Abstract:
In one embodiment, the invention provides a refrigeration system having a compressor configured to compress a refrigerant gas and a condenser fluidly coupled to the compressor to receive compressed refrigerant gas from the compressor, the condenser configured to condense the refrigerant gas. In addition the refrigeration system includes a heat exchanger having a first section fluidly coupled to the compressor, and a second section fluidly coupled between the condenser and the compressor, wherein the first section receives compressed refrigerant gas from the compressor, and wherein the second section receives condensed refrigerant from the condenser, evaporates the refrigerant, and delivers the evaporated refrigerant to the compressor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/289,555 filed on Dec. 23, 2009 and to U.S. Provisional Patent Application No. 61/324,475 filed on Apr. 15, 2010. The contents of these applications are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND 
       [0002]    Transporting and storing temperature sensitive cargo over periods of time may require a controlled climate in the space where the cargo is loaded. Climate control includes controlling the temperature of the cargo to be within a certain predefined acceptable range. Controlling the temperature includes bringing the temperature of the cargo into an acceptable range (by refrigerating or heating) and maintaining the temperature within that range. Climate control may also include controlling the humidity of the space where cargo is loaded. 
         [0003]    The temperature of temperature sensitive cargo should be kept within predefined acceptable limits. Some cargo must be maintained frozen, and the temperature of any part of the frozen cargo must be kept below a predefined freezing temperature which depends on the cargo, e.g. below 10 degrees Fahrenheit or lower, while commodities such as fresh fruit and vegetables should be kept chilled, but not frozen, to stay fresh. 
         [0004]    During operation of a refrigeration system water vapor will condensate on the evaporator and form a layer of ice that will degrade the efficiency of the evaporator and thereby of the refrigeration system. The ice is removed by running a defrosting cycle. Traditionally, defrosting cycles are initiated according to a predetermined schedule at time intervals which may depend on the nature of the cargo and the time since its loading into the container. 
         [0005]    Some cargoes need relative humidity to be kept below acceptable upper limits. Some of these cargoes are also sensitive to temperatures, while others are relatively insensitive to temperature. Examples of such products are electronic and optical products, scientific instruments, machinery and metals such as iron and steel that may corrode if the relative humidity is too high, clothing and other textiles where fungus growth can be prevented by keeping the relative humidity low. 
       SUMMARY 
       [0006]    In one embodiment, the invention provides a refrigeration system having a compressor configured to compress a refrigerant gas and a condenser fluidly coupled to the compressor to receive compressed refrigerant gas from the compressor, the condenser configured to condense the refrigerant gas. In addition the refrigeration system includes a heat exchanger having a first section fluidly coupled to the compressor, and a second section fluidly coupled between the condenser and the compressor, wherein the first section receives compressed refrigerant gas from the compressor, and wherein the second section receives condensed refrigerant from the condenser, evaporates the refrigerant, and delivers the evaporated refrigerant to the compressor. 
         [0007]    In another embodiment the invention provides a method of operating a refrigeration system, the method including compressing a refrigerant with a compressor and condensing compressed refrigerant gas from the compressor in a condenser. The method further includes receiving into a first section of a heat exchanger compressed refrigerant gas from the compressor, evaporating condensed refrigerant from the condenser in a second section of the heat exchanger, and delivering the evaporated refrigerant from the second section to the compressor. 
         [0008]    In yet another embodiment the invention provides a method of operating a refrigeration system, the method including measuring a relative humidity of a container. In addition, the method includes comparing the measured relative humidity to a humidity set point, and operating evaporator fans of a refrigeration system when the measured relative humidity is above the humidity set point. 
         [0009]    Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of a container for transporting cargo. 
           [0011]      FIG. 2  is a schematic view of a refrigeration system which includes a dehumidification system. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
         [0013]      FIG. 1  is a perspective view of a container  100  that is used for transporting cargo of various types. Coupled to one end of the container is a refrigeration system  10  which is used to control the climate, including the humidity level, of the interior of the container  100 . The container  100  could alternatively be a trailer, a railroad car, a straight truck cargo space, or other storage compartment used to transport cargo. 
         [0014]      FIG. 2  is a schematic view of the refrigeration system  10  which includes a dehumidification system. The illustrated embodiment includes a refrigeration system  10  with a compressor  20  which in operation compresses a refrigerant used in the refrigeration system  10 . Compressed and hot refrigerant is conducted from the compressor  20  through conduits  21  and  31  to a condenser  30  where heat energy is removed from the refrigerant. The shown condenser  30  is fan assisted, and condensed and cooled refrigerant leaves the condenser  30  through a conduit  32  and enters a receiver tank  33 . If additional cooling of the refrigerant is desired, an optional water-cooled condenser  30 ′ (shown in a dash-line frame) may be used. From the receiver tank  33  (or optionally the water-cooled condenser  30 ′) the condensed refrigerant is conducted through a conduit  34  (e.g., a liquid line) through a drier oil filter  35  to an economizer heat exchanger  40  and through a conduit  41  and a thermostatic expansion valve  42  to an evaporator  50 . Fans  55  circulate the air through the evaporator  50  and through the interior of the container  100  in a direction shown by the arrows. 
         [0015]    The evaporator  50  has a first part  102  and a second part  104 . The evaporator  50  is a tube-fin-type heat exchanger. The refrigerant in the first part  102  and the second part  104  remains separate until the refrigerant reaches a discharge point  105 . Thus, the refrigerant contained in the tubes of the first part  102  does not mix with any refrigerant contained in the tubes of the second part  104  until the refrigerant cycles through the first part  102  or the second part  104  to the discharge point  105 , where the tubes of the first and second parts  102 ,  104  combine into a discharge header, for example. When the refrigerant reaches the discharge point  105  the refrigerant from the first part  102  and the second part  104  mixes and is returned to the compressor  20  via a return conduit  22 . However, the first part  102  and the second part  104  are thermally connected. In other words, the fins that assist in transferring heat to and from the tubes are interconnected between both the tubes of the first and second parts  102 ,  104  of the evaporator  50 . 
         [0016]    The refrigeration system  10  has a first distributor  51  and a second distributor  52  each of which is connected to receive cold condensed refrigerant from the conduit  41  and the thermostatic expansion valve  42 . The first distributor  51  feeds refrigerant to the tubes of the first part  102  of the evaporator  50 , and the second distributor  52  feeds refrigerant to the tubes of the second part  104  of the evaporator  50 . On its upstream side the first distributor  51  is connected to a first control valve  53 . A second control valve  54  is connected to the conduit  21  that conducts hot compressed refrigerant gas from the compressor  20  to the second control valve  54 . A conduit  56  connects the outlet of the second control valve  54  with the inlet of the first distributor  51 . 
         [0017]    In an alternative construction the refrigeration system does not include the first control valve  53  and the first section  102  is not connected to the conduit  41  that conducts refrigerant from the economizer  40  and the condenser  30 . Thus, in this alternative construction, if the second control valve  54  is open then hot refrigerant is received into the first section  102 . If the second control valve  54  is closed, then no refrigerant whatsoever is circulated through the first section  102 . 
         [0018]    A controller  110  controls the operation of the refrigeration system  10 . A thermometer  108  measures the temperature of the interior of the container  100  and relays the temperature to the controller  110 . An electric heating element  60  is arranged adjacent the evaporator  50 . A humidity sensor  106  is arranged for sensing the relative humidity of the air in the container  100  and outputs a corresponding signal to the controller  110  for determining whether the relative humidity is within acceptable limits. 
         [0019]    The refrigeration system  10  addresses the problem of reducing the relative humidity, in particular when the cargo is relatively insensitive to temperature. The method of the invention uses a refrigeration system and operates the refrigeration system to cause the temperature of the air to increase whereby the relative humidity is reduced. Preferably, the evaporator fans  55  are initially operated to cause the air to circulate within the container  100 . The friction heat that is generated by the circulating air will cause the temperature to increase and in consequence the relative humidity will decrease. The refrigeration system  10  may further be operated to activate the electric heating element  60 . This use of the refrigeration system  10  for heating the air to reduce the relative humidity without refrigerating or dehumidifying is advantageous and allows a refrigeration system to be used for other purposes than refrigeration and other traditional uses. 
         [0020]    If it is determined that the relative humidity is higher than desired, i.e. higher than a predetermined value, heat generating means of the refrigeration system  10  are activated to heat the air in the container and thereby reduce the relative humidity. Humidity is not extracted from the air by heating alone and the absolute humidity will remain constant, but since the capacity of the air to absorb or contain water vapor increases with increasing temperature, the relative humidity will decrease with increasing temperature. 
         [0021]    Specifically, the heat generating means of the refrigeration system  10  that are activated to heat the air in the container  100  comprises one or more of the fans  55  that are arranged to circulate the air in the container  100  past the evaporator  50  and through the container  100 . Circulating the air in the container  100  requires energy which is dissipated as heat due to friction between the air and the container walls and the cargo in the container  100 . The dissipated heat will increase the temperature of the air and the relative humidity will thereby be correspondingly reduced. 
         [0022]    If the friction heat generated using one or more of the fans  55  to circulate the air in the container  100  is not enough to keep the relative humidity below the predetermined acceptable value, the electric heating element  60  may additionally be activated. The fan/fans  55  circulate the air in the container  100  past the heating element  60  whereby the air is further heated in addition to the friction heat generated by circulating the air. 
         [0023]    The refrigeration system  10  also addresses the problem of reducing the relative humidity, in particular when the cargo is sensitive to temperature. This invention is useful for dehumidifying the air in the container  100  while still maintaining the cargo chilled. For example, fresh fruit generates water vapor that needs be removed by dehumidification for which traditionally the refrigeration system is used. Dehumidification is done by operating the refrigeration system in a first mode to refrigerate the air whereby water vapor condensates on the evaporator coil. In case of high humidity, elevated dehumidification will be necessary which involves running one or more sections of the evaporator coil at correspondingly elevated refrigeration power in order to condensate the water vapor. Thereby the air may become refrigerated below a critical minimum temperature (e.g. bananas must be kept at a temperature not lower than 13 degrees C.). Refrigeration below the critical minimum temperature must be avoided. Traditionally, in order to compensate for the elevated refrigeration an electric heating element is activated. Instead, according to the invention, heating energy already produced by the refrigeration system  10  is used. When the refrigerant leaves the compressor it is “hot” and traditionally all the hot refrigerant is condensed and cooled in the condenser where a condenser fan removes the heat before the “cold” refrigerant is conducted to the evaporator. According to the invention, the refrigeration system will operate in a second mode of operation where a portion of the compressed refrigerant from the compressor bypasses the condenser and is fed to a section of the evaporator coil as “hot gas”. 
         [0024]    In the first mode of operation the first control valve  53  is open and the second control valve  54  is closed. The refrigerant will then flow in the closed circuit from the compressor  20  through conduits  21  and  31 , condenser  30 , receiver tank  33 , conduit  34 , drier oil filter  35 , heat exchanger  40 , conduit  41 , expansion valve  42 , first and second distributors  51 ,  52 , first part  102  and second part  104  of the evaporator  50  and return conduit  22  back to the compressor  20 . The first mode of operation is thus a traditional refrigeration mode where both the first and the second distributor  51 ,  52  receive cold refrigerant which is fed into both the first and the second parts  102 ,  104  of the evaporator  50 . 
         [0025]    In the second mode of operation the first control valve  53  is closed, and the first distributor  51  will no longer receive cold refrigerant as in the first mode of operation. The second control valve  54  is opened so that hot refrigerant from the compressor will be conducted through conduit  21 , the second control valve  54  and conduit  55  to the inlet of the first distributor  51  and into the first part  102  of the evaporator  50 . The second distributor  52  and the second part  104  of the evaporator  50  will still receive cold refrigerant like in the first mode of operation described above. Thus the second part  104  of the evaporator  50  can be operated to achieve the desired temperature. If the air in the container  100  is thereby refrigerated to an unacceptable low temperature, the second control valve  54  is opened to conduct hot refrigerant to the first part  102  of the evaporator  50  whereby the air that is drawn through the evaporator  50  by means of the fans  55  will be heated to raise the temperature of the air in the interior of container  100 . Thus the air in the interior of the container  100  is controlled to be at a desired relative humidity level. 
         [0026]    The refrigeration system  10  may also be used to defrost the evaporator  50  when ice has accumulated on the evaporator  50 . In order to defrost the evaporator  50 , the supply of cold refrigerant to the evaporator  50  is stopped and hot refrigerant from the compressor  20  is sent to the first part  102  of the evaporator  50  as described above. As the evaporator  50  is not receiving any cold refrigerant, the heat from the hot refrigerant in the first part  102  of the evaporator  50  will warm the entire evaporator  50 , thus melting the ice from the evaporator  50 . 
         [0027]    Thus, the invention provides, among other things, an apparatus for controlling humidity in a container. Various features and advantages of the invention are set forth in the following claims.