Patent Application
20130263619
This application claims the benefit of Provisional Patent Application Ser. No. 61/517,1-2 filed Apr. 13, 2011.
This invention relates to air conditioning systems and in particular to such systems based on the use of waste heat.
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.
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.
Applicant has developed over the past decade a miniature very high speed, high efficiency turbine technology such as shown in the Applicant'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.
Therefore, there is a great need for efficient and low cost, engine waste heat powered air-conditioning system.
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'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.
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.
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.
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
Preferred embodiments of the present invention are described by reference to the drawings.
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.
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.
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.
Above analysis shows that relatively small amount of engine waste heat is required to drive 4 ton capacity preferred embodiment air conditioning system.
Thermal analysis of the preferred system embodiment was conducted using Du Pont'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.
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.
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.
Preferred embodiments of the present invention utilize the same turbine design as is described in Applicant's U.S. Pat. No. 5,928,286 which describes a hydraulic supercharger system and is incorporated herein by reference.
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.
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.
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.
Start-up of system shown in
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
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.
