Vehicle for the Refrigeration Transport of Products the Energy Consumption of which is Improved by Incorporating a Phase-Change Material into the Walls of the Vehicle Body

Abstract

A vehicle for the refrigerated transport of products comprising at least one products storage chamber, characterized in that:—one or more panels made from a material of so-called “phase-change” type have been incorporated into the structure of all or part of the walls of at least one of the storage chambers of the lorry;—the phase-change material has a melting point that is just a few degrees higher than the target datum temperature for the chamber in question, preferably 2 to 10° C. higher than said datum temperature and more preferably still 3 to 5° C. higher than said datum temperature.

Description

The present invention relates to the area of transport and the distribution of thermosensitive products, such as pharmaceutical products and foodstuffs.

Transporting products at a controlled and regulated temperature has become a major issue with regard to cold chain distribution, which is essential for maintaining the quality and viability of organic products, whether they are foodstuffs or drugs, vaccines, bio-samples, etc. Typically, perishable foodstuffs are transported chilled or frozen (at a positive or negative temperature), whereas drugs and vaccines are transported chilled (at a positive temperature). The transportation generally takes place between the place of production, storage or distribution sites and places of sale and/or consumption.

Chilled or frozen products are transported in refrigerated lorries. This transport is essentially dependent on “mechanical” methods of generating cold. It is also possible to use “cryogenic” solutions based on the use of liquid nitrogen or CO₂ as cold sources for maintaining positive (chilled) or negative (frozen) temperatures.

The advantages of cryogenic solutions, which consist of “direct” injections into the interior of the chamber or chambers for storing the products (spray) or “indirect” injections (where cryogenic fluid is channelled from a cryogenic reservoir stored on the refrigerated lorry (generally underneath the lorry) to one or more heat exchangers located on the inside of the cold chamber or chambers of the lorry), are well known, but their penetration onto the market has been held back by the associated economic cost.

One factor that has a significant influence on the cost is of course the quantity of cryogen (nitrogen or CO₂) required to chill to the desired temperatures.

A physical analysis of heat exchanger mechanisms shows clearly that the thermal inertia of the walls of the storage chamber or chambers plays a significant part in the energy balance. It could, in itself, in some configurations be responsible for 50% of the overall consumption of cryogen.

The present invention therefore proposes a solution which makes it possible to recover at least a portion of the cold transferred to the walls for subsequent reuse during the operational phase of the lorry.

It is known that in refrigerated lorries the insulating walls used currently are most commonly made of polyurethane with a plastic coating on the outside and a conducting material on the inside (the “cold” side being in contact with the chamber). The cooling of this structure is very time-consuming and uses a lot of primary energy.

As explained in more detail below the present invention proposes a new wall structure that can be summarised as follows:

• • one or more panels made from a “less energy consuming” material is or are incorporated into the structure of all or a portion of the walls of at least one of the storage chambers of the lorry, said material is known as a “phase change” material;
  • this incorporation preferably covers all or a portion of half of the wall on the side of the cold source (side of the storage chamber, which comprises the injectors in a “direct” injection or exchangers in an “indirect” injection method);
  • by way of example according to one exemplary embodiment of the invention the succession of layers from the interior of the box would be: a conducting layer, a layer of phase change material, a layer of polyurethane and a layer of plastic material, the conducting layer on the inner side of the box acting as a thermal transmission sheet towards the phase-change material;
  • the phase-change material is selected in order to obtain a sufficient melting point according to the type of application intended (chilled, or frozen transport) and the range of temperatures needed (very specific temperature ranges for some organic products for example). For reasons that will be explained in more detail below, preferably according to the invention a phase-change material is used with a melting temperature which is only a few degrees higher than the intended set point temperature in the chamber in question: preferably 2 to 10° C. higher than the set point temperature and more preferably 3 to 5° C. higher.

As an example of the set point temperatures usually used in the transport industry it would be possible to have a set point temperature of 0 to 4° C. for the transport of chilled products, whereas set point temperatures of −20° C. are used for the transport of frozen products, both of these set point temperatures can be used in two adjacent chambers of the same lorry.

By way of example, according to the invention a material is selected with a melting temperature of +8° C. for chilled transport and a melting temperature of −10° C. for frozen transport.

It is also possible to select these materials from a range of organic materials including waxes, oils, fatty acids and polyglycols or even from a range of capsules filled with salt hydrates.

The advantage of including such a material in the wall of the box is associated with its ability to store cold at the time of cooling the lorry (when starting up, or even after opening the door . . . ), and then restore it when the temperature of the box is higher than the melting temperature.

The latent melting/solidification heat then makes it possible to save a significant amount of primary energy (nitrogen or CO2 in the case of cryogenic solutions) and thus reduce the consumption thereof.

Thus the present invention relates to a vehicle for the refrigerated transport of products, comprising at least one chamber for storing products, of the type where the cooling system used by the vehicle is cryogenic, by means of the direct or indirect injection of a cryogenic fluid into said at least one storage chamber, characterised in that:

• • one or more panels made from a so-called “phase-change” type of material are incorporated into the structure of all or a portion of the walls of at least one of the storage chambers of the lorry;
  • the phase-change material has a melting point that is only a few degrees higher than the intended set point temperature in the chamber in question, preferably 2 to 10° C. higher than said set point temperature and even more preferably 3 to 5° C. higher than said set point temperature.

According to one of the preferred embodiments of the invention the phase-change material is incorporated into all or a portion of half of the wall located on the side of the cold source (storage chamber side) and even more preferably into all or a portion of a third of the wall located on the side of the cold source.

The attached FIG. 1 illustrates in cross section in its two views a) and b):

• • in a) a wall structure that is found in some current lorries, with a sequence from the inside of the box of a conducting layer 1, a polyurethane layer 2 and layer of plastic material 3;
  • in b) an exemplary embodiment of the invention, where a layer 4 of phase-change material is incorporated into the preceding structure, it should be noted that this layer 4 is incorporated substantially into the half of the wall which is on the chamber side of the assembly.

In the following an example of the behaviour of the wall is explained during an operational phase of the lorry.

For a refrigerated lorry designed for transporting chilled products, the start-up of the cooling system (either the direct or indirect injection of cryogenic fluid) makes it possible to lower the temperature of the air inside the chamber to the set point temperature, then to maintain this temperature enabling the regulation of the system. In a manner known to a person skilled in the art the existing solutions for controlling the temperature of the internal air in the box storing the transported products use algorithms for controlling the opening/closing of valves supplying the injectors or the internal exchangers in the box with cryogen.

After each delivery of one or more pallets the doors are open to the outside air and the temperature of the air inside the lorry rises and the cooling system has to supply the necessary refrigerating power to restore the set point temperature as quickly as possible to maintain the chain of cold.

The time necessary to reach the set point temperature when first starting up and after each opening of the door depends on several parameters, principally the maximum refrigeration power that the cooling system can supply but also the removal of the inner/outer temperature and the thermo-physical properties (in particular the conductivity) of the materials forming the walls of the lorry.

Although the air reaches its set point temperature after a period defined by the functioning parameters mentioned above, the walls of the lorry continue to absorb energy as their thermal inertia is much greater than air. Consequently, they only achieve equilibrium after several hours of lowering the temperature of the internal air in the lorry (this time is known in the industry as “pull down”).

In the case of a refrigeration lorry according to the invention which is formed integrally or partially by walls containing phase-change materials, during the lowering of the air temperature when starting up or after opening the door the temperature in the walls also falls, in particular in the layer containing the phase-change material which will drop in temperature until it reaches its solidification temperature. Then the phase of storing energy is initiated in this material which is going to solidify progressively.

More precisely, at the start of a tour or after a prolonged opening of the door, cryogen is introduced to lower the internal temperature of the chamber for storing products to the level of a required set point temperature (for example from 20-25° C. to a set point temperature of +4° C. for chilled products), either by means of a direct injection technique (spray) or an indirect injection technique (exchangers). Following the introduction of cryogen the temperature in the walls lowers, particularly in the layer containing the phase-change material which will drop in temperature until it reaches its solidification temperature.

Then the phase of storing energy is initiated in this material which is going to solidify progressively.

On the basis of the material selected the storage of energy in the material will start before the set point temperature of the internal air in the chamber has been reached, and the partial or complete solidification of the material before the set point temperature of the internal air in the chamber has been reached is going to depend on different parameters, essentially on its thermo-physical properties (conductivity, specific heat) and the quantity of material used (mass), but it is preferable to select the correct amount of a suitable material so that the material is completely or almost completely solidified when the temperature has reached the internal set point temperature in the box.

When the door has been opened for a significant time during the tour and the temperature of the internal air has risen, the return to the set point temperature of the interior of the box will be more rapid as the phase-change material will restore to the air a portion of the energy that it has stored thus saving energy.

Thus at each point in the route of the vehicle:

• • if the internal temperature of the chamber is very slightly above the required set point temperature (1 K for example), the material will transfer a little energy (variation of sensible heat) contributing to the air returning to its temperature, it serves as a kind of buffer in order to even out the variation in temperature more effectively,
  • if the internal temperature in the chamber increases by several degrees following the opening of the door(s) for several minutes for example, the material transfers a significant portion of its energy up to the point of partly melting (variation of its latent heat) and facilitates the rapid return of the air to its set point temperature, requiring the addition of less primary cryogen: the system for controlling the temperature in such vehicles, by controlling the opening/closing of the valves supplying the injectors or the internal exchangers of the box with cryogen as a function of taking the internal temperature, takes into account (takes advantage) of the supply of energy coming from the panels of phase-change material.

And the choice in this respect of a phase-change material with a slightly higher melting temperature than the set point temperature of the desired air is very advantageous, since in contrast a material with melting temperature lower than the set point temperature would continue to store the energy during the maintenance phase (a useless process) and moreover, with each return to the set point temperature it would continue to consume energy as it would have the tendency to want to solidify naturally.

Claims

1-2. (canceled)

3. A vehicle for the refrigerated transport of products comprising at least one chamber for storing products, of the type where the cooling system used by the vehicle is cryogenic, by means of the direct or indirect injection of a cryogenic fluid into the said at least one storage chamber, characterized in that:

one or more panels made from a phase-change material are incorporated into the structure of all or a portion of the walls of at least one of the storage chambers of the lorry; and

the phase-change material has a melting point that is 2 to 10° C. higher than an intended set point temperature in the chamber in question.

4. The vehicle of claim 3, wherein, the phase-change material has a melting point that is 3 to 5 ° C. higher than said set point temperature.

5. The vehicle of claim 3, wherein the phase-change material is incorporated into at least half of the wall located on the storage chamber side.

6. The vehicle of claim 3, wherein the phase-change material is incorporated into at least one third of the wall located on the storage chamber side.