REFRIGERATOR AND METHOD OF OPERATING REFRIGERATION SYSTEM

Abstract

A refrigeration system 4 controlled by a control system 26, wherein the refrigeration system 4 comprises: an evaporator 8, a compressor 10, a condenser 12, and an expansion arrangement 15. The control system 26 is adapted: to establish a momentary cooling requirement based on the differential between a set-point temperature and an actual temperature averaged over time, to form a requirement variable relating to the momentary cooling requirement, to fix a first duration during which the compressor is switched on and a second duration during which the compressor is switched off, and to switch on and to switch off the compressor according to the first and second durations. The refrigeration system 4 comprises a first shut-off valve 20. The control system 4 is adapted: to close the first shut-off valve 20 in connection with switching off the compressor 10, and to open the first shut-off valve 20 in connection with switching on the compressor 10.

Claims

1. A method of operating a refrigeration system, wherein the refrigeration system comprises: an evaporator adapted to be arranged in thermal communication with a compartment to be cooled, a compressor, a condenser, an expansion arrangement, conduits interconnecting the evaporator, the compressor, the condenser, and the expansion arrangement, a first shut-off valve arranged in a conduit extending between the condenser and the evaporator, a by-pass conduit extending between an outlet side of the compressor and an inlet side of the compressor a valve arrangement in both a conduit between the compressor and the condenser and in the by-pass conduit, and a control system, wherein the method comprises: establishing a momentary cooling requirement of the compartment based on the differential between a set-point temperature and an actual temperature averaged over time forming a requirement variable relating to the momentary cooling requirement, the requirement variable being a ratio between a switch-on duration of the compressor and a switch-off duration of the compressor, fixing a first duration during which the compressor is switched on and a second duration during which the compressor is switched off on the basis of the requirement variable, and switching on and switching off the compressor according to the first and second durations, closing the first shut-off valve in connection with switching off the compressor, opening the first shut-off valve in connection with switching on the compressor, and equalizing a pressure difference between the outlet side and the inlet side of the compressor during the second duration.

2. The method according to claim 1, wherein the refrigeration system comprises the compartment and the compartment is adapted for domestic foodstuff storing.

3. The method according to claim 1, wherein the compressor is a single speed compressor controlled by a control system to run at a constant speed during the first duration.

4. The method according to claim 1, wherein the valve arrangement comprises a check valve in the conduit between the compressor and the condenser and a second shut-off valve in the by-pass conduit, and wherein the method further comprises: maintaining the second shut-off valve closed during the first duration, and opening the second shut-off valve during the second duration to achieve said equalizing the pressure difference.

5. The method according to claim 1, wherein the valve arrangement comprises a 3-way valve in the conduit between the compressor and the condenser and connected to the by-pass conduit, and wherein said equalizing the pressure difference includes: opening a connection between the outlet side of the compressor and the by-pass conduit and closing a connection between the compressor and the condenser by means of the 3-way valve, and wherein the method further comprises: closing the connection between the outlet side of the compressor and the by-pass conduit and opening the connection between the compressor and the condenser by means of the 3-way valve during the first duration.

6. The method according to claim 1, wherein the expansion arrangement comprises a capillary tube.

7. The method according to claim 1, wherein the first shut-off valve forms part of the expansion arrangement.

8. The method according to claim 1, wherein the first duration and the second duration collectively have a length of between 1-100 minutes.

9. The method according to claim 1, wherein the compressor is adapted to provide a cooling capacity of between 10-500 W according to ASHRAE LBP or HMBP.

10. A refrigerator comprising a compartment cooled by a refrigeration system comprising: an evaporator arranged in thermal communication with the compartment, a compressor, a condenser, an expansion arrangement, conduits interconnecting the evaporator, the compressor, the condenser, and the expansion arrangement, wherein one of the conduits extends between the condenser and the expansion arrangement, a first shut-off valve arranged in a conduit extending between the condenser and the evaporator, a by-pass conduit extending between an outlet side of the compressor and an inlet side of the compressor, a valve arrangement in both a conduit between the compressor and the condenser and in the by-pass conduit, and a control system adapted: to establish a momentary cooling requirement of the compartment based on a differential between a set-point temperature and an actual temperature averaged over time, to form a requirement variable relating to the momentary cooling requirement, the requirement variable being a ratio between a switch-on duration of the compressor and a switch-off duration of the compressor, to fix a first duration during which the compressor is switched on and a second duration during which the compressor is switched off on the basis of the requirement variable, and to switch on and to switch off the compressor according to the first and second durations, to close the first shut-off valve in connection with switching off the compressor, to open the first shut-off valve in connection with switching on the compressor, and to equalize a pressure difference between the outlet side and inlet side of the compressor during the second duration.

11. The refrigerator according to claim 10, wherein the compartment is adapted for domestic foodstuff storing.

12. The refrigerator according to claim 10, wherein the compressor is a single speed compressor controlled by the control system to run at a constant speed during the first duration.

13. The refrigerator according to claim 10, wherein the valve arrangement comprises a check valve in the conduit between the compressor and the condenser and a second shut-off valve in the by-pass conduit, and wherein the control system is adapted: to maintain the second shut-off valve closed during the first duration, and to open the second shut-off valve during the second duration to equalize the pressure difference between the outlet side and the inlet side of the compressor during the second duration.

14. The refrigerator according to claim 10, wherein the valve arrangement comprises a 3-way valve in the conduit between the compressor and the condenser and connected to the by-pass conduit, and wherein the control system is adapted: to open a connection between the outlet side of the compressor and the by-pass conduit and to close a connection between the compressor and the condenser by means of the 3-way valve during the second duration, and to close the connection between the outlet side of the compressor and the by-pass conduit and to open the connection between the compressor and the condenser, by means of the 3-way valve during the first duration.

15. The refrigerator according to claim 10, wherein the compressor is a variable speed compressor controlled by the control system to run at variable speed during the first duration.

16. The refrigerator according to claim 10, wherein the expansion arrangement comprises a capillary tube.

17. The refrigerator according to claim 10, wherein the first shut-off valve forms a part of the expansion arrangement.

18. The refrigerator according to claim 10, wherein the refrigeration system comprises a filter arranged in the conduit between the condenser and the expansion arrangement.

19. The refrigerator according to claim 18, wherein the first shut-off valve is arranged in the conduit between the filter and the expansion arrangement.

20. A refrigerator comprising a compartment cooled by a refrigeration system comprising: an evaporator arranged in thermal communication with the compartment, a compressor, a condenser, a shut-off valve forming a part of an expansion arrangement, conduits interconnecting the evaporator, the compressor, the condenser, and the expansion arrangement, wherein one of the conduits extends between the condenser and the expansion arrangement, and a control system adapted: to establish a momentary cooling requirement of the compartment based on a differential between a set-point temperature and an actual temperature averaged over time, to form a requirement variable relating to the momentary cooling requirement, the requirement variable being a ratio between a switch-on duration of the compressor and a switch-off duration of the compressor, to fix a first duration during which the compressor is switched on and a second duration during which the compressor is switched off on the basis of the requirement variable, and to switch on and to switch off the compressor according to the first and second durations, to close the first shut-off valve in connection with switching off the compressor, to open the first shut-off valve in connection with switching on the compressor, and to equalize a pressure difference between an outlet side and an inlet side of the compressor during the second duration.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The various aspects of the invention, including its particular features and advantages, will be readily understood from the following detailed description and the accompanying drawings, in which:

[0062] FIG. 1 illustrates schematically a refrigerator according to embodiments and a refrigeration system according to embodiments,

[0063] FIG. 2 illustrates a method of operating a refrigeration system according to embodiments,

[0064] FIGS. 3 and 4 illustrate portions of refrigeration systems according to embodiments, and

[0065] FIG. 5 illustrates a refrigeration system according to embodiments.

DETAILED DESCRIPTION

[0066] The present invention will now be described more fully with reference to the accompanying drawings, in which example embodiments are shown. However, this invention should not be construed as limited to the embodiments set forth herein. Disclosed features of example embodiments may be combined as readily understood by one of ordinary skill in the art to which this invention belongs. Like numbers refer to like elements throughout.

[0067] Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.

[0068] FIG. 1 illustrates schematically a refrigerator 2 according to embodiments and a refrigeration system 4 according to embodiments. The refrigerator 2 comprises the refrigeration system 4 and a compartment 6, e.g, for storing foodstuff. The refrigeration system 4 comprises an evaporator 8, a compressor 10, a condenser 12, a filter 14 and an expansion arrangement 15 comprising a capillary tube 16. Conduits are arranged to interconnect the mentioned components of the refrigeration system 4. Accordingly, the filter 14 is arranged in a conduit ext ending between the condenser 12 and the expansion arrangement 15.

[0069] A refrigerant circulates in the refrigeration system 4. Circulation of the refrigerant is driven by a pressure difference between the condenser 12 and the evaporator 8. The pressure difference is created by the compressor 10, compressing gaseous refrigerant which has evaporated from liquid refrigerant in the evaporator 8. The gaseous refrigerant is cooled and condenses to a liquid state in the condenser 12. The liquid refrigerant passes through the filter 14, which may collect debris and water in the refrigerant. In the expansion arrangement 15 the liquid refrigerant is subjected to a pressure drop to thereafter evaporate from the liquid state in the evaporator 8. The evaporator 8 is arranged in thermal communication with the compartment 6 and thus, cools the compartment 6 when refrigerant evaporates in the evaporator 8.

[0070] The refrigeration system 4 further comprises a first shut-off valve 20 arranged in a first conduit 22 extending between the condenser 12 and the evaporator 8, i.e. a conduit 22 also comprising the expansion arrangement 15. The first shut-off valve 20 is arranged in the first conduit 22 between the filter 14 and the expansion arrangement 15. The first conduit 22 may be closed by means of the first shut-off valve 20. The first shut-off valve 20 has two discrete positions, one fully closed position and one fully open position.

[0071] An electric motor 24 drives the compressor 10. A control system 26 is arranged to control the operation of the refrigeration system 4. The control system 26 may comprise a microprocessor programmed to control the operation of the refrigeration system 4. Alternatively, the control system 26 may comprise discrete electric components connected to control the refrigeration system 4. The control system 26 further comprises a temperature sensor 28 arranged in the compartment 6 and is connected to the electric motor 24 for controlling the compressor 10, and to the first shut-off valve 20. Control parameters of the refrigeration system 4 may be preset in the control system 26. Alternatively, at least some control parameters may be set via a control panel 30.

[0072] FIG. 2 illustrates a method of operating a refrigeration system according to embodiments.

[0073] The refrigeration system may be a refrigeration system 4 as described in connection with FIG. 1. The method comprises: [0074] Establishing 100 a momentary cooling requirement of the compartment 6 based on a differential between a set-point temperature and an actual temperature averaged over time. The set-point temperature may be set in the control system 26, e.g. by means of the control panel 30. The averaged temperature over time may be calculated by the control system 26 utilizing temperature measurements of the temperature sensor 28 in the compartment 6. The said establishing 100 the momentary cooling requirement may comprise simply establishing whether the refrigeration system 4 is to be switched on or off, i.e. whether the compressor 10 should be running or not. [0075] Forming 102 a requirement variable relating to the momentary cooling requirement. The requirement variable may be a ratio between a switch-on duration of the compressor 10 and a switch-off duration of the compressor 10 [0076] Fixing 104 a first duration during which the compressor 10 is switched on and a second duration during which the compressor 10 is switched off on the basis of the requirement variable. For example, if a compressor cycle length is 20 minutes and the requirement variable is 40% switch-on duration and 60% switch-off duration, the first duration is 8 minutes and the second duration is 12 minutes. [0077] Switching on 106 and switching off 108 of the compressor 10 according to the first and second durations. The control system 26 is adapted to switch on and off the compressor 10 by means of switching on and off the electric motor 24. [0078] Closing 110 the first shut-off valve 20 in connection with switching off the compressor 10. [0079] Opening 112 the first shut-off valve 20 in connection with switching on the compressor 10.

[0080] It may be clarified that in a refrigeration system without a first shut-off valve operated according to this method, the pressure between the condenser 12 and the evaporator 8 is gradually equalized via the expansion arrangement 15 during switch-off durations of the compressor, which causes cyclic losses as initially discussed under points 1-4.

[0081] A refrigeration system 4 operated according to this method is advantageous in that it firstly, thanks to the requirement variable and the average temperature over time is used allows the compressor 10 to be run for optimal durations from a cooling requirement and energy consumption point of view. Secondly, thanks to the closing and opening of the first shut-off valve 20, cyclic losses in the refrigeration system 4 may be avoided, at least to a large extent. Thus, the method allows a refrigeration system 4 to be operated with low energy consumption by optimizing running characteristics and by eliminating cyclic losses.

[0082] Method steps 100-104 are suitably performed at regular intervals by the control system 16 of the refrigeration system 4. Method steps 106-112 may be performed at the same regular intervals or at different intervals.

[0083] With reference to the method disclosed in connection with FIG. 2, it is accordingly concluded that the control system 26 illustrated in FIG. 1 is adapted: [0084] to establish a momentary cooling requirement of the compartment 6 based on the differential between a set-point temperature and an actual temperature averaged over time, [0085] to form a requirement variable relating to the momentary cooling requirement, the requirement variable being a ratio between a switch-on duration of the compressor 10 and a switch-off duration of the compressor 10, [0086] to fix a first duration during which the compressor 10 is switched on and a second duration during which the compressor 10 is switched off on the basis of the requirement variable, [0087] to switch on and to switch off the compressor 10 according to the first and second durations, [0088] to close the first shut-off valve 20 in connection with switching off the compressor 10, and [0089] to open the first shut-off valve 20 in connection with switching on the compressor 10.

[0090] The compressor 10 may be a single speed compress or controlled by the control system 26 to run at a constant speed during the first duration. That is, the electric motor 24 has only one operational speed and the control system 26 is adapted to switch on and off the electric motor 24. The control system 26 may include a start capacitor and/or a start relay in order to be able to start the compressor 10 with the high pressure maintained in the condenser 12, and at the outlet side of the compressor, due to the first shut-off valve 20 being closed during the second duration when the compressor 10 is switched off.

[0091] Alternatively, the compressor 10 may be a variable speed compressor controlled by the control system 26 to run at variable speed during the first duration. That is, the control system may either run the electric motor 24 at, at least, two different speeds during one first duration or alternatively, at a constant speed during one first duration and at a different constant speed during a following first duration. In the latter alternative, the requirement variable of the method may be specified to be maintained within a specified interval. If the requirement variable is outside the specified interval, the constant speed is increased or decreased, depending on whether the requirement variable is above or below the specified interval, in a following first duration. A variable speed compressor and its electric motor are adapted to be started against a high pressure difference between the condenser 12, i.e. the outset side of the compressor 10 and the evaporator 8, ie. inlet side of the compressor 10.

[0092] The compressor 10, single speed or variable speed, may be adapted to provide a cooling capacity of between 10-500 W according to ASHRAE LBP or HMBP standard (at 55 degrees Celsius condensing temperature and 23,3 degrees Celsius evaporating temperature). More specifically, in some applications the compressor 10 may be adapted to provide a cooling capacity of between 20-300 W according to ASHRAE LBP or HMBP standard. The first duration and the second duration may collectively have a length of between 1-100 minutes, i.e. the compressor cycle may have a length of 1-100 minutes. More specifically, the first duration and the second duration may collectively have a length of between 3-30 minutes.

[0093] FIG. 3 illustrates a portion of a refrigeration system 4 according to embodiments. According to these embodiments there is provided a solution which allows a compressor 10, such as a single speed compressor, to be started under low pressure difference conditions despite a high pressure prevailing in a condenser 12 arranged downstream of the compressor 10. The refrigeration system 4 comprises a valve arrangement 32 in a conduit 34 between the compressor 10 and the condenser 12. A by-pass conduit 36 extends between an outlet side of the compressor 10 and an inlet side of the compressor 10. The valve arrangement 32 comprises a check valve 38. A second shut-off valve 40 is arranged in the by-pass conduit 36. When the second shut-off valve 40 is open, any pressure difference between the inlet side and the outlet side of the compressor 10 is equalized to substantially the pressure prevailing at the inlet side of the compressor 10. The check valve 38 ensures that a high pressure in the condenser 10 cannot be equalized in an upstream direction from the condenser 10.

[0094] The second shut-off valve 40 is connected to a control system 26 of the refrigeration system 4. The control system 26 is adapted: [0095] to maintain the second shut-off valve 40 closed during a first duration when the compressor 10 is running, and [0096] to open the second shut-off valve 40 during a second duration to equalize a pressure difference between the outlet side and the inlet side of the compressor 10 during a second duration when the compressor 10 is not running.

[0097] Accordingly the method illustrated in FIG. 2 may further comprise: [0098] Equalizing 114 a pressure difference between the outlet side and the inlet side of the compressor 10 during the second duration. [0099] Opening 116 the second shut-off valve 40 during the second duration to achieve the said equalizing 114 the pressure difference between the outlet side and the inlet side of the compressor 10 during the second duration. [0100] Maintaining 118 the second shut-off valve 40 closed during the first duration.

[0101] FIG. 4 illustrates a portion of a refrigeration system 4 according to embodiments. Also these embodiments provide a solution which allows a compressor 10 to be started under low pressure difference conditions despite a high pressure prevailing in a condenser 12.

[0102] The refrigeration system 4 comprises a valve arrangement 32 in a conduit 34 between the compressor 10 and the condenser 12. A by-pass conduit 36 extends between an outlet side of the compressor 10 and an inlet side of the compressor 10. Via the by-pass conduit 36, any pressure difference between the inlet side and the outlet side of the compressor 10 may be equalized to substantially the pressure prevailing at the inlet side of the compressor 10. The valve arrangement 32 comprises a 3-way valve 42. The 3-way valve is connected to the by-pass conduit 36.

[0103] The 3-way valve is connected to a control system 26 of the refrigeration system 4. The control system 26 is adapted: [0104] to open a connection between the outlet side of the compressor 10 and the by-pass conduit 36 and to close a connection between the compressor 10 and the condenser 12, by means of the 3-way valve 42 during the second duration when the compressor 10 is not running to equalize pressure via the by-pass conduit 36, and [0105] to close the connection between the outlet side of the compressor 10 and the by-pass conduit 26 and to open the connection between the compressor 10 and the condenser 12, by means of the 3-way valve during the first duration when the compressor 10 is running.

[0106] Accordingly the method illustrated in FIG. 2 may comprise: [0107] Equalizing 114 a pressure difference between the outlet side and the inlet side of the compressor 10 during the second duration, the said equalizing 114 the pressure difference including: [0108] Opening 120 a connection between the outlet side of the compressor 10 and the by-pass conduit 36 and closing 122 a connection between the compressor 10 and the condenser 12 by means of the 3-way valve 42.

[0109] The method may further comprise: [0110] Closing 124 the connection between the outlet side of the compressor 10 and the by-pass conduit 36 and opening 126 the connection between the compressor 10 and the condenser 12 by means of the 3-way valve 42 during the first duration.

[0111] Thanks to the embodiments according to FIGS. 3 and 4, a constant speed compressor does not require any start capacitor or other means to permit starting despite a high pressure prevailing in the condenser 12. The embodiments of FIGS. 3 and 4 may be used in refrigeration systems 4 according to FIGS. 1 and 5.

[0112] FIG. 5 illustrates a refrigeration system 4 according to embodiments. The refrigeration system 4 comprises an evaporator 8, a compressor 10, a condenser 12, and an expansion arrangement 15. The expansion arrangement 15 comprises a first shut-off valve 20 or put differently, the first shut-off valve 20 forms part of the expansion arrangement 15. Accordingly, when the compressor 10 is running and liquid refrigerant evaporates in the evaporator 8, the first shut-off valve 20 acts as an expansion valve for liquid refrigerant. When the compressor 10 is not running the first shut-off valve 20 is closed to prevent cyclic losses in the refrigeration system 4. A control system 26 of the refrigeration system 4 controls inter alia the first shut-off valve 20.

[0113] A refrigeration system 4 according to embodiments may be operated according to a method according to embodiments for a period of time. Whereas during other periods of time the refrigeration system 4 may be operated according to a different method, e.g. if a difference between a set-point temperature and an actual temperature exceeds a threshold value.

[0114] Example embodiments and components described above may be combined as understood by a person skilled in the art. Accordingly, when herein reference is made to some components relating to the compressor, such as a start capacitor, the electric motor of the compressor is encompassed in the expression compressor.

[0115] Although the invention has been described with reference to example embodiments, many different alterations, modifications and the like will become apparent for those skilled in the art. For instance, the check valve 38 of the FIG. 3 embodiments may be arranged in the conduit extending between the evaporator 8 and the compressor 10 upstream of the by-pass conduit 36. Similarly, the 3-way valve 42 in the FIG. 4 embodiments may be arranged in the conduit extending between the evaporator 8 and the compressor 10 and be connected to the compressor inlet side of the by-pass conduit 36.

[0116] Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and the invention is not to be limited to the specific embodiments disclosed and that modifications to the disclosed embodiments, combinations of features of disclosed embodiments as well as other embodiments are intended to be included within the scope of the appended claims.

[0117] As used herein, the term comprising or comprises is open-ended, and includes one or more stated features, elements, steps, components or functions but does not preclude the presence or addition of one or more other features, elements, steps, components, functions or groups thereof.

[0118] As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.

[0119] As used herein, the common abbreviation e.g., which derives from the Latin phrase exempli gratia, may be used to introduce or specify a general example or examples of a previously mentioned item, and is not intended to be limiting of such item. If used herein, the common abbreviation i.e., which derives from the Latin phrase id est, may be used to specify a particular item from a more general recitation.

[0120] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0121] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0122] It will be understood that although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used top distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed herein could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.