Abstract:
A reversible HVAC heating/cooling refrigerant system includes a novel valve system that allows an outdoor heat exchanger to function as a subcooler during a cooling or defrost mode and function as a receiver tank for storing excess liquid refrigerant during a heating mode. In the heating mode, a cooling expansion valve is kept slightly open to flood the subcooler with liquid refrigerant while a heating expansion valve is regulated to maintain a desired level of superheat at the suction side of the refrigerant system&#39;s compressor. The novel valve system also serves as a pressure relief valve to protect the subcooler from excess pressure caused by thermal expansion of liquid refrigerant trapped within the subcooler.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The subject invention generally pertains to refrigerant systems and more specifically to a valve and subcooler arrangement for storing excess refrigerant charge during a heating mode. 
         [0003]    2. Description of Related Art 
         [0004]    Reversible HVAC refrigerant systems (e.g., a reversible heat pump) selectively operable in heating and cooling modes typically require a greater charge of refrigerant in the cooling mode than in the heating mode. To accommodate the difference in charge, many reversible refrigerant systems include a receiver or holding tank for storing excess liquid refrigerant during the heating mode. Such receivers, however, can be rather large and thus expensive. 
         [0005]    Consequently, there appears to be a need for a better way of dealing with a reversible refrigerant system&#39;s changing demand for refrigerant charge as the system switches between a heating a cooling mode. 
       SUMMARY OF THE INVENTION  
       [0006]    It is an object of some embodiments of the invention to provide a reversible heating/cooling refrigerant system with a heat exchanger that serves as a subcooler during the cooling mode and serves as a liquid storage vessel for storing excess liquid refrigerant during a heating mode. 
         [0007]    Another object of some embodiments is to provide the refrigerant system with a pressure-actuated switching valve that changes a heat exchanger from being a subcooler to being a receiver holding tank. 
         [0008]    Another object of some embodiments is to enable such a pressure-actuated switching valve to further function as a pressure relief valve to protect a heat exchanger from excess pressure caused by thermal expansion of a trapped charge of liquid refrigerant. 
         [0009]    Another object of some embodiments is to use a cooling expansion valve during a heating mode as a means for transferring excess liquid refrigerant to a subcooler for storage and to keep the subcooler pressurized to keep the charge subcooled. 
         [0010]    Another object of some embodiments is to configure a main coil and a subcooler of an exterior heat exchanger such that in a cooling mode the refrigerant in the subcooler flows in somewhat of a counter-flow pattern with respect to the outside air flowing across the heat exchanger. 
         [0011]    Another object of some embodiments is to configure a main coil and a subcooler of an exterior heat exchanger such that in a heating mode the refrigerant in the main coil flows in somewhat of a counter-flow pattern with respect to the outside air flowing across the heat exchanger. 
         [0012]    Another object of some embodiments is to provide a reversible heating/cooling refrigerant system with a transition mode that, without an operating compressor, naturally transfers liquid refrigerant to areas of the system where the liquid refrigerant will unlikely be inhaled later by the compressor upon switching to a cooling or defrost mode. 
         [0013]    One or more of these and/or other objects of the invention are provided by a reversible heating/cooling refrigerant system that includes a valve system operating in conjunction with a subcooler such that the subcooler functions as a liquid refrigerant holding receiver during the heating mode, and the valve system functions as a pressure relief valve to protect the subcooler from bursting should the stored liquid refrigerant thermally expand while being hermetically trapped within the subcooler. 
         [0014]    The present invention provides a refrigerant system being operable in at least a heating mode and containing a refrigerant in heat transfer relationship with an outside fluid for ultimately heating a comfort zone or a process. The refrigerant system comprises a heat exchanger system containing at least some of the refrigerant; a compressor periodically drawing the refrigerant at a suction pressure and discharging the refrigerant at a discharge pressure, thereby providing the refrigerant system with a high-pressure side and a low-pressure side; and a pressure relief valve defining an inlet and an outlet, wherein the inlet is connected in fluid communication with the heat exchanger system, the outlet is connected in fluid communication with the low-pressure side, and the pressure relief valve opens to release at least some of the refrigerant from within the heat exchanger system in response to the refrigerant within the heat exchanger system exceeding a maximum pressure limit, wherein the maximum pressure limit is even greater than the discharge pressure of the compressor. 
         [0015]    The present invention also provides a refrigerant system containing a refrigerant and being selectively operable in a heating mode and a cooling mode for respectively heating and cooling a comfort zone or a process. The refrigerant system absorbs heat from an outside fluid when the refrigerant system is in the heating mode heating the comfort zone or a process and releases heat to the outside fluid when the refrigerant system is in the cooling mode cooling the comfort zone or a process. The refrigerant system comprises an exterior heat exchanger system that includes a main coil and a subcooler. The exterior heat exchanger system is arranged to release heat to the outside fluid when the refrigerant system is in the cooling mode and absorb heat from the outside fluid when the refrigerant system is in the heating mode. The main coil defines a first main port and a second main port in refrigerant fluid communication with each other through the main coil. The subcooler defines a first subcooler port and a second subcooler port in refrigerant fluid communication with each other through the subcooler. The refrigerant system also includes a valve system with pressure relief. The valve system defines a coil valve port and a subcooler valve port. The coil valve port is connected in refrigerant fluid communication with the second main port of the main coil. The subcooler valve port is connected in refrigerant fluid communication with the second subcooler port of the subcooler. The valve system has an open position and a closed position such that: in the open position, the valve system connects the coil valve port in refrigerant fluid communication with the subcooler valve port; in the closed position, the valve system substantially blocks refrigerant fluid communication therethrough between the coil valve port and the subcooler valve port; the valve system is in the open position when the refrigerant system is in the cooling mode; the valve system is in the closed position when the refrigerant system is in the heating mode while the refrigerant within the subcooler is below a predetermined pressure limit; and the valve system is in the open position when the refrigerant system is in the heating mode while the refrigerant within the subcooler is above the predetermined pressure limit. 
         [0016]    The present invention further provides a method of operating a refrigerant system that is selectively operable in a heating mode and a cooling mode, wherein the refrigerant system includes a main coil and a subcooler containing a refrigerant that is in heat transfer relationship with an outside fluid. The method comprises: in the cooling mode, releasing heat from the main coil and the subcooler to the outside fluid; in the heating mode, transferring heat from the outside fluid to the main coil as the refrigerant flows therethrough; in the heating mode, trapping within the subcooler at least some of the refrigerant, wherein most of the refrigerant trapped within the subcooler is in a liquid state; and releasing at least some of the refrigerant from within the subcooler if the refrigerant within the subcooler reaches a predetermined maximum pressure limit while still retaining substantially all of the refrigerant within the refrigerant system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a schematic diagram of one example of a refrigerant system in a cooling or defrost mode. 
           [0018]      FIG. 2  is a schematic diagram of the refrigerant system in a heating mode. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]      FIGS. 1 and 2  schematically illustrate a refrigerant system  10  selectively operable in a cooling mode ( FIG. 1 ) and a heating mode ( FIG. 2 ) to cool or heat a comfort zone  12 , such as a room or other trea in a building or for heating or cooling some process (e.g., heating or cooling a chemical). The cooling mode can also be used as a defrost mode that periodically interrupts the heating mode to defrost an exterior heat exchanger system  14 . System  10  requires a greater refrigerant charge for cooling than for heating, so a tank receiver  16  helps store some excess liquid refrigerant during the heating mode. 
         [0020]    To minimize the required size of receiver  16 , a unique valve system  18  works in conjunction with exterior heat exchanger system  14  to store an additional amount of the heating mode&#39;s excess liquid refrigerant in a subcooler  14   a  of heat exchanger  14 . Although valve system  18  is shown as a single, multipurpose valve, valve system  18  could also be an equivalent circuit of multiple diverse valves including, for example, a 3-way directional valve  48 . 
         [0021]    The design of exterior heat exchanger  14  may also vary. The expression, “exterior heat exchanger” refers to any heat exchanger that exchanges heat with an outside fluid  22  (e.g., outdoor air); however, an exterior heat exchanger does not necessarily have to be installed physically outdoors. The heat transfer between exterior heat exchanger  14  and outside fluid  22  can occur directly or it can happen indirectly via an intermediate heat transfer fluid, such as water. 
         [0022]    Exterior heat exchanger  14  comprises a main coil  14   b  and subcooler  14   a.  The expression, “main coil,” and the term, “subcooler,” simply refer to any type of heat exchanger and are not meant to describe any particular design. Main coil  14   b  and subcooler  14   a  can be two separate heat exchangers, or they can be combined in some way, for instance, by sharing the same heat transfer fins. For sake of example, main coil  14   b  comprises a series of refrigerant-conveying tubes  24  traversing a plurality of heat transfer fins across which outside fluid  22  passes. Subcooler  14   a  also comprises a series of refrigerant-conveying tubes  26  traversing preferably the same fins as main coil  14   b.  For performance reasons, there are more tubes  24  in main coil  14   b  than there are tubes  26  in subcooler  14   a.    
         [0023]    Main coil  14   b  includes a first main port  28  and a second main port  30  (also known as a distributor) in refrigerant fluid communication with each other via tubes  24  (i.e., refrigerant flows between ports  28  and  30 ). First main port  28  preferably is upstream of second main port  30  with reference to a current of outside air or fluid  22 . The current of outside air or fluid  22  is driven by one or more fans  32  associated with exterior heat exchanger system  14 . Subcooler  14   a  includes a first subcooler port  34  and a second subcooler port  36  in refrigerant fluid communication with each other via tubes  26 . First subcooler port  34  preferably is upstream of second subcooler port  36  with reference to the current of outside air or fluid  22  (e.g., fluid  22  first flows generally across port  34  and then across port  36 ). 
         [0024]    In addition to exterior heat exchanger system  14 , receiver tank  16  and valve system  18 , refrigerant system  10  also includes at least one compressor  38  for compressing a refrigerant; a comfort zone heat exchanger  40  for heating or cooling comfort zone  12  or a process; a 2-position, 4-way directional valve  42  for selectively switching between the heating mode and the cooling mode (also defrost mode); a cooling expansion valve  44 ; a heating expansion valve  46 ; and a 2-position, 3-way directional valve  48  for controlling valve system  18 . In this example, valves  42  and  48  are solenoid otherwise electrically actuated with their normally de-energized state being as shown in  FIG. 1 , and their energized state being as shown in  FIG. 2 . Those of ordinary skill in the art should appreciate, however, that the energized and de-energized states could be reversed and that there are many other conceivable ways of actuating directional valves. 
         [0025]    With refrigerant system  10  in operation, compressor  38  draws in relatively cool gaseous refrigerant at a suction pressure from a low-pressure side  50  of system  10  and discharges gaseous refrigerant to a high-pressure side  52  at an appreciably higher discharge pressure and temperature. In the cooling mode, shown in  FIG. 1 , 3-way valve  48  applies suction pressure to a pilot port  54  that opens valve system  18 , and  4 -way valve  42  directs relatively hot discharge refrigerant to first main port  28  of main coil  14   b.  From first main port  28 , the refrigerant flows through tubes  24  to second main port  30 . Upon passing through main coil  14   b,  the relatively hot discharge refrigerant cools and may at least partially condense as it releases heat to outside fluid  22 . 
         [0026]    The now cooler and perhaps liquid refrigerant flows from second main port  30  to a tee  56 . A right leg  58  of tee  56  is blocked off by heating valve  46  being closed, so the refrigerant flows through a left leg  60  of tee  56  toward valve system  18 , which is open during the cooling mode. The refrigerant passes through open valve system  18  by flowing sequentially through a coil valve port  62 , an opening  64  through a valve seat  66 , an annular passageway  68  encircling opening  64 , and out through a subcooler valve port  70 . 
         [0027]    In this example of the invention, valve system  18  includes a valve housing  72  that includes valve seat  66  and defines opening  64 ; annular passageway  68 ; and ports  54 ,  62  and  70 . Although a compression spring  74  urges a valve element  76  (e.g., a valve plug, diaphragm, piston, etc.) in sealing engagement against valve seat  66  to urge valve system  18  to a closed position ( FIG. 2 ) where valve element  76  obstructs opening  64 , in this embodiment, valve element  76  is a piston with one side  78  exposed to refrigerant pressure at pilot port  54  and an opposite side  80  exposed to refrigerant at opening  64  and annular passageway  68 . In the cooling mode (and defrost mode), piston side  80  faces pressure at about that of high-pressure side  52 , and piston side  78  faces pressure at about that of low-pressure side  50 . The resulting pressure differential across piston  76  is sufficient to overpower the urging of spring  74 , thus valve element  76  moves to a spaced-apart position relative to valve seat  66  to open valve system  18  as shown in  FIG. 1 . 
         [0028]    After flowing through open valve system  18 , the refrigerant flows from subcooler valve port  70  to enter subcooler  14   a  through second subcooler port  36 . The refrigerant then flows through the subcooler&#39;s tubes  26  to the first subcooler port  34 . Upon passing through subcooler  14   a , the refrigerant releases more heat to outside fluid  22  to ensure that the relatively high-pressure refrigerant is thoroughly condensed and has some amount of subcooling. 
         [0029]    The condensed high-pressure refrigerant flows through cooling expansion valve  44 , which is regulated in a conventional manner to reduce the refrigerant pressure and thus cool the refrigerant by expansion. The relatively cool, low-pressure refrigerant leaving expansion valve  44  then flows through comfort zone heat exchanger  40  to cool comfort zone  12 . Upon absorbing heat from a secondary heat transfer fluid  82  that cools comfort zone  12 , the refrigerant vaporizes, and 4-way valve  42  directs the relatively cool gaseous refrigerant back to low-pressure side  50  where the refrigerant returns to compressor  38 , thereby perpetuating the refrigerant cycle in the cooling mode. 
         [0030]    Since receiver  16  is exposed to suction pressure of low-pressure side  50 , any liquid refrigerant that happens to be in receiver  16  (just prior to operating in the cooling mode) tends to vaporize, thus leaving receiver  16  substantially void of liquid refrigerant during the cooling mode. 
         [0031]    In the heating mode, shown in  FIG. 2 , 3-way valve  48  applies discharge pressure to pilot port  54  to close valve system  18 , and 4-way valve  42  directs relatively hot discharge refrigerant through comfort zone heat exchanger  40  to heat comfort zone  12 . As the refrigerant passes through comfort zone heat exchanger  40 , the refrigerant condenses by releasing heat to secondary heat transfer fluid  82 , which now heats comfort zone  12 . From heat exchanger  40 , the condensed refrigerant flows to receiver  16 , cooling expansion valve  44  and heating expansion valve  46 . 
         [0032]    During the heating mode, liquid refrigerant flowing through receiver  16  fills the receiver with liquid refrigerant, whereby that amount refrigerant is effectively removed from the active part of the refrigerant circuit. For additional storage of liquid refrigerant, cooling expansion valve  44  is held partially open (e.g., 10% open) to feed liquid refrigerant into subcooler  14   a  where liquid refrigerant stagnates between closed valve system  18  and cooling expansion valve  44 , thereby effectively removing that refrigerant from the active part of the refrigerant circuit. The liquid refrigerant flowing from comfort zone heat exchanger  40  through receiver  16  then to heating expansion valve  46  is the portion of refrigerant that is actively used in the heating mode. 
         [0033]    Heating expansion valve  46  can be regulated in a conventional manner to maintain a desired level of superheat of refrigerant at low-pressure side  50 . As the refrigerant passes through the regulated heating expansion valve  46 , the refrigerant cools by expansion. The relatively cool refrigerant then flows to tee  56 . Since valve system  18  is closed, the refrigerant flows from tee  56  to second main port  30  and then to first main port  28  by flowing through tubes  24  of main coil  14   b.  Upon passing through main coil  14   b,  the relatively cool refrigerant absorbs heat from outside fluid  22 . This causes the refrigerant to vaporize before 4-way valve  42  directs the now gaseous refrigerant back to low-pressure side  50  where the refrigerant returns to compressor  38 , thereby perpetuating the refrigerant cycle in the heating mode. 
         [0034]    Although relatively high discharge pressure at pilot port  54  forces valve element  76  to its closed position of  FIG. 2 , valve system  18  can still serve as a pressure relief valve for subcooler  14   a,  wherein subcooler valve port  70  becomes the pressure relief valve&#39;s inlet and coil valve port  62  becomes the pressure relief valve&#39;s outlet. If, for instance, system  10  is turned off with valves  18  and  44  closed, liquid refrigerant can be left trapped within subcooler  14   a  between valves  18  and  44 . If the ambient temperature then increases, this can cause the trapped liquid to expand by thermal expansion, which could increase the refrigerant&#39;s pressure to a magnitude that exceeds the compressor&#39;s maximum discharge pressure and perhaps exceed the burst pressure of tubes  26 . To avoid damaging tubes  26 , spring  74  and the cross-sectional areas of opening  64  and annular passageway  68  are designed such that if the pressure against side  80  of valve element  76  exceeds a predetermined maximum pressure limit, that pressure will be sufficient to force valve system  18  to its open position ( FIG. 1 ), whereby the excessively high pressure at stibcooler valve port  70  is relieved to the lower pressure at coil valve port  62 . It should be noted that said, “predetermined maximum pressure limit,” may vary as a function of the pressure on side  78  of valve element  76 . It might also be noted that valve system  18  could also function as a pressure relief for main coil  14   b,  wherein sufficient pressure at opening  64  could also force valve system  18  to open. In the later example where valve system  18  serves as a pressure relief valve for main coil  14   b,  the pressure relief valve would have its inlet at coil valve port  62  and its outlet at subcooler valve port  70 . 
         [0035]    Before suddenly switching from the heating mode ( FIG. 2 ) to the cooling or defrost mode ( FIG. 1 ), refrigerant system  10  preferably operates momentarily (e.g., 10-second period) in a transition mode to prevent compressor  38  from inhaling a slug of liquid refrigerant from receiver  16 . The transition mode is similar in configuration to the cooling mode with valve system  18  open and valves  42  and  48  de-energized as shown in  FIG. 1 ; however, in the transition mode, compressor  38  is inactive, fan  32  is inactive, heating expansion valve  46  is at least partially open (e.g., 25% open), and cooling expansion valve  44  is at least partially open (e.g., 10% open). The transition mode allows an appreciable amount of liquid refrigerant in receiver  16  to flow into exterior heat exchanger  14  and allows some liquid refrigerant in subcooler  14   a  to flow into main coil  14   b.    
         [0036]    Switching from the defrost mode of  FIG. 1  to the heating mode of  FIG. 2  preferably is done in the following sequence: step-1) compressor  38  is de-energized; step-2) valve  48  is shifted to the position of  FIG. 2  with little to no time delay between steps 1 and 2; step-3) close cooling expansion valve  44 ; step-4) is a time delay of 5 to 30 seconds (preferably about 15 to 20 seconds); step-5) valve  42  shifts to the position of  FIG. 2 ; step-6) energize compressor  38 , wherein steps 5 and 6 are performed simultaneously or within about two seconds of each other; step-7) cooling expansion valve  44  partially opens (e.g., about 20% open); and step-8) heating expansion valve  46  is regulated. 
         [0037]    Although the invention is described with respect to a preferred embodiment, modifications thereto will be apparent to those of ordinary skill in the art. The scope of the invention, therefore, is to be determined by reference to the following claims: