Patent Publication Number: US-6658867-B1

Title: Performance enhancement of vapor compression system

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to vapor compression systems and, more particularly, to performance enhancement in air conditioning systems utilizing economizer cycles. 
     Economizer cycles can be used to enhance vapor compression system performance in the refrigeration range of compressor operation. Pressure ratios in such systems are high and benefits in efficiency are sufficiently large to justify increased cost in circuit complexity. 
     In air conditioning operating range systems, however, the pressure ratio is much lower than in typical refrigeration systems, and this makes less desirable the use of economizer cycles and the like in such systems due to minimal return on increased cost and complexity. 
     It is clear that the need remains for enhanced system efficiency in air conditioning operating range systems. 
     It is therefore the primary object of the present invention to provide performance enhancement of vapor compression systems in connection with air conditioning operating range systems. 
     Other objects and advantages of the present invention will appear hereinbelow. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, the foregoing objects and advantages have been readily attained. 
     According to the invention, in an air conditioning system comprising a compressor, a condenser, and an evaporator, a process is provided which comprises the steps of feeding discharged refrigerant from said compressor to said condenser so as to provide a condensed refrigerant flow; splitting said condensed refrigerant flow into a main flow and an auxiliary flow wherein said auxiliary flow comprises between about 8 and about 12% wt. of total mass flow rate of said condensed refrigerant flow; reducing temperature and pressure of said auxiliary flow so as to provide an economizer flow; passing said economizer flow and said main flow through a heat exchanger so as to provide a sub-cooled main flow and an economizer discharge flow; feeding said economizer discharge flow to said compressor; and feeding said sub-cooled main flow through said evaporator to said compressor. 
     In further accordance with the invention, heat exchange with economized refrigerant flow can be carried out for multiple circuits in single heat exchangers, with one or more economizer flow circuits and with flow through the heat exchanger being carried out in parallel and/or in sequence. Further, with multiple circuits, economized and non-economized circuits can be combined. 
     Thus, in further accordance with the invention, in a multiple circuit air conditioning system comprising at least two circuits each including a compressor, a process is provided which comprises the steps of operating each compressor of said at least two circuits so as to produce at least two discharged refrigerant flows; feeding said at least two discharged refrigerant flows to condensing means for producing at least two condensed refrigerant flows; splitting a condensed refrigerant flow from at least one circuit of said circuits to obtain an auxiliary flow and at least two main condensed refrigerant flows; reducing temperature and pressure of said auxiliary flow so as to provide an economizer flow; passing said economizer flow and said at least two main condensed refrigerant flows through a heat exchanger so as to provide at least two sub-cooled main flows and an economizer discharge flow; feeding said economizer discharge flow to said compressor of said at least one circuit; and feeding said at least two sub-cooled main flows through evaporator means to said compressor of said at least two circuits. 
     A multiple circuit air conditioning system is also provided, which comprises a first circuit including a series connection of a first compressor, a first condenser, a heat exchanger and evaporator means; a second circuit including a series connection of a second compressor, a second condenser, said heat exchanger and said evaporator means; and at least said first circuit including an economizer circuit including a series connection of said first compressor, said first condenser, an expander, and said heat exchanger. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of preferred embodiments of the present invention follows, with reference to the attached drawings, wherein: 
     FIG. 1 schematically illustrates an economized air conditioning system in accordance with the present invention; 
     FIG. 2 schematically illustrates a multiple economized circuit system using a single heat exchanger in accordance with the present invention; 
     FIG. 3 schematically illustrates a multiple circuit system in accordance with the present invention with sub-cooling of multiple flows carried out in parallel from a single economized circuit; and 
     FIG. 4 schematically illustrates a multiple circuit system in accordance with the present invention with sub-cooling of multiple flows carried out sequentially from a single economized circuit. 
    
    
     DETAILED DESCRIPTION 
     The invention relates to air conditioning systems and, more particularly, to air conditioning systems having enhanced performance of the vapor compression system through incorporation of an economizer cycle. 
     In accordance with the present invention, a process is provided for operation of an air conditioning system which advantageously incorporates economizer circuits into the low-pressure ratio operating conditions of an air conditioning system to enhance operating efficiency of same. 
     FIG. 1 schematically illustrates an air conditioning system  10  in accordance with the invention, including a compressor  12 , a condenser  14 , an evaporator  16 , and a heat exchanger  18 . Each of these components per se is well known to a person of ordinary skill in the art. 
     As shown in FIG. 1, compressor  12  has a discharge  20  which leads to condenser  14 . Condenser  14  has a discharge line  22  which is split in accordance with the present invention into a main flow line  24  and an auxiliary flow line  26 . Auxiliary flow line  26  is fed through an expander  28  for reducing the temperature and pressure of auxiliary flow. From expander  28 , an economizer line  30  flows to heat exchanger  18 , as does main flow line  24 . Heat exchanger  18  has an economizer discharge line  32  and a main discharge line  34 . Economizer discharge line  32  feeds back to compressor  12 , while main discharge line  34  feeds to an expander  36 . From expander  36 , line  38  feeds to evaporator  16 , which has a discharge line  40  which also feeds to compressor  12 , thus defining an operating circuit for the system. 
     In operation, compressor  12  generates a discharged refrigerant which flows through discharge line  20  to condenser  14 . Condenser  14  is operated in accordance with the present invention to provide a minimal of sub-cooling, preferably an amount of sub-cooling which is sufficient to prevent flashing at expander  28 . This further advantageously serves to maximize the temperature differential which can be accomplished at heat exchanger  18 , which serves to provide for enhanced efficiency of operation of the system. In order to avoid flashing, it is preferred that the condenser be operated to provide condensed refrigerant at a temperature which is greater than the flashing temperature by an amount less than about 20° F. More preferably, it is preferred that the condenser be operated to provide the condensed refrigerant at a temperature which exceeds the flashing temperature by an amount between about 5° F. and about 20° F. This advantageously serves to avoid flashing while providing for operation as desired. 
     From condenser  14 , a condensed refrigerant flow exits through discharge line  22  and is split between main flow line  24  and auxiliary flow line  26 . 
     In accordance with the present invention, it has been found that excellent results can be obtained if the condensed refrigerant flow is split between main flow line  24  and auxiliary flow line  26  such that between about 8% and about 12% (wt.) of the total mass flow rate of the condensed refrigerant flow is fed to auxiliary flow line  26 . This splitting of the main and auxiliary flows serves to provide for an efficient balance of main and economizer flows, thereby rendering maximum enhancement in low pressure ratio air conditioning operating range systems. 
     The auxiliary flow through auxiliary flow line  26  is passed through expander  28  for reducing the temperature and pressure of the auxiliary flow so as to provide an economizer flow which is fed through economizer line  30  to heat exchanger  18 . The main flow through main flow line  24  is also fed to heat exchanger  18 , preferably in counter-current heat exchange arrangement with economizer flow through economizer line  30 . This results in a further sub-cooled refrigerant exiting heat exchanger  18  through main discharge line  34 , and an economizer discharge flow through economizer discharge line  32  back to compressor  12 . 
     The sub-cooled main flow is expanded at expander  36  as desired, and fed through line  38  to evaporator  16  wherein it is exposed to a flow of air shown schematically at  42  for allowing refrigerant to evaporate and generate an evaporated refrigerant flow which is fed through line  40  back to the main inlet of compressor  12 . 
     Expander  28  is preferably operated in accordance with the present invention so as to provide the economizer flow with a pressure which is preferably between about 5 and about 20% less, more preferably between about 10 and about 12% less than a conventionally accepted pressure X, wherein X is defined as follows: 
     
       
           X={square root over (P S )}   P   D , 
       
     
     wherein 
     P S  is suction pressure, and 
     P D  is discharge pressure. 
     It has been found in accordance with the present invention that operation of an air conditioning range system utilizing the preferred range of economizer refrigerant mass flow rate, coupled with economizer flow pressure lower than conventionally desired, and minimal sub-cooling in the condenser provide for particularly beneficial efficiency and desirable results when incorporating an economizer cycle into an air conditioning operating range system. In accordance with the present invention, an air conditioning system is considered to be one operated at a pressure ratio of less than about 20, and more preferably between about 2 and about 5. 
     It should be appreciated that the process as schematically illustrated in FIG. 1 provides for unexpected and advantageous benefits when incorporating an economizer cycle into an air conditioning range system despite the much lower pressure ratios used in such systems. 
     Turning now to FIGS. 2-4, alternative embodiments are described wherein additional circuits including at least one additional compressor, condenser and evaporator or evaporator portion are provided and economized, advantageously using a single heat exchanger. 
     FIG. 2 schematically illustrates an embodiment of the present invention wherein a first circuit  44  is defined including the elements substantially as discussed in connection with FIG. 1, and wherein an additional circuit  46  is provided including an additional compressor  12   a , an additional condenser  14   a , an additional expander  28   a , and an additional expander  36   a . Additional circuit  46  also flows through heat exchanger  18  and evaporator  16  as illustrated. As shown in FIG. 2, condensed refrigerant flow from condensers  14 ,  14   a , are both split to provide two main flows through main flow lines  24 ,  24   a  and two economizer flows through auxiliary flow lines  26 ,  26   a . Each auxiliary flow is passed through an expander  28 ,  28   a , and then to heat exchanger  18 . In the meantime, each main flow  24 ,  24   a  is also passed through heat exchanger  18  so as to provide main discharge  34 ,  34   a  which is fed to expanders  36 ,  36   a  and then to evaporator  16  and back to respective compressors  12 ,  12   a . Respective economizer discharge lines  32 ,  32   a  feed from heat exchanger  18  back to compressors  12 ,  12   a . In accordance with this embodiment, the same operating parameters as set forth above are particularly advantageous. Furthermore, and advantageously, a single heat exchanger and economizer are utilized to service both first circuit  44  and additional circuit  46 . 
     FIG. 3 illustrates a further alternate embodiment of the present invention, wherein an additional circuit  48  is provided which does not include an additional economizer cycle. In this embodiment, additional circuit  48  includes compressor  12   b , condenser  14   b , heat exchanger  18 , expander  36   b  and evaporator  16 . Discharge line  22   b  from condenser  14   b  feeds directly to heat exchanger  18  wherein the main condensed flow from first circuit  44  in main discharge line  34  of first circuit  44  and the main discharge in line  34   b  from condenser  14   b  are cooled by economizer flow from first circuit  44  in economizer line  30 , in parallel. This provides the benefits of the economizer cycle from first circuit  44  to both first circuit  44  and additional circuit  48 , which is particularly advantageous in accordance with the present invention. 
     FIG. 4 schematically illustrates a further alternative embodiment of the present invention wherein additional circuit  48  is defined in similar fashion to that described in connection with FIG. 3, but wherein main flow from first circuit  44  and main flow from additional circuit  48  are fed in sequence or series through heat exchanger  18 , both to be cooled by economizer flow from economizer line  30  as desired. In this embodiment, as well, the benefits of the economizer cycle of first circuit  44  are provided to both circuit  44  and additional circuit  48 . As shown, economizer line  30  travels through heat exchanger  18  for a distance, and a first portion of this distance runs adjacent to main flow from first circuit  44 , and a second portion of this distance runs adjacent to main flow from additional circuit  48 . 
     In connection with the embodiments of FIGS. 2-4, multiple circuits are disclosed which include at least a compressor. These circuits are also shown in the drawings to each include a condenser and an expander for the main flow prior to entering the evaporator. FIGS. 2-4 also show the multiple circuits advantageously passing through a single heat exchanger, and also passing through a single evaporator. In connection with the evaporator, separate evaporator units could be utilized, if desired. It is particularly advantageous in accordance with the present invention, however, to utilize a single heat exchanger and, preferably, a single evaporator as well. 
     Also as shown in the drawings, it is particularly advantageous that the single heat exchanger embodiment in accordance with the present invention can be utilized so as to expose multiple circuits to one or more economizer circuits, wherein all circuits can include an economizer circuit, if desired. However, it is particularly advantageous in accordance with the air conditioning system environment of the present invention to utilize a combination of economized and non-economized circuits wherein refrigerant flow from all circuits is exposed to the economized flow in the single heat exchanger. 
     It should readily be appreciated that the process in accordance with the present invention provides for advantageous incorporation of economizer cycles into one of more air conditioning operating range systems, which advantageously provides for enhanced efficiency in operation of same. 
     It should further be appreciated that the compressors, condensers, evaporators, expanders and heat exchangers described in accordance with the preferred embodiments can be any of a wide range of specific types of hardware, many variations of which would be readily apparent to a person of ordinary skill in the art. 
     The splitting of condensed flow in accordance with the preferred ranges as described above, coupled with minimal sub-cooling in condenser  14  and greater reduction in pressure in the economizer cycle than would conventionally be dictated combine to provide for excellent efficiency in operation at air conditioning operation ranges, all as desired in accordance with the present invention. 
     Further, use of a single heat exchanger with multiple circuits, and combination of economized and non-economized circuits through such heat exchangers, are advantageous improvements in accordance with the invention. 
     It is to be understood that the invention is not limited to the illustrations described and shown herein, which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts and details of operation. The invention rather is intended to encompass all such modifications which are within its spirit and scope as defined by the claims.