COMPLETE SPECIFICATION Invention Title: Solar Air Heaters Applications This complete specification should be associated with the Australian Provisional Specifications number 2009903216 of 09.07.2009 and 2010901660 of 6.04.2010 The following is a description of the invention and of a few ways to use it.
The field of the invention is the heating of air with solar energy. Even though the title might suggest diverse processes, the actual energizing process is that of solar air heating. Solar drying is achieved by passing of solar heated air though a substance or body and removal of part of its moisture because of reduced partial pressure of water in the heated air. Air ; cooling is achieved though evaporation of water in a mass of air that was dried with a desiccant that in turn was activated (regenerated) by using solar heated air. Therefore all these devices are versions of solar air heaters that are applied to different uses. The most significant advancements in the air heating technology have been achieved after 1989 when the transpired solar collectors were invented by Conserval (Solar Wall). 40 However, since the Solar Wall, which today utilizes the original technology involving perforated metal sheets, is too expensive because of the materials it uses and their design limitations, we have developed improved solar radiation absorbers and permeable covers as described in our Australian patent number 2002300258. Hereinafter we continued the development of the solar air heaters with new, economical designs aimed at decreasing the 1 cost of solar heat to less than that of fossil fuel heat. Generally, the solar air heaters described below consist of a permeable solar radiation absorber that transforms solar radiation into heat and transfers the heat to the air that passes through said solar radiation absorber. Also in most applications, after passing through the permeable solar radiation absorber, the heated air enters a plenum situated between said 2O solar radiation absorber and an impermeable boundary. After experimenting with many permeable solar radiation absorbers, we concluded that the heat exchange coefficient is higher for permeable solar radiation absorbers that force the air to sharply change its direction of flow while passing through them. This improves the heat exchange by creating a mixing effect in the interstices of the solar radiation absorber in a 75 manner similar to mixing fluids by submitting them to flow through sharply bent conduits. The boundary layer that separates the mass flow of air from the solar heated surface of the solar radiation absorber is much thinner in a turbulent than in a laminar flow, and the solidir heat exchange is improved. Obviously, as the heat exchange is improved, the overall efficiency of the solar air heater increases. Therefore it is an object of this invention to provide a solar air heater with permeable solar radiation absorber that collects solar radiation, transforms it into heat and transfers the heat 6 to the air that flows turbulently as it passes through sharp-tuming passageways of said permeable solar radiation absorber that has its edges tightly connected to an air impermeable boundary, so that a plenum is created between them, the air being heated as it flows through said permeable solar radiation absorber into said plenum from where it flows through an outlet. 110 In order to make solar heat more economical than fossil fuel heat, we have to simplify the design to the minimum necessary so that we make the solar air heater as inexpensive as possible, while retaining those design characteristics that gives it high performance. In order to reduce costs, we developed a solar air heater with thinned edges (margins) because there is no significant airflow at the edge of the plenum and so it does not need a thick fl. margin. Therefore, in a version of this invention, the solar air heater has its solar radiation absorber tightly joined on its edges to said boundary such that the thickness of said plenum gradually decreases from the area of said opening towards at least one of its edges, so that in any area of the solar air heater the thickness of said plenum is the minimum necessary to allow the proper flow of air. In most cases, the traditional thick margins of the solar air 20 heaters can be eliminated without any detriment to the functioning of the solar air heater. This way we have substantially decreased the manufacturing costs, the weight of the solar air heaters, the losses of heat through the margins, and we have improved the esthetics of the solar air heaters that do not have to look like bulky boxes. As the sun's position on the sky is inclined from the horizontal and oscillates between East and West, the optimum position of a fixed solar air heater is tilted towards the Equator. As the solar collectors are traditionally flat boxes and have to be tilted towards Equator, an unused space remains underneath. However, we envisaged ways to use that space. By pIacing a vertical wall between the top margin of the solar air heater and the ground, we can create a space that can be used for purposes relating to the air heater. For example, we can use that space as a drier in a unitary construction with the solar air heater. This way we can save the expense of building a separate drier. An additional advantage of the vertical ' wall is that the area of heat loss exposed to the wind is smaller than if there was no wall. If we need large solar arrays made out of many and/or long solar air heaters, we need air conduits to transport the heated air. A logical place through which to run the conduits is through said unused space under the tilted solar air heater. As both the solar air heater and the air conduit contain air of the same temperature, they do not need thermal insulation % between them. Therefore we can merge the solar collector and the air conduit in a unitary multifunctional and inexpensive unit. In a version of this invention, we can define an East West elongated solar air heater made out of a permeable solar radiation absorber that tilts towards the Equator and has a plenum that increases in thickness away from the Equator so that air flows across and through the permeable solar radiation absorber and then under it j and along the solar air heater, towards said opening situated at an end of said elongated solar air heater. Here we further define the cross-section of that type of solar air heater as having (besides a right angle) an angle of about 30 degrees and another of about 60 degrees, so that said solar air heater may be placed either on a roof with an angle of tilt of about 30 degrees, or on a vertical wall, or on the ground, or on a flat roof, in all situations its own 2AO aperture being tilted by about 30 degrees from the vertical, that makes the of solar air heater suitable for winter air heating. Also, for summer functioning and installation on the ground, on a wall or on a flat roof, the same solar air heater can be attached to that support so that its angle of tilt from the vertical is 60 degrees. The advantage is that such 30-60 solar air heaters may be mass-produced and then installed anywhere and for either summer or winter K5 functioning just by choosing which of their sides should be attached to the support. This also matches the needs for air heating at most geographical latitudes; therefore the 30-60 prism solar air heaters will be almost universally useful. The previous solar air heaters with permeable absorbers could not be built in large sizes because the suction of air through the solar radiation absorber was much larger near the 30 outlet of the solar air heater than in its remote areas. In case large solar air heaters are 4 Manufactured, the rate of airflow through different regions of their permeable solar radiation absorber has to be kept rather constant, so that the performance of the device is maximized. There are cases when the solar air heater is very large and the flow of air has to be regulated according to pressure requirements. In case of a large solar air heater, because 6 of the significant friction of the air when flowing along the plenum, the rate of air flow through different parts of the absorber would be too uneven. Installing many conduits into said plenum would be prohibitively expensive and would not assure a perfectly equal distribution of the airflow through said absorber. Therefore, in a version of this invention, way to achieve an even rate of airflow through the permeable solar radiation absorber is to 10 separate said plenum with a divider into at least one proximal plenum towards the solar radiation absorber and a distal plenum towards said boundary and to appropriately control the air flow through at least one aperture in the divider to achieve the desired rate of air flow through each region of the permeable solar radiation absorber. In a method to employ said divider, such a large solar air heater comprises a plurality of 6 proximal plenums situated adjacent one to another, each having the permeable solar radiation absorber tightly connected to the divider that has at least one aperture for each said proximal plenums. The apertures allow the air to flow into a distal plenum which is common to all said proximal plenums. Said distal plenum is enclosed between said divider and said impermeable boundary. As the heated air is drawn from said second plenum, the 20 rate of airflow through said permeable solar radiation absorber of each proximal plenum can be controlled through the size of each said at least one aperture. Another method to employ said divider is to provide only one proximal plenum for the entire solar air heater from where the air flows through at least one aperture into the distal plenum that is enclosed between said divider and the impermeable boundary. It is 6 understood that in this case by "at least one aperture" it is actually meant a multitude of apertures in said divider. As the heated air is drawn from said second plenum, because the air has the tendency to follow the path of least resistance, it will flow through said at least one aperture at a rate directly proportional to the size of said opening and the local 5 difference in static pressure. This way, the rate of airflow through each region of said permeable solar radiation absorber can be controlled through the size of a nearby aperture. Another way of controlling the rate of airflow is by placing a transparent and air impermeable cover towards the sun from said permeable solar radiation absorber so that it creates a space with said permeable solar radiation absorber, said space being closed from the outside environment except for at least one opening situated at the opposite end of the solar air heater from said outlet. The air is made to flow through said opening, into said space, through the permeable solar radiation absorber, and finally is extracted from said plenum through said outlet. The size and position of said at least one opening controls the 40 rate of airflow through the permeable solar radiation absorber. Said space gradually thins in the direction away from the opening, the air flowing along the space and being heated as it passes through the permeable solar radiation absorber and into said plenum that progressively thickens towards said outlet. In other cases, an already existing permeable substrate (like a mound of granules) can be used as a support for a dedicated permeable solar radiation absorber. Therefore a version of solar air heater with permeable solar radiation absorber can be described, wherein said permeable solar radiation absorber is laid upon a permeable substrate and heated air is extracted from under said permeable substrate. In one version, said permeable substrate consists of a tiled roof on which the permeable ZO radiation absorber is placed, heated air being drawn through the tiles and collected into an enclosure from underneath the tiles from where it is extracted with a fan. In another version, said permeable substrate consists of stacked particulate matter that is dried or just heated by the flowing-through air so that it stores the heat for when it is needed. The particulate matter may be stacked in an East-West elongated mound and its sidee that tilts towards the Equator is covered by said permeable solar radiation absorber while the other side is made air impermeable; air being drawn from the lowest part of said other side. 6 In another version of solar air heater with permeable substrate, said permeable solar radiation absorber consists of unconsolidated granules that are placed in a layer of constant thickness onto a perforated substrate that has an angle of tilt from the horizontal equal to the natural angle of rest of said unconsolidated granules, said perforated substrate consisting of 6 slats that tilt in the same direction as said layer to prevent small particles of said unconsolidated granules pass through said substrate, but to allow air to be drawn from under said perforated substrate and carry away the humidity it has received from the unconsolidated granules that are gradually replenished at the top edge of said layer as the dried ones are gradually removed from the lowest edge of said layer. If the granules are i dark in colour, no separate solar radiation absorber is needed on top, or a transparent cover may be provided only to protect from rain. If the granules are light colour, a black permeable solar radiation absorber may be placed above and parallel to the layer of granules, collecting more solar radiation and also protecting from rain. Another simple but very effective version of solar air heater with permeable solar radiation absorber consists of a permeable solar radiation absorber that is placed substantially parallel to a wall of a building representing said boundary, said solar radiation absorber having all its edges tightly attached to said wall, except the top edge that allows said outlet. Air heated by the solar radiation absorber flows upwards inside said plenum due to its natural buoyancy, heating said wall and afterwards exiting through said outlet. The natural out 2D flowing of the air creates a suction effect that attracts more air through the permeable solar radiation absorber into said plenum. Another method of controlling the rate of air flow and temperature increase through different regions of a large permeable solar radiation absorber consists in spraying on the underside of a region of the solar radiation absorber a quantity of hardening liquid that is in 2 inverse proportion to the distance of said region from said outlet, so that the size of said passageways and the permeability of the solar radiation absorber in said region become directly proportional with the distance of that region from said outlet. 7 It is to be observed that existing air-air heat pumps can be used for heating the buildings in winter in mild climates as the Mediterranean one, but cannot be used efficiently in rather cold climates of Central Europe, Central and North America, or most of Japan. A very important application of the solar air heaters according to this invention is to preheat the air 6 flowing onto the evaporator of a heat pump. In a version of this invention, air heated by a solar air heater is used to deliver heat to the evaporator of a heat pump that this way can work more efficiently and can deliver the heat at a temperature higher than that attained by the solar air heater. Obviously, if the heat pump switches in reverse cycle, the connection with the solar air heater has to be interrupted during summer when the heat pump needs 0 cooling of the outside heat exchanger. This way, heat pumps working with good coefficients of performance can be used in colder climates of 35-50 degrees of latitude. Some drying processes need to be conducted at near humidity saturation conditions or/and in an air tight environment. Therefore, in another version of this invention, the solar air heater is part of a solar drier with condensation that consists of a prism-shaped first , enclosure that is airtight and its side that tilts towards the Equator is covered with a transparent material, while the other sides are made out of a heat conducting material. Inside said first enclosure is installed a second prism-shaped enclosure that holds the product to be dried, said second enclosure having its side that tilts towards the sun covered with said permeable solar radiation absorber and the other sides made out of an air 20 impervious material into which at least one fan is installed. The fan can drive humid air from said second enclosure into the space between the first and the second enclosure, in good thermal contact with said heat conducting material on which water condenses and is discarded to outside, while the dried and cooled air flows towards the permeable solar radiation absorber where it is heated by the sunlight. The heated air passes into said second 25 enclosure, where it receives more moisture from the product to be dried and from where it is again re-circulated with said fan. Air heated in a solar air heater may be used for regenerating the liquid desiccant of a solar air cooling system. Some driers with liquid desiccant spray liquid desiccant into the air current in order to create a large heat and mass exchange area, but the result is the loss of 8 desiccant as carry-over and contamination of the air. Therefore, lately, heat and mass exchangers for liquid desiccant have been designed not to employ detrimental fine droplets, but to use a flow of liquid at the surface of a plate. Some models use only the top side of the plate and therefore have rather small heat exchange area, the others use both sides of a ' vertical plate, in which case the flow of desiccant is too rapid and the humidity exchange is again impaired. If a reticulated mass is used to provide high contact area between the plates, the loss in air pressure is too high. Also, many solar air coolers employ evaporative coolers that traditionally consist of wood shavings or another fibrous material wetted by the water that offers large heat exchange 4f area between the air stream and the wetted surface. These systems require large electricity consumption for their fans because of their reduced permeability. Also, pathologic bacteria like Legionella develop on these materials and their use has been lately prohibited. As these bacteria develop mostly when these systems are at rest, there is need for a system that would dry quickly after the evaporative cooling is stopped. 4 It is therefore an object of this invention to provide an improved heat and mass exchange device for a solar applications that consists of a plurality of plates that are vertically zigzagged and are made out of a material that is wetted by the working liquid and on which the liquid flows slowly on both sides of said plates and therefore has high heat and mass exchange coefficient. This is because the liquid flows on both the tilted and the overhang 2 segments of said plates with which it is retained in contact by the adhesion forces. Preferably, the air is made to flow upwards between many parallel zigzagged plates, so that the flow is turbulent and the heat and mass transfer are improved. Therefore the zigzagged shape of the plates has three roles: firstly to slow the vertical flow of the liquid to give it more time to react with the air, secondly to create a larger area of air-liquid contact, and 2( thirdly to create air turbulence and therefore further improve the heat and mass exchange. If the heat and mass exchanger presented above is used as an evaporative cooler, we have to observe that both the water and the air are cooled when water vapours exit the liquid and are entrained into the air flow. Most of the cooling energy tends to stay with the water which has a much larger heat capacity than air. The cooling process actually decreases the 30 evaporation process because at lower temperature the partial pressure of the water vapours 9 is smaller. Our interest would be to increase the temperature of the water to promote more evaporation. At the same time, if we need to cool another stream of air, we could use its heat to heat through plate conduction the water in an adjacent (but separate) channel of the heat exchanger. This requires that the plurality of plates are such connected at their inlets 6 and outlets so that alternative separate channels are created to allow the flow of two separate streams of air that can exchange heat through the material of the plates. Therefore, in one version of this invention, said heat and mass exchanger has said parallel plates made out of a thermally conductive material, alternating air channels being provided between the adjacent said parallel plates to convey two streams of air that each flows inside one set of 40 said channels, liquid flowing on the plates of at least one set of channels so that it exchanges heat and mass with its air stream, while heat is exchanged by the two streams of air through said material. If we employ the above mass and heat exchanger as an air drier by driving air between said plates and a flow of liquid desiccant on the plates, the liquid will be heated when it collects 6 the water vapours from the air. Again, most of the thermal effect of warming stays with the liquid. And, as with the evaporation process, our interest is to oppose the thermal process, therefore we need to cool the desiccant in order to favour the desired process of air drying. We could therefore combine the two processes of desiccant air drying and evaporative air cooling in a single heat and mass exchanger where the heat produced in an air drying 24) channel is used for water evaporation in the adjacent air cooling channel. This way the heat and mass exchanger can work as a heat exchanger between two adjacent channels and mostly as a mass exchanger within one channel. According to a version of this invention, said heat and mass exchanger uses one said set of channels to convey a stream of initially cool spent air and water which humidifies that stream of air, while the other set of channels 25 is used to convey a stream of initially warm fresh air and liquid desiccant which dries that stream of fresh air, the heat flowing through said material from said fresh air to the said spent air. This compact device not only replaces a classical combination of an evaporative cooler, a liquid desiccant air drier and two heat exchangers, but substantially improves the process because it allows a gradual transfer of heat from the process that rejects it and needs 30 cooling, to the process that needs that heat. 10 Heat is needed during regeneration of a liquid desiccant to replenish the heat lost through evaporation of water from that liquid. This heat can be provided from solar energy. The former solar regenerators of liquid desiccant heat the diluted desiccant in a classical solar liquid heater and then introduce the hot liquid in a mass exchanger where it releases part of 6 its water to a stream of air. Since the latent heat of water is much larger than the heat capacity of the desiccant for usual solar temperatures, only a small part of water can be evaporated this way, therefore existing solar regenerators are inefficient. We concluded that a better solution would be to continuously provide heat during the evaporation of water by directly submitting the liquid desiccant to solar radiation. Therefore, it is an object of this 1 invention to provide a solar regenerator for liquid desiccant that consists of a permeable solar radiation absorber made out of a dark colour fabric to which a liquid desiccant adheres, said fabric having large passageways that cannot be flooded by the liquid desiccant, thus allowing the air to flow through said large passageways, said fabric being wetted with diluted desiccant at its top edge, being stretched on a frame, covered with a /N transparent cover and heated by solar radiation, so that the air flowing through the permeable solar radiation absorber can receive humidity from the liquid desiccant and compensate with solar heat for the heat lost by the liquid desiccant through evaporation of water, humid air being evacuated from said solar regenerator, while the regenerated desiccant can be collected from the lower edge of said permeable solar radiation absorber. 20 The devices described above for solar air heating, evaporative cooling, solar regeneration of liquid desiccant and air drying may be used in a complex new system of solar air cooling that would be more economical, would require less electrical energy and no heat backup when compared to existing solar air coolers. The aim is also to provide a possibility for the system to work when there is no solar radiation available, for example in heavy cloudy 2 weather and at night. Therefore, in a version of this invention, a solar air heater sends heated air to a solar regenerator with permeable solar radiation absorber as shown above from where the humid air is discarded to the atmosphere, while the regenerated desiccant is sent to a heat exchanger where it is cooled and sent to the lowest part of a liquid desiccant tank where it is stored. When air cooling is needed, concentrated desiccant from the bottom 11I of said tank may be sent to a set of channels of the heat and mass exchanger as described above to dry the fresh air which is then cooled in an evaporative cooler and delivered to a building with the purpose of ventilation and cooling. The spent air from the building is cooled by evaporation of water in the other set of channels of said heat and mass exchanger 6 and collects heat from the fresh air stream and afterwards discarded to the atmosphere. The desiccant that was diluted in said heat and mass exchanger is discarded at the top part of said liquid desiccant tank. During the day when good solar radiation is available, diluted desiccant is collected from the top layers of the tank with a floating suction pipe and sent to said heat exchanger where it is preheated, then it is heated in a solar heater for liquid before 10 being delivered at the top edge of said solar regenerator. The liquid desiccant storage tank has a large capacity to allow functioning of the air cooler during periods of time without sunshine. As the tank has a large size, is placed in the shade and is not thermally insulated, it will also play the role of liquid cooler for the spent desiccant that is returned hot to the tank. Natural stratification and differences in specific gravity will prevent intermixing of 6 warm diluted desiccant and cold concentrated desiccant. If the entire desiccant in the tank has been diluted and there is no solar energy available (exceptionally long cloudy weather), then the cooling system shown above can still work (with reduced capacity) as a combined direct and indirect evaporative cooler, or as an indirect evaporative cooler by shutting down its evaporative cooler for the fresh air circuit. 20 It is to be understood that air cooling for a building with the general setup shown above is also possible if there is no need of ventilation. In that case, air from. the building is introduced into the air drying circuit of the heat and mass exchanger; its drying is possible because of the humidity expelled through breathing of the people in the building and because of the humidity introduced by the evaporative cooling. .7 In many cases of large size solar air heaters it is not necessary to manufacture a special bottom to the solar air heater, as it can use just the existing substrate on which it is installed, for example the ground or a roof. However, if the permeable solar radiation absorber is not covered with a transparent impermeable layer, some rainwater might seep through ii and 12 inside the plenum. Provisions have to allow this water to be evacuated from the solar air heater, while the bottom of the solar air heater still has to be thermally insulated. As rainwater may sometimes seep in, it is necessary to make that thermal insulation out of a material that is not influenced by water but which allows water to pass through it. Such a 6 material is the polyester bats made out of polyester fibres. Therefore, in one version of this invention, a water permeable thermal insulation which is made out of a material not damaged by water is placed onto said impermeable boundary to reduce the heat losses while allowing rainwater to seep through it. A similar arrangement is that for a solar tower. It was suggested previously by other authors 10 that the electric power output of a solar tower can be made more constant by storing the heat in the ground and in water-filled plastic bags that would render, during night, the heat they accumulate during the day. This suggestion is not correct because the maximum power requirement occurs during the day, because the ground is a powerful heat sink for any temperature larger than the ambient one, and because during the night the solar collector would lose too much heat through radiation. Therefore, in this patent application it is advocated that the solar tower power plant be used only during the day, when it would provide the peak day energy requirement, while the classic power plants would generate the power necessary for night-time use. In this application the ground represents a heat sink, therefore it has to be thermally insulated from the flow of air by placing on it thermal 20 insulation. We have found that the best way is to place a thick layer of permeable insulation (for example polyester wire blankets) directly on the ground. Rainwater easily seeps through it and the top layers of the insulation work even if the lower layers are wet. The thermal insulation can be fixed to the ground with pegs to keep it in place in case of floods. We designed permeable solar radiation absorbers that altemate narrow flat areas with passageways across those areas, this way forcing the air to take sharp turns and even create micro-vortices. This makes the high temperature air of the boundary layer detach from the substrate and mix into the main air stream. A logical resultant of this conceptual design is a material made out of woven tapes that bend the flow of air twice on two perpendicular directions and, this way, create sudden turbulence at the passing of the air through the solar 13 radiation absorber. Also, the thickness of this material does not need to be large if the air streams are thin. This way, the overall loss of air pressure when passing through the permeable solar radiation absorber may be very small, despite the contact with the solid being very good. 6 Following a very large number of experiments we have found out that the optimum width of the tapes is 1-2mm and the size of the openings in the absorber should be between 0.25mm and 0.5mm. A preferred material for the solar radiation absorber made out of woven tapes is polypropylene, that can be well protected against UV and which has a high enough melting 40 point. We have found out that rain and even dew can be a problem for permeable absorbers if water adheres to them. This is because it would immediately block the openings (passageways) in the absorber and interrupt the airflow. Also, it would allow water to pass through the absorber through seepage. Additionally, after the rain a material that adsorbs 4 water will dry much slower than a hydrophobic material. Therefore, it is highly advisable to make all the uncovered permeable solar radiation absorbers hydrophobic. Reference will now be made to the drawings where: Figure 1 represents a solar air heater with fan installed on the wall of a building Figure 2 represents a large solar air heater for a solar tower 20 Figure 3 represents a tiled roof air heater Figure 4 shows an attic drier Figure 5 shows a roof air heater with transparent cover Figure 6 represents a stack drier of particulate matter Figure 7 shows a mound drier 25 Figure 8 represents a cross-section through an elongated air heater Figure 9 shows in view from above a large solar air heater array 14 Figure 10 shows a drier for conveyor belt Figu= 1 represents an elongated solar air heater with transparent cover Figure 12 represents in vertical cross section a solar drier with condensation Figure 13 represents a wall solar air heater with natural circulation i Figure 14 shows in vertical cross section a solar air heater for a heat pump Figure 15 shows a vertical cross section through a solar drier for particulate material Figure 16 represents a heat and mass exchanger for an air stream Figure 17 represents a heat and mass exchanger for two air streams and one liquid Figure 18 represents a heat and mass exchanger for two air streams and two liquids (0 Figure 19 shows the diagram of a solar air cooling system Figure 20 represents a floating solar and wind drier Referring now to Figure 1, it is seen a central vertical cross section through an air heater for heating the air in a building, which is placed on the wall I of said building. A hole 2 is made in the wall I to allow the heated air in. Fresh air from outside is heated when passing through the permeable solar radiation absorber 3 that is tightly connected on its sides to the impermeable boundary 4 which, in this case, may be a component of the air heater, or just the wall. The absorber 3 is kept away from the boundary 4 only in a central axial area by a support structure 5; in the rest of the solar air heater the thickness of the plenum decreases to nil towards its margins, this way eliminating the useless and expensive margins of the 20 box-type solar air heaters. A rigid cover 6 creates an internal air collection box at the top part of the solar air heater and protects the fan 7 from the very small raindrops that would still penetrate through the absorber 3 during violent raining. The cover 6 also prevents an excessive air draw through the solar radiation absorber in that area. The heated air is pushed by the fan 7 into the building 8 that has to be heated. The support structure may be foldable 25 (slides upwards in a bayonet style) so that the solar air heater may be folded and freighted easily. Referring now to Figure 2, where it is shown in vertical cross-section a solar air heater used as a solar collector for a large scale application, for example a solar tower power plant. It consists of a peripheral solar air heater 9 without air flow control, and of air heaters with 15 airflow control that comprise permeable solar radiation absorber 3 above proximal plenums %that are enclosed with dividers II under said absorber 3. The dividers may be made out of tarpaulin material and have apertures 12 that discard the heated air into a distal plenum 13 from where the air is drawn for the given application. By varying the size of the apertures 12 the rate of airflow through the corresponding region of solar radiation absorber 3 can be controlled. This way the efficiency and the performance of the solar collector can be optimized. In the case of a solar tower, the heated air raises into a very tall tower 14 that creates a draft that actuates at least one turbine. The entire solar collector is supported by vertical poles 15. Thermal insulation 16 may be placed on the ground 17 and would allow ) water to seep through it. Because the static pressure in the solar collector decreases towards the tower, if the proximal plenums 10 have equal areas, the apertures 12 of the proximal plenums 10 that are closer to the tower 14 would be smaller than those of the plenums 10 that are further from the tower. This way the rate of airflow per unit of permeable cover area is constant. This type of peripheral collector 9 having an absorber 3 that tilts away 5 from the tower may be employed also for the classical solar tower with impermeable cover. Referring now to Figure 3, it is shown a vertical cross-section through a tiled roof 18 on which a solar radiation absorber 3 is laid, the air being heated as it passes through the absorber 3 and then through the passageways between the tiles into a thermally insulated enclosure 19 from where it is extracted with a fan 7 and sent through the conduit 20 to the 20 place of use. Referring now to Figure 4, it is shown a vertical cross-section through a drier arrangement under a tiled roof 18 on which a solar radiation absorber 3 is laid, the being heated as it passes through it and then through the passageways between the tiles into an enclosure defined by the floor of the attic and at least one wall 1. This space can be used as a drier and 25 the fan 7 extracts the humid air from the drier room. The wall 1 ensures that only the air passing through the part of the roof covered with permeable solar radiation absorber 3 would enter the drier room. 16 Ieferring now to Figure 5, it is shown a tiled roof 18 on which a permeable solar radiation absorber 3 is laid. Above the absorber 3 a space 21 is created by the transparent cover 23, the air passes from the space 21 through the permeable absorber 3 that heats it, then through the passageways between the tiles into a thermally insulated enclosure 19 from where it is ! extracted with a fan 7 and sent for example to heat a space in that building. The advantage of having a transparent cover above the solar radiation absorber (even if fresh air is drawn from outside) is that this way the absorber 3 is not influenced by wind, rain or dew. However, if the air entering the space 21 was re-circulated from inside the building, there is an additional advantage of delivering higher temperature air into the building than if the air 0 was taken from outside the building. Referring now to Figure 6, it is shown a vertical cross-section through a drier of particulate matter that consists of a permeable solar radiation absorber 3 that lays on a stack of particulate matter 23 that has to be dried, which in turn is supported by a perforated structure 24 which creates an enclosure 25 underneath from which the air is extracted with Vi the fan 7. The particulate matter can be grain or other agricultural crops, or can be mineral fragments or any other particulate matter that has to be dried. Referring now to Figure 7, which shows a vertical cross-section of a mound drier consisting of a permeable solar radiation absorber 3 laid onto a mound 26 of particulate matter 23 that surrounds and supports a vertical pipe 27 that is preferably black in colour and has 20 perforations at its lower part that allow the hot air to enter the pipe and rise because of its buoyancy and to create, this way, a suction at its base that attracts more air from the mound. The height of the pipe 27 should be inversely proportional with the permeability of the particulate matter 23 and directly proportional with the quantity of the material in the mound. An ideal crop to be dried in this way is corn on the cob that has a large :2 permeability. A good permeable solar radiation absorber is also impermeable to water, therefore it will protect the crop material from rain, insects and, for a short time, even from rodents. 17 Referring now to Figure 8, it is shown a North-South vertical cross-section through a solar air heater elongated in an East-West direction to receive maximum solar radiation and which is tilted towards the Equator. The general triangular prism shape exposes a maximum area to the sun and the smallest area to the wind in the shadowed areas and also allows for a E substantial air conduit under the solar radiation absorber. This large cross-section is necessary in case of very elongated air heaters to collect the air from the entire area of the solar collector and send it to one of the ends of the prism. The wall I has a thermal insulation 16 to diminish heat loses. A divider I I connects tightly to the sides of the solar radiation absorber 3 and some areas of the wall 1 and has at least one aperture 12. Air is 10 heated as it passes through the permeable solar radiation absorber 3 and flows naturally upwards through the proximal plenum 10 until it is sucked in the distal plenum 13 through the aperture 12 that allows the regulation of the rate of the airflow through the absorber 3. Therefore the rate of airflow through the aperture 12 at each place is a function of both the distance to the fan and the width of the aperture. By increasing the width of the aperture the 4 rate of airflow through the nearby area of the absorber 3 is increased, and vice-versa. This arrangement is necessary in order to assure a constant rate of airflow through the absorber along the entire solar air heater. Referring now to Figure 9, it is shown the view from above of a solar array comprising a plurality of East-West elongated solar air heaters 28 that have prism-shaped cross-section, 20 similar to those shown in Figure 8, that send with the fan 7 the heated air through conduits 20 to a place of use 29. Each solar air heater prism tilts towards the Equator and the distance between the prism air heaters is meant to avoid them shadowing each other. It also creates a foot-path that allows servicing them if necessary. Referring now to Figure 10, is shown a vertical cross-section through a solar air heater and 2 drier for a product placed on a conveyor belt 30. The tilted permeable solar radiation absorber 3 protects from rain and heats the air that dries the transported particulate matter 23. The impermeable boundary 4 creates a housing on the lower parts of the air heater. The humid air is extracted from many places along said plenum with a series of fans 7 that may be directly actuated by wheels 31 that are in friction contact with the moving conveyor belt. I8 7he fans are situated a few metres apart along the conveyor belt and they draw the air through the permeable solar radiation absorber and into the plenum where it dries the product and then it is evacuated to the outside. Long chains of conveyor belts have points of discharge of the load from one conveyor belt to another. During this operation the product 6 is turned over and because it is re-arranged and new layers come on top, it can be better accessed by the hot air and better dried. Also, fixed obstacles can be installed across the top moving product to make it turn-over and better dry. Also, these fixed obstacles create secondary air convection currents because of the longitudinal air current produced by the movement of the belt and of the product. These air currents help the drying process. For 10 example coal could be this way dried when conveyed many kilometers between the quarry and the power plant. The permeable absorber cover is hydrophobic; therefore it also protects the coal from rain. Overall, a drying of coal can be achieved with minimal cost while reducing the humidity of coal and therefore the coal consumption. Referring now to Figure 1 la, it shows in North-South vertical cross-section the inlet area of T an East-West elongated solar air heater comprising a wall I that has thermal insulation 16 at the inside. Thermal insulation is also placed on the horizontal area of the ground 17 or of a roof on which the solar air heater is placed. Above them is stretched a permeable solar radiation absorber 3 that defines underneath a plenum 32. The permeable solar radiation absorber 3 is protected from rain and wind with a transparent and impermeable cover 22 210 that is tightly connected to the permeable solar radiation absorber except at one of the ends of the solar air heater where it allows an opening 33 with the solar air heater. This way a space 21 is defined between said transparent cover and the solar radiation absorber 3. Air is admitted in the space 21 through the opening 33 and is heated as it passes through the solar radiation absorber 3 into the plenum 32. Once the air passes through the permeable solar radiation absorber and enters said plenum, it begins flowing towards the outlet end of the solar air heater, along the plenum 32 which becomes a longitudinal air conduit. The solar radiation absorber 3 is gradually more and more stretched towards the outlet, as seen in Figure 1 lb that represents a cross-section through the outlet end of the air heater. This way the plenum 32 increases in cross section as it receives more air that has passed through the 30 solar radiation absorber3 and ultimately is evacuated through the outlet 34. The solar air 19 beater can work in direct mode,.heating fresh air from outside (when said opening is opened to e atmosphere), or in re-circulation mode, re-heating the air received from its point of use. Other versions include installing the fan at the inlet (this way the air heater works at pressures larger than ambient), at the outlet (this way the working pressure of the solar air ! heater is smaller than ambient pressure), or installing a fan at the inlet and another fan at the outlet (therefore the air heater works at ambient pressure). Referring now to Figure 12, it can be seen in vertical cross-section a simple solar drier with condensation that consists of a prism-shaped and airtight first enclosure 25 that tilts towards the Equator and has a transparent cover 22 facing the sun and the other sides 35 10 made out of a heat conducting material, inside said first enclosure being installed a second prism-shaped enclosure 36 that holds the product to be dried, said second enclosure having its side that tilts towards the sun covered with a permeable solar radiation absorber 3 and the other sides made out of an air impervious material into which at least one fan 7 is installed so that humid air from said second enclosure is 1 pushed into the space 21 between the first and the second enclosure, in thermal contact with said heat conducting material 35 on which water condenses and is conducted to outside, while the dried and cooled air flows towards the permeable solar radiation absorber 3 where is heated by the sunlight that passes through the transparent cover 22, the air being heated as it passes through the permeable solar radiation absorber 3 and into 2.0 said second enclosure, where it receives more moisture from the product to be dried. Referring now to Figure 13a, it is shown in vertical cross section a solar air heater with natural circulation for buildings comprising a permeable solar radiation absorber 3 that is attached on a support structure 5 at a distance of a few centimeters from the wall 1 of a building. The permeable absorber is tightly attached to the wall on all its sides except the 25 top one that represents the outlet 34 of the air heater. The wind usually generates the first push of air through this air heater and pumps some hot air into the plenum. As the hot air in the plenum is lighter than the cold air from outside, it will rise in said plenum and in this process will heat the wall and in the end will exit the solar air heater through its outlet. This suction effect inside the plenum draws more air from outside and this way the 30 solar air heater does not need a fan. During summer (see Figure 13 b) when there is no 20 leed'to heat the wall, the lid 37 is closed and the flow of heated air takes place only on te outside of the solar radiation absorber, not on the wall side. This way the wall is kept cooler than if there was no air heater on the wall because the absorber 3 has a shadowing effect. If the wall is made out of concrete, stone or bricks, it has a large mass and rather small thermal conductibility. This way the heat received from the solar collector will slowly seep through the wall and will reach the other side of the wall only during afternoon and evening. Therefore, this arrangement acts as heat storage and delay system, as it delivers its heat at night, when it is needed most. An additional advantage of this type of solar air heater is that it keeps the rain away from the wall, this way preventing it 40 to seep as usual through the wall and cool it down, destroying the wall and favoring the growth of mold at the inside of the wall (as it happens with many old buildings). This air heater will present itself as large dark coloured strips or patches on the walls, or can completely cover the walls. In case of commercial buildings or similar, light colour inscriptions used as commercial advertising can be made on the solar radiation absorber 4 that will not lose its thermal properties if only a small part of its surface is not black. Referring now to Figure 14, it can be seen in vertical cross section a heat pump system (reverse cycle air conditioner) installed on the wall 1 of a building and comprising the outside heat exchanger 38 and the inside heat exchanger 39. It is known that heat pumps work with efficiencies (coefficients of performance) that are inversely proportional to the 20 difference in temperature of their heat exchangers. As they use electric power to move the heat, the larger the difference in temperature, the more expensive is the transferred heat. Therefore the air conditioners cannot be used now for heating in winter in cold countries. An important application of this invention is to heat during winter the air for the outside heat exchanger 38 of a heat pump, so that it can work with high coefficients of performance and therefore can deliver inexpensive heat. An additional advantage is that this way heat can be introduced in the building even if the solar air heater cannot rise by itself the temperature high enough to introduce that air into the building (as is the case in cloudy weather and very low atmospheric temperatures). Therefore this is a win-win co-operation between a solar air heater and a heat pump. Accordingly, Figure 14a shows 30 a permeable solar radiation absorber 3 that is installed on a support structure 5 so that the 21 outside heat exchanger 38 during its operation draws air that was heated with solar tradition. There is no need of a fan for the solar air heater, as the fan of the heat pump is powerful enough. As seen in Figure 14b, during summer the folded part 40 of the support structure and the corresponding solar radiation absorber allow the heat exchanger to draw 6 air from outside without heating it with the solar air heater because in this regime it has to expel heat through its outside heat exchanger 38. Referring now to Figure 15, it can be seen in vertical cross section a solar drier for particulate solid matter (for example coal). In our Australian patent number 2002300258 is described a solar radiation absorber that consists of dark coloured granules through which 40 outside air is drawn and heated, and serves either as a drier for those granules or the granules serve as a heat storage medium. Multiple versions are possible, as those skilled in the art can envisage. In these versions, the actual dark granules play the role of the solar radiation absorber. A very important application of the direct granular solar radiation absorber is drying the coal with solar energy. By removing the humidity in the coal, its heat j of combustion increases and therefore decreases the quantity of coal necessary to generate a required quantity of heat. Also, the temperature of burning will increase and will have as result a cleaner burn and a possibility to increase the thermal efficiency of the coal power plants. Therefore such a drier comprises a perforated structure 24 that tilts towards the Equator and is made of flat slats that run from East to West and are also tilted towards the 20 Equator. A plenum 32 is defined between the perforated structure and an enclosure 25. An upper conveyor belt 41 brings coal that is gradually removed from it for example with fix scrapers 42 and allowed to fall on the perforated structure 24 that is tilted at an angle equal with the natural angle of repose of that type of particulate matter (coal). Because of this, the thickness of the layer 43 of coal above the perforated structure 24 can be kept constant. 2) Depending on the average size of the coal particles, the thickness of the layer 43 should be between a few centimeters (as for rather fine particles) and tens of centimeters (for boulders). The large angle of tilt of the slats prevents the space between them from being clogged by particles of similar size with the distance between the slats. As the coal face is exposed to the sun, it is heated by the solar radiation. Air is drawn from between the coal '30 particles because in the plenum 32 the pressure is maintained lower than atmospheric by 22 Using at least one fan 7 or by employing a tall draft tower that uses the difference in specific gravity of the hot air and of atmospheric air to make a suction effect. This combination of solar radiation and air draft dries the coal that will gradually fall from the layer 43 because the mobile scraper 44 slides at the base of the layer 43 and removes the dried coal and 6 places it on the lower conveyor belt 45. A transparent cover or a high efficiency permeable solar radiation absorber may be placed above and at a distance from the coal layer 43 to protect it from rain and wind and to increase drying performance. Referring now to Figure 16, it can be seen in vertical cross section a heat and mass exchanger consisting of a plurality of plates 46 that are vertically zigzagged and are made 10 out of a material that is wetted by a liquid and on which the desiccant flows slowly on both sides and therefore has high exchange coefficient. The plates are placed in an enclosure 25 that confines the flow of air to the region of the plates. The liquid flows on both the tilted segments 47 and the overhang segments 48 of said plates with which it is retained in contact by the adhesion forces. Preferably, the air is made to flow upwards between many 4 parallel zigzagged plates, so that the flow is turbulent and the heat and mass transfer are improved. Therefore the zigzagged shape of the plates has three roles: firstly to slow the vertical flow of the liquid to give it more time to react with the air, secondly to create a larger area of air-liquid contact, and thirdly to create air turbulence and therefore further improve the heat and mass exchange. Such a device can also be used as a heat exchanger 20 only, by conveying heat from one stream of gas to another, without mass transport processes involved. Referring now to Figure 17, it can be seen a heat and mass exchanger that is used as an indirect evaporative cooler and has said parallel zigzagged plates 46 made out of a thermally conductive material that separate two different streams of air. Each plate 46 f would separate a zigzagged channel 49 of an air stream that is in contact with water flowing on the inside of its plates, from the zigzagged channel 50 of an air stream without liquid. The zigzagged channels are alternatively connected one to another to create one inlet and one outlet for each of the two streams of air, as those skilled in the art can do. Representation in two dimensions in this figure of such a complex three dimensional object 23 Is difficult. There also are many ways to deliver and to collect the liquid from the plates, as those skilled in the art can do. A very large surface of contact is created for each of the two streams of air. As water flows in contact with the air in the channel 49, the water stream cooled through evaporation cools the plate 46 which in turn cools the air stream on its reverse side. A hydrophilic fabric can be affixed onto the side of the plates on which liquid flows to slow it down further and improve wetting of the plate. The stream of air in which water is evaporated is usually sacrificed (humidified too much for human comfort), therefore that air is discarded to the atmosphere. The other stream of air was initially fresh warm air, but was cooled by conduction through said plate and can therefore be used for {0 cooling a building. This type of heat and mass exchanger can also be used in one set of channels for drying a stream of air with liquid desiccant while through the other set of channels air is made to flow to cool down said liquid desiccant and improve air drying. This type of heat and mass exchanger can also be used as a regenerator of liquid desiccant whereas a stream of air and diluted desiccant flow through a set of channels which are P heated by a stream of solar heated air flowing through the other channels. Referring now to Figure 18, it is shown a heat and mass exchanger employed to simultaneously act as an air cooler and an air drier. By driving air in the channels 51 between plates on which liquid desiccant flows, the air is dried but the liquid desiccant heats up in the process of water absorption. That liquid desiccant can be cooled by 20 conduction through the plate 46 by a stream of water flowing on the plates of the channels 49 which in turn was cooled by evaporation of water. This compact device not only replaces a classical combination of an evaporative cooler, a liquid desiccant air drier and two heat exchangers, but substantially improves the process because it allows a gradual transfer of heat. Hydrophilic fabric may be attached onto said plates to improve the mass 2 and heat exchange by retaining more liquid desiccant and water in contact with the plates. Referring now to Figure 19, is shown the diagram of a solar air cooler with storage for night functioning. The system comprises a solar air heater 28 with permeable solar radiation absorber 3 that sends heated air to a solar regenerator that consists of a dark colour fabric 52 covered with a transparent cover 22 from where the humid air is discarded to the 24 ahnosphere with the fan 7, while the regenerated desiccant is sent to a heat exchanger 53 where it is cooled and sent to the lowest part of a liquid desiccant tank 54 where it is stored. When air cooling is needed, concentrated desiccant from the bottom of tank 54 may be sent to a set of channels of the heat and mass exchanger 55 to dry the fresh air 56 which is then 6 cooled in an evaporative cooler 57 and delivered to a user 58 of cool air. The spent air 59 from the user 58 is cooled by evaporation of water in the other set of channels of the heat and mass exchanger 55 and collects heat from the fresh air stream 56 and afterwards is discarded to the atmosphere. The diluted desiccant 60 from the heat and mass exchanger 55 is discarded at the top part of the liquid desiccant tank 54. During the day when good solar 10 radiation is available, diluted desiccant 60 is collected from the top layers of the tank 54 with a floating suction pipe 61 and sent to the heat exchanger 53 where it is preheated, then it is heated in a solar heater 62 for liquid desiccant before being delivered at the top edge 63 of said solar regenerator. The regenerated desiccant is collected from the lower end 64 of said solar regenerator. It should be observed that in this figure the ensemble comprising the 1' solar air heater 28, the solar regenerator and the solar liquid heater 62 is not only diagrammatic, but also represents a vertical cross section of this ensemble which may be integrated in a single frame and placed for example on the roof of the user 58 of cooled air. The liquid desiccant storage tank 54 has a large capacity to allow functioning of the air cooler during periods of time without sunshine. As the tank 54 has a large size, is placed in 20 the shade and is not thermally insulated, it will also play the role of liquid cooler for the spent desiccant that is returned hot to it. The water tank 65 supplies the water necessary for cooling the air in the heat and mass exchanger 55. Natural stratification and differences in specific gravity will prevent intermixing of warm diluted desiccant and cold concentrated desiccant. 2! If the entire desiccant in the tank has been diluted and there is no solar energy available (exceptionally long cloudy weather), then the cooling system shown above can still work (with reduced capacity) as a combined direct and indirect evaporative cooler, or as an indirect evaporative cooler by shutting down its evaporative cooler 57 for the fresh air circuit. 25 It is to be understood that air cooling for a building with the general setup shown above is also possible if there is no need of ventilation. In that case, spent air 59 from the user 58 is introduced into the air drying circuit of the heat and mass exchanger 55; its drying is possible because of the humidity expelled through breathing of the people in the building ( and because of the humidity introduced by the evaporative cooling. Referring now to Figure 20a, it can be seen in lateral view a solar drier actuated by a solar air heater that uses solar radiation as source of heat and wind as its main power supply. According to claim 6, this system is placed on a floating platform 66 that can freely rotate around its anchor and this way it always exposes to the wind its front aperture 67. The wind 10 creates an air pressure in the space between an impermeable transparent cover 22 and the permeable solar radiation absorber 3 through which the air flows and is heated and then passes through the products to be dried in the drier room 68 and finally is evacuated to the atmosphere. In case there is no wind at all, the economical backup system 69 assures the necessary airflow. The solar air heater 28 would rarely need airflow from the backup 6 system because it is capable to use the slightest breeze through its amplification and air control system 70. Main qualities of the system are: small capital investment, almost nil running cost, small loss in air pressure, quick and even drying of the batches, does not occupy precious land. Such drier is suitable for marine or island products like algae, coconut, even seafood. Such a drier may also be employed on land, floating in small basins 2) or just installed on wheeled carriages that run on circular rails so that the wind can turn it around. 26