US20060130494A1

US20060130494A1 - Defrost refrigeration system

Info

Publication number: US20060130494A1
Application number: US11/015,034
Authority: US
Inventors: Serge Dube
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-12-20
Filing date: 2004-12-20
Publication date: 2006-06-22
Also published as: CA2529675A1

Abstract

A defrost refrigeration system of the type having a main refrigeration circuit comprising a first line extending from the compression stage to the evaporator stage and adapted to receive a portion of refrigerant in a high-pressure gas state. A valve system stops a flow of the refrigerant in a low-pressure liquid state to an evaporator of the evaporator stage and for conveying a flow of the refrigerant in the high-pressure gas state from the first line to release heat to defrost the at least one evaporator. A second line conveys the refrigerant having released heat directly to the condensing stage.

Description

TECHNICAL FIELD

The present invention generally relates to refrigeration systems and, more particularly, to a refrigeration system having a defrost cycle in parallel to the refrigeration cycle, with refrigerant of the refrigeration system being circulated in the evaporators to perform the defrost cycle.

BACKGROUND ART

Energy costs are an increasing concern for industries operating refrigeration systems, such as the food retailing industry. Due to the increasing costs of energy, refrigeration systems are evolving to provide refrigeration system solutions that optimize the use of energy.
Defrost cycles are common place in refrigeration systems, and are used to remove frost build-ups on evaporators. Frost build-ups typically result from the relatively high humidity content of the air to which the evaporators are exposed.
One type of defrost cycle consists in circulating hot refrigerant in the evaporators, such that the hot refrigerant releases heat to the frost build-up, which melts away. Such defrost cycles are operated in relatively short time spans, so as not to expose the foodstuff being refrigerated to unsuitable temperatures.
The overall installation costs of the defrost loops (e.g., piping, valves, controls) are being compared to the energy consumption of operating such defrost loops. It would therefore be desirable to optimize the consumption of energy for defrost cycles of refrigeration systems.

SUMMARY OF INVENTION

Therefore, it is a feature of the present invention to provide a novel defrost circuit for a refrigeration system.
It is a further feature of the present invention to provide a defrost circuit optimizing energy consumption.
It is a still further feature of the present invention to provide a novel method for defrosting evaporators of a refrigeration system.
Therefore, in accordance with the present invention there is provided a defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compression stage, wherein said refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein said refrigerant in said high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein said refrigerant in said high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein said refrigerant in said first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to said compression stage, said defrost refrigeration system comprising: a first line extending from the compression stage to the evaporator stage and adapted to receive a portion of said refrigerant in said high-pressure gas state; a valve system for stopping a flow of said refrigerant in said first low-pressure liquid state to at least one evaporator of the evaporator stage and for conveying a flow of said refrigerant in said high-pressure gas state from the first line to release heat to defrost the at least one evaporator; and a second line to convey said refrigerant having released heat directly to the condensing stage.
Further in accordance with the present invention, there is provided a method for defrosting evaporators in a refrigeration system operating a refrigeration cycle, comprising the steps of: providing a first line extending from a compression stage of the refrigeration system to an evaporation stage of the refrigeration system, a second line extending from the evaporation stage of the refrigeration system directly to a condensing stage of the refrigeration system; stopping a flow of cooling refrigerant to at least one evaporator; conveying hot gas refrigerant from the compressing stage to the at least one evaporator through said first line so as to defrost the at least one evaporator; and conveying the hot gas refrigerant from the at evaporator directly to the condensing stage by the second line so as to return the refrigerant to the refrigeration cycle.

BRIEF DESCRIPTION OF DRAWINGS

A preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which:
FIG. 1 is a schematic view of a defrost refrigeration system in accordance with a first embodiment of the present invention;
FIG. 2 is a schematic view of a defrost refrigeration system in accordance with a second embodiment of the present invention; and
FIG. 3 is a schematic plan view of the defrost refrigeration system of FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, and more particularly to FIG. 1, a refrigeration system in accordance with the present invention is generally shown at 10. The refrigeration system 10 comprises the stages found on typical refrigeration systems, such as the compression stage 12, the condensation stage 14, the expansion stage 16, and the evaporation stage 18.
Refrigerant circulates from one stage to another in a refrigeration cycle. The refrigerant is compressed to a high pressure gas state in the compression stage 12. The compression stage 12 is connected to the condensation stage 14 by line 13 (i.e., a hot gas line). The refrigerant then releases heat in the condensation stage 14, to reach a high pressure liquid state. The refrigerant is expanded in the expansion stage 16 to reach the evaporation stage 18 in a low pressure liquid/gas state. In the evaporators of the evaporation stage 18, the refrigerant absorbs heat to reach a low pressure gas state, to then reach the compression stage 12 and complete the refrigeration cycle.
For the purposes of illustrating the defrost system of the present invention, the evaporation stage 18 is shown having evaporators 20A and 20B. Sub-lines 21A and 21B of line 21 relate the expansion stage 16 to the evaporators 20A and 20B, respectively. Sub-lines 22A and 22B of line 22 relate the evaporators 20A and 20B, respectively, to the compression stage 12.
In known refrigeration systems having defrost loops, hot refrigerant is directed to one or more of the evaporators of the evaporation stage, so as to release heat to melt the frost build-up on the evaporators. In some systems, the lines extending between the evaporators of the evaporation stage and the compressors of the compression stage are then used, with appropriate valves, to direct the defrosting refrigerant exiting from the evaporators to a subsequent portion of the refrigeration system, such as a suction header, a suction accumulator, a pressure regulator device, or the like.
The suction lines relating the evaporators of the evaporation stage to the compression stage in multi-evaporator refrigeration systems are known to have relatively large diameters, so as to prevent suction pressure loss between the evaporation stage and the compression stage.
Accordingly, in order for the defrost cycle to operate rapidly, a substantial amount of defrost refrigerant must be used to fill the suction line, and effectively defrost the evaporators of the evaporation stage.
Non-negligible volumes of hot refrigerant are therefore used in known defrost loops in order to fill suction lines of relatively large diameters after the defrost. This hot refrigerant must thereafter be reconditioned so as to be re-injected in the refrigeration cycle. Therefore, the ratio of volume of refrigerant per defrosted evaporator is not optimized, for instance due to the use of the suction lines for conveying the refrigeration after defrost. Moreover, some components have been added to refrigeration systems to accommodate this hot refrigerant during reconditioning, such as accumulators and flushing systems.
Therefore, the defrost system in accordance with the present invention aims at reducing the ratio of volume of refrigerant per defrosted evaporator. Referring to FIG. 1, the defrost system in accordance with the preferred embodiment of the present invention is generally shown at 30. The defrost system 30 has a line 31 that directs refrigerant from line 13 to the evaporation stage 18, so as to direct hot refrigerant exiting from the compression stage 12. The line 31 diverges into a plurality of sub-lines to feed each of the evaporators 20 of the evaporation stage 18. The line 31 has a sub-line 31A connecting into the line 22A, and has a sub-line 31B connecting into the line 22B.
The defrost system 30 also has a line 32 that returns the defrost refrigerant in the line 13, upstream of the condensation stage 14, but downstream of the branching between the line 13 and the line 31. The line 32 has sub-lines 32A and 32B, which are respectively connected to the lines 21A and 21B.
This network of pipes is provided with a suitable valve system, so as to control the switch between refrigeration cycle and defrost cycle for each of the evaporators. As an example, the refrigeration system 10 has valve A1 on sub-line 31A, valve A2 on sub-line 22A, valve A3 on sub-line 32A, and valve A4 on sub-line 21A, to control the feed of refrigerant to the evaporator 20A. Similarly, the refrigeration system 10 has valve B1 on sub-line 31B, valve B2 on sub-line 22B, valve B3 on sub-line 32B, and valve B4 on sub-line 21B, to control the feed of refrigerant to the evaporator 20B. These valves are any suitable valve, such as solenoid valves, EPR valves (e.g., electronic EPR valves), pulse valves or the like.
A pressure regulating valve 40 is provided in the line 13 between the branching of line 13 and line 31, and the branching of line 13 and line 32. The valve 40 causes a pressure differential between upstream end and downstream end of line 13.
These valves are typically remotely operated valves, such as solenoid valves, wired to a controller 41 that operates the switch sequence between refrigeration cycle and defrost cycle for each of the evaporators.
A switch from refrigeration cycle to defrost cycle is operated as follows.
The evaporator 20A is in a refrigeration cycle, whereby valves A2 and A4 are opened, and valves A1 and A3 are closed, so as to allow cooling refrigerant to circulate through the evaporator 20A. It is required to put the evaporator 20A in a defrost cycle, whereby the valve positions are reversed. Valves A2 and A4 are closed, and valves A1 and A3 are opened.
The pressure differential across the pressure regulating valve 40 causes circulation of some of the hot gas refrigerant, compressed at the compression stage 12, through the evaporator 20A once the valves A1 and A3 are opened. Accordingly, the hot gas refrigerant flowing through the evaporator 20A releases heat to the build-up on the evaporator 20A, to then return directly to the refrigeration cycle at the condensation stage 14.
Therefore, the hot gas refrigerant is exposed to defrosting temperatures for a short time span, as the arrangement of the defrost system induces a rapid flow of refrigerant in the evaporator 20A. Moreover, the use of lines 31 and 32, which divert and return refrigerant to and from line 13, minimizes the amount of defrosting refrigerant. More specifically, the line 22 operates in suction, and therefore has a relatively large diameter.
As the lines 31 and 32 convey high pressure refrigerant through the evaporation stage 18 in the defrost cycle, they can have smaller diameters without significantly affecting the flow of refrigerant therethrough. For instance, the diameter of the lines 32 may typically be a third of the diameter of the suction lines 22.
Accordingly, a smaller volume of refrigerant is required using the defrost system 30 of the present invention, as opposed to systems using a greater portion of the suction lines connecting the evaporation stage 18 to the compression stage 12. Considering that the ratio of volume of refrigerant per defrosted evaporator is relatively lower than other defrost systems, more evaporators of the evaporation stage 18 may thus be defrosted simultaneously with the defrost system 30 of the present invention.
Referring to FIG. 2, a refrigeration system in accordance with another embodiment of the present invention is shown at 10′. The refrigeration system 10′ is similar to the refrigeration system 10 of FIG. 1, whereby like elements will bear like reference numerals.
The refrigeration system 10′ has a defrost system 30′. The defrost system 30′ has a dedicated compression stage (i.e., one or more dedicated compressors), illustrated as 12A, parallel to the compression stage 12. The high pressure gas refrigerant at the outlet of the dedicated compression stage 12A is selectively directed to the evaporator stage 18, so as to defrost the evaporators 20A and 20B from frost build-up thereon.
More specifically, a line 31′ extends from the dedicated compression stage 12A to the evaporators 20A and 20B, by way of sub-lines 31A′ and 31B′. The sub-lines 31A′ and 31B′ respectively connect to sub-lines 22A and 22B.
Similarly to the defrost system 30 of FIG. 1, the defrost system 30′ has a line 32 that returns the defrost refrigerant in the line 13, upstream of the condensation stage 14. The line 32 has sub-lines 32A and 32B, which are respectively connected to the lines 21A and 21B.
This network of pipes is provided with a suitable valve system, so as to control the switch between refrigeration cycle and defrost cycle for each of the evaporators. As an example, the refrigeration system 10′ has valve A1 on sub-line 31A′, valve A2 on sub-line 22A, valve A3 on sub-line 32A, and valve A4 on sub-line 21A, to control the feed of refrigerant to the evaporator 20A. Similarly, the refrigeration system 10′ has valve B1 on sub-line 31B′, valve B2 on sub-line 22B, valve B3 on sub-line 32B, and valve B4 on sub-line 21B, to control the feed of refrigerant to the evaporator 20B.
These valves are typically remotely operated valves, such as solenoid valves, wired to a controller 41 that operates the switch sequence between refrigeration cycle and defrost cycle for each of the evaporators.
Additionally, the dedicated compression stage 12A may be used to feed the refrigeration cycle, by way of line 50 and valve 51, as a function of the demand for defrost refrigerant for defrost cycles.
A switch from refrigeration cycle to defrost cycle for the refrigeration system 10′ is similar to that of the refrigeration system 10 and is operated as follows.
The evaporator 20A is in a refrigeration cycle, whereby valves A2 and A4 are opened, and valves A1 and A3 are closed, so as to allow cooling refrigerant to circulate through the evaporator 20A. It is required to put the evaporator 20A in a defrost cycle, whereby the valve positions are reversed. Valves A2 and A4 are closed, and valves A1 and A3 are opened.
Therefore, the hot gas refrigerant output from the compression stage 12A is directed through sub-line 31A′ to the evaporator 20A, so as to release heat to the build-up on the evaporator 20A, to then return directly to the refrigeration cycle at the condensation stage 14. The output pressure at the dedicated compression stage 12A is preferably higher than the output pressure at the compression stage 12, such that the refrigerant flows to the condensation stage 14, through line 32, after the defrost cycle. Alternatively, pumps and other devices could be used to re-inject the defrost refrigerant in the refrigeration cycle.
Therefore, the hot gas refrigerant is exposed to defrosting temperatures for a short time span, as the arrangement of the defrost system 30′ induces a rapid flow of refrigerant in the evaporator 20A. Moreover, the use of lines 31′ and 32, which divert and return refrigerant to and from line 13, minimizes the amount of defrosting refrigerant. More specifically, the line 22 operates in suction, and therefore has a relatively large diameter.
As the lines 31′ and 32 convey high pressure refrigerant through the evaporation stage 18 in the defrost cycle, they can have smaller diameters without significantly affecting the flow of refrigerant therethrough. For instance, the diameter of the lines 32 may typically be a third of the diameter of the suction lines 22.
Accordingly, a smaller volume of refrigerant is required using the defrost system 30′ of the present invention, as opposed to systems using a greater portion of the suction lines connecting the evaporation stage 18 to the compression stage 12. Considering that the ratio of volume of refrigerant per defrosted evaporator is relatively lower than other defrost systems, more evaporators of the evaporation stage 18 may thus be defrosted simultaneously with the defrost system 30′ of the present invention.
Additionally, the suction line 22 in both refrigeration systems 10 and 10′ is only used for the defrost cycle. Accordingly, the conditions of the refrigerant in the suction line 22 are generally constant, as opposed to refrigeration systems in which the suction line between the evaporation stage and the compression stage is used to convey defrost refrigerant as well as refrigerant from a refrigeration cycle. This latter use results in non-negligible thermal expansion/contraction of the suction pipes. Thermal expansion/contraction may cause pipe ruptures, may cause damages to insulation jackets onto the pipes, and results in energy losses.
Referring to FIG. 3, the refrigeration system 10 of FIG. 1 is shown as schematically laid out in a refrigeration plan, illustrating the use of known components, such as an oil separator 100, refrigerant tanks 101, a heat reclaim loop 102, and headers. It is pointed out that the evaporator stage 18 is illustrated as having a single bank of evaporators for simplicity purposes. Moreover, the evaporator stage 18 is shown having display cabinets 120A.
It is within the ambit of the present invention to cover any obvious modifications of the embodiments described herein, provided such modifications fall within the scope of the appended claims.

Claims

1. A defrost refrigeration system of the type having a main refrigeration circuit, wherein a refrigerant goes through at least a compression stage, wherein said refrigerant is compressed to a high-pressure gas state to then reach a condensing stage, wherein said refrigerant in said high-pressure gas state is condensed at least partially to a high-pressure liquid state to then reach an expansion stage, wherein said refrigerant in said high-pressure liquid state is expanded to a first low-pressure liquid state to then reach an evaporator stage, wherein said refrigerant in said first low-pressure liquid state is evaporated at least partially to a first low-pressure gas state by absorbing heat, to then return to said compression stage, said defrost refrigeration system comprising:

a first line extending from the compression stage to the evaporator stage and adapted to receive a portion of said refrigerant in said high-pressure gas state;

a valve system for stopping a flow of said refrigerant in said first low-pressure liquid state to at least one evaporator of the evaporator stage and for conveying a flow of said refrigerant in said high-pressure gas state from the first line to release heat to defrost the at least one evaporator; and

a second line to convey said refrigerant having released heat directly to the condensing stage.

2. The defrost refrigeration system according to claim 1, wherein the compression stage has at least one dedicated compressor connected to the first line so as to direct said portion of said refrigerant in said high-pressure gas state to the at least one evaporator being defrosted.

3. The defrost refrigeration system according to claim 2, further comprising a selectively openable bypass line connecting the dedicated compressor to the condensing stage so as to direct the refrigerant compressed by the dedicated compressor directly to the condensing stage, thereby bypassing the defrosting of the at least one evaporator.

4. The defrost refrigeration system according to claim 2, comprising a pressure reducing valve in a hot gas line between the compression stage and the condensing stage, the first line diverging from the hot gas line upstream of the pressure reducing valve, and the second line converging to the hot gas line downstream of the pressure reducing valve, whereby the pressure reducing valve induces a flow of said portion of said refrigerant through the first line and the second line to defrost the at least one evaporator.

5. A method for defrosting evaporators in a refrigeration system operating a refrigeration cycle, comprising the steps of:

providing a first line extending from a compression stage of the refrigeration system to an evaporation stage of the refrigeration system, a second line extending from the evaporation stage of the refrigeration system directly to a condensing stage of the refrigeration system;

stopping a flow of cooling refrigerant to at least one evaporator;

conveying hot gas refrigerant from the compressing stage to the at least one evaporator through said first line so as to defrost the at least one evaporator; and

conveying the hot gas refrigerant from the at evaporator directly to the condensing stage by the second line so as to return the refrigerant to the refrigeration cycle.