Patent Application
20170159983
The present invention relates to a method of operating a refrigeration system. The invention further relates to a refrigerator comprising a compartment cooled by a refrigeration system.
A refrigeration system, as used in connection with cooled domestic and commercial foodstuff storage compartments comprises: an evaporator, a compressor, a condenser, and an expansion arrangement, such as a capillary tube, interconnected by conduits. Such cooled domestic and commercial foodstuff storage compartments may form part of above freezing point refrigerators or below freezing point refrigerators, the latter are sometimes referred to as freezers. Hereinafter, both types will be referred to as refrigerators.
A refrigerant circulates in the refrigeration system while the compressor runs, compressing the gaseous refrigerant coming from the evaporator. As the refrigerant circulates, the gaseous refrigerant is cooled and condenses to a liquid state in the condenser, which is arranged outside of the compartment. Thereafter, the liquid refrigerant is subjected to a pressure drop in the expansion arrangement and evaporates from the liquid state in the evaporator. The evaporator is arranged in thermal communication with the compartment. Thus, the compartment is cooled by the refrigerant.
A refrigeration system is designed to provide a specific coding capacity. The refrigeration system provides the specific cooling capacity when it reaches a steady “on” state after the compressor has been running for a while. The specific cooling capacity is higher than the long term cooling requirement of the compartment. Thus, the compressor is running during a first duration, an on-period, and not running during a second duration, an off-period. One compressor cycle during the operation of the refrigeration system is constituted by one on-period and one off-period. Accordingly, during operation the refrigeration system runs through many compressor cycles. The operation of the compressor and its cycle length is dependent of the temperature inside the compartment. Commonly used compressor control parameters are a maximum allowed temperature in the compartment, at which the compressor is started, and a minimum temperature, at which the compressor is stopped.
EP 727628 discloses a control device for controlling temperature in a refrigerator and a method of controlling the temperature in refrigerators. The purpose is to provide a control device and a method of controlling the temperature in refrigerators by means of which the cooling source may be controlled to minimize the energy consumption of the refrigerator. This is achieved by means of a control algorithm in which a requirement variable is formed. The requirement variable formed indicates a ratio of the switch-on duration (the above-mentioned on-period) of the cooling source to the switch-off duration (the above-mentioned off-period) of the cooling source. Furthermore, an actual temperature averaged over time is used as the actual temperature for forming a differential between a set-point temperature and an actual temperature.
During each compressor cycle, a refrigeration system is subjected to cyclic losses. The losses are due to: 1. Liquid refrigerant, instead of gaseous refrigerant, being extracted from the evaporator at the beginning of an on-period. 2. Gaseous refrigerant being pumped through the expansion arrangement in the form of a capillary tube before a liquid seal is formed at the beginning of the on-period. 3. Improperly charged condenser and evaporator before equilibrium has been established during the on-period. 4. Gaseous and liquid refrigerant entering the evaporator through the expansion arrangement during the off-period. Furthermore, a high start up current may be required depending on the type of compressor operation, which also may contribute to losses in systems comprising a refrigeration system.
In refrigeration systems running with long compressor cycle times, cyclic losses are negligible in comparison with the total energy consumption of the refrigeration system. However, in refrigeration systems running with short cycle times the cyclic losses may be responsible for a considerable portion of the total energy consumption of the refrigeration system. In refrigerators, lowering energy consumption has been a goal for years. For instance the EU Directive 92/75/EC establishes an energy consumption labeling scheme applicable inter alia for refrigerators. A good energy consumption rating is thus aspired by refrigerator manufacturers.
The control device and method of EP 727628 does not take account of cyclic losses in a relevant refrigeration system.
WO 2006/044787 is concerned with a pressure equalization system which solves a problem specific to HVAC (Heating Ventilation Air Conditioning) systems. In connection with the background it is stated that pressure tends to equalize between low pressure and high pressure sides when the compressor stops operating, and that in a refrigeration cycle energy is required at start up to create a high pressure in the compressor. In HVAC systems however, pressure does not equalize between the condenser and the evaporator (high pressure side and low pressure side of the refrigeration system) during the off-periods of the compressor. This creates a need for additional components, which enable a high pressure difference start-up of the compressor. The pressure equalization system of WO 2006/044787 comprises a bleed port interconnecting the high pressure side of the compressor with the low pressure side of the compressor (outlet of compressor with inlet of compressor). Via the bleed port the pressure level in the compressor may be equalized to the low pressure level. Thus, the compressor may be started under low pressure difference conditions. Accordingly, the electrical system driving the compressor does not require any costly start capacitor or start relay.
There exists a need to decrease energy consumption in some types of refrigeration systems.
Accordingly, an object of the present invention is to further decrease energy consumption in refrigeration systems.
According to an aspect, the object is achieved by a method of operating a refrigeration system, wherein the refrigeration system comprises:
Since in a method, which provides an optimal refrigeration cycle length from an energy consumption point of view, further a first shut-off valve is closed when the compressor is switched off and not opened again until the compressor is switched on again to maintain a pressure difference between the condenser and the evaporator of the refrigeration system when the compressor is not running, cyclic losses in the refrigeration system as laid out above under points 1-4 are avoided, at least to a large extent. As a result, the above mentioned object is achieved.
The refrigeration system and compartment may form part of a refrigerator, such as a domestic or commercial refrigerator for foodstuffs. The averaged temperature may for instance be calculated over a fixed period of time or over a number of compressor cycles. The feature “ratio between a switch-on duration of the compressor and a switch-off duration of the compressor” encompasses both alternative calculations of the ratio, i.e. switch-on duration in relation to switch-off duration, as well as switch-off duration in relation to switch-on duration of the compressor. The requirement variable in the form of a ratio between a switch-on duration and a switch-off duration of the compressor may be applied to one compressor cycle length to establish the First duration and the second duration. The compressor cycle length may be fixed or may be set iteratively, e.g. to maintain a number of compressor cycles per time unit within a specified interval, such as e.g. 1-8 cycles/hour. More specifically, the conduit in which the first shut-off valve is arranged is the conduit in which also the expansion arrangement is arranged.
According to embodiments the refrigeration system may comprise the compartment and the compartment may be adapted for domestic foodstuff storing. In this manner the refrigeration system and the compartment may form part of a domestic refrigerator.
According to embodiments, the compressor may be a single speed compressor controlled by a control system to run at a constant speed during the first duration. Thanks to the method, a comparatively simple compressor may be operated in an economic manner. The compressor, and more specifically the electric motor driving the compressor, may be provided with a start capacitor and/or a start relay and/or other means to start under high pressure difference conditions prevailing between an inlet side and an outlet side of the compressor due to the first shut-off valve being closed during the second duration.
According to embodiments, the refrigeration system further may comprise a valve arrangement in a conduit between the compressor and the condenser, and a by-pass conduit extending between an outlet side of the compressor and an inlet side of the compressor. The method further may comprise:
According to embodiments, the valve arrangement may comprise a check valve and the refrigeration system further may comprise a second shut-off valve arranged in the by-pass conduit. The method further may comprise:
According to embodiments, the valve arrangement may comprise a 3-way valve, the 3-way valve being connected to the by-pass conduit. The said equalizing the pressure difference may include:
According to embodiments, the expansion arrangement may comprise a capillary tube.
According to embodiments, the first shut-off valve may form part of the expansion arrangement.
According to embodiments, the first duration and the second duration may collectively have a length of between 1-100 minutes. That is, the compressor cycle may have said length. According to further embodiments, the first duration and the second duration may collectively have a length of between 3-30 minutes. Generally, short total first and second durations, i.e. a short compressor cycle length, is advantageous from an energy consumption point of view. Further, a short compressor cycle length allows for a more even air temperature inside a compartment cooled by the evaporator, Furthermore, a higher humidity of air inside the compartment may be achieved.
According to embodiments, the compressor may be adapted to provide a cooling capacity of between 10-500 W according to ASHRAE LBP or HMBP standard. According to further embodiments, the compressor may be adapted to provide a cooling capacity of between 20-300 W according to ASHRAE LBP or HMBP standard. Such a compressor may provide sufficient cooling capacity for most domestic refrigerator applications.
According to a further aspect, the above-mentioned object is further achieved by a refrigerator comprising a compartment cooled by a refrigeration system controlled by a control system, wherein the refrigeration system comprises:
Embodiments mentioned above in relation to the method and the refrigeration system of the method, may be embodied in a refrigerator.
According to embodiments, the compressor may be a single speed compressor controlled by the control system to run at a constant speed during the first duration.
According to embodiments, the refrigeration system further may comprise a valve arrangement in a conduit between the compressor and the condenser, and a by-pass conduit extending between an outlet side of the compressor and an inlet side of the compressor.
According to embodiments, the valve arrangement may comprise a check valve and the refrigeration system further may comprise a second shut-off valve arranged in the by-pass conduit, and wherein the control system may be adapted:
According to embodiments, the valve arrangement may comprise a 3-way valve, the 3-way valve being connected to the by-pass conduit. The control system may be adapted:
According to embodiments, the compressor alternatively may be a variable speed compressor controlled by the control system to run at variable speed during the first duration. In this manner a compressor may be provided which may be started at high pressure difference conditions.
According to embodiments, the refrigeration system may comprise a filter arranged in a conduit between the condenser and the expansion arrangement.
According to embodiments, the first shut-off valve may be arranged in a conduit between the filter and the expansion arrangement. In this manner it may be ensured that when the first shut-off valve is opened in connection with switching on the compressor, liquid refrigerant will enter the expansion arrangement.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following detailed description. Those skilled in the art will realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention, as defined by the appended claims.
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:
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.
Well-known functions or constructions will not necessarily be described in detail for brevity and/or clarity.
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.
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.
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.
The refrigeration system may be a refrigeration system 4 as described in connection with
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.
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.
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.
With reference to the method disclosed in connection with
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.
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.
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.
The second shut-off valve 40 is connected to a control system 26 of the refrigeration system 4. The control system 26 is adapted:
Accordingly the method illustrated in
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.
The 3-way valve is connected to a control system 26 of the refrigeration system 4. The control system 26 is adapted:
Accordingly the method illustrated in
The method may further comprise:
Thanks to the embodiments according to
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.
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”.
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
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.
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.
As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
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.
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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 14347053 | Mar 2014 | US |
| Child | 15434931 | US |
