Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B1/00—Compression machines, plants or systems with non-reversible cycle
  • F25B1/10—Compression machines, plants or systems with non-reversible cycle with multi-stage compression
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2309/00—Gas cycle refrigeration machines
  • F25B2309/06—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/12—Inflammable refrigerants
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
  • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/13—Economisers

Definitions

• This application relates to refrigerant systems with at least two cascaded circuits, and more particularly, to cascade refrigerant systems with performance enhancement features.
• two distinct refrigerants can be utilized in each of the two circuits, with a hydrocarbon refrigerant utilized only in the upper stage circuit and another refrigerant utilized in the lower stage circuit.
• the hydrocarbon type of refrigerant can be, for example, propane or isobutene refrigerant. Since the upper stage circuit can be located outside of the enclosed conditioned compartment, it would offer an advantage of locating the flammable refrigerant also outside of the enclosed space, which would mitigate fiammability concerns of these refrigerants.
• the amount of charge in the upper stage circuit would be substantially reduced as compared to a single circuit refrigerant system. Since the amount of charge in the upper circuit is minimized, the concerns for the fiammability of the refrigerant in this circuit are also reduced.
• the lower stage circuit is charged with the CO 2 refrigerant. Since only the lower stage circuit is charged with CO 2 , this circuit would operate at much lower pressure as compared to a single circuit refrigerant system (not cascaded) charged with C02 refrigerant. Propane or a like refrigerant would be utilized in the upper circuit.
• the refrigerant system designer is still faced with many challenges dealing with further improvements of the system efficiency and capacity control.
• an economizer cycle may be incorporated into a refrigerant system for its performance boost.
• An economizer cycle operates to subcool a main refrigerant flow, and does so, in one variation, by tapping a portion of refrigerant from the main refrigerant flow and expanding this tapped refrigerant to some intermediate pressure. This expanded refrigerant is at a cooler temperature, and passes in a heat exchange relationship with the main refrigerant flow in an economizer heat exchanger.
• a flash tank replaces the heat exchanger, where vapor and liquid refrigerant phases are separated, with the liquid flow continuing through the main circuit and the vapor flow injected into the compression process at some intermediate pressure.
• a vapor refrigerant is returned to the compressor.
• Another enhancement feature is a refrigerant bypass function.
• a bypass function at least a portion of partially compressed refrigerant is returned to a refrigerant suction line, allowing for unloading of the refrigerant system.
• Still another enhancement feature is a liquid-suction heat exchanger.
• refrigerant downstream of an evaporator passes in heat exchange relationship with a refrigerant downstream of the condenser, allowing for additional subcooling and capacity increase of the refrigerant system.
• these enhancement features were associated with a standard circuit, where the circuit had an evaporator and gas cooler (or condenser).
• each of the cascaded circuits does not operate with an evaporator and gas cooler. Instead, the lower stage circuit has an evaporator and shares the common refrigerant-to-refrigerant heat exchanger with the upper stage circuit.
• the upper circuit has the gas cooler and shares the same common refrigerant-to-refrigerant heat exchanger with the lower circuit. In other words, there is no evaporator associated with the upper circuit and there is no gas cooler associated with the lower circuit.
• This invention provides additional design features enhancing the cascaded system performance and functionality to become comparable to the traditional refrigerant systems for a wide spectrum of operating and environmental conditions as described in the main body of this application.
• cascaded refrigerant circuits are incorporated into a refrigerant system design.
• an upper stage circuit includes a hydrocarbon refrigerant, such as for example propane or isobutene, which can be located outdoors.
• the upper stage circuit is positioned in a cascaded relationship with a lower stage circuit, which would normally utilize the CO 2 refrigerant.
• the upper stage circuit is mainly located in the outdoor environment, while the lower stage circuit is normally located in the indoor environment. However, other locations would also fall within the scope of this invention.
• the lower stage inside CO 2 circuit operates in a subcritical region while the upper stage outside cascaded circuit would operate in a transcritical region if it was charged with the same CO 2 refrigerant.
• the combination of the two circuits provides performance enhancements for the supercritical region operation of the CO 2 circuit.
• at least one of the circuits can be equipped with the economized cycle, utilizing either economizer heat exchanger or flash tank arrangements.
• at least one of the circuits can be equipped with a liquid suction heat exchanger.
• an unloading feature can be provided for one or both cascaded refrigerant circuits.
• Figure 1 shows a schematic of prior art system
• Figure 2 generally illustrates a feature of this prior art.
• Figure 3 shows a first embodiment of the present invention.
• Figure 4 shows a second embodiment of the present invention.
• Figure 5 shows a third embodiment of the present invention.
• Figure 6 shows a fourth embodiment of the present invention.
• Figure 7 shows a fifth embodiment of the present invention.
• Figure 8 shows a sixth embodiment of the present invention.
• Figure 9 shows a seventh embodiment of the present invention.
• Figure 10 shows an eighth embodiment of the present invention.
• FIG. 1 shows a prior art refrigerant system 20 incorporating two cascaded circuits 21 and 23.
• a lower stage circuit 23 includes a compressor 22 delivering a compressed refrigerant into a refrigerant-to-refrigerant heat exchanger 24.
• Refrigerant passes from the heat exchanger 24 through an expansion device 26, and to an indoor heat exchanger 28.
• a fan 30 blows air over external surfaces of the indoor heat exchanger 28 and delivers that conditioned air into the environment 32.
• the lower stage circuit 23 would normally be charged with a refrigerant that would operate in a subcritical region.
• One such refrigerant that can be used for this circuit would be CO 2 refrigerant that, while in the lower cascaded circuit, would still be in the subcritical region. If this same
• CO 2 refrigerant would have been used in the upper cascaded circuit, it is likely to operate at transcritical regime.
• a compressor 34 compresses a refrigerant and delivers it to a second outdoor heat exchanger 36.
• a fan 38 blows air over the heat exchanger 36.
• Refrigerant passes from the heat exchanger 36 downstream to an expansion device 40, and then back through the refrigerant-to-refrigerant heat exchanger 24 to the compressor 22.
• Figure 2 shows a P-h chart for the refrigerant system 20.
• the upper stage circuit 21 can be charged with a hydrocarbon refrigerant, and in particular, this refrigerant is disclosed as one of propane or isobutene. It is known that propane and isobutene have great thermo-physical properties as refrigerants, however, they are both potentially explosive, and there are safety concerns to use them, especially in confined environments. By limiting hydrocarbon refrigerant applications to the outdoor heat exchangers, the problem of explosiveness is significantly reduced. Further, by charging only the upper stage cascaded circuit 21 with the hydrocarbon refrigerant, the refrigerant system designer reduces the total amount of the hydrocarbon refrigerant used within the refrigerant system 20, consequently decreasing the flammability risk from using hydrocarbon refrigerants. Moreover, by positioning the fans 38 in an optimum orientation with respect to heat exchanger 36, any leakage or accidental discharge of the hydrocarbon refrigerant into the conditioned space can be directed toward the outdoor environment, thus further minimizing risks of explosion.
• the lower stage cascaded circuit 23 preferably operates in a subcritical region. Further, while it is disclosed that the upper stage cascaded circuit 21 operates with a hydrocarbon refrigerant, the circuit 21 can operate with other suitable refrigerants. In disclosed embodiments, additional enhancement features are provided to allow the cascaded circuits to perform more efficiently.
• the upper stage cascaded circuit 100 is equipped with an economizer function 102 that would increase the capacity and amount of subcooling to the main refrigerant flow for this upper stage cascaded economized circuit 100. Consequently, the performance of the lower stage cascaded circuit 101 is also enhanced, since the performance of the refrigerant-to-refrigerant heat exchanger 104, that provides heat transfer interaction means between the upper stage cascaded circuit 100 and the lower stage cascaded circuit 101 and serves as a condenser for the lower stage cascaded circuit 101, is increased.
• An economizer heat exchanger 109 and an economizer expansion device 99 are shown. Therefore, the capacity and efficiency of the overall cascaded refrigerant system shown in Figure 3 is augmented.
• a bypass valve 106 can be installed to connect an intermediate pressure side 107 of the upper stage cascaded circuit 100 to the suction pressure side 108 of this circuit. Selective opening of the bypass valve 106 provides the compressor unloading and capacity control means for the upper stage cascaded circuit 100, and therefore for the entire refrigerant system.
• the economizer function 102 provided for the upper stage cascaded circuit 100 by the economizer heat exchanger 109 in the Figure 3 embodiment can be also provided by a flash tank 112, as shown in Figure 4, and an expansion device 199.
• the upper stage cascaded circuit 100 can also be equipped with a liquid-suction heat exchanger (LSHE) 114, as shown in Figure 5, once again for the purpose of improving the capacity and amount of subcooling achieved in this upper stage cascaded circuit 100, by transferring heat from the hot refrigerant in a refrigerant line 116 to the suction refrigerant vapor in a refrigerant line 108.
• LSHE liquid-suction heat exchanger
• Figure 6 shows another embodiment where the economizer heat exchanger 109 and the liquid- suction heat exchanger 114 features are combined to achieve even further capacity and efficiency improvements for the upper stage cascaded circuit 100, and thus for the entire cascaded refrigerant system.
• Figure 7 represents another cascaded schematic, where an economizer heat exchanger 120 is incorporated into the lower stage cascaded circuit 101.
• this lower stage cascaded circuit 101 can also be equipped with an unloader valve 122, which would allow for bypass of a portion of refrigerant from an intermediate pressure side to suction pressure side.
• Figure 8 shows yet another cascaded schematic where a flash tank 130 is incorporated into the lower stage cascaded circuit 101.
• Figure 9 shows still another cascaded schematic where a liquid-suction heat exchanger 132 is incorporated into the lower stage cascaded circuit 101.
• Figure 10 yet shows another yet another cascaded schematic where both functions of the liquid-suction heat exchanger 132 and economizer heat exchanger 120 are incorporated into the lower stage cascaded circuit 101.
• These enhancement features can be used independently or in combination with each other.
• This embodiment shows a lower stage compressor 202 and an upper stage compressor 201.
• Figure 10 also schematically shows a "black box" 300, which illustrates a performance enhancement feature such as disclosed in any of the above embodiments. That is, both circuits can be provided with such a feature.
• performance enhancement features described above could be incorporated and operated independently or in combination with each other for each of the cascaded circuits within the refrigerant system. Also, it has to be understood that there could be more than two cascaded circuits operating within a refrigerant system. Obviously, in many cases, it would make more sense to apply performance enhancement features listed above to the cascaded circuits charged with the refrigerants that don't operate well in the basic refrigerant cycle.
• compressor types could be used in this invention.
• scroll, screw, rotary, or reciprocating compressors can be employed.
• refrigerant systems that utilize this invention can be used in many different applications, including, but not limited to, air conditioning systems, heat pump systems, marine container units, refrigeration truck-trailer units, and supermarket refrigeration systems.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Compression-Type Refrigeration Machines With Reversible Cycles (AREA)
• Other Air-Conditioning Systems (AREA)

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• 2007
  • 2007-06-04 CN CN200780053241A patent/CN101755175A/zh active Pending
  • 2007-06-04 US US12/528,642 patent/US20100147006A1/en not_active Abandoned
  • 2007-06-04 WO PCT/US2007/070288 patent/WO2008150289A1/en active Application Filing
  • 2007-06-04 EP EP07798044.9A patent/EP2162686A4/de not_active Withdrawn

Patent Citations (5)

Non-Patent Citations (2)

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