Patent Publication Number: US-2021179908-A1

Title: Refrigerant composition

Description:
The present invention relates to a refrigerant composition and more particularly to a refrigerant composition comprising carbon dioxide (CO 2 , R-744) that is useful in a transcritical refrigeration cycle. The present invention is particularly concerned with a refrigerant composition comprising carbon dioxide that is useful in automotive air-conditioning and heat pump systems that utilise a transcritical refrigeration cycle, especially systems for electric vehicles. 
     1,1,1,2-tetrafluoroethane (R-134a) was for some years the refrigerant of choice in automotive air conditioning systems following the phase out of dichlorodifluoromethane (R-12) which being a CFC has a high ozone depletion potential. The EU F-Gas Directive was then implemented which mandates a Global Warming Potential (GWP) limit of 150 for new car mobile air-conditioning (MAC) systems. As a result, the use of R-134a has now been largely superseded for new systems in Europe by the use of flammable 2,3,3,3-tetrafluoropropene (R-1234yf). R-1234yf is slightly less efficient than R-134a and new system designs now include extra equipment (an internal heat exchanger) to recover the loss in efficiency. 
     Mobile air-conditioning systems which utilise carbon dioxide in a transcritical vapour compression refrigeration cycle are known. Carbon dioxide has a Global Warming Potential of 1 and, as such, is an acceptable refrigerant according to the EU F-Gas Directive. 
     The basic transcritical cycle consists of the following steps:
     1. evaporation of liquid refrigerant at low pressure, removing heat from a low temperature source fluid (such as air);   2. compression of the resultant refrigerant vapour in a compressor to yield a hot, high pressure gas;   3. cooling of the high-pressure gas by heat exchange with a sink fluid, at higher temperature than the source, to yield a cooler, dense refrigerant gas at high pressure. This gas is said to be a “supercritical” fluid because it is above its critical temperature; and   4. expansion of the supercritical fluid through an expansion valve or other restriction device to give a two-phase mixture of liquid refrigerant with vaporised refrigerant vapour at low pressure; this mixture then being fed back to the evaporator stage to complete the cycle.   

     In some systems which utilise carbon dioxide in a transcritical refrigeration cycle, the compression is carried out in two stages. This can improve cycle efficiency by cooling the gas between the two compression stages. 
     The performance and specifically the efficiency of a transcritical refrigeration cycle using carbon dioxide is typically lower than that of a conventional subcritical cycle using, for example, R-134a operating between the same source and sink temperatures. 
     It would be desirable to improve the efficiency of a transcritical refrigeration system using carbon dioxide. 
     We have found unexpectedly that the addition of difluoromethane (R-32) and optionally one or more additional fluorinated refrigerants to carbon dioxide can result in improvements to the efficiency of a transcritical refrigeration system, as well as reducing the operating pressure of such a system. The refrigerant can also meet the GWP limit of 150 set by the EU F-Gas Directive and be non-flammable. 
    
    
     Accordingly, in a first aspect the present invention provides a refrigerant composition comprising carbon dioxide (CO 2 , R-744) and from 1 to 32 weight % difluoromethane (R-32) based on the total weight of the refrigerant composition. 
     Preferably, the refrigerant compositions of the present invention comprise from 1 to 25 weight % R-32 based on the total weight of the refrigerant composition, such as from about 2 to about 22%. 
     It has been found that adding R-32 to carbon dioxide can increase the energy efficiency of the fluid above that of pure carbon dioxide when used in transcritical vapour compression cycles that have been developed to use carbon dioxide as a refrigerant for a range of applications. The refrigerant composition of the invention will preferably have a Global Warming Potential of less than 150 and is preferably non-flammable. 
     In one embodiment, the difluoromethane is present in an amount of from 20 to 25 weight % based on the total weight of the refrigerant composition. This amount of R-32 offers a good balance of cycle properties while keeping temperature glide to an acceptable level. In another embodiment, the difluoromethane is present in an amount of less than 22 weight %, e.g. less than 21 weight %, based on the total weight of the refrigerant composition. 
     Specific compositions of the invention are binary refrigerant compositions comprising from 75 to 99 weight % carbon dioxide and from 25 to 1 weight % difluoromethane. Preferred binary refrigerant compositions comprise from 75 to 80 weight % carbon dioxide and from 25 to 20 weight % difluoromethane. One suitable binary refrigerant composition comprises 78 weight % carbon dioxide ±1 weight % and 22 weight % difluoromethane ±1 weight %. Another suitable binary refrigerant composition comprises 79 weight % carbon dioxide ±1 weight % and 21 weight % difluoromethane ±1 weight %. Binary refrigerant compositions comprising less than 22 weight % difluoromethane have a GWP below 150. 
     Binary compositions of R-32 and carbon dioxide having up to about 22% by weight can exhibit the following benefits: non-flammable as formulated; improved energy efficiency relative to carbon dioxide; reduced operating pressure relative to carbon dioxide; temperature glide in the evaporator of less than 10° C.; and Global Warming Potential below 150, which is a requirement for car air-conditioning in Europe and also for some stationary refrigeration/air-conditioning systems covered by the European F-Gas directive. 
     In one embodiment of the present invention, the compositions can additionally comprise 1,1-diflluoroethylene (R-1132a). 
     In one embodiment, R-1132a is present in the compositions of the present invention in an amount of up to 20 or 22 weight %, such as from 2 to 15 weight %, preferably from 4 to 14 weight % based on the total weight of the refrigerant composition. 
     Conveniently, such compositions of the present invention comprise from 50 to 95 weight % of carbon dioxide, from 1 to 32 weight % difluoromethane and from 1 to 20 weight % of R-1132a, such as from 55 to 93 weight % of carbon dioxide, from 2 to 32 weight % difluoromethane and from 2 to 15 weight % of R-1132a, preferably from 64 to 93 weight % of carbon dioxide, from 2 to 25 weight % of difluoromethane and from 2 to 14 weight % of R-1132a, such as from 65 to 93 weight % of carbon dioxide, from 2 to 22 weight % of difluoromethane, for example from 2 to 14 weight % of R-1132a based on the total weight of the refrigerant composition 
     The preferred compositions of the present invention additionally comprise 1,1,1,2-tetrafluoroethane (R-134a). The proportions of R-32 and R-134a in the composition are preferably selected to ensure that the overall composition will be considered non-flammable as formulated, and preferably non-flammable as per the ASHRAE Standard 34 protocol, and will have a Global Warming Potential (GWP) below 150. These preferred compositions are suitable for use in automotive air-conditioning and heat pump applications amongst other uses. 
     In another embodiment of the present invention, the proportions of R-32 and R-134a in the composition are selected to ensure that the overall composition is non-flammable as per the ASHRAE Standard 34 protocol and has a Global Warming Potential (GWP) below 300. These preferred compositions are believed to be suitable for use in stationary refrigeration applications. 
     Preferred ternary compositions comprise 86 weight % carbon dioxide ±1 weight %, 7 weight % difluoromethane ±1 weight % and 7 weight % 1,1,1,2-tetrafluroethane ±1 weight %. 
     Another preferred refrigerant composition of the present invention is a quaternary composition comprising carbon dioxide, difluoromethane, R-1132a and 1,1,1,2-tetrafluoroethane. 
     The refrigerant composition of the invention can also include other refrigerant compounds in place of or in addition to the 1,1,1,2-tetrafluroethane (R-134a) that is used in the above described ternary composition to provide other ternary or higher refrigerant compositions. Suitable refrigerant compounds for inclusion in the refrigerant composition of the invention include 2,3,3,3-tetrafluoropropene (R-1234yf) and 1,3,3,3-tetrafluoropropene (R-1234ze(E)). If R-1234yf or R-1234ze(E) are used in the composition in addition to R-134a, the amounts of the compounds are preferably selected so that the binary mixture of either R-1234yf or R-1234ze(E)e with R-134a is non-flammable. 
     In one embodiment, the compositions of the present invention may consist essentially of the stated components. By the term “consist essentially of”, we include the meaning that the compositions of the invention contain substantially no other components, particularly no further (hydro)(fluoro)compounds (e.g. (hydro)(fluoro)alkenes or (hydro)(fluoro)alkenes) known to be used in heat transfer compositions. The term “consist of” is included within the meaning of “consist essentially of”. 
     By “substantially no” we include the meaning that the compositions of the invention contain 0.5% by weight or less of the stated component, preferably 0.1% by weight or less, based on the total weight of the refrigerant composition. 
     The compositions of the present invention are useful in mobile air-conditioning applications as well as mobile heat pump applications which use transcritical refrigeration cycles. The compositions may provide particular benefits where the air-conditioning and/or heat pump system is used in an electric vehicle, whether a purely electric or hybrid vehicle. 
     Accordingly, in a second aspect the present invention provides a transcritical air-conditioning and/or heat pump system which uses a refrigerant composition of the first aspect of the invention. The refrigerant composition can be as described in any of the embodiments discussed above. 
     Transcritical cycle technology is also used with carbon dioxide in the following applications: heat pump water heaters for production of domestic hot water; supermarket refrigeration at medium temperature and low temperature levels; residential air-conditioning; and refrigerated transport systems. In some of these applications the vapour compression cycle used is a single compression cycle as is typical in mobile air-conditioning applications. In other applications, the gas compression is carried out in two stages, which permits efficient operation over a large temperature difference between heat source and heat sink temperatures. Accordingly, the compositions are suitable for use in single and dual compression stage cycle. 
     The refrigerant compositions of the invention will typically be combined with a lubricant when used in a refrigeration, air-conditioning or heat pump system. Suitable lubricants include polyol esters, such as neopentyl polyol esters, and polyalkylene glycols, preferably end capped at both ends with an alkyl, e.g. a C 1-4  alkyl, group. 
     The present invention is now illustrated but not limited by the following examples. 
     EXAMPLE 1 
     The performance of a transcritical air-conditioning cycle for mobile air-conditioning (MAC) applications was investigated using standard vapour compression cycle modelling techniques. Thermodynamic properties of the mixtures were calculated using the REFPROP9.1 property calculation software. The default REFPROP interaction parameters for mixtures of CO 2  with R-32 were used in all calculations. For mixtures containing R-134a, CO 2  and R32, the REFPROP interaction parameters were used for the R-32/R-134a pair and experimentally-derived interaction parameters were used for the CO 2 /R-134a pair. 
     First a cycle using a single stage compressor was simulated under conditions that are representative of an automotive air conditioning application. A suction line/high pressure gas heat exchanger was included in the cycle as this is a standard technical feature of transcritical CO 2  systems. The cycle simulated is shown schematically in  FIG. 1 . 
     The following cycle parameters were used: 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 parameters used for modelling single-stage MAC cycle 
               
            
           
           
               
               
               
            
               
                 Parameter 
                 Units 
                 Value 
               
               
                   
               
               
                 Ambient air temperature 
                 ° C. 
                 33, 43, 58 
               
               
                 Minimum difference between refrigerant and 
                 K 
                 4 
               
               
                 air temperature in gas cooler 
               
               
                 Mean (average) refrigerant evaporation 
                 ° C. 
                 7 
               
               
                 temperature 
               
               
                 Evaporator superheat 
                 K 
                 0 
               
               
                 Gas side temperature rise in suction line 
                 K 
                 20 
               
               
                 heat exchanger 
               
               
                 Compressor isentropic efficiency 
                   
                 65% 
               
               
                   
               
            
           
         
       
     
     The model did not account for pressure drops in the system components. 
     The cycle model was implemented in Microsoft Excel. The cycle calculation varied the evaporator pressure so that the calculated mean evaporation temperature met the target value. Simultaneously the gas cooler pressure was varied to maximise the cycle Coefficient of Performance (COP). 
     Binary mixtures of CO 2  with R32 were simulated over a range of compositions at three different ambient air temperatures. The results are shown in Table 2 below and selected data are graphed in  FIGS. 2 to 5 . 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Binary compositions of R-32/CO 2  at various ambient air temperatures 
               
               
                   
               
             
            
               
                 Ambient air temperature = 33° C. 
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 100% 
                 95% 
                 90% 
                 85% 
                 80% 
                 79% 
                 75% 
                 70% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 0% 
                 5% 
                 10% 
                 15% 
                 20% 
                 21% 
                 25% 
                 30% 
               
               
                   
               
               
                 Coefficient of Performance 
                 COP 
                 2.69 
                 2.77 
                 2.86 
                 2.97 
                 3.09 
                 3.12 
                 3.19 
                 3.27 
               
               
                 Volumetric cooling capacity 
                 Q 
                 14497 
                 14029 
                 13553 
                 13078 
                 12763 
                 12763 
                 12650 
                 12401 
               
               
                 Compressor discharge temperature 
                 Tdis 
                 102.6 
                 103.7 
                 104.4 
                 104.5 
                 105.3 
                 105.8 
                 107.7 
                 109.8 
               
               
                   
                 (° C.) 
               
               
                 Evaporator pressure 
                 Pev 
                 41.8 
                 39.1 
                 36.6 
                 34.3 
                 32.0 
                 31.6 
                 30.0 
                 28.0 
               
               
                   
                 (bar) 
               
               
                 Gas cooler pressure 
                 Pco 
                 90.2 
                 84.9 
                 79.5 
                 74.1 
                 69.4 
                 68.8 
                 66.3 
                 63.2 
               
               
                   
                 (bar) 
               
               
                 Evaporator temperature glide 
                 DTev 
                 0.0 
                 1.4 
                 2.8 
                 4.2 
                 5.5 
                 5.7 
                 6.7 
                 7.8 
               
               
                   
                 (K) 
               
               
                   
               
            
           
           
               
            
               
                 Ambient air temperature = 43° C. 
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 100% 
                 95% 
                 90% 
                 85% 
                 80% 
                 79% 
                 75% 
                 70% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 0% 
                 5% 
                 10% 
                 15% 
                 20% 
                 21% 
                 25% 
                 30% 
               
               
                   
               
               
                 Coefficient of Performance 
                 COP 
                 1.76 
                 1.79 
                 1.82 
                 1.86 
                 1.90 
                 1.91 
                 1.95 
                 2.01 
               
               
                 Volumetric cooling capacity 
                 Q 
                 12923 
                 12477 
                 12026 
                 11559 
                 11176 
                 11090 
                 10746 
                 10257 
               
               
                 Compressor discharge temperature 
                 Tdis 
                 129.1 
                 131.4 
                 133.3 
                 135.1 
                 136.8 
                 137.0 
                 137.4 
                 136.8 
               
               
                 Evaporator pressure 
                 Pev 
                 41.8 
                 39.1 
                 36.5 
                 34.1 
                 31.8 
                 31.4 
                 29.7 
                 27.7 
               
               
                 Gas cooler pressure 
                 Pco 
                 115.6 
                 109.8 
                 104.0 
                 98.3 
                 93.1 
                 91.9 
                 87.4 
                 81.1 
               
               
                 Evaporator temperature glide 
                 DTev 
                 0.0 
                 1.3 
                 2.6 
                 3.9 
                 5.0 
                 5.2 
                 6.0 
                 6.8 
               
               
                   
               
            
           
           
               
            
               
                 Ambient air temperature = 58° C. 
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 100% 
                 95% 
                 90% 
                 85% 
                 80% 
                 79% 
                 75% 
                 70% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 0% 
                 5% 
                 10% 
                 15% 
                 20% 
                 21% 
                 25% 
                 30% 
               
               
                   
               
               
                 Coefficient of Performance 
                 COP 
                 1.10 
                 1.12 
                 1.13 
                 1.15 
                 1.17 
                 1.18 
                 1.19 
                 1.21 
               
               
                 Volumetric cooling capacity 
                 Q 
                 11092 
                 10697 
                 10295 
                 9941 
                 9553 
                 9476 
                 9171 
                 8796 
               
               
                 Compressor discharge temperature 
                 Tdis 
                 165.1 
                 168.1 
                 170.9 
                 174.4 
                 176.9 
                 177.4 
                 179.0 
                 180.6 
               
               
                 Evaporator pressure 
                 Pev 
                 41.8 
                 39.0 
                 36.4 
                 33.9 
                 31.6 
                 31.1 
                 29.4 
                 27.4 
               
               
                 Gas cooler pressure 
                 Pco 
                 159.4 
                 152.2 
                 145.3 
                 139.5 
                 133.1 
                 131.8 
                 126.7 
                 120.2 
               
               
                 Evaporator temperature glide 
                 DTev 
                 0.0 
                 1.2 
                 2.4 
                 3.5 
                 4.5 
                 4.7 
                 5.4 
                 6.1 
               
               
                   
               
            
           
         
       
     
     It is seen that the following trends apply:
     Coefficient of Performance increases as R-32 is added to CO 2 . The extent of improvement is dependent on the ambient air temperature experienced by the gas cooler.   Optimum operating pressure of the gas cooler drops as R-32 is added, which is beneficial for the compressor.   Volumetric capacity drops slightly as R-32 is added, falling to about 85% of pure CO 2  for a blend having 21% R32.   Evaporator temperature glide increases as R-32 content increases. For compositions having a GWP of less than 150 (&lt;22% R-32 by weight) the evaporator glide is less than 6° C., meaning that it should cause little adverse impact on evaporator performance   

     It is evident that the addition of R-32 in quantities below 22% by weight can improve the energy efficiency of the cycle and significantly reduce operating pressures. 
     EXAMPLE 2 
     The performance of R-32/ CO 2  blends in an automotive heat pump cycle was next investigated by cycle modelling. Heat pump cycles are used in battery powered electric vehicles (pure electric and hybrid powertrains). The cycle model of the previous example was used, with altered parameters as shown in Table 3. These were chosen to be representative of conditions for an automotive application. 
     The following cycle parameters were used: 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 cycle modelling conditions for automotive heat pump mode 
               
            
           
           
               
               
               
            
               
                 Parameter 
                 Units 
                 Value 
               
               
                   
               
               
                 Ambient air temperature 
                 ° C. 
                 −15 exterior, 
               
               
                   
                   
                 0 in the cabin; 
               
               
                   
                   
                 40 C. target air 
               
               
                   
                   
                 temperature 
               
               
                 Minimum difference between refrigerant and 
                 K 
                 25 
               
               
                 air inlet temperature in gas cooler 
               
               
                 Mean (average) refrigerant evaporation 
                 ° C. 
                 −25 
               
               
                 temperature 
               
               
                 Evaporator superheat 
                 K 
                 0 
               
               
                 Gas side temperature rise in suction line 
                 K 
                 20 
               
               
                 heat exchanger 
               
               
                 Compressor isentropic efficiency 
                   
                 65% 
               
               
                   
               
            
           
         
       
     
     Selected results are shown in  FIGS. 6 to 9 . In this work the COP refers to the heating mode Coefficient of Performance. 
     It is seen that the same general trends of performance enhancement with addition of R-32 occur in heat pump mode and thus the use of R-32/CO 2  blends offer improved energy efficiency and reduced operating pressures over the use of pure CO 2 . Improved energy efficiency is especially important for heat pumps installed electric vehicles since it reduces the energy consumed for passenger comfort and hence enhances the effective range of the battery. 
     EXAMPLE 3 
     A cycle model was constructed of a two-stage compression cycle, with intermediate cooling of the compressed gas leaving the first compression stage and with holdup of liquid refrigerant in a flash tank held at the inter-stage pressure. The cycle modelled is shown in  FIG. 10 . 
     Cycle simulations were carried out for CO 2  and selected R-32/CO 2  blends using this cycle with the input parameters as shown in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Cycle parameters for two-stage cycle 
               
            
           
           
               
               
               
            
               
                 Parameter 
                 Value 
                 Units 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Cooling duty 
                 6 
                 kW 
               
               
                 Ambient air temperature 
                 35 
                 ° C. 
               
               
                 Air-off temperature from gas coolers 
                 45 
                 ° C. 
               
               
                 Approach in gas coolers 
                 4 
                 K 
               
               
                 Mean refrigerant evaporation temperature 
                 −5 (Medium 
                 ° C. 
               
               
                   
                 temp) or −40 
               
               
                   
                 (Low temp) 
               
               
                 Approach in evaporator 
                 4 
                 K 
               
               
                 Evaporator superheat 
                 5 
                 K 
               
               
                 Suction line superheat 
                 15 
                 K 
               
               
                 Minimum pressure differential (flash tank to 
                 1 
                 bar 
               
               
                 evaporator) 
               
               
                 Suction pressure drop 
                 0.1 
                 bar 
               
               
                 Evaporator pressure drop 
                 0.2 
                 bar 
               
               
                 Gas cooler pressure drop 
                 0.5 
                 bar 
               
               
                 Compressor isentropic efficiency 
                 70% 
               
               
                   
               
            
           
         
       
     
       FIGS. 11 to 14  show selected results for two levels of refrigeration: Medium temperature (evaporator at −5° C.) and Low temperature (evaporator at −40° C.). 
     “Series 1” as used within  FIGS. 12 to 14  refers to “medium temperature” conditions. 
     It is seen that similar trends in performance are seen in the two-stage cycle as with the earlier single-stage cycle modelling when R-32 is added to carbon dioxide (CO 2 ; R-744):
     Increased energy efficiency   Reduced operating pressure   Temperature glide in evaporator remains below 10K if R-32 content is less than about 25% by weight   Volumetric cooling capacity is reduced as R-32 is added   

     EXAMPLE 4 
     REFLEAK4.0 was used to investigate the vapour leakage of a 21% R-32/79% CO 2  mixture at the worst-case conditions mandated by Standard 34, namely a vapour leak at −40° C. from a storage cylinder initially filled to 90% of the permitted maximum filling density. It was found that if more than about 77% of the charge leaked then the remaining liquid in the cylinder would contain more than 59% by weight R-32 and thus would be flammable. 
     This procedure was repeated for a 10% R-32/90% CO 2  mixture and it was found that this would also fractionate to a flammable liquid composition on removal of 90% of the charge as vapour at −40° C. 
     The fractionation of a mixture of 86% CO 2 , 7% R-32 and 7% R-134a was investigated using NIST REFLEAK for the same cylinder leakage case as considered for the binary blend. This composition would have a GWP of 148. Binary interaction parameters for R-32 with CO 2  and R-134a with CO 2 , derived by fitting experimental vapour-liquid equilibrium data, were input to the model for this simulation 
     It was found that the addition of R-134a to the blend ensured that at all times in the leakage process the vapour and liquid compositions would be non-flammable. This is illustrated in  FIG. 15 , which represents the trajectory taken by liquid and vapour phases during the fractionation on a ternary composition diagram. The apex of the triangle represents pure R-32; the bottom left vertex is pure R-134a, and pure CO 2  is the bottom right vertex. In this diagram the compositions are shown on a molar basis as this allows easy depiction of the region of anticipated flammable ternary compositions (which is shaded). 
     The upper curved line starting from the CO 2  vertex shows the vapour phase composition during leakage and the lower curved line starting from the CO 2  vertex shows the liquid phase composition during leakage. The leak starts in the bottom right corner of the triangle near the CO 2  vertex. 
     It is evident that both phase compositions stay well away from the flammable region at all points in the leakage event. This mixture would therefore be classed as non-flammable under fractionation. 
     EXAMPLE 5 
     The performance of a composition comprising 86% CO 2 , 7% R-32 and 7% R-134a was then investigated using the air-conditioning cycle model previously described in Example 1. The results are shown in Table 5 below: 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 comparison of performance of a ternary 
               
               
                 R-744/R-32/R-134a blend with R-744 
               
            
           
           
               
               
               
               
            
               
                   
                   
                   
                 R-744/R-32/R-134a 
               
               
                 Parameter 
                 Units 
                 R-744 
                 86/7/7% 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 COP 
                   
                 2.69 
                 2.84 
               
               
                 Volumetric capacity 
                 kJ/m 3   
                 14497 
                 12794 
               
               
                 Compressor discharge 
                 ° C. 
                 102.6 
                 107.3 
               
               
                 temperature 
               
               
                 Evaporator pressure 
                 bar 
                 41.8 
                 34.0 
               
               
                 Gas cooler pressure 
                 bar 
                 90.2 
                 75.3 
               
               
                 Evaporator glide 
                 K 
                 0.0 
                 6.4 
               
               
                   
               
            
           
         
       
     
     EXAMPLE 6 
     The performance of selected ternary compositions comprising CO 2 , R-32 and R-1132a was then investigated using the following transcritical air-conditioning cycle model: 
     
       
         
           
               
             
               
                   
               
               
                 INPUT CONDITIONS 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Gas cooler air inlet temperature 
                 33° 
                 C. 
               
               
                   
                 Gas cooler air exit temperature 
                 43° 
                 C. 
               
               
                   
                 Minimum temperature difference 
                 4 
                 K 
               
               
                   
                 between refrigerant and gas in the 
               
               
                   
                 gas cooler 
               
               
                   
                 Cooling capacity 
                 4 
                 kW 
               
               
                   
                 Mean evaporator temperature 
                 7° 
                 C. 
               
               
                   
                 Evaporator superheat 
                 0 
                 K 
               
               
                   
                 Suction line temperature rise 
                 20 
                 K 
               
            
           
           
               
               
               
            
               
                   
                 Compressor isentropic efficiency 
                 65% 
               
               
                   
                   
               
            
           
         
       
     
     The results are shown in Tables 6 and 7 below. 
     
       
         
           
               
             
               
                 TABLE 6 
               
               
                   
               
               
                 ternary compositions comprising CO 2 /R-32/R-1132a 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 92% 
                 88% 
                 84% 
                 80% 
                 76% 
                 72% 
                 68% 
                 64% 
               
            
           
           
               
               
            
               
                   
                 R1132a 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 4% 
                 4% 
                 4% 
                 4% 
                 4% 
                 4% 
                 4% 
                 4% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 4% 
                 8% 
                 12% 
                 16% 
                 20% 
                 24% 
                 28% 
                 32% 
               
               
                   
               
               
                 Coefficient of Performance (COP) 
                   
                 2.73 
                 2.80 
                 2.87 
                 2.97 
                 3.07 
                 3.17 
                 3.24 
                 3.29 
               
               
                 Volumetric cooling capacity 
                 kJ/m 3   
                 13948 
                 13584 
                 13213 
                 12840 
                 12500 
                 12472 
                 12323 
                 12092 
               
               
                 Compressor discharge temperature 
                 ° C. 
                 102.6 
                 103.4 
                 103.9 
                 103.9 
                 103.7 
                 105.6 
                 107.3 
                 108.9 
               
               
                 Evaporator pressure 
                 bar 
                 39.5 
                 37.5 
                 35.5 
                 33.6 
                 31.8 
                 30.2 
                 28.6 
                 27.1 
               
               
                 Gas cooler pressure 
                 bar 
                 85.6 
                 81.4 
                 77.2 
                 72.9 
                 68.7 
                 66.2 
                 63.7 
                 61.3 
               
               
                 Evaporator temperature glide 
                 K 
                 1.1 
                 2.3 
                 3.3 
                 4.4 
                 5.3 
                 6.4 
                 7.3 
                 8.1 
               
               
                   
               
            
           
           
               
            
               
                 RESULTS 
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 88% 
                 84% 
                 80% 
                 76% 
                 72% 
                 68% 
                 64% 
                 60% 
               
            
           
           
               
               
            
               
                   
                 R1132a 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 8% 
                 8% 
                 8% 
                 8% 
                 8% 
                 8% 
                 8% 
                 8% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 4% 
                 8% 
                 12% 
                 16% 
                 20% 
                 24% 
                 28% 
                 32% 
               
               
                   
               
               
                 Coefficient of Performance (COP) 
                   
                 2.71 
                 2.77 
                 2.85 
                 2.94 
                 3.04 
                 3.15 
                 3.23 
                 3.28 
               
               
                 Volumetric cooling capacity 
                 kJ/m 3   
                 13729 
                 13375 
                 13014 
                 12648 
                 12285 
                 12214 
                 12094 
                 11878 
               
               
                 Compressor discharge temperature 
                 ° C. 
                 101.8 
                 102.6 
                 103.1 
                 103.2 
                 102.8 
                 104.1 
                 105.8 
                 107.3 
               
               
                 Evaporator pressure 
                 bar 
                 39.2 
                 37.2 
                 35.3 
                 33.4 
                 31.6 
                 30.0 
                 28.4 
                 26.9 
               
               
                 Gas cooler pressure 
                 bar 
                 85.2 
                 81.0 
                 76.9 
                 72.6 
                 68.3 
                 65.5 
                 63.0 
                 60.6 
               
               
                 Evaporator temperature glide 
                 K 
                 1.1 
                 2.2 
                 3.3 
                 4.3 
                 5.3 
                 6.2 
                 7.1 
                 7.9 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 7 
               
               
                   
               
               
                 ternary compositions comprising CO 2 /R-32/R-1132a 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 88% 
                 84% 
                 80% 
                 76% 
                 72% 
                 69% 
                 64% 
                 60% 
               
            
           
           
               
               
            
               
                   
                 R1132a 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 10% 
                 10% 
                 10% 
                 10% 
                 10% 
                 10% 
                 10% 
                 10% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 2% 
                 6% 
                 10% 
                 14% 
                 18% 
                 21% 
                 26% 
                 30% 
               
               
                   
               
               
                 Coefficient of Performance (COP) 
                   
                 2.66 
                 2.73 
                 2.79 
                 2.87 
                 2.97 
                 3.05 
                 3.18 
                 3.25 
               
               
                 Volumetric cooling capacity 
                 kJ/m 3   
                 13789 
                 13446 
                 13077 
                 12717 
                 12359 
                 12084 
                 12028 
                 11875 
               
               
                 Compressor discharge temperature 
                 ° C. 
                 100.8 
                 101.8 
                 102.5 
                 102.9 
                 102.8 
                 102.4 
                 104.3 
                 105.9 
               
               
                 Evaporator pressure 
                 bar 
                 40.2 
                 38.1 
                 36.0 
                 34.1 
                 32.3 
                 31.0 
                 29.0 
                 27.5 
               
               
                 Gas cooler pressure 
                 bar 
                 87.0 
                 82.9 
                 78.8 
                 74.6 
                 70.3 
                 67.1 
                 63.8 
                 61.4 
               
               
                 Evaporator temperature glide 
                 K 
                 0.6 
                 1.7 
                 2.7 
                 3.8 
                 4.8 
                 5.4 
                 6.6 
                 7.5 
               
               
                   
               
            
           
           
               
            
               
                 RESULTS 
               
            
           
           
               
               
            
               
                   
                 CO2 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 82% 
                 78% 
                 74% 
                 70% 
                 65% 
                 60% 
                 56% 
               
            
           
           
               
               
            
               
                   
                 R1132a 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 14% 
                 14% 
                 14% 
                 14% 
                 14% 
                 14% 
                 14% 
               
            
           
           
               
               
            
               
                   
                 R32 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 4% 
                 8% 
                 12% 
                 16% 
                 21% 
                 26% 
                 30% 
               
               
                   
               
               
                 Coefficient of Performance (COP) 
                   
                 2.67 
                 2.73 
                 2.81 
                 2.89 
                 3.02 
                 3.16 
                 3.24 
               
               
                 Volumetric cooling capacity 
                 kJ/m 3   
                 13383 
                 13045 
                 12696 
                 12347 
                 11903 
                 11784 
                 11654 
               
               
                 Compressor discharge temperature 
                 ° C. 
                 100.6 
                 101.4 
                 101.9 
                 102.1 
                 101.6 
                 102.9 
                 104.4 
               
               
                 Evaporator pressure 
                 bar 
                 38.8 
                 36.8 
                 34.8 
                 33.0 
                 30.8 
                 28.7 
                 27.2 
               
               
                 Gas cooler pressure 
                 bar 
                 84.4 
                 80.4 
                 76.2 
                 72.1 
                 66.8 
                 63.1 
                 60.6 
               
               
                 Evaporator temperature glide 
                 K 
                 1.1 
                 2.2 
                 3.2 
                 4.2 
                 5.4 
                 6.5 
                 7.3 
               
               
                   
               
            
           
         
       
     
     As can be seen, although addition of R-1132a results in a small reduction of energy efficiency and cooling capacity, it ameliorates compressor discharge temperature and reduces the temperature glide in the evaporator. 
     The effect of R-1132a and R-32 content on selected performance parameters is further illustrated in  FIGS. 16 and 17 . 
       FIG. 16  demonstrates the effect of R-1132a and R-32 content on the cooling coefficient of performance (COP). 
       FIG. 17  demonstrates the effect of R-1132a and R-32 content on the volumetric cooling capacity. 
     The term “binary” as used within  FIGS. 16 and 17  refers to a binary composition of R-32 and CO 2  (no R-1132a present).