EP2722619A1

EP2722619A1 - No-frost refrigerator

Info

Publication number: EP2722619A1
Application number: EP13189431.3A
Authority: EP
Inventors: Alessandro Pizzutti; Giorgio Sabatini
Original assignee: Indesit Co SpA
Current assignee: Whirlpool EMEA SpA
Priority date: 2012-10-19
Filing date: 2013-10-18
Publication date: 2014-04-23
Also published as: ITTO20120923A1

Abstract

The present invention relates to a refrigerating appliance (1), such as a "no-frost" refrigerator, comprising at least one refrigerated cell (2), cooling means comprising at least one evaporator (6), a first duct (7) that puts the cell (2) in fluidic communication with an external surface of the evaporator (6) for feeding air to be cooled, and further comprising a second duct (8) that puts the external surface of the evaporator (6) in fluidic communication with the cell (2) for feeding cooled air, and further comprising air circulation means (10) for circulating air within the first duct (7) and the second duct (8), further comprising defrosting means (6b) adapted to remove ice and/or frost accumulated on the external surface of the evaporator (6), and control means (14) adapted to adjust the operation of the defrosting means (6b); it further comprises a temperature sensor (11) and a humidity sensor (12), which are adapted to measure the temperature and humidity, respectively, of the air flowing in the first duct (7) and are operationally connected to the control means (14), so that the operation of the defrosting means (6b) can be adjusted depending on the readings of the temperature sensor (11) and humidity sensor (12).

Description

[TECHNICAL FIELD]

The present invention relates to a refrigerating appliance, in particular for household use. The present invention is applicable, in particular, to refrigerating appliances of the "no-frost" type.

[PRIOR ART]

"No-frost" refrigerating appliances for household use have now become widespread, which are refrigerating appliances wherein refrigeration of one or more cells adapted to contain foods occurs through circulation of cold air. In no-frost refrigerating appliances, the evaporator is positioned in a volume which is separate from the cell(s), and circulation of cooled air in contact with the evaporator occurs through suitable circulation means, typically comprising ducts and one or more fans. In this way, it is possible to prevent the formation of ice or frost on the walls of the food-containing cell.
One example of a no-frost refrigerating appliance is described in document KR20100009676A published on 29-1-2010, filed on 21-7-2008 under application number KR20080070415 . Said document relates to a refrigerating appliance comprising a cell, an evaporator and two humidity sensors, one measuring the air directed towards the evaporator and the other measuring the air discharged downstream of the evaporator. The control means of the described refrigerating appliance operate on the basis of the humidity variation between the two readings, controlling the evaporator defrosting operation accordingly.
However, the above-described solution suffers from a number of drawbacks: in general, the readings of humidity sensors are particularly subject to disturbances; therefore, when controlling the defrosting operation as proposed by the above-mentioned document, i.e. on the basis of the humidity variation measured by the two sensors, the latter may be affected by disturbances and lead to the risk that the control of the evaporator defrosting operation will be neither optimal nor efficient.

[OBJECTS AND SUMMARY OF THE INVENTION]

The object of the present invention is to provide a refrigerating appliance capable of solving some of the problems suffered by the prior art.
It is a particular object of the present invention to provide a refrigerating appliance which can automatically and efficiently control the evaporator defrosting operation.
It is another object of the present invention to provide a refrigerating appliance wherein the sensors of the control means are less exposed to disturbance sources which might jeopardize the proper operation of the appliance.
It is a further object of the present invention to provide a refrigerating appliance having a simple and robust construction.
It is yet another object of the present invention to provide a refrigerating appliance through which it is possible to reduce the waste of electricity while maximizing the efficiency of operation.
These and other objects are achieved through a refrigerating appliance as set out in the appended claims, which are an integral part of the present description.
One idea at the basis of the present invention is to provide a refrigerating appliance comprising at least one refrigerated cell, cooling means comprising at least one evaporator, at least one first duct that puts the cell in fluidic communication with an external surface of the evaporator for feeding air to be cooled from the cell to the evaporator, and further comprising a second duct that puts the external surface of the evaporator in fluidic communication with the cell for feeding cooled air from the evaporator to the cell, and further comprising air circulation means for circulating air within the first duct and the second duct. The refrigerating appliance further comprises defrosting means adapted to remove ice and/ or frost accumulated on the external surface of the evaporator, and control means for controlling the operation thereof. The refrigerating appliance further comprises a temperature sensor and a humidity sensor, which are adapted to measure the temperature and humidity, respectively, of the air flowing in the first duct, and which are operationally connected to the control means, so that the operation of the defrosting means can be adjusted depending on the readings of the temperature sensor and humidity sensor.
In this way, it is possible to estimate with better accuracy the quantity of water which is sent in the form of moisture to the evaporator and then freezes and/or frosts thereon. This allows to optimize the execution of the evaporator defrosting operation. In fact, the readings of the sensors will thus be less affected by external disturbance factors. Moreover, this solution allows to use the temperature sensor in order to estimate the cell temperature, i.e. the temperature at which foods are being preserved, which represents an important operating parameter of the refrigerating appliance. Furthermore, the control means can operate on the basis of easily measurable parameters, and hence of properly conditioned measurements.
Preferably, the control means comprise computing means adapted to estimate the quantity of ice and/or frost deposited on the surface of the evaporator, through acquisition, at subsequent time instants, of the readings of the temperature and humidity sensors, and through a parameter related to the volumetric flow rate of the air within the duct.
Preferably, the parameter that estimates the volumetric flow rate depends on the cross-section of the duct and on the pressure head of the air circulation means that allow recirculation of cooled air from the cell to the evaporator. In a preferred embodiment, the parameter that estimates the volumetric flow rate is further computed on the basis of the time of operation of the air circulation means, which may comprise a fan and/or a damper.
Preferably, the control means are adapted to turn on the defrosting means based on the estimate provided by the computing means, and to turn off the defrosting means after a predetermined time.
Preferably, the control means are further adapted to turn on/off the defrosting means, the operating time of the defrosting means being controlled based on the estimate provided by the computing means.
Said refrigerating appliance, therefore, reduces the waste of electricity and keeps the evaporator frost-free to ensure the utmost cooling efficiency, while keeping the power consumption of the defrosting means to a minimum.
Further advantageous and particular aspects will become apparent from the following detailed description and from the dependent claims.

[BRIEF DESCRIPTION OF THE DRAWINGS]

Some preferred and advantageous embodiments will now be described by way of non-limiting example with reference to the annexed drawings, wherein:

Figure 1 schematically shows one embodiment of a refrigerating appliance according to the present invention. The drawings show different aspects and embodiments of the present invention and, where appropriate, similar structures, components, materials and/or elements in the various drawings are designated by the same reference numerals.

[DETAILED DESCRIPTION OF THE INVENTION]

Figure 1 schematically shows a cross-section of a refrigerating appliance 1 of the "no-frost" type according to the present invention.
The refrigerating appliance 1 comprises a cell 2 adapted to contain fresh foods, accessible through a door 3. The refrigerating appliance 1 further comprises a cell 2b adapted to contain frozen foods, accessible through a respective door 3b. Therefore, the embodiment described herein relates to a type of refrigerating appliance which is commonly referred to as "double-door".
The cell 2 comprises a plurality of shelves 4 or drawers 5 adapted to contain the objects to be refrigerated, typically fresh foods.
The refrigerating appliance 1 further comprises known cooling means, of which only a few components specifically involved in the present invention will be illustrated in detail herein. Wherever no explicit reference to particular elements is made, the refrigerating appliance 1 will have to be understood as comprising all known means which are necessary for the proper operation of the appliance itself, in accordance with the state of the art.
The refrigerating appliance 1 comprises an evaporator 6 in which a refrigerated fluid circulates, the evaporator 6 having such a shape and characteristics as to interact with an air flow lapping its external surfaces for the purpose of cooling the air, which in turn will cool the cell 2.
The evaporator 6 is connected to further elements (not shown in Figure 1) that create a refrigeration cycle in accordance with the teachings of the prior art.
The air is taken from the inside of the cell 2 and is directed, through a first duct 7, towards the evaporator 6. While passing through the evaporator 6, the air is cooled by contact with the external surfaces thereof, and then re-enters the cell 2 via a second duct 8, which comprises a respective plurality of apertures 9 through which cooled air exits and cools the foods in the cell. Various ducting solutions are available in the art which may differ from the one shown herein, e.g. comprising a plurality of ducts 7 and/or 8, depending on specific design choices.
The path followed by the air in the ducts is shown by arrows in Figure 1. The air is moved in the ducts by suitable air circulation means, which typically comprise at least one fan 10 that gives the air flow a sufficient pressure head for it to follow the path in the ducts.
In this embodiment of the refrigerating appliance 1, the air circulation means 10 are adapted to circulate cooled air also within the cell 2b for frozen foods, which is separated by a bulkhead having an aperture 9b and also comprising a further (separate) duct 7b for feeding air to be cooled, coming from the cell 2b, towards the evaporator 6.
In this preferred embodiment, the refrigerating appliance comprises a selective air circulation element 10b, typically referred to as "damper". Said element 10b is adapted to adjust, by reducing or preventing it, the air flow within the duct 8.
The presence of the damper 10b is therefore particularly appropriate when combined with the technical features of a refrigerating appliance such as the refrigerating appliance 1 described herein, which comprises two cells 2 and 2b to be selectively cooled to different temperatures by means of a single evaporator 6.
The damper 10b allows to adjust and/or partialize the flow of cooled air delivered to the cell 2 for fresh foods, thereby ensuring an effective operation of both the refrigerator and freezer parts of the refrigerating appliance. The damper 10b may operate in accordance with the teachings of the prior art, typically based on the temperature detected in the cell 2.
In general, a refrigerator like the one described above is called "no-frost" because the configuration of the evaporator 6, and in particular of the ducts 7 and 8, along with the duct 7b and the aperture 9b, prevents the humidity which is present inside the cell 2 from freezing on the shelves 4, in the drawers 5 or on the walls of the cell 2 itself.
Air-borne humidity will still tend to condensate and freeze instantaneously, thus forming a layer of frost on the external surfaces of the evaporator 6 itself, to which it is sent via the duct 7; in operating conditions, in fact, said surfaces have a temperature which is typically in the range of -30°C to -35°C, also when the refrigerating appliance 1 is operating as a freezer.
Since the air that laps the external surfaces of the evaporator 6 runs into conditions that cause it to almost completely lose its moisture content, the air that recirculates in the duct 8 when the damper 10b is open and exits through the outlets 9 is dry air, i.e. it contains no residual water vapour or only a negligible quantity thereof. In a no-frost refrigerator, as aforesaid, the moisture content of the air condenses and freezes on the evaporator 6. The layer of ice and/or frost accumulates on the evaporator 6 and grows thicker and thicker, because additional ambient humidity enters the cell 2 every time the door 3 is opened. In the long run, after many hours of operation, the quantity of ice and/or frost accumulated on the evaporator 6 will become considerable, thus worsening the thermal exchange between the evaporator 6 itself and the air in the duct 7.
Since the efficiency of the evaporator decreases due to the accumulated ice and/or frost, leading to reduced performance of the refrigerating appliance 1, it is necessary to provide suitable defrosting means 6b to remove the ice and/or frost from the external surfaces of the evaporator.
The defrosting means 6b typically comprise a heatable element such as an electric resistor, and preferably comprise a suitable hydraulic circuit (not shown) allowing the thawed ice and/or frost previously present on the evaporator to be drained away as water.
The operation of the defrosting means 6b is appropriately controlled in a way that will be described more in detail below. In general, it is appropriate to provide that, when the defrosting means 6b are in operation, e.g. heating the evaporator 6, the air circulation means 10 are inactive, so that no air will flow through the ducts and the cells 2 or 2b, which air would otherwise be heated, not cooled.
In order to improve the control of the operation of the defrosting means 6b, the refrigerating appliance 1 comprises suitable control means and sensors. In particular, the refrigerating appliance 1 comprises a temperature sensor 11 and a humidity sensor 12, which are adapted to measure the temperature and the relative humidity, respectively, of the air flowing in the first duct 7.
In particular, the humidity sensor 12 and the temperature sensor 11 are positioned in that portion of the duct 7 which is closest to the cell 2.
In a preferred embodiment, the temperature sensor 11 and the humidity sensor 12 are integrated into a single sensing device, so as to reduce their dimensions and cost.
In the embodiment of Fig. 1, the refrigerating appliance 1 comprises a separation grid 13 between the cell 2 and the first duct 7, and the humidity sensor 12 and the temperature sensor 11 are positioned immediately downstream of the separation grid 13; in fact, this is the most advantageous position for an accurate reading of the properties of the air flow.
The temperature sensor 11 is also adapted to measure a temperature representative of the cell 2 as a whole, for monitoring the operation of the refrigerating appliance 1. In fact, said temperature sensor 11 can detect, in particular also when the air circulation means 10 are inactive, any temperature variations due to the placing of warm foods into the cell 2 or to the opening of the door 3.
Advantageously, thanks to the presence and position of the temperature sensor 11, it is possible to avoid using any further temperature sensors in the cell 2, thus reducing the cost and simplifying the construction of the refrigerating appliance 1. This arrangement of the temperature sensor also offers the advantage that a forced air flow is obtained along the duct 7; in this way, the temperature sensor 11 is less susceptible to the placing of foods into the cell 2, and the air flow near the temperature sensor 11 cannot be hindered by bulky food or be affected by the local temperature of the foods themselves, thus improving the reading by the temperature sensor 11. The temperature sensor 11 can therefore be used for controlling the operation of the cooling means of the appliance.
The control means of the refrigerating appliance 1 further comprise a plurality of sensors, control units and electronic devices according to the prior art, which for brevity's sake will not be described in detail below.
It must be pointed out that, in the refrigerating appliance 1, the control means 14 are adapted to adjust the operation of the defrosting means 6b, to which they are operationally connected. For example, the control means 14 are adapted to selectively supply power to the electric resistors of the defrosting means 6b, thereby causing them to only heat up when necessary, in accordance with the particular logic of the control means 14.
The temperature sensor 11 and the humidity sensor 12 are operationally connected to the control means 14 via suitable electric and/or electronic connections of a known nature (not shown in the drawing), whether analog or digital.
The control means 14 utilize the readings taken by said sensors 11 and 12 to adjust the operation of the defrosting means 6b.
In particular, the control means 14 comprise computing means, such as a processor, which can estimate the efficiency of the evaporator 6, which is essentially correlated to the quantity of ice and/or frost deposited on the surface thereof, by acquiring a plurality of readings via the temperature sensor 11 and the humidity sensor 12; such readings are taken at subsequent time instants during the operation of the refrigerating appliance 1.
In order to estimate the quantity of ice and/or frost formed on the evaporator 6 for controlling the activation of the defrosting means 6b, the computing means use a parameter that estimates the volumetric flow rate of the air within the first duct 7 in combination with the relative humidity and temperature information to estimate the mass flow rate of the water borne by the air flowing in the duct 7 and directed towards the evaporator 6.
In other words, since the sensors 11 and 12 measure the temperature and humidity of the air in the duct 7, it is possible to derive the moisture/water/steam content thereof; the volumetric flow rate, in particular the average volumetric flow rate, of the air within the duct 7 being known instant by instant, it is possible to estimate the mass flow rate of the water directed towards the evaporator 6.
The instantaneous volumetric flow rate essentially depends on the cross-section of the duct 7 and on the pressure head provided by the air circulation means 10, in accordance with known criteria of fluid dynamics. This can be complemented by the intervention of the damper 10b, when it throttles the duct 8 that feeds cooled air back into the cell 2.
The computing means are therefore adapted to estimate the average volumetric flow rate in the duct 7 within a time interval by taking into account the above-mentioned information.
Assuming that all the mass of water vapour being transported by the air flow and coming in contact with the surfaces of the evaporator 6 will freeze thereon, and knowing the mass flow rate of water vapour being fed to the evaporator, the computing means can estimate the evolution over time of the deposit of ice and/or frost on the evaporator 6.
The temperature-dependent characteristics of the humid air (preferably in the range of -5°C to +20°C, with relative humidity between 0% and 100%) are preferably stored into a suitable memory of the control means 14, thus representing a psychrometric chart according to the prior art, which the computing means will use in operation to make the calculations necessary for determining the corresponding quantity of frost. In this manner, the computing means can calculate the time necessary for a predetermined quantity of ice and/or frost to deposit on the evaporator 6, so that the defrosting means 6b can be turned on for a suitable time that will ensure the removal of said predetermined quantity of ice and/or frost.
In particular, since the air circulation means 10 and the damper 10b typically operate intermittently, the average volumetric flow rate is computed on the basis of the operating time of the air circulation means 10 and/or of the damper 10b. The air circulation means 10, for example, will be activated when the cooling circuit that cools the evaporator comes on. The damper 10b, instead, as aforesaid, will be turned on in accordance with specific control logics of the refrigerating appliance.
In one embodiment, therefore, the control means 14 will turn on the defrosting means 6b when the estimate of the quantity of ice and/or frost made by the computing means reaches a predetermined value (e.g. when the weight of the ice and/or frost reaches a value of 280 g); the control means 14 will then turn off the defrosting means 6b after a predetermined time, e.g. a time that allows the electric resistors to thaw all the ice and/or frost which is present on the evaporator 6. In another embodiment, the control means 15 are further adapted to turn on the defrosting means 6b after a predetermined time, without necessarily waiting for a predetermined quantity of ice and/or frost to deposit on the evaporator 6. In this case, the control means 14 will adjust the operation of the defrosting means 6b by controlling their on time, which will be computed by the computing means based on the estimate of the quantity of ice and/or frost deposited on the evaporator, in accordance with selected criteria.
In brief, it is conceivable that the defrosting means 6b are turned on for a predetermined time when a limit quantity of ice and/or frost is reached, and also that the defrosting means 6b are turned on for a shorter time at predetermined intervals, e.g. 24 hours after the last defrosting operation, in order to appropriately thaw the ice and/or frost deposit on the evaporator 6. In this way, the evaporator 6 can always be kept at its maximum efficiency, ensuring an optimal cooling of the refrigerator and reducing the waste of electricity.
In the light of the above description of some preferred and advantageous embodiments of the present invention, it will be apparent to the man skilled in the art that the invention may be subject to further modifications and variations.
For example, the present invention has been described herein with reference to a refrigerating appliance such as a double-door refrigerator. It is clear that the teachings of the present invention can also be adapted, through appropriate technical changes, to single-cell refrigerators or combined refrigerators comprising cells for frozen foods and/or other types of cells for preserving any kind of contents.
It is also apparent that the teachings of the present invention are also applicable, through a system similar to the one described herein, to the cell for frozen foods 2b and to the duct 7b, by implementing suitable technical measures which will not be described herein for the sake of brevity, and which are within the grasp of the man skilled in the art in the light of the present description.

Claims

A refrigerating appliance (1) comprising at least one refrigerated cell (2), cooling means comprising at least one evaporator (6), at least one first duct (7) that puts said cell (2) in fluidic communication with an external surface of said evaporator (6) for feeding air to be cooled from said cell (2) to said evaporator (6), and further comprising at least one second duct (8) that puts said external surface of said evaporator (6) in fluidic communication with said at least one cell (2) for feeding cooled air from said evaporator (6) to said cell (2), and further comprising air circulation means (10) for circulating air within said first duct (7) and said second duct (8), further comprising defrosting means (6b) adapted to remove ice and/or frost accumulated on said external surface of said at least one evaporator (6), and control means (14) adapted to adjust the operation of said defrosting means (6b), characterized in that said refrigerating appliance (1) further comprises a temperature sensor (11) and a humidity sensor (12), wherein said temperature sensor (11) and said humidity sensor (12) are adapted to measure the temperature and humidity, respectively, of the air flowing in said first duct (7), and wherein said temperature sensor (11) and said humidity sensor (12) are operationally connected to said control means (14), so that the operation of said defrosting means (6b) can be adjusted depending on the readings of said temperature sensor (11) and humidity sensor (12).
A refrigerating appliance according to claim 1, wherein said control means (14) comprise computing means adapted to estimate a quantity of ice and/or frost deposited on said surface of said at least one evaporator (6), wherein said computing means are adapted to acquire a plurality of said readings of said temperature sensor (11) and humidity sensor (12) taken at subsequent time instants, and are further adapted to acquire an estimate of an air volumetric flow rate parameter within said first duct (7).
A refrigerating appliance according to claim 2, wherein said volumetric flow rate parameter depends on the cross-section of said first duct (7) and on the pressure head provided by said air circulation means (10).
A refrigerating appliance according to claim 3, wherein said volumetric flow rate parameter further depends on the operation of a selective air circulation element, such as a damper (10b).
A refrigerating appliance according to claim 3 or 4, wherein said average volumetric flow rate parameter is further computed based on the operating time of said air circulation means (10).
A refrigerating appliance according to any one of claims 1 to 5, wherein said control means (14) are adapted to turn on said defrosting means (6b) based on said estimate of said quantity of ice and/or frost made by said computing means, and are further adapted to turn off said defrosting means (6b) after a predetermined time.
A refrigerating appliance according to any one of claims 1 to 6, wherein said control means (14) are further adapted to turn on said defrosting means (6b) at a predetermined time instant, and are further adapted to turn off said defrosting means (6b) based on said estimate of said quantity of ice and/or frost computed by said computing means.
A refrigerating appliance according to any one of claims 1 to 7, wherein said first duct (7) comprises a portion proximal to said cell, and wherein said humidity sensor (12) and said temperature sensor (11) are positioned in said portion proximal to said cell, preferably downstream of a separation grid (13) located between said cell (2) and said first duct (7).
A refrigerating appliance according to claim 8, wherein said temperature sensor (11) and said humidity sensor (12) are integrated into a single sensing device.
A refrigerating appliance according to any one of claims 1 to 9, further comprising means for controlling the operation of said cooling means (6) based on at least one reading of said temperature sensor (11).