Patent Publication Number: US-7905099-B2

Title: Predictive maintenance method and apparatus for HVACR systems

Description:
FIELD OF THE INVENTION 
     This invention relates to heating, ventilation, air-conditioning and refrigeration (HVACR) systems, and, more particularly, to a method and apparatus capable of detecting malfunctions in the system before they become catastrophic and cannot be remedied by routine maintenance. 
     BACKGROUND OF THE INVENTION 
     HVACR systems that operate using a vapor-compression cycle generally comprise a compressor, a condenser, an expansion valve and an evaporator interconnected by a line having an interior within which a refrigerant fluid is circulated. Although this technology is mature and is currently used in a wide variety of commercial and residential applications, malfunctions can arise as a result of leaks in the system or failure of one or more components. In many instances, the malfunction may not be catastrophic, e.g. wherein the system ceases to heat or cool altogether, but may result in a gradual or progressive decrease in performance and/or efficiency that can nevertheless create spoilage of foodstuffs and other inventory, for example, or other problems. 
     Periodic maintenance of HVACR systems can be time consuming, expensive and in many cases unnecessary at the time performed. Recognizing that a failure to maintain such systems will eventually cause a problem, the issue becomes how often such maintenance should be performed and what should be done. Approaches that rely solely on the passage of time are often ineffective and ignore the specific requirements of a particular installation and/or type of system. 
     Automated preventative maintenance devices for HVACR systems have been proposed, such as disclosed, for example, in U.S. Pat. No. 5,596,507. The device disclosed in the &#39;507 patent relies upon a number of temperature sensors and electrical current sensors to detect a variety of operating parameters of the system, and to provide inputs to a computer capable of analyzing the data and identifying potential trouble spots in the system that may need maintenance. While systems of this type may be effective, they are not economically feasible for residential applications and many smaller commercial operations. 
     SUMMARY OF THE INVENTION 
     This invention is directed to a predictive maintenance method and apparatus for HVACR systems including a sensor capable of detecting the presence of a gaseous phase in the refrigerant fluid at a location wherein solely liquid phase should be present if the system is functioning properly. 
     In the presently preferred embodiment, the method and apparatus of this invention is particularly intended for use in a vapor-compression system including a compressor, a condenser, an expansion valve and an evaporator interconnected by a line having an interior within which a refrigerant fluid is circulated. The apparatus comprises a sensor positioned in the line at a location between the condenser and expansion valve wherein the refrigerant fluid, if the system is functioning properly, is in liquid phase. The sensor is effective to detect the presence of gas bubbles in the refrigerant fluid, and provide a warning indication that maintenance of the system is required. 
     Unlike prior predictive maintenance systems, the method and apparatus of this invention is relatively simple, inexpensive and may be easily installed in residential and commercial HVACR systems. While no specific indication of the cause of a problem in the system is provided, it is contemplated that competent service personnel can readily identify and repair the HVACR system when notified of a maintenance issue, thus substantially eliminating the need for periodic inspections of such system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic view of a vapor-compression system incorporating the predictive maintenance system of this invention; 
         FIG. 2  is an enlarged view of one embodiment of the sensor herein, shown in position relative to the line within which the refrigerant fluid is circulated; and; 
         FIG. 3  is a view similar to  FIG. 2 , except with the sensor components positioned on opposite sides of the line. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, an HVACR system  10  is schematically depicted that operates by vapor compression in a conventional manner. The details of system  10  form no part of this invention and are therefore discussed generally herein. The system  10  includes a compressor  12 , a condenser  14 , an expansion valve  16  and an evaporator  18  interconnected by a line  20  having an interior  22  within which a refrigerant fluid  24  is circulated in the direction of the arrows shown in  FIG. 1 . The fluid  24  may be a hydrofluorocarbon or a similar environmentally suitable refrigerant. 
     The fluid  24  undergoes phase changes and temperature changes in the course of passage through the system  10  that may be used for heating or cooling purposes depending upon the particular application for which the system  10  is employed. Assuming for purposes of discussion that the system  10  is utilized in a refrigeration or air conditioning application, fluid  24  in saturated vapor form is initially directed to the intake of the compressor  12 . The compressor  12  is effective to compress the saturated vapor which increases its pressure and temperature, forming a superheated vapor. The superheated vapor is discharged from the compressor  12  and enters the condenser  14 . The condenser  14  is formed with a number of coils (not shown) through which the superheated vapor is directed. The coils are cooled by circulating air or water in order to remove heat from the superheated vapor and convert it into a saturated liquid that is transmitted to the expansion valve  16 . If the system  10  is functioning properly, the fluid  24  is in a saturated liquid phase throughout the passage within line  20  from the condenser  14  to the expansion valve  16 . 
     The purpose of the expansion valve  16  is to create an abrupt lowering of the pressure of the saturated liquid received from the condenser  14 . This causes adiabatic flash evaporation which lowers the temperature of the refrigerant fluid  24  and produces a mixture of cold refrigerant liquid and vapor. The liquid/vapor mixture discharged from the expansion valve  16  is transmitted to the evaporator  18 . In most designs, the evaporator  18  is formed with a number of coils or tubes (not shown) and a fan  26  directs relatively warm air, e.g. from the space that is being cooled, over the coils or tubes. See arrows  27  in  FIG. 1 . The liquid portion of the liquid/vapor mixture evaporates, and the circulating air is cooled by the mixture thus reducing the temperature of the area to be cooled. The warmer, circulating air passing over the coils or tubes of the evaporator  18  increases the temperature of the fluid  24 , and the fluid  24 , which is now in saturated vapor form, is transmitted by line  20  to the intake of compressor  12 . The cycle described above is then repeated. 
     As noted above, if the system  10  is operating properly, the refrigerant fluid  24  is in a saturated liquid phase in the course of passage within line  20  between the output of the condenser  14  and the input of the expansion valve  16 . The presence of a gaseous phase of the fluid  24  at this location is an indication of a maintenance issue, e.g. that there is a leak in the system  10  or one or more of the components  12 - 18  is not functioning normally. In accordance with a presently preferred embodiment of this invention, a predictive maintenance sensor  26  is located in the line  20  between the expansion valve  16  and condenser  14 , and preferably immediately upstream from the expansion valve  16 . The sensor  26  is effective to detect the presence of a gaseous phase within the fluid  24 , and to cause a warning to be produced indicating that maintenance is needed. 
     The sensor  26  comprises an emitter  28 , a detector  30  and an optical aperture  32  formed in the line  20 . A controller  34 , discussed in more detail below, is coupled to the emitter  28  and the detector  30 . In the embodiment depicted in  FIG. 2 , the optical aperture  32  is located on one side of the line  20 . The optical aperture  32  may be a section of plastic, glass or the like through which radiant energy may be transmitted. The emitter  28  may be a source of radiant energy, such as one or more light emitting diodes (LEDs), that is capable of directing radiant energy through the optical aperture  32  at a wavelength which is not entirely absorbed by the refrigerant fluid  24  circulating within the line  20 . As shown in  FIG. 2 , the emitter  28  is positioned immediately adjacent to the optical aperture  32  to ensure that substantially all of the radiant energy it produces enters the line  20 . It is contemplated that a housing (not shown) may be provided to enclose the sensor  26  and protect it from damage. 
     The detector  30  in the  FIG. 2  embodiment of this invention is located on the same side of the line  20  as the emitter  28 , preferably side-by-side with the emitter  28  and immediately adjacent to the optical aperture  32 . The detector  30  may be a phototransistor or any other suitable means of detecting radiant energy. With the detector  30  located on the same side of the line  20  as the emitter  28 , and adjacent thereto, it senses radiant energy that is reflected back from the fluid  24  and/or interior wall  36  of the line  20 . 
     An alternative embodiment of this invention is illustrated in  FIG. 3  wherein the emitter  28  and detector  30  of the sensor  26  are located on opposite sides of the line  20  is substantial alignment with one another. The optical aperture  32  may be formed as a continuous section of radiant energy transmitting material in this embodiment, e.g. extending completely around the line  20 , or in two aligning sections  38  and  40  as shown in  FIG. 3 . Radiant energy produced by the emitter  28  is directed toward the detector  30  which is effective to sense that portion of the radiant energy not absorbed by the fluid  24  within line  20 . 
     For purposes of illustration, the fluid  24  circulating through the line  20  is shown in liquid phase in  FIG. 2  and as a mixture of liquid and gaseous phase, e.g. with gas bubbles  42 , in  FIG. 3 . The detector  30  is effective to produce a first signal which is representative of the radiant energy it senses when the fluid  24  is in liquid phase. When the fluid  24  within the line  20  is a combination of liquid and gaseous phase, as depicted in  FIG. 3 , the detector  30  produces a second signal representative of this condition. Radiant energy is absorbed and transmitted through the fluid  24  in a different manner when it is solely in liquid phase, compared to a mixture of liquid and gaseous phase, and therefore the first and second signals produced by the detector  30  are different from one another. 
     In the presently preferred embodiment, the optical aperture  32  or the two aligning sections  38 ,  40  that form an optical aperture are sized to be smaller than at least some of the gas bubbles  42  that are present in the refrigerant fluid  24  when it is a mixture of liquid and gaseous phase. In particular, the optical aperture  32 , or sections  38 ,  40 , have a height dimension measured in a direction generally perpendicular to the flow of fluid  24  through the line  20  that is smaller than the diameter of at least some of the gas bubbles  42  present in the fluid  24 . For example, an optical aperture  32 , or sections  38 ,  40 , having a height dimension of 0.02 inches would readily permit the detection of gas bubbles  42  of that diameter or larger. It is also contemplated that the sections  38  and  40  forming an optical aperture could be oriented 90° from their position shown in  FIGS. 2 and 3 , thus exhibiting a width dimension measured in a direction generally parallel to the flow of fluid  24  through the line  20 . Such width dimension, like the height dimension described above, is also preferably less than the size of gas bubbles  42  that may be present in the fluid  24 . 
     The controller  34  may be any suitable processor capable of operating the emitter  28 , receiving the signals produced by the detector  30  and producing a warning indication in the event a second signal is produced. In one presently preferred embodiment, following initial start-up of the system  10 , the controller  34  may record a “baseline” value representative of the first signal produced by the detector  30  wherein it is known that the system  10  is operating properly and fluid  24  in the form of a saturated liquid is circulating through the line  20  between the output of the condenser  14  and the input of the expansion valve  16 . The controller  34  may operate the emitter  28  and detector  30  periodically or continuously, as desired, to check on the status of the system  10 . Subsequent signals produced by the detector  30  are compared to the baseline value, and, if such signals noted above are within a predetermined range of the baseline value, e.g. “first” signals, no warning indication is produced. On the other hand, if a “second” signal is produced representative of the presence of both liquid and gaseous phase within the line  20 , a comparison by the controller  34  of such second signal to the baseline value results in the production of a warning indication that maintenance of the system  10  is required. It is contemplated that the warning indication may comprise a flashing light or the like on a refrigeration unit, on the thermostat of an air conditioning system or other suitable indicia. 
     While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.