Abstract:
A high-efficiency, enhanced, generator-absorber heat exchange (EnGAX) cycle, particularly useful in gas-fired, air-cooled absorption heat pumps, increases the heat output of the absorber in the temperature overlap range with the generator to equal the heat usable by the generator. This is accomplished by establishing a solution pathway from a portion of the absorber in the temperature overlap region to a portion of the generator in order to increase solution flow in the high temperature regions of the absorber and generator. Further improvements in cycle efficiency are obtainable by increasing the operating pressure of the absorber.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to refrigeration and heat pump equipment and particularly to an absorption refrigeration cycle of the generator-absorber-heat-exchange type. The invention is especially adapted for use in gas-fired, absorption heat pumps. The present invention is a continuation-in-part of application Ser. No. 07/668,198, filed on Mar. 12, 1991, now abandoned. The present invention was developed with support from the Federal Government and as such, the Government has certain rights in the invention. 
    
    
     The potential energy saving benefits of heat activated heat pumps for medium temperature heating and cooling functions, including space heating and cooling, have been known. For example, the air conditioning of residential and commercial structures is a large user of electrical energy. The natural-gas-fired heat pump has the ability to slow the requirement for the addition of electrical generating capacity by supplanting such electrically-operated systems. In addition, an alternative is provided to the use of CFC&#39;s as a working fluid, which CFC&#39;s are considered to be harmful to the environment. Furthermore, in its heating made, the absorption heat pump has the potential of reducing the gas usage to half that of a state-of-the-art gas furnace and to match the primary energy-efficiency of a good electric air conditioner in the cooling mode. 
     In order to realize its potential, for general application across the United States, it has been determined that an air-to-air residential and small commercial absorption heat pump system should operate at a coefficient of performance (COP) at ARI rating conditions approaching 1.8 in the heating mode and 0.9 in the cooling mode, based on gas-firing at flue efficiencies of 90 percent or greater and using the high heating value of the gas. It is additionally deemed desirable for such system to be capable of meeting the total heat requirements of a building without supplemental heat, under a full range of operating conditions, including outside ambient air temperatures of as low as -10° F. 
     While water-cooled absorption cycles used in large scale industrial and commercial applications have been devised that meet or exceed these cooling COP&#39;s, such water-cooled cycles and their fluids do not meet those COP&#39;s in air-to-air applications, nor are they suited for the low outdoor temperatures. In order to be commercially successful in the residential and small commercial applications, a natural-gas-fired heat pump must be an air-to-air system and free from undue complexities and have a predicted lifetime of 20 years or greater. Furthermore, all applicable codes and standards must be met. 
     The present inventor has evaluated known absorption cycles and has determined that one cycle having the potential for meeting the above requirements is the generator-absorber heat-exchange (GAX) cycle. The GAX cycle is a further refinement on the absorber heat-exchange (AHE) cycle, which uses absorber heat to warm the strong solution of absorbent and refrigerant and utilizes the sensible heat of the weak solution as heat input to the generator. Such AHE cycles have been used in ammonia/water air conditioner production units for at least twenty-five years and have been found to have gas-fired COP&#39;s of up to 0.5 at ARI rating conditions. This cycle has also been used in experimental gas-heat pumps to produce heating COP&#39;s of 1.25. In the AHE cycle, the recuperation of absorber heat is limited by the sensible heat of the strong solution. Similarly, recuperation heating of the generator is limited to the sensible heat in the weak solution leaving the generator. 
     The GAX cycle adds to the recuperation gains of the AHE cycle by increasing the absorber and generator temperature ranges so that the two temperature ranges overlap. Under these conditions, absorption heat is transferred to the generator at the overlap temperatures using various means such as a separate heat transfer loop. This heat transfer can occur whenever the weak solution concentration is decreased to the point that the temperature of the hot end of the absorber is above that of the cool end of the generator. All of the heat of absorption in the overlap range can be utilized by the generator, except for heat-transfer temperature differences. By increasing the extent of overlap between the temperature ranges of the absorber and generator, improved system COP&#39;s may be obtained. Therefore, the need exists for ways to increase the extent of overlap between the temperature range of the generator and the temperature range of the absorber, and to increase the heat of absorption in the absorber overlap range. 
     Hybrid systems have been proposed in which absorption systems are augmented with mechanical compressors. However, such systems merely reflect combinations of alternate forms of energy inputs to the system, without greatly altering the overall COP of the system. One such system is proposed in U.S. Pat. No. 5,024,063 to Erickson which discloses the use of a mechanical compressor on the vapor outlet of an absorption system generator to elevate the temperature at which thermal energy may be transferred from the condenser to the surroundings. 
     In the known prior system, a heat pump 10 operated on the generator-absorber heat-exchange (GAX) principle provides low-pressure refrigerant vapor leaving evaporator 12 through conduit 14 to enter absorber 16 where it is absorbed in a weak solution of absorbent and refrigerant, such as ammonia and water (FIG. 1). This process takes place at temperatures above that of the surroundings, generating heat. A lower temperature portion of that heat is transferred to a coolant (for example a water-antifreeze mixture) circulating during this process in a heat exchanger 18. The strong absorbent/refrigerant solution is then transferred by a solution pump 20 to the generator 22, where a higher pressure is maintained. Refrigerant vapor is driven from the solution in generator 22 as a result of heat transfer from a high temperature source 24, which is assisted by the additions of heat transfer fins 45. The refrigerant vapor is expelled from generator 22 through conduit 26 to a condenser 28 where it is condensed and fed through an expansion valve 30 and expanded in evaporator 12. The weak solution is returned through conduit 32 to absorber 16. At very low outdoor temperatures heat may be transferred in a liquid heat exchanger (not shown) between the strong solution conduit 36 and the weak solution conduit 38. In accordance with the AHE cycle principle, absorber heat is also used to warm the strong solution at 40, and the sensible heat of the weak solution is provided as a heat input to a section of the generator at lower temperature 42. In addition, as disclosed in detail in U.S. Pat. No. 4,127,010 issued to the present inventor, entitled HEAT ACTIVATED HEAT PUMP METHOD AND APPARATUS, the disclosure of which is hereby incorporated herein by reference, additional efficiencies may be gained by exchanging heat between the strong solution conduit 36 and the refrigerant/absorbant vapor mixture at 44 and by providing a pre-cooler 46 to transfer condensate heat to the refrigerant vapor and excess liquid. 
     In the case of the generator-absorber heat transfer function, illustrated in FIG. 1, the high temperature heat transfer is performed by a GAX heat transfer means 48, including, for example, a pair of heat exchange coils 50 and 52 and a pump 54 to circulate heat-transfer fluid such as pressurized water. Because the vertical temperature gradients of absorber 16 and generator 22 are reversed, it is necessary to cross-connect the lines between coils 50 and 52, as illustrated in FIG. 1. The transfer of GAX heat from the absorber to the generator can be accomplished in various ways. The transfer should be provided over the full overlap temperature range. The principle of the GAX cycle is illustrated in the pressure-temperature-composition diagram of FIG. 2 in which line C-G represents the low temperature portion of the absorber, line G-F the high temperature portion of the absorber, line D-I the low temperature portion of the generator and line I-E the high temperature portion of the generator. Points A and B represent the condenser and evaporator, respectively. The line from C to D represents the strong solution pathway and line from E to F the weak solution pathway. The temperature overlap between the G to F region of the absorber and the D to I region of the generator provides the generator-absorber heat-exchange as illustrated by the arrows, indicating heat transfer. 
     SUMMARY OF THE INVENTION 
     The purpose of the present invention is to provide a new high-efficiency, enhanced, GAX cycle (EnGAX) which achieves a significant improvement in COP with respect to the known GAX cycle. This is accomplished by increasing the extent of overlap of operating temperature ranges in an absorber and generator of a GAX absorption system and by increasing the absorption in the overlap area of the absorber. The invention may be embodied in an absorption heat pump including a generator, a condenser, an evaporator, an absorber, a strong solution pathway from a low temperature portion of the absorber to the generator, and a weak solution pathway from the generator to a high-temperature portion of the absorber. A refrigerant pathway is provided from the generator to the condenser, from the condenser to the evaporator and from the evaporator to the absorber. A GAX heat transfer pathway is provided between regions of the absorber and generator having overlapping temperatures. 
     According to one aspect of the invention, the temperature range overlap may be increased by elevating the absorber operating pressure. This may be accomplished by locating a vapor compressor in the vapor stream between the evaporator and the absorber, to increase the operating pressure of the absorber. According to another aspect of the invention, means are provided for increasing the flow of absorbent/refrigerant solution in the temperature overlap region of the absorber and in a portion of the generator in order to increase the absorber heat output in the overlap range. This enhanced cycle is capable of enlarging the overlap range and of providing all of the heat that the generator can utilize in the overlap range and, therefore, provides an improvement in performance over the basic GAX cycle. 
     According to yet another aspect of the invention, a GAX cycle is provided that operates to a peak generator temperature of approximately 500 Fahrenheit. This may be accomplished by providing a ternary working fluid that includes ammonia, water, and a dissolved salt. Not only does this aspect of the invention produce an increase in cycle COP of a GAX cycle by increasing the overlap range, it produces an unexpectedly large enhancement due to the solution concentrations in the overlap range when combined with other aspects of the invention. 
     Although the invention is illustrated embodied in a gas-fired residential heat pump, its principles apply to use with other sources of heat and to other refrigeration and chemical processes. These and other objects, advantages and features of this invention will become apparent upon review of the following specification in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram illustrating a conventional generator-absorber heat-exchange (GAX) cycle; 
     FIG. 2 is a pressure-temperature-composition diagram (P-T-X) of the cycle in FIG. 1; 
     FIG. 3 is a flow diagram illustrating an enhanced GAX cycle according to one aspect of the invention; 
     FIG. 4 is a pressure-temperature-composition diagram (P-T-X) of the cycle in FIG. 3; 
     FIG. 5 is a pressure-temperature-composition diagram (P-T-X) of a high-efficiency GAX cycle, using a ternary working fluid; 
     FIG. 6 is a flow diagram illustrating an enhanced generator-absorber heat-exchange (GAX) cycle according to another aspect of the present invention; 
     FIG. 7 is a pressure-temperature-composition diagram (P-T-X) of the cycle in FIG. 6; 
     FIG. 8 is a flow diagram illustrating a hybrid enhanced GAX cycle using both aspects of the invention; 
     FIG. 9 is a pressure-temperature-composition diagram (P-T-X) of the cycle in FIG. 8; 
     FIG. 10 is a pressure-temperature-composition diagram (P-T-X) of the cycle of FIG. 8 showing the heating of the recirculating stream by the overlap absorption heat; 
     FIG. 11 is a flow diagram illustrating a variation of the enhanced GAX cycle according to another aspect of the invention; and 
     FIG. 12 is a pressure-temperature-composition diagram (P-T-X) of the cycle of FIG. 11. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As used herein, the terms weak absorption solution and strong absorption solution refer to the concentration of the refrigerant in the solution. Thus a weak absorption solution has less absorbed refrigerant, such as ammonia, and more absorbent, such as water, than a strong absorption solution. Also, the term absorption heat pump, as used herein, is intended to include any apparatus that transforms heat between low, medium and high temperature states and is intended to include not only the commonly understood meaning of the term, but also is intended to include heat transformers as well as more traditional uses such as refrigeration and related processes. 
     Referring now specifically to the drawings, and the illustrative embodiments depicted therein, a heat pump 60, incorporating a high-efficiency enhanced GAX (ENGAX) cycle includes the components of the conventional GAX cycle heat pump 10, illustrated in FIG. 1, and further includes augmenting means for increasing the flow of absorbent in the overlap temperature region of the absorber, (line G-F in FIG. 2) and in the high temperature region of the generator, (line I-E in FIG. 2). This is accomplished by adding flow increasing means, generally illustrated at 62, for transferring additional solution from an intermediate to high temperature portion of absorber 16 to a portion of generator 22 (FIG. 3). In the illustrated embodiment, flow increasing means 62 is a solution pathway from an intermediate temperature portion G of absorber 16 to a high temperature portion H of generator 22, although the pathway may initiate at the bottom of the high temperature portion of the absorber and terminate at a different portion of the generator. This solution exchange pathway includes a collector 64 for collecting intermediate-temperature solution at point G in absorber 16, a second solution pump 66 and a conduit 62 from pump 66 to region H in generator 22. Conduit 62 includes a portion 70 that extends into high temperature region F of absorber 16, in order to heat the solution transferred by flow increasing means 62, and a second portion 72 in heat transfer association with weak solution conduit 32, in order to further increase the temperature of the fluid to point H of the generator, when necessary. 
     A comparison of the pressure-temperature-composition diagram of the conventional GAX cycle in FIGS. 1 and 2 and that of augmented GAX cycle, illustrated in FIGS. 3 and 4 reveals that the heat transferred by the absorber in the conventional GAX across its overlap range, illustrated as the line D-I in FIG. 2 is less than the heat that the generator could utilize over the full overlap temperature range shown in FIG. 4. It has been discovered that the main reason for this inequality is that greater quantities of absorption solution flow at the lower temperature portions of the generator and absorber than at the higher temperature portions thereof. This inequality of flow results in higher heat quantities per degree of temperature in the cooler portions of the absorber and generator than in the hotter of the two components. 
     In the enhanced GAX cycle, the solution recirculation pathway, illustrated in FIG. 4 as the line from points G to H, H to E, E to F and F to G, increases the flow in the high temperature regions of the absorber (line F-G) and of the generator (like H-E) and in the weak liquid pathway (E-F). This increased flow increases the absorption and the absorber heat output in the overlap temperature range so that all of the heat that the generator can utilize over range D-I in FIG. 4 is being provided. The transferred solution is heated from the temperature at point G to the temperature at point H by heat transfer from the higher temperature region 70 of absorber 16 (line G-F in FIG. 4) and heat transfer from the weak solution pathway at 72 (line E-F in FIG. 4) as indicated in FIG. 3. 
     The flow in the circuit GHEFG must be sufficient to provide the increased heat input to the generator overlap region D-I and to also heat the fluid in circuit 62 (line G to H in FIG. 4) by both absorption heat from the absorber overlap region F-G and by sensible heat transfer at 72 (See FIG. 3 and line E-F, FIG. 4) from the weak liquid circuit. This increase in GAX heat to the generator increases the COP and can be used to reduce the gas heat input, or to increase the refrigerating capacity at the same input, or a combination of the two. 
     A comparison of the heat balances of the conventional GAX cycle with the enhanced, or augmented, GAX cycle, at the same operating conditions, as shown in tables 1 and 2, indicates an increase in cycle COP in the cooling mode of from 1.027 to 1.191, or approximately 16%. This increase in cooling mode performance is especially significant. It should be noted that the estimated 16% increase in cooling COP is expected to approach 20% as cycle operation is further refined. Complete heat and mass balance calculations for the enhanced GAX cycle (EnGAX) are set forth in Appendix A, which forms a part of this application. 
     
                       TABLE 1______________________________________OPERATING CONDITIONSAll Cycles       PRESSURE TEMP       PSIA     °F.______________________________________Condenser     272.6      117.0Evaporator    68.67      37.0Absorber      68.67      105.0-289.4Generator     272.6      199.7-398.8______________________________________ 
    
     
                       TABLE 2______________________________________HEAT OUTPUTS AND INPUTSPer Pound of Refrigerant       GAX        ENHANCED GAX       CYCLE      CYCLE       (FIGS. 1 and 2)                  (FIGS. 3 and 4)______________________________________Rectifier Output         78.44 Btu    78.77 BtuCondenser Output         504.92 Btu   504.92 BtuEvaporator Input         -503.02 Btu  -503.02 BtuAbsorber Net Output         409.05 Btu   341.78 BtuGenerator Input         -489.73 Btu  -422.45 BtuGAX Heat Transferred         295.96       355.70Cooling COP   1.027        1.191Heating COP   2.027        2.191______________________________________ 
    
     The enhanced, or augmented, GAX cycle in FIG. 3 has been illustrated with collector 64 being positioned at the lower temperature portion of the region of temperature overlap with the generator. However, according to the principles of the invention, it would be possible to position collector 64 at a higher temperature portion of the absorber. When solution is collected from the higher temperature portion of the temperature overlap region, the narrower temperature range from which solution is collected increases the amount of solution which must be circulated through the enhancing circuit, but the heat is at a higher temperature and is therefore more readily transferred to the generator. Thus, depending upon the parameters of the system, there are optimum temperature ranges over which the enhancement liquid can be circulated. 
     A method of increasing the overlap temperature range is to use working fluids with a greater temperature difference between the boiling points of the refrigerant and the absorbent. An example is shown in FIG. 5 in which the refrigerant is ammonia and the absorbent is a solution of 60% lithium bromide and 40% water. As can be seen in FIG. 5, the vapor pressure line of the lithium bromide - water absorbent is at a significantly higher temperature than that of water alone. As a result the temperature ranges of the absorber and generator can be made longer than with ammonia/water and the absorber overlap range GF can also be longer. 
     An additional improvement to the GAX cycle may be obtained by the use of ternary fluids composed of ammonia, water and a dissolved salt. A suitable salt extends the temperature range of the fluid beyond that of ammonia and water to 500° F., or more, as illustrated in FIG. 5. The increase in temperature range of the cycle increases the overlap temperature range between the absorber and generator. One such ternary fluid is ammonia, water and lithium bromide, whose vapor pressure properties were determined by R. Radermacher in a published PhD thesis entitled, &#34;Working Substance Combinations for Absorption Heat Pumps.&#34; 
     It has been discovered that the increased overlap temperature range provided by the use of a ternary working solution has less than expected benefits in a conventional GAX cycle. This is believed to be a result of a redistribution of the ammonia/water concentration gradients toward a low temperature portion of the P-T-X diagram. However, the increased flows of the enhanced GAX (EnGAX) can be used to overcome the effects of the concentration gradients for effective performance. Accordingly, the 16% increase in performance over the conventional GAX cycle may be increased to 40% or more by the use of a ternary working fluid and a higher peak generator temperature, in the range of 500° F. with an enhanced GAX cycle. The enhanced GAX cycle therefore, provides additional unexpected results with respect to the conventional GAX cycle when combined with a ternary working fluid. 
     The ternary fluid combination of water/ammonia/lithium bromide, has a disadvantage of being very corrosive at operating temperatures, even when used with stainless steels. Other ammonia/water/salt combinations and other fluids with wide temperature overlap potential are being investigated. Salts that are believed to have potential include lithium nitrate and calcium nitrate. 
     It has been determined that a significant improvement in system COP&#39;s may be obtained in GAX or enhanced GAX systems described herein by increasing the operating pressure within absorber 16. By increasing the absorber pressure, the extent of overlap between the operating temperatures of absorber 16 and generator 22 is increased. Thus, a greater proportion of the total generator heat requirement can be supplied by absorption heat, thereby increasing system COP&#39;s. FIG. 6 illustrates a GAX cycle 110 which is the basic GAX cycle 10 of FIG. 1 modified by the addition of vapor compressor 80 in conduit 14 between absorber 16 and evaporator 12. A cycle diagram of the GAX cycle 110 in FIG. 6 is shown in FIG. 7. In FIG. 7 the solid lines represent the increased-pressure absorber cycle and the dotted lines the basic GAX cycle of FIG. 2. 
     FIG. 7 illustrates the effects of increasing the operating pressure of absorber 16. In the basic GAX, without increasing the operating pressure of absorber 16 by use of compressor 80, the overlap between the temperature ranges of the absorber and the generator is represented by the dotted lines G-F and D-I. After increasing the operating pressure of absorber 16 by approximately 20 psia, the operating line for the absorber is modified from C-G-F to C&#39;-G&#39;-F&#39;. As a result, the line of constant composition C-D is relocated to C&#39;-D&#39;. Thus, the point of intersection between lines G-D and A-E is changed from D to D&#39;. This results in the low temperature end of the overlap between operating temperature ranges of absorber 16 and generator 22 being extended. 
     In terms of the physical process, the strong solution increases in concentration, reducing the temperature at the solution feed point to generator 22, FIG. 6 (point D&#39; in FIG. 7) as well as the temperature of the heat transfer liquid exiting the generator to GAX pump 54. Besides broadening the GAX overlap region, this enrichment of the strong solution also reduces the rectifier losses occurring along line D-A of FIG. 7. An increase in operating pressure of absorber 16 also results in a shift of the point of intersection between lines F-I and A-E, from I to I&#39;. Thus, the high temperature end of the overlap between operating temperature ranges of absorber 16 and generator 22 is also extended. In terms of the physical process, the concentration of the weak solution is not changed, but the heat transfer fluid flowing from the absorber to the generator in line 48 of FIG. 6 is increased in temperature, thus perhaps requiring relocating the entry of line 48 into the generator at a lower (and higher temperature) spot. The result is that provision of means for increasing pressure in the absorber from C to C&#39; results in an increase in the overlap temperature range of the absorber and generator at both the high end and low end of the overlap range. This increase appears to exceed, to a significant degree, the mechanical energy required to raise the absorber pressure. 
     The amount of pressure increase is to be limited in view of the additional power required for compressing the vapor, so that the savings from reduced heat requirements for generator 22 (from burner 24) will be greater than the extra costs incurred in operating compressor 80. More specifically, the extent of pressure increase in absorber 16 should be adjusted to maximize the difference between the reduction in energy requirements of generator 22 and the power requirement of compressor 80. 
     Alternatively, the enhanced GAX cycle may be modified according to the present invention, as shown in FIG. 8, in which vapor compressor 80 is likewise located in conduit 14 between absorber 16 and evaporator 12. Because conduit 14 discharges to absorber 16, the insertion of compressor 80 serially in conduit 14 increases the operating pressure within absorber 16 to a level higher than that in FIGS. 1 and 3. FIGS. 8 and 9 illustrate GAX cycle 160, the combination of the pressurized absorber aspect of this invention with the increased flow of absorbent through the overlap portion of the absorber and the absorbent. Tables 3 and 4 indicate the performance gains possible by this combination. The cycle diagram in FIG. 10 shows that the heat output from the absorber overlap area is to be sufficient to supply the needs of the generator and to heat the recirculated liquid in circuit 62 of FIG. 4. 
     
                       TABLE 3______________________________________HEAT OUTPUTS AND INPUTSPer Pound of Refrigerant       GAX         COMPRESSION       CYCLE       GAX CYCLE       (FIGS. 1 AND 2)                   (FIGS. 6 AND 7)______________________________________Rectifier Output         78.44 Btu     45.93 BtuCondenser Output         504.92 Btu    504.92 BtuEvaporator Input         -503.02 Btu   -503.02 BtuAbsorber Net Output         409.05 Btu    372.39 BtuGenerator Input         -489.73 Btu   -420.22 BtuGAX Heat Transferred         295.96        407.74Cooling COP   1.027         1.197Heating COP   2.027         2.197______________________________________ 
    
     
                       TABLE 4______________________________________                 ENHANCED +      GAX        COMPRESSION      CYCLE      GAX CYCLE      (FIGS. 1 AND 2)                 (FIGS. 8, 9 AND 10)______________________________________Rectifier Output        78.44 Btu    66.19 BtuCondenser Output        504.92 Btu   504.92 BtuEvaporator Input        -503.02 Btu  -503.02 BtuAbsorber Net Output        409.05 Btu   297.73 BtuGenerator Input        -489.73 Btu  -365.82 BtuGAX Heat     295.96       519.26TransferredCooling COP  1.027        1.375Heating COP  2.027        2.375______________________________________ 
    
     In another embodiment of this technique of improving the system COP in GAX cycles, it has been found that increases in absorber operating pressures may be limited to specific portions of absorber 16. An example is to compress only the vapor flowing to the absorber GAX section. FIG. 11 illustrates GAX cycle 210, increasing the operating pressure in only the temperature overlap (GAX) portion of absorber 16. In this application vapor compressor 80 has been moved from the vapor inlet 81 of absorber 16 to the vapor inlet 82 of the GAX section of absorber 16. The cooler portion of absorber 16 remains at evaporator pressure, with only the GAX, overlap, portion being at a higher pressure. The absorbent liquid flowing from the higher pressure GAX section to the lower pressure AHE section is throttled by a suitable restriction 85, to allow only liquid to flow from one absorber portion to another. Restriction 85 may be in the form of a float valve, or other means known to those skilled in the art. 
     In the cycle diagram of FIG. 12 the operation for this concept is shown in solid lines, while that of the normal GAX is in dotted. Before increasing absorber pressure 16, the overlap temperature range between the temperature ranges of absorber 16 and generator 22 is represented by lines D-I and G-F. After increasing the operating pressure in only a portion of absorber 16, the operating line for that particular portion is modified from G-F to G&#39;-F&#39;. This results in the higher end of the generator overlap being extended from D-I to D-I&#39;. Thus, reduced operating expenses are realized as only a portion of the refrigerant vapor entering absorber 16 needs to be increased in pressure, rather than all of the refrigerant entering the absorber. In the illustrated embodiment it has been estimated that generally less than 25% of the total refrigerant to be absorbed need be compressed. 
     The absorber vapor can be compressed to the higher pressure at any point between B and F, with varying advantages in the pumping power required, in equipment cost and in GAX enhancement. The best temperature at which to pump the gas is also likely to depend on the relative costs of natural gas and electricity. The invention is therefore intended to be useable for compression of the vapor at any temperature, from point B to point F, that is best suited to the application. 
     While the enhanced GAX cycle has been illustrated in a residential or light commercial heat pump, its benefits are not limited to such applications. The enhanced performance provided by the EnGAX cycle set forth herein, may be applied to industrial absorption systems for applications to processes requiring medium temperature heating and cooling such as brewing, food processing, pasturizing and paper making, to mention but a few examples. Furthermore, the principles of the invention are not limited to absorption heat pump cycles that efficiently convert heat from a combination of low and high temperatures heat sources to heat at a medium temperature. The invention is equally applicable to heat transformers which convert heat from a medium-high temperature, such as heated waste water discharged from a processing plant, to a useful high temperature output plus a low temperature output. 
     Changes and modifications in the specifically described embodiments can be carried out without departing from the principles of the invention. Accordingly, while the means for increasing the flow of solution from the temperature overlap region of the absorber to the generator is provided in the illustrative embodiments by a solution pump and a conduit in heat transfer association with higher temperature portions of the system, other techniques may be utilized to transfer the fluid while raising its temperature. For example, pressurized transfer vessels incorporating appropriate check valves and control valves, and other fluid propelling techniques, as are known to those skilled in the art, may be utilized. Other changes and modifications will suggest themselves to those skilled in the art. The protection afforded the invention is intended to be limited only by the scope of the appended claims, as interpreted according to the principles of patent law, including the Doctrine of Equivalents. 
     
                                           APPENDIX A__________________________________________________________________________Heat and Mass Balance Calculation EnGAX CycleDATA   P    T    X   Y  Hx   Hy     M__________________________________________________________________________COND W 272.60       117 .995               .999947                   96.426                        558.03777                              1EVAP W 68.667        37 .995               .999995                   3.9331                        546.33132                              1GEN PEAK  272.60         398.8           .02 .109387                   370.64                        1151.5539                              1.5755ABS OUT  68.667       105 .477465               .993235                   -26.89                        589.76183                              1.9121FEED W 272.60         199.7           .477465               .974549                   78.866                        629.35701                              1.9121COND IN  272.60         151.7           .667030               .995                   43.677                        586.90823                              1V TO RCT  272.60       207 .454553               .968844                   87.180                        636.79318                              1.0521L FR RCT  272.60       203 .466941               .972067                   82.582                        632.69173                               .05211COND OUT  227.72       105 .995               .999962                   81.984                        557.58175                              1PCVL OUT  68.667          98.17           .502676               .995                   -34.05                        585.00282                              1ABS WL I  68.667         289.4           .02 .172467                   254.66                        1093.5071                              1.5755ABS ILGX  68.667       210 .178611               .817280                   129.24                        734.76669                              1.2740ABS IVGX  68.667       200 .202760               .855527                   112.63                        710.45895                               .36184EGL ABS  68.667       210 .178611               .817280                   129.24                        734.76669                               .66332ENG T HG  186.29       283 .178611               .745258                   207.94                        797.15268                               .66332GEN IL W  272.60       280 .259710               .843155                   188.55                        740.89614                              1.4900GEN IV W  272.60       290 .235659               .811610                   204.06                        761.62881                               .57784__________________________________________________________________________  P   T     X, Y               Hx, Hy                       Lbs                         Btu__________________________________________________________________________HEAT AND MASS BALANCERCTIFIERVap In 272.60      207  .968844               636.793                     1.0521                         669.98RfL OUT  272.60      203  .466941               82.5820                      .05211                         4.30RfV Out  272.60      151.7           .995               586.908                     1   586.91  RECTIFIER HEAT OUT     78.77CONDENSERRfV In 272.60      151.7           .995               586.908                     1   586.91RfL Out  227.72      105  .995               81.9839                     1   81.98  CONDENSER HEAT OUT     504.92EVAPORATOR-PRECOOLERRfL In 227.72      105  .995               81.9839                     1   81.98RfV Out  68.667      98.17           .995               585.003                     1   585.00Liq Out  68.667      98.17           .502676               -34.045                     0   .00  EVAPORATOR HEAT IN     -503.02  MAX PRECOOLER HEAT     -283.46ABSORBERWL In  68.667      289.4           .02 254.662                     1.5755                         401.21Vap In                    1   585.00Liq In                    0   .00RL Out 272.60      199.7           .477465               78.8659                     1.9121                         150.80EGL OUT  186.29      283  .178611               207.940                      .66332                         137.93  HEAT OF ABSORPTION     697.48LOW TEMP ABSORBERIL IN  68.667      210  .178611               129.244                     1.2740                         164.65Vap In                        585.00LIQ IN                        0RL OUT 272.60      199.7           .477465               78.8659                     1.9121                         150.80IV OUT 68.667      200  .855527               710.459                      .36184                         257.08  HEAT OUT               341.78HIGH TEMP ABSORBERIV IN  68.667      200  .855527               710.459                      .36184                         257.07521WL IN  68.667      289.4           .02 254.662                     1.5755                         401.20969IL OUT 68.667      210  .178611               129.244                     1.2740                         164.65482EGL OUT  186.29      283  .178611               207.940                      .66332                         137.93058  GAX HEAT               355.69949GENERATORRL IN  272.60      199.7           .477465               78.8659                     1.9121                         150.80264EGL IN 186.29      283  .178611               207.940                      .66332                         137.93058V TO RCT  272.60      207  .968844               636.793                     1.0521                         669.97840L FR RCT  272.60      203  .466941               82.5820                      .05211                         4.3035998WL OUT 68.667      289.4           .02 254.662                     1.5755                         401.20969                         -778.1513LO TEMP GENERATORRL IN  272.60      199.7           .477465               78.8659                     1.9121                         150.80264V TO RCT  272.60      207  .968844               636.793                     1.0521                         669.97840L FR RCT  272.60      203  .466941               82.5820                      .05211                         4.3035998GIL OUT  272.60      280  .259710               188.546                     1.4900                         280.93086GIV IN 272.60      290  .811610               761.629                      .57784                         440.10317  GAX HEAT               -355.6999HI TEMP GENERATORGIL IN 272.60      280  .259710               188.546                     1.4900                         280.93086GIV OUT  272.60      290  .811610               761.629                      .57784                         440.10317EGL IN 186.29      283  .178611               207.940                      .66332                         137.93058WL OUT 68.667      289.4           .02 254.662                     1.5755                         401.20969  HEAT IN                -422.4514TOTAL HEAT IN        -925.47 TOT HEAT OUT                          925.47073COOLING COP    1.19071                HEATING COP                           2.1907152__________________________________________________________________________