EP0326049A1

EP0326049A1 - Multi-temperature refrigerating apparatus having a single-compressor refrigerating circuit and a single temperature control device

Info

Publication number: EP0326049A1
Application number: EP89101047A
Authority: EP
Inventors: Paolo Marega
Original assignee: Industrie Zanussi SpA
Current assignee: Industrie Zanussi SpA
Priority date: 1988-01-29
Filing date: 1989-01-20
Publication date: 1989-08-02
Also published as: IT8845703A0; IT1220739B

Abstract

Two-temperature refrigerator wherein a single static evaporator (11) has a different heat-exchange relationship with the storage compartment (7) in which it is arranged and with a conduit (18) which is separate from the storage compartment and communicates with the freezing compartment (8). A fan (23) forces an air flow in a closed-loop along the conduit (18) and through the freezing compartment (8).

Description

The present invention relates to a multi-temperature refrigerating apparatus of the type provided with a single-compressor refrigerating circuit and a single thermostatic temperature control device.
The so-called two-temperature refrigerators are well known, having a couple of main compartments which are kept at different temperatures and provided with separate access doors.
One of the compartments is usually kept at a rating temperature of about +5°C for storing fresh food, while the other compartment is kept at a rating temperature of about -18°C for preserving frozen foodstuffs.
Refrigerators of this kind may be provided with separate refrigerating circuits for the different compartments, or may comprise a single refrigerating circuit having a single compressor and relevant evaporators which are hydraulically connected through valves which are controlled according to the various operative conditions.
The above solution are complicated, costly and scarcely reliable.
It is, therefore, preferable to utilize one single-compressor refrigerating circuit wherein the evaporators associated with the different storage and freezing compartments are connected directly, usually in series, without provision of any valve means.
A solution of this kind is disclosed for example in Italian patent application No. 45732 A/87, filed on 09.07.1987 in the name of the present Applicant.
According to the above solutions, the operating temperature is determined by ON/OFF cycling of the compressor and is usually controlled by means of one single adjustable thermostatic device capable of monitoring the temperature of the evaporator which is associated with the storage compartment and possibly the temperature of the air inside the storage compartment. For instance, the compressor is switched off when the temperature of the storage compartment evaporator decreases below a relevant, predetermined minimum value, whereas it is switched on again when the temperature of the storage compartment evaporator raises over a given maximum value. The temperature inside the compartments depends on the duty cycle of the compressor, as well as on the general sizing of the refrigerator, the loading conditions and the environment temperature. Preferably, the evaporator of the freezing compartment is of the ventilated type, whereas the evaporator of the storage compartment is a so-called "static", i.e. non-ventilated, evaporator to prevent fresh food from being excessively dehydrated.
Thus, it is advisable to avoid use of solutions, like the one disclosed for instance in U.S. patent No. 4,614,092, utilizing a single ventilated evaporator to cool both the storage and freezing compartments by means of relevant forced air flows; in this case, in fact, the storage compartment cannot preserve fresh food with a sufficient degree of humidity, which is only ensured if an evaporator of the static type is used.
Refrigerators of the kind referred to above automatically provide for substantial defrosting of the static evaporator of the storage compartment during the common off-phases of the compressor (which are usually performed every hour and last about 30 min.).
On the contrary, the ventilated evaporator of the freezing compartment is defrosted periodically (every 24 hours, for example) by means of a timer that for short periods (e.g., 15 min.) operates suitable defrost resistances and de-energizes the fan of the ventilated evaporator, and the compressor as well.
Utilization of the timer involves a costly and complicated construction of the whole refrigerator, which is also scarcely reliable in operation.
On the other hand, it was until now practically unimaginable to provide a refrigerating apparatus of the above-mentioned type wherein also the automatic defrost of the freezing compartment is carried out cyclically, by means of a thermostatic control device. In this case, in fact, the defrost periods of the freezing compartment would occur so frequently as to cause a remarkable energy waste by the defrost resistance of the ventilated evaporator, as well as an excessive temperature raise in the freezing compartment which would damage the frozen foodstuffs.
It is the main scope of the present invention to provide a multi-temperature refrigerating apparatus having a single-compressor refrigerating circuit and a single temperature control device in which the number of the basic components which are required for operation of the apparatus is substantially reduced, with a corresponding increase in reliability.
It is another scope of the invention to provide a refrigerating apparatus of the kind mentioned above in which, without affecting performances thereof and contrary to a technical prejudice, there is no need to defrost the freezing compartment by means of a timing device.
According to the invention, these scopes are attained in a multi-temperature refrigerating apparatus having a single-compressor refrigerating circuit and a single thermostatic temperature control device. The apparatus comprises at least a storage compartment at a temperature suitable to preserve goods and at least a further compartment at a lower temperature, each compartment being separate and provided with a relevant access door, and further comprises a static evaporator which is connected in the said circuit and is arranged in correspondence of and in heat-exchange relationship with the storage compartment. The temperature control device detects the temperature of the evaporator and is capable of controlling operation of the compressor to perform cyclical evaporator defrost phases. The refrigerating apparatus is characterized in that the static evaporator at least partially is in heat-exchange relationship also with a conduit substantially separate with respect to the storage compartment and provided with at least an inlet and at least an outlet which communicate with the said further compartment to form a closed-loop path for an air-flow which can be forced by blowing means.
The characteristics and advantages of the invention willbe more apparent from the following description, given by way of non-limiting example, with reference to the accompanying drawings, in which:

Figure 1 diagrammatically shows a preferred embodiment of the refrigerating apparatus according to the invention;
Figures 2 and 3 diagrammatically show sections II-II and III-III, respectively, of the apparatus as in Fig. 1;
Figure 4 shows an electric circuit for controlling operation of the apparatus as in Fig. 1;
Figure 5 shows a different embodiment of the electric circuit as in Fig. 4.

With reference particularly to Fig. 1, the refrigerating apparatus according to the invention comprises an insulated cabinet 6 provided with at least two separate compartments 7 and 8, respectively for preserving fresh food and frozen foodstuffs, for instance. Compartments 7 and 8 are provided with relevant access doors 9,10. In correspondence of the compartment for preserving fresh food, a storage compartment, 7 it is arranged a static evaporator 11 which is connected in a refrigerating circuit including also a compressor 12, a condenser 13, a dehydrating filter 14 and a throttling element 15.
The refrigerating apparatus is further provided with a thermostatic temperature control device 16, known per sè and preferably located inside the storage compartment 7.
At least a probe 17, capable of detecting the temperature of the evaporator 11, is associated to the control device 16; in a way know per sé, the control device 16 determinates start and duration of the ON/OFF phases of the compressor, so as to normally keep the storage compartment 7 at a predetermined average temperature of about +5°C.
As it will be more apparent from the following description, the thermostatic control device also determinates the temperature of the further compartment 8 to be normally kept at an average value of about -18°C, for instance, which value also depends on the general sizing of the refrigerating apparatus, its loading conditions, etc.
In a known way, during the OFF periods of the compressor 12 cyclical defrost phases of the static evaporator 11 occur automatically.
Preferably, the static evaporator 11 has a substantially plane configuration, is arranged vertically and forms an air-tight partition wall between the storage compartment 7 and a conduit 18 extending upwards in correspondence of the rear wall of the cabinet 6. With reference also to Fig. 2, the conduit 18 is preferably U-shaped and is in heat-exchange relationship with the rear surface 19 of the static evaporator 11, whose front wall 20 - on the contrary - obviously is in heat-exchange relationship with the storage compartment 7.
The upper portion of conduit 18 terminates with at least an inlet aperture 21 and at least an outlet aperture 22 which communicate with the further, or freezing, compartment 8 to form a closed-loop path for an air-flow which can be forced by blowing means like a motor-driven fan 23, or the like, preferably located in the same compartment 8. This air-flow is indicated by the arrows in Figs. 1 and 2 and circulates from the freezing compartment 8 through the conduit 18, where it is in heat-exchange relationship with the surface 19 of the evaporator, and then is conveyed again into the freezing compartment 8. Hence, compartment 8 advantageously is of the ventilated type and is indirectly refrigerated by the same static evaporator 11 which also refrigerates the storage compartment 7 in which it is accomodated.
In the present example, in order to keep compartments 7 and 8 at a rating temperature of about +5°C and -18°C, respectively, it may be advisable that the surface of evaporator 11 which is in heat-exchange relationship with the conduit 18 be larger than the one in heat-exchange relationship with the storage compartment 7. This feature can counterbalance the fact that the temperature difference between static evaporator 11 and storage compartment 7 is higher than the one between static evaporator 11 and further compartment 8. In fact, the higher heat-exchange coefficient between the evaporator 11 and the further compartment 8, which is obtained thanks to the forced air-flow through the conduit 18, might even be insufficient to counterbalance the phenomenon mentioned above.
Therefore, the static evaporator 11 is preferably provided with a substantially plane surface 20 and a surface 19 which is shaped in the most suitable way, for example with a finned or corrugated configuration, or with a fred cross-section as shown in Fig. 3, in order to increase the surface which is in heat-exchange relationship with the conduit 18.
In order to cool the further compartment 8 effectively, the fan 23 is controlled (in a way known per sè and now shown in Figs. 1 and 2) by the thermostatic control device 16. In particular, the control device 16 operates fan 23 only during the ON phases of the compressor, whereas it de-energizes the fan during the cyclical defrost phases of the static evaporator 11. Thus, an air flow is forced by the fan 23, in order to transfer to the further compartment 8 the heat-exchange occurring between evaporator 11 and conduit 18, only during the normal operation of the refrigerating circuit. On the contrary, the de-energization of the fan 23 during the defrost phases keeps the freezing compartment 8 thermally insulated with respect to static evaporator 11, in this way preventing an undesirable temperature increase from occurring in the same compartment 8. The operation of the refrigerating apparatus can be further improved by cyclically operating and de-energizing the fan 23, at the end and at the beginning, respectively, of the defrost phases with a delay which enables to take advantage of the thermic inertia of the static evaporator 11.
This can be obtained, for instance, by means of the circuit shown in Fig. 4, wherein the compressor 12 is connected across terminals 25, 26 of a power supply source through the thermostatic switch 16, which is controlled by probe 17 to be opened and closed when the temperature of evaporator 11 for instance has a value of -25°C and +5°C, respectively.
Across terminals 25, 26 it is arranged the series connection including the electric motor driving fan 23 and an electric switch 27 which is normally open and can be closed with a delay (e.g., 5 min.) when a time-constant device 28, connected in parallel with compressor 12, is supplied. The time-constant device 28 may be of any suitable type; for instance, it can be an electronic or thermoelectric device, or the like. The operation of this circuit is apparent: compressor 12 and device 28 are supplied and de-energized at the same time by the thermostatic control device 16, 17, depending on the temperature of evaporator 11; the motor-driven fan 23 is operated and de-energized via swith 27 according to the operation of the refrigerating circuit, but with a delay (determined by device 28) which enables to take advantage of the thermic inertia of static evaporator 11, as stated above.
This operation of the refrigerating apparatus can be even more precise if the circuitry embodiment of Fig. 5 is used, wherein the delay device 28 as in Fig. 4 is replaced by a further probe 29 (not shown in Figs. 1 to 3) capable of controlling switch 27, which in this case is a thermostatic switch. More particularly, probe 29 is suitable to detect the temperature of static evaporator 11, like probe 17 does, and to open, respectively close, swith 27 when such a temperature for instance has a value of -10°C (higher than the value in response to which switch 16 opens), respectively -15°C (lower than the value in response to which switch 16 is closed).
The operation of the control circuit is apparent also in this case: the operation of the whole refrigerating apparatus substantially occurs as described above with reference to Fig. 4, with the only difference that the fan 23 is cyclically actuated and de-energized with a delay, with respect to the corresponding operation of the compressor 12, which is not fixed but rather depends on the actual temperature of evaporator 11.
More particularly, bearing in mind the temperature values mentioned above as an example, the fan 23 can transfer to the freezing compartment 8 the heat-exchange occurring between the static evaporator 11 and the conduit 18 when the temperature of the same evaporator certainly has a value which at least is lower than -10°C.
This happens regardless of the times at which the compressor is actuated and de-energized and enables the whole apparatus to take advantage in the best way of the thermic inertia of evaporator 11 to provide for an optimum refrigeration of the freezing compartment 8.
At any rate, it is apparent that the refrigerating apparatus according to the invention has very good performances with regard to both compartments 7 and 8, even though it requires one single common evaporator instead of an evaporator for each compartment. Furthermore, the single evaporator 11 is of the static type and is cyclically defrosted, thanks to the thermostatic control device 16, without requiring specific defrost heating resistances and a timer for controlling the same.
Hence, it is apparent that the refrigerating apparatus according to the invention not only has a simple construction and can be easily assem bled, but is also particularly reliable in operation.
Of course, the refrigerating apparatus described above may undergo several modifications without departing from the scopes of the invention. For example, the conduit 18 can be shaped with a different configuration and/or can be arranged in a different region of the apparatus, for instance in correspondence of a side wall of the cabinet 6; moreover, the refrigerating apparatus can be arranged and set up substantially upside down with respect to the embodiment shown in Fig.1.
Furthermore, the static evaporator 11 can be made and/or positioned in a different way; for instance, it can be of the kind which is "concealed" with respect to the storage compartment 7, as disclosed in Italian utility model No. 201.063.
In any case, the refrigerating apparatus described above further includes a channel duct 24, communicating with the bottom of the conduit 18 and with a collecting vessel 30 located beneath the evaporator 11 inside compartment 7, in order to perform drainage of the melting water from both evaporator surfaces 19 and 20, in a way known per sè.

Claims

1. Multi-temperature refrigerating apparatus having a single-compressor refrigerating circuit and a single thermostatic temperature control device, the apparatus comprising at least a storage compartment at a temperature suitable to preserve goods and at least a further compartment at a lower temperature, each compartment being separate and provided with a relevant access door, and further comprising a static evaporator which is connected in the said circuit and is arranged in correspondence of and in heat-exchange relationship with the storage compartment, the temperature control device detecting the temperature of the evaporator and being capable of controlling operation of the compressor to perform cyclical evaporator defrost phases, characterized in that the static evaporator (11) at least partially is in heat-exchange relationship also with a conduit (18) substantially separate with respect to the storage compartment (7) and provided with at least an inlet (21) and at least an outlet (22) which communicate with the said further compartment (8) to form a closed-loop path for an air-flow which can be forced by blowing means (23).

2. Multi-temperature refrigerating apparatus according to claim 1, characterized in that the surface (19) of the static evaporator (11) which is in heat-exchange relationship with said conduit (18) is larger than the one (20) in heat-exchange relationship with the storage compartment (7).

3. Multi-temperature refrigerating apparatus according to claim 1, characterized in that the static evaporator (11) forms a partition wall between the storage compartment (7) and said conduit (18).

4. Multi-temperature refrigerating apparatus according to claim 1, characterized in that said blowing means (23) is arranged inside the said further compartment (8).

5. Multi-temperature refrigerating apparatus according to claim 1, characterized in that said temperature control device (16) is capable of cyclically actuate and de-energize said blowing means (23) in correspondence of the end and the beginning, respectively, of each defrost phase of the static evaporator (11).

6. Multi-temperature refrigerating apparatus according to claim 5, characterized in that said temperature control device (16) is capable of actuating and de-energizing said blowing means (23) by means of delay means (27,28; 27,29).