Abstract:
The invention provides cooling apparatus comprising: a solar heat collection means ( 2 ); two or more absorption refrigeration modules ( 1 ), each module being arranged to receive heat from the heat collection means and to re-circulate refrigerant through an evaporator ( 16 ); and means for putting a fluid to be cooled into thermal contact with each of the evaporators.

Description:
FILED OF THE INVENTION 
       [0001]    This invention relates to a cooler, particularly an air cooler, and is applicable to the cooling of air in rooms e.g. as part of an air conditioning system; or the cooling of air in a confined space such as a refrigerator. 
       BACKGROUND TO THE INVENTION 
       [0002]    Many parts of the world that suffer high climatic temperatures, where refrigeration and air conditioning are therefore important, are too remote to have a mains electricity supply. Solar power has the potential to resolve this problem but most solar powered refrigeration systems have the problem that they rely on moving mechanical compressors and other parts that are liable to failure. This makes the existing solar powered systems unsuitable for prolonged use in regions where there is no facility for repair and maintenance. Another problem is that most existing designs are electrically driven and employ photoelectric panels to generate the electricity. Unless provided with electric storage facilities, such designs are unable to function during periods when there is no sunlight. Compounding these problems is often a lack of local skilled maintenance personnel. 
       SUMMARY OF THE INVENTION 
       [0003]    The invention is defined in the appended independent claim, to which reference should now be made. 
         [0004]    The invention provides cooling apparatus comprising: a solar heat collection means; two or more absorption refrigeration modules, each module being arranged to receive heat from the heat collection means and to re-circulate refrigerant through an evaporator; and means for putting a fluid to be cooled into thermal contact with each of the evaporators. 
         [0005]    Each module preferably incorporates its own individual evaporator. A housing for this, defining a path for air to be cooled, can conveniently be formed by partition walls within a main outer casing of the module. In one particularly effective design, the outer casing of each module is formed with lines of weakness defining knock-out areas allowing interconnection between evaporator housings of adjoining modules. 
         [0006]    By employing a modular construction it becomes possible to obtain any desired cooling power by employing any appropriate number of modules. Furthermore, by using absorption refrigeration principles the invention makes it possible to eliminate the need for moving parts, allowing the system to function for many years without maintenance. 
         [0007]    1. Preferably each module has: a generator containing a solution of refrigerant in a liquid, the generator being arranged to receive heat from the heat collector and to cause evaporation of the refrigerant, 
         [0008]    2. a bubble pump for pumping the liquid from the generator to an absorber, 
         [0009]    3. a condenser arranged to receive gaseous refrigerant from the generator and to condense the same, 
         [0010]    4. an evaporator, 
         [0011]    5. means for passing liquid refrigerant from the condenser to the evaporator, and 
         [0012]    6. absorbing means for receiving gaseous refrigerant from the evaporator, absorbing it into the liquid from the bubble pump and returning the liquid to the generator. 
         [0013]    Bubble pumps rely on surface tension to operate and are for that reason not scalable to larger sizes. If the diameter of the tube of the bubble pump exceeds around 12 mm, then the meniscus will be prone to collapse. This limits the amount of cooling a bubble pump driven system can deliver. The invention makes it possible to provide any desired amount of cooling by using a plurality of modules. 
         [0014]    The modular configuration proposed by the invention also gives economies of manufacturing and distribution costs. This is because only one module design is required, which can be produced in large quantities and assembled in banks of different sizes depending on the power requirements of a particular situation. Typically a residential property might require 8 to 15 modules for air conditioning purposes whilst a refrigerator might require just one module. 
         [0015]    It would be possible for the generator to be included within, or in direct contact with, the solar collector but this is not preferred because it would be difficult, without recourse to powered fans or the like, to ensure that heat is efficiently transferred to the generator. It is therefore proposed that a heat pipe be included having its hot end within the solar collector. The cold end of the heat pipe and the generator can then be arranged in thermal contact with each other. In a preferred arrangement the thermal contact is achieved by a phase-change heat storage medium, the cold end of the heat pipe and the generator preferably being in close thermal contact with (but preferably not immersed in) this medium. Heat stored in the phase change heat store is able to drive the refrigeration system into the evening after sunset. 
         [0016]    Each module preferably has a casing which encloses the components (1) to (6) listed above and includes means for attaching the modules rigidly together. The attachment means is preferably in the form of clips or other fastening devices that permit easy assembly. It is best if the casing has parallel sides that are flat or otherwise shaped so as to conform to each other so that the sides of adjacent modules lie against each other when attached. 
         [0017]    The invention can be used for cooling air in an air conditioning system, where there is normally a need for continued operation into the evening but not throughout the night. When the system is for use in air conditioning, the modules are preferably installed in a roof space or, for a flat-roofed building, on top of the roof. 
         [0018]    The invention is also applicable to refrigeration systems for storage of food or medicines. In such a system, since the space to be cooled is relatively small, the stored latent heat of the phase change material may be sufficient to last throughout the night or at least for sufficient time to ensure that the temperature of air within the relevant space does not rise unacceptably. When for use as a refrigerator, the modules are preferably mounted on an outside panel, e.g. a panel defining the top surface of the cabinet. 
         [0019]    The invention is not limited to environments where it is used for cooling air. It could be used for cooling liquids such as drinks; and fluids that require cooling in industrial processes. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which: - 
           [0021]      FIG. 1  is a schematic illustration of the components of an air conditioning system constructed in accordance with the invention; 
           [0022]      FIG. 2  shows a vertical cross-section through a house having a pitched roof and fitted with the system of  FIG. 1 ; 
           [0023]      FIG. 3  is a perspective view of a solar collector and a module into which most of the other components shown in  FIG. 1  are contained; 
           [0024]      FIG. 4  shows a variation of the module design for use on a flat roof or on a rectilinear cabinet for use as a refrigerator; and 
           [0025]      FIG. 5  shows a perspective view of a group of similar modules connected in parallel. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Referring firstly to  FIG. 1 ; there is shown a refrigeration module  1  comprising a solar collector  2  exposed to sunlight on the outside of a roof  3  of a building and a housing  4  mounted inside a roof space defined between the roof  3  and a ceiling  5 . The solar collector  2  is formed by three evacuated tubes  6  (only one shown for simplicity of description) each having a seal  7 . Arrangements having a different number of tubes  6 , e.g. two or four would also be suitable. 
         [0027]    The module  1  also includes heat pipes  8 , one for each collector  2 , containing, in this particular example, water as its operating fluid. The pressure inside the heat pipe varies so that it is always at the saturation pressure for any given temperature. In this example, the heat pipe reaches around 220° C., at which point the pressure inside the heat pipe is well above ambient pressure. The hot end of each heat pipe is located within the heat collector tube and it passes through the seal  7  and through the roof  3  to its cold end within the housing  4 . 
         [0028]    A heat store is formed by an insulated vessel  9  containing a phase-change material  10 . In this example the phase change material is a eutectic mixture of sodium nitrate and lithium nitrate, having a melting point of 195° C. Other materials having melting points in the range of 190° C. and 220° C. would also be suitable for use with an ammonia solution refrigerant. The heat pipe  8  passes through the wall of the heat store vessel  9  so that its colder end is in close thermal contact with the phase-change material  10 . 
         [0029]    A generator  11 , containing strong ammonia solution in water, is in close thermal contact with the phase-change material  10  and is connected via a bubble pump  12  and collector  13  to a condenser  14 , a trap  15 , an evaporator  16 , a junction  17 , a heat exchanger  18  and a reservoir  19 . 
         [0030]    Ammonia is the refrigerant and has a boiling point of around 190° C. For optimal operation the phase change material should have a melting point above, but within 20° C. of, the boiling point of the refrigerant. 
         [0031]    The housing  4  is formed from pressed metal sheet and defines an air duct  20 . The evaporator  16  is located in a heat exchange chamber  24  where hot air drawn through port  24 A is cooled and flows by convection down through port  24 B into a living area of the building. The heat exchange chamber is defined between side walls of the housing  4  and partition walls as shown in  FIG. 1 . These partition walls extend downwardly towards an exit  24 B for cool dry air and an exit port  24 C for condensed water. The latter can be drained away via a flexible pipe (not shown). 
         [0032]    The housing is formed with holes  22  and  23  and with circular lines of weakness defining disc shapes  21 ,  24 A and  24 B that can be pushed out to define holes as required. The shapes  21  are formed on opposite parallel vertical faces of the housing  4  in the region of the heat exchange chamber  24 . In a single module system just the shapes  24 A and  24 B are pushed out to allow entry of air to be cooled into chamber  24  exit of cooled air from it. Where additional modules are connected to the first module, the shapes  21  are removed on the contiguous faces of all adjoining modules so that the heat exchange chambers  24  of all modules are connected, while sharing a common entry and exit  24 A and  24 B provided by just one of them. 
         [0033]    It is necessary to heat the generator  11  to a temperature of about 230° C. to start the refrigeration cycle but, once started, it will continue to operate unless the temperature of the generator  11  drops to about 190° C. or below. Operation is as follows. 
         [0034]    Sunlight during the day heats the hot, lower, end of the heat pipe  8 . The pipe  8  contains water, which acts as a refrigerant. The resulting water vapour rises to the upper, relatively cold, end of the heat pipe, where it condenses, giving up its Is heat to the phase change material  10 . 
         [0035]    The temperature of the phase change material increases until it reaches its phase change temperature of 200° C. at which point it remains at that temperature whilst continuing to absorb heat from the heat pipe as it changes phase. When the phase change material has become entirely liquid, its temperature continues to rise again until it reaches 230° C., the start-up temperature of the refrigeration system. The refrigeration system then starts to operate and the temperature of the phase change material drops, say to 210° C., as the heat is drawn from it to drive the refrigeration system. 
         [0036]    The refrigeration cycle itself is entirely conventional in operating principles as follows. 
         [0037]    The generator  11  contains a strong solution of ammonia in water. Heat from the phase change material boils the solution, releasing bubbles of ammonia gas and resulting in weakening of the solution. The bubbles raise the weakened solution to the separator  13  by the action of the bubble pump  12 . 
         [0038]    In the separator  13 , the ammonia gas is separated from the weak ammonia solution and travels to the condenser  14  where heat is released to the air in duct  20  causing the ammonia gas to condense as liquid ammonia. The latter passes through trap  15  into the evaporator where it is exposed to hydrogen gas. The hydrogen environment lowers the vapour pressure of the liquid ammonia sufficiently to cause the ammonia to evaporate, extracting heat from air in the duct  24 . This produces cool, dehumidified air for air conditioning purposes and pure water which exits from port  24 C and can be collected for use. 
         [0039]    The ammonia gas and hydrogen mixture passes to the mixer  17  where the ammonia dissolves in the weakened solution from the separator  13 , producing a more concentrated solution which flows into the heat exchanger  18  where it loses its heat to air within the duct  20 . The concentrated solution then passes into the reservoir  19  and thence to the generator  11  whereupon the cycle is complete. 
         [0040]    When the power of the sun becomes insufficient to retain the phase change material above 200° C., the latter starts to solidify and the latent heat of fusion maintains the generator  11  at a sufficient temperature to sustain the refrigeration cycle. In this way the refrigeration mechanism can remain operational throughout the night or at least a sufficient part of it to ensure that cooling is maintained until the ambient temperature drops to an acceptable level. A larger volume of phase change material may also be provided in the space below the evaporator  16 . This phase change material will solidify when the system is providing cooling during the day but will melt at night, to provide further cooling at night. This can provide cooling for long periods. Indeed a small medicine refrigerator can store five days worth of cooling in this way. 
         [0041]      FIG. 2  shows how the various parts that have been described are installed in a building having a pitched roof  3 . From this drawing it can be seen that the solar collector  2  lies against the roof surface, on the outside of the building whilst the housings  4  and their contents are in the roof space isolated from the main living area of the building (i.e. the area to be cooled). A chimney  27  connects to the port  23  (or each of the ports where there are multiple modules) to provide improved draft of cooling air. 
         [0042]      FIG. 3  shows how the housing  4  is formed with parallel flat faces  4 A, a sloping edge  4 B arranged parallel to the tubes  2  and to the roof surface so that it can be mounted on the inner face of the roof; a short horizontal top edge  4 C formed with vent hole  23  and adapted to be connected to a chimney duct (not shown) and an open relatively long, bottom horizontal edge  2 D formed with vent hole  22 . The faces  4 A have gaskets  72  which provide a seal between adjoining units when they are connected together in the manner described below to give the required power depending on the installation. 
         [0043]      FIG. 4  shows a variation where the tubes  2  are angled so as to be perpendicular to the bottom faces  2 D of the modules to permit mounting on a wall.  FIG. 5  shows a modular construction comprising a stack of housings connected physically together, face to face by clips  28 . 
         [0044]    A system as shown in  FIG. 4  or  5  can readily be adapted for use as a refrigerator instead of an air conditioning system. In such an arrangement, one or more modules would be mounted on an outer surface (e.g. the top surface) of an insulated cabinet with pipes analogous to those shown at  25 A and  26 A on  FIG. 2  extending through that surface into the cabinet interior so as to circulate and cool air in the cabinet. In this arrangement it is envisaged that the cabinet would normally be located inside a building with the tubes  6  projecting through the outside wall and fixed on and parallel to the outside of the wall to collect solar heat. 
         [0045]    It is emphasised that the particular systems that have been described and , illustrated are just examples of an unlimited number of variations that are possible within the scope of the invention as defined by the accompanying claims.