the fiber reinforced plastics have the characteristics of light in weight, high in structural strength, and very low in heat loss rate, so as to achieve favorable thermal insulation. For these reasons, the size and thickness of the heat insulating plate  120  using the said material are reduced significantly, and the structural strength and thermal insulation performance are enhanced. In addition, the fiber reinforced plastics have corrosion resistance for various environments. 
     With such a configuration, the heat absorbing plate  110  and the heat insulating plate  120  of this embodiment together define the heat collecting channel CH, and the thermal energy of sunlight is efficiently transferred to the heat transfer medium in the heat collecting channel CH through the heat absorbing plate  110  with high heat conductivity, while the heat insulating plate  120  having favorable thermal insulation properties prevents loss of the thermal energy. Thus, the solar thermal collector  100  of this embodiment has favorable solar energy collection efficiency and structural strength. What is more, the size and overall thickness thereof are reduced and the wind resistance is lowered to improve the applicability and design flexibility of the solar thermal collector  100  in building integration. 
     In this embodiment, the solar thermal collector  100  includes a plurality of heat absorbing plates  110  and one heat insulating plate  120 , as shown in  FIG. 2 . The first engaging parts  114  are respectively disposed on two opposite ends of each heat absorbing plate  110 , and the heat insulating plate  120  includes a plurality of second slabs  122 , as shown in  FIG. 2 , respectively corresponding to the first slabs  112  of the heat absorbing plate  110 . More specifically, any two adjacent second slabs  122  are connected with each other by the corresponding second engaging parts  124 . The first engaging parts  114  of each heat absorbing plate  110  are respectively engaged with the corresponding second engaging parts  124 , so as to fix the heat absorbing plates  110  side by side onto the heat insulating plate  120  and form a plurality of independent passages. 
     To be more specific, each of the second engaging parts  124  includes an extending groove  124   a  and a hook groove  124   b  that communicate with each other, while each of the first engaging parts  114  includes an extending section  114   a  and a hook section  114   b  connected with each other. Each extending section  114   a  is disposed in the corresponding extending groove  124   a,  and each hook section  114   b  is connected with the corresponding extending section  114   a  and engaged with the corresponding hook groove  124   b,  so as to fix the heat absorbing plates  110  side by side to the heat insulating plate  120 . Furthermore, the extending sections  114   a  of two adjacent heat absorbing plates  110  are disposed in the same extending groove  124   a,  and the hook sections  114   b  connected with the extending sections  114   a  are hooked with the corresponding hook grooves  124   b,  so as to secure two adjacent heat absorbing plates  110  on the heat insulating plate  120 . 
     In one embodiment, the solar thermal collector  100  further includes a filler  140  disposed in the hook groove  124   b  where the hook section  114   b  is engaged. In the present embodiments. A plurality of fillers  140  can be filled in the hook groove  124   b  and disposed between the hook sections  114   b  of any two adjacent heat absorbing plates  110  and the corresponding hook groove  124   b  to further secure the engagement between the two adjacent heat absorbing plates  110  and the heat insulating plate  120 . In this embodiment, the filler  140  includes a curable adhesive, a sealant, or a wedge. Each wedge may be inserted between the hook sections  114   b  of any two adjacent heat absorbing plates  110  and the corresponding hook groove  124   b  to enhance the structural strength of the solar thermal collector  100  and a bonding force between the heat absorbing plates  110  and the heat insulating plate  120 , thereby preventing overflow of the heat transfer medium under a working pressure. 
     It should be noted that this embodiment is merely an example of the invention, and this disclosure is not intended to limit the number of the heat absorbing plates  110  and the number of the heat insulating plates  120  of the solar thermal collector  100 . In other embodiments of the invention, the solar thermal collector may include one heat absorbing plate  110  and one heat insulating plate  120 , or multiple heat absorbing plates  110  and multiple heat insulating plates  120 , as long as the first engaging parts  114  of the heat absorbing plate  110  can be securely engaged with the second engaging parts  124  of the heat insulating plate  120 . 
     Moreover, in this embodiment, the first slab  112  and the second slab  122  are both curved slabs for increasing the strength against the working pressure of the heat transfer medium. Specifically, each first slab  112  and the corresponding second slab  122  are curved in the same direction. In other words, each first slab  112  and the corresponding second slab  122  may be curved slabs that are parallel to each other. Generally speaking, the curved slab withstands higher pressure than a planar slab because any pressure applied to any part of the curved slab can be evenly dispersed. In addition, each first slab  112  and the corresponding second slab  122  of this embodiment are curved in the same direction, which not only enhances the structural strength and pressure resistance of the solar thermal collector  100  but also reduces the overall thickness of the solar thermal collector  100 . Meanwhile, the curve of the first slab  112  also increases a contact area between the first slab  112  and the heat transfer medium to enhance thermal transfer efficiency. The curve of the second slab  122  also improves the structural strength of the solar thermal collector  100  in the longitudinal direction D 1 . 
       FIG. 3  is a schematic view showing a stress distribution of the solar thermal collector of  FIG. 2  applied with internal pressure.  FIG. 3  shows the stress distribution when an internal fluid pressure of 6 kgf/cm 2  is applied in the independent passage defined by the heat absorbing plate  110  and the heat insulating plate  120  of the solar thermal collector  100  of this embodiment. To be more specific, the upper part of  FIG. 3  shows the stress distribution when an internal fluid pressure of 6 kg/cm 2  is applied to a solar thermal collector  100   a  with a heat insulating plate made of a thermoplastic resin (e.g., ABS resin); and the lower part of  FIG. 3  shows the stress distribution when an internal fluid pressure of 6 kgf/cm 2  is applied to a solar thermal collector  100   b  with a heat insulating plate made of a composite material (e.g. FRP). It is proven by experiment that the solar thermal collector  100  of this embodiment withstands an internal fluid pressure of at least 6 kgf/cm 2 , and under this pressure, displacement of the first slab  112  and the second slab  122  is minimal. 
     More specifically, the maximum displacement of the first slab  112  and the second slab  122  of the solar thermal collector  100   a  under the internal fluid pressure of 6 kgf/cm 2  is approximately between 0.28 mm and 2.59 mm, and the maximum stress the first slab  112  bears is about 2122 MPa, which is far less than the stress that causes permanent deformation of stainless steel. Similarly, the maximum displacement of the first slab  112  and the second slab  122  of the solar thermal collector  100   b  under the aforementioned pressure is approximately between 0.1 mm and 1.42 mm, and the maximum stress the first slab  112  bears is about 1494 MPa, which is also far less than the stress that causes permanent deformation of stainless steel. In addition, Young&#39;s modulus of the solar thermal collectors  100   a  and  100   b  of this embodiment are both greater than 20 GPa, which shows that the solar thermal collectors  100   a  and  100   b  have favorable structural strength in the longitudinal direction D 1 . Therefore, the solar thermal collector  100  of this embodiment has excellent structural strength and pressure resistance. 
       FIG. 4  is a schematic partially enlarged view of the solar thermal collector of  FIG. 1 .  FIG. 5  is a schematic cross-sectional view of the solar thermal collector of  FIG. 4  along the line B-B′. With reference to  FIG. 4  and  FIG. 5 , in this embodiment, the solar thermal collector  100  further includes a connecting pipe  130  that is connected to and covers a side of the heat absorbing plate  110  and the heat insulating plate  120 . Specifically, the connecting pipe  130  includes a plurality of openings  132  connected to the edges of the heat collecting channel CH to allow the heat transfer medium to flow in and out of the heat collecting channels CH through the connecting pipe. The solar thermal collector  100  of this embodiment is applicable to a solar water heater, for example, for converting solar radiation energy absorbed by the solar thermal collector  100  to thermal energy for heating water. The connecting pipe  130  includes an inlet  134  and an outlet  136 . The heat transfer medium flows into the heat collecting channel CH through the inlet  134  of the connecting pipe  130 , as indicated by the arrow in  FIG. 4 , and then flows out of the heat collecting channel CH after absorbing thermal energy and flows out of the solar thermal collector  100  through the outlet  136  of the connecting pipe  130 . 
     It should be noted that the configuration of the connecting pipe  130  is not limited to the above. The connecting pipe  130  may be disposed on two opposite sides of the heat absorbing plate  110  and the heat insulating plate  120 , for example, to respectively communicate with two opposite ends of the heat collecting channel CH. The heat transfer medium may flow into the connecting pipe  130  at one end of the heat collecting channel CH and flow out of the solar thermal collector  100  from the connecting pipe  130  at the other end of the heat collecting channel CH after absorbing thermal energy. This disclosure is not intended to limit the number and configuration of the connecting pipe  130  of the invention. 
       FIG. 6  is a schematic partially enlarged cross-sectional view of the heat absorbing plate according to an embodiment of the invention. With reference to  FIG. 6 , in this embodiment, the solar thermal collector  100  further includes a solar selective absorption coating  150  disposed to cover a solar-receiving surface S of the heat absorbing plate  110 . The solar selective absorption coating  150  includes a damping layer  152 , an absorption layer  154 , and an anti-reflective layer  156  disposed sequentially to cover the solar-receiving surface S. That is to say, the damping layer  152  covers the solar-receiving surface S, the absorption layer  154  covers the damping layer  152 , and the anti-reflective layer  156  covers the absorption layer  154 . The damping layer  152  is formed on the solar-receiving surface S by sputtering, for example. A material of the damping layer  152  includes metal nitride, metal carbide, or metal carbon nitride. More specifically, the material of the damping layer  152  is selected from one or any combination of ZrN, TiN, TiAlN, CrN, TiC, CrC, TiCN, TiAlCN, ZrCN, and CrCN, for example. 
     In addition, the absorption layer  154  may also be formed on the damping layer  154  by sputtering. A material of the absorption layer  154  includes metal oxide and metal nitride, metal carbide, or metal carbon nitride. In other words, the material of the absorption layer  154  may be obtained by mixing the material of the damping layer  152  with metal oxide. The anti-reflective layer  156  may be formed on the absorption layer  154  by deposition. A material of the anti-reflective layer  156  includes silicon oxide or silicon nitride. However, it should be noted that the aforementioned materials of the damping layer  152 , the absorption layer  154 , and the anti-reflective layer  156  are merely examples and should not be construed as a limitation to the invention. By depositing the solar selective absorption coating  150  on the solar-receiving surface S, sunlight enters the absorption layer  154  and the damping layer  152  through the anti-reflective layer  156  and radiation energy of the sunlight is converted into thermal energy by the absorption layer  154 . The thermal energy is then transferred to the heat transfer medium through the heat absorbing plate  110 . 
       FIG. 7  is a schematic view of a building accessory structure according to an embodiment of the invention. With reference to  FIG. 1  and  FIG. 7 , in this embodiment, a building accessory structure  10  is applicable to an external area of a building. The building accessory structure  10  includes at least one frame  200  and a plurality of solar thermal collectors  100  shown in  FIG. 1  to  FIG. 6 . The frame  200  is configured to hold the solar thermal collectors  100 , which are disposed in parallel to each other in the frame  200 . The frame  200  includes at least one light-transmissive front cover  210 , which is placed on the front side facing the heat absorbing plates  110  of the solar thermal collector  100  shown in  FIG. 1 . The frame  200  also includes at least one light-transmissive back cover  220 , which is placed on the back side facing the heat insulating plates  120  of the solar thermal collector  100  shown in  FIG. 1 . It should be noted that this embodiment is given as an example of the invention. This disclosure is not intended to limit the number or the dimensions of the solar thermal collector  100  can be implemented in frame  200 . 
       FIG. 8A  to  FIG. 8C  are schematic exploded views and assembled view of a light-transmissive sleeve tube and a solar thermal collector according to an embodiment of the invention. With reference to  FIG. 8A  to  FIG. 8C , in this embodiment, the frame  200  includes at least one light-transmissive sleeve tube  230  to hold the solar thermal collector  100  shown in  FIG. 1  to  FIG. 6 , and the light-transmissive sleeve tube  230  is made in one piece. The light-transmissive sleeve tube  230  defines a receiving space. The solar thermal collector  100  is assembled and disposed in the receiving space. In the present embodiment, the light-transmissive sleeve tube  230  is made of non-glass materials. To be more specific, the light-transmissive sleeve tube  230  is made of plastic materials. The reinforcing fins  235  are disposed between the heat insulating plate  120  and the light-transmissive sleeve tube  230  for supporting the structure. In this embodiment, a longitudinal length L 1  of the solar thermal collector  100  is about 245 cm, a transverse width W 1  is about 20 cm, and a height H 1  is about 4.5 cm. Moreover, a transverse width of the assembly of the heat absorbing plate  110  and the heat insulating plate  120  is about 18 cm. It should be noted that this embodiment is given as an example of the invention. This disclosure is not intended to limit the dimensions of the solar thermal collector  100 . 
       FIG. 9  to  FIG. 11  are schematic views showing uses of a building accessory structure according to different embodiments of the invention. With reference to  FIG. 9 , the aforementioned solar thermal collector  100  may be modularized as a building accessory structure to be disposed on an external area of the building for absorbing solar radiation energy and converting the solar radiation energy into thermal energy for heating water or providing heating for the building. For example, a building accessory structure  10  includes the above mentioned frame  200  and a plurality of the above mentioned solar thermal collectors  100 , as shown in  FIG. 9 . The frame  200  is configured to surround and define the receiving space, and the solar thermal collectors  100  are disposed in the receiving space of the fame  200 . More specifically, the solar thermal collectors  100  may be disposed in parallel to each other in the frame  200 , for example, to form a discontinuous wall for increasing the solar absorbing area of the building accessory structure  10 . The building accessory structure  10  may be disposed on the external area of the building that is easily exposed to sunlight, such that the building accessory structure  10  not only serves as a shading structure but also absorbs the solar radiation energy to be converted into thermal energy for heating water or providing heating for the building. 
     With reference to  FIG. 9 , in this embodiment, the external area for disposing the building accessory structure  10  may be a balcony, a patio or a terrace of the building and the building accessory structure  10  may be a railing or barrier to be applied to the balcony, patio or terrace. To be more specific, the building accessory structure  10  may be disposed on an outer edge of the balcony, patio or terrace to serve as fences. Further, with reference to  FIG. 10  and  FIG. 11 , in these embodiments, the external area for disposing the building accessory structure  10  may be a rooftop, a window, a patio, or a terrace of the building or an open space adjacent to the building (e.g., front yard, backyard, or arcade of the building). The building accessory structure  10  may be disposed on the aforementioned external area to serve as a shading structure or a covering structure of the building. For example, the building accessory structure  10  may serve as blinds for keeping out sunlight when disposed on the window of the building. Moreover, the building accessory structure  10  may serve as sunshades when disposed at the balcony, patio, front yard, or backyard of the building. Thus, the building accessory structure  10 , used as the external shading structure, reduces the heat of solar radiation and sunlight that enter the building through the walls, or provides shading for the open space adjacent to the building. What is more, the building accessory structure  10  absorbs the solar energy received by the building and the surroundings for cooling the building. In comparison with the conventional external shading structure, the building accessory structure  10  of the invention achieves more favorable cooling effects for the building. Furthermore, the building accessory structure  10  converts the heat of solar radiation into thermal energy for heating water for daily use or providing heating for the building. 
     To sum up, the heat absorbing plate and the heat insulating plate of the solar thermal collector of the invention are engaged with each other and have the gap in between to define the heat collecting channel allowing the heat transfer medium to flow through. In addition, the heat conductivity of the heat absorbing plate is substantially 30 times or more greater than the heat conductivity of the heat insulating plate. Thus, the thermal energy of sunlight is efficiently transferred to the heat transfer medium in the heat collecting channel through the heat absorbing plate with high heat conductivity while the heat insulating plate providing favorable thermal insulation effectively prevents loss of the thermal energy. Moreover, the solar thermal collector of the invention is light in weight, strong in structural strength and low in heat loss, and therefore the size and thickness of the heat insulating plate and the casing are effectively reduced without sacrificing the structural strength and the triennial insulation performance. Hence, the solar thermal collector of the invention not only achieves favorable efficiency in collection of solar energy but also has smaller size and overall thickness. Consequently, the wind resistance of the solar thermal collector is reduced. 
     Furthermore, the solar thermal collector of the disclosure may be modularized as the building accessory structure. That is, a plurality of solar thermal collectors are disposed in the frame to modularize the solar thermal collectors and increase the efficiency of collection of solar energy. The building accessory structure of the disclosure may be disposed on the external area of the building, for example, for absorbing the solar energy received by the building and converting the solar energy into thermal energy for use of the building. Thus, the invention increases the applicability and design flexibility of the solar thermal collector in building integration. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the invention covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.