WO2015062662A1

WO2015062662A1 - Refrigerator with an improved defrost circuit and method for controlling the refrigerator

Info

Publication number: WO2015062662A1
Application number: PCT/EP2013/072842
Authority: WO
Inventors: Gokmen PEKER; Vasi Kadir Ertis; Tolga Nurettin AYNUR; Tolga APAYDIN; Egemen TINAR
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2013-10-31
Filing date: 2013-10-31
Publication date: 2015-05-07
Anticipated expiration: 2016-04-30

Abstract

The present invention relates to a refrigerator (1) comprising: a refrigeration circuit which includes a compressor (2), a condenser (3), a capillary (4), a freezer evaporator (5) and a fresh food evaporator (6) which are serially arranged and fluidly connected to one another by respective lines for circulating a refrigerant, wherein the freezer evaporator (5) and the fresh food evaporator (6) are arranged to respectively refrigerate a freezer compartment and a fresh food compartment, a defrost circuit for defrosting the freezer evaporator (5) and the fresh food evaporator (6) and a control unit for controlling the refrigeration circuit and the defrost circuit, wherein the control unit has a defrost mode and a refrigeration mode.

Description

REFRIGERATOR WITH AN IMPROVED DEFROST CIRCUIT AND METHOD FOR CONTROLLING THE REFRIGERATOR

The present invention relates to a method for controlling a refrigerator, in particular a domestic refrigerator which includes one freezer evaporator and one fresh food evaporator. The present invention particularly relates a method for controlling the refrigerator to defrost the evaporators.

A conventional domestic refrigerator typically includes a refrigeration circuit which has a compressor (2´), a condenser (3´), a capillary (4´), a freezer evaporator (5´), and a fresh food evaporator (6´) which are serially arranged and fluidly connected to one another by respective lines for circulating a refrigerant (Fig. 1). The refrigerant which is circulated through the evaporators cools the respective surfaces of the evaporators. As the temperature of the evaporator surfaces decrease, an ambient vapor inside the compartments starts to condense on the evaporator surfaces and forms frost. Frost has a relatively low thermal conductivity. Therefore, the cooling performance of the refrigerator decreases and an energy consumption of the refrigerator increases. Hence, the frost must be intermittently removed from the evaporator surfaces.

Several techniques have been developed to remove frost formed on an evaporator surface. In a commonly known technique, a heater wire is utilized to melt the frost. The heater wire is arranged in the vicinity of the evaporator. According to this technique, the refrigeration cycle is terminated and the heater wire is energized to melt the frost. A drawback of this technique is that an energizing of the electric wire incurs extra consumption of energy.

In another commonly known technique, the hot refrigerant inside the condenser or the hot refrigerant discharged by the compressor is utilized to melt the frost on the evaporator surface. This technique is also known as the hot gas defrost technique. According to the hot gas defrost technique, the hot refrigerant is directly conveyed into the evaporator being defrosted. The hot refrigerant conveyed into the evaporator dissipates its energy to the frost and partly condenses. A drawback of this technique is that the liquid refrigerant later on enters into the compressor. The liquid refrigerant easily impairs critical components of the compressor during a compression cycle. Thus, a life time of the compressor degrades and maintenance thereof becomes unavoidable. Therefore, the hot gas defrost technique has relatively low reliability.

CN 2937962 (Y) discloses a refrigerator which has a refrigeration circuit and a hot gas defrost circuit. The refrigeration circuit includes two evaporators. The hot gas defrost circuit includes a bypass circuit for circulating the hot gas through the evaporators.

An objective of the present invention is to provide a refrigerator and a method for controlling the refrigerator which overcomes the aforementioned problems of the prior art and improves a defrost efficiency.

This objective has been achieved by the refrigerator according to the present invention as defined in claim 1, and the method for controlling the refrigerator according to the present invention as defined in claim 8. Further achievements have been attained by the subject-matters respectively defined in the dependent claims.

In the refrigerator of the present invention, the defrost circuit includes either a first bypass line which fluidly connects the output of the compressor directly with the input of the freezer evaporator and a corresponding first valve unit for respectively controlling a convey of the refrigerant output from the compressor to an input of the condenser and to the first bypass line, or alternatively a second bypass line which fluidly connects the output of the condenser directly with the input of the freezer evaporator and a corresponding second valve unit for respectively controlling a convey of the refrigerant output from the condenser to an input of the capillary and to the second bypass line. In the refrigerator of the present invention, the defrost circuit further includes a first electrical heater and a first fan. The first electrical heater is utilized for heating the fresh food evaporator. The first fan is utilized for conveying an ambient air inside the fresh food compartment towards the fresh food evaporator.

The defrost circuit of the present invention enables a hybrid defrost technique in which the thermal energy of the hot refrigerant output from either the condenser or the compressor is used in combination with thermal energy generated by the first electrical heater or the thermal energy of the ambient air inside the fresh food evaporator. During the defrost mode when the hot refrigerant conveyed through the first bypass line or the second bypass line enters into the freezer evaporator, it dissipates a relatively large amount of thermal energy to the frost which is accumulated on the surface of the freezer evaporator. Consequently, the hot refrigerant inside the freezer evaporator partly condenses. The liquid refrigerant which is conveyed from the freezer evaporator into the fresh food evaporator transforms from a liquid state into a gaseous state by virtue of the thermal energy which is generated by the first electrical heater or the thermal energy in the ambient air which is transported by the first fan towards the fresh food evaporator. Thereby, the compressor is prevented from receiving liquid refrigerant. Thus, the hybrid defrost technique effectively protects the compressor. In the refrigerator of the present invention, the hot refrigerant can be reliably used for defrosting the freezer evaporator without jeopardizing the critical parts of the compressor. In addition, as the compressor receives the refrigerant in a totally gaseous state, it effectively compresses the refrigerant to relatively high temperatures. This accelerates the defrost process. Consequently, the defrost efficiency is further increased. The frost is melted in a relatively short time.

In an embodiment, the first electrical heater of the fresh food evaporator is concurrently energized in the defrost mode as the hot refrigerant is bypassed to the freezer evaporator. The first electrical heater is kept in an energized state throughout the defrost mode which is performed with hot refrigerant. Thereby, the hot refrigerant which condenses due to the frost is transformed into a gaseous state by the thermal energy generated by the first electrical heater. The gaseous refrigerant in the fresh food evaporator is subsequently sucked into the compressor and conveyed via the first/second bypass line again into the freezer evaporator.

In an alternative embodiment, the first fan of the fresh food evaporator is concurrently energized in the defrost mode as the hot refrigerant is bypassed to the freezer evaporator. The fan is kept in an energized state throughout the defrost mode which is performed with hot refrigerant. Thereby, the hot refrigerant which condenses through the frost is transformed into a gaseous state by the thermal energy of the ambient air which is imparted to the surface of the fresh food evaporator by means of the first fan. The gaseous refrigerant in the fresh food evaporator is subsequently sucked into the compressor and conveyed via the first/second bypass line again into the freezer evaporator.

In another embodiment, the hot refrigerant is circulated through the freezer and the fresh food evaporator via the first/second bypass lines until a temperature of the freezer evaporator or a temperature of the ambient air in the fresh food evaporator respectively reaches a cutout temperature or a limit temperature. The defrost mode is terminated whenever one of the cutout temperature and the limit temperature is reached.

In another embodiment, it is monitored whether the defrost mode has prolonged beyond a predetermined duration while neither the cutout temperature nor the limit temperature has been reached. If such prolongation is detected, then it is determined that the thermal energy of the hot refrigerant is not sufficient for effectively melting the frost. Consequently, the circulation of the hot refrigerant in the defrost mode is terminated. The compressor is halted. The valves controlling the first/second bypass lines are switched to their normal positions specified for the normal refrigeration mode. Subsequently, the second electrical heater of the freezer evaporator is energized to melt the frost on the surface of freezer evaporator. The defrost mode is continued with the thermal energy generated by the second electrical heater. The second electrical heater is de-energized when the cutout temperature of the freezer evaporator is reached.

The present invention provides an improved hybrid defrost technique by which the overall energy efficiency of the refrigerator is improved. Most importantly, the refrigerator of the present invention prevents liquid refrigerant from entering into the compressor. Thereby, a life time of the compressor is considerably prolonged. The maintenance requirement of the refrigerator of the present invention is low. Hence, a consumer satisfaction is also improved.

Additional advantages of the refrigerator according to the present invention and the control method according to the present invention will become apparent with the detailed description of the embodiments with reference to the accompanying drawings in which:

Figure 1 - is a schematic view of a conventional refrigeration circuit.

Figure 2 - is a schematic view of a refrigeration circuit and a defrost circuit of a refrigerator according to an embodiment of the present invention.

Figure 3 - is a schematic view of a refrigeration circuit and a defrost circuit of a refrigerator according to another embodiment of the present invention.

Figure 4 - is a flow chart showing a method for controlling the refrigerator to defrost its evaporators according another embodiment of the present invention.

Figure 5 - is a flow chart showing a method for controlling the refrigerator to defrost its evaporators according another embodiment of the present invention.

Figure 6 - is a flow chart showing a method for controlling the refrigerator to defrost its evaporators according another embodiment of the present invention.

The reference signs appearing on the drawings relate to the following technical features.

Refrigerator
Compressor
Condenser
Capillary
Freezer evaporator
Fresh food evaporator
First bypass line
First valve unit
Second bypass line
Second valve unit
First electrical heater
Second electrical heater

The refrigerator (1) includes a refrigeration circuit which comprises a compressor (2), a condenser (3), a capillary (4), a freezer evaporator (5) and a fresh food evaporator (6) which are serially arranged and fluidly connected to one another by respective lines for circulating a refrigerant (Figs. 2 and 3). The freezer evaporator (5) and the fresh food evaporator (6) are arranged to respectively refrigerate a freezer compartment (not shown) and a fresh food compartment (not shown). The refrigerator (1) further includes a defrost circuit for defrosting the freezer evaporator (5) and the fresh food evaporator (6). The refrigerator (1) further includes a control unit (not shown) for controlling the refrigeration circuit and the defrost circuit. The control unit has a defrost mode and a refrigeration mode.

In the refrigerator (1) of the present invention, the defrost circuit includes either a first bypass line (7) which fluidly connects the output of the compressor (2) directly with the input of the freezer evaporator (5) and a corresponding first valve unit (8) for respectively controlling a convey of the refrigerant output from the compressor (2) to an input of the condenser (3) and to the first bypass line (7), or alternatively a second bypass line (9) which fluidly connects the output of the condenser (3) directly with the input of the freezer evaporator (5) and a corresponding second valve unit (10) for respectively controlling a convey of the refrigerant output from the condenser (3) to an input of the capillary (4) and to the second bypass line (9) (Figs. 2 and 3). In the refrigerator (1) of the present invention, the defrost circuit further includes a first electrical heater (11) for heating the fresh food evaporator (6) (Figs. 2 and 3). In the refrigerator (1) of the present invention, the defrost circuit further includes a first fan for conveying an ambient air inside the fresh food compartment towards the fresh food evaporator (6) (Figs. 2 and 3).

The hot refrigerant which is conveyed through the first bypass line (7) or the second bypass line (9) into the freezer evaporator (5) loses a relatively large amount of thermal energy. Consequently, the hot refrigerant inside the freezer evaporator (5) partly condenses. By virtue of the first electrical heater (11) and the first fan, the refrigerant which is conveyed from the freezer evaporator (5) into the fresh food evaporator (6) is transformed from a liquid state into a gaseous state. Thereby, the compressor (2) is prevented from receiving liquid refrigerant.

In an embodiment, the defrost circuit further includes a second electrical heater (12) for heating the freezer evaporator (5) (Figs. 2 and 3). Thereby, the frost on the surface of the freezer evaporator (5) can be melted by using the second electrical heater (12), for example, when the thermal energy of the hot refrigerant drawn into the freezer evaporator (5) is insufficient for totally melting the frost. The second electrical heater (12) is provided separately from the first electrical heater (11). In this embodiment, the defrost circuit further includes a second fan (not shown) for conveying an ambient air inside the freezer compartment towards the freezer evaporator (5).

In another embodiment, the defrost circuit further includes a first temperature sensor (not shown) for detecting a temperature T1 of the freezer evaporator (5) and for outputting a signal to the control unit. The signal is indicative of the detected temperature T1. By virtue of the temperature sensor, a temperature of the surface of the freezer evaporator (5) is monitored. Thereby, the melting process can be better watched. The first temperature sensor is preferably a bimetal sensor.

In another embodiment, the defrost circuit further includes: a second temperature sensor (not shown) for detecting a temperature T2 of the ambient air inside the fresh food compartment and for outputting a signal to the control unit. The signal is indicative of the detected temperature T1.

In another embodiment, the defrost circuit further includes a timer (not shown) for detecting an elapsed time during the defrost mode and for outputting a signal to the control unit. The signal is indicative of the elapsed time. By virtue of the timer, the duration necessary for melting the frost on the freezer evaporator (5) can be monitored.

In another embodiment, the first valve unit (8) is configured by a three-way valve which includes an input, a first output and a second output (Figs. 2 and 3). The input of the first valve unit (8) is fluidly connected to the output of the compressor (2), the first output of the first valve unit (8) is fluidly connected to the input of the condenser (3), and the second output of the first valve unit (8) is fluidly connected to the first bypass line (7). The use of a three-way valve simplifies control of the defrost circuit.

In another embodiment, the second valve unit (10) is configured by a three-way valve which includes an input, a first output and a second output (Figs. 2 and 3). The input of the second valve unit (10) is fluidly connected to the output of the condenser (3), the first output of the second valve unit (10) is fluidly connected to the capillary (4), and the second output of the second valve unit (10) is fluidly connected to the second bypass line (9).

The method for controlling the refrigerator (1) of the present invention comprises the steps of: initiating (S1, S11, S21) the defrost mode, conveying (S2, S12, S22) the output of the compressor (2) directly to an input of the freezer evaporator (5) by inhibiting a convey of the refrigerant output from the compressor (2) to the condenser (3) and by allowing a convey of the refrigerant output from the compressor (3) to the first bypass line (7), or alternatively conveying (S2, S12, S22) the output of the condenser (3) directly to an input of the freezer evaporator (5) by inhibiting a convey of the refrigerant output from the condenser (3) to the capillary (4) and by allowing a convey of the refrigerant output from the condenser (3) to the second bypass line (9) (Figs. 4 to 6). The method for controlling the refrigerator (1) of the present invention further comprises a step of energizing (S2, S22) the first electrical heater (11), or alternatively a step of switching (S12, S22) the first fan on (Figs. 4 to 6).

In an embodiment, the method further comprises the steps of: comparing (S3, S13) the temperature T1 of the freezer evaporator (5) with a cutout temperature T_cutout, comparing (S3, S13) the temperature T2 of the ambient air inside the fresh food compartment with a limit temperature T_limit, terminating (S4, S14) the defrost mode if the temperature T1 of the freezer evaporator (5) exceeds the cutout temperature T_cutout or if the temperature T2 of the ambient air inside the fresh food compartment exceeds the limit temperature T_limit and initiating (S4, S14) the refrigeration mode (Figs. 4 and 5).

In another embodiment, the method further comprises the step of: comparing (S23) the time t elapsed in the defrost mode with a predetermined defrost duration t_max, halting (S24) convey of the refrigerant, energizing (S24) the second electrical heater (12), de-energizing the first electrical heater (11), and switching the first fan off if the elapsed time t during the defrost mode exceeds the predetermined defrost duration t_max (Fig. 6).

In another embodiment, the step of halting (S24) convey of the refrigerant includes a step of deactivating the compressor (2) and a step of switching both the first valve unit (8) and the second valve unit (10) to their default positions which correspond to the refrigeration mode (Fig. 6).

In another embodiment, the method further comprises the step of: comparing (S25) the temperature T1 of the freezer evaporator (5) with a cutout temperature T_cutout and
terminating (S25) the defrost mode by switching the second electrical heater (12) off if the temperature T1 of the freezer evaporator (5) exceeds the cutout temperature T_cutout (Fig. 6).

The program of the present invention comprises computer-readable codes which are suitable for causing a computer-implemented refrigerator to execute the steps of the above described methods of the present invention.

The computer-readable storage medium of the present invention stores the above described program of the present invention.

In another embodiment, the control unit of the refrigerator of the present invention is configured to execute the steps defined in the above control method of the present invention. In this embodiment, the control unit is provided with program which are is stored in a non-volatile storage medium.

The present invention provides a hybrid defrost technique which constitutes a reliable and energy efficient technique for defrosting a refrigerator (1) with at least two evaporators (5, 6). The combined use of the hot gas defrost technique and the electrical heater defrost technique improves the total defrost process in view of energy efficiency. Most importantly, the refrigerator (1) of the present invention prevents liquid refrigerant from entering the compressor (2). Thereby, a life time of the compressor (2) is considerably prolonged and a proper operation thereof is safeguarded.

Claims

A refrigerator (1) comprising a refrigeration circuit which includes a compressor (2), a condenser (3), a capillary (4), a freezer evaporator (5) and a fresh food evaporator (6) which are serially arranged and fluidly connected to one another by respective lines for circulating a refrigerant, wherein the freezer evaporator (5) and the fresh food evaporator (6) are arranged to respectively refrigerate a freezer compartment and a fresh food compartment, a defrost circuit for defrosting the freezer evaporator (5) and the fresh food evaporator (6) and a control unit for controlling the refrigeration circuit and the defrost circuit, wherein the control unit has a defrost mode and a refrigeration mode,

the refrigerator (1) being characterized in that

- the defrost circuit comprising a first bypass line (7) which fluidly connects the output of the compressor (2) directly with the input of the freezer evaporator (5) and a first valve unit (8) for respectively controlling a convey of the refrigerant output from the compressor (2) to an input of the condenser (3) and to the first bypass line (7) or a second bypass line (9) which fluidly connects the output of the condenser (3) directly with the input of the freezer evaporator (5) and a second valve unit (10) for respectively controlling a convey of the refrigerant output from the condenser (3) to an input of the capillary (4) and to the second bypass line (9),

- a first electrical heater (11) for heating the fresh food evaporator (6) and

- a first fan for conveying an ambient air inside the fresh food compartment towards the fresh food evaporator (6).
The refrigerator (1) according to claim 1, characterized in that the defrost circuit further comprising a second electrical heater (12) for heating the freezer evaporator (5), wherein the second electrical heater (12) is provided separately from the first electrical heater (11) and a second fan for conveying an ambient air inside the freezer compartment towards the freezer evaporator (5).
The refrigerator (1) according to claim 1 or 2, characterized in that the defrost circuit further comprising a first temperature sensor for detecting a temperature T1 of the freezer evaporator (5) and for outputting a signal to the control unit, wherein the signal is indicative of the detected temperature T1.
The refrigerator (1) according to any one of claims 1 to 3, characterized in that the defrost circuit further comprising a second temperature sensor for detecting a temperature T2 of the ambient air inside the fresh food compartment and for outputting a signal to the control unit, wherein the signal is indicative of the detected temperature T1.
The refrigerator (1) according to any one of claims 1 to 4, characterized in that the defrost circuit further comprising a timer for detecting an elapsed time during the defrost mode and for outputting a signal to the control unit, wherein the signal is indicative of the elapsed time.
The refrigerator (1) according to any one of claims 1 to 5, characterized in that the first valve unit (8) is configured by a three-way valve which includes an input, a first output and a second output, wherein the input is fluidly connected to the output of the compressor (2), the first output is fluidly connected to the input of the condenser (3), and the second output is fluidly connected to the first bypass line (7).
The refrigerator (1) according to any one of claims 1 to 6, characterized in that the second valve unit (10) is configured by a three-way valve which includes an input, a first output and a second output, wherein the input is fluidly connected to the output of the condenser (3), the first output is fluidly connected to the capillary (4), and the second output is fluidly connected to the second bypass line (9).
A method for controlling a refrigerator (1) as defined in any one of claims 1 to 7, comprising the steps of:

- initiating (S1, S11, S21) the defrost mode

- conveying (S2, S12, S22) the output of the compressor (2) directly to an input of the freezer evaporator (5) by inhibiting a convey of the refrigerant output from the compressor (2) to the condenser (3) and by allowing a convey of the refrigerant output from the compressor (3) to the first bypass line (7) or conveying (S2, S12, S22) the output of the condenser (3) directly to an input of the freezer evaporator (5) by inhibiting a convey of the refrigerant output from the condenser (3) to the capillary (4) and by allowing a convey of the refrigerant output from the condenser (3) to the second bypass line (9) and

- energizing (S2, S22) the first electrical heater (11) or switching (S12, S22) the first fan on.
The method according to claim 8, characterized in that the steps of:

- comparing (S3, S13) the temperature T1 of the freezer evaporator (5) with a cutout temperature T_cutout,

- comparing (S3, S13) the temperature T2 of the ambient air inside the fresh food compartment with a limit temperature T_limit,

- terminating (S4, S14) the defrost mode if the temperature T1 of the freezer evaporator (5) exceeds the cutout temperature T_cutout or if the temperature T2 of the ambient air inside the fresh food compartment exceeds the limit temperature T_limit and

- initiating (S4, S14) the refrigeration mode.
The method according to claim 8 or 9, characterized in that the steps of:

- comparing (S23) the time t elapsed in the defrost mode with a predetermined defrost duration t_max,

- halting (S24) convey of refrigerant,

- energizing (S24) the second electrical heater (12),

- de-energizing the first electrical heater (11), and

- switching the first fan off if the elapsed time t during the defrost mode exceeds the predetermined defrost duration t_max.
The method according to claim 10, characterized in that the steps of:

- halting (S24) convey of refrigerant by deactivating the compressor (2) and

- switching both the first valve unit (8) and the second valve unit (10) to positions which correspond to the refrigeration mode.
The method according to claim 10 or 11, characterized in that the steps of:

- comparing (S25) the temperature T1 of the freezer evaporator (5) with a cutout temperature T_cutout and

- terminating (S25) the defrost mode if the temperature T1 of the freezer evaporator (5) exceeds the cutout temperature T_cutout.
A program comprising computer-readable codes for causing a computer-implemented refrigerator to execute the steps of the method according to any one of claims 8 to 12.
A computer-readable storage medium storing the program codes according to claim 13.