WO1994020803A1 - Procede et appreil de refrigeration - Google Patents

Procede et appreil de refrigeration Download PDF

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Publication number
WO1994020803A1
WO1994020803A1 PCT/AU1994/000108 AU9400108W WO9420803A1 WO 1994020803 A1 WO1994020803 A1 WO 1994020803A1 AU 9400108 W AU9400108 W AU 9400108W WO 9420803 A1 WO9420803 A1 WO 9420803A1
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WO
WIPO (PCT)
Prior art keywords
heat
heat exchange
defrost
circuit
refrigeration
Prior art date
Application number
PCT/AU1994/000108
Other languages
English (en)
Inventor
Keith Matthew Greenhalgh
Original Assignee
Greenhalgh Refrigeration Pty Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Greenhalgh Refrigeration Pty Ltd filed Critical Greenhalgh Refrigeration Pty Ltd
Priority to AU62774/94A priority Critical patent/AU6277494A/en
Publication of WO1994020803A1 publication Critical patent/WO1994020803A1/fr

Links

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
    • F25B47/00—Arrangements for preventing or removing deposits or corrosion, not provided for in another subclass
    • F25B47/02—Defrosting cycles
    • F25B47/022—Defrosting cycles hot gas defrosting

Definitions

  • THIS INVENTION relates to a refrigeration process and apparatus and in particular but not limited to a defrost process and apparatus for a low temperature refrigeration system.
  • Refrigeration systems for cooling a refrigerated space usually employ an evaporator having coils which are prone to frost-up and accumulation of ice on the evaporator inhibits proper operation of the system. It is common to periodically defrost the system to remove ice.
  • defrost processes suffer from a number of disadvantages.
  • One common process involves hot gas defrosting where a hot gas from a compressor is passed through coils of the evaporator. This process does not work efficiently and has particular disadvantages where there is heavy accumulation of ice. The capacity of the compressor to deliver heat can be exceeded. This results in a drop in compression at the compressor giving high defrost times and a temperature rise in the refrigerated space.
  • the present invention resides in a defrost process for a refrigeration system involving a heat exchanger for removing heat from a refrigerated space, the process comprising:- (i) providing a heat exchanger for removing heat from the refrigerated space; (ii) providing a defrost heat exchange circuit having a heat source portion; (iii) circulating a heat exchange fluid through a refrigeration heat exchange circuit having a heat sink portion in the heat exchanger so that ice accumulates on or adjacent the heat sink portion;
  • the invention resides in a refrigeration system for removing heat from a refrigerated space comprising refrigeration and defrost heat exchange circuits, the refrigeration heat exchange circuit having a heat exchanger including a heat sink portion, the defrost heat exchange circuit having a heat source portion in heat exchange relation with the heat sink portion and a controller for periodically circulating the heat exchange fluid through the circuits, the heat exchanger having independent heat sink and heat source portions through which a heat exchange fluid can flow, the heat sink and heat source portions being in heat exchange relation so that when heat exchange fluid flows through the heat source portion, heat is delivered to the heat sink portion to melt accumulated ice adjacent the heat sink portion of the heat exchanger.
  • the invention resides in a heat exchanger for a refrigeration system, the heat exchanger having independent heat sink and heat source portions through which a heat exchange fluid can flow, the heat sink and heat source portions being in heat exchange relation so that when heat exchange fluid flows through the heat source portion, heat is delivered to the heat sink portion to melt accumulated ice adjacent the heat sink portion of the heat exchanger.
  • the refrigeration heat exchange and defrost heat exchange circuits are preferably parallel circuits alternately supplied with heat exchange fluid from a shared compressor circuit portion during respective refrigeration and defrost cycles of operation.
  • the heat exchanger is preferably a unitary structure where the heat sink and heat source portions are intertwined to maximise heat transfer between the two.
  • the heat sink and heat source portions typically comprise serpentine tubes arranged in interdigitated fashion within the heat exchanger.
  • the heat exchanger typically includes a sump or drain pan section for accumulation of condensate which flows into the sump.
  • the heat source portion of the defrost circuit preferably includes a sump portion in heat exchange relation with the sump and being upstream of the heat sink portion so that ice which accumulates in the sump is melted by heat transferred from the sump portion of the defrost circuit to the ice accumulating in the sump.
  • the drain pan is typically insulated so there is minimal heat transfer to the surroundings.
  • the heat sink and source portions preferably share a common outlet manifold leading to the compressor circuit portion.
  • the defrost heat exchange circuit preferably employs a flow metering device downstream of the heat source portion.
  • the flow metering device typically limits return pressure of heat exchange fluid to the compressor circuit so that a predetermined pressure differential in the compressor circuit is maintained across the compressor during a defrost cycle.
  • the flow metering device is preferably a flow restrictor located between the heat source portion and the outlet manifold.
  • the flow restrictor is typically adjustable or includes an interchangeable orifice assembly so that the mass flow of heat exchange fluid metered from the heat source portion to the compressor circuit portion can be configured to match the heat sink portion capacity and the capacity of the compressor.
  • the heat source portion, compressor circuit and controller are typically operatively arranged to maximise the temperature differential between the heat source portion and the heat sink portion during a defrost cycle so that the defrost time is minimised.
  • the controller typically includes a main control unit exercising peripheral control of the refrigeration system.
  • a typical system employs, in addition to the above elements, fans operable by the controller for distributing cold air through the refrigerated space and peripheral temperature sensors providing feedback to the controller for initiating and terminating the cycles.
  • the fans are stopped.
  • the refrigeration cycle recommences before the fans are restarted so that any local heat adjacent the heat exchanger is sunk into the heat sink portion rather than circulated through the refrigerated space.
  • Figure 2 is similar to Figure 1 but illustrating a defrosting cycle; and Figures 3A, 3B and 3C are schematic diagrams illustrating a preferred heat exchanger for use in a refrigeration system according to the present invention.
  • a refrigeration system 10 comprising a refrigeration heat exchange circuit 1 1 involving a condenser 12, a liquid receiver 13, a liquid line 14, a thermal expansion valve 1 5, an evaporator coil 16, a suction manifold 1 7, a suction line 18, a compressor 19 and a discharge line 20.
  • the system also includes a defrost circuit comprising a solenoid 21 , superheated gas delivery line 22, a condenser 23 and a flow restrictor 24 which joins the suction line 18 at the suction manifold 1 7.
  • the defrost circuit shares the suction line 18, compressor 19 and the discharge line 20 with the refrigeration circuit 1 1.
  • the system operates in accordance with a controller (not shown) and as can be seen from Figure 1 during a refrigeration cycle, the heat exchange fluid is circulated through the refrigeration circuit described above.
  • ice can accumulate on the evaporator 16 and in particular in the drainage pan illustrated generally at 25.
  • the solenoid valve 21 is open and heat exchange fluid flows into the line 22 (also backflowing from the refrigerator circuit) to a first portion 26 of the condenser 23.
  • the first portion 26 is located in the pan 25 and applies heat to ice accumulated in the pan.
  • the heat exchange fluid then flows into the second portion 27 of the condenser to defrost the evaporator coil 16.
  • the heat exchange fluid then flows through the restrictor 24 so that the correct operating pressure differential across the compressor is maintained during the defrost cycle.
  • the restrictor 24 is fitted between the condenser 27 and the suction manifold 17 to interrupt the flow of subcooled saturated heat exchange fluid back into the suction line 18. This maintains a high discharge pressure consistent with the condensing temperature, so that the heat exchange fluid is in the form of a high superheated discharge gas being delivered to the condenser 23 for the complete defrost cycle.
  • the restrictor 24 provides enough resistance to the gas flow for the compressor 19 to maintain the lower condensing discharge pressure, and consequently superheating of the gas continues.
  • some liquid refrigerant, the liquid line 14 and the liquid receiver 13, if fitted, is evaporated due to the sudden drop in pressure.
  • This relatively high temperature gas also gives up its superheat and is subcooled to a saturated vapour in the condenser 23. This phenomena may be evidenced by sharp drop in temperature in the condenser 12 and liquid line 14.
  • the pressure in the evaporator 16 now rises well above normal working pressure as some of the saturated gas flowing through the restrictor 24 will condense to a liquid in the evaporator until equilibrium pressure and temperature is reached.
  • the first gas flowing to the condenser 23 is passed through the coil portion 26 fitted to the drain pan 25 to clear the drain pan of any accumulated ice.
  • the condenser portion 26 comprises a single row extending across the bottom and below the evaporator 16 as this is generally where the largest concentration of ice accumulates.
  • the refrigerant gas then flows through a serpentine tube path interdigitated with a serpentine tube of the evaporator to provide a heat source generally down the centre of the evaporator.
  • the saturated refrigerant gas derived through this process flows through the restrictor 24 back to the compressor.
  • the restrictor in this embodiment has a replaceable orifice.
  • the orifice size is selected against the capacity of the evaporator coil and mass flow of refrigerant through the compressor. This is done to give the correct flow rate and maintain only subcooled saturated refrigerant vapour back to the compressor.
  • FIG. 3A, 3B and 3C there is illustrated a typical heat exchanger and where appropriate, like numerals have been used to illustrate like features.
  • the Figures are drawn so that when Figure 3B is superimposed upon Figure 3A in order to the arrangement of the evaporator 16 relative to the condenser 23 can be seen. These have been illustrated schematically and separately for clarity.
  • the drain pan 26 is fitted with a double skin with a bonded laminate of weatherproof high density insulation material. Because the defrost heat is confined to the centre of the heat exchanger and travels outward, the system operates so that only enough latent heat is added to clear the ice from fin surfaces of the evaporator and minimal heat is lost through the drain pan. For this reason, there is minimal temperature rise in the refrigerated space during the defrost cycle.
  • the defrost time is considerably short and then consequently energy is conserved. Trials to date have confirmed that defrost times are reduced by up to 50% while energy consumption during the defrost cycle is reduced by up to 50% with lower deterioration of product quality in the refrigerated space.
  • the evaporator fans are shut down and the compressor discharge branch line solenoid 21 opens.
  • the defrost termination is controlled by a thermostat sensing the temperature of coil fins in the evaporator coil 16.
  • the compressor 19 discharge branch line solenoid valve 21 closes. As the evaporator is still charged with liquid refrigerant, the cooling cycle commences quickly as liquid is evaporated by the falling suction pressure.
  • the condenser 23 is circuited in such a way that no recirculating oil may be left logged in the coil, and will be entrained in suction gas flowing through the restrictor at all times.
  • the controller incorporates a fan delay switching function in conjunction with a defrost termination thermostat.
  • the fans will not operate until the fin temperature is at a desired saturated suction temperature. This prevents the higher temperature of the evaporator, after defrost, displacing heat into the refrigerated space and prevents free water from being entrained into the air stream.

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Mechanical Engineering (AREA)
  • Thermal Sciences (AREA)
  • General Engineering & Computer Science (AREA)
  • Defrosting Systems (AREA)

Abstract

L'invention concerne un système de réfrigération (10) comprenant un circuit d'échange thermique de réfrigération (11) avec un condenseur (12), un réceptacle pour liquide (13), une ligne pour liquide (14), une valve d'expansion thermique (15), un enroulement d'évaporateur (16), un collecteur d'aspiration (17), une ligne d'aspiration (18), un compresseur (19) et une ligne d'évacuation (20). Le système comporte également un circuit de dégivrage comprenant une électrovanne (21), une ligne d'alimentation en gaz surchauffé (22), un condenseur (23) et un dispositif d'étranglement de flux (24) qui joint la ligne d'aspiration (18) au collecteur d'aspiration (17). Le circuit de dégivrage partage la ligne d'aspiration (18), le compresseur (19) et la ligne d'évacuation (20) avec le circuit réfrigérant (11). Le système est géré par un système de commande et, durant un cycle de réfrigération, le fluide d'échange thermique circule dans le circuit de réfrigération. Durant ce cycle, de la glace peut s'accumuler sur l'évaporateur (16) et en particulier dans le plateau de drainage indiqué globalement par (25). Durant le cycle de dégivrage, l'électrovanne (21) est ouverte et le fluide d'échange thermique circule dans la ligne (22) (refluant également du circuit réfrigérant) vers une première portion (26) du condenseur (23). La première portion (26) se trouve disposée dans le plateau (25) et applique de la chaleur à la glace accumulée dans le plateau. Le fluide d'échange thermique circule alors dans la seconde portion (27) du condenseur pour dégivrer le serpentin de l'évaporateur (16). Le fluide d'échange thermique circule alors par le dispositif d'étranglement (24) pour maintenir le différentiel de pression de fonctionnement correct entre l'entrée et la sortie du compresseur durant le cycle de dégivrage.
PCT/AU1994/000108 1993-03-08 1994-03-08 Procede et appreil de refrigeration WO1994020803A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU62774/94A AU6277494A (en) 1993-03-08 1994-03-08 Refrigeration process and apparatus

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPL7700 1993-03-08
AUPL770093 1993-03-08

Publications (1)

Publication Number Publication Date
WO1994020803A1 true WO1994020803A1 (fr) 1994-09-15

Family

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1994/000108 WO1994020803A1 (fr) 1993-03-08 1994-03-08 Procede et appreil de refrigeration

Country Status (1)

Country Link
WO (1) WO1994020803A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU669459B2 (en) * 1993-10-29 1996-06-06 Daikin Industries, Ltd. Operation control device for air conditioning equipment
AU669460B2 (en) * 1993-10-29 1996-06-06 Daikin Industries, Ltd. Operation control device for air conditioning equipment
US7251947B2 (en) * 2005-08-09 2007-08-07 Carrier Corporation Refrigerant system with suction line restrictor for capacity correction

Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1023571A (fr) * 1975-04-22 1978-01-03 Emhart Industries Systeme de refrigeration
US4102151A (en) * 1976-04-20 1978-07-25 Kramer Trenton Company Hot gas defrost system with dual function liquid line
GB1524366A (en) * 1974-08-15 1978-09-13 Emhart Ind Control and method for defrosting regrigeration systems
GB2044425A (en) * 1979-03-16 1980-10-15 Electrolux Sigmund Gmbh Freezer chest
US4246760A (en) * 1978-10-02 1981-01-27 Carrier Corporation Non-reverse hot gas defrost system
US4279129A (en) * 1978-10-02 1981-07-21 Carrier Corporation Hot gas defrost system
US4646539A (en) * 1985-11-06 1987-03-03 Thermo King Corporation Transport refrigeration system with thermal storage sink
AU5761986A (en) * 1985-05-24 1987-11-26 Mitsubishi Denki Kabushiki Kaisha Heat exchanger
AU8174987A (en) * 1986-10-22 1988-05-25 Alfa-Laval Thermal A.B. Plate heat exchanger with a double-wall structure
US4922728A (en) * 1989-04-28 1990-05-08 Carrier Corporation Heater plate assembly
EP0477475A2 (fr) * 1990-09-28 1992-04-01 Costan S.P.A. Circuit frigorifique et procédé de dégivrage pour celui-ci
US5157933A (en) * 1991-06-27 1992-10-27 Carrier Corporation Transport refrigeration system having means for achieving and maintaining increased heating capacity

Patent Citations (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1524366A (en) * 1974-08-15 1978-09-13 Emhart Ind Control and method for defrosting regrigeration systems
CA1023571A (fr) * 1975-04-22 1978-01-03 Emhart Industries Systeme de refrigeration
US4102151A (en) * 1976-04-20 1978-07-25 Kramer Trenton Company Hot gas defrost system with dual function liquid line
US4246760A (en) * 1978-10-02 1981-01-27 Carrier Corporation Non-reverse hot gas defrost system
US4279129A (en) * 1978-10-02 1981-07-21 Carrier Corporation Hot gas defrost system
GB2044425A (en) * 1979-03-16 1980-10-15 Electrolux Sigmund Gmbh Freezer chest
AU5761986A (en) * 1985-05-24 1987-11-26 Mitsubishi Denki Kabushiki Kaisha Heat exchanger
US4646539A (en) * 1985-11-06 1987-03-03 Thermo King Corporation Transport refrigeration system with thermal storage sink
AU8174987A (en) * 1986-10-22 1988-05-25 Alfa-Laval Thermal A.B. Plate heat exchanger with a double-wall structure
US4922728A (en) * 1989-04-28 1990-05-08 Carrier Corporation Heater plate assembly
EP0477475A2 (fr) * 1990-09-28 1992-04-01 Costan S.P.A. Circuit frigorifique et procédé de dégivrage pour celui-ci
US5157933A (en) * 1991-06-27 1992-10-27 Carrier Corporation Transport refrigeration system having means for achieving and maintaining increased heating capacity

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU669459B2 (en) * 1993-10-29 1996-06-06 Daikin Industries, Ltd. Operation control device for air conditioning equipment
AU669460B2 (en) * 1993-10-29 1996-06-06 Daikin Industries, Ltd. Operation control device for air conditioning equipment
US7251947B2 (en) * 2005-08-09 2007-08-07 Carrier Corporation Refrigerant system with suction line restrictor for capacity correction

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