Abstract:
A vapor compression system includes a vapor compression circuit including a compressor, a condenser, an expansion device and an evaporator communicated along refrigerant conveying lines; an evaporator air reheat circuit communicated with the vapor compression circuit for reheating air from the evaporator; and a refrigerant subcooling circuit communicated with the vapor compression circuit for subcooling refrigerant from the condenser, whereby humidity in the air from the evaporator can be controlled while system efficiency is maintained by the refrigerant subcooling circuit. The system further enhances system unloading capability, and part-load operation and reliability are also enhanced.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to vapor compression systems and, more particularly, to humidity control and efficiency enhancement in connection with same. 
     Typical vapor compression systems such as rooftop refrigeration systems and the like are widely used, and some of the chief concerns in use of such units include efficiency enhancement and humidity control. 
     Unfortunately, typical approaches for providing humidity control detract from compressor efficiency. Furthermore, as refrigerants evolve toward more ecologically acceptable alternatives, such alternatives tend to be less efficient. 
     Thus, the need exists for a vapor compression system which is both efficient and capable of humidity control. 
     It is therefore primary object of the present invention to provide such a system. 
     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, a vapor compression system is provided which comprises a vapor compression circuit comprising a compressor, a condenser, an expansion device and an evaporator communicated along refrigerant conveying lines; an evaporator air reheat circuit communicated with said vapor compression circuit for reheating air from said evaporator; and a refrigerant subcooling circuit communicated with said vapor compression circuit for subcooling refrigerant from said condenser, whereby humidity in said air from said evaporator can be controlled while system efficiency is maintained by said refrigerant subcooling circuit. 
     The added efficiency in the system of the present invention which is provided by the refrigerant subcooling circuit compensates for performance degradation associated with incorporation of the evaporator air reheat circuit, which advantageously allows for over-cooling of the air to reduce humidity as desired, followed by reheat to the desired temperature. 
    
    
     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 a system in accordance with the present invention utilizing liquid discharge from the condenser for air reheat; 
     FIG. 1 a  illustrates a variation in the system of FIG. 1; 
     FIG. 2 illustrates an alternative embodiment of the present invention utilizing compressor discharge gas for air reheat; and 
     FIG. 2 a  illustrates a variation in the system of FIG.  2 . 
    
    
     DETAILED DESCRIPTION 
     The invention relates to vapor compression systems and, more particularly, to vapor compression systems including an economizer refrigerant subcooling circuit for enhancing system efficiency and an evaporator air reheat circuit for reheating over-cooled air from the evaporator to allow for humidity control. The enhanced efficiency of the system due to the refrigerant subcooling circuit compensates for performance degradation associated with incorporation of the evaporator air reheat circuit, thereby providing humidity control in a system with acceptable efficiency as desired in accordance with the present invention. 
     Furthermore, implementation of the system of the present invention advantageously allows for a higher degree of flexibility in unloading strategy enhancing part-load efficiency and system reliability. 
     Turning to FIG. 1, a vapor compression system  10  in accordance with the present invention is illustrated and includes a compressor  12 , a condenser  14 , an expansion device  26 , and an evaporator  16  connected by refrigerant lines to operate as desired and as is well known to a person of ordinary skill in the art. As is well known, compressor  12  is fed by a refrigerant suction line  20 , and discharges compressed refrigerant through discharge line  22  to condenser  14 . Condenser  14  discharges liquid through discharge line  24  and ultimately through expansion device  26  to evaporator  16 , wherein air is cooled and humidity or moisture removed from same. Discharge from evaporator  16  is passed through line  28  and back to compressor suction inlet  20 . 
     In accordance with the present invention, an economizer refrigerant subcooling circuit is provided for enhancing operating efficiency of system  10 . This refrigerant subcooling circuit includes a main refrigerant line  30  and a subcooling refrigerant line  32 . Main refrigerant line  30  and subcooling refrigerant line  32  feed through an economizer heat exchanger  34 , with subcooling refrigerant line  32  first passing through an expansion device  36 , so that refrigerant in main refrigerant line  30  is further sub-cooled in heat exchanger  34  as desired, thereby enhancing efficiency of operation of system  10  as desired. Sub-cooled discharge from economizer heat exchanger  34  then passes to expansion device  26  and evaporator  16  as described above. Discharge from subcooling refrigerant line  32  passing through economizer heat exchanger  34  returns to compressor  12  at an economizer port  38  as shown. 
     In further accordance with the present invention, an evaporator air reheat circuit is also advantageously provided, and is shown in FIG. 1 as an air reheat coil  18  to which evaporator air is fed, where evaporator air is exposed to all or a portion of the liquid discharge from condenser  14 , in this embodiment through air reheat refrigerant line  40 . 
     Following air reheat heat exchanger  18 , refrigerant discharge is passed through line  42  and rejoined with main refrigerant line  30  for feed to expansion device  26  and evaporator  16 . 
     In accordance with the invention, and advantageously, evaporator air reheat allows for evaporator  16  to be operated so as to over-cool air passed therethrough. This serves to provide enhanced moisture removal from the air, with the air then being reheated to the desired temperature, thereby advantageously providing for control of humidity as desired in accordance with the present invention. This humidity control is desirable in many applications. 
     In further accordance with the present invention, the subcooling of refrigerant in main refrigerant line  30  provided by the economizer circuit in accordance with the present invention advantageously enhances efficiency of system  10  so as to allow for the evaporator air reheat as described above without adversely impacting overall system efficiency. Thus the resulting system as illustrated in FIG. 1 advantageously provides for efficient operation and humidity control as desired in accordance with the present invention. 
     FIG. 1 a  shows an alternative embodiment to that described in connection with FIG. 1, wherein the primary difference is in connection with return of refrigerant from air reheat heat exchanger  18 . In the embodiment of FIG. 1, refrigerant discharge from air reheat heat exchanger  18  is combined with refrigerant discharge from economizer heat exchanger  34  upstream of expansion device  26 . In the embodiment of FIG. 1 a  refrigerant discharge from air reheat heat exchanger  18  is instead combined with refrigerant discharge from condenser  14  upstream of economizer heat exchanger  34 . The embodiment of FIG. 1 a  is in all other respects identical to that of FIG.  1 . 
     Turning now to FIG. 2, an alternative embodiment of a system  10 ′ in accordance with the present invention is illustrated. In this embodiment, system  10 ′ includes compressor  12 , condenser  14 , evaporator  16  and refrigerant lines connecting same in similar fashion to that described in connection with FIG.  1 . An air reheat heat exchanger  18  is also provided, as are compressor suction inlet line  20 , compressor discharge line  22 , condenser discharge line  24 , expansion device  26  and evaporator discharge line  28 . In this embodiment, an economizer refrigerant subcooling circuit is also provided, and includes main refrigerant line  30 , subcooling refrigerant line  32 , economizer heat exchanger  34  and expansion device  36  all as described above in connection with FIG.  1 . This advantageously serves to further sub-cool refrigerant in main refrigerant line  30  as described above. 
     In this embodiment, however, evaporator air reheat is accomplished using a different source of heat for the air. In this embodiment, discharge gas from compressor  12  is fed through air reheat line  40 ′ to air reheat exchanger  18  for reheating of evaporator air, and discharge from heat exchanger  18  is fed through line  42 ′ back to be combined with an economizer discharge flow. 
     The economizer refrigerant subcooling circuit of this embodiment operates identically to that described in FIG. 1, and enhances system efficiency, while the evaporator air reheat circuit provides for reheating of air that has been over-cooled in evaporator  16 , for humidity control purposes, as desired and also as described above in connection with FIG.  1 . Thus, the embodiment of FIG. 2 also advantageously provides for efficient system operation and humidity control as desired. 
     Turning now to FIG. 2 a , an alternative embodiment to that disclosed in connection with FIG. 2 is provided. In this embodiment, refrigerant discharge from air reheat heat exchanger  18  is combined with refrigerant discharge from condenser  14  upstream of economizer heat exchanger  34 , rather than combined with refrigerant discharge from economizer heat exchanger as is illustrated in the embodiment of FIG.  2 . The embodiment of FIG. 2 a  is in all other respects identical to that of FIG.  2 . 
     FIGS. 1,  1   a ,  2  and  2   a  show different configurations of a system wherein refrigerant which is warmer than over-cooled evaporator air is exposed to the evaporator air in an additional heat exchanger, in this case shown as an air reheat heat exchanger, for reheating the air after over-cooling of same. It should of course be appreciated that the re-heating can be accomplished utilizing different connections of components, and utilizing warm refrigerant, that is refrigerant which is warmer than the over-cooled air, from other locations in the system, well within the scope of the present invention. 
     It should also be understood that the air reheat circuit and economizer refrigerant subcooling circuit of the present invention can function simultaneously, requiring a 3-way regulating valve, or conventional cooling and dehumidification modes of operation can be executed separately requiring a 3-way shutoff valve only, at the point where warm refrigerant is separated or diverted to the air reheat circuit. In both scenarios mentioned above, the benefits of the present invention are realized. 
     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.