Abstract:
The invention relates to an absorption air conditioner that comprises a desorber ( 100 ), a condenser, an evaporator and an absorber, wherein the absorbing fluid may consist of lithium bromide. The method comprises the following steps: calculating the concentration of the absorbing fluid solution at the outlet of the desorber ( 100 ); and comparing the calculated concentration with a predetermined critical value and, if the calculated concentration gets closer to the predetermined critical value, increasing the charge loss in the duct ( 20 ) connecting the desorber ( 100 ) to the condenser, which interrupts the condensation in the condenser and results in a pressure increase in the desorber that stops the desorption and in a concentration increase, the charge loss being on the other hand reduced for resuming the desorption when the calculated concentration deviates from the predetermined critical value. The invention can be used in automobiles and absorption air-conditioners.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the US national stage under 35 U.S.C. §371 of International Application No. PCT/FR2008/051562 which claims the priority of French application 0757841 filed on Sep. 25, 2007, the content of which (description, claims and drawings) is incorporated herein by reference. 
     BACKGROUND 
     This invention concerns a method of calculation and adjustment—also named “control process” in this text—of the absorbing fluid concentration, for example of lithium bromide, in an absorption air-conditioning device. 
     This invention also involves an absorption air-conditioning device for the implementation of the method. 
     Finally, this invention involves a vehicle, in particular an automotive vehicle, equipped with such an absorption air-conditioning device. 
     An absorption air-conditioning device consists diagrammatically of an element in which desorption takes place (denoted “desorber” in the following text), an absorber, a condenser and an evaporator. In order to operate, the desorber and absorber are filled with a mixture of at least two miscible substances formed by a coolant fluid and an absorbing fluid. This mixture is combined in the absorber, in which the absorption of the coolant fluid by the absorbing fluid takes place. The coolant fluid and the absorbing fluid have sufficiently different evaporation pressures so that, when the desorber is heated, the most volatile of the two, that is the coolant fluid, evaporates and changes into a liquid in the condenser. 
     The desorber receives heat, and this outside contribution permits the evaporation of the liquid coolant from the mixture. This coolant fluid is then condensed in the condenser by cooling. The liquid obtained is trapped and evaporated in the evaporator and thus produces the cold of the air-conditioning. The absorber allows the solution to fix the coolant fluid molecules and, in this way, to maintain a low pressure and, therefore, a low evaporation temperature. The solution/coolant fluid reaction is exothermic. The absorber solution, therefore, must be cooled so that it retains its absorbing power. 
     BRIEF SUMMARY 
     A first goal of this invention is to provide a method of calculating and adjusting the concentration of the solution, that means the concentration of absorbing fluid. This permits guaranteeing good control over the risk of crystallization of the aforesaid solution in the entire air conditioning circuit. 
     Another goal of this invention is to provide such a method, that is faster and as accurate as the known adjustment processes from the prior art. 
     Another goal of this invention is to provide such a method, that contributes a better reactivity to the air-conditioning device than the one offered by the existing technical solutions. 
     One goal of this invention is also to provide an absorption air-conditioning device for the implementation of such a method, in which the risk of crystallization of the absorbing fluid in the entire air-conditioning circuit is optimally managed. 
     Finally, it is also a goal of this invention to provide a vehicle, in particular an automotive vehicle, equipped with such an absorption air-conditioning device which can adjust the absorbing fluid concentration. 
     To reach these goals, this invention conceives of a new control method of the absorbing fluid concentration in an absorption air-conditioner by including a desorber, a condenser, an evaporator and an absorber. This new process is comprised of the following stages, taken in combination:
         the concentration of the absorbing fluid solution is calculated at the output of the desorber, and   the concentration calculated is compared to a predetermined critical value. If the calculated concentration approaches the predetermined critical value, the head loss in the duct connecting the desorber to the condenser is increased, thereby shutting down condensation in the condenser and increasing the pressure in the desorber. This causes desorption to stop and increases the concentration of the absorbing fluid solution. The head loss being decreased, on the other hand, restarts desorption, and the calculated concentration moves away from the predetermined critical value.       

     According to the preferred mode, the concentration of the absorbing fluid solution is calculated at the output of the desorber by measuring, on the one hand, the coolant vapor pressure in the desorber and simultaneously, on the other hand, the temperature of the absorbing fluid solution at the output of the desorber. 
     According to the equally preferred mode, the calculation of the concentration at the time t is obtained by using the concentration at the time t−1, and by calculating a corrector for concentration by determining the concentration variation between t−1 and t, the aforesaid calculation of the corrector uses the coolant pressure measurement values and solution temperature at time t. 
     The calculation of the concentration at the time t responds to the following formula: 
     
       
         
           
             
               X 
               t 
             
             = 
             
               
                 X 
                 
                   t 
                   - 
                   1 
                 
               
               - 
               
                 
                   f 
                   ⁡ 
                   
                     ( 
                     
                       X 
                       t 
                     
                     ) 
                   
                 
                 
                   
                     f 
                     ′ 
                   
                   ⁡ 
                   
                     ( 
                     
                       X 
                       t 
                     
                     ) 
                   
                 
               
             
           
         
       
     
     in which: 
     
       
         
           
             
               
                 f 
                 ⁡ 
                 
                   ( 
                   X 
                   ) 
                 
               
               = 
               
                 
                   
                     A 
                     ⁡ 
                     
                       ( 
                       X 
                       ) 
                     
                   
                   · 
                   
                     t 
                     e 
                   
                 
                 + 
                 
                   B 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
                 - 
                 
                   t 
                   s 
                 
               
             
             , 
             
               
 
             
             ⁢ 
             with 
           
         
       
       
         
           
             
               A 
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   A 
                   3 
                 
                 · 
                 
                   X 
                   3 
                 
               
               + 
               
                 
                   A 
                   2 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 
                   A 
                   1 
                 
                 · 
                 X 
               
               + 
               
                 A 
                 0 
               
             
           
         
       
       
         
           
             
               B 
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   B 
                   3 
                 
                 · 
                 
                   X 
                   3 
                 
               
               + 
               
                 
                   B 
                   2 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 
                   B 
                   1 
                 
                 · 
                 X 
               
               + 
               
                 B 
                 0 
               
             
           
         
       
       
         
           And 
         
       
       
         
           
             
               
                 f 
                 ′ 
               
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   
                     ⅆ 
                     
                       A 
                       ⁡ 
                       
                         ( 
                         X 
                         ) 
                       
                     
                   
                   
                     ⅆ 
                     X 
                   
                 
                 · 
                 
                   t 
                   e 
                 
               
               + 
               
                 
                   ⅆ 
                   
                     B 
                     ⁡ 
                     
                       ( 
                       X 
                       ) 
                     
                   
                 
                 
                   ⅆ 
                   X 
                 
               
             
           
         
       
       
         
           
             
               
                 ⅆ 
                 
                   A 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
               
               
                 ⅆ 
                 X 
               
             
             = 
             
               
                 3 
                 · 
                 
                   A 
                   3 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 2 
                 · 
                 
                   A 
                   2 
                 
                 · 
                 X 
               
               + 
               
                 A 
                 1 
               
             
           
         
       
       
         
           
             
               
                 ⅆ 
                 
                   B 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
               
               
                 ⅆ 
                 X 
               
             
             = 
             
               
                 3 
                 · 
                 
                   B 
                   3 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 2 
                 · 
                 
                   B 
                   2 
                 
                 · 
                 X 
               
               + 
               
                 B 
                 1 
               
             
           
         
       
     
     And A i , B i  (i going from 0 to 3) are the constants pertaining to the absorbing fluid used (lithium bromide, for example). 
     In a preferential manner, the head loss is increased or decreased in the duct connecting the desorber to the condenser by operating a valve, for example a butterfly valve, arranged inside the aforesaid duct. 
     By preference, but without restricting the object of this invention, the absorbing fluid is lithium bromide, and the constants A i , B i  (i going from 0 to 3) have the values determined experimentally and pertaining to this type of fluid. 
     The coolant fluid is, by preference, water. 
     This invention also provides an absorption air-conditioning device for the implementation of the method in conformity with what is described above in outline. This device includes, in a classic manner, a desorber, a condenser, an evaporator and an absorber. But, the desorber of this new device includes a pressure sensor for the measurement of the vapor pressure of the coolant of the aforesaid desorber and a temperature sensor for measuring the temperature of the absorbing fluid solution at the output of the desorber. Further, this new device includes a means to vary the head loss in the duct conducting the coolant fluid vapor to the condenser. 
     By preference, the means to vary the head loss in the duct leading the coolant fluid vapor to the condenser is a regulating valve, of the butterfly type. 
     According to the preferred embodiment, the desorber of the device includes a main heat exchange system of the plates type system, located over the tank of absorbing fluid solution, and a plate exchanger to reheat the solution going into the main thermal exchange system with the solution coming down from the solution tank. 
     In addition, an additional heating system of the solution, of the electrical resistance type, can bathe in the solution tank. 
     Finally, the invention supplies a vehicle, by preference an automotive vehicle, characterized in that it includes a absorption air-conditioning device of the type, conforming to the one described above in outline. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other goals, advantages and features of the invention shall appear in the description of a preferred mode of embodiment, unrestricted in the object and the scale of this patent application, accompanied by drawings in which: 
         FIG. 1  represents, in a diagrammatic manner, the operating principle and the constituent elements of an absorption air-conditioning device, 
         FIG. 2 , also in a diagrammatic manner, represents the desorber of the absorption air-conditioning device of  FIG. 1 . 
         FIG. 3  illustrates, in a diagrammatic manner, the general design principle of a desorber, and 
         FIG. 4  represents, in a diagrammatic manner, the general design principle of a desorber according to this invention, 
     
    
    
     DETAILED DESCRIPTION 
     In reference to the drawing of  FIG. 1 , the constituent elements and the operating principle of an absorption air-conditioning device are shown in schematically. It includes, in classic fashion, a desorber  100 , a condenser  200 , an evaporator  300  and an absorber  400 . The motive coolant liquid of the vehicle contributes (contribution illustrated diagrammatically by arrow A) the heat necessary for the separation of a coolant fluid, for example the water vapor, from an absorbing fluid or salt solution, for example a lithium bromide (LiBr) solution. 
     Water as vapor is then conducted by the piping  20  into the condenser  200  to be condensed by the cooling action of the outside air (cooling contribution illustrated diagrammatically by the arrow B). Water in liquid phase is conducted by the piping  10  into the evaporator  300 . The cold produced at the time of the evaporation is transmitted to the cabin of the vehicle (not represented), as illustrated diagrammatically by the arrow C. For this purpose, a pump  310  and a forced convection air cooler  320  are provided, that are joined to the evaporator  300  by the piping  11 ,  12  and  13 . The piping assembly  10  to  13  forms the water circuit in the liquid phase. The water vapor that comes out of the evaporator  300  is brought into the absorber  400  by the piping  21 . The solution is cooled by the outside air to absorb the water vapor (cooling contribution illustrated diagrammatically by the arrow D). For this purpose, a pump  410  and a radiator  420  are provided, that are connected to the absorber  400  by the piping  16 ,  17 ,  18  and  19 . The absorber  400  is connected to the desorber  100  by the piping  14 ,  15  and  16 . The piping assembly  14  to  19  forms the salt solution circuit. 
       FIG. 2  represents, in a very diagrammatic manner, the desorber  100 , with its input  14  and its output  15  for the salt solution, and its outlet piping  20  of the coolant vapor phase leading to the condenser  200 . 
     The concentration of the solution S at the output of the desorber  100  is the highest in the entire circuit of the air-conditioning device. 
     By concentration of the solution, designated X, one understands the ratio between the mass of absorbing fluid (lithium bromide, for example) and the total mass of the absorbing fluid and cooling fluid mixture of the two fluids. 
     The concentration of absorbing fluid is determined to depend on the two following physical measurements:
         the measurement of the coolant vapor pressure P in the desorber  100  by means of the pressure sensor  102 , and   the measurement of the temperature (t s ) of the solution S at the output of the desorber  100  by means of the temperature probe  101 .       

     Calculation of the Concentration 
     The concentration X is linked to the temperature of coolant (water) t e  and to the temperature of the solution t s  by the following relationship, designated R 1 : 
     
       
         
           
             
               t 
               e 
             
             = 
             
               
                 
                   t 
                   s 
                 
                 - 
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       0 
                     
                     3 
                   
                   ⁢ 
                   
                     
                       B 
                       i 
                     
                     · 
                     
                       X 
                       i 
                     
                   
                 
               
               
                 
                   ∑ 
                   
                     i 
                     = 
                     0 
                   
                   3 
                 
                 ⁢ 
                 
                   
                     A 
                     i 
                   
                   · 
                   
                     X 
                     i 
                   
                 
               
             
           
         
       
     
     In which, the constants have the following values: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
             
             
               
                   
                 A0 
                 −2.007550E+00 
                 B0 
                 1.249370E+02 
               
               
                   
                 A1 
                 1.697600E−01 
                 B1 
                 −7.712490E+00 
               
               
                   
                 A2 
                 3.133362E−03 
                 B2 
                 1.522860E−01 
               
               
                   
                 A3 
                 1.976680E−05 
                 B3 
                 7.950900E−04 
               
               
                   
               
             
          
         
       
     
     The coolant vapors extracted from the desorber  100  are in the saturated state. Consequently, it is possible to connect the measured pressure P to a coolant temperature t e . 
     We use, for example, the following formula: 
     
       
         
           
             
               log 
               ⁡ 
               
                 ( 
                 P 
                 ) 
               
             
             = 
             
               C 
               + 
               
                 D 
                 
                   
                     t 
                     e 
                   
                   + 
                   273.15 
                 
               
               + 
               
                 E 
                 
                   
                     ( 
                     
                       
                         t 
                         e 
                       
                       + 
                       273.15 
                     
                     ) 
                   
                   2 
                 
               
             
           
         
       
     
     With P in kPa (kilo Pascals) and t e  in ° C., we have the following relationship, designated R 2 : 
     
       
         
           
             
               t 
               e 
             
             = 
             
               
                 
                   
                     - 
                     D 
                   
                   + 
                   
                     
                       
                         D 
                         2 
                       
                       - 
                       
                         4 
                         · 
                         
                           ( 
                           
                             C 
                             - 
                             
                               log 
                               ⁡ 
                               
                                 ( 
                                 P 
                                 ) 
                               
                             
                           
                           ) 
                         
                         · 
                         E 
                       
                     
                   
                 
                 
                   2 
                   · 
                   
                     ( 
                     
                       C 
                       - 
                       
                         log 
                         ⁡ 
                         
                           ( 
                           P 
                           ) 
                         
                       
                     
                     ) 
                   
                 
               
               - 
               273.15 
             
           
         
       
     
     in which the constants have the following values: 
     
       
         
               
               
               
             
           
               
                   
               
             
             
               
                   
                 C 
                 7.05 
               
               
                   
                 D 
                 −1596.49 
               
               
                   
                 E 
                 −104095.5 
               
               
                   
               
             
          
         
       
     
     From the relationship R 1  stated previously, we draw: 
     
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       0 
                     
                     3 
                   
                   ⁢ 
                   
                     
                       t 
                       e 
                     
                     · 
                     
                       A 
                       i 
                     
                     · 
                     
                       X 
                       i 
                     
                   
                 
                 - 
                 
                   t 
                   s 
                 
                 + 
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       0 
                     
                     3 
                   
                   ⁢ 
                   
                     
                       B 
                       i 
                     
                     · 
                     
                       X 
                       i 
                     
                   
                 
               
               = 
               0 
             
           
         
       
       
         
           
             
                 
             
             ⁢ 
             
               
                 
                   
                     ∑ 
                     
                       i 
                       = 
                       0 
                     
                     3 
                   
                   ⁢ 
                   
                     
                       ( 
                       
                         
                           
                             t 
                             e 
                           
                           · 
                           
                             A 
                             i 
                           
                         
                         + 
                         
                           B 
                           i 
                         
                       
                       ) 
                     
                     · 
                     
                       X 
                       i 
                     
                   
                 
                 - 
                 
                   t 
                   s 
                 
               
               = 
               0 
             
           
         
       
       
         
           
             
               
                 
                   ( 
                   
                     
                       
                         t 
                         e 
                       
                       · 
                       
                         A 
                         3 
                       
                     
                     + 
                     
                       B 
                       3 
                     
                   
                   ) 
                 
                 · 
                 
                   X 
                   3 
                 
               
               + 
               
                 
                   ( 
                   
                     
                       
                         t 
                         e 
                       
                       · 
                       
                         A 
                         2 
                       
                     
                     + 
                     
                       B 
                       2 
                     
                   
                   ) 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 
                   ( 
                   
                     
                       
                         t 
                         e 
                       
                       · 
                       
                         A 
                         1 
                       
                     
                     + 
                     
                       B 
                       1 
                     
                   
                   ) 
                 
                 · 
                 X 
               
               + 
               
                 ( 
                 
                   
                     
                       t 
                       e 
                     
                     · 
                     
                       A 
                       0 
                     
                   
                   + 
                   
                     B 
                     0 
                   
                   - 
                   
                     t 
                     s 
                   
                 
                 ) 
               
             
             = 
             0 
           
         
       
     
     Solution of the Equation. 
     The temperature t e  is calculated using the pressure measurement and the equation designated R 2  stated previously. The temperature i s  is the temperature of the solution S at the output  15  of the desorber  100 . 
     The resolution of the equation R 1  normally takes place using an iterative method. In general, three iterations are required to converge on the solution sought. The interest of the method presented is to achieve only a single iteration by taking the starting concentration as determined at time t−1. 
     We have, therefore, only one equation to solve of the type:
 
 X   t   =f ( X   t−1   ,P,t   s ) or  X   t   =f ( X   t−1   ,t   e   ,t   s )
 
     If we use a Newton type formula, for example, we obtain a formula R 1  equivalent to: 
     
       
         
           
             
               f 
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   A 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
                 · 
                 
                   t 
                   e 
                 
               
               + 
               
                 B 
                 ⁡ 
                 
                   ( 
                   X 
                   ) 
                 
               
               - 
               
                 t 
                 s 
               
             
           
         
       
       
         
           With 
         
       
       
         
           
             
               A 
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   A 
                   3 
                 
                 · 
                 
                   X 
                   3 
                 
               
               + 
               
                 
                   A 
                   2 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 
                   A 
                   1 
                 
                 · 
                 X 
               
               + 
               
                 A 
                 0 
               
             
           
         
       
       
         
           
             
               B 
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   B 
                   3 
                 
                 · 
                 
                   X 
                   3 
                 
               
               + 
               
                 
                   B 
                   2 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 
                   B 
                   1 
                 
                 · 
                 X 
               
               + 
               
                 B 
                 0 
               
             
           
         
       
       
         
           And 
         
       
       
         
           
             
               
                 f 
                 ′ 
               
               ⁡ 
               
                 ( 
                 X 
                 ) 
               
             
             = 
             
               
                 
                   
                     ⅆ 
                     
                       A 
                       ⁡ 
                       
                         ( 
                         X 
                         ) 
                       
                     
                   
                   
                     ⅆ 
                     X 
                   
                 
                 · 
                 
                   t 
                   e 
                 
               
               + 
               
                 
                   ⅆ 
                   
                     B 
                     ⁡ 
                     
                       ( 
                       X 
                       ) 
                     
                   
                 
                 
                   ⅆ 
                   X 
                 
               
             
           
         
       
       
         
           
             
               
                 ⅆ 
                 
                   A 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
               
               
                 ⅆ 
                 X 
               
             
             = 
             
               
                 3 
                 · 
                 
                   A 
                   3 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 2 
                 · 
                 
                   A 
                   2 
                 
                 · 
                 X 
               
               + 
               
                 A 
                 1 
               
             
           
         
       
       
         
           
             
               
                 ⅆ 
                 
                   B 
                   ⁡ 
                   
                     ( 
                     X 
                     ) 
                   
                 
               
               
                 ⅆ 
                 X 
               
             
             = 
             
               
                 3 
                 · 
                 
                   B 
                   3 
                 
                 · 
                 
                   X 
                   2 
                 
               
               + 
               
                 2 
                 · 
                 
                   B 
                   2 
                 
                 · 
                 X 
               
               + 
               
                 B 
                 1 
               
             
           
         
       
     
     X t−1  is the concentration at the acquisition time t−1 
     
       
         
           
             
               X 
               t 
             
             = 
             
               
                 X 
                 
                   t 
                   - 
                   1 
                 
               
               - 
               
                 
                   f 
                   ⁡ 
                   
                     ( 
                     
                       X 
                       t 
                     
                     ) 
                   
                 
                 
                   
                     f 
                     ′ 
                   
                   ⁡ 
                   
                     ( 
                     
                       X 
                       t 
                     
                     ) 
                   
                 
               
             
           
         
       
     
     It should be noted that the calculation of f(X) and of f′(X) uses the concentration at time t−1 and the measurements of pressure P of the coolant and temperature t s  of the solution at time t. 
     In reality, only a concentration corrector is calculated which determines the variation of concentration according to new measured values of pressure and temperature. 
     The concentration of the solution is fixed at time t=0 as desired. For example, we fix X t=0 =60%. 
     The concentration of the solution at time t=0 can also be fixed according to the shut-off strategy used. For example, if one envisages, at the time of the last shut-down, a target concentration of 58%, the concentration at t=0 will be fixed at 58%. 
     Adjustment of the Concentration. 
     The calculation of the concentration, as described above, permits controlling the risk of crystallization of the salt solution (LiBr). 
     According to this invention, the adjustment of the concentration is based on the control of the condensation. 
     If the calculated concentration approaches a predetermined critical value, the head loss is increased in the duct  20  leading to the condenser  200  by activating, for example, a butterfly valve  103 , represented diagrammatically in  FIG. 2  at maximum closing position. The shut-down of the condensation causes an increase of the pressure in the desorber  100 . This pressure increase stops the desorption and increases the concentration. Conversely, when the concentration moves away from the critical zone, the head loss decreases to restart the desorption. 
     Design of the Desorber 
     In reference to the drawing of  FIG. 3 , the desorber  100  possesses a minimum reserve level below the referenced thermal exchange zone ZET. When the operating of the device is shut-down, the reserve of the desorber reached this minimum level. Thus, the thermal inertia of the heating system is decreased and the temperature rises throughout the entire circuit at the time of restarting the device. 
     The previously referenced regulating valve  103  of the desorber performance is used and situated in the piping  20  between the desorber  100  and the condenser  200 . 
     In a preferential manner, and in reference to  FIG. 4 , a compact desorber  100  is used, taking on three functions. 
     A plate exchanger  160  is incorporated within the desorber  100 . The exchanger  160  functions to heat the solution going into the main exchange zone ZET with the solution coming down from the solution tank  140 . The solution tank  140  is completely separated from the principal heating system by the coolant liquid of the motor. We can therefore free ourselves from a “by-pass” of the hot water required to permit a fast rise in the motor temperature. 
     The solution circuit is represented by the arrowed lines of the input  110  at the output  111  of the solution. 
     An additional heating system of the solution, of an electrical resistance type, not shown in  FIG. 4 , can bathe in the solution tank  140 . 
     The main exchange system ZET is a plate type system permitting sufficient compaction of the device. 
     Valve  103 , situated in the piping  20  leading to the condenser, permits controlling the concentration more quickly than by adjustment of the power contributed to the desorber  100 . Valve  103  also permits dispensing with an adjustment of the exchange capacity of the condenser  200 . 
     If the pressure in the condenser  200  is very low, there is a risk that the coolant cannot circulate from the condenser  200  to the coolant reserve of the absorber  400 . Effectively, on an automotive vehicle, an operating difference in level cannot be guaranteed in all cases compatible with a gravity flow between the condensation zone and the evaporation zone. With the solution of this invention, we can open the valve  103  briefly to increase the pressure in the condenser and, thereby, “push” the coolant into the absorber&#39;s circuit. 
     The invention described above presents many advantages, among which are the following advantages: 
     The calculation method of the absorbing solution concentration stated above is faster and as accurate as the concentration calculation methods of the solutions known from the prior art. 
     The calculation method of the invention permits managing the risk of crystallization of the absorbing fluid, the lithium bromide for example, in the entire air-conditioning circuit. 
     The adjustment of the concentration by the control of the condensation contributes a better reactivity to the system. Effectively, the technical solutions known from the prior art generally consist in reducing the energy contribution to the desorber by activation of a valve that regulates the incoming hot water flow. These solutions, because of the thermal inertia brought into play, are a lot less effective than the solution from the invention that proposes a shutdown of the condensation, which shutdown has an almost immediate effect. Further, for an automotive application, the performances of the front panel (and therefore the condenser) can vary widely. The installation of a regulating valve between the desorber and the condenser, in accordance with this invention, permits isolating the condenser from the rest of the air-conditioning circuit. 
     Of course, this invention is not limited to the mode of embodiment described above as an example; other modes of embodiment can be conceived by a person skilled in the art without leaving the scope and the range of this invention.