EP1766297B1

EP1766297B1 - Improvement in a fluid heating means

Info

Publication number: EP1766297B1
Application number: EP05740061A
Authority: EP
Inventors: Andrea Taurian; Livio Plos; Daniele Marino
Original assignee: IRCA SpA Industria Resistenze Corazzate e Affini
Current assignee: IRCA SpA Industria Resistenze Corazzate e Affini
Priority date: 2004-05-13
Filing date: 2005-04-26
Publication date: 2008-12-17
Anticipated expiration: 2025-04-26
Also published as: DK1766297T3; WO2005114062A1; ES2320017T3; DE602005011809D1; EP1766297A1; ATE418048T1; ITPN20040033A1; PL1766297T3; HK1105145A1

Abstract

Space-heating radiator with an outer casing containing a fluid to be heated, an electric heating element, a connection fitting applied on the outside of the casing for the power-supply wires to pass therethrough, a TRIAC for controlling the current on the heating element, a heat-sink means for dissipating the heat generated by the TRIAC, a set of TRIAC driving circuits, in which the heat-sink means is at least partially in a tight contact with said connection fitting, so as to provide a direct heat-exchange relationship therewith, and said TRIAC-based control means is applied on a portion of the outer surface of said heat-sink means. This heat-sink means is a metal plate, an end portion of which is formed in a ring- like shape and is applied around said connection fitting; as an alternative thereto, the TRIAC-based control means and the heat-sink means are positioned within the connection fitting.

Description

The present invention relates to an electric heating element for heating up a fluid in which it is submerged according to the preamble of claim 1; a typical application for such heating element is in a space heating radiator provided with an outwards leading connection fitting for the power-supply wires energizing the electric heating element to pass therethrough.
Document US4978833 discloses an electric resistance heating element within a reservoir supplied with AC current through a series-connected bilateral switch device which is periodically switched on and off in accordance with the temperature of water sensed by a sensor at the faucet to maintain a constant dispensing temperature. The switch device is thermally coupled to the bottom of the reservoir such that the reservoir acts as a heat sink to dissipate heat generated during switching. An indicator lamp conditioned by the sensor confirms to the user that the dispensing temperature is within a predetermined range.
Document DE10209905 discloses a device with a triac, for controlling the power of at least one electric heating body. The semiconducting body of the switch or switches is attached to a heat conducting closure part of a chamber of the heating device containing the medium on the side facing away from the chamber for switch cooling. The first connection pole is electrically connected to the closure part, which is connected to the heating body.
Although reference will be made to a space-heating radiator throughout the following description, will be readily appreciated that the present invention may equally apply to any kind of electric heater submerged in a fluid.
Residential-type space-heating radiators are adapted to contain fluids, particularly oil, and are provided with electric heating elements that are arranged in a variety of largely known manners inside an oil batch contained in said radiators, such that the thermal energy released by said submerged elements is readily transferred to the oil and - from the oil- to the outer surface of the radiator.
In view of complying with practical operation-related requirements, these electric heating elements must be energized via an appropriate, preferably electronic control circuitry.
Owing to reasons connected with the need for an adequate heat conductivity to be ensured along with an adequate heat resistance, these tubes are usually made of an appropriate metal, or metal alloy, although this fact is of no relevance as far as the present invention is concerned and is indicated here to the sole purpose of better elucidating the context and actual scope of the present invention.
In general, the electric energy supplied to said electric heating elements to energize the same is not applied in a continuous manner, but is rather supplied in an intermittent manner in accordance with the actual operating requirements, i.e. depending on the temperature of the fluid or the ambient to be heated, which is detected by an appropriate probe or sensor outputting a temperature-representative signal that is sent to said electronic control and switching circuitry, the components of which are usually assembled on a board arranged in a remote position separately from the radiator.
Figure 1 is a symbolical and simplified view illustrating - in a manner that is readily understood by those skilled in the art - a block diagram of the above-described devices and arrangement according to the prior art
For controlling the current to be supplied to the heating element of the radiator use may in principle be made of any controllable switching element, such as for instance a relay; however, the high on/off switching frequency that is generally considered as highly desirable in view of an optimum control of the heating power output, would quite soon jeopardize the efficiency thereof.
In view of doing away with such problem, use is therefore largely made of a suitably driven device known as TRIAC (i.e. Triode Alternating Current Switch), as appropriately driven by said control circuits according to techniques that are widely known as such to those skilled in the art and shall therefore not be dealt with here any further.
The use of such TRIAC device, although ensuring a maximum extent of safety and reliability, is however connected with a major drawback: a TRIAC is in fact a power switching device and, during its operation, it generates thermal energy, which must of course be duly dissipated, so that it tends to heat up quite rapidly to fully unacceptable temperature values that are fully incompatible with its correct operation.
In view of reducing the extent of such problem, it is a largely known practice to have the TRIAC applied into close contact with an appropriate metal cool-down radiator-type heat-sink arrangement adapted to dissipate the heat generated by the TRIAC itself. Owing to reasons of compact construction and uncomplicated, straight circuit arrangements, this TRIAC device and the related radiator-type heat-sink arrangement are inserted in the same box containing the circuits and the electronic driving and control components for the same TRIAC.
However, this solution does not prove fully satisfactory, either, since it still has some drawbacks, i.e.:

a first drawback is of an economic, production-related nature, and lies in the fact that such metal cool-down radiator-type heat-sink arrangement is a rather expensive component part; in addition, it requires a certain amount of mounting space, which thing is seriously prejudicial when the same box is due to contain also the user-operated temperature control and adjustment means, so that it must therefore be capable of being positioned in a simple and conveniently accessible manner:

a second drawback is a consequence of the kind of operation, i.e. the inherent nature of the TRIAC itself; even if it is cooled down by means of a suitable heat-sink arrangement, the TRIAC is anyway subject to heating up, so that it heats up also the air contained in the enclosed, sealed volume accommodating the control board; owing to the fact that housed in the same enclosed volume there is also the temperature probe or sensory, the latter is practically forced to detect a temperature that is different from i.e. generally hotter than the actual temperature in the room in which the temperature control box is placed, and to issue a correspondingly "doped"; i.e. altered signal that ultimately has the effect of negatively effecting the correct operation, of the whole temperature control arrangement contained in the box.

It would therefore be desirable, and it is actually a main object of the present invention to provide a kind of electric heating element and related control circuits, including the power control circuit which do away with the afore-cited drawback and are capable of being manufactured in a low-cost, simple manner using readily available materials and techniques.
According to the present invention, this aim, along with further ones that will become apparent in the course of the following description, is reached by means of a fluid heating device according to claim 1.
The present invention may be implemented in the form of a preferred, although not sole embodiment that will be described in greater detail and illustrated below by mere way of non-limiting example with reference to the accompanying drawings, in which:

Figure 2 is a perspective view of a cutaway representation of the devices and the general arrangement in a first embodiment of the present invention;
Figure 3 is a view of the devices illustrated in Figure 2, in the assembled state thereof;
Figures 4A, 4B and 4C are respective orthogonal views of the devices illustrated in Figure 3;
Figure 5 is a perspective view of a cutaway representation of the devices and the general arrangement in a second embodiment of the present invention;
Figure 6 is a partially cross-sectional view of the devices illustrated in Figure 5, in the assembled state thereof;
Figure 7 is a partially cross-sectional view of the assembled devices in a further improvement of the embodiment illustrated in Figure 6;
Figure 8 is a symbolical view of the wiring diagram of the further improved embodiment of Figure 7.

With reference to Figures 2 to 4C, a fluid heating apparatus according to the present invention comprises an outer casing adapted to contain the fluid to be heated, one or more electric heating elements 2 submerged in the fluid to be heated, a connection fitting 3 applied externally on to said outer casing, through for the electric power-supply wires 4 energizing said electric heating elements 2 to pass therethrough, wherein this connection fitting is of course duly provided with appropriate sealing means (not shown) to prevent the fluid contained in the radiator from leaking outside.
Associated to said connection fitting there is provided externally a metal dissipating, i.e. heat-sink plate, which is so shaped and applied as to provide a large contact surface, and hence an optimum extent of heat conducting capacity, with said connection fitting 3. In an advantageous manner, this heat-dumping plate features, at an end portion thereof, a ring-like conformation, so that this ringshaped portion is in this way capable of acting as both the contact surface and a mechanical coupling means, when fastened on by means of an appropriate nut 6 that locks it in place against said connection fitting.
On the other end portion of said metal plate 5 there is provided a planar surface 7, on which there is applied - with the aid of means largely known as such in the art, e.g. a spring 8 - the TRIAC 9.
This TRIAC device is connected, via three electric wires 10, to a board 11, on which there are arranged the electronic components (not shown) included in the TRIAC driving circuit.
To the same board there are also connected the two electric wires 4 used to supply power to the electric heating element 2, along with the electric wires 12 for conveying the signal issued as an output be the temperature probe 25 or any possible signal processing circuits associated thereto.
It should in fact be particularly pointed out that, although the temperature signal processing and TRIAC driving functions can in principle be physically arranged on different assemblies, in view of making the radiator apparatus fully self-sufficient, i.e. self contained and autonomous from an operating point of view, all these assemblies are however collected, i.e. brought together in a most appropriate manner on said single board 11.
It may therefore be most readily appreciated how, in this case, the physical position of both the TRIAC and the heat-sink arrangement thereof, as formed by the above-mentioned metal plate 5, is totally different from any typical arrangement found in the prior art, since according to the present invention the TRIAC is in this case thermally connected to said metal plate 5, which in turn ensures a thermal, i.e. heat-conduction continuity with the huge external mass of the radiator, thereby ensuring a most efficient cooling-down, i.e. heat dumping effect.
In this connection, it should in fact be kept in mind that the TRIAC works usually at temperatures of approx. 100°C, while the mass of a radiator does on the contrary not exceed a temperature of approx. 70°C; therefore, even if the radiator becomes certainly much hotter than the ambient it is due to heat up, it nevertheless forms a quite effective means for dissipating the heat generated by said TRIAC and keeping the latter at an optimally stabilized temperature within sure safety limits.
A further advantage of the present invention derives from the fact that said metal plate 5 is a part that can be manufactured in a most low-cost and simple manner.
However, the above-described solution, although surely simple and effective, still has a drawback in that the proposed cantilever-type mounting of the TRIAC on the connection fitting is certainly a delicate and mechanically risky one, owing to the shock hazards which it may be subject to, and which may cause it and the related electrical connections to suffer damages.
In order to do away withy such drawback, following advantageous embodiment is therefore proposed: with reference to Figures 5 to 7, this improved solution is based on mounting the TRIAC not on the outside of the connection fitting, but rather fully inside the latter.
According to this embodiment, the TRIAC 9 is applied - with the aid of means generally known as such in the art - on a planar face of a solid member 21 that is markedly heat-conductive, e.g. of metal, whereas the opposite surface thereof is a portion of a cylinder that is so shaped as to be able to perfectly fit into the channel 22 that passes internally across the connection fitting 3.
In a preferred manner, between the base of the TRIAC and said solid member 21 there is inserted - in a tight contact therewith - an electrically insulating, but highly heat-conductive planar support 20 of a limited size, in which said planar support 20 is applied to both provide a double insulation to the TRIAC and comply with a number of other purely commercial, i.e. marketing reasons.
As far as this planar support 20 is concerned, it may be made of any appropriate material combining electrically insulating (so as to insulate the TRIAC from the surrounding fitting) and heat conduction properties; appropriate materials of this kind are anyway available in the art; one of these materials is for example the one that is currently available under the trade-name Kapton®.
The assembly formed by the TRIAC, the planar support 20 and the solid member 21 is then inserted as a whole into a conductive ring or part of a conductive ring 23, so as to form a single assembled block; finally, this single assembled block is fitted into said channel 22, whereupon the electric connections are completed.
As far as the electric wires 4 connecting the electric heating element 2 are concerned, these continue beyond the connection fitting 3 to join - by soldering or similar technique - with the contacts from which said electric heating element moves off, wherein said electric heating elements consists usually of a sheathed-type heating element as widely known as such in the art, i.e. provided with a rigid outer sheathing 24.
Care will also be of course taken to ensure that the various above-described items and elements are sized relative to each other so as to make it possible for the whole assembly operation to be carried out in a most convenient manner, while at the same time providing as great a contact surface as possible between the inner cylindrical surface of said channel 22, on the one side, and the surfaces facing the outside of said solid member 21 and said ring 23 on the other side, so as to provide for the best possible heat transfer from the TRIAC to the connection fitting.
As far as the sequence of manufacturing operations required and the construction principles involved are on the other hand concerned, these are certainly within the abilities of those skilled in the art, who may also opt for any of a number of different possibilities existing in this connection, so that they shall not be dealt with here to any further extent.
The above-described solution also enables a further advantage to be reached. In this connection, it should again be pointed out how, in the prior art (Figure 1), the various components of the control and driving circuits are substantially arranged on the same board carrying also the TRIAC; since quite strong currents flow across the TRIAC, actually, the latter turns of course into a source of interferences radiating therefrom and propagating to the various components arranged close therearound, which are usually not shielded against these interferences and are generally supplied with low voltages and currents.
On the contrary, according to this improvement of the present invention, the signal processing and control circuits, as well as the TRIAC driving circuits, are still all arranged on the same board 11, while the TRIAC itself, owing to its being housed within the metal fitting 3, cannot radiate any electromagnetic field that may reach and affect the circuits on said board 11.
Ultimately, the further and certainly not trivial result of a greatly reduced vulnerability to self-induced interferences is obtained in this way.
Anyway, although greatly improved and inherently efficient, the above-illustrated configuration still has a drawback in that the power-supply wires 4 used to energize the heating element are connected to the power-supply line and still pass across the afore-cited board 11 carrying the TRIAC control and driving circuits.
This represents a kind of constraint that gives rise to some problems and drawbacks connected with safety and standard regulations. As a matter of fact, the line current that is necessarily present on the board implies a number of construction-related constraints, which complicate the overall construction and weigh heavily on the related costs.
In addition, in the case of a change in the line voltage, as this may for instance occur if the radiator is installed in a country having line voltages different from the usual value of 220V, such as for example in the USA, said control board 11 cannot be used any longer, with a resulting penalty of having to produce as many specific boards as the line voltages existing in the various countries in which radiators are going to be marketed.
In view of doing away with this problem, the improvement is proposed, which consists in adopting the solution that is symbolically illustrated in Figures 7 and 8, where it can be noticed that the voltage used to energize the TRIAC 9 is brought in directly from the line via the connection 35, thereby fully omitting any intermediate passage across the board 11.
In this case, the heating element 2 is supplied from a connection 33 coming directly from the line, and a connection 34 coming from said TRIAC, which acts as a "gate" with respect to the current reaching it via said connection 35.
The TRIAC driving signals reach it via two connections 38, 39 that are independent of the line voltage; advantageously, these driving signals may be caused to reach a switching means 40, as preferably consisting of an optoelectronic switch of any known type, which then sends the resulting control signal to said TRIAC 9 via a respective connection 41.
Again, all of the afore-described solutions allow for another advantageous improvement to be duly implemented. In fact, if the TRIAC is driven with an easily modulable low voltage, e.g. 12V, which may therefore be provided also by a common battery, a specific line-voltage power supply can be simply omitted.
Basically, according to this improvement, the line voltage reaches the TRIAC via the two connections 33 and 35, which do not contemplate any passage across the board 11, whereas the two connections 38, 39 that drive the same TRIAC are derived from the same board and are independent of said connections 33 and 35.
Accordingly, the invention and the afore-cited improvements can be readily appreciated to be such as to allow for a maximum extent of flexibility in the use of a space-heating radiator, owing to the latter being capable of being supplied independently of the power-supply line voltage and, furthermore, a dedicated control board, to be specifically designed and provided for any standard line voltage in use, not being strictly needed.
This in fact enables the practical advantage to be reached, which derives from the possibility for the control board 11 and, similarly, the whole set of electronic control and driving circuits to be produced as a single, functionally and constructively autonomous and standardized component part

Claims

A fluid heating device comprising: - an outer casing (1) adapted to contain a fluid to be heated,
- one or more electric heating elements (2) submerged in said fluid to be heated,

- a connection fitting (3) applied on the outside of said casing (1) for the power-supply wires (4) energising said electric heating elements (2) to pass therethrough,

- a current regulation device (9), preferably of the TRIAC-type, for controlling the current supplied to said one or more electric heating elements (2),

- heat-sink means for dissipating the heat generated by said current regulation device (9),

- control circuits (11) for driving said current regulation device (9), - power-supply means adapted to energise said one or more electric heating elements (2) via said current regulation device (9), characterized in that
said heat-sink means is a metal plate (5), an end portion of which is formed in a ring-like shape and is applied in a tight contact around said connection fitting (3) so as to provide a direct heat-exchange relationship therewith, and the other end portion of the metal plate (5) comprises a surface (7), on which said current regulation device (9) is applied.
A fluid heating means according to claim 1, wherein said one or more electric heating elements (2) are supplied from a terminal thereof via a first connection (33) that is directly connected with the power-supply line, while, from the other terminal thereof, it is supplied via a second connection (34) that is connected to said current regulation device (9), from which there branches off a third power-supply connection (35), in which said first connection and said third connection are not connected to said set of driving circuits(11).
A fluid heating means according to claim 2, wherein said current regulation device (9) is driven by a low-voltage signal that is carried through two isolated connections (38,39), both of which are independent of the power-supply line connections.
A fluid heating means according to claim 3, wherein between said two isolated connections (38, 39) of the driving signal and said current regulation device (9) there is provided a switching means (40), preferably of an opto-electronic type