Abstract:
Vapor compression air conditioning systems are provided with a flow restrictor for transferring working fluid to and from at least one of the compressor low pressure inlet conduit and compressor high pressure outlet conduit to provide for accurate charge adjustment to achieve predetermined fluid sub-cooling. Pressure and temperature measurements are taken at a condenser fluid outlet conduit and provided to a microcontroller for determining fluid sub-cooling and comparing sub-cooling with a predetermined target sub-cooling. A charge addition or recovery apparatus may include a solenoid valve controlled by the microcontroller to more accurately control the addition or recovery of refrigerant fluid charge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a divisional application of the prior filed and co-pending U.S. patent application Ser. No. 11/486,874 filed Jul. 14, 2006 and entitled “System And Method For Controlling Working Fluid Charge In A Vapor Compression Air Conditioning System” which is incorporated herein by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Vapor compression refrigeration, air conditioning and heating (heat pump) systems have long been plagued with less than optimum operating efficiencies due to an inadequate or excessive working fluid charge within the system. Vapor compression air conditioning and heat pumps systems, for example, typically are designed to operate with a working fluid charge which provides a small amount of sub-cooling of the working fluid in its condensed state. However, initial installation, servicing and repair operations are difficult to carry out with respect to providing a proper fluid charge within the system. For example, when removing fluid or adding fluid to the system, there is often inadequate control of flow of the fluid (refrigerant) resulting in an excessive charge of fluid to a system or a system which is undercharged. Historically, it has been necessary to add or subtract fluid and operate the system to “wait and see” if the system comes into a balanced condition or achieves the desired amount of sub-cooling of the fluid in its condensed state. However, the present invention overcomes the inaccuracies and excessive delays in providing properly charged vapor compression air conditioning systems, in particular. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention provides a vapor compression air conditioning (heating, cooling or both heating and cooling) or refrigeration system adapted for optimum operating efficiency with respect to the proper quantity or charge of working fluid disposed in the system. The present invention also provides a method, particularly, for adding working fluid to a vapor compression-type air conditioning or refrigeration system. However, a method of extracting fluid is also contemplated. 
         [0004]    In accordance with one aspect of the present invention, a vapor compression air conditioning or refrigeration system is adapted for connection to a fluid adding or fluid extracting unit which may include at least one reservoir of working fluid and one or more conduits for connection to fluid conduits associated with the working fluid compressor of the air conditioning system. A fluid flow restrictor device may be provided in one or more conduits adapted to be connected to the so-called low pressure side of a compressor as well as the high pressure side for adding fluid to or removing fluid from the system circuit, respectively. The flow restrictor device may be adapted for throttling fluid flow in one direction while providing for substantially unrestricted flow of fluid in an opposite direction. The flow restrictor devices may be connected to a portable fluid adding and fluid extracting unit or the devices may be permanently connected to the working fluid conduits associated with or connected to the compressor of a vapor compression air conditioning or refrigeration system. 
         [0005]    In accordance with another aspect of the present invention, a vapor compression-type air conditioning system or refrigeration system is adapted to include a control circuit or controller and associated instrumentation which monitors the operating condition of the system during a working fluid charge adding or extracting process to calculate actual sub-cooling of the working fluid as it leaves a condenser unit of the system. The controller is operable to provide a suitable output signal indicating the need to remove additional fluid, add additional fluid or indicate no action needed. Still further, the controller may be adapted to automatically shutoff the flow of working fluid to the system when an optimum operating or selected operating condition is reached. 
         [0006]    In accordance with yet a further aspect of the present invention, an improved method is provided for adding working fluid to or subtracting working fluid from a vapor compression air conditioning or refrigeration system which achieves an optimum fluid charge, or at least a fluid charge providing a selected amount of sub-cooling of the working fluid flowing in the system. 
         [0007]    Those skilled in the art will further appreciate the above-mentioned advantages and superior features of the invention as well as other important aspects thereof upon reading the detailed description which follows in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a schematic diagram of a vapor compression air conditioning system including a working fluid charge adding and evacuating unit and a controller in accordance with the invention; 
           [0009]      FIG. 2  is a longitudinal central section view of one preferred embodiment of a flow restrictor device in accordance with the invention and for use with the system of the invention; 
           [0010]      FIG. 3  is a detail section view taken generally along the line  3 - 3  of  FIG. 2 ; 
           [0011]      FIG. 4  is a flow diagram illustrating at least the major steps in a process for adding or subtracting working fluid with respect to a vapor compression air conditioning or refrigeration system in accordance with the invention; and 
           [0012]      FIG. 5  is a schematic diagram of an alternate embodiment of a system in accordance with the invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0013]    In the description which follows like elements are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale and certain features may be shown in generalized or schematic form in the interest of clarity and conciseness. 
         [0014]    Referring to  FIG. 1 , there is illustrated a schematic diagram of a vapor compression-type air conditioning system which may also be configured as a refrigeration system, and generally designated by the numeral  10 . The system  10  includes respective heat exchangers  12  and  14  operably interconnected by a compressor  16 . For the sake of discussion, the system  10  may be considered to be an air conditioning (cooling) system although it will be understood by those skilled in the art that the invention may be used in connection with a so called heat pump system, both reversible and nonreversible and the invention may also be used in connection with a refrigeration system used for purposes other than conditioning ambient air for human comfort or the like. 
         [0015]    The compressor  16  is connected to heat exchanger  14  acting as a condenser by way of a high pressure discharge conduit  18  and condenser  14  is connected to heat exchanger  12 , acting as an evaporator unit, by way of a further high pressure conduit  20  and an expansion device  22 . Typically, the heat exchanger  12 , expansion device  22  and a portion of a conduit  24  interconnecting the compressor  16  with the heat exchanger  12  are located within the interior of a structure being cooled. A system controller  26  is operably connected to certain components including an indoor fan or blower, not shown, and a second portion  28  of the controller is provided for controlling on and off operation of compressor  16  and for controlling flow of air over heat exchanger  14  by way of a motor driven fan  30 . A heat exchange medium other than forced air may be used to control heat exchange by one or both of the heat exchangers  12  and  14 . When used as an air conditioning or heat pump system, the system  10  also includes a thermostat  32  connected to controller units  26  and  28 . Controller unit  26  is also connected to a source of electrical power via conductor means  36  and for communicating such power to controller unit  28 . 
         [0016]    Conduit  24  is considered a so-called low pressure conduit leading to compressor  16  for delivering working fluid thereto for compression to a higher pressure. Conduit  24  includes a suitable releasable connector  25   a  associated therewith disposed in proximity to the compressor  16  and including a one way poppet valve  25   c , or so-called Schrader valve known in the art, for conducting refrigerant fluid to or from the system  10 , which fluid may be one of several types known to those skilled in the art and used as the working fluid in vapor compression systems. A second releasable connector  27   a  is connected to high pressure conduit or so called liquid line  20 , but may be connected to conduit  18 , alternatively. Connector  27   a  includes a Schrader valve  27   c . Conduit  18  is connected to the so-called high pressure side of compressor  16  for conducting heated vapor to heat exchanger  14  for at least partial condensation therein and then discharge to conduit  20 . 
         [0017]    Accordingly, working fluid flowing out of the heat exchanger  14  through conduit  20  to expansion device  22  is typically in liquid form and the pressure and temperature of such fluid may be sensed by respective temperature and pressure sensors  40  and  42 , as shown in  FIG. 1 . Sensors  40  and  42  may include direct readout displays or gauges  40   a  and  42   a  and are operatively connected to a further controller unit or circuit  44  which may be operably connected to the controller unit  28  to receive power therefrom and deliver certain control signals thereto. Controller  44  may be a suitable programmable microcontroller or an application specific integrated circuit previously programmed for operation in accordance with the invention. Controller  44  includes a part  45  including visual indicators  46  and  48  for indicating the status of a refrigerant or working fluid charge in the system  10 . A visual display  48   a  may also be provided for displaying information to a user. The controller part  45  is also adapted to provide an electric output signal to conductor means  50  which may be releasably connected to the controller part  45  at a plug or connector  52 . 
         [0018]    Referring further to  FIG. 1 , a working fluid adding and evacuation or subtracting apparatus is illustrated and generally designated by the numeral  54 . The apparatus  54  includes a pressure vessel and reservoir  56  for new working fluid, such as one of the common refrigerant fluids previously mentioned. A conduit  58  is connected to reservoir  56  and to a motor operated or solenoid type valve  60  connected to conductor means  50  and to the controller part  45  via the connector  52 . Conduits  62 ,  64  and  66  are operable to be in communication with the reservoir  56  by way of the valve  60 . Suitable manual or remotely controllable valves  63 ,  65  and  67  may be arranged as illustrated for controlling the flow of working fluid between the new fluid reservoir  56 , a fluid recovery reservoir  70  and connector parts  25   b  and  27   b  which are operable to connect the apparatus  54  to the conduit  24  and the conduit  20 , respectively. Connector parts  25   a  and  27   a  are associated with Schrader valves  25   c  and  27   c  operably connected to the respective conduits  24  and  20 , as illustrated and previously described. When connectors  25   a  and  25   b  are engaged, valve  25   c  is open and when connectors  27   a  and  27   b  are engaged, valve  27   c  is open. 
         [0019]    Referring to  FIGS. 2 and 3 , a flow restrictor  72  is shown in one preferred and exemplary embodiment and is characterized by a housing  74  having suitable ports  76  and  78  opening to opposed housing end faces  77  and  79 , respectively. An enlarged, internal, longitudinal passage  80  is provided in housing  74  in communication with ports  76  and  78 . Suitable guide bosses  82  are opposed to each other, as illustrated in  FIGS. 2 and 3 , for journaling a flow restrictor element in the form of a somewhat bullet-shaped movable plug or closure member  84  slidably disposed in passage  80  and operable to engage a seat  86  formed in housing  74  adjacent port  78 . Plug or closure member  84  is also operable to engage internal stops  88  opposed to each other and aligned with the guide bosses  82  when the closure member moves in a direction toward the port  76 . Housing  74  would normally be fabricated in two or more parts to enable insertion and removal of plug  84 . A conical or tapered wall  90  remains spaced from the closure plug  84  when the plug engages the stops  88  to provide a substantially unrestricted flow path from port  78  to port  76 . However, when the closure member  84  engages seat  86 , flow from port  76  to port  78  is restricted and must flow through a reduced diameter passage  85  formed in the closure member  84 , as shown. Alternatively, fixed orifice type flow restrictors or capillary (small diameter) tubes could be used in place of devices  72  for restricting fluid flow. 
         [0020]    As previously mentioned, flow restrictor devices  72  may be interposed in conduits  62  and  66 , as illustrated or mounted on and connected to conduits  24  and  20 . One preferred arrangement for the devices  72  is to be interposed in the conduits  62  and  66 , as indicated in  FIG. 1 , wherein when the conduit  62  is connected to the conduit  24  via connector parts  25   a  and  25   b  and Schrader valve  25   c , flow of working fluid into conduit  24  is restricted since the closure member  84  will move to the position shown in  FIG. 2  forcing working fluid to flow through the restricted passage  85  from port  76  through port  78  into conduit  24 . Typically, when adding fluid to system  10  via conduit  62 , valves  65  and  67  are closed and valves  60  and  63  are opened, see  FIG. 1 . However, if device  72  connected to conduit  62  is arranged as shown in  FIG. 1 , or mounted permanently on system  10  and oriented in the same direction, and it is desired to evacuate fluid from the system by way of conduit  24 , for example, substantially unrestricted flow of fluid will occur since the closure member  84  will move to the left, viewing  FIG. 2 , allowing such unrestricted flow of fluid between ports  78  and port  76 . 
         [0021]    If it is desired to evacuate working fluid from the system  10  in the event of a fluid overcharge, conduit  66  may be connected to conduit  20  via connector parts  27   a  and  27   b  and the arrangement of the flow restrictor device  72  interposed in conduit  66  is such as to provide restricted flow of fluid from conduit  20  to conduit  66  so that control of evacuation of working fluid from the system  10  may be more closely maintained than if there was substantially no restriction to flow of fluid from conduit  20  to conduit  66 . When evacuating fluid, valve  67  is opened, valve  65  or valves  60  and  63  are closed, and fluid flows from conduit  66  through valve  67  and conduit  69  to recovery reservoir  70 . Accordingly, the flow restrictor devices  72  may be arranged as illustrated in  FIG. 1  or may be mounted directly on the conduits  20  and  24  in the orientation shown and described for a permanent installation in the system  10 . Moreover, the arrangements of the flow restrictor devices  72  may be reversed if desired to provide flow restriction in one direction of flow and substantially unrestricted flow in the opposite direction. 
         [0022]    Accordingly, the devices  72 , whether mounted permanently on system  10  in communication with the conduits  24  and  20 , or mounted on a fluid charge adding and evacuation apparatus, such as the apparatus  54 , assist in providing an improved method for adjusting the charge of working fluid in a vapor compression system, such as the system  10  or an equivalent. Thanks to the provision of the programmable controller unit  44 , including part  45 , a process may be carried out for adding a charge of working fluid to the system  10  or evacuating a portion of the charge of working fluid from the system  10  to provide the desired degree of sub-cooling of the fluid as it exits a heat exchanger, such as the condenser  14 . By monitoring the temperature and pressure of the fluid flowing through the conduit  20 , for example, restricted flow of fluid into or out of the system allows for adjusting a steady state operating condition and the desired degree of sub-cooling of the fluid. 
         [0023]    In accordance with a preferred process of the present invention, the controller unit  44 ,  45  is operable to monitor the addition or subtraction of working fluid with respect to the system  10  by causing the controller to enter the so-called charging mode at step  100 , see  FIG. 4 . At step  102  the controller  44 ,  45  and system  10  are caused to become ready to check the charge condition by querying whether or not the system has been running more than a preset period of time, such as “y” minutes indicated at step  104 . If the system  10  has been running less than a preset period of time and the variance of sub-cooling of the fluid, as measured by the sensors  40  and  42 , is less than a “z” predetermined amount for “x” predetermined period of time, as measured at step  106 , or if the run time at step  104  is greater than the preset period of time, the process proceeds to step  108 . If steps  104  and  106  are both “false”, the process repeats itself as indicated by step  110  and a signal may be provided to the user indicating time to complete the process. 
         [0024]    At step  108 , controller unit  44 ,  45  reads the fluid pressure and temperature and calculates the actual fluid sub-cooling or a pressure representation thereof. The process proceeds to step  112  to determine if the actual sub-cooling of the working fluid is greater than or less than a so-called target sub-cooling condition and a charge error is calculated at step  114 . If the charge error indicates excessive sub-cooling at step  116 , a suitable indicator is illuminated, such as one of the indicators  46  or  48 , or a message is provided at visual display  48   a , indicating the need to reduce the charge of working fluid in the system  10 , as indicated at step  118 . Such may be carried out by pumping fluid or allowing the bleeding of fluid through device  72  connected to conduit  66  for recovery into the reservoir  70 . Thanks to the restriction of fluid flow through the device  72  connected to conduit  66  the rate of change of sub-cooling can be closely monitored. In fact, as the process continues to monitor removal of fluid until the total charge is correct at step  120  and the process repeats itself, the controller  44  may generate a suitable control signal or a visual or audible signal. 
         [0025]    However, if it is determined at step  116  that recovery or evacuation of working fluid from system  10  is not required but addition of fluid is required, such as indicated at step  122 , controller unit  44  may energize valve  60 ,  FIG. 1 , for example, causing same to open and to allow fluid to flow from pressure vessel or reservoir  56  through conduit  62  and device  72  at a restricted flow rate to add working fluid to system  10  via valve  25   c  and conduit  24  until the total fluid charge is correct, as measured by the amount of sub-cooling at sensors  40  and  42  and monitored by controller  44 ,  45 . Steps  124  and  126  reflect this process. 
         [0026]    If no addition of working fluid is required at step  122 , a suitable indicator is illuminated, such as indicator  46 , or a message is displayed at display  48   a  at step  128  advising the operator or user to cease adding fluid to or removing fluid from the system  10 , as indicated at step  130 . The process is then completed as indicated at step  132 . Operation of the valves  63 ,  65  and  67  to allow flow of fluid between reservoirs  56  and  70  and the system  10 , as required by the process described above, is believed to be within the purview of one skilled in the art. 
         [0027]    Referring briefly to  FIG. 5 , a system  10   a , illustrated schematically, is substantially like that shown and described with regard to  FIG. 1  with the exception that the devices  72  are essentially permanently mounted to the system in communication with the conduits  24  and  20  in the manner illustrated whereby restricted flow of fluid into the system  10   a  is provided by the device  72  connected to conduit  24  but substantially unrestricted flow out of the system may be provided when the connector  25   a  is connected to a modified charge addition or evacuation apparatus  54   a , for example. In like manner restricted flow of fluid out of the system  10   a  may be provided by the so-called permanent connection between a device  72  and conduit  20  for purposes of fluid evacuating at a controlled or restricted rate from the system if an overcharge, and consequent excessive sub-cooling, is occurring. 
         [0028]    In the arrangement of  FIG. 5 , a charge addition and subtraction apparatus  54   a  may be connected to either connector  25   a  or  27   a  and the aforementioned check valves or so-called Schrader valves  25   c  and  27   c  may be interposed the respective connectors  25   a  and  27   a  and the devices  72 , as shown in  FIG. 5 . The valves  25   c  and  27   c  are, of course, held open by the connectors  25   a ,  25   b  and  27   a ,  27   b  when such are engaged in a known manner. In all other respects the system  10   a  and the charge addition or evacuation apparatus  54   a  are substantially like the system  10  and apparatus  54 . 
         [0029]    Accordingly, in accordance with the systems and process described above, vapor compression air conditioning and refrigeration systems may be properly charged with working fluid to prevent flooding of the compressor, provide a faster method of charging and greater accuracy of obtaining the proper charge of working fluid in a system of the types described. Although preferred embodiments of a system and method have been disclosed in detail herein, those skilled in the art will appreciate that various substitutions and modifications may be made without departing from the scope and spirit of the appended claims.