EP2444762A1

EP2444762A1 - Refrigeration appliance having a 0 degree compartment

Info

Publication number: EP2444762A1
Application number: EP10188172A
Authority: EP
Inventors: Tushar Kulkarni; Enrica Monticelli
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2010-10-20
Filing date: 2010-10-20
Publication date: 2012-04-25

Abstract

A refrigeration appliance comprises a compartment with an evaporator (12) in heat exchange relationship with the liner (14) of the compartment and which contains an auxiliary compartment (22) at or near 0°C. The auxiliary compartment (22) has at least a cooling wall (20), the liner having a reservoir (16) for a coolant in heat exchange relationship with said evaporator (12), a piping system (18) being provided for connecting the reservoir (16) with the cooling wall (20) of the auxiliary compartment (22) in order to maintain a predetermined temperature in such compartment.

Description

The present invention refers to a refrigeration appliance comprising a fresh food compartment with an evaporator in heat exchange relationship with the liner of the compartment on the outer surface thereof and which contains an auxiliary compartment at or near 0°C. The customer desire is that the stored food is not frozen to the temperatures in the freezer (-17deg C or below), while at the same time prolonging the shelf life.
In the art of refrigeration appliances, refrigerators with so called 0 degree compartments are well known; usually such compartments are in fact subcompartments, i.e. they are sub-cavities divided from the main fresh food cavity, having a foamed in evaporator, by means of insulated walls or they are defined as drawers or bins which are cooled at the desired temperature by means of a ad-hoc cool air circulation. The source of the cold air is fresh food or freezer evaporator.
All the known solutions of compartments near, at or slightly below zero degree make use of a peculiar air circulation for delivering cool air from a zone near the evaporator towards the 0 degree compartment. Such known solutions need the use of fans and moreover require air channels which reduce the useful overall volume of the fresh food compartment. Moreover the air circulation may be affected by frost formation or by accidental insertion of objects in the air channel or by obstruction of the inlets or outlets of such channels. Further, by driving cold and dry air, there is risk to drive moisture from food and deposit it onto the evaporator. This affects the quality of the preserved food.
Some appliance manufacturers also provide the 0 degree compartment feature by means of an additional evaporator in the subcavity. The refrigerant flowing through the additional evaporator will cool the compartment to 0° C. However, this is more complex and extremely capital intensive.
It is therefore an object of the present invention to provide a refrigeration appliance of the type specified at the beginning of the description which does not present the above drawbacks.
It is another object of the present invention to provide a refrigeration appliance which allows a more precise and reliable temperature control of a sub-compartment at or near 0°C. Lastly, it is proposed to preserve the humidity inside the 0 degree compartment and not deposit the humidity in the form of frost in the evaporator, thereby improving the quality of food preserved.
These objects are reached tanks to the features listed in the appended claims.
According to the present invention, the fresh food compartment evaporator is used as a heat sink for the 0°C sub-compartment. According to a further feature of the present invention, a secondary coolant is stored in a reservoir-heat exchanger attached as a flat tank (such that it is in heat exchange communication with the evaporator) to the back wall where the fresh food evaporator is located. Another heat exchanger (liquid to air) is attached to the top hollow wall or the back hollow wall of an insulated compartment. The insulated compartment can therefore maintain a predetermined temperature. When the temperature in the auxiliary compartment is higher than a pre-determined threshold, the coolant is circulated through the heat exchanger in the insulated compartment. In one embodiment, the circulation of the coolant is by means of a pump which is energized when the temperature in the compartment exceeds a pre-determined threshold. In another embodiment, the circulation of the coolant may be due to natural convection. Since the evaporator temperature drops well below 0°C , the coolant in the reservoir attached to the back wall is chilled to cold temperature and becomes heavier in the process. Further, as the coolant in the heat exchanger in the 0 deg compartment is warmed from the heat of the food stored as well as the heat ingress from the surroundings, it is able to flow by means of natural convection to displace the colder fluid in the coolant buffer attached to the evaporator.
Secondary coolant is essentially a mixture of water with some salt to depress its freezing point substantially below 0° C. As such, its thermal capacitance is close to that of water. Hence, the coolant sitting in either heat exchangers (the one attached to the evaporator or the one present in the 0 degree compartment) is able to absorb sufficient amount of heat and store significant amount of cooling before the temperature rises. Hence, the heat exchange can occur more by batch mode rather than due to coolant circulation. As such, the pump needs to be run only intermittently. In the embodiment with the valve, the valve needs to be energized to only change its state from on to off and vice versa.
When the heat exchange occurs more by batch mode rather than due to coolant circulation, this has obvious benefits in terms of energy savings. Thus, the cold coolant in the heat exchanger in the insulated compartment provides cooling buffer to the compartment while the warm coolant contained in the reservoir attached to the evaporator is being cooled. Various means of controlling the temperature (using a thermostat, thermistor or bi-metal) are well known in art. According to a preferred feature of the present invention, the insulated compartment is located at the bottom of the fresh food compartment of the refrigerator. Since the evaporator is at a higher place than the insulated compartment, natural convection can be used to facilitate the flow of coolant. Thus, the heat from the food warms the coolant in the heat exchanger located either in the lid or in one or more side walls of the insulated compartment. The warm coolant moves to replace the cold coolant from the reservoir-heat exchanger located at the back wall of the liner (near the foamed in evaporator) due to gravity and buoyancy induced natural convection gradients. The coolant flow can be stopped as required by means of a valve. This valve can be a solenoid activated valve or merely a manual ball valve that customer can regulate to control the flow of coolant. In the latter version, no further electronics is required. In the former version, an electronic signal is required to drive the opening and closing of the solenoid valve. Either of these versions would lead to a lower cost solution than using a pump to regulate the coolant flow.
Lastly, it is clear that since there is no air-exchange between the 0 degree compartment and the exterior of the 0 degree compartment, the humidity is preserved inside the 0 degree compartment. Periodically, there will be frost and moisture deposited on the heat exchanger located in the top or back wall of the 0 degree compartment. This condensation will have to be periodically drained in a manner similar to the frost formed on the back wall. So, a heater may be used on the heat exchanger in the 0 degree compartment. The heater will be periodically activated to cause defrost and condensation drained. As a heater is present, an auxiliary purpose of the compartment would be to create temperatures warmer than the fresh food compartment to enable storage of tropical fruit and create a tropical fruit zone.
Further advantages and features of a refrigeration appliance according to the present invention will be clear from the following detailed description, with reference to the attached drawings in which:

figure 1 is a cross section view of a refrigerator according to the present invention,
figure 2 is an enlarged detail of figure 1,
figure 3 is a perspective view of a portion of the refrigerator of figure 1, from above the 0 degree compartment,
figure 4 is a perspective view of the 0 degree compartment of figure 1,
figure 5 is a schematic perspective view showing the preferred dimensions of the 0 degree compartment tested by the applicant; and
figure 6 is a diagram showing the performances vs. time of the 0 degree compartment with an ambient temperature of 43°C.

With reference to the drawings, a refrigerator 10 presents a freezer compartment FC and a fresh food compartment RC. The fresh food compartment RC has an evaporator 12 in contact with the outer surface of a plastic liner 14.
On the inner surface of the liner 14, in a configuration facing at least a portion of the evaporator 12, there is provided a flat reservoir 16 full of a coolant, for instance a glycol-water mixture, and acting as a liquid to liquid heat exchanger. The reservoir 16 is connected, by means of circulation pipes 18, with an insulated lid 20 of a bin 22 which defines the auxiliary zero degree compartment Below the insulation 20a of the lid 20, we have an heat exchanger 21. The lid 20, which in an alternative embodiment can include other walls of the bin or can be replaced by one or more side walls of the bin 22, acts therefore as a liquid to air heat exchanger since it cool the air (and the content) of the bin 22 to the desired temperature near 0°C. In another embodiment the lid 20 can be hollow, i.e. the glycol-water mixture can be circulated within it.
The circulation of the coolant in the heat exchanger 21 of the lid 20, in the pipes 18 and in the reservoir 16 can be obtained by natural convection and adjusted by valves 19 (figures 3 and 4) which are manual valves or driven by a control circuit including a temperature sensor (not shown) provided in the bin 22. The circulation of coolant can be obtained by means of a circulation pump (not shown) driven by the temperature control circuit.
The 0 degree compartment can be for an all-refrigerator (cabinet) or refrigerator-freezer (combi-type) platform. In all-refrigerator and hybrid combi, the heat sink is the fresh food evaporator. In combi (entire no-frost), the heat sink is freezer evaporator. To enhance the cooling of the coolant stored in the reservoir attached to the fresh food evaporator, the refrigerant line can passing through the tank. Finally, the tank needs to be not necessarily attached to the back wall; but needs to be in heat transfer communication with the fresh food evaporator.
The embodiment which has the heater can be selected by customer to be set to tropical fruit zone.
Lastly, in embodiments where the 0 degree compartment is not only well insulated but also well sealed and since there is no air-exchange with the rest of the fresh food compartment, it is possible to preserve the humidity in the 0 degree compartment and not drive it outside of it to be deposited on the evaporator. In any of the embodiments, the temperature control is precise due to buffering action of the water-based liquid coolant.
In figure 5 it is shown a 0 degree compartment tested by the applicant and having dimensions of 320 x 220 x 150 mm. In figure 6 the performances of a 0 degree compartment are shown when the ambient temperature is about 43°C. The temperature variations within the fresh food compartment RC are shown by line C, while with line P are shown the temperatures of testing packages inside the 0 degree compartment. With the line F is is shown the temperature inside the freezer compartemtn FC, while with the line W it is shown the power consumption of the refrigerator. By considering the diagram of figure 6 it is clear that the temperature controllability of the 0 degree compartment is maintained in the range of 0°C +/- 1 °C and it is not affected during defrost cycle shown in figure 6 with reference D.
The heat gain into the 0 degree compartment is comprised between 2 and 3 W, depending on ambient and internal conditions.
Tests carried out by the applicant have shown that the heat exchanger 21 (i.e. a cold plenum) should be 3-4°C colder than the 0 degree compartment:

Heat load [W] 2,00

Internal T° [°C] 0

h_int [W/m² °C] 7

Exchange surface [m²] 0,07

ΔT[°C] 4,06

T_plenum [°C] -4,06

The flat reservoir 16 should be preferably at a temperature about -6°C.

Claims

Refrigeration appliance comprising a compartment with an evaporator (12) in heat exchange relationship with the liner (14) of the compartment and which contains an auxiliary compartment (22) at or near 0°C, characterized in that such auxiliary compartment has at least a cooling wall (20), the liner having a reservoir (16) for a coolant in heat exchange relationship with said evaporator (12), a piping system (18) being provided for connecting such reservoir (16) with the cooling wall (20) of the auxiliary compartment (22) in order to maintain a predetermined temperature in such compartment.
Refrigerator according to claim 1, wherein the evaporator (12) is in heat exchange relationship with the liner of the fresh food compartment on the outer surface thereof.
Refrigeration appliance according to claim 1 or 2, wherein the reservoir (16) is placed on the inner surface of the liner (14).
Refrigeration appliance according to any of claims 1 to 3, wherein the auxiliary compartment is a box-shaped container (22) with a lid (20).
Refrigeration appliance according to any of claims 1 to 3, wherein the cooling wall is a top wall (20) of the auxiliary compartment (22).
Refrigeration appliance according to claim 5, wherein the top wall (20) has an insulation (20a) and underneath it there is provided a liquid-to-air heat exchanger (21).
Refrigeration appliance according to any of the preceding claims, wherein the piping system (18) is provided with at least a valve (19) for controlling the coolant circulation.
Refrigeration appliance according to any of the preceding claims, wherein the piping system (18) is provided with a circulation pump.
Refrigeration appliance according to claim 7 or 8, wherein it comprises a control circuit for adjusting the flow of the coolant.
Refrigeration appliance according to any of the preceding claims, wherein the cooling wall (20) of the auxiliary compartment (22) has a heating element used for defrosting or for maintaining the temperature in the auxiliary compartment (22) at a predetermined temperature above 0°C.
Refrigeration appliance according to any of the preceding claims, wherein the auxiliary compartment (22) is air sealed in order to maintain a predetermined humidity therein.