RU2380627C2 - Cooling unit with adaptive automatic defrosting system - Google Patents

Abstract

FIELD: heating systems.

SUBSTANCE: cooling unit includes heat-insulated housing (1) enveloping cooling chamber (2), evaporator (7) installed in air channel (4, 5) interconnected with cooling chamber (2), heating device (8) for heating evaporator (7) and control diagram (10) to control operation of heating device (8). Control diagram (10) is connected to signal transmitting measuring device installed in air channel (4, 5) and characterising air flow passing through channel (4, 5), and is provided with possibility of switching on heater (8) when measured air flow decreases below some limit value. Measuring device has two temperature sensors installed in various proximity as to heat to heat source or to heat flux sink, or to air in channel (4, 5). Control diagram (10) has the possibility of determining air flow decreased below limit flow value when difference of temperatures measured with two sensors is beyond limit temperature difference value.

EFFECT: simplifying and improving cooling unit reliability.

5 cl, 5 dwg

Description

Technical field

The present invention relates to a refrigerating apparatus with an automatically defrosting evaporator and a defrosting method for it.

State of the art

In the so-called refrigerators such as No Frost or Frost Free, i.e. without freezing frost and ice on the evaporator, the evaporator, designed to cool the refrigerated compartment filled with refrigerated products inside the heat-insulating casing, is located in the chamber, which is separated from the refrigeration compartment and communicates with it with openings for air passage. This chamber together with the openings for the passage of air forms a channel through which air circulates, being cooled by the evaporator and returning to the refrigerator compartment.

Placing the evaporator in a separate chamber allows heating and thereby thawing the evaporator when a critical mass of ice builds up on it, turning off the air circulation between the evaporation chamber and the refrigeration compartment at that time so that the refrigeration compartment with the refrigerated products inside it does not heat up.

In order for the operation of such a refrigeration apparatus to be economical, it is important that the evaporator is thawed reliably when the mass of ice on the evaporator exceeds a critical value, since ice isolates the evaporator from the surrounding chamber and this degrades the cooling efficiency. The design of such a refrigeration apparatus usually does not allow the user to look into the evaporation chamber to check for ice and decide whether thawing is required or not. Therefore, automatic defrost control is required.

Generally speaking, it would be desirable to be able to directly measure the thickness of the ice layer on the evaporator and, on this basis, automatically decide whether thawing is required or not. However, sensors that can directly measure the thickness of the ice layer on the evaporator are expensive and their service life is much shorter than that of other components of conventional refrigeration units, so their use in a refrigeration unit would significantly increase its need for repairs.

For this reason, most modern No Frost refrigeration units use time-controlled defrosting, when the control system of the refrigeration unit starts the defrosting process at fixed intervals. Although this method is reliable and cheap, however, it has the disadvantage of being unable to adapt to the various climatic conditions under which the refrigeration apparatus is operated. This means that the “proportionate” average interval between two defrosts can easily turn out to be too long if the unit is operated in a warm environment, when a large amount of moisture is introduced into the refrigerator compartment each time the door is opened, and as a result, the ice layer on the evaporator grows rapidly. At the same time, in the case of operation of the refrigeration apparatus in a cold environment with a small amount of moisture introduced, a longer period than the established one could increase the efficiency of the refrigeration apparatus. In addition, this method does not take into account the fact that the amount of moisture introduced depends not only on the duration of the refrigerator, but also on the number of door openings, and on the nature of the products contained in the device.

Disclosure of invention

The objective of the invention is to create a refrigeration apparatus that allows you to reliably estimate the amount of ice that has grown on the evaporator with simple and reliable means, and a method that provides reproducible thawing whenever the amount of ice on the evaporator reaches a certain value.

This problem is solved by a refrigerating apparatus with the features of paragraph 1 of the claims and a method with the characteristics of paragraph 10.

The invention uses the fact that the free section of the air channel in which the evaporator is installed is limited and tapers as the amount of ice deposited on the evaporator increases. By measuring the change in the flow rate of air passing through the channel caused by this, we can indirectly conclude about the amount of ice and, therefore, the need for thawing.

Various methods can be used to measure the air flow through the channel. The simplest, probably, is to install in the channel some body, driven by the flow of air in the channel, and to adapt a sensor to this body to measure movement. When the air flow in the channel decreases so that the speed becomes less than the specified limit value, this will mean that thawing is required.

Instead of a movable element, an elastic element can be installed in the air channel, which will be statically deflected by the air flow, and measure this deviation by the sensor. In this case, thawing will be deemed necessary when the deviation of the elastic element becomes less than a predetermined limit value.

Another possibility of measuring air flow is to use the Bernoulli effect, i.e. the fact that hydrostatic pressure in a moving medium is less than in a motionless one. So that in this case the measurement signal is as large as possible, a restriction in which the flow rate will be especially high can be provided in the air channel, and a pressure sensor can be installed near this restriction.

Another possibility is to use a temperature gradient dependent on the air flow in the channel. This requires two temperature sensors installed in different proximity to the heat source or to the heat sink, or to the air in the channel. The smaller the air flow in the channel causing temperature equalization, the greater the temperature difference between the two sensors. As a result, a decrease in air flow to a critical level will be recorded when the temperature difference measured by the two sensors exceeds the limit value.

As a heat source for this embodiment of the invention, an electrically heated wire, known for its use in the automotive industry in devices for measuring air flow, can be used. The heat power released by such a wire can be so small that it will not have a noticeable effect on the energy balance of the refrigeration unit. However, it is preferable that the evaporator located in the channel itself be used as a heat sink.

In order to obtain the largest possible temperature difference, the first of the temperature sensors is preferably mounted directly on the evaporator.

It is especially advantageous to install this temperature sensor on that part of the evaporator which may be iced so that the insulating layer of ice, which, as appropriate, covers the temperature sensor, would further increase the temperature difference measured by the two sensors as the layer thickness increases.

The second temperature sensor is preferably installed at the outlet of the channel.

Brief List of Drawings

Further features and advantages of the invention result from the following description of exemplary embodiments with reference to the accompanying drawings. On them are presented:

Figure 1 is a schematic sectional view of a refrigeration apparatus according to a first embodiment of the invention;

Figure 2 - detail of the air channel according to the second embodiment of the invention;

Figure 3 - detail of the air channel according to the third embodiment of the invention;

4 is a device for measuring air flow according to a fourth embodiment of the invention; and

5 is a partial sectional view of the housing of a refrigeration apparatus according to a fifth embodiment of the invention.

The implementation of the invention

Figure 1 shows in a highly schematic form a No Frost type refrigeration apparatus according to a first embodiment of the invention. The refrigeration apparatus has a thermally insulating body 1 made in the usual way, in which a refrigerating chamber 2 is located for accommodating the cooled products and an evaporation chamber 5 is separated from the refrigerating chamber 2 by a partition 3 and communicates with the refrigerating chamber 2 through openings 4 in the partition 3. In the evaporation chamber 5 there is a plate the evaporator 7, into which the refrigerant is supplied from the refrigeration machine 6, and the defrosting heater 8, which is in close contact with the evaporator.

The evaporation chamber 5, together with the openings 4, is also called the air channel. The control circuit 10 controls the operation of the chiller 6 and the fan 11 installed at the upper hole 4, depending on the measurement signal from the temperature sensor (not shown) installed in the chiller 2. The chiller 6 and fan 11 can be turned on and off at the same time. However, it is preferable that the fan 11 is turned on and off with some delay relative to the refrigerating machine 6, in order to first allow the evaporator 7 to cool before the air circulation starts, and to use the residual cold of the evaporator 7 for some time after turning off the refrigerating machine 6.

An impeller 12 is installed in the lower hole 4, which is driven by a stream of air created by the fan 11, and the rotation of which is measured by a rotation sensor 13 connected to the control circuit 10. Based on the signals from the rotation sensor 13, the control circuit can determine the speed of rotation of the impeller 12 and thereby the amount of air flow in the channel. When this rotation speed drops below the set limit value, this indicates that the free cross section of the evaporation chamber 5 has noticeably narrowed due to the formation of ice on the evaporator 7, and thawing is required.

For thawing, the control circuit 10 through the switch 9 supplies the heater 8 for a fixed period of time with a heating current. This time period is chosen so that the thermal energy released during this period by the heater 8 is sufficient to completely thaw the ice cover on the evaporator. Since the thickness of the ice sheet at which the control circuit 10 includes a thawing process is always basically the same, adaptive regulation of the thawing time is not required.

In the case of jamming of the impeller 12, this can be mistakenly perceived as the need to start the defrosting process, and it will be started. The probability of jamming can be reduced if each time the fan 11 is turned on, it is briefly started at a higher rotation speed than its continuous rotation speed, so that the air flow at the impeller 12 is sufficient to bring it into rotation. It is also conceivable that the control circuit 10 could distinguish a sharp drop in the speed of the impeller 12 from a gradual decrease in speed and in the first case, briefly switch the fan 11 to an increased rotation speed, and if rotation is not fixed after that, give an alarm message.

Figure 2 shows a cutout from the air channel, for example, at the level of one of the holes 4, according to the second embodiment of the invention. A flexible plate 14 is fixed in the channel wall, protruding into the channel and deflected by the air flow from the resting position shown by the dashed line into the elastic bending position shown by solid lines. The position of the plate 14 is perceived by the proximity sensor 15 installed in the channel, for example, in the form of an oscillating circuit with a coil 16, the resonant frequency of which depends on the distance between the plate 14 and the coil 16. Since there are no continuously moving parts in this embodiment, the wear of the device is negligible, and reliability is high.

Figure 3 shows a cutout from an air channel according to a third embodiment of the invention. The air channel here has a local narrowing in the form of a nozzle 17, at the outlet of which a chamber 19 is formed with a pressure sensor 18 located therein. The high air velocity at the exit of the nozzle 17 causes, like a jet pump, a strong pressure drop in the chamber 19, which can be measured by the pressure sensor 18. The control circuit to which the sensor 18 is connected can thus estimate the speed of the air flow, and thereby the flow rate in the air channel, and start defrosting when the air flow reaches a critical low pressure.

With the fourth embodiment shown in FIG. 4, two wires 20, 21 are located in the air channel, the resistance of which depends on the temperature.

Each wire 20, 21 corresponds to a measuring circuit 22, 23. The measuring circuit 22 supplies a small measuring voltage to the wire 20, measures the resulting current in the wire 20 and determines the corresponding resistance value and, therefore, the temperature of the wire 20. The measuring voltage applied to the wire 20, is selected so small that the heating of the wire 20 due to the current flowing through it can be neglected.

The first measurement circuit 22 transmits the obtained temperature value to the control circuit 10. The latter transmits this value, increased by a fixed difference, as the set temperature value to the second measuring circuit 23. This circuit regulates the voltage supplied from it to the wire 21, so that the set temperature is established in this wire. The measuring circuit 23 determines the temperature of the wire 21 by its resistance, just like the measuring circuit 22. The value of the required heating power for this, the measuring circuit 23 transmits back to the control circuit 10. The heating power is greater, the greater the air flow in the air channel. If it falls below a predetermined limit value, the control circuit 10 determines that the amount of ice has reached a critical value and turns on defrosting.

The fifth embodiment of the invention is shown in partial section of the housing of the refrigeration apparatus, in Fig.5. The housing structure basically corresponds to the construction described with reference to FIG. 1, so that the elements in both figures, denoted by the same numbers, are not described repeatedly. In the embodiment shown in FIG. 5, there is no impeller and rotation sensor in the lower hole 4 of the air channel; instead, temperature sensors 24 and 25 are installed in the upper opening forming the outlet of the air channel and on the evaporator plate 7. The hatched surface indicates an ice layer 26 that can form around the evaporator and heater 8. When there is no ice on the evaporator 7, there is a free section for the air passage in the evaporation chamber 5 is relatively large, and the air flow required for efficient cooling of the refrigerating chamber 2 can be achieved at a low flow rate and, accordingly, a longer duration n Air circulation in contact with the evaporator 7. Therefore, the air at the evaporator 7, intensely cooled, and the temperature difference measured by the sensors 24, 25 is small.

As the thickness of the ice cover 26 on the evaporator 7 increases, the free section of the evaporation chamber 5 decreases. At the same time, the air flow also decreases, and the flow velocity in the evaporation chamber 5 increases. As a result, the time during which the air can be cooled is shortened, and the difference between the temperatures measured by the sensors 24, 25 increases.

If, as shown here, the temperature sensor 25 is installed in a place in the evaporator 7 in which ice can accumulate, then the ice cover 26 itself further increases the temperature difference between the two sensors. When this temperature difference becomes greater than the set limit value, the control circuit 10 connected to the sensors 24, 25 will start the defrosting process.

Claims (5)

1. A refrigerating apparatus comprising a thermally insulated body (1) surrounding a refrigerating chamber (2), an evaporator (7) installed in an air channel (4, 5) in communication with a refrigerating chamber (2), a heating device (8) for heating the evaporator (7) and a control circuit (10) for controlling the operation of the heating device (8), wherein the free section of the air channel narrows as the amount of ice deposited on the evaporator increases, while the control circuit (10) is connected to that installed in the air channel (4, 5) measuring device (20, 23; 24, 25) for issuing a signal characterizing the flow rate of air passing through the channel (4, 5), and is configured to turn on the heater (8) when the measured air flow rate falls below a certain limit value, characterized in that the measuring device has two temperature sensors (20, 21; 24, 25) installed in thermally different proximity to the heat source or to the heat sink (7), or to the air in the channel (4, 5), and that the circuit (10) the control is configured to determine a drop in air flow below a limit value I flow when the temperature difference measured by two sensors goes over the limit value of the temperature difference. 2. The refrigeration apparatus according to claim 1, characterized in that the heat sink is an evaporator (7), 3. Refrigeration apparatus according to claim 2, characterized in that the first of the temperature sensors (25) is mounted directly on the evaporator (7). 4. The refrigeration apparatus according to claim 3, characterized in that the first of the temperature sensors (25) is installed in such a place of the evaporator (7), in which ice can accumulate. 5. The refrigeration apparatus according to one of claims 2 to 4, characterized in that the second of the temperature sensors (24) is installed at the outlet of the channel (4, 5).

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