ES2579170T3 - Operating procedure for a horizontal refrigerated display case for storing products outside opening hours - Google Patents

Abstract

Operating procedure of a horizontal refrigerated display case for storing products outside the opening hours, said showcase (1) comprising at least one heat exchanger (2), connected to a cooling circuit and intended to absorb heat, and suitable ventilation means for generating an air flow (D), which circulates between the heat exchanger (2) and the exposure compartment (3) of said showcase, passing through a supply opening (4) and an opening of return (5), said method comprising a step a) of placing a protective screen (6) inside the showcase to separate the exposure compartment (3) from the external environment, in which said protective screen (6) is located between the supply opening (4) and the return opening (5), so that the supply opening (4) opens directly in the exposure compartment (3) and the return opening (5) opens over directly on the external environment, characterized in that it comprises a stage b) of regulation of the ventilation means, so that the speed (V1) of the air flow (D) is barely sufficient to flow inside the low space of the screen protective, returning said air flow (D) to the heat exchanger (2) passing through the protective screen (6), which is made of an air-permeable material or provided with holes for the passage of air, for later reaching the return opening (5), said protective screen (6) creating a pressure drop in the circulation of the air flow between the supply opening (4) and the return opening (5), such that the Air flow (D) tends to fill the entire exposure compartment (3) under the protective screen (6) before passing through the screen and reaching the return opening (5).

Description

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description

Operating procedure of a horizontal refrigerated display case for storing products outside opening hours

Aplioaoion field

The present invention relates to a method of operating a horizontal refrigerated display cabinet for the storage of products outside opening hours.

"Outside opening hours" refers, in particular, to the closing periods of the point of sale where the showcase is located, for example, during the night or during lunch.

The term "refrigerated display case" refers to display cases at medium temperature, that is, suitable display cases to guarantee storage temperatures of products close to zero. In particular, with reference to the UNI EN 23953 standard, the showcases referred to in the present invention belong to the M0 climate class with temperatures between -1 ° C and + 4 ° C, Ml class with temperatures between -1 ° C +5 ° C, or type M2 with temperatures between -1 ° C and + 7 ° C.

The horizontal refrigerator showcase referred to in the present invention is, in particular, of the type of assisted service or self-service sales. Said horizontal refrigerator showcase can be of the independent type with a built-in condenser / compressor group (showcase known in the jargon as "plug-in") or of the type with a remote condenser group / compressor. In the latter case, the remote group can be dedicated or shared with other showcases and can be installed, for example, in a central plant.

Teonioa State

In general, as shown in Figures 1 or 3, a horizontal refrigerated display cabinet B for ease of service or self-service comprises a bottom F in which food products, possibly contained in trays, and a heat exchanger are placed E for heat absorption. The heat exchanger E may be inside a technical compartment made on the rear side of the showcase (see Figure 1) or on the bottom F (see Figure 3). By means of fans (not shown) an air circulation A is created through the heat exchanger A and the cabinet of the showcase is used to display the products. The air circulates back to the heat exchanger through two openings, one for the supply and one for the return, which place the exposure compartment in fluid communication with the technical compartment.

As shown in Figure 1, the two openings are made in the back of the showcase. A first opening, indicated as A1, serves for the supply of air; A second opening, indicated as A2, serves to return the air and is made above the first.

As shown in Figure 3, the supply opening A1 can be made on the rear side of the showcase, while the return opening A2 can be made on the front side of said showcase.

In general, during the nighttime closing of the point of sale, the refrigerated showcases that exhibit easily perishable products, such as fresh meat, certain types of cheeses, fresh pasta, etc., are emptied. The products are covered with a protective film or with cloths and placed in cold rooms, and the next day they are removed from the cold store and put back in the showcase.

During the closing at lunch time (for example, the closing from 1:00 p.m. to 3:00 p.m.), the products are covered, directly inside the showcase, with sheets of paper or other food compatible films to reduce the effect of "drying" of the products caused by the circulation of the cooling air.

From the above, it is clear that the preparation of a refrigerated display case during the closing periods at night or at lunch is very laborious.

Every night, the operator takes a long time to cover the products with the film and put them inside the cold store. On average, for a showcase with fresh meat 7 meters long this operation for the preparation and transfer of products to the cold store takes an operator approximately 60 minutes.

When they move from the showcase to the cold store, the products suffer an increase in temperature. Once inside the refrigerating chamber, the products must recover the maintenance temperature and in this phase there will be humidity in the environment or, if protected, in the film that covers them in the form of condensation water (the classic drops that can be seen inside the meat packages).

Once the showcase has been turned off and emptied, it must be thoroughly cleaned, otherwise debris from

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food, blood or fluids derived from the products themselves will degrade. For a fresh meat showcase 7 meters long, this cleaning process takes an operator 60 more minutes.

In general, in the period before closing (one or two hours before) the operator, knowing that he will soon have to empty the showcase and close the store, begins to gradually reduce the amount of products on display for sale, without replacing food sold, despite having the time available to do so. This can result in a loss of sales to customers who come a couple of hours before closing.

In the morning, the operator has to arrive at the store very early, since he has to turn on the showcase, wait for it to reach the temperature and then fill it with the products he picked up the night before, as well as throw away the movie that they had covering them. This operation, for a meat showcase 7 meters long, takes approximately 60 minutes. At this point, the operator also has to prepare all the products that had been sold out the night before.

For less perishable products, the showcase emptying operations described above are completely avoided, separating the exhibition compartment (where cooling air circulates) from the outside environment with special protective structures located inside the exhibition compartment to create a closed and protected compartment within which cold air is circulated. These protective structures are positioned in such a way that the two supply openings A1 and return A2 communicate directly with the closed and protected compartment and are separated from the external means. In this way the amount of outside air entering the cabinet is reduced, with a consequent energy saving, and the insects are prevented from entering the exposure compartment. Said protective structures may be rigid structures, such as "night covers", indicated by C in Figure 1, or "sliding or tilting plexiglass panels", or flexible structures, such as "blinds" indicated by T in Figure 2 .

However, the use of such protective structures has drawbacks.

The night covers, made of plastic material, placed on the products to reduce energy consumption, cool and produce the condensation normally spilled in the display case and on the products when they are removed. Night covers made with insulating material do not present the problem of condensation, but being very thick, when removed and stored, they take up a lot of space.

In any case, regardless of what type of protective structure is used, there is still an important operational limit. The permanence of the products inside the showcase does not guarantee the storage conditions offered by a cold store. This is detrimental to the products.

Normally, to cool the product shown at the furthest point of the heat exchanger (i.e. near the front of the showcase) as required, the cooling air flow must be set at a specific speed. This problem arises in particular for showcases in which the two supply and return openings are both made on the rear side of the showcase. Equaling other conditions (such as relative humidity or temperature), the faster the air velocity, the more food dries. From this point of view there is no difference between the types of protection used (blinds, night covers or sliding covers). The products left in the showcase during the night are subject to more marked drying phenomena than those stored in a cold store.

In the case of showcases with the supply opening made on the rear side of the showcase and the return opening made on the front side of the showcase, the phenomena described above are less marked. However, these are subject to another problem. The flow of fresh air entering the exposure compartment tends to flow near the bottom of the exposure compartment due to its higher density and to leave the exposure compartment through the return opening. Therefore, the products placed in the lower part are cooled much more than the products placed towards the upper part, which are only slightly bathed by the air flow. In this case, high velocity air flows are also used to determine a jet effect that contrasts with the downward stratification of the cold air flow. In this case, also the high speed of the air flow accentuates the drying phenomena of the products.

A method of operating a horizontal refrigerated display cabinet according to the preamble of claim 1 is known from DE 42 02 189 A1.

Presentation of the invention

Accordingly, the purpose of the present invention is to eliminate or at least mitigate the drawbacks of the prior art mentioned above, by providing a method of operating a horizontal refrigerated display cabinet for storing products outside the opening hours. which makes it possible to keep the products inside the showcase, achieving a good distribution of the cold air flow inside the exposure compartment, while substantially reducing the drying phenomena of the products.

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A further purpose of the present invention is to have a method of operating a horizontal refrigerated display cabinet for the storage of products outside opening hours that is operatively simple to implement.

A further purpose of the present invention is to have a method of operating a horizontal refrigerated display case for the storage of products outside the opening hours, which makes it possible to avoid the formation of condensation on a protective screen located inside the showcase to separate the exhibition compartment from the outside environment.

An additional purpose of the present invention is to have a method of operating a horizontal refrigerated display cabinet for the storage of products outside the opening hours, which allows the operator to reduce the intervention on the products placed inside the showcase without undermine storage quality.

Brief desoripoion of the drawings

The technical characteristics of the invention, according to the purposes mentioned above, can be clearly seen from the content of the following claims, and the advantages thereof will become more clearly understandable from the detailed description made below. with reference to the attached drawings, which show one or more embodiments by means of non-limiting examples, in which:

- Figure 1 shows a schematic view of a traditional horizontal refrigerated display cabinet for assisted or self-service service provided with a rigid protective cover, with supply and return openings, both made in the rear wall;

- Figure 2 shows a schematic view of a horizontal refrigerated display case for the assisted service or self-service provided with a protective shutter, with supply and return openings, both made in the rear wall;

- Figure 3 shows a schematic view of a traditional horizontal refrigerated display case for assisted service or self-service with the supply opening made in the rear wall of the showcase and the return opening made in the front wall;

- Figure 4 shows a schematic view of a horizontal refrigerated display cabinet for assisted service or self-service operated using the method according to the present invention outside the opening hours, with supply and return openings, both made in the rear wall. ;

- Figure 5 shows the horizontal refrigerated display case in Figure 4 operated using the method according to the present invention in the opening hours; Y

- Figure 6 shows another type of horizontal refrigerated display cabinet for assisted service or self-service operated using the method according to the present invention outside the opening hours, with the supply opening made in the rear wall of the showcase and the return opening made in the front wall.

Detailed desoripoion

To simplify the description, controllable refrigerated display cabinet will first be described using the method according to the invention and, subsequently, the relative operating procedure will be described.

With reference to the accompanying drawings, the reference number 1 generally represents a horizontal refrigerating showcase (in particular of the type for assisted or free service) according to the invention.

Here and hereafter in the description and claims, reference will be made to showcase 1 under conditions of use. Therefore, references to a higher or lower position should be understood in this regard.

According to a general embodiment of the invention, the horizontal refrigeration display case 1 comprises:

- at least one heat exchanger 1, connected to a refrigeration circuit (not shown in the figures) and intended to absorb heat; Y

- ventilation means (not shown in the figures), suitable for generating a flow of air D circulating between the heat exchanger 2 and the exposure compartment 3 of said showcase which passes through a supply opening 4 and an opening return 5.

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In particular, the refrigeration circuit may be of the steam compression type; in this case the heat exchanger 2 constitutes the evaporator. The cooling circuit may also be of any other type suitable for the purpose, such as, for example, the type of direct expansion.

Preferably, the showcase 1 is provided with a support structure 11 that defines a horizontal tank 12. Inside the tank 12, a lower part 8 (fixed or mobile) is placed that acts as a support base for the products to be They will expose. The showcase 1 is provided on the front (ie, the client side) with a glass wall 13. On the back (ie, sales side), the showcase is provided with a raised parapet 14 that can be Use as a support surface for the seller.

As shown in Figure 1, the inside of the tank, against the parapet 14, a technical compartment 15 can be created inside which, in particular, the heat exchanger 2 and the ventilation means are placed. The technical compartment is separated from the exposure compartment by a 7 'rear wall.

Alternatively, as shown in Figure 3, the heat exchanger 2 may be located under the bottom 8 in a special technical compartment fluidically connected to the supply opening 4 and the return opening 5.

According to the preferred embodiment illustrated in Figures 4 and 5, the supply opening 4 and the return opening 5 are both made in the aforementioned rear wall 7 'of the showcase 1 near the heat exchanger 2. The opening of return 5 is located higher than the supply opening 4. In other words, the return opening 5 is higher than the supply opening 4 in relation to the lower part 8.

According to the solution of the alternative embodiment illustrated in Figure 6, the supply opening 4 is made in a rear wall 7 'of the showcase 1, while the return opening 5 is made in a front wall 7' ' of the showcase 1.

The display case 1 is provided with a protective screen 6 which is placed inside the display case to separate the exposure compartment 3 from the outside environment outside the opening hours (for example, closing at night or for lunch).

The display case 1 is provided with first means 9 'for associating an end portion 6' of the protective screen 6 with the rear wall 7 'of the display case. Advantageously, the display case is provided with second means 9 "for associating a second end 6" of the protective screen 6, opposite the second, to the front wall 7 'of the display case 1 to stretch the protective screen over the exposure compartment.

According to the solution of the embodiment illustrated in Figure 4, the first means 9 'for associating the protective screen 6 with the rear wall 7' are located at an intermediate height between the supply opening 4 and the return opening 5.

According to the embodiment illustrated in Figure 6, the first means 9 'for associating the protective screen 6 with the rear wall 7' are located above the supply opening 4, while the second means 9 "for associating the screen protective 6 to the rear wall 7 "are located near the return opening 5, in a position such that when the protective screen 6 is positioned to protect and limit the exposure compartment 3, the return opening 5 opens directly to the environment outside and not to the exposure compartment, confined by the protective screen, which instead opens the discharge opening 4.

When in use, that is, once coupled to the first and second association means mentioned above 9 'and 9 ", the protective screen 6 is located between the supply opening 4 and the return opening 5.

The protective screen 6 is made of an air-permeable material or provided with holes for the passage of air. In particular, the protective screen is made of a flexible or rigid material.

In particular, woven flexible materials can be used, for example, made of polyester or fiberglass, coated with plastic material, for example PVC, in which the air traffic holes are distributed evenly. Each hole has an opening of the order of 1 -2 mm2 '

In the case where the protective screen is made of rigid material, for example a PVC or polycarbonate sheet, the size and distribution of the air transit holes are chosen so that they have a pressure drop for the flow of air that passes through the screen similar to that of a protective screen made of flexible material with holes of 1 to 2 mm2,

As further described in the procedure, the function of the protective screen 6 is to separate the exposure compartment from the outside environment and separate the supply opening from the return opening, so that the supply opening 4 opens directly to the storage compartment. exposure 3 and the opening of

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Return 5 opens directly to the outside environment.

Operationally, in the case where the showcase has the supply opening 4 and the return opening 5 made in the rear wall 7 '(see Figure 4), the function of the protective screen is to create a barrier that prevents flow of air at the outlet of the supply opening 4 at low or very low speeds short circuit with the return opening 5, passing through the exposure compartment 3. At the same time, the protective screen 6 must allow air to escape from the compartment exposure to move back to the return opening 5 and return to the heat exchanger 2.

Operationally, in the case where the cabinet has the supply opening 4 made in the rear wall 7 'and the return opening 5 made in the front wall 7 "(see Figure 6), the function of the protective screen is create a barrier that prevents the flow of air from leaving the exposure compartment through the return opening 5 without first filling the entire exposure compartment under the protective screen 6. Also in this case, the protective screen 6 must allow air to escape from the exposure compartment to circulate back to the return opening 5 and return to the heat exchanger 2.

According to an advantageous embodiment illustrated in Figure 4, the protective screen 6 may include a part 10 not permeable to air or not provided with holes (and, therefore, impervious to air). Said non-permeable part 10 defines the end portion 6 'of the protective screen 6 intended to be connected to the first association means 9' between the supply opening 4 and the return opening 5.

Preferably, said portion 10 includes a strip of the protective screen which extends in length at least for the extension of the length of the supply and return openings. Under conditions of use, said non-permeable portion 10 is located between the supply opening 4 and the return opening 5. The function of this part not permeable or not provided with holes is to avoid any short circuit between the supply opening 4 and the opening return 5. The extension of the width of said tape (ie, in the front / rear direction) is chosen according to the tests performed on the showcase.

According to a general embodiment of the invention, the operating procedure of a horizontal refrigerated display cabinet for storing products outside the opening hours is applied to a horizontal refrigerated display cabinet of the type described above, is that is, comprising at least one heat exchanger 2, connected to a refrigeration circuit and intended to absorb heat, and adequate ventilation means (not shown) to generate an air flow D circulating between the heat exchanger 2 and the exposure compartment 3 of said showcase passing through a supply opening 4 and a return opening 5.

The operating procedure comprises a step a) of placing a protective screen 6 inside the cabinet to separate the exposure compartment 3 from the external environment.

According to the invention, and uneven from the conventional approach, the protective screen 6 is located between the supply opening 4 and the return opening 5, so that the supply opening 4 opens directly to the exposure compartment 3 and the return opening 5 opens directly to the outside environment.

The method further comprises - subsequent to stage a) - a stage b) for regulating the ventilation means so that the air flow D has a velocity V1 just sufficient to flow inside the space under the protective screen.

The air flow D returns to the heat exchanger 2 passing through the protective screen 6, which is made of an air-permeable material or provided with holes for the passage of air, to then reach the return opening 5.

The protective screen 6 - at the same time that it is air permeable or provided with holes - creates a pressure drop in the circulation of the air flow between the supply opening 4 and the return opening 5 such that the flow of Air D tends to fill the entire exposure compartment 3 under the protective screen 6 before passing through the screen and reaching the return opening 5.

In the case of the showcase with the supply and return openings located at the back, and in any case close to each other, thanks to the presence of the protective screen located between the supply opening 4 and the return opening 5, it is possible to drastically reduce the speed of the air flow leaving the supply opening 4, without causing the undesirable phenomenon of short-circuiting of the air, which will prevent the cooled air from reaching the front of the exposure compartment, i.e. , the furthest part of the heat exchanger.

In the case of the showcase with the supply opening and the return opening located respectively on the rear wall and on the front wall, thanks to the presence of the protective screen located between the supply opening 4 and the return opening 5, it is possible to ensure that the air flow charges the display case under the screen

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protective without falling stratification adopting low or very low flow rates. Thanks to the invention, the descending stratification of the air flow is avoided without having to determine the turbulence in said flow by adopting high flow rates.

The adoption of a low or very low speed dramatically reduces the drying phenomena of the exposed products. Thanks to the presence of the barrier that isolates the outdoor exposure compartment, "almost static" cooling of the exposed products can be achieved, intended to be cooled with air flows at low or very low speeds, similar to those of a cold storage chamber .

More specifically, the flow of air leaving the supply opening tends to fill all the protected space between the bottom of the display case and the protective screen, despite having a low speed, properly cooling all the products that are exposed without subject them to moisture elimination phenomena that increase with increasing air flow velocity. Progressively, the (hotter) air that has come into contact with the products on display tends to rise and then cross the protective screen and return to the heat exchanger through the return opening, as a result of the suction action exerted by the ventilation means.

This phenomenon is attributable to the difference in air density at various temperatures (cold air is denser and tends to fall compared to hot air, which is less dense and tends to rise), but mainly to the fact that the protective screen permeable to air or provided with holes - while in itself does not prevent the passage of air - introduces a pressure drop for the air circuit between the supply and return openings. Therefore, air tends to fill the protected volume before crossing the barrier defined by the protective screen.

Thanks to the invention and the "almost static" cooling achievable in the display case, the products can thus be left in the display case outside the opening hours, without subjecting them to drying phenomena.

This greatly simplifies the task of the showcase operator, which reduces the frequency of emptying the showcase to that required by law.

Thanks to the control procedure according to the invention, considering the fact that the current regulations require a thorough cleaning of the showcase, at least every three days, the showcase operator can enjoy the following benefits:

- reduction of the frequency of emptying, cleaning and filling the showcase from once a day (as currently required) to once every three days, saving time, cleaning items and packaging material, and also minimizing thermal shock for the food;

- keep the refrigerator showcase full of products (at the ideal level of exposure for sale) even close to closing time, two days out of three, to have the same sales opportunities also at night;

- have more time to prepare the products to be exhibited, at the time it deems most appropriate;

- product storage, even in the short closing times during the day, as if it were in the cold store;

- arrive at the store later two days out of three;

- have no problems with storage of thermal insulating covers.

In prior art solutions, in which the protective screen is positioned such that the return opening opens to the screen compartment below the protective screen, it is impossible to use low or very low speeds. The air flow will short circuit between the two openings (in the case where the two openings are on top of each other on the same wall) or stratified downwards (in the case where the two openings are located in opposite walls). Therefore, the above-mentioned drying phenomena of the products will be produced, requiring the transfer of the products to the cold room overnight or to protect them during the lunch closing hours.

Thanks to the method according to the invention, the problem of the formation of condensation on the protective screens is also avoided. The air coming from the showcase that has reached through the protective screen forms a flow parallel to the outer surface of the screen towards the return opening. This air flow creates a curtain that prevents ambient air from coming into contact with the coldest protective screen and, therefore, creating condensation on it. Any ambient air that must, in any case, approach the screen is drawn to the heat exchanger by the flow. Therefore, all the problems of condensation formation present in traditional solutions are avoided.

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In the case of the showcase with the supply and return openings located at the back and in any case close together, to further reduce the possibility of short-circuiting the air flow between the two supply and return openings, it can be provided the use of a protective screen 6 that includes a portion not permeable to air 10 or not provided with holes in the area between the two openings.

Advantageously, in the regulation stage b) the ventilation means are regulated so that the air flow has a speed V1 less than the speed V2 that the air flow must have in the display case 1 when the products are stored during the hours opening without the presence of the protective screen 6, with the exposure compartment 3 open to the outside environment.

Advantageously, in the regulation stage b) the ventilation means are regulated so that the air flow has a velocity V1 of not more than / of the speed V2 that the air flow must have in the display case 1 when the products are stored during opening hours without the presence of the protective screen.

Preferably, the speed V1 is not greater than 1/5 of the speed V1 with the unprotected display case, and even more preferably it is not greater than 1/10 of said speed V2.

In fact, it has been tested experimentally in a refrigerated test display case that without the protective screen (i.e., in the conditions of sale; Figure 5), the air flow must have a speed of 0.6 m / s for keep the meat between -1 ° C and 4 ° C throughout the showcase, while to keep the meat between -1 ° C and 4 ° C with the protective screen installed in accordance with the invention (that is, under conditions of no sale; figure 4), the air flow could have a speed of 0.06 m / s.

The invention allows to obtain several advantages, partly already described.

The operation procedure of a horizontal refrigerated display cabinet for the storage of products outside the opening hours according to the invention makes it possible to keep the products inside the showcase, which substantially reduces the drying phenomena of the products. .

The procedure according to the invention is also operatively simple to implement. The correct placement of an air permeable screen and the proper adjustment of the air flow rate are simply required.

The process according to the invention makes it possible to avoid the formation of condensation on the protective screen.

Thanks to the invention, the operator can significantly reduce the intervention on the products placed inside the cabinet without taking away the storage quality.

The invention conceived in this way thus achieves the intended objectives.

Obviously, their practical embodiments can assume different shapes and configurations from those described while remaining within the scope of protection defined by the appended claims.

Claims (9)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 55 claims 1. Operating procedure of a horizontal refrigerated display case for storing products outside opening hours, said showcase (1) comprising at least one heat exchanger (2), connected to a refrigeration circuit and intended to absorb heat , and adequate ventilation means for generating an air flow (D), which circulates between the heat exchanger (2) and the exposure compartment (3) of said showcase, passing through a supply opening (4) and a return opening (5), said method comprising a step a) of placing a protective screen (6) inside the display case to separate the exposure compartment (3) from the external environment, in which said protective screen (6) is located between the supply opening (4) and the return opening (5), so that the supply opening (4) opens directly in the exposure compartment (3) and the return opening (5) opens about address especially on the external environment, characterized in that it comprises a stage b) of regulation of the ventilation means, so that the speed (V1) of the air flow (D) is barely sufficient to flow inside the low space of the screen protective, returning said air flow (D) to the heat exchanger (2) passing through the protective screen (6), which is made of an air-permeable material or is provided with holes for the passage of air, then reaching the return opening (5), said protective screen (6) creating a pressure drop in the circulation of the air flow between the supply opening (4) and the return opening (5), such that the Air flow (D) tends to fill the entire exposure compartment (3) under the protective screen (6) before passing through the screen and reaching the return opening (5). 2. Method according to claim 1, wherein in the regulation stage b) the ventilation means are regulated so that the air flow has a speed (V1) less than the speed (V2) that the air flow must have in the showcase (1) when the products are stored during opening hours without the presence of the protective screen (6), with the exhibition compartment (3) open to the outside environment.
3. Method according to claim 1 or 2, wherein in the regulation stage b) the ventilation means are
regulate so that the air flow has a speed (V1) no greater than / of the speed (V2) than the flow of Air must be in the cabinet (1) when the products are stored during opening hours without the presence of the protective screen (6), with the exposure compartment (3) open to the outside environment.
4. Method according to claim 1 or 2, wherein in the regulation stage b) the ventilation means are
regulate so that the air flow has a velocity (V1) not greater than 1/5, and preferably not greater than 1/10, of the speed (V2) that the air flow must have in the showcase (1) when the products are stored during opening hours without the presence of the protective screen (6), with the exposure compartment ( 3) open to the outside environment. 5. Method according to one or more of the preceding claims, wherein the protective screen is made of flexible or rigid material. Method according to one or more of the preceding claims, in which the supply opening (4) and the return opening (5) are both made in a rear wall (7 ') of the showcase (1), the return opening (5) located higher than the supply opening (4), the protective screen (6) being between the supply opening (4) and the return opening (5). 7. Method according to claim 6, wherein the showcase (1) is provided with first means (9 ') for associating an end portion (6') of the protective screen (6) with the rear wall (7 ' ), said first association means (9 ') being located between the supply opening (4) and the return opening (5). Method according to claim 7, in which the protective screen comprises a part (10) not permeable to air or without holes for the passage of air, said non-permeable part (10) defining the end portion (6 ') of the protective screen (6) intended to be connected to the first association means (9 '), said non-permeable portion (10) situated between the supply opening (4) and the return opening (5) being in use condition. 9. Method according to one or more of claims 1 to 5, wherein the supply opening (4) is made in a rear wall (7 ') of the showcase (1), while the return opening (5 ) is made in a front wall (7 ") of the showcase (1), the protective screen (6) being located between the supply opening (4) and the return opening (5).