FIELD OF THE INVENTION

This invention relates to a building cladding element, especially a building cladding element with built in passive solar efficiency, and has been devised particularly, though not solely, for use as a house brick designed to maximise solar heat absorption during winter months and minimise solar hear absorption during summer months.

BACKGROUND OF THE INVENTION It has been recognised that a large portion of household energy use is utilised for space heating and cooling. For example, in the region of Sydney, Australia, which is generally regarded as a mild climate, almost 40% of household energy is used on space cooling and heating.

It is therefore apparent that there is the need to capture the maximum amount of heating from the sun over winter months in order to reduce the amount of household energy currently consumed in heating over the winter period. It is also desirable that the solar heat so captured, should not significantly impact on the solar load on a domestic dwelling during the summer months so as to require significantly increased energy use for space cooling.

SUMMARY OF THE INVENTION

The present invention therefore provides a cladding element for an external wall of a building, said element having an exterior surface provided with a series of parallel ribs extending horizontally in use, each rib having an upper face orientated in use at an angle to the horizontal selected to provide enhanced solar heat absorption through the upper face.

Preferably, each rib has two faces, being said upper face and a lower face. Preferably, the two faces together form an elongate triangular section rib on the exterior surface of the cladding element.

Preferably, each rib adjoins the neighbouring ribs such that the upper and lower faces of all the ribs form, in section, a saw-tooth pattern on the exterior face of the cladding element.

Preferably, the included angle between the upper and lower faces of each rib is approximately 90°.

Preferably, the upper faces of the ribs are orientated at an angle to the horizontal selected to receive an optimum amount of solar irradiation during the winter period. hi one form of the invention the cladding element comprises a house brick, with the ribs formed in the external face of the brick.

Preferably, the brick is formed by an extrusion process whereby the brick is extruded in the direction of the length of the brick, allowing the ribs to be formed by the shape of an extrusion die as the brick is extruded. Preferably, the texture of the upper faces of the ribs is selected to reflect heat upwardly onto the lower faces of the adjacent ribs during the winter months.

Preferably, the texture of the lower faces of the ribs is selected to absorb solar radiation reflected from the upper faces of adjacent ribs.

Preferably, the angles of inclination of the upper and lower faces, and the included angle between them are selected to give maximum solar irradiation onto the upper face during mid- winter while providing maximum shading of the upper face of the rib immediately below during mid-summer.

It will be recognised that the angles of inclination of the upper and lower faces will be designed differently for cladding used in different regions at different latitudes.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms that may fall within its scope, one preferred form of the invention will now be described by way of example only with reference to the accompanying drawings in which:

Fig. 1 is an isometric view of a house brick designed for use as a cladding element according to the invention;

Fig. 2 is a partial view to an enlarged scale of two adjacent ribs on the face of the brick shown in Fig. 1, showing angles of solar irradiation during mid-summer and mid- winter months;

Fig. 3 is a diagram showing the relationship between the angles and widths of the various faces of the ribs used in the brick shown in Fig. 1; and

Fig. 4 is a graph showing the amount of heat transmitted through a brick plotted against the angle of incidence of the heat source to the face of the brick for normal (flat faced) bricks and bricks with ribs orientated at three different angles.

DESCRIPTION OF PREFERRED EMBODIMENT One preferred form of the invention will now be described with reference to a cladding element in the form of a household brick, but it will be appreciated that the invention can be applied to any other form of building cladding where the exterior face of the cladding can be configured into ribs of similar configuration to those described below. It is a well established technique often used by architects and building engineers in the design of buildings to utilise solar charts which are applicable to the particular latitude of a proposed building, to calculate the angle of elevation of the sun at various times of the day during both summer and winter months. For example, using such charts for a latitude of 32.5°south one is able to ascertain that the midday elevation of the summer sun varies between 52° and 81° to the horizontal whereas the midday elevation of the winter sun varies between 34° and 48°. Using the knowledge that the winter sun is at an angle of 48° elevation at midday and the summer sun at 81° elevation, it is possible to design shade elements and other building elements to give maximum solar heat input to a building during the winter months while minimising the summer heat load on the building.

The present invention makes use of this knowledge to configure the external face of a cladding element, in this instance a household brick, to maximise solar heat absorption during the winter months, while minimising heat absorption during the summer months. To this end, a household brick is designed with a profile shown in Fig. 1 with a normally flat top surface 1, back surface 2 and bottom surface 3, designed to be separated and adhered to adjacent layers of bricks by a mortar bed 4. The brick may be of any desired shape and general configuration, but typically has a length of 230mm and a height of 75mm as shown in Fig. 1. The front face 5 of the brick according to the invention is provided with a series of parallel ribs 6, extending horizontally in use along the front face 5 of the brick. Each rib has an upper face 7 and a lower face 8 which together form a triangular section rib on

- A - the exterior surface 5 of the brick. Each rib adjoins the neighbouring ribs such that the upper and lower faces of all the ribs form, in section, a saw-tooth pattern on the exterior face of the brick as can be clearly seen in Fig. 1.

A brick designed according to this shape is economical to manufacture by the extrusion process, which is commonly used in the manufacture of household bricks. Rather than extruding the bricks in the direction of the height of each brick as is common with bricks known in the prior art, a brick according to the invention is extruded in the direction of the length of the brick as indicated by arrow 9 so that the ribs 6 can be simply extruded on the front face of the brick by controlling the shape of the extrusion die to give the desired cross-sectional shape of the brick. It will also be appreciated that a brick of this shape could be made by other processes such as pressing or moulding from various materials including clay, concrete, or calcium silicate.

The angle of the upper face 7 of each rib to the horizontal as indicated by angle α at 10 in Fig. 1 is determined by the latitude at which the brick is to be used. For example, following the data given above for a building located at latitude 32.5°south, it has been found that the optimum angle of inclination of the upper faces 7 of the ribs is approximately 50°. Referring to Fig. 2 where the angle 10 is shown as 50°, and where the lower faces of each rib are orientated at right- angles to the upper face of the same rib, it can be seen that the midday winter sun angle of 48° as represented by broken line 11 results in substantially the full upper face 7 of each rib being exposed to the heat of the solar irradiation.

By way of contrast, the midday summer sun at an overhead angle of 81 ° as represented by solid line 12 results in a substantial portion of the upper face 7 being in shadow as shown by area 13 in Fig. 2. Referring to Fig. 3 there is represented the geometrical size of the ribs for a typical household brick of the type shown in Fig. 1 where the spacing between each rib is 21mm as represented by side 14, the angle of inclination of the upper face of each rib is 50°, the width of the lower face of each rib is 13.4mm as represented at 15 and the width of each upper face of each rib is 16.2mm as represented at 16. This geometry, results in the width of the upper face of each rib which is exposed to the sun during summer at midday as low as 4.4mm compared with 29.6mm at midday in the winter.

In this manner it is possible to provide a brick with an external surface which has an enhanced solar radiation absorption capability in winter by increasing the area exposed to the sun, and orientating that area at right angles to the solar load, while reducing the solar heat absorption in summer due to the shading effect of adjacent ribs when the sun is more directly overhead i.e. at a midday angle of 81 °.

This effect can be further enhanced by providing the upper surface of the ribs with a glazed finish designed to reflect heat upwardly onto the lower face of the adjacent rib during winter. This effect is not apparent during summer as the angle of incidence of the solar load on the glazed surface tends to reflect the heat downwardly and out into the atmosphere rather than upwardly onto the adjacent surface of the rib immediately above. The effect could be further enhanced by selecting the texture of the lower face of each rib to absorb solar radiation reflected from the upper face of the adjacent rib in the manner described above.

In laboratory trials, the effect of the rib profiling on the outer face of the brick is most apparent and the optimisation of the angle of inclination of the upper face of each rib at 50° (for use of a latitude at 32.5°south) also apparent.

Fig. 4 shows the heat flow through a typical brick in watts per square metre as the vertical axis and the angle of irradiation by a heat source (in this case a heat lamp) shown on the horizontal axis. The four lines graphed represent three bricks formed with ribs on the exterior face with the upper faces at angles of inclination of 50°, 60° and 70°, together with a brick with a normal flat face for comparison. It can be clearly seen that the transmission of heat through bricks of all four designs is very similar over the summer months represented by an angle of incidence of the solar load between 60° and 80°, with the brick with a rib angle of 50° having a slightly superior performance (reduced heat transfer) during those months.

By comparison, over the winter months when the angle of solar irradiation is at 50° or less, the configurations with the ribbed faces demonstrate significantly higher heat absorption characteristics, with the example with the ribs angled at 50° being significantly superior once the angle of irradiation falls below 40°. This clearly demonstrates the effectiveness of a cladding element formed in accordance with the

present invention, and can be described as having a built in passive solar efficiency due to the configuration of the ribs.

It is felt that although cladding elements of the type described above would have benefit on all faces of a building which are subjected to solar irradiation, the maximum benefit would be felt on walls which face north or close to north in the building orientation.