US20070068188A1

US20070068188A1 - Ice maker circuit

Info

Publication number: US20070068188A1
Application number: US11/532,922
Authority: US
Inventors: Joseph Newland; Randall Ries
Original assignee: Tecumseh Products Co
Current assignee: Tecumseh Products Co
Priority date: 2005-09-29
Filing date: 2006-09-19
Publication date: 2007-03-29
Also published as: CA2561514A1; CA2561514C

Abstract

A refrigeration system for freezing fluid in a tray during a first operating mode and defrosting the ice during a second operating mode to facilitate the removal of the ice from the tray. In the first operating mode, refrigerant circulates through a circuit in a first direction and, in the second mode, the flow of refrigerant is reversed in a portion of the circuit. In the first operating mode, cool refrigerant exits an expansion device in the circuit and enters into the evaporator to freeze a fluid in the tray. In the second operating mode, a valve is operated to permit warm refrigerant exiting the compressor to enter into the evaporator to melt a portion of the ice reversing the flow of refrigerant therein. A second valve permits the reverse flow of refrigerant through the evaporator to return to the compressor inlet instead of passing through the expansion device and condenser.

Description

CROSS REFERENCE TO RELATED APPLICATION

This non-provisional patent application claims priority under 35 U.S.C. §119(e) to co-pending U.S. provisional patent application Ser. No. 60/721,914 entitled ICE MAKER CIRCUIT and filed on Sep. 29, 2005

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to refrigeration circuits for ice makers, e.g., and, more specifically, to reversing the flow of refrigerant in a segment of the refrigeration circuit to defrost, and to facilitate the removal of, ice in the ice maker.
2. Description of the Related Art
In typical refrigeration systems, a refrigerant is compressed by a compressor and then cooled in a condenser. After the refrigerant is cooled in the condenser, it is passed through an expansion device, or valve, to lower its pressure and temperature. The cold, low-pressure refrigerant then enters an evaporator where the refrigerant absorbs thermal energy from an environment surrounding the evaporator. Subsequently, the refrigerant in the evaporator is drawn back into the compressor and re-cycled through the circuit.
These refrigeration systems can be utilized as ice makers. In particular, an ice tray is placed in thermal communication with the evaporator where the ice tray is filled with water, or, alternatively, the ice tray receives a continuous flow of water thereover. During the operation of the refrigeration system, the cool refrigerant in the evaporator absorbs heat from the water and turns it into ice. The ice is then removed from the tray and the process is repeated. However, ice bonds to the surface on which it freezes, making removal difficult. To resolve this problem, existing ice makers utilize a by-pass circuit to direct warm refrigerant exiting from the compressor into the evaporator inlet to melt a small layer of ice that bonds the consumable portion of the ice to the tray. The by-pass circuit allows at least a portion of the warm refrigerant exiting the compressor to bypass the condenser and expansion device through a series of valves and enter into the evaporator inlet without changing the direction of the refrigerant flow through the evaporator.

SUMMARY OF THE INVENTION

The present invention provides a refrigeration system for making ice in an ice tray during a first operating mode and melting a portion of the ice during a second operating mode to facilitate the removal of the ice from the tray. In the first operating mode, refrigerant circulates through a circuit of the refrigeration system in a first direction and, in the second operating mode, the flow of refrigerant is reversed in a portion of the circuit. In the first operating mode, cool refrigerant exits an expansion device in the circuit and enters into the evaporator. Therein, the cool refrigerant draws heat from a fluid, such as water, in the ice tray and freezes the fluid in the tray. The refrigerant then flows to a compressor in the circuit and the refrigerant is re-circulated therethrough. In the second operating mode, in order to facilitate the harvesting of the ice from the tray, the flow of refrigerant through the evaporator is reversed. In one embodiment, a valve is operated to permit warm refrigerant exiting the compressor to enter into the evaporator in a reverse direction. A second valve can be operated to permit the reverse flow of refrigerant through the evaporator to return to the inlet of the compressor before the reverse flow of refrigerant passes through the expansion device and condenser.
During the second operating mode, the warm, compressed refrigerant melts a portion of the ice into a liquid. The liquid provides a lubricant between the ice and the tray surface allowing the ice to slide out of the tray. Further, if the tray is in a tilted or vertical orientation, the liquid can accelerate harvesting by flowing downwardly and melting the ice beneath it as it flows. In these embodiments, the downward flow of the liquid can be facilitated by introducing warm refrigerant into the evaporator, during the second operating mode of the refrigeration circuit, through an opening that is vertically above an opening in the bottom of the evaporator. In a further embodiment, a storage vessel is in fluid communication with the compressor outlet where refrigerant exiting the compressor outlet may accumulate in the storage vessel during the first operating mode and provide a reservoir of warm refrigerant to flow into the evaporator to heat the ice tray when the refrigeration system is placed into the second operating mode. Once the ice has been harvested, the first and second valves can be operated to return the refrigeration system to the first operating mode in order to make more ice.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and objects of this invention will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a schematic of a prior art refrigeration system;
FIG. 2 is a schematic of a refrigeration system in accordance with a first embodiment of the present invention in a first operating mode;
FIG. 3 is a schematic of the refrigeration system of FIG. 2 in a second operating mode;
FIG. 4 is a schematic of a refrigeration system in accordance with a second embodiment of the present invention;
FIG. 5 is a schematic of a refrigeration system in accordance with a third embodiment of the present invention;
FIG. 6 is a perspective view of an evaporator and ice tray in accordance with an embodiment of the present invention; and
FIG. 7 is a schematic of a further embodiment of the invention.
Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplifications set out herein illustrate embodiments of the invention, the embodiments disclosed below are not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.

DETAILED DESCRIPTION

Referring to FIG. 1, a conventional refrigeration system 10 includes, in serial order, compressor 12, a first heat exchanger, e.g., condenser 14, an expansion device, e.g., expansion device 16, and a second heat exchanger, e.g., evaporator 18, connected in series by fluid conduits. As is well known in the art, compressor 12 draws a refrigerant or working fluid through compressor inlet 11, compresses the refrigerant, and expels the compressed refrigerant through compressor outlet 13.
The refrigerant expelled from compressor 12 is communicated into condenser 14 through conduit 22. The compressed refrigerant enters condenser 14 through inlet 15 and exits condenser 14 through outlet 17. Between inlet 15 and outlet 17, the refrigerant passes through a series of tubes and conduits having fins or thin plates (not shown) affixed thereto for dissipating thermal energy from the refrigerant contained within. Alternatively, condenser 14 may be any type of heat exchanger including a shell-and-tube type heat exchanger where water or another refrigerant flows over the tube containing the system refrigerant.
Subsequently, the cooled, compressed refrigerant is communicated to expansion device or capillary tube 16 through conduit 24. The refrigerant enters expansion device 16 through inlet 23 and passes through an orifice within expansion device 16 allowing the refrigerant to expand and decompress. The cooled, low-pressure refrigerant exits expansion device 16 through outlet 25 and is communicated to evaporator 18 through conduit 26. The refrigerant enters evaporator 18 from conduit 26 through inlet 27 and exits evaporator 18 through outlet 29. Similar to condenser 14, evaporator 18 may be a conventional heat exchanger where refrigerant passes between inlet 27 and outlet 29. However, unlike condenser 14 where the refrigerant is cooled, the refrigerant in evaporator 18 draws heat from an ice tray associated with the evaporator. Subsequently, the refrigerant exits evaporator 18 through outlet 29 and is communicated to compressor 12 through conduit 28, and the cycle described above is repeated.
In an ice maker, referring to FIG. 1, ice tray 30 is associated with evaporator 18 and, during operation of the ice maker, water within tray 30 is frozen by the cold, decompressed refrigerant entering into evaporator 18. For purposes of the present application, “ice tray” means any receptacle having one or more compartments adapted to receive water which is then frozen for the production of ice cubes or chunks. Thereafter, the ice is removed from tray 30, however, ice bonds to the surface on which it freezes, making removal difficult. To ameliorate this problem, bypass circuit 32 is added to refrigeration system 10 to partially defrost the ice before it is removed from the tray. As illustrated in FIG. 1, bypass circuit 32 includes valve 34 and conduit 36. Valve 34 is positioned in line 22 extending between compressor 12 and condenser 14. Valve 34, in a first operating mode in which the water in tray 30 is being frozen, permits refrigerant exiting compressor 12 to flow to condenser 14 without entering conduit 36. Valve 34 is operable to permit, in a second operating mode, at least a portion of the refrigerant passing through conduit 22 to enter into conduit 36. As illustrated in FIG. 1, conduit 36 extends from valve 34 to conduit 26 and, accordingly, warm compressed refrigerant exiting compressor 12 is permitted to bypass condenser 14 and expansion device 16 and flow into inlet 27 of evaporator 18. The warm refrigerant in evaporator 18 warms tray 30 and the ice contained therein to melt a portion of the ice into liquid water. When removing the ice from tray 30, the liquid water lubricates the ice to facilitate removal thereof. The refrigerant in evaporator 18 exits evaporator 18 through outlet 29 and is communicated into compressor 12 through inlet 11. Notably, the direction of the flow of refrigerant through evaporator 18 is not changed under any operating conditions of refrigeration system 10.
Referring to FIG. 2, refrigeration system 50, a first embodiment of the present invention, includes compressor 12, condenser 14, expansion device 16 and evaporator 18 as described above. During a first operating mode in which water in tray 30 is frozen, refrigerant exiting compressor 12 flows into line 22 and is prevented from flowing into line 54 by valve 52. As a result, the warm, compressed refrigerant passes through condenser 14 and expansion device 16 into evaporator 18 as described above. As illustrated in FIG. 2, refrigeration system 50 further includes valve 58 which is placed in fluid communication with line 26. In the present embodiment, valve 58 is a spring biased check valve selected to have a cracking pressure such that, during the first mode of operation, its valve element (not illustrated) is not lifted away from its valve seat (not illustrated) by the low-pressure refrigerant exiting expansion device 16 into line 26. As a result, in the first operating mode of refrigeration system 50, the refrigerant flows into evaporator 18 through inlet 27 and exits outlet 29 into inlet 11 of compressor 12. The flow path of the refrigerant in the first operating mode is illustrated in FIG. 2 and is represented by arrows 40. Check valve 58, referring to FIG. 2, also prevents refrigerant from flowing from line 60 into line 26 during the first operating mode of the refrigeration system, as the pressure of the refrigerant in line 60 is substantially equal to the pressure of refrigerant in line 26. Although two separate valves 52 and 56 have been shown schematically for the purpose of illustrating the functioning of the refrigeration circuit, the valving functions could be combined into a single, multi-functional valve (not shown) as is well known in the art.
FIG. 3 illustrates refrigeration system 50 in a second operating mode in which the ice in tray 30 is defrosted by warm, compressed refrigerant exiting compressor 12 into evaporator 18. To accomplish this, valve 52 is opened and at least a portion of the compressed, warm refrigerant exiting compressor 12 enters into line 54, and evaporator 18 through evaporator exit 29. To prevent the refrigerant from flowing directly back into the compressor inlet through line 63, valve 56 is placed between lines 28 and 63. In the first operating mode described above, valve 56 is open, and in the second operating mode, valve 56 is closed. Owing to the operation of valves 52 and 56 to place refrigeration system 50 in the second operating mode, the refrigerant in evaporator 18 flows in a direction that is opposite, or reverse, to the direction of the refrigerant flowing through evaporator 18 in the first operating mode. The refrigerant in the second operating mode exits evaporator 18 through evaporator inlet 27 and, owing to its high pressure, lifts the valve element of check valve 58 from its seat such that the refrigerant enters into line 60. Check valve 58 can be a commercially available check valve purchased from Swagelok Co., 29500 Solon Road, Solon, 44139. In one embodiment, Swagelok model SS-4CA-150 is used which can be set to have a cracking pressure around 350 psi when the refrigerant is CO₂.
An advantage of using a check valve in the present embodiment is that, although the valve is opened, the check valve can still restrict the flow of refrigerant passing therethrough thereby providing a pressure differential across the check valve. When the check valve is operated in this way, a pressure differential is also present between inlet 11 and outlet 13 of compressor 12 which requires the compressor to do work. The work input of the compressor is converted to thermal energy in the refrigerant which is useful for defrosting the ice. This is especially advantageous with an efficient compressor that produces little waste heat. Another advantage of using a check valve is that the pressure differential can be selected to optimize the heat delivered to the evaporator in the second, i.e., harvest, operating mode. More particularly, the cracking pressure of check valve 58 can be selected to control the amount of time that the warm refrigerant spends in the evaporator before flowing through check valve 58 to compressor 12. Check valves having a high cracking pressure allow refrigerant to accumulate in evaporator 18 when the refrigeration system is initially placed into the second operating mode. As a result, the warm, compressed refrigerant in the evaporator can have a longer period of time to defrost the ice tray before building sufficient pressure to crack the check valve and return to the compressor inlet. Other types of valves can be used for valve 58 which maintain a pressure differential across valve 58. For example, an electronic expansion device using a stepper motor can be used to control the pressure differential across valve 58. In another embodiment, a solenoid valve can be used such that, when opened, the valve does not open entirely thereby restricting the flow of refrigerant therethrough.
After the refrigerant passes through valve 58, the refrigerant enters line 61 and then compressor 12 through inlet 11. The flow path of the refrigerant in the second operating mode is illustrated in FIG. 3 and represented by arrows 42. In the second operating mode, the pressure of the refrigerant at inlet 23 and outlet 25 of expansion device 16 is substantially the same and, as a result, in the present embodiment, the refrigerant does not flow through condenser 14 and expansion device 16.
In one embodiment, referring to FIG. 6, inlet 27 of evaporator 18 is located at the bottom of the evaporator, and outlet 29 is located at the top. In the first operating mode, refrigerant enters evaporator 18 through inlet 27 and exits evaporator 18 through outlet 29. Having outlet 29 positioned vertically above inlet 27 allows evaporator 18 to be filled with liquid refrigerant during the first operating mode, which can absorb much more heat from the ice tray than vaporous refrigerant. More particularly, liquid refrigerant entering evaporator 18 from the bottom accumulates in the evaporator before the level of the liquid refrigerant is sufficient for the liquid refrigerant to flow out of evaporator 18 through outlet 29. Also, advantageously, when the refrigeration system is switched from the first operating mode into the second operating mode, the cool, liquid refrigerant in evaporator 18 can be drained from the bottom of the evaporator while it is filled with warm vapor from the compressor. More particularly, the liquid refrigerant in the evaporator can quickly flow out of the bottom of the evaporator when pushed by the hot, high pressure vaporous refrigerant entering the top of the evaporator from the compressor. An additional advantage of having outlet 29 positioned vertically above first opening 27 is that the ice at the top of ice tray 30, which is proximal to outlet 29, will, during the second operating mode, begin to melt before the other ice in the ice tray. By melting first, the liquid water from the ice at the top of the ice tray can flow downwardly across the ice beneath it and facilitate the release and harvest of the ice below.
While the present embodiment discloses that the fluid in tray 30 is water, the invention is not so limited. Rather, this invention can be used to freeze, defrost and harvest the ice or solid phase of other fluids. Further, while the above embodiment generally refers to an ice tray, the term ice tray is used to describe any device suitable for the creation of ice. For example, the term ice tray can refer to a shallow flat receptacle with a plurality of raised edges and/or rims for storing a fluid therein or, alternatively, for example, the term ice tray can refer to a substantially flat sheet where water flows thereover and freezes in layers when the refrigeration system is in its first operating mode. This sheet can also include ridges and/or recesses for making thinner or thicker sections of the ice.
Referring to FIG. 4, refrigeration system 50 can also include a third heat exchanger, i.e., suction-liquid heat exchanger 19 to improve the efficiency of the refrigeration system. Heat exchanger 19 is a heat exchanger, or a series of heat exchangers, that exchanges thermal energy between the high pressure refrigerant that passes between condenser 14 and expansion device 16 in conduit 24 and the refrigerant that passes between evaporator 18 and compressor 12 in conduit 60. Ultimately, heat exchanger 19 cools the high-pressure refrigerant before it passes to expansion device 16 and heats the refrigerant in conduit 60 before it enters compressor 12.
In some operating conditions, the refrigerant entering into compressor 12 may be in a two-phase state, i.e., partially a liquid and partially a gas. Some compressors, however, are designed to compress the refrigerant only in a gas form. For these compressors, if refrigerant in liquid form enters into the compressor, the compressor may malfunction or become damaged. In view of this, referring to FIG. 4, refrigeration system 50 can further include accumulator 62. Accumulator 62 allows refrigerant in liquid form to separate from refrigerant in gas form and accumulate in a chamber therein. As a result, the refrigerant in liquid form is substantially prevented from entering into the compressor. In some embodiments, accumulator 62 may have a heating element to evaporate the liquid refrigerant so that it may pass through the compressor.
Referring to FIG. 4, refrigeration system 50 can further include storage vessel 64 placed in line 22. Storage vessel 64 includes a chamber for storing and accumulating a quantity of refrigerant therein. However, when refrigeration system 50 is switched from the first operating mode to the second operating mode, the accumulated warm, compressed refrigerant in storage vessel 64 is readily available to pass through valve 52 and enter evaporator 18 to immediately begin to defrost the ice in tray 30. Absent storage vessel 64, the quantity of warm refrigerant immediately available to enter evaporator 18 may be limited thereby increasing the time required to defrost the ice in tray 30. Insulation may be applied to vessel 64 to better contain the thermal energy of the refrigerant therein.
Referring to FIGS. 2-4, valves 52 and 56 can be electronically controlled solenoid valves which toggle between open and closed positions. To facilitate the control of these valves, the ice maker can further include a temperature sensor for sensing the temperature of the fluid in tray 30, or a chamber surrounding tray 30, and a microprocessor for receiving a signal from the sensor. The microprocessor, based on information conveyed by the sensor signal, can determine whether the refrigeration system should be in the first operating mode or the second operating mode, and operate valves 52 and 56 to place refrigeration system 50 in the appropriate mode.
Referring to FIG. 5, refrigeration system 70, also an embodiment of the present invention, includes three way valve 72, in lieu of solenoid valves 52 and 56, for switching the refrigeration circuit between first and second modes of operation as described above. Three way valve 72 includes two configurations, a first configuration placing lines 22 and 28 substantially out of direct fluid communication, as illustrated in FIG. 5, and a second configuration placing lines 22 and 28 in direct fluid communication. Valve 72, when arranged in its first configuration, places the refrigeration system in a first operating mode, as illustrated in FIG. 5, in which the water in tray 30 is cooled. The flow of refrigerant in the first operating mode is represented by arrows 44. In order to place refrigeration system 70 in the second operation mode, valve 72 is arranged in its second configuration. Similar to refrigeration system 50 described above, when valve 72 is placed in its second configuration, refrigerant exiting compressor 12 is permitted to flow in a reverse direction through evaporator 18. In this embodiment, fewer valves are required to accomplish the function described above.
FIG. 7 illustrates a modified form of the arrangement of FIG. 4 wherein line 63′ is connected to line 60′ at a position between heat exchanger 19′ and check valve 58′. In the first operating mode this routes refrigerant exiting the evaporator through the suction-to-liquid heat exchanger thereby improving efficiency especially when the condenser 14′ is air cooled. Primed reference numerals in this figure correlate to the elements of FIG. 4.
While this invention has been described as having an exemplary design, the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.

Claims

1. An ice maker, comprising:

an ice tray; and

a refrigeration system, comprising:

a compressor having an inlet and an outlet,

a condenser having an inlet and an outlet, said condenser inlet in fluid communication with said compressor outlet;

an expansion device having an inlet and an outlet, said expansion device inlet in fluid communication with said condenser outlet;

an evaporator, said evaporator having an inlet and an outlet, said evaporator in thermal communication with said ice tray, said inlet in fluid communication with said expansion device outlet;

said refrigeration system having a first operating mode in which refrigerant flows in a first direction from said expansion device outlet, into said evaporator through said inlet and out of said evaporator through said outlet to said compressor inlet,

said refrigeration system having a second operating mode in which refrigerant flows through said evaporator in a direction opposite said first direction from said compressor outlet to said evaporator through said evaporator outlet, wherein refrigerant exiting said evaporator during said second operating mode is returned to said compressor inlet instead of passing through said expansion device and said condenser, and

a first valve arrangement operable to place said refrigeration system alternatively in said first operating mode and said second operating mode.

2. The ice maker of claim 1, further comprising a second valve in fluid communication with said expansion device outlet and said evaporator inlet, said second valve operable to place each said evaporator inlet in fluid communication with said compressor inlet when said refrigeration system is in said second operating mode, wherein refrigerant flowing into said evaporator through said evaporator outlet will flow into said compressor inlet.

3. The ice maker of claim 2, wherein said second valve is selected to maintain a predetermined pressure drop between said evaporator inlet and said compressor inlet when said refrigeration system is in said second operating mode.

4. The ice maker of claim 2, wherein said second valve is a check valve.

5. The ice maker of claim 2, wherein said second valve is a check valve having an adjustable cracking pressure.

6. The ice maker of claim 1, further comprising a storage vessel in fluid communication with said compressor outlet, wherein refrigerant exiting said compressor may accumulate in said storage vessel during said first operating mode and provide a reservoir of refrigerant to flow into said evaporator to warm said ice tray when said refrigeration system is placed into said second operating mode, whereby warming said ice tray can melt at least a portion of ice within said ice tray to facilitate release of said ice from said ice tray.

7. The ice maker of claim 6, wherein said second valve is selected to maintain a predetermined pressure drop between said evaporator inlet and said compressor inlet when said refrigeration system is in said second operating mode.

8. The ice maker of claim 1, wherein said second valve is a check valve.

9. An ice maker, comprising:

an ice tray; and

a refrigeration circuit, comprising:

a compressor having an inlet and an outlet,

an expansion device having an inlet and an outlet, said expansion device inlet in fluid communication with said condenser outlet; and

an evaporator having an inlet and an outlet, said evaporator outlet positioned vertically above said evaporator inlet, said evaporator in thermal communication with said ice tray, said evaporator inlet in fluid communication with said expansion device outlet,

wherein said refrigeration system has a first operating mode in which refrigerant flows from said expansion device outlet into said evaporator through said evaporator inlet up through said evaporator, and through said evaporator outlet into said compressor inlet, and

wherein said refrigeration system has a second operating mode in which refrigerant flows from said compressor outlet into said evaporator through said evaporator outlet, downward through said evaporator, and out of said evaporator through said evaporator inlet,

whereby the flow of refrigerant during said second operating mode from said evaporator outlet downward to said evaporator inlet facilitates the release of ice within said ice tray by first melting ice at an upper portion of said ice tray and then flowing downwardly.

10. The ice maker of claim 9, further comprising a storage vessel in fluid communication with said compressor outlet, wherein refrigerant exiting said compressor outlet may accumulate in said storage vessel during said first operating mode and provide a reservoir of refrigerant to flow into said evaporator to warm said ice tray when said refrigeration system is placed into said second operating mode.

11. The ice maker of claim 9, further comprising a check valve in fluid communication with said expansion device outlet and said evaporator inlet to place said evaporator inlet in fluid communication with said compressor inlet when said refrigeration system is in said second operating mode, wherein refrigerant flowing into said evaporator through said evaporator outlet may flow into said compressor inlet.

12. An ice maker, comprising:

an ice tray; and

a refrigeration circuit, comprising:

a compressor having an inlet and an outlet,

a storage vessel having an inlet and an outlet, said storage vessel inlet in fluid communication with said compressor outlet;

a condenser having an inlet in communication with the storage vessel outlet and an outlet,

an evaporator having an inlet and an outlet, said evaporator in thermal communication with said ice tray, said evaporator inlet in fluid communication with said expansion device outlet,

wherein said refrigeration system has a first operating mode in which warm refrigerant is stored within said storage vessel and the storage vessel outlet is out of fluid communication with the evaporator outlet and a second operating mode in which said storage vessel outlet is in fluid communication with said evaporator outlet and warm refrigerant stored within said storage vessel is released into said evaporator through its outlet to warm said ice tray; and

a valve arrangement in fluid communication with said evaporator outlet and said compressor outlet to place said refrigeration system in said first operating mode and said second operating mode.

13. The ice maker of claim 12, wherein said outlet of said evaporator is positioned vertically above said evaporator inlet, wherein during said first operating mode refrigerant flows from said expansion device outlet into said evaporator through said evaporator inlet, up through said evaporator, and into said compressor inlet through said evaporator outlet, wherein during said second operating mode refrigerant flows from said storage vessel into said evaporator through said outlet, downward through said evaporator, and out of said evaporator through said evaporator inlet.

14. The ice maker of claim 13, wherein said evaporator is mounted to said ice tray, and wherein the downward flow of refrigerant during said second operating mode facilitates the release of ice within said ice tray, as ice melted at an upper portion of said ice tray flows downwardly to release ice at the bottom of said ice tray.

15. The ice maker of claim 12, wherein said second valve is selected to maintain a predetermined pressure drop between said evaporator inlet and said compressor inlet when said refrigeration system is in said second operating mode.