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
  • F25B41/00—Fluid-circulation arrangements
• • 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

• the invention relates to cooling systems. More particularly, the invention relates to the control of refrigerant phase in evaporators of air conditioning and refrigeration systems.
• a distributor receives two-phase refrigerant from the expansion device and provides balanced delivery of liquid and gas refrigerant phases among the various coils of an evaporator so as to prevent uneven performance.
• Various types of distributors have been developed. These include capillary-type distributors and impingement/turbulence distributors. Exemplary distributors are shown in US 2,148,414, 2,461,876, 3,795,259, 4,543,802, 5,832,744, and 5,842351, EP 0160542, and JP 5-322378 and 10-185363.
• One aspect of the invention involves an apparatus including a compressor having suction and discharge ports, a condenser, first and second expansion devices, an evaporator, and a heat exchanger having first and second portions in heat exchange relation with each other.
• One or more conduits form a main flowpath and a bypass flowpath.
• the main flowpath runs from the discharge port through the condenser, the heat exchanger first portion, the first expansion device, and the evaporator, and returns to the suction port.
• the bypass flowpath bypasses the neat excnanger first portion, the first expansion device, and the evaporator, but passes through the second expansion device and the heat exchanger second portion.
• the evaporator may lack a distributor.
• the second expansion device may be a TXV having a bulb essentially in heat exchange relation with a suction port condition.
• the second expansion device may be an EXV.
• a controller may be coupled to the EXV and programmed to control the EXV responsive to indicated superheat.
• the heat exchanger first portion may be downstream of the condenser and upstream of the evaporator along the main fiowpath.
• the heat exchanger second portion may be downstream of the condenser along the bypass fiowpath.
• the heat exchanger first portion may be upstream of the first expansion device along the main fiowpath.
• the evaporator may be a refrigerant-to-air heat exchanger.
• a bypass flow along the bypass fiowpath may enter the heat exchanger second portion in a two-phase gas/liquid condition and exit the heat exchanger second portion in a single-phase superheated gas condition.
• a main flow along the main flowpath may remain essentially a single-phase liquid in said heat exchanger second portion.
• the compressor may be selected from the group consisting of screw compressors and scroll compressors.
• Another aspect of the invention involves a method for operating such an apparatus. At least one operational parameter is detected. Responsive to the detection, at least the second expansion device is operated so as to maintain essentially single-phase liquid refrigerant entering the evaporator along the main flowpath.
• the at least one operational parameter may include at least one of saturated suction temperature and actual suction temperature.
• Another aspect of the invention involves a method for operating a cooling system.
• a main flow of refrigerant is caused to pass through an evaporator.
• the main flow is precooled upstream of the evaporator so as to maintain the main flow essentially as a liquid entering the evaporator.
• the precooling may comprise controlling a bypass flow in heat exchange relation with the main flow.
• the method may further comprise determining whether, absent the precooling, the main flow would enter the evaporator essentially as a two-phase flow.
• Another aspect of the invention involves a system comprising a compressor, a condenser, an expansion device, and an evaporator, a discharge line couples the compressor to the condenser to carry at least a main flow of refrigerant from the compressor to the condenser.
• a suction line couples the evaporator to the compressor to carry refrigerant from the condenser to the compressor.
• the system includes means for precooling refrigerant entering the expansion device so as to maintain the main flow essentially as a liquid while flowing along a flowpath length at least from the expansion device to the evaporator.
• the evaporator may lack a distributor.
• the main flow may transition to a two-phase liquid/gas flow and then to a one-phase superheated gas flow.
• the bypass flow may represent 10% ⁇ 35%, by weight, of a total refrigerant flow through the compressor.
• FIG. 1 is a schematic representation of a refrigeration or air conditioning system employing the present invention.
• FIG. 2 is a phase diagram for a prior art system.
• FIG. 3 is a phase diagram for the system of FIG. 1.
• FIG. 1 shows an exemplary closed refrigeration or air conditioning system 10.
• the system 10 has a hermetic compressor 12, from which a compressor discharge conduit or line 14 extends downstream to a condenser 16.
• An intermediate line 18 extends downstream from the condenser 16 to an expansion device 20 and an evaporator 22.
• a suction line 24 extends downstream from the evaporator 22 to the compressor 12 to complete the main circuit/flowpath 26.
• bypass line 30 branches off from the intermediate line 18 and contains an auxiliary expansion device 32 and connects with the suction line 24.
• a heat exchanger 34 is located such that the bypass line 30, downstream of the expansion device 32, and the line 18, upstream of the main expansion device 20, are in heat exchange relationship.
• the exemplary evaporator 22 is a cross-flow refrigerant-to-air heat exchanger having a number of parallel refrigerant coils 36 extending from inlet ends at a liquid collector or manifold 38 to outlet ends at a suction collector or manifold 40.
• a fan 42 drives an airflow 44 across the coils 36 so that the refrigerant passing through the coils may draw heat from the airflow.
• Exemplary expansion devices 20 and 32 are electronic expansion valves (EEVs) and are illustrated as coupled to a monitoring/control system 44 (e.g., a microprocessor-based controller) for receiving control inputs via control lines 45 and 46, respectively.
• the exemplary control system 44 may receive inputs such as zone inputs from one or more sensors 47, system condition inputs from one or more sensors (e.g., suction temperature sensor 50 and suction pressure sensor 52), and external control inputs from one or more input devices (e.g., thermostats 60).
• any of a variety of expansion devices may be used (e.g., a thermal expansion valve (TXV) 32 having a remote bulb 70, a fixed orifice device, or a capillary tube device).
• TXV thermal expansion valve
• FIG. 2 shows pressure 100 and enthalpy 102 for the refrigerant flow in such a basic system (or'tne preseriFsystem with no bypass flow).
• a boundary 104 separates a two-phase gas/liquid mixture domain 106 from a single phase sub-cooled liquid domain 108 and a single phase superheated gas domain 110.
• Suction conditions are shown as point or condition 120 at enthalpy 122 and pressure 124. These conditions are essentially present in the flowpath downstream from the suction manifold 40 to the compressor suction port.
• the refrigerant is compressed (plot compression segment 125) in the compressor 12 to a compressed point 126 with increased enthalpy 128 and increased pressure 130.
• the refrigerant may typically remain in the superheated gas domain 110 or may transition thereto from the two-phase domain 106.
• the refrigerant is condensed (condensing segment 131) in the condenser 16 to a condensed point 132 with reduced enthalpy 134 but at the same pressure as the compressed/discharge condition.
• the refrigerant state may transition from the superheated gas domain 110 to the two-phase domain 106 and even into the sub-cooled liquid domain 108.
• the refrigerant is expanded (expansion segment 135) in the expansion device 34 to an expanded point 136 with decreased pressure 138.
• enthalpy may remain essentially constant at 134.
• the refrigerant may reenter or remain in the two-phase domain 106 during the expansion 135.
• This expanded two-phase refrigerant must enter the evaporator.
• the refrigerant is evaporated (evaporation segment 139) in the evaporator to return to the suction point 120 with substantially increased enthalpy and slightly decreased pressure relative to the expanded point 136.
• FIG. 3 shows how the bypass flow of the present invention may be utilized to achieve advantageous refrigerant conditions entering the evaporator 22.
• the suction condition/point 220 may be essentially the same as point 120 of FIG. 2.
• the compressed/discharge/point 226 may be similar to the point 126 of FIG. 2.
• the condensing 231 brings the combined main flow and bypass flow to a condensed/point 232 which may be similar to point 132.
• the bypass flow splits from the main flow.
• the bypass flow refrigerant is expanded (segment 233) to reach a point 234 which may be essentially at the suction pressure 124 and the enthalpy 134.
• Heat exchange (235 for the bypass flow and 236 for the main flow) from the main flow to the bypass flow in the heat exchanger 34 then returns the bypass flow conditions to point 220 and cools the main flow to a precooled/point 238 with further reduced main flow enthalpy 240.
• the main flow of refrigerant is expanded (segment 241) in the expansion device 20 to a point 242 with decreased pressure 244 (which may be essentially the same as 138).
• the main flow of refrigerant is evaporated (segment 245) in the evaporator 22 to return the main flow to the initial suction point 220.
• the heat exchange from the bypass flow to the main flow tends to shift the point 242 to a lower enthalpy condition.
• the required amount of heat exchange may depend upon ambient conditions.
• a basic operation of the expansion device 32 may be responsive to sensed superheat of the refrigerant exiting the evaporator 22.
• the degree of superheat (actual temperature minus saturated temperature) may be determined based upon the output of the temperature sensor 50 for the actual temperature and the pressure sensor 52 for the saturated temperature (e.g., in view of known refrigerant properties which may be programmed into the control system 44).
• the expansion device 32 may be opened either in a binary fashion or a progressive fashion in response to the presence or degree of superheat or superheat parameter (e.g., superheat above a threshold).
• control could be achieved by placing its bulb 70 in heat exchange relation with the refrigerant at suction conditions. Much more complex arrangements are also possible.
• the expansion device 32 and/or other components of the bypass flowpath may be dimensioned in view of main flowpath components to permit an appropriate balance between bypass and non-bypass flows.
• an exemplary balance involves having the bypass flow be approximately 30% of the total flow through the compressor (i.e., 3/7 of the non-bypass flow) by weight/mass.
• Broader exemplary figures for binary operation are 25%-33%, and 10%-35%.
• Progressive or stepwise operation may permit maximums in such ranges and may, optionally, permit flows smaller than the lower ends of such ranges.

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• 2004
  • 2004-09-29 US US10/954,499 patent/US20060064997A1/en not_active Abandoned
• 2005
  • 2005-09-07 EP EP05794299A patent/EP1800071A2/de not_active Withdrawn
  • 2005-09-07 WO PCT/US2005/031179 patent/WO2006039042A2/en not_active Application Discontinuation
  • 2005-09-07 CN CNA2005800331253A patent/CN101031763A/zh active Pending

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