Abstract:
The present invention relates to methods and systems for introducing one or more hydrohalocarbon refrigerants into a heat transfer system from a vessel by recovering the one or more hydrohalocarbon refrigerants from the heat transfer system; monitoring the vapor pressure in the vessel and if the vapor pressure in the vessel becomes greater than 3 psi over the expected saturation pressure for the one or more hydrohalocarbon refrigerants then releasing vapor from the vessel; and returning said one or more hydrohalocarbon refrigerants to the heat transfer system by drawing liquid refrigerant from the vessel.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority benefit of U.S. Provisional Application No. 61/364,373, filed on Jul. 14, 2010, the contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to refrigerant handling systems and, in particular, to systems for recovering, recycling and/or recharging refrigerant to/from cooling systems, such as those know as Mobile Air Conditioning (MAC) systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Many refrigeration systems, including MAC systems and similar heat transfer devices, use refrigerant liquids as the heat transfer medium. Because of certain suspected environmental problems, including the relatively high global warming potentials, associated with the use of some of the compositions that have heretofore been used in these applications, it has become increasingly desirable to use fluids having low or even zero ozone depletion potential, such as hydrofluorocarbons (“HFCs”). For example, a number of governments have signed the Kyoto Protocol to protect the global environment and setting forth a reduction of CO2 emissions (global warming). One fluid that has been disclosed as having tremendous environmental advantages, as well as excellent heat transfer performance characteristics, is 2,3,3,3-tetrafluoropropene (HFO-1234yf). See U.S. Pat. No. 7,279,451, the contents of which are incorporated herein by reference. Another refrigerant liquid that has been commonly used in MAC systems is HFC-134a, also known as R-134a. 
         [0004]    During service or repair of refrigeration systems, such as automotive vehicle air-conditioning systems, it is common that the refrigerant, or at least a portion of the refrigerant, present in the system is removed from the system and then stored. The stored refrigerant is thereafter recycled for use in the same or different air conditioning system, or forwarded to other processing before it is reused. In either event, the system after servicing and/or checking is complete, must be recharged with recycled refrigerant, new refrigerant, or a combination of recycled and new refrigerant. 
         [0005]    One type of impurity which may be present and must be removed from recovered refrigerant is non-condensable material, such as air, which may be present in the removed refrigerant as the result infiltration into the refrigeration system as a result of leaks or the like. In many repair and service operations, the non-condensables are typically vented to atmosphere by way of a purge valve associated with the vapor space of the container or vessel storing the removed refrigerant and/or the new refrigerant that will be added thereto. 
         [0006]    Refrigerants possess characteristic saturation vapor pressures, which generally vary with temperature in a known manner. Thus, as long as refrigerant is present in substantial equilibrium conditions in both liquid and vapor phases, such as would typically occur in the refillable recovered refrigerant vessel of a refrigerant recycling system, the pressure of the vapor is known. However, if air or other non-condensables are present in the recovered refrigerant vessel, a differential pressure above the saturation pressure is created. This differential pressure is generally considered to be proportional to the quantity of non-condensables present, and it is common to use this relationship for automatically venting the non-condensables. More specifically, an ideal pressure of the refrigerant at a given temperature is determined and, when the actual measured pressure of the refrigerant exceeds that ideal by a certain amount, a venting valve is opened. In a typical operation, the venting event will produce a reduction in the pressure in the vessel until the tolerance pressure is reached, at which point the valve closes and venting ceases. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, the present invention relates to a method for introducing one or more hydrohalocarbon refrigerants into a heat transfer system by recovering from a heat transfer system one or more hydrohalocarbon refrigerants; monitoring the vapor pressure in the vessel and if the vapor pressure in the vessel becomes greater than 3 psi over the expected saturation pressure for the one or more hydrohalocarbon refrigerants then releasing vapor from the vessel; and returning said one or more hydrohalocarbon refrigerants to the heat transfer system by drawing liquid refrigerant from the vessel. 
         [0008]    The hydrohalocarbon refrigerants of this embodiment may include, but are not limited to, HFC-134a, HFO-1234yf, and combinations thereof. They may be stored in the vessel as both a liquid phase and a vapor phase. To this end, the vapor phase comprises at least one or a combination of such hydrohalocarbon refrigerants. In further aspects, the vapor phase also includes one or more non-condensable gases, such as, but not limited to, CO 2 . 
         [0009]    In further aspects of this embodiment, the vapor pressure may be released at certain thresholds above 3 psi over the expected saturation pressure. For example, in certain aspects of the invention, the vapor pressure is released from the vessel when it becomes at least 5 psi greater than the expected saturation pressure for the one or more hydrohalocarbon refrigerants. In further aspects, the vapor pressure is released from the vessel when it becomes at least 6 psi greater than the expected saturation pressure for the one or more hydrohalocarbon refrigerants. In even further aspects, the vapor pressure is released from the vessel when it becomes between 7 psi and 8 psi greater than the expected saturation pressure for the one or more hydrohalocarbon refrigerants. 
         [0010]    In another embodiment, the present invention relates to a method for introducing one or more hydrohalocarbon refrigerants selected from the group consisting of HFC-134a, HFO-1234yf, and combinations thereof, to a heat transfer system from a vessel by releasing vapor pressure from the vessel when the vapor pressure becomes greater than 3 psi over the expected saturation pressure for the one or more hydrohalocarbon refrigerants; and providing the one or more hydrohalocarbon refrigerants to the heat transfer system by drawing liquid refrigerant from the recovery vessel. In one aspect of this embodiment, the one or more hydrohalocarbon refrigerants comprise a combination of HFC-134a and HFO-1234yf. 
         [0011]    The hydrohalocarbon refrigerants may be stored in the vessel in both a liquid phase and a vapor phase. To this end, the vapor phase comprises at least one or a combination of such hydrohalocarbon refrigerants. In further aspects, the vapor phase also includes one or more non-condensable gases, such as, but not limited to, CO 2 . 
         [0012]    In another embodiment, the present invention relates to a system for introducing one or more hydrohalocarbon refrigerants into a heat transfer system. The system includes a vessel for storing one or more hydrohalocarbon refrigerants; an automatic purge valve assembly set to release vapor pressure in the vessel when it becomes greater than 3 psi over the expected saturation pressure for the one or more hydrohalocarbon refrigerants; an input line for providing the one or more hydrohalocarbon refrigerants from the heat transfer system to the vessel; and an output line for returning liquid refrigerant from the vessel to the heat transfer system. 
         [0013]    In certain aspects of this embodiment, the one or more hydrohalocarbon refrigerants that may be used within the system may include HFC-134a, HFO-1234yf, and combinations thereof. 
         [0014]    In further aspects of this embodiment, the automatic purge value assembly includes a purge line, a purge valve, and a control system. In even further aspects, the automatic purge value assembly also includes a pressure transducer and, optionally, a temperature transducer. 
         [0015]    Additional embodiments, aspects and advantages to the present invention will be readily apparent to one of skill in the art, based on the disclosure provided below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a simplified schematic representation of a refrigerant recovery vessel having an automatic pure system. 
           [0017]      FIG. 2  is a plot of experimental data based upon system bench tests performed on an Opel Astra automobile air-conditioning system using a 50/50 weight percent mixture of HFC-134a and HFO-1234yf based upon SAE CRP 45° C. and 35° C. conditions. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0018]    Applicants have come to recognize that a problem may occur in connection with automatic purging systems of the type described above as a result of the presence, whether intentional or not, of certain amounts of HFC-134a in HFO-1234y based refrigerant, and likewise as a result of the presence, whether intentional or not, of certain amounts of HFO-1234yf in HFC-134a based refrigerant. Furthermore, applicants have come to appreciate that this problem might arise with a significant frequency due to the increased use of HFO-1234yf as a refrigerant in systems that have previously used, and potentially continue to use, HFC-134a. 
         [0019]    For example, applicants have come to appreciate that during the normal removal, recovery and/or recharging operations for HFO-1234yf refrigerant, that HFC-134a may be introduced or otherwise present as a contaminant in the HFO-1234yf refrigerant. The presence of HFC-134a may be the result, for example, of this material being present as a remnant in a conduit or other portion of the system from a previous removal, recycle and/or recharging operation of a system using HFC-134a refrigerant. Applicants have come to appreciate that, in such a case, the presence of more than about 5% by weight of HFC-134a as a contaminant in a refrigerant based on HFO-1234yf would cause, assuming prior methods were used, an automatic purge of the vapor space in the recovery vessel notwithstanding that there are no non-condensable gases in the vapor space. In other words, the automatic purging system, if set at a pressure relief of approximately 1.5 psi to about 3 psi above the known expected saturation pressure of the refrigerant, which has heretofore been the common pressure differential used to trigger a purging event, will be falsely activated by the presence of more than about 5% of HFC-134a in the refrigerant. This false activation would occur as a result of the increased vapor pressure associated with the presence of more than 5% by weight of HFC-134a in HFO-1234yf. Moreover, this problem is even more difficult because of applicants recognition that the normal purging cycle in such a case will not reduce the pressure, and therefore that purging will continue unabated until the recovery vessel is substantially depleted of refrigerant. 
         [0020]    Likewise, applicants have found and come to appreciate that during the normal removal, recovery and/or recharging operations for HFC-134a, it may be possible that HFO-1234yf may be introduced as a contaminant in HFC-134a refrigerants as a result, for example, of being present as a remnant in a conduit or other portion of the system from a previous removal, recycle and/or recharging of a system based upon HFC-1234yf refrigerant. Applicants have come to appreciate that, in such a case, the presence of more than about 5% by weight of HFO-1234yf as a contaminant in a refrigerant based on HFO-134a will cause an automatic purge of the vapor space in the recovery vessel notwithstanding that there are no non-condensable gases in the vapor space. In other words, the automatic purging system, if set at a pressure relief of approximately 1.5 psi to about 3 psi above the expected saturation pressure of HFC-134a, will be falsely activated by the presence of more than about 5% of HFO-1234yf in the refrigerant. This false activation would occur as a result of the increased vapor pressure associated with the presence of more than 5% by weight of HFO-1234yf. Moreover, this problem is even more difficult because of applicants recognition that the purging cycle in such a case will not reduce the pressure, and therefore that purging will continue until the recovery vessel is essentially empty. 
         [0021]    According to one aspect, the present invention therefore provides methods for conducting removal, recycle and/or recharging of HFO-1234yf refrigerants in heat transfer systems, particularly MAC systems. The preferred systems are of the type which includes a recovery vessel, tank or the like having an automatic purge valve, and in such cases the preferred methods comprise: (a) setting the purge valve to release at a pressure that is approximately at least more than about 3 psi greater, and more preferably more than about 5 psi greater, and even more preferably at least about 6 psi greater than the expected saturation pressure for HFO-1234yf; and (b) returning refrigerant to the heat transfer system by drawing liquid refrigerant from the liquid space in the recovery vessel, tank or the like. In one aspect of the invention, therefore, the present methods and systems involve ensuring that refrigerant is returned to the heat transfer system only from the liquid space in the recovery vessel, tank or the like, preferably in certain embodiments by locating the refrigerant withdrawal point at or near the lowest point of the recovery vessel. Applicants have found that such a method can provide substantial advantage in such operations by helping to prevent operation of the automatic purge valve except when non-condensable gases are in fact present in the recovery vessel. Furthermore, the present methods provide an additional protection or safeguard against the inadvertent return of air or other non-condensable gases to the refrigeration system, even in the event that at least a portion of the pressure increase in the vapor space is due to presence of such non-condensable gases, by drawing the refrigerant from the liquid space in the vessel. In certain highly preferred embodiments, the methods comprise setting the purge valve to release at a pressure that is from about 6 to about 8 psi greater than the expected saturation pressure for HFO-1234yf, and even more preferably at pressure that is from about 7 to about 8 psi greater than the expected saturation pressure for HFO-1234yf. 
         [0022]    According to another aspect, the present invention provides methods for conducting removal, recycle and/or recharging of HFO-134a refrigerants in heat transfer systems, particularly MAC systems. The preferred systems are of the type which includes a recovery vessel, tank or the like having an automatic purge valve, and in such cases the preferred methods comprise: (a) setting the purge valve to release at a pressure that is more than about 3 psi greater, more preferably more than about 5 psi greater, and even more preferably at least about 6 psi greater than the expected saturation pressure for HFO-134a; and (b) returning refrigerant to the heat transfer system by drawing liquid refrigerant from the liquid space in the recovery vessel, tank or the like, preferably in certain embodiments by locating the refrigerant withdrawal point at or near the lowest point of the recovery vessel. Applicants have found that such a method can provide substantial advantage in such operations by helping to prevent operation of the automatic purge valve except when non-condensable gases are in fact present in the recovery vessel. Furthermore, the present methods provide an additional protection or safeguard against the inadvertent return of air or other non-condensable gases to the refrigeration system, even in the event that at least a portion of the pressure increase in the vapor space is due to presence of such non-condensable gases, by drawing the refrigerant from the liquid space in the vessel. In certain highly preferred embodiments, the methods comprise setting the purge valve to release at a pressure that is from about 6 to about 8 psi greater than the expected saturation pressure for HFO-134a, and even more preferably at pressure that is from about 7 to about 8 psi greater than the expected saturation pressure for HFO-134a. The term “HFC-134a” is used herein to refer to 1,1,1,2-tetrafluoroethane. 
         [0023]    Those skilled in the art will appreciate, based upon the teachings and description contained herein, the present methods are adaptable for use with all known refrigerant recovery, recycling and/or recharging systems that utilize an automatic purge valve to remove non condensable gases, particularly air, CO2 and the like, from the recovered/recharging refrigerant. For example, the following US Patents each describe such systems, and each such patent is incorporated herein by reference as if fully set forth below: U.S. Pat. Nos. 6,442,963; 5,369,959; and 5,189,889. It is contemplated that the present methods are adaptable for use with each of the systems described in the patents, as well as any other systems currently known or yet to be designed which operate using a similar automatic purge valve. 
         [0024]    By way of non-limiting example, reference is made herein to the attached  FIG. 1  which depicts schematically a recovery vessel, tank or the like  10  having at least one inlet line  11  for introducing potentially contaminated refrigerant into the tank and at least one outlet line  12  for removing refrigerant from the tank for the purpose of returning the refrigerant, either directly or after further processing, to the heat transfer system. In preferred embodiments, the tank includes a liquid space  10 A which contains substantially only liquid refrigerant and a vapor space  10 B which contains refrigerant in the vapor phase as well as any non-condensable gases introduced into the vessel. Located appropriately in or on the vessel  10  is a temperature transducer  13  for monitoring and/or estimating the temperature of the vapor contained in space  10 B. A purge line  14  is in fluid communication with the vapor space  10 B and in fluid communication with a pressure transducer  15  for measuring and monitoring the pressure of the vapor located in the vapor space  10 B. The purge line  14  also includes, downstream of the pressure transducer  15 , a purge valve  16 . The signals from the pressure transducer  15  and the temperature transducer  13  communicate with a control system  17 , which in turn is connected to and serves to operate, either directly or indirectly, purge valve  16 . The term “control system” is used herein in its broad sense to refer to any mechanism or apparatus, either mechanical, electronic or a combination of mechanical and electronic, which is capable of being responsive to the temperature and pressure transducers so as to activate the purge valve  16  when the transducer  15  registers a pressure in accordance with the present invention. It is contemplated that any known device for performing this function may be used, including those devices described in the aforementioned patents. In accordance with the present invention, the control system is preferably configured such that purge valve  16  remains closed during the recycle/recovery operation unless the pressure registered by transducer  15  is in accordance with the temperature differential described herein. In the event the present pressure differentials are exceeded, then the purge valve  16  would open. Furthermore, according to the preferred aspects of the present invention, the return line  12  for the reclaimed refrigerant is in communication with the liquid space  10 A of the recovery vessel, tank or the like, such that the refrigerant to be returned to the heat transfer system is drawn substantially exclusively from the liquid space. 
         [0025]    In one non-limiting aspect the pressure transducer uses a string gauge technology to convert pressure into an amplified electrical signal (typically millivolts per volts). The temperature transducer uses a thermocouple, thermistor, or RTD (resistance temperature devise) to similarly convert temperature readings into amplified electrical signals. The electrical signals of both the pressure and temperature tranducers are routed to an electronic circuit, i.e. comparator, which compares the signal level with the preset values. If the temperature and pressure readings are above the preset threshold the comparator outputs a logical on signal to the normally closed solenoid. If below the threshold, then the comparator outputs a logical off signal and the solenoid either closes (if previously opened in response to a logical on signal) or remains closed. This embodiment is not considered limiting to the invention, however, and the control system could be adapted using other temperature and pressure based technologies, such as, but not limited to, bimetallic coils or strips or the like. 
         [0026]    One reason for the importance of the methods according to the present invention is applicants&#39; recognition that even relatively large amounts of HFC-134a in HFO-1234yf, whether in the form of an unintentional contaminant or as an intentionally added ingredient, do not have a substantially deleterious effect on the performance of the refrigerant, especially in connection with MAC systems. Similarly, applicants have also come to recognize that relatively large amounts of HFO-1234yf in HFC-134a, whether in the form of an unintentional contaminant or as an intentionally added ingredient, do not have a substantially deleterious effect on the performance of the refrigerant, especially in connection with MAC systems. For example, as illustrated in  FIG. 2 , system performance parameters such as relative capacity, relative suction pressure, relative discharge pressure and relative COP are all well within acceptable ranges even with substantial mixtures of HFC-134a and HFO-1234yf. Accordingly, whereas in other cases the presence of such a contaminant might otherwise disqualify the use of the refrigerant with the contaminant, applicants have come to recognize that the use of such mixtures of refrigerants will generally be acceptable for the intended purpose. Accordingly, there is generally not a great incentive to ensure that HFC-134a is not present in HFO-1234yf refrigerant, and vice versa, and under such circumstances there is an increased possibility that, in the absence of the methods provided by the present invention, substantial and severe problems would arise with the operation of many existing automatic purge systems. However, the present methods overcome these problems and add reliability, safety and efficiency to the systems. 
         [0027]    Those skilled in the art will appreciate that the present invention is adaptable for use in accordance with a wide variety of existing and yet to be designed systems, and all such uses and methods are within the scope of the present invention, the true scope of which is defined by the appended claims and/or versions thereof as might be amended during prosecution of the application.