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
  • F25B40/00—Subcoolers, desuperheaters or superheaters
  • F25B40/04—Desuperheaters
• • 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
  • F25B40/00—Subcoolers, desuperheaters or superheaters
  • F25B40/02—Subcoolers
• • 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
  • F25B41/30—Expansion means; Dispositions thereof
  • F25B41/39—Dispositions with two or more expansion means arranged in series, i.e. multi-stage expansion, on a refrigerant line leading to the same evaporator
• • 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
  • F25B5/00—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity
  • F25B5/02—Compression machines, plants or systems, with several evaporator circuits, e.g. for varying refrigerating capacity arranged in parallel
• • 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
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
  • F25B9/008—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant 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
  • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
  • F25D16/00—Devices using a combination of a cooling mode associated with refrigerating machinery with a cooling mode not associated with refrigerating machinery
• • 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
  • F25B2309/061—Compression machines, plants or systems characterised by the refrigerant being carbon dioxide with cycle highest pressure above the supercritical pressure
• • 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
  • F25B2400/22—Refrigeration systems for supermarkets
• • 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
  • F25B2400/24—Storage receiver heat
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
  • F28D20/02—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat
  • F28D20/021—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using latent heat the latent heat storage material and the heat-exchanging means being enclosed in one container

Definitions

• the present invention relates to a transcritical refrigeration system, and in particular the present invention relates to a transcritical refrigeration system intended for a supermarket.
• heat release from the refrigerant is based on condensation of the refrigerant.
• the "real life" upper limit for heat release based on condensation of CO 2 will be around 20 0 C ambient temperature. Below this temperature, the CO 2 stays below the critical point and the refrigeration system operates in subcritical cycles.
• cooling of the CO 2 is a single-phase cooling, namely a gas cooling.
• CO 2 is above the critical point at the high- pressure side of the system, and the refrigeration system operates in transcritical cycles.
• the efficiency and the cooling capacity of the refrigeration system are lower in transcritical operation than in subcritical operation.
• a transcritical refrigeration system comprising a flow circuit for recirculation of a refrigerant, the flow circuit comprising a compressor for generation of a refrigerant flow from a low-pressure side to a high-pressure side of the compressor and, in the order defined by the flow direction, connected in series with a gas cooler for cooling of the refrigerant towards the ambient temperature, a first pressure reducing device, such as a reduction valve, separating the low-pressure side and the high pressure side of the compressor, and a first evaporator for evaporation of the refrigerant, e.g. in a cooling furniture.
• a heat exchanger with a refrigerant flow channel is connected in the flow circuit between the gas cooler and the pressure-reducing device.
• the heat exchanger also has a thermal medium flow channel for a thermal medium flow.
• the thermal medium flow channel is connected in series with a storage tank for storage of the thermal medium, e.g. water, the storage tank further comprising a second evaporator connected with the flow circuit in parallel with the first evaporator for cooling of the thermal medium.
• the thermal medium is water, and preferably the water is cooled to ice in the storage tank during subcritical operation of the system.
• the thermal storage tank may also comprise a thermal medium flow path connected in series with the thermal medium flow path of the heat exchanger so that the thermal medium flows into thermal contact with a second thermal medium, e.g. water, stored in the thermal storage tank and cooled by the second evaporator during subcritical operation of the system.
• the second thermal medium may undergo a phase transition, e.g. water to ice, during cooling.
• a phase transition e.g. from water to ice, makes it possible to store a large cooling capacity in the storage tank.
• GWP global warming potential
• a second pressure reducing device may be connected in series with and between the gas cooler and the heat exchanger for adjustment of a desired pressure in the gas cooler.
• the second pressure reducing device such as an expansion valve, may be controlled so that the gas cooler pressure attains the optimum value or approximately the optimum value.
• the heat exchanger also causes a pressure reduction from the input to the output of the heat exchanger as a result of the cooling of the refrigerant.
• the heat exchanger may also function as the second pressure reducing device and the flow of thermal medium through the heat exchanger may be controlled so that the gas cooler pressure attains the optimum value or approximately the optimum value.
• a second heat exchanger with a refrigerant flow channel may be connected in the flow circuit between the compressor and the gas cooler and with a thermal medium flow channel connected with the storage tank for fluid flow of the thermal medium and heat exchange with the refrigerant at the high pressure side of the compressor for heating of the thermal medium and storage of the heated medium in the thermal storage tank.
• the thermal storage tank may also comprise a thermal medium flow path connected in series with the thermal medium flow path of the second heat exchanger so that the thermal medium flows into thermal contact with a second thermal medium, e.g. water, stored in the thermal storage tank.
• a method of operating a transcritical refrigeration system for improved cooling capacity comprising the steps of operating the refrigeration system in subcritical cycles when the ambient temperature is below a temperature that allows cooling of the refrigerant by condensation, during at least part of the time of subcritical operation, cooling a thermal medium contained in a storage tank, operating the refrigeration system in a transcritical cycle process when the ambient temperature is above the temperature that allows cooling of the refrigerant by condensation, and during at least part of the time of transcritical operation, utilizing the thermal medium in a heat exchanger for cooling of the refrigerant at the high-pressure side of the refrigeration system.
• a method of operating a transcritical refrigeration system for supplemental heating comprising the steps of operating the refrigeration system in subcritical cycles when the ambient temperature is below a temperature that allows cooling of the refrigerant by condensation, during at least part of the time of subcritical operation, heating a thermal medium contained in a storage tank with the refrigerant in a heat exchanger at the high- pressure side of the refrigeration system, and operating the refrigeration system in transcritical cycles when the ambient temperature is above the ambient temperature that allows cooling of the refrigerant by condensation.
• Fig. 1 is a blocked schematic of a first embodiment of a transcritical cooling system according to the present invention
• Fig. 2 is a plot of a subcritical cooling cycle
• Fig. 3 is a plot of a transcritical cooling cycle
• Fig. 4 is a plot illustrating control of gas cooler pressure
• Fig. 5 is a blocked schematic of a second embodiment of a transcritical cooling system according to the present invention.
• Fig. 1 is a blocked schematic of a first embodiment 10 of a transcritical cooling system according to the present invention.
• the system 10 comprises a refrigerant flow circuit for recirculation of CO 2 refrigerant 12, the flow circuit comprising a compressor 14 for generation of a refrigerant flow in the direction of the arrow 16 from a low-pressure side to a high- pressure side of the compressor 14 and, in the order defined by the flow direction, connected in series with a gas cooler 18 for cooling of the refrigerant 12 towards the ambient temperature, a valve 20 for pressure reduction as will be further explained below, a heat exchanger 22 with a refrigerant flow channel 24 connected in the flow circuit between the gas cooler 18 and a receiver 26 for accommodation of CO 2 refrigerant 12.
• the receiver 26 is connected to an expansion valve 28 that separates the low-pressure side and the high- pressure side of the compressor 14, and a first evaporator 30 for evaporation of the CO 2 refrigerant.
• the refrigerant flow channel 24 of the heat exchanger 22 may alternatively be connected between the gas cooler 18 and the valve 20, or, between the receiver 26 and the expansion valve 28.
• Fig. 2 illustrates subcritical operation of the system 10 in a conventional Log (p), h (enthalpy) diagram.
• the compressor 14 compresses the CO 2 refrigerant, and subsequently heat is released from the refrigerant from point 2 to 3 below the critical point 32 by condensation of the refrigerant in the gas cooler 18 at a constant pressure.
• the expansion from point 3 to 4 takes place at constant specific enthalpy at passage of the expansion valve 28.
• the heat absorption takes place in the evaporator 30 in the cooling furniture of the system 10 from point 4 to 1 at constant pressure.
• the control valve 20 is fully open when the system 10 operates subcritically.
• Fig. 3 illustrates transcritical operation of the system 10.
• the most important difference between the plot of Fig. 3 and the plot of Fig. 2 is that the CO 2 refrigerant is above the critical point 32 at the high-pressure side of the compressor 14 and thus, heat is released from the refrigerant by CO 2 gas cooling in the gas cooler 18.
• the coefficient of performance (COP) of the system 10 is less for transcritical cycles than for subcritical cycles due to the lacking phase transition, i.e. no condensation, during heat release.
• the expansion from point 3 to 4 takes place in two steps, namely from point 3 to 5, and subsequently from point 5 to 4.
• the valve 20 reduces the pressure from point 3 to point 5 so that CO 2 in the liquid phase enters the heat exchanger 22 and is collected in the receiver 26. Further, the valve 20 is controlled in such a way that the pressure in the gas cooler 18 attains a value that gives the best possible COP. This is further illustrated in Fig. 4. In addition to the transcritical cooling cycle, Fig. 4 shows two isotherms 34, 36.
• the COP decreases for increased gas cooler pressure.
• the valve 20 is adjusted in such a way that the gas cooler pressure attains, at least approximately, this optimum pressure value.
• the gas cooler pressure is app. 120 bar while the pressure at the low-pressure side of the compressor 14 is app. 40 bar.
• a processor 100 is adapted to control the valve 20 based on the temperature and pressure on the low pressure side of the compressor 14 downstream the evaporator 30 and on the pressure at the output side of the gas cooler 18 in such a way that the gas cooler pressure attains, at least approximately, its optimum pressure value.
• the heat exchanger 22 also comprises a thermal medium flow channel 38 for a thermal medium flow and connected in series with a storage tank 40 for storage of water and ice.
• the storage tank 30 further comprises an evaporator 42 connected to an expansion valve 44 so that the evaporator 42 is connected in the flow circuit in parallel with the first evaporator 30.
• the evaporator 42 operates in parallel with the evaporator 30 so that the water in the storage tank 20 is cooled to ice.
• the pump 46 is operated and the three-way valve 50 is opened to pump water at the freezing point through the thermal medium flow channel 38 for further cooling of the CO 2 refrigerant whereby the capacity of the system 10 is increased during transcritical operation.
• the phase transition from water to ice, and vice versa, makes it possible to store a large cooling capacity for later use.
• the embodiment of Fig. 5 corresponds to the embodiment of Fig. 1 with a further heat exchanger 50 inserted in the flow circuit between the compressor 14 and the gas cooler 18.
• the heat exchanger 50 has a refrigerant flow channel 52 connected in the flow circuit between the compressor 14 and the gas cooler 18.
• the heat exchanger 50 also comprises a thermal medium flow channel 54 for a thermal medium flow and connected in series with the storage tank 40 for storage of water and ice.
• the valves 48, 56, 58 are opened allowing the pump 46 to pump water from the storage tank 40 through the heat exchanger 50 for heating of the water, and back into the storage tank.
• the storage tank may further be connected to a heating system (not shown) that utilizes the heated water.
• the water is cooled to ice, when the system 10 operates in subcritical cycles and the ice water is used for cooling of the refrigerant in the heat exchanger 22 when the system 10 operates in transcritical cycles as described above with reference to Fig. 1.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Combustion & Propulsion (AREA)
• Devices That Are Associated With Refrigeration Equipment (AREA)
• Compression-Type Refrigeration Machines With Reversible Cycles (AREA)

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• 2006
  • 2006-08-24 EP EP06761869A patent/EP1920203A1/de not_active Withdrawn
  • 2006-08-24 WO PCT/DK2006/000459 patent/WO2007022778A1/en active Application Filing
• 2008
  • 2008-03-18 NO NO20081411A patent/NO20081411L/no not_active Application Discontinuation

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