Abstract:
A transcritical R-744 refrigeration systems for supermarkets with dehumidifying capability where the heat of the R-744 leaving the gas cooler is used for dehumidifying. The same heat exchanger is used for heat reclaim and dehumidifying purposes.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to transcritical R-744 refrigeration systems, and more specifically to transcritical R-744 refrigeration systems for supermarkets and the like, which use multiple compressors and multiple evaporators to refrigerate and/or to maintain in frozen conditions perishable food products. The refrigeration system used is transcritical R744 system having heat reclaim and dehumidifying capability. 
       BACKGROUND OF THE INVENTION 
       [0002]    During some periods of the year when the ambient temperatures and humidity are elevated, it is necessary to provide, in addition to the air conditioning, a system which will reduce the relative air humidity in the supermarket. Failing to do so will result in high air relative humidity inside the store, frequent defrosts, frosting of the surface of the food products and discomfort for the customers. 
         [0003]    The most frequently used dehumidifying method in supermarkets is to install heating coil downstream of the air conditioning coil. The air from the outlet of the air conditioning coil has low temperature and very high relative humidity. By reheating this air to a comfortable temperature level the relative humidity is lowered to acceptable level (around 40%). Most often the heat of the high pressure compressed refrigerant that vapors directly from the discharge outlet of the compressors is used as a heat source for the heating coil. This method provides sufficient heat for the dehumidification process but in the case of R744 transcritical system, having into consideration that the dehumidification process is used mainly during the summer period, does not provide increase of efficiency of the transcritical refrigeration system which during the summer period is significantly lower than that of the freon refrigeration systems. 
         [0004]    The need to improve the cycle efficiency during the warmer periods of the year is obvious. 
         [0005]    Accordingly, there is a need for an improved transcritical R-744 refrigeration system. 
       SUMMARY OF THE INVENTION 
       [0006]    It is therefore a general object of the present invention to provide an improved transcritical R-744 refrigeration system and method. 
         [0007]    An advantage of the present invention is that the transcritical R-744 refrigeration system and method, instead of using the high pressure compressed refrigeration vapors directly from the discharge outlet of the compressors as a heat source for the heating coil, uses the vapors from the outlet of the gas cooler are as a heat source for the heating coil. 
         [0008]    Another advantage of the present invention is that the transcritical R-744 refrigeration system and method uses only one heat exchanger for heat reclaim and dehumidifying purposes. 
         [0009]    A further advantage of the present invention is that the transcritical R-744 refrigeration system and method, by using the vapors from the outlet of the gas cooler as a heat source for dehumidification, a significant amount of subcooling capacity is provided thus increasing the efficiency of the system without installing additional equipment and without adding to the power consumption of the system. 
         [0010]    Still another advantage of the present invention is that the transcritical R-744 refrigeration system and method, by feeding vapors with lower temperature through the dehumidifying heat exchanger, reduces the thermal stress to the heat exchanger thus increasing the reliability and the useful life of the dehumidifying system. 
         [0011]    According to an aspect of the present invention, there is provided a transcritical R-744 refrigeration system for supermarket with dehumidifying capability, the transcritical R-744 refrigeration system comprising a modulating valve allowing the heat of at least a portion of the R744 refrigerant leaving the gas cooler to dehumidify the heat reclaim/dehumidifying heat exchanger. 
         [0012]    According to another aspect of the present invention, there is provided a method of dehumidifying a heat reclaim/dehumidifying heat exchanger of a transcritical R-744 refrigeration system, the method comprising the step of modulating a modulating valve to allow the heat of at least a portion of the R-744 refrigerant leaving the gas cooler to dehumidify the heat reclaim/dehumidifying heat exchanger. 
         [0013]    Other objects and advantages of the present invention will become apparent from a careful reading of the detailed description provided herein, with appropriate reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    Further aspects and advantages of the present invention will become better understood with reference to the description in association with the following Figure, wherein: 
           [0015]      FIG. 1  is a schematic view of a transcritical R-744 refrigeration system having the gas cooler outlet vapors used as a heat source for the dehumidifying the heating coil in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    With reference to the annexed drawings the preferred embodiment of the present invention will be herein described for indicative purpose and by no means as of limitation. 
         [0017]    Referring to  FIG. 1 , there is schematically shown a transcritical R-744 refrigeration system having the gas cooler outlet vapors used as a heat source for the dehumidifying the heating coil in accordance with an embodiment of the present invention. 
         [0018]    The refrigeration system shown on  FIG. 1  is a simplified schematic of the transcritical R-744 system with the low temperature compressors and all evaporators not being specifically shown since they are not participating directly into the dehumidifying and heat reclaim process. 
         [0019]    If heat reclaim or dehumidifying are not required, the compressed refrigerant vapors from compressors  11  are fed through conduit  12  and conduit  18  to the gas cooler  5 , and then through conduit  19  and conduit  20  to the throttling device  9  and then to the receiver (flash tank)  10 . During this operational configuration, valves  25  and  7  are fully open, while valves  3 ,  4 ,  6  and  8  are completely closed. 
         [0020]    If heat reclaim is required, valve  25  is adjusted to maintain a pressure higher than the pressure maintained by valve  3 . Valve  4  is completely open. The compressed vapors from compressors  11  are fed through conduit  12 , valve  4  and conduit  13  to the heat reclaim/dehumidifying heat exchanger  1  where the heat of the vapors is transferred to the air flowing through the heat exchanger. The valve  3  maintains the necessary pressure in order to provide maximum efficiency. From heat exchanger  1 , the vapors are fed through valve  3 , conduit  14 , conduit  16 , conduit  17  and conduit  18  to the gas cooler  5 . Valve  6  and  8  are completely closed and valve  7  is completely open. From the gas cooler  5 , the vapors and/or liquid refrigerant, depending on the operation conditions, are fed through conduit  19  and conduit  20  to the throttling device  9  and from there to the receiver  10 . 
         [0021]    If dehumidifying is required, valve  25  is completely open, valves  3 ,  4  and  7  are completely closed and valves  6  and  8  are completely open. The compressed refrigeration vapors from compressors are fed through conduit  12 , valve  25  and conduit  18  to the gas cooler  5 . The vapors from the outlet of the gas cooler  5  are fed through conduit  19 , valve  6 , conduit  22 , conduit  23 , conduit  24  and conduit  13  to the heat reclaim/dehumidifying heat exchanger  1 . Cooled by the air-conditioning heat exchanger  2 , air is reheated by the dehumidifying heat exchanger  1 , using the heat of the vapors from the gas cooler  5  outlet, thus reducing its relative humidity. From heat exchanger  1 , the refrigerant is fed through conduit  14 , conduit  15 , conduit  21  and valve  8  to conduit  20  and then to throttling device  9  and receiver  10 . 
         [0022]    Although the present invention has been described with a certain degree of particularity, it is to be understood that the disclosure has been made by way of example only and that the present invention is not limited to the features of the embodiments described and illustrated herein, but includes all variations and modifications within the scope of the invention as hereinabove described.