HIGH PERFORMANCE REFRIGERATOR HAVING EVAPORATOR OUTSIDE CABINET
A high performance refrigerator includes a cabinet with a refrigerated interior, a refrigeration fluid circuit having an evaporator located within an insulated evaporator compartment outside the cabinet, and at least one damper that opens to permit air circulation from the refrigerated interior through the evaporator compartment. The refrigerator also includes a eutectic member configured to melt at an operating temperature of the refrigerator. The evaporator cools the refrigerated interior to a temperature below the operating temperature so that the eutectic member melts to cool the refrigerated interior or the evaporator compartment during a defrost cycle. The insulated evaporator cover limits heat transfer into the refrigerated interior during the defrost cycle to avoid temperature spikes in the refrigerated interior.
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The present application claims the priority benefit of U.S. Provisional Patent Application No. 61/548,807 (pending), filed Oct. 19, 2011, the disclosure of which is hereby incorporated by reference in its entirety herein.
FIELD OF THE INVENTIONThe present invention relates generally to refrigerators or freezers and, more particularly, to refrigeration systems for use with high performance blood bank refrigerators or plasma freezers.
BACKGROUND OF THE INVENTIONRefrigeration systems are known for use with laboratory refrigerators and freezers of the type known as “high performance refrigerators,” which are used to cool their interior storage spaces to relative low temperatures such as about −30° C. or lower, for example. These high performance refrigerators are used to store blood and/or plasma, in one example.
Known refrigeration systems of this type include a single loop circulating a refrigerant. The system transfers energy (i.e., heat) from the refrigerant to the surrounding environment through a condenser, and the system transfers heat energy to the refrigerant from the cooled space (e.g., a cabinet interior) through an evaporator. The refrigerant is selected to vaporize and condense at a selected temperature close to the desired temperature for the cooled space, such that the refrigeration system can maintain the cooled space near that selected temperature during operation.
One common problem with known refrigeration systems is that the evaporator includes coils that tend to produce and accumulate frost along the outer surface if any moisture is ambient within the cooled space. If enough frost accumulation occurs, the ability of the evaporator to remove heat from the cooled space is detrimentally impacted. Consequently, known refrigeration systems require a defrost cycle where the evaporator coils are heated to remove the frost. This defrost cycle may be a manual defrost or an automatic defrost, but both types of defrost cycles are undesirable for various reasons.
In a manual defrost cycle, all of the products stored in the cabinet are removed and the cooled space is left exposed to the ambient environment to heat up the evaporator coils and melt the frost. This cycle is undesirable because the products stored in the cabinet need to be stored in an alternative refrigerator for the duration of the defrost cycle, and also because the melting process can produce a significant amount of moisture that needs to be removed from the cabinet. In an automatic defrost cycle, the evaporator coils are rapidly heated by a local heating unit or hot gas flow to remove the frost, which is collected by a trough and delivered out of the cooled space. The cooled space necessarily undergoes a temperature spike during this automatic defrost cycle, which can jeopardize the products stored in the cabinet.
There is a need, therefore, for a refrigerator that substantially minimizes or eliminates a temperature spike within the cooled space during a defrost cycle.
SUMMARY OF THE INVENTIONIn one embodiment, a refrigerator includes a cabinet with a refrigerated interior and a refrigeration fluid circuit for circulating a refrigerant. The refrigeration fluid circuit includes a compressor, a condenser, an expansion device, and an evaporator located within an insulated evaporator compartment outside the cabinet. The evaporator includes an evaporator coil and an evaporator fan producing air flow through the evaporator coil. The refrigerator includes at least one damper which opens to permit air circulation from the refrigerated interior through the evaporator compartment. The refrigerator also includes a eutectic member that melts at an operating temperature of the refrigerator. The evaporator cools the refrigerated interior to a temperature below the operating temperature such that when the at least one damper is closed for a defrost cycle, the eutectic member melts to cool at least one of the refrigerated interior and the evaporator compartment.
In one aspect, the eutectic member is mounted along one of the side walls of the cabinet or along the top wall of the cabinet. The at least one damper is also formed in the top wall such that the eutectic member acts as a temperature ballast as well as a cold generation device. In another aspect, the eutectic member is mounted within the evaporator compartment such that the eutectic member melts to cool the evaporator compartment during operation of a defrost heater within the evaporator compartment.
In another embodiment, a refrigerator includes a cabinet with a refrigerated interior and a refrigeration fluid circuit for circulating a refrigerant. The refrigeration fluid circuit includes a compressor, a condenser, an expansion device, and an evaporator located within an insulated evaporator compartment outside the cabinet. The evaporator includes an evaporator coil, an evaporator fan producing air flow through the evaporator coil, and a defrost heater. The refrigerator includes at least one damper which opens to permit air circulation from the refrigerated interior through the evaporator compartment. The refrigerator also includes a controller operable to command the refrigerator to perform a series of steps defining a defrost cycle when the evaporator coil requires defrosting. The series of steps includes stopping operation of the compressor and the evaporator fan, closing the at least one damper to thermally isolate the evaporator compartment from the refrigerated interior, and starting operation of the defrost heater. The refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.
In one aspect, the refrigerator also includes a temperature sensor for detecting the temperature of the evaporator. The controller operates during defrosting as follows: when the temperature sensor detects that the evaporator has reached a first target temperature above the freezing point of water, the defrost heater stops and any remaining moisture is allowed to drip off the evaporator coil. After any remaining moisture drips off the evaporator coil, the compressor starts. When the temperature sensor detects that the evaporator has reached a second target temperature below the freezing point of water, the at least one damper opens and the evaporator fan starts. In one example, the first target temperature is about 10° C. and the second target temperature is about −25° C. The controller may also be operable to perform the defrost cycle steps as an adaptive defrost cycle, which includes varying time periods between defrost cycles and varying lengths of defrost cycles dependent upon multiple operating parameters.
In yet another embodiment of the invention, a refrigerator includes a cabinet with a refrigerated interior and a refrigeration fluid circuit for circulating a refrigerant. The refrigeration fluid circuit includes a compressor, a condenser, an expansion device, and an evaporator located within an insulated evaporator compartment outside the cabinet. The evaporator includes an evaporator coil and an evaporator fan producing air flow through the evaporator coil. The refrigerator includes at least one valve which opens to permit air circulation from the refrigerated interior through the evaporator compartment. The cabinet includes a top wall adjacent the evaporator compartment, a door, a rear wall, and side walls (including a rear wall) extending between the rear wall and the door. The rear wall includes an inlet duct in communication with the evaporator and a plurality of inlet ports leading into the refrigerated interior. The side walls include an outlet duct in communication with the evaporator and a plurality of outlet ports leading from the refrigerated interior. The at least one valve controls flow between the evaporator and the refrigerated interior via the inlet duct and the outlet ducts.
In another embodiment of the invention, a method of operating a refrigerator is provided, the refrigerator including a cabinet with a refrigerated interior and a refrigeration fluid circuit including a compressor, a condenser, and an evaporator located in an insulated evaporator cover outside the cabinet. The evaporator includes an evaporator fan and a defrost heater. The refrigerator also includes at least one damper separating the evaporator compartment from the refrigerated interior. The method includes stopping operation of the compressor and an evaporator fan. The at least one damper closes to thermally isolate the evaporator compartment from the refrigerated interior. A defrost heater starts operation to remove moisture from evaporator. The refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
With reference to the figures, and more specifically to
With reference to
The refrigeration fluid circuit 20 is configured to circulate the refrigerant 36 between the condenser 24 and the evaporator 30. Generally speaking, heat energy in the refrigerant 36 is transferred to ambient air outside the cabinet 12 at the condenser 24. Heat energy is removed from the interior 18 of the cabinet 12 and transferred to the refrigerant 36 at the evaporator 30. Thus, circulating the refrigerant 36 through the fluid circuit 20 continuously removes heat energy from the interior 18 to maintain a desired internal temperature, such as, for example −30° C.
The refrigerant 36 enters the compressor 22 in a vaporized state and is compressed to a higher pressure and higher temperature gas in the compressor 22. The fluid circuit 20 of this exemplary embodiment also includes an oil loop 54 for lubricating the compressor 22. Specifically, the oil loop 54 includes an oil separator 56 in fluid communication with piping 34 downstream of the compressor 22 and an oil return line 58 directing oil back into the compressor 22. It will be understood that the oil loop 54 may be omitted in some embodiments of the fluid circuit 20.
Upon leaving the compressor 22, the vaporized refrigerant 36 travels to the condenser 24. A fan 60 controlled by the control interface 52 directs ambient air across the condenser 24 and through a filter 62 so as to facilitate the transfer of heat from the refrigerant 36 to the surrounding environment. The air flow through the condenser 24 is shown by arrows in
In the evaporator 30, the refrigerant 36 receives heat from the interior 18 through a plurality of evaporator coils (not shown in
The refrigerant 36 used in the refrigeration fluid circuit 20 may be chosen based on several factors, including the expected operating temperature within the cabinet 12 and the boiling point and other characteristics of the refrigerant 36. For example, in refrigerators with an expected cabinet temperature of about −30° C., an exemplary refrigerant 36 suitable for the presently described embodiment includes refrigerants commercially available under the respective designations R404A. Moreover, in specific embodiments, the refrigerant 36 may be combined with an oil to facilitate lubrication of the compressor 22. For example, and without limitation, the refrigerant 36 may be combined with Mobil EAL Arctic 32 oil. It will be understood that the precise arrangement of the components illustrated in the figures is intended to be merely exemplary rather than limiting.
With reference to
As shown in
Also shown in
Turning to
The evaporator 30 also includes a defrost heater 114 for removing frost build up on the evaporator coil 112 as needed or on a regular basis. The defrost heater 114 is shown mounted adjacent to the evaporator coil 112 in
With reference to
The refrigerator 10 also includes one or more eutectic members 122 as shown in
The eutectic plate 122 may be mounted along the side walls 78 or the top wall 76 within the cabinet 12. In these embodiments, any heat energy that enters the interior 18 or is generated within the interior 18 is counteracted by the melting of the eutectic plate 122, which acts as a supplemental cooling device during the defrost cycle. To this end, the eutectic plate also limits the temperature spike within the cabinet 12. When the eutectic plate 122 is located along the top wall 76 of the cabinet housing 14, the eutectic plate 122 may operate as a temperature ballast or additional insulation between the refrigerated interior 18 and the evaporator compartment 72.
In another embodiment, the eutectic plate 122 may alternatively be mounted within the evaporator compartment 72. Similar to the previous embodiment, the eutectic plate 122 melts to counteract the detrimental heating effects of the defrost heater 114. In this regard, the defrost heater 114 heats the evaporator coil 112 to melt frost from the evaporator coil 112 but the heat energy fills the remainder of the evaporator compartment 72 where the heat energy is unnecessary. Once the defrost cycle is completed, the melting of the eutectic plate 122 assists the refrigerant 36 flowing through the evaporator coil 112 to more rapidly cool the evaporator compartment 72 back to the intended operating temperature of the refrigerator 10. Consequently, the eutectic plate 122 may reduce any temperature spike encountered within the cabinet 12 during a defrost cycle or may reduce the overall length of a defrost cycle by more rapidly cooling the evaporator compartment 72 at the end of such a defrost cycle.
An alternative embodiment of the refrigerator 130 is shown in
In a similar manner, each of the side walls 78b extending between the rear wall 78a and the door 16 includes an outlet or return duct 140 with a plurality of outlet ports 142 disposed along the length of the side walls 78b. To this end, a return flow of warmed air (indicated by arrows 144) flows from the interior 18 through the outlet ports 142 and the outlet or return ducts 140 to inlet valves 146 at the insulated cover 70. Thus, the inlet valves 146 and the outlet valve 132 control air flow through the evaporator 30 via the inlet duct 134 and the outlet ducts 140. Because the inlet duct 134 and the outlet ducts 140 extend from the top wall 76 to the bottom wall 80 of the cabinet housing 14, the air duct and valve assembly of this embodiment of the refrigerator 130 enable more thorough air flow through the cabinet 12.
As previously described with reference to the refrigerator 10 of
An exemplary operation of the refrigerator 10 (or 130) is shown schematically in the flowchart of
Returning to
One of the sensors S3 connected to the evaporator 30 may be configured to measure the temperature of the evaporator 30. At step 212, the controller 50 determines whether that sensor S3 is reading a temperature of the evaporator 30 which is at or exceeding a first target temperature above the freezing point of water (0° C.). In one example, this first target temperature may be about 10° C. If the evaporator 30 is not at or above that first target temperature, then the controller 50 continues to operate the defrost heater 114 to remove frost from the evaporator coil 112. If the evaporator 30 is at or above the first target temperature, then the controller 50 turns off the defrost heater 114 and allows a set period of time for additional moisture to drip off the evaporator coil 112 onto the drip pan 116 at step 214. After this “drip time” has occurred, the controller 50 starts the compressor 22 to cause refrigerant flow through the evaporator 30 again at step 216, thereby cooling the evaporator compartment 72.
At step 218, the temperature sensor S3 measures the temperature of the evaporator 30 and the controller 50 determines whether this temperature is at or below a second target temperature below the freezing point of water (0° C.). In one example, this second target temperature may be about −25° C. If the evaporator 30 is not at or below the second target temperature, the controller 50 continues to operate the compressor 214 to cool the evaporator 30. Once the controller 50 determines that the evaporator 30 is at or below the second target temperature, then the controller 50 opens the first and second dampers 66, 68 (or the outlet valve 132 and inlet valves 146) at step 220. The controller 50 also starts the evaporator fan 64 at step 220, to thereby force air flow from the refrigerated portion 74 through the evaporator compartment 72 and the evaporator 30 for further cooling. This final step of the defrost cycle or method 200 returns the refrigerator 10 to the operational state shown in
As briefly noted above, in one alternative embodiment the defrost cycle will be an adaptive defrost cycle selectively actuated at step 202 of the method 200. In this adaptive defrost cycle, the period between defrost cycles and the time duration of the defrost cycles are modified based on a plurality of operational parameters monitored by the controller 50. For example, the conventional time-based defrost cycle may operate the defrost heater 114 for 10 minutes every six hours. By contrast, the adaptive defrost cycle may monitor the actual temperature being maintained in the cabinet 12, as well as the number of door openings and amount of total time the door is open. These and other factors are considered to determine how long the period should be before the next defrost cycle is started, and also how long the defrost heater 114 should be operated in the next defrost cycle. In this regard, if the door of the cabinet 12 is not opened often during a six hour period and the evaporator 30 is having little trouble maintaining the desired temperature within the refrigerated portion 74, then the next defrost cycle may be delayed by an additional number of hours and/or shortened in duration. Thus, the adaptive defrost cycle is highly energy efficient because the evaporator coil 112 is only defrosted when that cycle becomes necessary. Moreover, the adaptive defrost cycle automatically adjusts the refrigerator 10 for proper and efficient operation in a variety of environmental conditions.
While the present invention has been illustrated by a description of exemplary embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, the air ducts 134, 140 may be combined with the eutectic plates 122 shown in the various embodiments 10, 130 of the refrigerator. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
Claims
1. A refrigerator, comprising:
- a cabinet having a refrigerated interior;
- a refrigeration fluid circuit for circulating a refrigerant, the circuit including a compressor, a condenser, an expansion device, and an evaporator located within an insulated evaporator compartment outside the cabinet, and including an evaporator coil and an evaporator fan producing air flow through the evaporator coil;
- at least one damper that may open to permit air circulation from the refrigerated interior through the evaporator compartment; and
- a eutectic member configured to melt at an operating temperature of the refrigerator,
- wherein the evaporator cools the refrigerated interior to a temperature below the operating temperature such that when the at least one damper is closed for a defrost cycle, the eutectic member cools at least one of the refrigerated interior and the evaporator compartment by melting.
2. The refrigerator of claim 1, wherein the cabinet includes side walls and a top wall, the at least one damper is formed in the top wall, and the eutectic member is mounted along one of the side walls.
3. The refrigerator of claim 1, wherein the eutectic member is a plate-shaped member.
4. The refrigerator of claim 1, wherein the operating temperature is about −32° C.
5. The refrigerator of claim 1, wherein the cabinet includes a top wall, the at least one damper is formed in the top wall, and the eutectic member is mounted along the top wall.
6. The refrigerator of claim 1, wherein the eutectic member is mounted within the evaporator compartment such that the eutectic member cools the evaporator compartment by melting during a defrost cycle.
7. The refrigerator of claim 1, wherein the cabinet further includes:
- a top wall adjacent the insulated evaporator compartment,
- a door,
- a rear wall including an inlet duct in communication with the evaporator and a plurality of inlet ports leading into the refrigerated interior, and
- side walls extending between the rear wall and the door, each side wall including an outlet duct in communication with the evaporator and a plurality of outlet ports leading from the refrigerated interior,
- wherein the at least one damper is a valve controlling flow between the evaporator and the refrigerated interior via the inlet duct and the outlet ducts.
8. A refrigerator, comprising:
- a cabinet having a refrigerated interior;
- a refrigeration fluid circuit for circulating a refrigerant, the circuit including a compressor, a condenser, an expansion device, and an evaporator located within an insulated evaporator compartment outside the cabinet and including an evaporator coil, an evaporator fan producing air flow through the evaporator coil, and a defrost heater;
- at least one damper that may open to permit air circulation from the refrigerated interior through the evaporator compartment; and
- a controller operable to command the refrigerator to perform the following steps when the evaporator coil requires defrosting: stop operation of the compressor and the evaporator fan; close the at least one damper to thermally isolate the evaporator compartment from the refrigerated interior; and start operation of the defrost heater,
- wherein the refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.
9. The refrigerator of claim 8, further comprising a temperature sensor for detecting the temperature of the evaporator, and wherein the controller is further operable to command the refrigerator to perform the following steps during defrosting of the evaporator:
- when the temperature sensor detects that the evaporator has reached a first target temperature above the freezing point of water, stopping operation of the defrost heater and allowing for any remaining moisture to drip off the evaporator coil;
- starting the compressor after the remaining moisture drips off the evaporator coil; and
- when the temperature sensor detects that the evaporator has reached a second target temperature below the freezing point of water, opening the at least one damper and starting operation of the evaporator fan.
10. The refrigerator of claim 9, wherein the first target temperature is about 10° C. and the second target temperature is about −25° C.
11. The refrigerator of claim 8, wherein the at least one damper includes a first damper and a second damper, the first damper in an open position permitting air flow into the evaporator compartment from the refrigerated interior, the second damper in an open position permitting air flow from the evaporator compartment into the refrigerated interior.
12. The refrigerator of claim 8, wherein the insulated evaporator compartment further includes a plurality of vacuum insulated panels.
13. The refrigerator of claim 8, further comprising:
- a eutectic member located within the cabinet and configured to melt at an operating temperature of the refrigerator,
- wherein the evaporator cools the refrigerated interior to a temperature below the operating temperature such that when the at least one damper is closed for a defrost cycle, the eutectic member cools the refrigerated interior by melting.
14. The refrigerator of claim 13, wherein the cabinet includes side walls and a top wall, the at least one damper is formed in the top wall, and the eutectic member is mounted along one of the side walls.
15. The refrigerator of claim 13, wherein the cabinet includes a top wall, the at least one damper is formed in the top wall, and the eutectic member is mounted along the top wall.
16. The refrigerator of claim 13, wherein the operating temperature is about −30° C.
17. The refrigerator of claim 8, further comprising:
- a eutectic member located within the evaporator compartment and configured to melt at an operating temperature of the refrigerator,
- wherein the evaporator cools the refrigerated interior to a temperature below the operating temperature such that when the at least one damper is closed for a defrost cycle, the eutectic member cools the evaporator compartment by melting.
18. The refrigerator of claim 8, wherein the cabinet further includes:
- a top wall adjacent the insulated evaporator compartment,
- a door,
- a rear wall including an inlet duct in communication with the evaporator and a plurality of inlet ports leading into the refrigerated interior, and
- side walls extending between the rear wall and the door, each side wall including an outlet duct in communication with the evaporator and a plurality of outlet ports leading from the refrigerated interior,
- wherein the at least one damper is a valve controlling flow between the evaporator and the refrigerated interior via the inlet duct and the outlet ducts.
19. A method of operating a refrigerator including a cabinet having a refrigerated interior, a refrigeration fluid circuit including a compressor, a condenser, and an evaporator located within an insulated evaporator compartment outside the cabinet and having an evaporator fan and defrost heater, the refrigerator further including at least one damper configured to separate the evaporator compartment from the refrigerated interior of the cabinet, and the method comprises:
- stopping operation of the compressor and the evaporator fan;
- closing the at least one damper to thermally isolate the evaporator compartment from the refrigerated interior; and
- starting operation of the defrost heater,
- wherein the refrigerated interior remains thermally isolated from the evaporator during operation of the defrost heater.
20. The method of claim 19, further comprising:
- when the evaporator has reached a first target temperature above the freezing point of water, stopping operation of the defrost heater and allowing for any remaining moisture to drip off the evaporator coil;
- starting operation of the compressor after the remaining moisture drips off the evaporator coil; and
- when the evaporator has reached a second target temperature below the freezing point of water, opening the at least one damper and starting operation of the evaporator fan.
21. The method of claim 20, wherein the first target temperature is about 10° C. and the second target temperature is about −25° C.
22. The method of claim 19, wherein the system further includes a eutectic member located within the cabinet or the evaporator compartment and configured to melt at an operating temperature of the refrigerator, and the method further comprises:
- cooling the refrigerated interior with the evaporator to a temperature below the operating temperature before a defrost cycle; and
- melting the eutectic member to cool at least one of the refrigerated interior and the evaporator compartment during the defrost cycle.
23. A refrigerator, comprising:
- a cabinet having a refrigerated interior;
- a refrigeration fluid circuit for circulating a refrigerant, the circuit including a compressor, a condenser, an expansion device, and an evaporator located within an evaporator compartment outside the cabinet and including an evaporator coil and an evaporator fan producing air flow through the evaporator coil; and
- at least one valve that may open to permit air circulation from the refrigerated interior through the evaporator compartment,
- wherein the cabinet further includes: a top wall adjacent the evaporator compartment, a door, a rear wall including an inlet duct in communication with the evaporator and a plurality of inlet ports leading into the refrigerated interior, and side walls extending between the rear wall and the door, each side wall including an outlet duct in communication with the evaporator and a plurality of outlet ports leading from the refrigerated interior, wherein the at least one valve controls flow between the evaporator and the refrigerated interior via the inlet duct and the outlet ducts.
24. The refrigerator of claim 23, wherein the cabinet includes a bottom wall, and the inlet duct and outlet ducts each extend between the top wall and the bottom wall.
Type: Application
Filed: Oct 16, 2012
Publication Date: Apr 25, 2013
Applicant: THERMO FISHER SCIENTIFIC (ASHEVILLE) LLC (Asheville, NC)
Inventor: Thermo Fisher Scientific (Asheville) LLC (Asheville, NC)
Application Number: 13/652,992
International Classification: F25D 21/06 (20060101); F25B 1/00 (20060101); F25D 21/08 (20060101); F25D 17/06 (20060101); F25D 21/02 (20060101);