WO2016096358A1

WO2016096358A1 - Freezer for frozen products

Info

Publication number: WO2016096358A1
Application number: PCT/EP2015/077690
Authority: WO
Inventors: Edward Baginski; Savvas Andreou TASSOU
Original assignee: Unilever Plc; Unilever N.V.; Conopco, Inc., D/B/A Unilever
Priority date: 2014-12-18
Filing date: 2015-11-25
Publication date: 2016-06-23

Abstract

A freezer for frozen products comprising: a substantially sealed openable chamber suitable for storing frozen products, wherein the chamber has a base, side walls and upper surface; an evaporation circuit (6); and phase changing material (PCM), (7). The evaporation circuit (6) is embedded in the PCM (7), such that at least part of the evaporation circuit surface area is in direct thermal contact with the inner wall (8). At least 50% of the surface of the inner wall (8) is in thermal contact with the PCM (7).

Description

FREEZER FOR FROZEN PRODUCTS

Field of the invention

The present invention relates to a freezer for frozen products and method of its operation. The present invention more particularly relates to a freezer for frozen products comprising an evaporation circuit and phase change material and method of its operation.

Background of the invention

Most frozen products, like for example frozen food products such as frozen

confectionary products like water ice and ice cream type products, are to be stored at a sufficiently low temperature and within narrow temperature ranges in order to maintain product quality. Frozen confectionary is conventionally stored at a maximum temperature of minus 18 degrees Celsius, but for novel frozen confectionary the freezer can be operated at higher temperature like e.g. minus 10 degrees Celsius to maintain specific product attributes like e.g. a soft texture.

Refrigeration by its very nature requires energy to maintain the desired temperature difference between the inside of the freezer and the outside environment. To reduce the environmental impact of operating freezers there is an ongoing desire to reduce the energy consumption of freezers for frozen products.

Freezers for frozen products are known and are normally relying on a vapour compression/expansion cycle to generate the cooling effect inside the freezer located in a room temperature environment. They typically consist of a refrigerating circuit with a compressor, a condenser and an evaporator (often referred to as 'evaporation circuit'), the evaporator being intended to cool the inner space by evaporating a refrigerant. A target internal temperature (often referred to as 'set temperature') is maintained by means of defining an upper and lower temperature at which the refrigeration cycle starts and stops. This results in a temperature range (i.e.

temperature fluctuation) that from a product quality point of view preferably should be narrow. In freezers equipped with a digital thermostat the set temperature can be entered as the desired set temperature. However, some freezers are not equipped with such a digital thermostat and rely on a thermostat that consists of a simple dial numbered typically between 1 to 7, where 7 is coldest (this type of thermostat is usually used in domestic freezers).

A phase change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of heat. Heat is absorbed when the material changes from solid to liquid and released vice versa. The use of PCMs, more specifically eutectic mixtures, in freezers for frozen products is known. PCM has been used to charge a freezer at night and use during the day either because there is no electricity available to power the evaporation unit, like e.g. in an ice cream hawker unit, or to use the availability of cheaper electricity during the night. A typical example can be found in DE2521757 disclosing a hawker cabinet using a eutectic mixture. PCM is also used as a measure to limit defrosting damage in case of a power failure; this is usually done by providing the freezer with cooling elements comprising a eutectic mixture. The ability of PCM to maintain a desired low temperature in a freezer in the absence of a powered evaporation unit depends inter alia on the heat capacity of the PCM, the amount of PCM, the volume of the freezer and the amount of frozen product. Ultimately the PCM will completely melt with a rising freezer temperature as a result. US 2010/0170286 A1 discloses the use of a combination of evaporation cooling and PCM to achieve energy savings and minimize temperature fluctuations thereby maintaining a more controlled temperature inside the freezer.

EP 0 794 396 A1 discloses a heat exchanger comprising a heat bank in a conductive relationship with a refrigerant, the sizing of which is said to make it possible to reduce the compressor run time and the compression ratio of the compressor and, thereby, the energy consumption of the cold-generating appliance. The compressor is kept running until the phase change of a eutectic liquid is complete. US 3,721 ,104 discloses a refrigeration, freezing and/or storage system for use on marine vessels having insulated enclosures or cabinets comprises a plurality of components which may be flexibly located depending upon the size and available space in any particular boat or ship, the system comprising a compressor, nonelectrical means for operating the compressor, a container, a eutectic solution disposed in said container and means for freezing the eutectic solution. There is still a need for alternative and/or improved freezers for frozen products. Such freezers preferably show improved energy consumption (i.e. consume less energy) and/or are able to maintain a narrow temperature range inside the freezer, and at all parts of the freezer.

Summary of the invention

Commercial freezers for frozen products are commonly constructed with an

evaporation circuit in thermal contact with the inner surface of the freezer chamber, thereby extracting heat from the interior of the freezer. Conversely condenser tubes are mounted in thermal contact with the outer surface of the freezer, thereby rejecting heat to the environment. It was found that if PCM was incorporated between the evaporation circuit, with thermal contact maintained between the inner walls and evaporation circuit and the inner walls and PCM, electrical energy savings could be obtained while maintaining product temperatures at required levels.

Accordingly, the present invention relates to a freezer for frozen products comprising:

• a substantially sealed openable chamber suitable for storing frozen products,

wherein the chamber has a base, side walls and upper surface;

• an evaporation circuit;

· phase change material (PCM).

The invention further relates to a method of operating a freezer according to the invention wherein the evaporation circuit is operated such that the temperature inside the chamber is maintained within a temperature range of plus or minus 0 to 5 degrees Celsius in relation to a set temperature.

Detailed description of the invention

The present invention will be further described with reference to the following figures wherein:

Figure 1 represents a schematic view of a freezer for frozen products according to the invention;

Figure 2 represents a schematic view of a freezer for frozen products according to the invention showing a further wall element according to the invention; Figure 3 represents a schematic view of a cross section of a side wall showing the PCM and evaporation circuit;

Figure 4 represents a schematic view of a cross section of a further wall element spaced away from the inner surface of a side wall showing the PCM and evaporation circuit;

For the avoidance of doubt, any feature of one aspect of the present invention may be utilised in any other aspect of the invention. The word "comprising" is intended to mean "including" but not necessarily "consisting of or "composed of." Thus, the term

"comprising" is meant not to be limiting to any subsequently stated elements but rather to optionally also encompass non-specified elements of major or minor functional importance. In other words, the listed steps or options need not be exhaustive.

Whenever the words "including" or "having" are used, these terms are meant to be equivalent to "comprising" as defined above. It is noted that the examples given in the description below are intended to clarify the invention and are not intended to limit the invention to those examples per se.

Except in the examples, or where otherwise explicitly indicated, all numbers in this description indicating amounts of material or conditions of reaction, physical properties of materials and/or use are to be understood as modified by the word "about". Unless specified otherwise, numerical ranges expressed in the format "from x to y" are understood to include x and y. When for a specific feature multiple preferred ranges are described in the format "from x to y", it is understood that all ranges combining the different endpoints are also contemplated.

In a first aspect a freezer 1 for frozen products according to the invention comprises:

• a substantially sealed openable chamber 2 suitable for storing frozen products, wherein the chamber has a base 3, side walls 4 and upper surface 5;

• an evaporation circuit 6;

· phase change material 7 (PCM);

wherein

• the side walls comprise an inner wall portion 8 facing the inside of the chamber; • the PCM is distributed such that it is in thermal contact with at least part of the surface of the inner wall 9 facing away from the inside of the chamber;

• the evaporation circuit is embedded in the PCM, such that at least part of the

evaporation circuit surface area is in direct thermal contact with the inner wall; and · at least 50% of the surface of the inner wall is in thermal contact with the PCM.

The chamber also comprises an opening to enable a consumer to extract the chosen product. A common arrangement is for the upper surface to comprise a viewing window so that the consumer can view the frozen product before opening the chamber to take the chosen product. In many cases the viewing window takes up the entire upper surface of the freezer in so-called glass-lid freezers. It is also common for the chamber to comprise baskets, which contain the frozen product and prevent them contacting the cold walls of the chamber. The side walls and base are thermally insulated 14 such that heat loss is controlled and minimized. Such methods and constructions of insulation are well established in the area of freezers for frozen products.

The freezer of the invention comprises an evaporation circuit as commonly used in existing freezers and further comprises PCM. The PCM is incorporated between the evaporation circuit, such that the evaporation circuit is embedded in the PCM but with at least part of the evaporation circuit surface area still in direct thermal contact with the inner wall. The PCM is distributed such that it is in thermal contact with at least part of the surface of the inner wall facing away from the inside of the chamber and at least 50% of the surface of the inner wall is in thermal contact with the PCM. It was found that such a construction allows for electrical energy savings while maintaining product temperatures at required levels. The PCM is thus placed in thermal contact with the inner wall portion facing the inside of the chamber and sandwiched between the inner wall and a back plate 13a. The back plate can be made of any material but preferably is made of a thermally conductive material like for example metal for improved thermal conductivity and therefore performance of the freezer.

At least 50% of the surface of the inner wall is in thermal contact with the PCM.

Although not necessary it may be preferred to have at least 60%, more preferably at least 70%, even more preferably at least 80% and still even more preferably at least 90% of the surface of the inner wall is in thermal contact with the PCM as this may result in greater energy savings and/or maintaining a narrow temperature inside the freezer. The evaporation circuit is embedded in the PCM, that is, at least part of the surface of the evaporation circuit is in thermal contact with the PCM. In addition at least part of the evaporation circuit surface area is in thermal contact with the inner wall. Preferably at least 50%, more preferably at least 70%, even more preferably at least 90% and still even more preferably at least 95% of the evaporation circuit surface area is in contact with the PCM.

Preferably the ratio of the evaporation circuit surface area that is in direct thermal contact with the PCM to the evaporation circuit surface area that is in direct thermal contact with the inner wall is between 100:1 and 1 :1. Suitable ratios are between 50:1 and 1 :1 like for example between 20:1 and 1 :1 . Phase Change Material (PCM)

PCM are well known in the art. PCM is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy. Heat is absorbed when the material changes from solid to liquid and in that capacity can be used as a cooling device. In reverse, heat is released when the material changes from liquid to solid and this transition can be achieved by cooling the PCM with for example the use of an evaporation circuit.

The temperature at which this phase change takes place is usually referred to as 'phase change temperature'. Preferred PCMs have a large phase change enthalpy as such PCMs are able to provide a lot of heat storage compared to the amount of PCM. When the PCM changes from solid to liquid it will stay at the phase change

temperature until the PCM is completely liquid. The PCM used in the freezer of the invention therefore preferably has a phase change temperature that is lower than, but close to, the set temperature of the freezer, more preferably PCM has a phase change temperature that is within 15 °C of the set temperature, more preferably still within 10 °C and most preferably within 1 to 5 °C of the set temperature. For instance, if the phase change temperature of the PCM is too low compared to the set temperature, it cannot be completely frozen. If the phase change temperature of the PCM is too high compared to the set temperature, the PCM gets completely frozen but has very low cooling potential in terms of latent heat. Thus, it is imperative to use a PCM with a phase change temperature in the correct range of temperature, depending upon the set temperature of the freezer.

Commercial freezers for frozen products usually operate with a set temperature between minus 30 and minus 5 degrees Celsius. A preferred set temperature range is between minus 25 and minus 10 degrees Celsius with a more preferred temperature range between minus 20 and minus 15 degrees Celsius. Therefore, freezers of the invention preferably use PCM with a phase change temperature between minus 30 and minus 5 degrees Celsius, like for example between minus 25 and minus 10 degrees Celsius, with a preferred temperature range between minus 20 and minus 15 degrees Celsius. Suitable PCMs are known in the art and commercially available. Suitable PCMs are for example eutectic mixtures as sold by DuPont Nutrition & Health under the trade name VAMUS^® which consist of a gelatinized eutectic salt solution.

As suitable PCMs will change phase from solid to liquid and vice versa, it will be appreciated that the PCM will not retain its shape. The PCM will therefore usually be packed in containers, like for example a bag, which allows for better handling of the PCM. In addition a gelatinized eutectic mixture can be used. The packaging material for aqueous based PCMs typically consists of a multilayer packaging material that is substantially impermeable to water vapour and ionic salts, thereby preventing drying out of the PCM and corrosion between the PCM and external surfaces. Preferably the packaging material is chosen such that disruption of the thermal conductivity between the PCM and the inner wall as well as the PCM and the evaporation circuit is minimized. This can be achieved for example by using a thermally conductive material and/or thin container wall.

The evaporation circuit may be present as conventional evaporation tubing or as a roll bond evaporator. Roll bonding

Roll bonding is a standard manufacturing process, particularly for the production of evaporators, wherein an enclosed channel is an integral part of a sheet. The enclosed channel is often referred to as 'evaporation circuit'. In this process, a pattern is applied onto a first sheet, preferably a metal sheet, more preferably an aluminium sheet, and preferably using a stop-weld material, a second sheet is then placed face to face with the first sheet after what the resulting metal sandwich is heated and rolled. Hot rolling process completes the bond and subsequent cold rolling reduces the laminated structure to the right thickness. After rolling, the laminated sheet is annealed and, subsequently, a needle is inserted into the stop-weld pattern and hydraulic pressure is applied, through the hollow needle to inflate the non-welded pattern. Areas where the stop-weld compound has been applied become the enclosed channel which are an integral part of the laminated sheet. It will be appreciated that when a roll bond evaporator is used to provide the evaporation circuit, the sheet will form the inner wall portion facing the inside of the chamber.

The freezer of the present invention is a freezer for frozen products. Preferably the frozen products are frozen food products, like frozen confectionary products. Preferably the frozen products are water ice and ice cream type products.

In a second aspect a freezer 1 for frozen products according to the invention comprises:

· a substantially sealed openable chamber 2 suitable for storing frozen products, wherein the chamber has a base 3, side walls 4 and upper surface 5;

• an evaporation circuit 6;

• phase change material 7 (PCM);

wherein the freezer comprises a further wall element 10 placed substantially parallel to but spaced away from the inner surface of the side wall;

wherein the further wall element comprises

• an inner wall portion 11 facing the inside of the chamber, • the PCM, distributed such that it is in thermal contact with at least part of the surface of the further wall 12 facing away from the inside of the chamber and wherein the surface area of the PCM facing away from the inside of the chamber is covered with a further plate such that the PCM is encased by the further plate 13b and the inner wall portion;

evaporation circuit surface area is in direct thermal contact with the inner wall; and

• at least 50% of the surface of the inner wall is in thermal contact with the PCM. In this aspect the cooling means comprising of the evaporation circuit and PCM is contained in a further wall element placed substantially parallel to but spaced away from the inner surface of the side wall. This results in an air gap 15 between the inner surface of the side wall and the further wall element. The PCM is sandwiched between the inner wall portion and further plate 13b to provide for a better holding of the PCM and/or easier construction. The further plate can be made of any material but preferably is made of a thermally conductive material like for example metal for improved thermal conductivity and therefore performance of the freezer.

At least 50% of the surface of the inner wall of the further wall element is in thermal contact with the PCM. Although not necessary it may be preferred to have at least 60%, more preferably at least 70%, even more preferably at least 80% and still even more preferably at least 90% of the surface of the inner wall is in thermal contact with the PCM as this may result in greater energy savings and/or maintaining a narrow temperature inside the freezer

Preferably the ratio of the evaporation circuit surface area that is in direct thermal contact with the PCM to the evaporation circuit surface area that is in direct thermal contact with the inner wall of the further wall element is between 100:1 and 1 :1 .

Suitable ratios are between 50:1 and 1 :1 like for example between 20:1 and 1 :1.

The evaporation circuit is embedded in the PCM, that is, at least part of the surface of the evaporation circuit is in thermal contact with the PCM. In addition at least part of the evaporation circuit surface area is in thermal contact with the inner wall of the further wall element. Preferably at least 50%, more preferably at least 70%, even more preferably at least 90% and still even more preferably at least 95% of the evaporation circuit surface area is in contact with the PCM. Suitable and preferred PCMs are as described above.

The evaporation circuit may be present as conventional evaporation tubing or as a roll bond evaporator, with the roll bond evaporator being preferred. When a roll bond evaporator is used the ratio of the evaporation circuit surface area that is in direct thermal contact with the PCM to the evaporation circuit surface area that is in direct thermal contact with the inner wall of the further wall element will usually be about 1 :1.

Method of operating

In a further aspect the invention relates to a method of operating a freezer according to invention as described wherein the evaporation circuit is operated such that the temperature inside the chamber is maintained within a temperature range of plus or minus 0 to 5 degrees Celsius in relation to a set temperature.

This characterises the difference between the freezer of the present invention and freezers known in the art that utilize PCM in combination with an evaporation circuit. The known freezers use the PCM as an alternative means of cooling in case the evaporation circuit is not able to provide cooling because electrical power is not available. The unavailability of electrical power can be deliberate, like for a hawker cabinet. It can also be because of a power outing that without the presence of PCM, usually in the form of containers places inside the freezer basket, would lead to a rising temperature.

The present invention uses both an evaporator circuit and PCM to maintain the set temperature in a freezer with the refrigeration cycle of the evaporation circuit being responsive and/or aiding to maintain the set temperature within a temperature range of plus or minus 0 to 5 degrees Celsius (i.e. if the set temperature is minus 25 degrees Celsius, the maximum temperature range will be between minus 30 and minus 20 degrees Celsius). Preferably the temperature range is plus or minus 1 to 4, more preferably 2 to 3 degrees Celsius. Preferably the set temperature is between minus 30 and minus 5 degrees Celsius, preferably between minus 25 and minus 10, and more preferably between minus 20 and minus 15.

The invention is now illustrated by the following non-limiting examples.

Examples

The energy consumption and product temperature range (i.e. 'maximum product temperature' minus 'minimum product temperature') was measured for five freezers as described below. Testing was done according to BS EN ISO 23953 with the freezer chamber being filled with ice cream products. Testing was at Climate Class 3 (i.e. 25 degrees Celsius and 60% relative humidity). The results can be found in TABLE 2.

Comparative example A

A commercial 300 litre horizontal ice cream freezer (model NUCAB VT300) with non- glass lids.

Comparative example B

A prototype cabinet was constructed according to dimensions of model NUCAB VT300 but the conventional evaporator construction ("skin evaporator") was not used but was replaced with a roll bond evaporator that was mounted away from the inner surface of the cabinet insulated body, see FIGURE 4. A microchannel condensor was used and vacuum insulation panels were used for cabinet body insulation instead of conventional polyurethane foam insulation. Glass lids were used. For examples 1 and 2, the NUCAB VT300 was modified according to the present invention as described below with further details being provided in TABLE 1.

For example 3, the freezer of comparative example B was modified according to the present invention as described below with further details being provided in TABLE 1. Example 1

PCM was inserted between the existing evaporator tubing. The PCM used is a commercially available eutectic mixture that consist of a gelled aqueous inorganic salt mixture sold under the trade name VAMUS Standard -25' supplied by DuPont Nutrition & Health. The PCM was packed in plastic pouches before being inserted. About 9.7 kg of PCM at a thickness of about 8 mm was used.

Example 2

The original evaporator tubing was removed and replaced with a longer length (21.3 meters instead of the original 19 meters) which was spaced evenly down the depth of the cabinet enabling a higher surface area of PCM to be used than in Example 1 . It was found that this construction minimised product temperature cycling towards the bottom of the cabinet: The temperature fluctuation in products at the bottom of the cabinet was less than 1 °C, whereas for the construction of Example 1 it was greater than 1 °C and in some cases greater than 2 °C. The products at the bottom were also maintained at a narrower temperature range with this construction (-24.2 °C to -22.2 °C compared with Example 1 where the products at the bottom had temperatures ranging from -24.4 to -21 .9 °C). The same PCM and amount was used as for Example 1 .

Example 3

In this example, PCM was mounted to the rear of the roll bond evaporator such that it faced the cabinet insulated body and maintained an air gap between the inner wall of the insulated cabinet body and the outer wall of the PCM assembly. The same PCM and amount was used as for Example 1.

TABLE 1 , Details of Example 1 to 3 freezers

TABLE 2, Results

Maximum product Product Energy temperature temperature range consumption (°C) (°C) (kWhr/day)

Comparative A -18.0 -27.2 to -18.0 2.41

Example 1 -19.0 -24.4 to -19.0 1 .96

Example 2 -18.1 -24.2 to -18.1 2.06

Comparative B -18.0 -24.0 to -18.0 1 .18

Example 3 -18.0 -23.8 to -18.0 0.96

Claims

A freezer (1 ) for frozen products comprising:

a substantially sealed openable chamber (2) suitable for storing frozen products, wherein the chamber has a base (3), side walls (4) and upper surface (5);

an evaporation circuit (6);

phase change material (7) (PCM);

wherein

the side walls comprise an inner wall portion (8) facing the inside of the chamber;

the PCM is distributed such that it is in thermal contact with at least part of the surface of the inner wall (9) facing away from the inside of the chamber; the evaporation circuit is embedded in the PCM, such that at least part of the evaporation circuit surface area is in direct thermal contact with the inner wall; and

A freezer according to claim 1 wherein at least 60%, preferably at least 70%, more preferably at least 80% and even more preferably at least 90% of the surface of the inner wall is in thermal contact with the PCM.

A freezer according to claim 1 or 2 wherein at least 50%, preferably 70%, more preferably 90% and even more preferably 95% of the evaporation circuit surface area is in contact with the PCM.

A freezer according to claim 1 or 2 wherein the ratio of the evaporation circuit surface area that is in direct thermal contact with the PCM to the evaporation circuit surface area that is in direct thermal contact with the inner wall is between 100:1 to 1 :1 . A freezer (1 ) for frozen products comprising:

an evaporation circuit (6);

phase change material (7) (PCM);

wherein the freezer comprises a further wall element (10) placed substantially parallel to but spaced away from the inner surface of the side wall;

wherein the further wall element comprises

an inner wall portion (1 1 ) facing the inside of the chamber,

the PCM, distributed such that it is in thermal contact with at least part of the surface of the further wall (12) facing away from the inside of the chamber and wherein the surface area of the PCM facing away from the inside of the chamber is covered with a further plate (13b) such that the

PCM is encased by the further plate and the inner wall portion;

the evaporation circuit is embedded in the PCM, such that at least part of the evaporation circuit surface area is in direct thermal contact with the inner wall; and

A freezer according to claim 5 wherein at least 60%, preferably at least 70%, more preferably at least 80% and even more preferably at least 90% of the surface of the inner wall of the further wall element is in thermal contact with the PCM.

A freezer according to claim 5 or 6 wherein the ratio of the evaporation circuit surface area that is in direct thermal contact with the PCM to the evaporation circuit surface area that is in direct thermal contact with the inner wall of the further wall element is between 100:1 to 1 :1 . Method of operating a freezer according to any one of claims 1 to 7 wherein the evaporation circuit is operated such that the temperature inside the chamber is maintained within a temperature range of plus or minus 0 to 5 degrees Celsius in relation to a set temperature, and wherein the PCM has a phase change temperature that is lower than, but close to, the set temperature of the freezer. Method according to claim 8 wherein the phase change temperature is within 15 °C of the set temperature. Method according to claim 9 wherein the phase change temperature is within 10 °C of the set temperature, preferably within 1 to 5 °C. Method according to any one of clams 8 to 10 wherein the temperature range is plus or minus 1 to 4, preferably 2 to 3 degrees Celsius. Method according to any one of claims 8 to 10 wherein the set temperature is between minus 30 and minus 5 degrees Celsius, preferably between minus 25 and minus 10, and more preferably between minus 20 and minus 15.