Very low temperature refrigeration system with controlled cool down and warm up rates and long term heating capabilities

• US 6,574,978 B2
• Filed: 05/30/2001
• Issued: 06/10/2003
• Est. Priority Date: 05/30/2000
• Status: Expired due to Term

• Current Assignee: Edwards Vacuum, LLC (Atlas Copco AB)
• Original Assignee: IGC Polycold Systems, Inc. (Azenta, Inc.)
• Inventors: Flynn, Kevin, Hall, Paul H.
• Primary Examiner(s): Tanner, Harry B.
• Application Number:
  US09/870,385
• Publication Number:
  US 20020017106A1
• Time in Patent Office: 741 Days
• Field of Search: 622/77, 622/78, 62/81, 621/51, 621/56, 621/961, 621/964, 621/97, 621/98, 621/99, 622/00
• US Class Current: 62/278
• CPC Class Codes: F25B 40/00 Subcoolers, desuperheaters or superheaters
• CPC Class Codes: F25B 41/24 Arrangement of shut-off valves for disconnecting a part of the refrigerant cycle, e.g. an outdoor part
• CPC Class Codes: F25B 47/022 hot gas defrosting
• CPC Class Codes: F25B 9/00 Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point

Abstract

Heating/defrost constructions of a very low temperature refrigeration system having a defrost supply circuit and a defrost return bypass circuit optimizing the heating/defrost cycle, preventing overload (excessive pressure) of its refrigeration process and protecting components from damaging temperatures. The defrost cycle operates continuously, when required, and provides a shorter recovery period between heating/defrost and cooling operating modes. The rate of the temperature change during cool down or warm up is controlled in an open loop fashion by controlled refrigerant flow in bypass circuits.

Claims

1. A refrigeration system for long term continuous operation in cooling and defrost modes, comprising:

a compression unit having an inlet and an outlet, and taking in refrigerant at said inlet at a low pressure and discharging high pressure refrigerant at said outlet;

a refrigeration process unit having a high pressure circuit and low pressure circuit, said high pressure circuit receiving said high pressure refrigerant from said compression unit, said low pressure circuit delivering said low pressure refrigerant to said low pressure circuit of said compression unit, heat exchange occurring between the refrigerant in said high and low pressure circuits;

a primary throttle unit having an inlet and an outlet, said primary throttle unit inlet receiving high pressure refrigerant from said high pressure circuit of said refrigeration process unit and discharging low pressure refrigerant at said primary throttle unit outlet;

an evaporation unit having an inlet and an outlet for selectively cooling or heating a load, said evaporation unit receiving low pressure refrigerant from said primary throttle unit, and refrigerant from said evaporation unit outlet flowing to said low pressure circuit of said refrigeration process unit;

a condenser unit upstream of said primary throttle unit and said refrigeration process unit, said condenser unit removing heat from said refrigerant at said high pressure from said compressor unit and rejecting said heat externally of said refrigeration system;

a first bypass circuit including at least one high pressure branch circuit for circumventing refrigerant flow around said refrigeration process unit high pressure circuit;

a second bypass circuit including at least one low pressure branch circuit for circumventing refrigerant flow around said refrigeration process unit low pressure circuit; and

a control system for directing, in selected sequences, said refrigerant in selected closed cycles between said compression unit and said evaporation unit.

2. A refrigeration system as in claim 1, wherein one said branch of said second bypass circuit includes components that are properly operative continuously and undamaged in a first temperature range, and in a second temperature range that is lower than said first temperature range, are subject to at least one of improper operation and damage when operated continuously.

3. A refrigeration system as in claim 2, wherein said control system directs said low pressure refrigerant continuously to said one branch of said second bypass circuit only when refrigeration temperature in said one branch is maintained such that none of improper operation and damage occurs.

4. A refrigeration system as in claim 2, wherein said control system has a first controllable device in said second bypass circuit regulating refrigerant flow through said second bypass circuit, said first controllable device having at least one of on/off operation and variable flow operation, said control system further having first blocking means in series with said low pressure circuit of said refrigeration process unit, said first blocking means obstructing return refrigerant flow through said low pressure circuit of said refrigeration processing unit when said first controllable device permits flow.

5. A refrigeration system as in claim 4, wherein said first controllable device permits refrigerant flow through said second bypass circuit when temperature at said refrigeration process unit low pressure circuit equals or exceeds a selected temperature.

6. A refrigeration system as in claim 5, wherein said selected temperature is an upper limit of said second temperature range.

7. A refrigeration system as in claim 2, wherein said first bypass circuit includes at least one branch, each branch having a respective defrost throttle unit to reduce pressure in refrigerant passing through said first bypass circuit, said branches being in one of parallel and series/parallel arrangement, said control system having in each said branch a second blocking means in series with said defrost throttle unit, said second blocking means providing at least on/off operation of refrigerant flow toward said evaporation unit.

8. A refrigeration system as in claim 4, wherein said first blocking means is a pressure check valve only permitting refrigerant flow from said evaporation unit towards said inlet of said compression unit.

9. A refrigeration system as in claim 7, wherein said primary throttle unit and said defrost throttle unit respectively, include at least one of a capillary tube, orifice, proportional valve with feedback, porous element, and any other restrictive element that controls flow.

10. A refrigeration system as in claim 1, wherein said compression unit includes at least one of a single compressor, two compressors in parallel, compressors in series, a two stage compressor, branches respectively with compressors in series, parallel, and series/parallel arrangements.

11. A refrigeration system as in claim 1, wherein said condenser unit includes at least one of a gas and liquid cooled condenser, said at least one condensers being arranged in one of parallel, series, and series/parallel circuitry.

12. A refrigeration system as in claim 1, wherein said evaporating unit includes at least one of an evaporation coil having metal tubing and a metal platen.

13. A refrigeration system as in claim 1, further comprising an oil separator between said compression unit high pressure outlet and said condenser unit inlet.

14. A refrigeration system as in claim 2, wherein said lower end of said first temperature range is in a range of approximately −

50 to −

40 centigrade degrees, and said second temperature range has a lower end in a range from −

250 to −

150 centigrade degrees and an upper end in a range of −

40 C degrees and −

50 C degrees.

15. A refrigeration system as in claim 1 wherein said refrigeration process unit includes at least one of a single refrigerant system, a mixed refrigerant system, normal refrigeration processes, an individual stage of a cascade refrigeration process, an auto refrigerating cascade cycle, and a Klimenko cycle.

16. A refrigeration system as in claim 1, further comprising heating means in said second bypass circuit for adjusting a temperature of refrigerant flowing therethrough and protecting valve components in said second bypass circuit.

17. A refrigeration system as in claim 1, wherein said second bypass circuit includes a flow metering device such that the rate of flow through said second bypass can be controlled.

18. A refrigeration system as in claim 1, and further comprising a heat source positioned in a low pressure refrigerant line connecting to said compressor inlet and upstream of said second bypass circuit to warm return refrigerant.

19. A refrigeration system as in claim 1, and further comprising at least one supplemental bypass circuit, said at least one supplemental bypass circuit at one end connecting upstream to the low pressure circuit of the refrigeration process unit and at the other end connecting to said low pressure refrigeration circuit within said refrigeration process unit, said at least one supplemental circuit including a bypass valve for regulating flow through said supplemental bypass circuit, said supplemental bypass circuit being activated by said control system when the refrigerant for flow in said supplemental bypass circuit has the same temperature as in said refrigeration processing unit at a connection between said supplemental bypass circuit and said low pressure circuit of said refrigeration process unit, said supplemental bypass flow reducing time required for cool down of said evaporation unit.

20. A refrigeration system as in claim 7, wherein said first bypass circuit includes a heat source, heating said refrigerant flow from said at least one branch, said heat source being located down stream of said defrost throttle units and upstream of said input to said evaporator unit.

21. A refrigeration system as in claim 20, wherein a bypass valve circumvents at least a portion of said refrigeration flow heated by said heat source, said bypass valve being controlled by said control system to control temperature of refrigerant delivered to said compressor unit inlet.

22. A refrigeration system as in claim 21, wherein said bypass valve is a chopper type valve that pulses on or off for different lengths of time as determined by said control system.

23. A refrigerant system as in claim 1 and further including a variable flow valve shunting between said compressor outlet to said compressor inlet, compressor high pressure discharge temperature being controllable by adjusting said variable shunt valve.

24. A refrigeration system for long term continuous operation in cooling and defrost modes, comprising:

a compression unit having an inlet and an outlet, and taking in at said inlet refrigerant at a low pressure and discharging high pressure refrigerant at said outlet;

a refrigeration process unit having a high pressure circuit and low pressure circuit, said high pressure circuit receiving said high pressure refrigerant from said compression unit, said low pressure circuit delivering said low pressure refrigerant to said low pressure circuit of said compression unit, heat exchange occurring between the refrigerant in said high and low pressure circuits;

a primary throttle unit having an inlet and an outlet, said primary throttle unit inlet receiving high pressure refrigerant from said high pressure circuit of said refrigeration process unit and discharging low pressure refrigerant at said primary throttle unit outlet for connection to an evaporation unit for selectively cooling or heating a load, and returning to said low pressure circuit of said refrigeration process unit;

a condenser unit upstream of said primary throttle unit and said refrigeration process unit, said condenser unit removing heat from said refrigerant at said high pressure from said compressor unit and rejecting said heat externally of said refrigeration system;

a first bypass circuit including at least one high pressure branch circuit for circumventing refrigerant flow around a downstream portion of said refrigeration process unit high pressure circuit;

a second bypass circuit including at least one low pressure branch circuit for circumventing refrigerant flow around said refrigeration process unit low pressure circuit; and

a control system for directing, in selected sequences, said refrigerant in selected closed cycles including said compression unit.

25. A refrigeration system as in claim 24, wherein said refrigeration process unit includes a plurality of heat exchangers in sequence exchanging heat between said high pressure circuit and said low pressure circuit, and a refrigerant gas/liquid separator located between a pair of said heat exchangers, said first bypass circuit being fed with high pressure gaseous refrigerant from said phase separator, a heat exchanger being in said high pressure line from said liquid/gas separator and said at least one branch of said first bypass circuit.

26. A refrigeration system as in claim 24, further including a plurality of refrigerant lines in parallel, each said line being connected at a different location in said high pressure circuit of said refrigeration process unit, a control flow valve being located in each said line, and a heat exchanger at one end connected to said lines in parallel and the other end of said heat exchanger connected to said first bypass circuit said control system operating said control flow valves.

27. A refrigeration system as in claim 26, wherein said control system selects a flow line for flow based upon temperatures in the refrigeration system.

28. A refrigeration system for long term continuous operation in cooling and defrost modes, comprising:

a compression unit having an inlet and an outlet, and taking in refrigerant at said inlet at a low pressure and discharging high pressure refrigerant at said outlet;

a refrigeration process unit having a high pressure circuit and low pressure circuit, said high pressure circuit receiving said high pressure refrigerant from said compression unit, said low pressure circuit delivering said low pressure refrigerant to said low pressure circuit of said compression unit, heat exchange occurring between the refrigerant in said high and low pressure circuits;

a primary throttle unit having an inlet and an outlet, said primary throttle unit inlet receiving high pressure refrigerant from said high pressure circuit of said refrigeration process unit, and discharging low pressure refrigerant at said primary throttle unit outlet for connection to an evaporation unit selectively cooling or heating a load, and for returning to said low pressure circuit of said refrigeration process unit;

a condenser unit upstream of said primary throttle unit and said refrigeration process unit, said condenser unit removing heat from said refrigerant at said high pressure from said compressor unit and rejecting said heat externally of said refrigeration system;

a first bypass circuit including at least one high pressure branch circuit for circumventing refrigerant flow around said refrigeration process unit high pressure circuit;

a second bypass circuit including at least one low pressure branch circuit for circumventing refrigerant flow around said refrigeration process unit low pressure circuit; and

a controlsystem for directing, in selected sequences, said refrigerant in selected closed cycles including said compression unit.