Abstract:
An air conditioning system in which a high-pressure refrigerant vapor turbine is driving a low-pressure high-speed centrifugal compressor both supported on liquid refrigerant hydrostatic journal bearings. Due to required turbine miniaturization, the turbine blades surface finish and blade accuracy are of critical importance in order to produce high turbine adiabatic efficiency.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Provisional Patent Application Ser. No. 61/517,1-2 filed Apr. 13, 2011. 
       FIELD OF THE INVENTION 
       [0002]    This invention relates to air conditioning systems and in particular to such systems based on the use of waste heat. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventional air-conditioning systems in motor vehicles utilize predominantly direct driven refrigerant compressors which provides suction pressure causing evaporation of liquid refrigerant in evaporator that produces cooling capacity to the air flow circulated through the vehicle interior. Compressor vapor discharge is condensed in a condenser where it is usually cooled by ambient air. Condensed liquid is further expanded through a throttle valve back into the evaporator thus forming a closed loop. 
         [0004]    Typical direct driven air-conditioning system in a hot climate uses approximately 1 kW of engine power per 1 ton cooling capacity, equivalent to 12,000 BTU/hr. Current retail price of gasoline and diesel fuels in US is approximately 5 dollars per gallon or about 85 cents per pound of fuel. Typical 4 ton automotive air-conditioning requires approximately 4 kW or 5.4 HP worth of engine power. With average specific fuel consumption of approximately 0.55 lb/HP-hr this translates into approximately three dollars per hour fuel cost just to run the vehicle air conditioning. Besides the fuel cost this contributes to vehicle exhaust emission and needless use of world fuel supply. 
         [0005]    Applicant has developed over the past decade a miniature very high speed, high efficiency turbine technology such as shown in the Applicant&#39;s U.S. Pat. No. 5,924,286. This proven technology is directly applicable to the waste heat powered refrigeration system, subject of this invention. 
         [0006]    Therefore, there is a great need for efficient and low cost, engine waste heat powered air-conditioning system. 
       SUMMARY OF THE INVENTION 
       [0007]    Present invention provides an air conditioning system in which a high-pressure refrigerant vapor turbine is driving a low-pressure high-speed centrifugal compressor both supported on liquid refrigerant hydrostatic journal bearings. Due to required turbine miniaturization, the turbine blades surface finish and blade accuracy are of critical importance in order to produce high turbine adiabatic efficiency. Because of the possibility of occasional refrigerant liquid mist passing through turbine blades it is extremely important that turbine blades are resistant to liquid droplets erosion. Turbine efficiencies of 80% and higher have been achieved with very high speed turbines similar in size to the refrigerant turbine subject of this invention. Turbine blades are manufactured of a Du Pont high-temperature Vespel plastic encased in metal wheel for dimensional and thermal stability. This technology, including specific turbine design details is shown in Applicant&#39;s U.S. Pat. No. 5,924,286. Those blades were proven as extremely erosion resistant over years of operation in hydraulic fluids with up to 600 ft/sec fluid velocities. 
         [0008]    The system is powered by waste heat of a combustion engine having a coolant pump, a radiator and a coolant flow control valve said air conditioning system. The system includes a refrigerant boiler in fluid communication with hot coolant exiting said combustion engine, a hot coolant flow control valve adapted to control flow of the hot coolant to the refrigerant boiler, a coolant return line for returning fluid exiting the refrigerant boiler to an inlet of the coolant pump, a high-pressure refrigerant pump adapted to provide the refrigerant boiler with high-pressure refrigerant, a refrigerant compressor defining a low-pressure refrigerant vapor inlet and a high-pressure fluid refrigerant outlet, a first refrigerant vapor turbine, in vapor communication with the refrigerant boiler, driven by high-pressure refrigerant vapor produced by the refrigerant boiler and adapted to drive the refrigerant compressor, a refrigerant condenser adapted to condense refrigerant vapor discharged by the first refrigerant vapor turbine and the refrigerant compressor, and a refrigerant evaporator in high-pressure refrigerant fluid communication with the refrigerant compressor outlet and in low pressure refrigerant vapor communication with the low-pressure refrigerant compressor inlet and adapted to provide cooling of an enclosed space as a consequence of evaporation of evaporation to the high-pressure refrigerant. 
         [0009]    In preferred embodiments, the engine waste heat contained in the engine cooling water loop is transmitting the heat to high pressure refrigerant boiler generating the vapor flow that drives the turbine. As shown in tabulated data bellow, the engine coolant heat input to the refrigerant boiler is more than sufficient to power the novel air conditioning system down to idle speeds in most vehicular applications. Optionally, the system can be augmented with the engine exhaust heat (not shown) if necessary. In a typical engine about ⅓ of heat input into the engine is rejected via engine coolant and ⅓ is contained in the engine exhaust. 
         [0010]    In some embodiment the costs associated with electric driven pump or belt driven pump systems can be eliminated, saving an additional 0.5 HP of engine power and greatly improves reliability of the overall system by simplicity of zero leak self-contained bearing system in the  FIG. 7  turbo-pump. Mass production cost of the  FIG. 7  turbo-pump is estimated to be comparable or better than other commercial electric or belt driven refrigerant pumps. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  shows overall system diagram that includes engine and its cooling system connected to refrigerant boiler, turbine-compressor, evaporator, condenser and control valves. 
           [0012]      FIG. 2  is a cross sectional drawing of the turbo-compressor. 
           [0013]      FIG. 3A  is a thermodynamic diagram of the refrigerant loops. 
           [0014]      FIG. 3B  compares radiator flow to A/C boiler flow. 
           [0015]      FIGS. 4A and 4B  are cross sectional drawings of a typical plastic-metal turbine wheel design as shown in U.S. Pat. No. 5,924,286. 
           [0016]      FIGS. 5A and 5B  show design details of a typical 80 percent plus efficient turbine nozzle as shown in U.S. Pat. No. 5,924,286. 
           [0017]      FIGS. 6A and 6B  show design details of a typical 80 percent plus efficient turbine blade as shown in U.S. Pat. No. 5,924,286. 
           [0018]      FIG. 7  is a drawing showing a second preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0019]    Preferred embodiments of the present invention are described by reference to the drawings. 
         [0020]      FIG. 1  shows engine radiator  55  receiving hot engine coolant from engine  51  via hot coolant pipe  61  and radiator flow control valve  62 . Pump  52  forces coolant through engine  51  radiator control valve  62  and radiator  55 . A pressure drop across valve  62  forces hot engine coolant into refrigerant boiler  31  via line  59  and hot coolant control valve  53 . Line  57  provides for engine coolant return from the refrigerant boiler  31  to the radiator return line  58  and to inlet of engine coolant pump  52 . Hot coolant control valve  53  adjusts the flow rate of the hot coolant into the refrigeration boiler  31  as air conditioning load requires. Radiator flow control valve  62  reduces coolant flow to radiator  55  as the engine load and speed decreases while hot coolant control valve  53  opens up more as air conditioning load requires. At maximum air conditioning load heat rejection into refrigerant boiler  31  stays constant while amount of heat rejected from radiator  55  changes as function of engine power level as shown in Table 1. 
         [0021]    Water heated in engine  51  is circulated via line  59  and hot coolant control valve  53  into refrigerant boiler  31  where high pressure refrigerant received from electric driven or engine shaft driven refrigerant pump  32  via line  33  is boiled off. Refrigerant vapor generated in refrigerant boiler  31  flows via line  28  and further on via turbine control valve  27  into refrigerant turbine  13  which is directly driving refrigerant compressor  12 . Refrigerant vapor discharged out of the refrigerant turbine  13  joins the refrigerant vapor discharged by the refrigerant compressor  12  via line  15  into the line  19 . Total refrigerant flow discharged by the refrigerant turbine  13  and by the refrigerant compressor  12  flows via line  21  into the refrigerant condenser  22  which is cooled by ambient air or air-water mixture or cooling water or swimming pool water. Refrigerant line  23  provides liquid refrigerant flow into line  26  and further on via refrigerant cooler control valve  18  into the refrigerant evaporator  17  which provides cooling to the air conditioned air by means of refrigerant evaporation in the refrigerant evaporator  17 . Refrigerant vapor flow is than compressed by the refrigerant compressor  12  into the line  15  and further on as previously described. 
       Performance and Design Details of the Preferred System Embodiment 
     Engine Coolant Capacity Driving the Refrigerant Loop 
       [0022]    Thermal analysis of engine coolant and refrigerant system preferred embodiment was conducted for constant air conditioning load of 4 ton cooling capacity and variable engine power levels for typical 250 HP and 500 HP heavy duty truck diesel engines. 
         [0023]    Tables 1 and 2 below show the effect of engine part load on percentage of total engine coolant used by the refrigeration boiler to drive refrigerant turbine-compressor producing 4 ton cooling capacity. Hot coolant temperature is conservatively assumed to be 220 deg. F. which is equivalent to 4 psig engine coolant pressure. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 250 HP Engine 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Engine load % 
                 100 
                 75 
                 50 
                 25 
                 5 
               
               
                 Engine power HP 
                 250 
                 187.5 
                 125 
                 62.5 
                 12.5 
               
               
                 Estimated engine SFC 
                 0.45 
                 0.45 
                 0.48 
                 0.65 
                 1.30 
               
               
                 (lb/HP-hr) 
               
               
                 Fuel flow lb/hr 
                 112.5 
                 84.4 
                 60 
                 40.6 
                 16.25 
               
               
                 Total fuel heat BTU/hr 
                 1.97 
                 1.47 
                 1.05 
                 0.75 
                 0.28 
               
               
                 (×10 −6 ) 
               
               
                 Cooling water heat 
                 0.59 
                 0.44 
                 0.31 
                 0.21 
                 0.085 
               
               
                 BTU/hr (×10 −6 ) 
               
               
                 Refrigerant boiler 
                 0.077 
                 0.077 
                 0.077 
                 0.077 
                 0.077 
               
               
                 BTU/hr (×10 −6 ) 
               
               
                 Engine radiator BTU/hr 
                 0.513 
                 0.363 
                 0.233 
                 0.133 
                 0.008 
               
               
                 (×10 −6 ) 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 500 HP Engine 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Engine load % 
                 100 
                 75 
                 50 
                 25 
                 5 
               
               
                 Engine power HP 
                 500 
                 375 
                 250 
                 125 
                 25 
               
               
                 Estimated engine SFC 
                 0.45 
                 0.45 
                 0.48 
                 0.65 
                 1.3 
               
               
                 (lb/HP-hr) 
               
               
                 Fuel flow lb/hr 
                 225 
                 168 
                 120 
                 81 
                 32 
               
               
                 Total fuel heat BTU/hr 
                 3.94 
                 2.95 
                 2.10 
                 1.42 
                 0.57 
               
               
                 (×10 −6 ) 
               
               
                 Cooling water heat 
                 1.18 
                 0.89 
                 0.63 
                 0.43 
                 0.17 
               
               
                 BTU/hr (×10 −6 ) 
               
               
                 Refrigerant boiler 
                 0.077 
                 0.077 
                 0.077 
                 0.077 
                 0.077 
               
               
                 BTU/hr (×10 −6 ) 
               
               
                 Engine radiator BTU/hr 
                 1.10 
                 0.81 
                 0.55 
                 0.35 
                 0.093 
               
               
                 (×10 −6 ) 
               
               
                   
               
             
          
         
       
     
         [0024]    Above analysis shows that relatively small amount of engine waste heat is required to drive 4 ton capacity preferred embodiment air conditioning system. 
         [0025]    Thermal analysis of the preferred system embodiment was conducted using Du Pont&#39;s refrigerant HCFC-124 which for ecological reasons replaces old R-114 refrigerant. Refrigerant compressor efficiency of 75% and refrigerant turbine efficiency of 80% were assumed in the system analysis. 
         [0026]    Table 3. below show the effect of air-conditioning cooling capacity on thermal rating of the refrigerant evaporator  17 , refrigerant boiler  31  and on the optimum size and speed of the refrigerant turbine  13  and refrigerant compressor  12 . 
         [0027]    As shown in Table 3, the optimum size of turbine and compressor wheels is quite small and operating RPM high requiring advanced high speed miniature turbine technology. 
         [0000]    
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 3 
               
             
             
               
                   
                   
               
               
                   
                 COOLING CAPACITY (ton) 
               
             
          
           
               
                   
                 2 
                 4 
                 10 
                 100 
               
               
                   
                   
               
             
          
           
               
                 Refrigerant 
                 24,000 
                 48,000 
                 120,000 
                 1,200,000 
               
               
                 evaporator heat 
               
               
                 load (BTU/hr) 
               
               
                 Refrigerant boiler 
                 35,530 
                 71,600 
                 177,651 
                 1,776,515 
               
               
                 heat load (BTU/hr) 
               
               
                 Refrigerant turbine- 
                 1.47 
                 2.94 
                 7.35 
                 73.54 
               
               
                 compressor power 
               
               
                 (kW) 
               
               
                 Refrigerant turbine- 
                 99,929 
                 70,661 
                 44,690 
                 14,132 
               
               
                 compressor (RPM) 
               
               
                 Refrigerant turbine 
                 15.67 
                 22.16 
                 35.04 
                 110.81 
               
               
                 wheel diameter 
               
               
                 (mm) 
               
               
                 Refrigerant 
                 36.01 
                 50.93 
                 80.53 
                 254.66 
               
               
                 compressor 
               
               
                 diameter (mm) 
               
               
                   
               
             
          
         
       
     
         [0028]      FIG. 3A  shows typical pressure-enthalpy (P-H) refrigerant process diagram and how it relates to the system component numbers shown in  FIG. 1 . Line  17  shows the amount of heat absorbed per one pound of refrigerant in the refrigerant evaporator  17 . Line  12  shows compression process in the refrigerant compressor  12 . Line  22  shows the amount of heat rejected per one pound of refrigerant in the refrigerant condenser  22 . Line  18  represents throttling process in the refrigerant cooler control valve  18 . Line  32  represents pumping process in the refrigerant pump  32 . Line  31  shows the amount of heat absorbed per one pound of refrigerant in the refrigerant boiler  31 . Line  13  shows expansion work process in the refrigerant turbine  13 . 
         [0029]      FIG. 3B  shows the estimated coolant flow split between the radiator flow and the refrigerant flow. 
         [0030]    Preferred embodiments of the present invention utilize the same turbine design as is described in Applicant&#39;s U.S. Pat. No. 5,928,286 which describes a hydraulic supercharger system and is incorporated herein by reference.  FIGS. 4A and 4B  are cross sectional drawings of a typical plastic-metal turbine wheel design as shown in U.S. Pat. No. 5,924,286.  FIGS. 5A and 5B  show design details of a typical 80 percent plus efficient turbine nozzle as shown in U.S. Pat. No. 5,924,286.  FIGS. 6A and 6B  show design details of a typical 80 percent plus efficient turbine blade as shown in U.S. Pat. No. 5,924,286. 
       Second Preferred Embodiment 
       [0031]      FIG. 7  shows second preferred system embodiment which is similar to the first preferred embodiment shown in  FIG. 1  with exception that refrigerant pump  32  which is electric driven or belt driven by the engine shown in  FIG. 1  is being replaced by high speed refrigerant pump  81  that is driven by refrigerant vapor turbine  82  as shown in  FIG. 7 . Refrigerant pump  81  and refrigerant vapor turbine  82  rotor is supported on liquid refrigerant hydrostatic journal bearings in the same fashion as refrigerant turbo-compressor  12  rotor shown in  FIG. 3 , thus avoiding need for oil lubrication. 
         [0032]    Thermal analysis of engine coolant and refrigerant system has shown that amount of engine coolant waste heat available in typical heavy duty diesel engine is more than sufficient to generate refrigerant vapor in refrigerant boiler  31  to drive both compressor drive turbine  13  and refrigerant pump drive turbine  82 . 
         [0033]    In case of 4 ton air conditioning system the compressor drive turbine  13  produces 5.5 HP@70,600 rpm and the boiler feed pump drive turbine  82  produces only 0.5 HP@37,000 rpm thus requiring approximately 10% refrigerant vapor flow of the compressor drive turbine  13  flow. 
         [0034]    Table 4 below shows optimized parameters of the refrigerant pump  81  driven by refrigerant vapor turbine  82  for a 4 ton HCFC-124 air-conditioning system. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                 TABLE 4 
               
               
                   
                   
               
             
             
               
                   
                 Pump inlet pressure (psia) 
                 110 
               
               
                   
                 Pump pressure rise (psid) 
                 190 
               
               
                   
                 Pump flow rate (gpm) 
                 2.51 
               
               
                   
                 Pump/Turbine power (HP) 
                 0.51 
               
               
                   
                 Pump speed (rpm) 
                 37,790 
               
               
                   
                 Pump impeller diameter (mm) 
                 19.16 
               
               
                   
                 Turbine wheel diameter (mm) 
                 40.8 
               
               
                   
                   
               
             
          
         
       
     
         [0035]    Start-up of system shown in  FIG. 7  requires initiation of refrigerant vapor flow through refrigerant vapor turbine  82 . To achieve this, the engine must be warmed-up to its operating temperature with refrigerant boiler  31  filled with refrigerant fluid. At start-up the refrigerant fluid is contained in the refrigerant boiler  31  by closing turbine control valve  27  and closed check valve  74  installed in the pump discharge line  75  preventing reverse flow through pump discharge line  75 . With hot coolant control valve  53  partially open, the heat input into refrigerant boiler  31  starts to generate refrigerant vapor flow which via refrigerant boiler discharge line  28  and with closed turbine control valve  27  forces the refrigerant vapor flow through the refrigerant vapor turbine  82  starting rotation of refrigerant pump  81  and pressurizing the refrigerant pump discharge line  75  which opens the check valve  74  and starts refrigerant circulation through refrigerant boiler  31 . Further opening of the hot coolant control valve  53  increases the amount of refrigerant vapor flow generated by refrigerant boiler  31  at which point the turbine control valve  27  starts opening and driving the refrigerant vapor turbine  13  which drives the refrigerant compressor  12  and starts producing desired amount of air-conditioning cooling. 
       Variations 
       [0036]    The present invention has been described above in terms of preferred embodiments. Persons skilled in the air condition and motor vehicles arts will understand that many changes and additions could be made within the general scope of the present invention. Applicant expects that the big market for systems according to the present invention will be motor vehicles, but the invention can be adapted for utilization of other sources of waste heat or even heat sources that are not waste heat, such as a solar concentrator. For solar powered air conditioning an electric pump replacing pump  52  in  FIG. 1  or  FIG. 7  could be used to circulate coolant through the concentrator directly to and through refrigerant boiler  31  back to the input of the electric pump. An alternative would be to replace the electric pump with a high speed refrigerant pump such as refrigerant pump  81  shown in  FIG. 7 . In this case the system could be completely solar powered. Electric controls could be powered with a solar panel or a thermoelectric device. 
         [0037]    Therefore the scope of the present invention should be determined by the appended claims and their legal equivalence and not by the specific embodiment described above.