EP1442630B1 - Heating cabinet - Google Patents

Description

The present invention relates to a heating cabinet to electronic control dedicated to an explosive atmosphere, especially for the maintenance in particular of an index of viscosity required for their use of liquids such as paint, lacquer, plaster, varnish or other a modular radiant electrical panel that can be incorporated into such a cabinet.

Many products today have to be stored at thermostatic cabinet interior in conditions corresponding to their temperature of use. This is the in particular water-based or solvent-based paints, to allow the realization of dosages ready to employment. These cabinets are also likely to be exposed to explosive atmospheres that we will be called "EX" and whose definition is given in the European Directive ATEX n ° 94/9 / CE. As a result, retained design must be compatible with such atmospheres. So far, all the solutions developed remained solutions dedicated to non-explosive atmospheres because they would be extremely expensive if they were to be made as is with technologies "EX" without providing a complete satisfaction to the user. Thus, a first solution is to use an electric heater with or without heat transfer fluid inside the cabinet heating. This solution is particularly expensive in "EX" version. In addition, its establishment requires a large footprint generating an elevation of the cabinet frame or a reduction in the number of pots of Storable products. This solution generates a rise in weight of the cabinet and implies the obligation to position the radiator in the bottom of the cabinet to use the natural rise of heat. This results in a source of concentrated heat in one place, this source being likely to cause overheating in his neighborhood which, especially in the case of painting, cause a hardening of the latter.

Another solution is to have under the shelves of storage of the cabinet of the electric resistances. AT again, this solution would be very expensive "EX". Moreover, it generates variations of important temperatures capable of causing overheating products placed on storage shelves.

Finally, a third solution consists in positioning a electrical resistance outside the heating cabinet and to heat the contents of the cabinet via pulsed air. Thus, cold air pulsed from the outside is warms in passing on the temperature resistance of very high surface by inducing energy consumption important. This results in a diffusion of hot air to around 70 ° C in the cabinet inducing again points of overheating that may cause a hardening of the painting. The distribution of heated air in all the cabinet is channeled by chutes. Resistance is usually installed at the top of the cabinet at outside of the latter to avoid reducing the storage capacity of the cabinet.

None of these solutions therefore makes it possible to avoid a point overheating of stored products. Otherwise, when these solutions are technically suitable for explosive atmospheres, this results in significant additional costs such prohibitive facilities for the application considered. Finally, these heating installations are relatively bulky and reduce important storage capacity of the cabinet.

German document DE-A-2,327,000 illustrates one of the solutions described above. In this case, the device for heating, intended in particular for applications such as heating or drying of clothing, consists of electrical resistors housed in an insulating box, heating being effected by blowing air by means of a fan, this air being heated by passage through the heater.

A similar solution is described in EP-A-0.758.694. In this case, heating elements constituted electrical resistors, in form helical windings, are attached to the top wall of a cabinet so as to extend over the wall used to delimit the heating chamber, a fan being provided in this compartment. Again, the heating is done by blowing hot air, the air is heating in contact with the electric resistances.

US Pat. No. 4,585,923 describes a cabinet heating element whose heating element consists of a heating rod curved in meanders. This stem, which has two points of electrical connection and / or mechanical to the cabinet, is arranged so as to be away from the walls of the heating chamber. Passages air are provided between the heating chamber and the compartment containing the heating element.

A similar heating cabinet is described in the patent US Patent 6,121,583. Again, heating cables are arranged between the outer and inner walls of said cabinet and constitute a source of heat. These cables are in this case inserted into an insulation made of glass fibers, the insulation being function of maintaining the heat developed by the cable of heating inside the compartment containing the said cables.

As a result, in all the solutions described above, heating is done either by heating a blown air, either by means of heating positioned in an external compartment to the cabinet and separated from the walls used for delimitation of the enclosure containing the products to be regulated in temperature.

All these solutions are further developed for a use in normal atmosphere, ie not being likely to reach a threshold between two values explosion limits called LEL% (Lower Limit Explosive) and LSE% (Upper Explosive Limit) because of the concentration of gas present in the air. A classification of chemical substances, issue of the INRS (National Institute of Scientific Research) taken by the "EX" certification bodies, such as the INERIS or the LCIE, makes it possible to evaluate the risk class in which the electrical or electronic equipment must be designed: IIA, IIB or IIC. Very precise standards of construction of electrical equipment for atmospheres explosive exist and describe the different modes of protection, in particular the EN50020 "i" standard for intrinsically safe and the EN50028 "m" standard for encapsulation.

The goal is to avoid all ignition sources such as hot surfaces or arches or sparks of sufficient energy of electrical origin to cause a risk of explosion.

For each level of risk, to which a class of temperature can be associated as specified by the standard EN50014 "general rules", correspond to values critical energies that should not be exceeded and to design equipment used in potentially explosive atmospheres calculating the acceptable limits of the parameters inductance L (μH), capacitance C (ηF), voltage U (V), current I (A) and power P (W) with appropriate safety factors.

An object of the present invention is to provide a cabinet heating whose design means heating allows to obtain uniform heating and substantially homogeneous inside said cabinet, without creating thermal shock, while limiting the bulk of such heating device.

Another object of the present invention is to propose a heated cabinet whose design avoids any direct contact of the heating means with the products stored inside the cabinet.

Another object of the present invention is to propose a heated cabinet whose design makes it possible to integrate heating means without having to proceed to a modification of the cabinet frame and to allow to heat very varied volumes by adapting the power of heating according to the geometry of the cabinet.

Another object of the present invention is to propose a heating cabinet whose design allows installation of such a cabinet in an explosive atmosphere without generate significant additional cost of the whole.

Another object of the invention is to provide performance optimal regulation of the cable heating system heating thanks to the contribution of electronics which allows a better management of a slave system.

For this purpose, the invention relates to a cabinet heating, especially for the maintenance in particular to a Viscosity index required for their use of materials liquids such as paint, lacquer, coating, varnish or another, said heating cabinet being equipped with adjacent to a wall, a perforated panel doubling at least partially said wall, creating a space buffer between wall and panel, characterized in that the perforated panel is a radiant panel equipped on its face forming a back facing the lined wall of the cabinet, profiles supporting at least one electrical element heating, with a view to promoting the heat exchange between heating element and panel, and in that the element electric heating consists of an electric cable heated snaking to contact along the back of the panel to create inside the cabinet at least by conduction a temperature maintenance of the cabinet within a certain range.

According to a preferred embodiment of the invention, the subject of the invention is a heated cabinet, in particular for maintaining in particular at a viscosity index required for their use of liquid materials such as paint, lacquer, coating, varnish or other, characterized in what it is equipped, near the bottom part, a perforated radiant panel doubling in a vertical plane at less partially said background, creating a buffer space between the bottom and the panel, this panel supporting, on its face forming back opposite the bottom of the cabinet, at least one electrical heating cable snaking to contact along the back of the panel to create inside the cabinet at less by conduction a maintenance of the temperature of the cabinet within a certain range.

The design of the perforated radiant panel allows a thermal transfer of the cable fitted to the panel by conduction and radiation conjugated on said panel then serving as the diffusion radiator of the heat, the cable itself having a surface of exchange much too weak. Moreover, such provision allows easy adjustment of the power of heating, in particular according to the length of the cable chosen. Finally, the size of such a device heating is extremely low thanks to the use of a extremely flat panel in upright position and the panel positioning at the back of the cabinet heating does not cause any inconvenience in handling products stored inside the cabinet, or risk of being polluted by the products contained in inside the cabinet.

According to another preferred embodiment of the invention, the electric heating cable is a cable self-limiting type whose heating power is depending on the outside temperature, this cable being compatible with an explosive atmosphere.

The use of a self-limiting cable makes it possible to positioning of such a cabinet in an atmosphere explosive while offering a very economical solution.

The invention also relates to an electrical panel radiant heating cabinet, this panel being arranged for at least partially doubling a wall of said cabinet, characterized in that the face of the panel coming next to the wall of the cabinet called back of the panel is equipped with profiles, preferably in the form of chute, these profiles carrying at least one heating cable snaking to contact along the face of the panel intended coming next to the wall of the cabinet so as to create, inside the cabinet at least by conduction, a temperature maintenance of the cabinet inside a certain beach.

According to a preferred embodiment of the invention, the double panel in vertical plane at least partially the bottom of the cabinet, the back of the panel, intended to come in the bottom of the cabinet, being equipped with shaped chutes to wrap the cable in the laid condition.

la figure 1 représente une vue arrière schématique de l'armoire, le fond de l'armoire ayant été enlevé pour permettre la visualisation du panneau radiant ;

la figure 2 représente une vue schématique de face de l'armoire en position ouverte des portes équipant l'armoire;

la figure 3 représente une vue schématique du panneau assemblé à un bâti servant à délimiter un coffre en partie haute de l'armoire ;

les figures 4A et 4B représentent une vue de détail de la figure 3 correspondant au positionnement des goulottes et à leur possibilité de repli ;

la figure 5 représente des courbes de l'évolution de la température à l'intérieur de l'armoire, en fonction du temps, ces courbes correspondant respectivement à l'évolution de la température au niveau de l'étage du bas, au niveau de l'étage du milieu et au niveau de l'étage du haut de l'armoire ventilée comparativement à la courbe de la température extérieure ambiante variant entre -2°C et +2°C ;

les figures 6 et 7 représentent respectivement des courbes de régulation de la température intérieure d'une armoire en fonction du temps, la figure 7 correspondant à l'état de la technique et

la figure 8 représente un synoptique d'une carte électronique intelligente avec composant microcontrôleur de la famille PIC adaptée pour une atmosphère explosible.

The invention will be better understood on reading the following description of exemplary embodiments, with reference to the appended drawings in which:

Figure 1 shows a schematic rear view of the cabinet, the bottom of the cabinet has been removed to allow viewing of the radiant panel;

Figure 2 shows a schematic front view of the cabinet in the open position of the doors fitted to the cabinet;

Figure 3 shows a schematic view of the panel assembled to a frame for delimiting a chest in the upper part of the cabinet;

FIGS. 4A and 4B show a detail view of FIG. 3 corresponding to the positioning of the chutes and to their possibility of folding;

FIG. 5 represents curves of the evolution of the temperature inside the cabinet, as a function of time, these curves respectively corresponding to the evolution of the temperature at the level of the bottom stage, at the level of the middle floor and at the top floor of the ventilated cabinet compared to the outdoor ambient temperature curve of -2 ° C to + 2 ° C;

FIGS. 6 and 7 respectively represent curves for regulating the internal temperature of a cabinet as a function of time, FIG. 7 corresponding to the state of the art and

FIG. 8 represents a block diagram of an intelligent electronic card with microcontroller component of the PIC family adapted for an explosive atmosphere.

The heating cabinet 1, object of the invention, is more particularly intended for the storage of liquid materials, such as paint, lacquer, plaster, varnish or other generally packaged in pots 9 as illustrated by figure 2. Such products require for their use the maintenance at a determined viscosity index, index that can only be maintained within a determined temperature range. The purpose of such a cabinet 1 heating is therefore to maintain inside the storage enclosure a temperature included in within a predetermined range, preferably the order of 20 ° C ± 2 ° C, at room temperature outside of 0 ° C minimum.

This cabinet 1 is constituted in a manner known per se a frame delimiting a shape storage enclosure general parallelepipedic. The anterior side of the cabinet is closed by means of two doors, the front rear of the cabinet being closed by means of a wall of background 2.

Characteristically to the invention, this cabinet is equipped, in the vicinity of a wall of a radiant panel 3 perforated. In all the examples, this wall is constituted by the bottom part 2 of the cabinet. However, the walls side and floor could have, so equivalent, be equipped with such a panel. This panel 3, which can consist of a blank of sheet metal, can be perforated through cuts in said sheet. The 3B perforations or openings can still be made by other means such as laser cutting, stamping, etc. The void surface constituted by the openings or perforations is usually between 5 and 15%, and preferably at least 10% relative to the surface total of the panel 3 to prevent a large part of the heating cable power is used to heat the panel sheet metal radiator. As a result, the role of panel is double because it ensures a combined function of the conduction of heat and its radiation in the wardrobe. The perforations or perforations 3B also allow, in the installed state of the panel, a circulation of air to inside the enclosure avoiding any accumulation of air hot in the buffer space 8 which will be described below. These perforations have the further advantage of reducing weight total panel and optimize the exchange surface with the air.

This double perforated radiant panel, in vertical plane, at less partially the bottom 2 of the cabinet, creating a space 8 buffer between bottom 2 and panel 3. This space 8 buffer avoids direct contact of the panel with the external cold walls of the heating cabinet of to avoid yield losses. This configuration allows to develop a transfer thermal through a fair surface of Conduction and radiation of heat around the cable heating and to avoid the contacts of the heating cable with an external cold wall source of yield loss.

This panel 3 supports on its back face 3A, corresponding to the face of the panel facing the bottom 2 of the cabinet, at least one electric heating cable 4. This 4 electric cable winds to contact along the back 3A of the panel 3 to create inside the cabinet 1 at least by radiation a maintenance of the temperature of the cabinet 1 within a certain range. This provision of cable allows efficient conduction of heat on the Panel 3 to avoid the user any direct contact with the heating cable.

The electric heating cable 4 used is preferably a self-limiting cable of the type whose heating power depends on the outside temperature, this cable 4 being compatible with an explosive atmosphere. Such a cable is usually used for frost protection or maintenance in pipe temperature, faucet, circuit measuring devices or electrical control cabinets.

The principle of such a cable is as follows: varying with temperature is placed between two Copper conductors in parallel. Resistance modulates and limits the heat release of the cable according to the ambient temperature. If the ambient temperature increases, the heating power of the cable decreases. This behavior self-limitation prevents overheating even in case of overlay. Thanks to the parallel power supply, the entire heating circuit is subjected to a voltage of 230 Volts. It is therefore possible to adapt the cable to a chosen length respecting the intensity values required. Generally, this cable comes in form a tinned copper connection conductor, a cross-linked self-regulating heating resistor synthetic material, an inner insulation sheath, example polyolefin in complete connection with the resistance, an additional insulation sheath, a tinned copper or stainless steel braid and a external protective sheath made of fluorinated resin or polyolefin. Such self-limiting cables toric or dishes, particularly in the form of strips, the technology is now well known, including manufactured and / or marketed by companies such as RAYCHEM, BARTEC, CETAL, FLEXELEC or ETIREX SA, one of which reference of the latter is SRL 10-2C.

The advantage of this technology is to get a cable the surface temperature remains low and below predetermined value. Of course, this cable 4 is connected to an electronic card 12 incorporating means of triggering the heating of the cable according to at least a threshold value, this electronic card 12 receiving itself signals from at least one measuring probe of temperature measuring the temperature inside of the enclosure of the cabinet and able to control outputs auxiliaries such as a fan or options information such as a temperature display. This electronic card has the particularity of being designed according to complementary protection modes "i" intrinsic safety and "m" encapsulation specific for use in potentially explosive atmospheres.

Indeed, this card manages a slave system. This is a system of order ^1, i.e. the relationship between the input and the output is a differential equation of ^1st order.

A widespread existing system is to use an electromechanical thermostat.

These standard heating control systems are all all-or-nothing type in closed loop. Disadvantage major feature of this regulatory principle is its instability he reacts with great inertia because of a lack of precision in the control loop.

In its operating cycle, the transitional regime is characterized by an unstable index response known as overshoot, as shown in Figure 7, this is to say that there will be, on the one hand, an overtaking systematically the high value of tolerance, and other in steady state the difference between the value of the set point of 20 ° C +/- Δt ° C, and the system response will never reach 0 at infinity.

• Une commande chrono-proportionnelle (ou PWM : pulse Width Modulation pour microcontrôleur) qui évite le phénomène de dépassement de consigne à la mise en chauffe (régime transitoire) sollicitant constamment le système de chauffage et créant alors des risques de surchauffe continuelle dans l'armoire chauffante.
• Un ajustage de l'hystérésis en fonction des variations d'inertie des volumes à chauffer et des déperditions thermiques.
• Un pilotage de composant de puissance type TRIAC avec un réamorçage au 0 volt de tension pour assurer la commutation de puissance à un faible niveau d'énergie.
• Des options de sécurité de type rupture de capteur de mesure de la température interdisant alors la fonction de chauffage.

This one-step response curve, corresponding to the set point of the desired temperature, is much more controllable in the electronic application developed as shown in FIG. 6 due to the use of either a microcontroller technology of which an example is given by the PIC product family (see FIG. 8), or of a specific component, an example of which is given by MOTOROLA with the reference UAA2016P. The new functionalities then exploited for the heating cabinet are as follows:

• A chrono-proportional control (or PWM: Pulse Width Modulation for microcontroller) which avoids the phenomenon of exceeding setpoint when warming up (transient) constantly stresses the heating system and creating risks of continual overheating in the cabinet heating.
• An adjustment of the hysteresis according to the variations of inertia of the volumes to be heated and the thermal losses.
• A triac power component control with a 0 volt reboot to ensure power switching at a low energy level.
• Safety options such as breaking the temperature sensor prevent the heating function.

At least the above features are incorporated in the electronic card. These features are good obviously nonexistent for a regulation carried out with a thermostat.

Moreover, the reflection of an "Ex" heating system can advantageously be implemented thanks to the modes of intrinsic safety "i" type protection and "m" encapsulation, the combination of which makes it possible develop integrated display features of the temperature or operational status information by control diodes. This type of function is impossible to be realized in «EX» version with classical solutions previously described.

To allow the attachment of the electric cable (s) 4 on the panel 3, the back 3A of the panel 3 is equipped with shaped sections 5 in the form of a chute used to wrap the cable 4 in the installed state. These chutes 5, plus particularly shown in FIGS. 3 and 4A, 4B, are arranged in preferably parallel rows, possibly with variable spacing, to obtain a homogenization of the temperature from bottom to top of the cabinet 1. Thus, the gap is generally reduced between rows in the lower part so as to increase the heating power in the lower part.

To facilitate the installation of such cables 4, each chute 5 has a foldable marginal edge 5A to wrap each heating cable section 4. Thus, the principle of pose is the following: in the open state of the chute 5, as shown in Figure 4A. Cable 4 is introduced by the upper part of the chute 5 inside said chute. This cable is automatically positioned by gravity at the bottom of the chute. A fold of the game Marginal 5A of the chute is then made to enclose the cable section in the chute 5. Installation such a cable is extremely easy. So the chute 5 can be made by means of a sheet metal strip folded and has a marginal edge 5A separated from the rest of the band by a plurality of slots 6 delimiting a line of folding allowing a withdrawal of the marginal edge 5A and its positioning parallel to another edge previously folded the band to form a cage inside which is positioned the cable 4. These chutes 5 allow to promote the heat exchange between cable 4 and panel 3 and increase the conduction surface of the heat around the heating cable 4.

The enclosure of the cabinet 1 still has in the upper part an internal ventilation 7 to homogenize the temperature the atmosphere of the enclosure. This breakdown 7 is housed inside a chest in the upper part of the enclosure, this box forming an insulating air space in high part the storage volume of the cabinet of the outside atmosphere. As illustrated in Figure 3, this chest can be bounded by a panel 10 extending substantially perpendicular to the panel 3 and taking support against the top of the panel 3. This panel 10 is provided a rim delimiting with the rest of the enclosure a closed volume. The fan is housed inside this volume. Openings 11 are provided in the panel 10 to allow the circulation of hot air brewed by the fan 7. This provision of ventilation 7 allows to perform a forced mixing of the hot air, naturally stored in the upper part of the heating cabinet and the redistribute only in the enclosure. Use internal ventilation makes it possible not to introduce the inside of the polluted air cabinet and ensures homogenization of heat throughout the volume of the heating cabinet in the easiest way possible for a minimum temperature difference between the bottom and the top of the cabinet. Ventilation 7 directs hot air down the cabinet with enough airflow to create an air flow around the heating panel 3, thus avoiding the storing of hot air in the volume 8 buffer.

The tests carried out show, in the presence of a ventilation and the use of a 31 Watt / meter cable at 10 ° C, results consistent with those shown in Figure 5. So, in this case, despite an outside temperature of 0 ° C and very significant heat loss due to the design of cabinets that are poorly insulated, the use of a fan, which will brew the hot air without giving him time to escape to be redistributed in the volume to be maintained, limits the differences temperature between the top and bottom of the cabinet.

Each radiant panel 3 is also an element modular buildable to a similar contiguous panel for cover the dimensional characteristics of the background 2 of a wardrobe. The result is the possibility to integrate the same type of heating module (s) without constraint of transforming an existing cabinet by a exterior cladding. Such a possibility allows to heat very varied volumes by adapting the power of heating according to the geometry of the cabinet. The design of the electric radiant panel 3 as described above, its combination with a self-limiting cable and its incorporation into a cabinet of the aforementioned type allow to obtain a set able to maintain a temperature within a predetermined range in a storage enclosure while allowing the implementation place such a cabinet inside an atmosphere explosive.

Claims (12)

1. Heating cabinet (1), in particular for keeping liquid materials, such as paint, lacquer, render, varnish or other, in particular at a viscosity index required for their use, the said heating cabinet (1) being equipped, in the vicinity of a wall (2), with a perforated panel (3) at least partially covering the said wall (2), creating a buffer space (8) between wall (2) and panel (3),
   characterised in that the perforated panel (3) is a radiant panel equipped, on the surface thereof forming the back facing the covered wall of the cabinet, with sections (5) supporting at least one electrical heating element, with a view to promoting the heat exchange between heating element and panel (3), and in that the electrical heating element consists of a snaking electrical heating tape (4) in contact along the back (3A) of the panel (3) to establish maintenance of the temperature of the cabinet (1) within a set range in the interior of the cabinet (11(sic)), at least by conduction.
2. Heating cabinet (1) according to Claim 1,
   characterised in that it is equipped, in the vicinity of the base part (2) with a perforated radiant panel (3) at least partially covering the said base (2) in the vertical plane, creating a buffer space (8) between base (2) and panel (3), this panel (3) supporting, on the surface thereof forming the back (3A) facing the base (2) of the cabinet (1), at least one snaking electrical heating tape (4) in contact along the back (3A) of the panel (3) to establish maintenance of the temperature of the cabinet (1) within a set range in the interior of the cabinet (1), at least by conduction.
3. Heating cabinet (1) according to one of Claims 1 and 2,
   characterised in that the back (3A) of the panel (3) is equipped with sections (5) in the form of conduits to enclose the tape (4) when fitted.
4. Heating cabinet (1) according to Claim 3,
   characterised in that the conduits (5) are arranged in rows, which are preferably parallel, optionally with variable spacing, in order to achieve homogenisation of the temperature from the bottom to the top of the cabinet (1).
5. Heating cabinet (1) according to one of Claims 3 and 4,
   characterised in that each conduit (5) has a peripheral edge (5A) that can be manually folded to envelop each section of heating tape (4).
6. Heating cabinet (1) according to one of Claims 1 to 5,
   characterised in that the electrical heating tape (4) is a self-regulating tape of the type for which the heating power depends on the external temperature, this tape (4) being compatible with an explosive atmosphere.
7. Heating cabinet (1) according to one of Claims 1 to 6,
   characterised in that the tape (4) is connected to an electronic board (12) incorporating at least one time-proportional control, adjustment of the hysteresis depending on inertia variations in the volumes to be heated and thermal losses, a TRIAC type power component control with resetting at 0 volt voltage to ensure switching of the power at a low energy level and safety features of the type where the temperature measurement sensor is cut off, so barring the heating function.
8. Heating cabinet (1) according to one of Claims 1 to 7,
   characterised in that the chamber of the cabinet (1) has an internal fan (7) in the upper part to make the temperature of the chamber atmosphere homogeneous.
9. Heating cabinet (1) according to Claim 8,
   characterised in that the fan (7) is housed inside a box provided in the upper part of the chamber, this box forming a layer of air insulating the storage volume of the cabinet from the outside atmosphere in the upper part.
10. Heating cabinet (1) according to one of Claims 1 to 9,
    characterised in that each radiant panel (3) constitutes a modular element that can be assembled on a similar contiguous panel for overlaying the dimensional characteristics of a wall such as the base (2) of a cabinet (1) .
11. Radiant electric panel (3) for heating cabinet (1), this panel being equipped to at least partially cover a wall of the said cabinet,
    characterised in that the surface (3A) of the panel intended to face the wall of the cabinet (1), termed the back (3A) of the panel, is equipped with sections (5) preferably in the form of conduits, these sections (5) bearing at least one snaking heating tape (4) in contact along the surface (3A) of the panel intended to face the wall of the cabinet (1) so as to establish, inside the cabinet, maintenance of the temperature of the cabinet within a set range, at least by conduction.
12. Radiant panel according to Claim 11,
    characterised in that the heating tape (4) is a self-regulating tape of the type for which the heating power depends on the external temperature.

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