With light is meant here not only light visible for the eye but electromagnetic light in general, comprising ultraviolet light and infrared light.

Sun panels exist in a plurality of different embodiments. Mostly, the sun panel comprises a box-like construction with an external glass plate, which transmits solar radiation. A liquid medium is circulated in a conduit system in a substantially closed space under the glass plate. Thereby, the medium is heated by the in- cident solar radiation. The heated medium may be used to heat the air in buildings or for producing hot tap water. By using a liquid medium, the risk for leakage always exists. Furthermore, in order to transport the medium, an arrangement of a conduit system and of a pump arranged to circulate the medium in the conduit system, is required. The most sun panels with all in- cluded components are relatively expensive to procure and in- stall.

Usually, the sun panels are placed on the roof of a building.

They have often a construction and a shape, which differ mark- edly from the building. Therefore, the sun panels are unneces- sary conspicuous.

SUMMARY OF THE INVENTION The object of the present invention is to provide heating and cooling by a light absorber, which is inexpensive to procure and to install at the same time as it may be operated without a sup- ply of electric energy. Another object is to give the light ab- sorber such a construction that it harmonises with the sur- rounding environment.

This object is achieved by the light absorber of the initially men- tioned kind, which is characterised in that it comprises an inter- nal material layer provided at a distance from the external mate- rial layer, which internal material layer comprises a material having radiation absorbing properties and constitutes at least one delimiting surface of said space, and means arranged to allow a natural circulation of a gaseous first medium through said space. In connection with incident solar radiation, such a radiation absorbing internal material layer may obtain a high temperature. The gaseous first medium, which advantageously is air, obtains an increased temperature when it comes in con- tact with the internal material layer in the space. Advanta- geously, the heated air is supplied to a room or a place, which have a heating requirement. The air obtains here a direct heat- ing and a conduit system with a heat-transporting liquid medium may be excluded. Thereby, the risk for a liquid leakage is also eliminated. Since the light absorber comprises means for natural circulation of the gaseous medium, any feeder of the medium such as a blowing fan or pump is thus not needed. Thereby, the operating costs of the light absorber are non-existent. Since no conduit needs to be arranged in the space, the light absorber may be produced fairly thin. Consequently, it can in more easy way be suited to the surrounding environment. The surface of the light absorber may be provided with a decorative appear- ance and/or a structure for reminding about a traditional front- age.

According to a preferred embodiment of the present invention, said means comprises an element which is arranged to divide the space into at least a first subspace comprising a first open- ing and a second subspace comprising a second opening such that a passage of the gaseous medium, between said first and second subspaces, only will occur at a lower level in the space than the levels of both the first and second openings. The pres- ent gaseous medium in the space is heated, by the incident so- lar radiation through the first material layer, to a higher tem- perature than the air provided in the room or the like and which is intended to be heated. Inevitably, the incident solar radiation provides not an exactly equally high air temperature in the first and the second subspaces. The heated air in the respective first and second subspaces obtains by this heating a lower density and the air in the respective subspace endeavour to raise up- wardly. In the subspace, having the higher air temperature, an upward airflow is obtained. This heated air is guided out through the opening arranged in the subspace. Hereby, a negative pres- sure is obtained in the lower portion of the space and air is sucked from the subspace with the somewhat lower air tem- perature over to the subspace with the somewhat higher tem- perature. Hereby, the air with a lower temperature is sucked in through the opening in the subspace with the somewhat lower air temperature. This difference between the subspaces in air temperature increases in its turn the natural draught. Advanta- geously, the first and second openings are arranged at a sub- stantially highest level in the respective first and second sub- spaces. Thereby, the air having the highest temperature in the subspace, which has the highest air temperature, may be guided out through the opening in order to be used for heating pur- poses. By such a placing of the openings, the air having the highest temperature is prevented from being immobile in the highest located portion of the respective subspaces. The here described natural circulation thus starts automatically when the air in the space is heated by the incident solar radiation and it stops automatically when no solar radiation is supplied.

According to another preferred embodiment of the present in- vention, said external and internal material layers are provided substantially in parallel. Thereby, the light absorber may be fairly thin. According to a first embodiment, said space is delim- ited by a surface of the internal material layer, which is turned to the first material layer. The circulating gaseous medium is here circulated in a space between the external material layer and the internal material layer. The light absorber may here be very thin. According to a second embodiment, said space is delimited by a surface of the internal material layer, which is turned away from the first material layer. The circulating gaseous medium is here circulated in a space, which is located behind the inner material layer. The second space, which here is formed between the external material layer and the internal material layer, com- prises advantageously air or a vacuum. Such a second space constitutes an insulation between the cooled external material layer and the warm internal material layer at operation of the light absorber. Another advantage with this embodiment, it is that the circulating gaseous medium is not in contact with the external material layer. Such a contact results generally in a fouling of the transparent inner surface of the external material layer. Such a fouling prevents the sunbeams from passing through the external material layer and thereby also the capacity of the light absorber. Thus, the inner surface of the external material layer here needs to be cleaned only in exceptional cases.

According to another preferred embodiment of the present in- vention, the light absorber comprises members to allow adjust- ment of the gaseous medium flow through at least one of said first and second openings. In order to allow adjustment of the air flow through said space in the light absorber, it is suitable that a member, for example, in form of an air valve is arranged in a channel or the like which leads to one of said openings.

Thereby, the supply of hot air may be adjusted or entirely

stopped when no heating requirement exists. Such an air valve may also be adjusted automatically dependent on the air tem- perature in, for example, the room which has to be heated. A light meter may be used to control the opening percentage of said member for allowing adjustment of the medium flow through the light absorber. A tubular connection member may be ar- ranged for the supply of heated air to a room, which has a heating requirement. Preferably, such a connection member is curved, for example, 90° upwardly such that draught of fun- nel"is obtained with an increased natural draught as a conse- quence.

According to another preferred embodiment of the present in- vention, said second layer comprises a metal plate with a black surface. Generally, metal plates obtain a high temperature when they are subjected to sunlight. Consequently, such radiation ab- sorbing plates have a high radiation absorbing capacity and a low emission of heat capacity. For a metal material with a black coloured surface these properties are optimal. Probably, other coloured surfaces may be used for the internal material layer and also other material than metals may be used.

According to another preferred embodiment of the present in- vention, said second layer comprises internal channels, which are arranged to permit through-flowing of a second medium. Hot days, when a heating of the air in a room is not desired, such a modified second material layer may be used for heating a sec- ond medium. Such a second medium may be water, which is ar- ranged to be heated and to be used as hot tap water. Necessar- ily, a liquid medium does not need a conventional pump to be circulated but may be provided with a feeding device, which pro- vides a natural circulation of the medium. Alternatively, such a second medium may also be arranged to be circulated in an area below the ground surface such that it is cooled and that the medium delivers this cold to the second material layer. By guid- ing the second medium down into, for example, a bore hole in

the ground, it obtains a relatively low temperature. This low me- dium temperature is transferred to the second material layer, which cools the air, which is naturally circulated in the space of the light absorber. Therefore, hot summer days a comfort cool- ing of the air may be obtained in the same room, which other- wise is heated by the light absorber. At the same time, storing of heat is obtained in such a bore hole, which may be used as a source of heat for a heat pump. Advantageously, the gaseous medium comprises air and said space comprises at least an opening, which allows communication with air outside the light absorber. Here, the possibility arises to use the light absorber, by the natural circulation of air, as an exhaust air device. In this case, a useful negative pressure for the house is created. Alter- natively, the light absorber may be used as an air intake device, which may provide a cleaner air environment, for example, in houses with high radon contents.

According to another preferred embodiment of the present in- vention, the light absorber is arranged to be applied onto an external surface of a building. Here, air in the building may be guided to and from the light absorber by short air conduits. The light absorber may, by its thin construction, be arranged such that its external material layer is placed at a corresponding level as the external material layer of the building. Hereby, the light absorber may, by a suitable toning of the external or the internal material layer, gets to harmonise substantially completely with the external surface and the colour of the building. The light ab- sorber may be applicable onto a wall surface of the building.

Advantageously, such a wall surface is directed to the south. By a suitable construction of the light absorber, it may remind about a window construction or a part of the wall frontage. Alterna- tively, the light absorber may be applicable onto a roof surface of the building. In this case, the light absorber may be arranged such that the external material layer lies in the level of the ex- ternal roof material. The external material layer of the light ab- sorber may here comprise a shape, which corresponds to the

shape of roofing tiles. According to a further alternative, the light absorber may be comprised in an outer door of the build- ing. The light absorber may thereby obtain a relatively simple mounting.

According to another preferred embodiment of the present in- vention, the internal material layer comprises at least one ele- ment, which is arranged to generate electric energy. Such ele- ments may be solar cells. The solar cells obtain here a desired cooling by the naturally circulating gaseous first medium.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, preferred embodiments of the invention are de- scribed as examples with reference to the attached drawings, in which: Fig 1 shows a light absorber according to a first embodi- ment, Fig 2 shows the light absorber in Fig 1 seen from the side.

Fig 3 shows a light absorber according to a second em- bodiment, Fig 4 shows the light absorber in Fig 3 seen from the side, Fig 5 shows an internal material layer according to a second embodiment and Fig 6 shows a light absorber according to a third embodi- ment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION Figs 1 and 2 show a light absorber 1 according to a first em- bodiment of the present invention. The light absorber 1 com- prises an external material layer of a light transmitting material, here exemplified as a glass plate 2. The glass plate 2 is at- tached in a frame construction 3, which extends around the

edge of the glass plate. The frame construction 3 gives the light absorber a box-like shape. The light absorber 1 comprises here an internal material layer in form of a radiation-absorbing plate 4 with a black surface. Such a black radiation-absorbing plate 4 has good radiation absorbing properties and it obtains therefore a high temperature when it is subjected to solar radiation. The internal material layer, the glass plate 2 and the radiation- absorbing plate 4 are provided substantially in parallel. Between the glass plate 2 and the radiation-absorbing plate 4, a substan- tially closed space 5 is formed. In the space, an elongated ele- ment 6 is provided, which is arranged to divide the space 5 in a first subspace 7 and a second subspace 8. The elongated ele- ment 6 has an extension between an upper end 6a, which lies close to an upper edge surface of the space 5, and lower end 6b, which is located at a distance from a lower edge surface 6b of the elongated element 6. The elongated element 6 has also an extension between the glass plate 2 and the radiation- absorbing plate 4 such that the air only may pass between the first 7 and the second 8 subspaces below the lower end of the elongated element 6. The first subspace 7 comprises a first opening 9 at an upper portion and the second subspace 8 com- prises a second opening 10 at an upper portion. The light ab- sorber 1 is here attached to a wall 11 of a building. The light ab- sorber 1 is applied such that the first 9 and the second 10 openings are located at the same height level. Through the wall, two passages 12 extend, which ends in the respective first and second openings 9,10, one of which is shown in Fig 2. The pas- sages 12 allow passage of air between the building and the space 5. A member in the form of an air valve is arranged in or- der to allow adjustment of the airflow through at least one of said passages 12. A narrow air passage 14 is arranged at the lower portion of the light absorber 1 in order to equalise the pressure difference between the air in the space 5 and the sur- rounding air. The space 5 of the light absorber also comprises three openings, which allow connection with surrounding air ex- ternally of the light absorber 1. A valve 15,16 and 17 is ar-

ranged for the respective openings such that it is possible to adjust the openings between an open and closed position.

When the sun lights on the light absorber 1, the solar radiation passes through the transparent glass plate 2 and the radiation- absorbing plate 4 is heated. The radiation-absorbing plate 4 heats in its turn the air in contact with the space 5. In any one of the first 7 or the second 8 subspaces, the air necessarily obtains a somewhat higher air temperature. When the air in the space 5 obtains a higher temperature than in the building, the heated air from the subspace 7,8, which has the somewhat higher air tem- perature, flows upwardly and out through the opening 9,10 of the subspace 7,8. By the existence of the narrow air passage 14, it is prevented that a too high air pressure is obtained in the space 5 before the natural circulation of air through the space 5 starts. If, for example, the air temperature initially is somewhat higher in the second subspace 8 than in the first subspace 7, the heated air in the second subspace 8 rises upwardly and out through the opening 10. This airflow results in that the air in the first subspace 7 is sucked downwards. The air from the first subspace 7 is sucked, via the passage between the lower end 6b of the elongated element and the lower edge surface of the space, to the second subspace 8. Since the air in the first space 7 is sucked downwards, air is at the same time sucked in through the opening 9 from the building. Since the air sucked in from the building has a lower temperature than the air in the second subspace 8, a temperature difference arises between the air in the first and the second subspaces 7,8. This tem- perature difference, results in a natural circulation of the air through the space 5 between the openings 9,10 when the light absorber is subjected to solar radiation. Hot days, when no heating of the air in the building is desired, the valve 15 may be open at the same time as the air valve 13 is closed for the opening 10 in the second subspace 8. Hereby, an airflow is ob- tained from the building, via the air channel 12, the first opening 9, the first subspace 7 and the second subspace 8, before the

heated air is guided out through the open valve 15 in the light absorber 1. In this case, the light absorber 1 is used to provide an exhaust airflow. An alternative ventilation through the light absorber 1 may be obtained if the valves 16 and 17 instead are open and the valve 15 is closed. When incident solar radiation heats the air in the space 5, the air in the space rises upwardly and out through the openings 9,10 and to the building. Hereby, air is sucked in from the outside, via the valves 16,17, to the space 5. Here, the light absorber 1 is used for providing a sup- ply airflow to the building. When the solar radiation ceases, the air temperature in the space 5 also drops. The difference in temperature between the air in the space 5 and the air in the building decreases. This results in that the temperature differ- ence between the air in the first 7 and in the second 8 sub- spaces decreases until the natural circulation of air in the space 5 of the light absorber ceases. The air valve 13 then ought to be closed in order to guarantee that no air is circulated through the space 5.

Figs 3 to 5 show a light absorber according to a second em- bodiment. This embodiment differs from the one showed above in that the space 5 for the circulation of air is here located be- hind the radiation-absorbing plate 4. Consequently, the circu- lating air here comes in contact with the surface of the radiation- absorbing plate 4, which is turned away from the glass plate 2.

A second space 18 is here formed between the glass plate 2 and the radiation-absorbing plate 4. The second space 18 works here as a heat-insulating layer between the glass plate 2 and the radiation-absorbing plate 4. Preferably, the second space 18 comprises air but it may also contain any other kind of gas or a vacuum. The light absorber comprises a narrow air passage 14.

With such an air passage 14, a pressure equalisation is ob- tained between the air in the space 18 and the surrounding air.

An advantage of providing the space 5 for the air circulation in- side the radiation-absorbing plate 4, is that the circulating air here does not come into contact with the glass plate 2. Thereby,

fouling of the inner surface of the glass plate 2 is prevented.

Such a fouling would imply that the glass plate 2 has to be cleaned internally regularly since a dirt cover decreases the transparent properties of the glass plate 2 and thereby the ca- pacity of the light absorber 1. The radiation-absorbing plate 2 of the light absorber 1 comprises in this embodiment also internal channels 19, see hereby Fig 5, which shows a portion of such a radiation-absorbing plate 2. These channels 19 are arranged to guide a second medium, which may be a liquid or a gas. In this embodiment, a third opening 20 is arranged at a lower portion of the space 5. An air channel 21, which ends in the opening 20, extends through the wall 11. The air channel 21 allows an air- flow between the space 5 and the building. An air valve 22 is arranged in order to open and close the air channel 21.

The second embodiment showed in Figs 3 to 5 works in the same way as the first embodiment showed in Figs 1 and 2 and related to a basic embodiment with a natural circulation of air through the space 5 and heating of air in the building. When a heating requirement does not exist in the building, the air valve 13 is closed and a second medium in form of, for example, water may be circulated through the channels 19 in the radiation- absorbing plate 4. The radiation-absorbing plate 4 heats the cir- culating water in the channels 19 to such a temperature that the water may be used as hot tap water. Alternatively, the second medium, which is circulated in the channels 19 of the radiation- absorbing plate 4, may be arranged to supply comfort cooling to the air in the building during hot days. Such a second medium may be arranged to be circulated between the radiation- absorbing layer 4 and a bore hole located in the ground surface.

The second medium is cold during the circulation in the bore hole whereafter the cooled medium cools the radiation- absorbing plate 4 which in its turn cools the air which is natu- rally circulated in the space 5. The third opening 20 is in this case open. The air in the space 5 is cooled in contact with the radiation-absorbing plate 4. The cooled air falls downwards in

the space 5 and is guided, via the third opening 20 and the air channel 21, to the building. At the same time, new air is sucked into the space 5 from the building via the openings 9,10. By such a construction, cooling of the air in the building may be obtained during hot days. In connection with such a process, heat is loaded down in the bore hole. This heat in the bore hole may be taken care of by means of a heat pump, when a heating requirement of the building exists.

Fig 6 shows a light absorber according to a third embodiment. In this embodiment, the first subspace 7 has been separated from the second subspace 8 by a box-like element 23. The box-like element 23 comprises a covering surface 24, which prevents that the air in the first subspace 7 comes into contact with the radiation-absorbing plate 4. Thereby, the air in the second sub- space 8 will always be heated before the air in the first sub- space 7. In this case, a circulation of air from the first subspace 7 to the second subspace 8 is always obtained. In this embodi- ment, an upper hole 25a and a lower hole 25b have been pro- vided in the wall 11. Said holes are arranged to extend into the insulating material of the wall. When the air circulates between the first space 7 and the second space 8, a pressure difference between the upper hole 25a and the lower hole 25b is obtained.

Thereby, a small airflow through the insulating material is ob- tained. This ventilation is small but has the positive effect that it removes possible moisture in the insulating material.

Advantageously, the external material layer 2 comprises a shape, which corresponds to the external material layer of the building. By levelling the light absorber into a roof or into a wall of a building, the external material layer of the light absorber may be provided at substantially the same level as the roof or the external surface of the wall material. Hereby, the light ab- sorber 1 will harmonise nearly completely with the building. The external material layer 2 may, for example, be provided with textured glass, which looks like traditional frontages or roof con-

structions. Roof mounted light absorbers may be provided with a transparent surface formed as roofing tiles or another roof cov- ering. Hereby, whole roofs or frontages may be used as light absorbers. The light absorber may also be arranged in an outer door. The light absorber obtains thereby a very simple mounting on an existing building.

The present invention is not in any way restricted to the em- bodiments described above in the drawings but may be modified freely within the scope of the claims. For example, the light ab- sorber, which is shown in Fig 1 and 2, may also be provided with channels 19 in the radiation-absorbing plate 4. Probably, several light absorbers may be used and the produced heated air may, for example, be collected in a central space to be used when a heating requirement exists.