GB2152651A - Wall module - Google Patents

Abstract

A wall module comprises an inner panel 1 having an electrically conductive, spectrally selective solar energy absorbing surface 1a and an outer panel 2 of translucent or transparent material. Between the absorbing surface 1a and the outer panel 2 are a series of transparent screens 4, 5, 6, 7, one or more of which may be provided with a spectrally selective reflecting surface. One of the screens may be of a thermochromic material, or a mechanical blind may be included to provide adjustment of the solar energy absorbed by the module. The electrically conductive absorbing surface may be employed as a heating element in the absence of sunlight. The thermal resistance of the absorber and screen array in the absence of sunlight is equivalent to conventional thermally insulated walls. <IMAGE>

Description

SPECIFICATION Wall module The present invention relates to a module for use in forming an outside wall of a building.

Walls in modern buildings are often made of a double skin of facing bricks and breeze blocks. Not only are such walls expensive to construct, but they result in expensive running costs because heat is lost through them, especially on winter days when the difference between inside and outside temperatures is high.

The present invention provides a module for use in constructing an outside wall that radically reduces the heat lost through the building wall during daylight hours and at night has insulating properties comparable to standard walls.

According to the present invention, there is provided a module for use in forming a wall of a building, which module comprises an inner panel having an outwardly-facing selectively absorbing metallic surface, an outer panel that is translucent tolight in the visible spectrum and one or more films that are transulcent to light in the visible spectrum and that lie substantially parallel to, and are located between, the inner and outer panels to form a series of sealed compartments.

The module of the present invention is not solely intended as a device for heating buildings, but also to prevent heat from the building being lost to the atmosphere particularly in winter. The module will in appropriate circumstances provide a net flow of heat into the building, but that is not its only object.

The module operates by providing a selectively absorbing surface that is maintained at approximately room temperature by incident light and thus the energy that is inevitably lost to the atmosphere due to the maintenance of a temperature differential between the inside and the outside of the building comes from solar heating rather than from the expensive heating system of the building. Furthermore, the selectively absorbing material, being metallic can be employed as a heating element, and so act as the heating system of a building, on those occasions when solar energy is inadequate, by passing an electrical current through the metallic material. Heat losses from the selectively absorbing surface are cut down as far as possible by the arrangement of sealed compartments of the module which reduce convection and radiation losses as will be discussed later.

A selectively absorbing surface is a surface that has a high absorptivity in the visible spectrum (absorptivity is a measure of the amount of radiation of a given wavelength that is absorbed by a body as compared with the amount absorbed by a perfect black body) and a low emissive power in the infra-red spectrum (emissive power is a measure of the amount of radiation emitted by a body as compared to the amount of radiation emitted by a perfect black body under identical conditions.) The surface should be chosen on the basis of a high ratio of absorptivity to emissive power which means that the module will operate to reduce outflow of heat from the building even at low light intensities i.e. early in the morning and towards sunset.It is preferred that the selectivity absorbing surface is made of a substance known as "Maxorb" (Maxorb is a trademark), which is a thin foil with a black surface having an absorptivity in the visible spectrum (i.e. up to about 3 ym) of 0.95 and emissive power of 0.08 at 100"C.

Although "Maxorb" is preferred because of the high absorptivity and low emissive power, other materials may alternatively be used. By using a module with a low infra-red heat emission, radiation losses are kept to a minimum.

The foils located between the inner and outer panels of the module are important to reduce convection and radiation losses. They may be made of any material that is translucent and preferably transparent to light in the visible spectrum e.g. acrylic polymers. The foils together with the edges of the module form sealed compartments in which the convection of gas is kept to a minimum. In this respect the spacing between the foils is important since the heat flow as a result of convection in a sealed compartment with a given temperature difference between two vertical sides thereof decreases as the separation between the two vertical sides decreases and there comes a point at a finite separation where convection is more or less eliminated.

This critical separation is dependent on the temperature differential across the cell and the greater the differential, the smaller is the ctritical separation. can be discovered by experiment. The number of foils that are incorporated into the cell should be chosen according to the difference that it is desired to maintain between the temperature inside the building and the external temperature.

Another factor must also be taken into account when considering the separation between adjacent foils and that is heat conduction by the gas in each compartment. The separation between adjacent foils should be set at just less than the critical separation that, for the estimated temperature difference across a compartment, gives rise to minimum convection. The number of sealed compartments will generally be less than 9 for cost reasons and it is believed that 5 or 6 compartments will generally be satisfactory under most conditions.

Heat losses by way of conduction can be greatly decreased by insulating the edge of each module or group of modules with an insulating material.

The radiation losses from the inner panel can be decreased by providing the inwardlyfacing surface of one or more of the foils or the outer screen with a layer that selectively refiects light in the infra-red spectrum but allows visible light to pass therethrough.

Thus, infra-red thermal radiation emitted by the inner panel and foils of the module is reflected back to the panel where it is reabsorbed. Foils with thin metal coatings are suitable and well-known. Although these foils transmit most of the visible light incident upon them, the amount of light transmitted is inevitably less than that transmitted by an uncoated foil and therefore it is preferred to limit the number of coated foils in a module.

Furthermore, the positioning of these foil coated screens in relationship to the other screens is dependent upon the radiative properties of the screen materials. Ideally, the screens nearest to the absorber should be transparent to thermal-infra-red radiation and therefore demonstrates very low emittance.

Such materials are typified by polyethylene films. The screens with a reflective coating which may well exhibit greater emittance of the outwardly facing surface should be employed farthest from the absorber, and thus at the lowest temperatures.

The outer panel may be made by any rigid, translucent material, e.g. glass or a polycarbonate plastics material and serves mainly to provide strength to the outside of the module.

Obviously, it is preferred that the transmission of the outside panel is as high as possible.

In order to even out the temperature of the inner panel due to differing intensities of incident light, the module of the present invention may include a heat sink in thermal contact with the inner panel to absorb and store heat generated by the selectively absorbing surface. The heat sink may be any body with a high heat capacity e.g. a block of concrete or a tank of water.

At night when there is no light incident on the selectively absorbing surface, the insulating properties of the module and the low emissive power of the back panel means that the module provides excellent insulation in comparison to the breeze blocks and facing brick construction described above.

The module is primarily designed to operate to reduce the heat losses of a building during winter. It will be appreciated that on hot summer days, the selectively absorbing surface will generate temperatures above room temperature and thus would heat an already over-heat room. This problem can be overcome by providing a screen or lattice blind arrangement which can be adjusted to shade the selectively absorbing surface. The use of a thermochromic polymer film as one of the foil screens of the module would be particularly suitable. In such a case, the varying appearance of the screen with varying temperature may be employed for aesthetic or advertising purposes. The module is capable of providing excess energy during most of the year in all orientations as indicated in Fig. 2 which compares the computed annual energy contribution of the module with that of a standard wall.The ammount of shading of the module will depend upon the use which the user requires to make of this available energy. In the particular configuration used to develop this data upon which Fig. 2 is based, the module employed a five screen array, with two inner screens of polyethylene, two subsequent acrylic screens with an Indium Oxide spectrally selective reflecting surface, and a glass outer screen, with a 25mm gap between each screen.

One form of the module of the present invention will now be described, by way of example only, with reference to the accompanying drawing in which: Figure 1 is a partly cut-away perspective view of the module.

The module shown in Fig. 1 has an inner panel 1 designed to back onto a room wall on the inside of a building and an outer panel 2 that is intended to form the outside of the building. Panel 1 is composed of a sheet of "Maxorb" and has an outwardly facing selectively absorbing surface 1a. Although "Maxorb" is preferred. other selectively absorbing material may be used instead. The outer panel 2 is made from clear glass or a sheet of some other transparent rigid material e.g. polycarbonate plastic.

The inner panel 1 lies against, and is in thermal contact with, a block of concrete 3 so that heat generated by light incident on the selectively absorbing surface 1 a is absorbed by block 3.

Located between panels 1 and 3 are four equally spaced films, 4, 5, 6 and 7 that divide the interior of the module into five separate compartments 8 to 1 2. The films are made of a thin, highly transparent material e.g. acrylic plastics. Two of the films have an inwardly facing metallic coating, the thickness of which is such that it selectively reflects infra-red radiation but allows visible light to be transmitted. Thus, infra-red radiation emitted by surface 1 a hits the metallic coating and is reflected back to the surface 1 a.

The edge of each film 4 to 8 is firmly secured to a rigid border frame 1 3 to 1 7. The border frames are of such a size that they fit snugly inside a sleeve 1 8 (only two sides of which are shown in Fig. 1). As shown, the border frames 1 3 to 1 7 nest inside the sleeve 1 8 and the depth of each frame is the same as the desired separation between adjacent films in the modules, the depth of the frame being the dimension perpendicular to the plane of the films. Thus the frames not only support the films, they also act as spacers. An additional frame 1 8 is located between film 7 and panel 1 to space them apart. Although the films as shown are stretched and wrinklefreee, this need not always be the case.

The module is fitted with a screen or lattice blind (not shown) that can be adjusted to shade or reflect at least part of the selectively absorbing surface 1 a from the sun's rays to prevent the surface 1 a from heating up the inside of the building.

When the module is installed as part of a non-load-bearing wall of a building, light incident on it passes through the outer panel 2 and foils 4 to 7 and is absorbed on the selectively absorbing surface 1 a of panel 1.

This causes the temperature of panel 1 and the concrete block 3 to rise, preferably to approximately room temperature. When the temperature of panel 1 and block 3 is approximately the same as that prevailing inside the building, no heat is lost from inside the building because there is no temperature difference between the room and the wall of the room.

Heat will, however, be lost from the panel 1 but, under optimum conditions, this heat loss is matched by the heat obtained by absorption of light and the heat lost will be generated by solar power not only by the heating system of the building. The heat loss of panel 1 is kept to a minimum by the arrangement of the module. Radiative loss is minimised by the use of the "Maxorb" panel 1, which has low emissive power and by the infra-red selectively reflecting metal coating of the foils discussed above. Convection losses are kept to a minimum by the judicious spacing of the films discussed above.

Conduction losses will inevitably occur both through the edges of the module and through panel 2. However, the loss through the edges can be kept to a minimum by sheets of insulating material around each edge (not shown). Groups of modules will require insulation only at the group periphery.

In the prolonged absence of sunlight, the module cannot prevent the net flow of heat trom the inside of a building to the atmos phere. However, these losses are not large because of the excellent insulative properties of the module due to the arrangement of sealed compartments etc., discussed above.

The module is as good an insulator at night time as the standard materials now used to construct walls. By arranging for an electric current to flow through the metallic material of the absorber, the internal temperature of the building can be maintained and controlled in the absence of sunlight. The thermal losses of such an arrangement are not as great as the thermal resistance of the screen arrangement lies between the absorber and the atmosphere. The module thus also performs the function of an inexpensive heating system.

Claims (3)

1. A wall, or roof, construction comprising a spectrally selective solar energy absorbing surface which is separated from the external air by a series of transparent or translucent membranes or glazed areas one or more of which are spectrally reflective the number and spacing of which is designed to optimise or adjust the resistance of the construction to heat flow, wherein the absorbing surface is electrically conductive and may be employed as a heating element.

2. A construction as described in claim 1 in which one or more of the translucent or transparent membranes or glazed areas consists of the thermochromic or photochromic material, or mechanical device, such that the resistance of the construction to the passage of solar energy to the absorbing surface can be automatically or manually adjusted.

3. A construction as described in any preceeding claim in which one or more of the translucent or transparent membranes or glazed areas consists of a thermochromic or photochromic material, or mechanical device, such that the resistance of the construction to the passage of solar energy to the absorbing surface can be automatically or manually adjusted.

3. A construction as described in any preceeding claim in which the absorbing surface is mounted upon a material designed to provide thermal capacity or mechanical strength.

4. A construction as described in any preceeding claim wherein the construction is designed as a discrete module which may be subsequently assembled to form a structure or structural feature.

5. A solar wall module substantially as described herein with reference to the accompanying drawing.

Amendments to the claims have been filed, and have the following effect Claims 1 and 3 above have been deleyted or textually amended New or textually amended claims have been filed as follows CLAIMS

1. A wall, or roof, construction comprising a spectrally selective solar energy absorbing surface which is separated from the external air by a series of transparent or translucent membranes or glazed areas one or more of which have a spectrally selective reflective surface the number and spacing of which is designed to optimise or adjust the resistance of the construction to heat flow from the building of which the construction is part, which resistance can be reduced to less than 0.6 Watts/m2/ C by the use of an outer glazing and two or three translucent plastic screens largely transparent in the thermal infra-red spectrum and one or two screeens each with a surface having a reflectivity of 80% or more in the thermal infra-red spectrum used as the outer screens or near outer screens of the construction dependent upon whether a reflective surface is employed on the inner surface of the outer glazing. Which resistance is equivalent to that required of conventional cavity insulated wall constructions. The screens being spaced approximately 25 mm apart or greater.

2. A construction as described in Claim 1 in which the spectrally selective absorbing surface is electrically conductive and may be employed as the heating element of a heating system, and in which heat arising at the absorbing surface by means of solar energy or electrical energy may be transferred to the interior of the building or other suitable area.