Abstract:
In known filter-drier cases for refrigerant circuits, the refrigerant flows through filter and drying means in a serial manner. During operation of the refrigerant circuit, this causes an undesirably large pressure drop. It is the task of the invention to provide an improved filter-drier arrangement ( 1, 1 ′) with a smaller pressure drop. For this purpose, it is proposed to design the filter-drier arrangement so that a part of the refrigerant flows in parallel through the filter ( 21, 43 ) and the drying means ( 17, 43 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Applicant hereby claims foreign priority benefits under U.S.C. § 119 from German Patent Application No. 10 2007 009 760.5 filed on Feb. 27, 2007, the contents of which are incorporated by reference herein. 
       FIELD OF THE INVENTION 
       [0002]    The invention concerns a filter-drier system for refrigerant circuits with at least one drier arrangement and at least one filter arrangement. Further, the invention concerns a refrigerant circuit with at least one drier arrangement and at least one filter arrangement for the refrigerant. 
       BACKGROUND OF THE INVENTION 
       [0003]    Refrigeration systems, air-conditioning systems and heat pumps are commonly used for very different applications. The presently most frequent design of such systems is the so-called compression refrigeration machine, in which a refrigerant is pumped in a closed circuit by a compressor. The compressor and an expansion member divide the circuit into an area with refrigerant under higher pressure and an area with refrigerant under lower pressure. In both areas is located a heat exchanger, which transfers heat from the refrigerant to the environment or heat from the environment to the refrigerant, respectively. 
         [0004]    The presently most common refrigerants are pentane, ammonia, R 134a and R 22. At present also the use of CO 2  as refrigerant (R 744) is tested. 
         [0005]    For a reliable operation of a compression refrigerant circuit over a long period it is also required that impurities are removed from the circulating refrigerant. Common impurities in this case are mechanical impurities, for example swarf, which partly originate from the manufacturing of the system or the system components, and partly originate from mechanically moving parts (for example the compressor) during operation. Such particles have to be filtered away, as otherwise they could obstruct the circuit or cause an increased wear of the components. In this connection, particularly the expansion member or the compressor, respectively, must be mentioned. To remove such mechanical impurities, filters are built into the refrigerant circuit. 
         [0006]    A further contamination of the refrigerant occurs by the releasing of substances, which diffuse into the refrigerant circuit. As traditional refrigerants are heavily hygroscopic; water turns out to be particularly problematic in this connection. Water dissolved in the refrigerant can reduce the performance and efficiency of the system and additionally cause internal corrosion. To avoid this, drying means are provided in the circuit, which absorb the water dissolved in the refrigerant. Usually zeolites and silicates are used as drying means. 
         [0007]    To ensure a sufficient effect of the filters and the drying means, filters and drying means are usually looped into the refrigerant circuit, so that they are passed in series, after each other, by the refrigerant. In the flow direction of the circulating refrigerant the filter arrangement is located before the drying means to avoid that the drying means is obstructed by the mechanical impurities. 
         [0008]    For space and cost reasons, however, a combined filter-drier unit has become popular, which is looped into the refrigerant circuit as a unit. Both the filter and the drying means are integrated in a common housing, the refrigerant also here flowing through the filter and the drying means serially. 
         [0009]    Such a filter-drier arrangement is, for example, described in U.S. Pat. No. 6,106,596. The arrangement shown here has an additional volume, so that the drier-collector unit also serves as refrigerant accumulator. The described unit has a housing, in which a filter-drier cartridge is inserted. It is ensured that both the inlet and the outlet connection of the housing are provided on the same side of the housing. To make this possible, the supplied refrigerant flows through a tube into a lower area of the tank, where the refrigerant is deflected and changes its flow direction. The inlet tube extends through a central opening of the circular filter-drier cartridge. After the deflection, the refrigerant first flows through a filter and then through a granulated drying means, both filter and drying means being located in a case arrangement. Subsequently, a further hollow is provided that serves as accumulator. The refrigerant flows serially, first through the filter area and subsequently through the drying area of the filter-drier cartridge. 
         [0010]    U.S. Pat. No. 5,440,898 describes a further filter-drier unit. Here, the drying means is adopted in the cylindrical housing as a cylindrical member. A centrically arranged, through recess is provided in the centre of the cylindrical drying means member, so that the drying means member ends up being a hollow cylinder with increased wall strength. On the inlet side of filter-drier unit a filter arrangement is fixed on the front side of the drying means member. Housing, filter arrangement and drying means member are made to be fluid-tight in relation to each other, so that the refrigerant is forced to pass through the filter to reach the central opening of the drying means hollow cylinder. Further, on the outlet side of the filter-drier unit is located a closing element that closes the central through-opening of the drying means member is a likewise fluid-tight manner. With this design of the filter-drier unit the refrigerant flows serially through firstly the filter and subsequently the drying means, before the refrigerant leaves the filter-drier unit again. 
         [0011]    A major problem with such filter-drier units is to combine a good filtering and drying effect, a small pressure drop of the circulating refrigerant during operation of the refrigerant circuit, low costs and the smallest possible dimensions of the filter-drier unit. 
         [0012]    If, for example, an arrangement with small dimensions is chosen, the surface, through which the refrigerant can pass the drier unit, is correspondingly small, so that a high flow resistance occurs. During operation of the refrigerant circuit this causes a high pressure drop of the refrigerant in the area of the filter-drier unit. If, on the other hand, it is endeavored to minimise the pressure drop, the passage surface for the refrigerant through the drier unit must be chosen to be correspondingly large. This causes correspondingly large dimensions of the filter-drier unit and correspondingly high costs. 
       SUMMARY OF THE INVENTION 
       [0013]    The invention is based on the task of providing an improved filter-drier arrangement. 
         [0014]    Further, the task of the invention is to provide an improved refrigerant circuit. 
         [0015]    With a filter-drier arrangement for refrigerant circuits having at least one drier arrangement and at least one filter arrangement, it is proposed to provide at least one short-circuiting path extending through the filter arrangement, said path bypassing the drier arrangement and connecting an inlet connection and an outlet connection of the filter-drier arrangement. In other words, the flow runs at least partially in parallel through the filter arrangement and the drier arrangement. A part of the refrigerant flows through the filter arrangement without necessarily having to flow through the drier arrangement. On the other hand, it is also possible that a part of the refrigerant only flows through the drier arrangement, without flowing through the filter arrangement. However, it is also possible that a (further) part of the refrigerant flows through both the filter arrangement and the drier arrangement. In this connection, please note that traditional drier arrangements also have a certain filtering effect. Additionally to the “normal” filter arrangement, it is also possible to provide an additional filter arrangement in connection with the drier arrangement. The provided additional filter arrangement or the drier arrangement, respectively, can have a filter quality that deviates from that of the “normal” filter arrangement. 
         [0016]    The proposed design is based on the surprising recognition that the drying effect of the drier arrangement does usually not, or at least only to a small extent, depend on whether the total amount of refrigerant flows through the drier arrangement, whether only parts of the refrigerant flow through the drier arrangement, or whether the refrigerant only flows past a surface of the drier arrangement. It has turned out that with a typical refrigerant circuit the time constant of the absorption process is in the range of days, also when the whole refrigerant flow passes through the drier arrangement. With such time constants, the proposed arrangement only increases the time constant of the absorption process to a small extent. To have the smallest possible reduction of the drying effect, it is of course expedient, depending on the application concerned, to let a suitably large amount of the refrigerant flow through the drier arrangement, or to select a corresponding size of the drier arrangement surface that is passed by the refrigerant flow. 
         [0017]    On the other hand, the proposed filter-drier arrangement can under certain circumstances considerably reduce the flow resistance, to which the passing refrigerant flow is exposed. This again causes that, compared to the known filter-drier arrangements; the pressure drop can be considerably reduced. This is possible, even though the filter-drier arrangement does not, or at least to a reduced extent, have to be enlarged. 
         [0018]    It is possible for the drier arrangement and the filter arrangement of the filter-drier arrangement to be at least partly placed in different housings, if this should, for example, be required for space reasons. 
         [0019]    It is, however, preferred to place the drier arrangement and the filter arrangement in a common housing. In this case a particularly compact design can be realised. Also, fewer connecting spots with piping components or other components of the refrigerant circuit will be needed, which can reduce the mounting costs and improve the tightness of the whole arrangement. Also a replacement of the filter-drier arrangement will be simpler. 
         [0020]    It is advantageous that the short-circuiting path extends adjacent to at least one surface of the drier arrangement. In this case, also the amount of refrigerant only passing through the filter arrangement can experience a certain drying. The effect can be increased, if the surface of the drier arrangement that is passed by the refrigerant, and/or the dwell time of the refrigerant in the area of this surface are selected to be relatively large in relation to the fluid flow passing this surface. 
         [0021]    Further, it is advantageous, if the drier arrangement is made to be cylindrical. As the currently used drier arrangements are typically cylindrical, a drop-in solution can thus be realised. Further, a particularly compact design occurs, and under certain circumstances advantages in manufacturing and during operation of the drier arrangement may occur. 
         [0022]    It is particularly advantageous, if the drier arrangement has a through, central recess. The refrigerant can then flow through the drier arrangement from the inside to the outside (or vice versa), so that with a relatively simple design a large surface can be provided, with which the refrigerant can get in contact or which the refrigerant can penetrate to get into the drier arrangement. Thus, the resulting pressure drop of the refrigerant flowing through the filter-drier arrangement can be reduced again. 
         [0023]    In this connection it may prove to be expedient, if the cross-section of the central recess tapers, particularly if it tapers conically. In this connection, a tapering particularly means a monotonous or strictly monotonous reduction of the cross-section. The change may be constant or stepwise. For example, a kind of funnel shaped central recess may be provided in the drier arrangement. With the tapering of the central recess the parts of the refrigerant flow passing through the filter arrangement can be taken into account. Alternatively or additionally, the tapering recess can also cause that the speed of the refrigerant flow in the central recess increases in the direction of the tapering. For example in the case, where a filter arrangement is provided at the end of the central recess, the larger speed may cause that the filter arrangement is cleaned of impurities by the incoming fluid jet. Under certain circumstances, the higher speed can also improve the passage of the refrigerant through the filter arrangement. It is also possible that the central recess only tapers in a partial area. 
         [0024]    If the drier arrangement comprises an inherently stable material, a particularly simple design of the filter arrangement, and thus of the complete filter-drier arrangement, can be supported. In this case, for example, a supporting structure and/or a structure enclosing the drying material, which would, for example, be required for a granulate-like drying material, can be avoided. Of course, it can still be imagined to make at least parts of the drier arrangement from a granulate-like drying material. 
         [0025]    A particularly favourable design occurs, if the filter arrangement is located in the area of the outlet connection and touches particularly the drier arrangement. With such a design a particularly compact filter-drier arrangement can be realised. Further, the pressure drop caused by the filter arrangement can be used to form a pressure difference between the inlet surface and the outlet surface of a drier arrangement, so that a part of the refrigerant flowing through the filter-drier arrangement flows through the drier arrangement. 
         [0026]    A further favourable embodiment occurs, if the filter arrangement is made as a resilient membrane, and is particularly made of polyester. When made as a resilient membrane, the filter arrangement can be deformed during operation because of the pressure difference occurring at the membrane. The deformation may cause a slight increase of the pore size of the filter, so that the pore size of the filter arrangement can increase in connection with an increased refrigerant flow, meaning that the pressure difference occurring at the filter arrangement must not increase excessively. 
         [0027]    It is advantageous if the housing of the filter arrangement has a hollow in the outlet side next to the filter arrangement. In this way, the fluid leaving the filter arrangement and, under certain circumstances, also the refrigerant part having passed the drier arrangement can be gathered and/or calmed, and subsequently led to the outlet of the filter-drier arrangement. Particularly in the case of a resilient filter membrane, the proposed embodiment can also provide a correspondingly dimensioned chamber, into which the filter membrane can move. With correspondingly large dimensions of the hollow, also an accumulator function is possible. 
         [0028]    A particularly advantageous embodiment occurs, if the size, the fixing and the resiliency of the filter arrangement are chosen so that, in connection with a flow of refrigerant through the filter arrangement, the filter arrangement is resiliently deformed in such a manner that at least one cavity is formed between the filter arrangement and an adjacent supporting surface. In this way, the arrangement can be designed so that during the flow through the filter-drier arrangement a refrigerant flow is generated, of which a part of the refrigerant flows into the cavity, that is, into a hollow. The impurities taken along by the refrigerant are thus forced into the formed cavity. The cavity can thus act as pick-up for the impurities trapped by the filter arrangement. When, after turning off the system, the filter arrangement resiliently reassumes its shape, the impurities gathered in the cavities can be retained. The exposed area of the filter arrangement can thus be kept free of impurities, so that a particularly low pressure drop of the filter-drier arrangement can be supported. 
         [0029]    Further, a refrigerant circuit is proposed, with at least one drier arrangement and at least one filter arrangement for the refrigerant circulating in the refrigerant circuit, in which at least a part of the refrigerant flows in parallel through the filter arrangement and the drier arrangement. A refrigerant circuit with this embodiment has the advantages already mentioned in an analogue form. 
         [0030]    It is particularly advantageous, if for the refrigerant circuit a filter-drier arrangement is chosen, which has at least one feature according to the possible designs mentioned above. Also here, the advantages already described appear in an analogue form. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    In the following the invention is described in detail on the basis of a preferred embodiment with reference to the enclosed drawings, showing: 
           [0032]      FIG. 1  shows a filter-drier unit according to a first embodiment of the invention, 
           [0033]      FIG. 2  shows a filter-drier unit according to a second embodiment of the invention, 
           [0034]      FIG. 3  shows the filter area of a filter-drier unit during operation, 
           [0035]      FIG. 4  shows a flow simulation of a filter-drier unit, 
           [0036]      FIG. 5  shows the speed distribution of a filter-drier unit, 
           [0037]      FIG. 6   a ,  6   b  shows the water absorption capacity and the water absorption speed of different filter-drier units, and 
           [0038]      FIG. 7   a ,  7   b  is a schematic view of refrigerant circuits according to a third and a fourth embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0039]      FIG. 1  shows a first embodiment of a combined filter-drier case that can, for example, be used for the refrigerant circuit of vehicle air-conditioning systems or domestic refrigeration or freezing appliances. In the embodiment shown in  FIG. 1 , the housing is made of two identical, cup-shaped housing parts  3 ,  4 . One end of each of the two housing halves  3 ,  4  has a projection  5 ,  6 . The projection  5 ,  6  enables a simple fluid-tight connection with the respective other housing part  3 ,  4 . 
         [0040]    At the respective other end of each housing part  3 ,  4 , facing the projection  5 ,  6 , a tub shaped housing bottom  7 ,  8  is provided. In the centre of each housing bottom  7 ,  8  a circular recess  15 ,  16  is provided, into which a connection tube  13 ,  14  is inserted and connected in a fluid-tight manner with the housing bottom  7 ,  8 . Between the housing bottom  7 ,  8  and the cylindrically shaped cup area  11 ,  12  of the respective housing part  3 ,  4  is provided a ring-shaped, circumferential support  9 ,  10 . These supports  9 ,  10  serve as supports for the inner components of the filter-drier case  1  adopted in the housing  2 . 
         [0041]    Inside the housing  2  of the filter-drier case  1  is located a drying means  17 . The outer contour of the drying means  17  is adapted to the design of the housing  2  to fill the largest possible share of the inner volume of the housing  2  with a drying means. The volume required by the filter-drier case  1  is thus optimally utilised. In the embodiment concerned the drying means  17  thus have a cylindrical outer contour. Further, a projecting area  18  of the drying means  17  can be seen in  FIG. 1 , said area  18  extending somewhat into the tub shaped housing bottom  7  of the left housing part  3  shown in the drawing, so that also this volume area is utilised. A conically tapering recess  19  is provided in the centre of the drying means member  17 . Merely in an end area  20  of the recess  19 , which is immediately adjacent to the filter membrane  21 , the cross-section of the recess remains the same or increases slightly. In the present example, the recess  19  and its end area  20  together with the corresponding area of the filter membrane  21  form the short-circuiting path that connects the fluid inlet  13  and the fluid outlet  14  by passing the drying means  17 . 
         [0042]    At the inlet side front end  22  (shown to the left of  FIG. 1 ) the drying means member  17  has, between its main area  26  and its projecting area  18 , a support  24 . Between the support  24  of the drying means member  17  and the support  9  of the housing part  3  shown to the left of the drawing is provided a wave spring  25 . This wave spring  25  pushes the drying means member  17  towards the other housing half  4 , where the facing, outlet side front end  23  of the drying means member  17  is pressed against the annular support  10  of the outlet side housing part  4 . Thus, the drying means member  17  is firmly supported in the housing  2  of the filter-drier case  1 . Further, the preloading of the drying means member  17  caused by the wave spring  25  in connection with the filter membrane  21  ensures a fluid-tight sealing between the drying means member  17  and the housing  2  at the outlet side front end  23 . During operation a refrigerant pressure difference occurs between the inlet side area  13  and the outlet side area  14 , said difference improving the sealing effect. 
         [0043]    In the present example, the filter membrane  21  is made of a polyester material with the commercial name of Feltmat. However, it can also be made of other materials, for example fibre glass or the like. The filter membrane  21  is resilient, so that it deforms resiliently on the occurrence of a pressure difference between the fluid inlet  13  and the fluid outlet  14 , as shown in  FIG. 3 . The pressure difference between the fluid inlet  13  and the fluid outlet  14  is bound to occur, when during operation of the refrigerant circuit refrigerant flows through the filter-drier case  1 . The filter membrane  21  surrounds the outlet side front end  23  as well as a part  27  of the outside of the drying means member  17  in a bowl-like manner. In this part  27  of the outside of the drying means member  17  as well as in the area of the support  10  of the outlet side housing part  4  of the filter-drier case  1  the filter membrane  21  acts as sealing means for the refrigerant. 
         [0044]    In the present embodiment example the drying means member  17  is made of an aluminium silicate that is reinforced by fibres and a resin. The composition has been chosen so that the drying means member  17  is self-supporting, meaning that no separate housing or support means is required. 
         [0045]    Due to the through, central recess  19  in the drying means member  17 , the drying means member has, compared with other drying means members having no or a smaller internal recess, with the same dimensions a smaller drying means volume. Preferably, however, the outer dimension of the drying means member is increased so that the resulting drying means volume of the drying means member  17  corresponds to the drying means volume of known filter-drier units. 
         [0046]    During operation of the filter-drier case  1  shown in  FIG. 1 , the picture shown in  FIG. 3  occurs. For reasons of clarity,  FIG. 3  merely shows an enlarged view of the outlet side  14  area of the filter-drier case  1 . In  FIG. 3  the refrigerant flow is shown schematically by means of arrows. The refrigerant takes along impurities  28 , which have to be removed by the filter  21 . Due to the flow of refrigerant passing the filter-drier case  1 , a pressure difference occurs between the fluid inlet  13  and the fluid outlet  14 , as both the drying means member  17  and the filter membrane  21  expose the flowing refrigerant to a flow resistance. Said pressure difference causes a deformation of the centre of the resilient fibre membrane  21 , typically by about 1 mm, which gives rise to cavities  29  between the filter membrane  21  and the outlet side front end  23  of the drying means member  17 . The flow resistance of the filter membrane  21  is usually clearly smaller than the flow resistance of the drying means member  17 . For this reason, the amount of refrigerant flowing through the central recess  19  of the drying means member  17  and its end area  20  is clearly larger than the amount of refrigerant passing through the drying means member  17 . This is shown in  FIG. 3  by different numbers of arrows. Further, in the area of the transition edge  30  between the end area  20  of the recess  19  provided in the drying means member  17  and the cavities  29 , a flow component occurs into the cavities  29 . For reasons of space, this flow component is not shown in  FIG. 3 . The flow causes a movement of the impurities  28  into the cavities. Thus, the cavities  29  can serve as collecting area for the impurities. If, on turning off the refrigerant circuit, the filter membrane  21  returns to its starting position, the impurities  28  in the cavity area  29  will be jammed between the filter membrane  21  and the outlet side front end  23  of the drying means member  17 . 
         [0047]    As, in the filter-drier case  1  shown in the  FIGS. 1 and 3 , a part of the refrigerant flows through the filter  21  without having to pass through the drying means member  17 , a clearly smaller flow resistance for the refrigerant occurs for the complete filter-drier case  1 . Due to the design with the resilient filter membrane  21 , in which the filter membrane  21  lifts off from the outlet side front end  23  of the drying means member  17  during operation of the refrigerant circuit, substantially the whole cross-section of the housing  2  is available as filter cross-section, which further reduces the flow resistance of the filter-drier case  1  during operation. 
         [0048]    The refrigerant flowing through the central recess  19  of the drying means member  17  still flows past the surface  46  of the recess  19  and thus experiences a certain degree of drying. 
         [0049]    The flow conditions during operation of the filter-drier case  1  of  FIG. 1  are shown schematically in  FIG. 3 , and in  FIGS. 4 and 5  they are shown again in a quantitative view.  FIG. 4  shows a numerical flow simulation, whereas  FIG. 5  shows the speed distribution of the refrigerant flowing through the filter-drier case  1 . 
         [0050]    Even though, in the filter-drier case  1  shown in  FIG. 1  or  3 , a large part of the refrigerant does not flow though the drying means member  17 , the drying performance of the filter-drier case  1  is surprisingly approximately as good as that of filter-drier units according to the state of the art. This is clearly seen from the  FIGS. 6   a  and  6   b . Here, type A is a known filter-drier case, whereas type B corresponds to a filter-drier case  1  as shown in  FIG. 1 . To enable a comparison of data, the same mass of drying means has been chosen for both types. 
         [0051]    In  FIG. 6   a  the total water absorption capacity of the drying means (ordinate) in relation to the relative humidity of the refrigerant (abscissa) is shown in logarithmic units. In the present case, R22 was used as refrigerant. As can be seen from the graphic, the difference, if any, between the two curves is marginal. 
         [0052]    Astonishingly, also the speed, at which the water is absorbed, is only minimally smaller in the design shown in  FIG. 1  than it is with traditional filter-drier cases. This is shown in  FIG. 6   b , in which the humidity of the drying means (ordinate) is shown in relation to the time (abscissa). 
         [0053]      FIG. 2  shows a filter-drier case  1 ′, which is slightly changed in relation to  FIG. 1 . The basic design of the filter-drier case  1 ′ shown in  FIG. 2 , however, corresponds to the design of the filter-drier case  1  shown in  FIG. 1 . Similar components therefore have the same reference numbers. 
         [0054]    In the filter-drier case  1 ′ shown in  FIG. 2 , the drying means member  17  has a large outer dimension. At the same time, the size of the conically tapering central recess  19  inside the drying means member  17  has been enlarged. The dimensioning of the drying means member  17  and the recess  19  therein has been chosen so that the overall mass of drying means is the same as in the drying means member  17  shown in  FIG. 1 . Of course, also the size of the housing  2 ′ has been adapted accordingly. 
         [0055]    A further difference is that the housing  2 ′ of the filter-drier case  1 ′ shown in  FIG. 2  is made of three parts  31 ,  32 ,  33 . The housing  2 ′ consists of an inlet side, first housing part  31 , an outlet side, second housing part  33  and an intermediately arranged, cylindrical housing sleeve  32 . The first housing part  31  and the housing sleeve  32  are in contact with each other in an overlapping area  34  and, for example, connected to each other by soldering. The same applies for the overlapping area  35  between the second housing part  33  and the cylindrical housing sleeve  32 . 
         [0056]    Also in the embodiment of a filter-drier case  1  shown in  FIG. 2  the first housing part  31  and the second housing part  33  are made to be identical. The housing parts  31 ,  33  substantially comprise the cup-shaped housing bottoms  7 ,  8 , which form the collecting chambers  15 ,  16 , as well as the supports  9 ,  10  for the drying means member  17 . For the main length of the filter-drier case  1 ′, however, as opposed to the filter-drier case  1  shown in  FIG. 1 , a separate housing sleeve  32  is provided. Particularly in connection with large filter-drier cases  1 ′, the embodiment according to  FIG. 2  may have advantages for the production. Also different lengths of the filter-drier case  1 ′ can more easily be realised, as, in spite of different lengths of the filter-drier case  1 ′, the two outer housing parts  31 ,  33  can be used in the identical shape. 
         [0057]      FIG. 7   a  shows a schematically simplified view of a refrigerant circuit  36 . The refrigerant circuit  36  has a compressor  37 . The compressor pumps the refrigerant in the refrigeration circuit  36  through the refrigerant tubes  38 . Further shown is a condenser  39  (in super critical refrigerant circuits accordingly a gas cooler), via which the refrigerant compressed in the compressor  37  can emit heat to the environment. Subsequently, the refrigerant flows through an expansion member  40 , which reduces the pressure so that the refrigerant is cooled. For example, fixed orifice tubes or expansion valves known from the state of the art can be used as expansion member  40 . Then the refrigerant cooled by the expansion flows through the evaporator  41 , where the refrigerant assumes heat from the environment, thus cooling the environment. Before the refrigerant enters the compressor  37  again, it flows through the filter-drier case  1 , for example of the type shown in  FIG. 1 . However, in this connection also other embodiments are possible. 
         [0058]      FIG. 7   b  shows a refrigerant circuit  36 ′ that is slightly modified in relation to  FIG. 7   a . Same components again have the same reference numbers. Also here the refrigerant is pumped through the circuit by a compressor  37 . After compression in the compressor  37 , the refrigerant, like in the refrigerant circuit  36  shown in  FIG. 7   a , flows through a condenser (gas cooler)  39 , an expansion member  40  and an evaporator  41 . However, in the refrigerant circuit  36 ′ according to  FIG. 7   b , the refrigerant tube branches off into two refrigerant branches  42 ,  44  extending in parallel. The first refrigerant branch  42  flows through a pure filter case  43 , whereas the second refrigerant branch  44  leads to a pure drying means case  45 . Also in the refrigerant circuit  36 ′ shown in  FIG. 7   b  a small flow of refrigerant through the drying means case  45  is ensured, as inevitably the filter case  43  generates a flow resistance against the passing refrigerant, so that a pressure difference occurs between the inlet and the outlet of the filter case  43 , said pressure difference also ruling between the inlet and the outlet of the drying means case  45 . 
         [0059]    While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present invention.