SK9684Y1 - PTC electric heater - Google Patents

Abstract

An electric liquid heater comprising a plastic container for liquid consisting of an upper cylindrical part (1) and a lower conical part (2), which are water tightly connected to each other. An essentially cylindrical plastic concentric wall (5) defining an internal circulation channel (31) and an external circulation channel (32) is firmly arranged inside the plastic container, while the external circulation channel (32) is connected to the outlet (4) of the heated liquids. It also includes a heating module (6), which is equipped with a connection socket (61) for supplying the liquid intended for heating, a continuous cavity (65) for conducting the liquid intended for heating and external surfaces (64). The hollow heating module (6) is arranged in the internal circulation channel (31), at least one PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) is arranged on the outer surfaces (64) of the heating module (6), generating heat and each PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) includes a flexible metal electrical conductor (11) to apply electrical voltage and to press the PTC heating assembly to the concentric wall (5) and to the heating module (6).

Description

The field of technology

The technical solution concerns an electric heater for heating liquids circulating mainly in heating circuits of residential buildings and especially in systems with a closed circuit of heat-carrying liquid.

Current state of the art

Electric heaters used for heating liquids in the heating circuits of residential buildings, such as instantaneous water heaters, backup electric heaters for heating the heat-carrying medium in heat pump systems and other similar devices, have heating elements usually assembled from resistance wires insulated with a layer of magnesium oxide and placed in a stainless steel jacket. Their basic feature is that the heating elements provide power proportional only to the supply voltage, and the construction of such a heater is simple.

However, the very use of such simple heating elements for heating the heat-carrying medium, on the other hand, requires a complex safety concept, including heating control based on the outputs of temperature sensors, flow sensors, safety temperature limiters and other necessary components, since the temperature of the heating elements can reach a temperature of up to 800 °C.

Such devices are described, for example, in document EP 3910260 A1 or in document EP 3869118 A1.

Newer electric liquid heaters use other suitable elements to heat the heat-carrying medium, while the so-called PTC heating elements (PTC = positive temperature coefficient).

PTC elements are elements that are electrically conductive at low temperatures, but after reaching a certain temperature barrier, the electrical conductivity drops sharply. As the temperature of the PTC element increases, its resistance increases. Negative feedback is used, acting during the self-heating of the PTC element due to the passing current. When powered from a constant voltage source, this will cause a drop in power on the PTC element, which counteracts further temperature rise. The result is simple heating with stabilization of the temperature of the heated space.

Heating using PTC elements is therefore safe due to automatic temperature regulation and the fact that the maximum temperature of the heated element is lower than 300 °C. Independent power regulation does not require control using a thermostat.

PTC elements can be made from ceramics or organic polymers, they are mainly produced as plates with two electrically conductive electrodes for connecting the supply voltage, heating assemblies from PTC elements can contain insulating foils and other components, for example electrically conductive adhesives.

EP 3910260 A1 discloses an electric water heater for a closed circuit heating water system comprising a water tank connected to a flange, at least one heating element extending from the flange into the water tank and a central wall arranged in the water tank, the water tank being connected to cold water inlet and hot water outlet. The water tank cover consists of a cylindrical part that is attached to the flange at the top and a conical part that is connected to the cylindrical part of the water tank cover at the bottom, and the shape of the concentric wall corresponds to the cylindrical part of the water tank. The water tank cover is placed inside the water tank so that an external circulation channel is defined between the water tank cover and the concentric wall. The electric water heater integrates the function of a filter of solid impurities, which during electric heating are mainly formed on the heating elements, but can also be formed in other places of the heating system, in such a way that the solid particles are separated from the fluid stream after hitting the concentric wall and slow down. into the conical part of the water tank, where they can settle. Deposits are removed using the drain valve.

The concentric wall can be formed together with the cylindrical part of the tank cover, as its integral part by molding from plastic.

In the published document, resistance coils and a safety temperature limiter are used, and it is assumed that the heating is controlled by an electronic control unit.

The task of the technical solution is to create an electric heater of similar dimensions and performance using PTC elements in such a way that the function of the integrated solid dirt filter is preserved.

In the state of the art, liquid heaters with PTC heating elements inserted into a tank intended for heating the liquid are known. Existing PTC liquid heating devices generally include a PTC heating element with a heat transfer structure that is typically very complex and therefore has disadvantages such as low heat transfer rate and uneven heat transfer.

The solution presented in publication EP3716730 A2 improves the uniformity of heat transfer, while the individual components of the structure are glued with a conductive adhesive and require placement in a sleeve. But the heaters do not provide the function of a filter integrated in the tank with the heated liquid, and the implementation of the PTC heating assembly is complex and expensive.

Another technical solution with simple integration of the PTC heating assembly is published in the document CN 210267475. The heating body is formed by a hollow body with a passage for the liquid, the body has a cross-section of a regular hexagon or a square. The body is heated using surfaces equipped with PTC elements. The surfaces are connected to the installation cavities for the insertion of PTC elements, during assembly, the PTC heating component is first gradually inserted into the installation cavity, and then a press is used to deform the PTC. The outer surface of the heating element is pressed to form the final product.

The disadvantage of this solution is that pressing can damage the heating PTC component. The arrangement of a continuous cavity with reinforcing ribs in the entire volume of the passage to the liquid, in turn, causes significant pressure losses.

The presented technical solution solves the shortcomings of the known state of the art. It is based on the design of an electric heater with an integrated filter function published in document EP 3910260 A1 and its features are listed in the preamble of the independent claim, while the concentric wall is advantageously used as an electrical insulator. The electric heater uses a simple PTC heating assembly with an innovative arrangement with a flexible wire to heat the liquid.

The essence of the technical solution

The electric heater according to the presented technical solution includes a plastic tank for liquid consisting of an upper cylindrical part and a lower conical part, which are watertightly connected to each other, for example by a screw or welded joint, while inside the plastic tank there is arranged an essentially cylindrical plastic concentric wall defining an internal circulation channel for supply of the liquid intended for heating and an external circulation channel for the removal of the heated liquid, which is simultaneously freed of solid impurities. The external circulation channel is arranged between the concentric wall and the cylindrical part of the cover, while the external circulation channel is connected to the outlet of the heated liquid. In the lower conical part of the tank, there is a space for the settling of solid impurities, which are separated from the liquid stream by hitting obstacles and fall into the area with the lowest flow speed. The conical part has a connection for connecting the drain valve, for removing impurities.

Furthermore, the electric heater includes a hollow heating module arranged in the internal circulation channel (along the axis of the upper cylindrical part of the water tank). The heating module is equipped with a connection socket for supplying the liquid intended for heating to the heater and a continuous cavity for conducting and heating this liquid.

The hollow heating module is made of a metal material that conducts heat and electric current well. Extruded aluminum is preferably used for the production of the module due to its low weight, but other materials are also possible. The hollow heating module has arranged surfaces bounded by protrusions on its outer surface. On its inner surface (in the continuous cavity) in a preferred embodiment, it has arranged ribs to increase the heating surface and thus also the heating efficiency.

After inserting the hollow heating module into the internal circulation channel, installation gaps are created between the plastic concentric wall and the outer surfaces of the hollow heating module to insert the PTC heating assembly.

The concentric plastic wall has a pair of protrusions arranged on its inner surface facing the internal circulation channel, which are shaped so that the protrusions arranged on the outer surface of the hollow heating module fit between these protrusions.

The PTC heating assembly has a layered structure, known in the state of the art. The PTC plates are arranged in long strips, while the length and number of strips used determine the power of the heater (for example, to use a PTC heater as a backup electric heater in heat pump systems, power from 6 to 12 kW is required).

Each PTC heating assembly in the presented technical solution includes two electrical conductors (the first electrical conductor and the second electrical conductor) which are connected to two opposite surfaces of the PTC layer. The PTC layer is assembled from PTC plates, with a graphite pad inserted between the PTC layer and each electrical conductor to improve electrical and thermal conductivity. The pad can be glued with electrically conductive glue, its task is to ensure the best possible contact between the PTC plate and the conductor, it eliminates any unevenness on both materials, at the point of their contact.

An improvement of the state of the art is that instead of a conventional electrical conductor or conductive strip in the present solution, a spring, for example a shaped electrically conductive flexible strip, is used as the first electrical conductor. The first electrical conductor rests on the concentric wall with its flexible part.

Between the second electric conductor and the hollow heating module, an electrically insulating film (for example Kapton film) is applied, which forms insulation for the second electric conductor and at the same time does not prevent the transfer of heat from the PTC heating assembly to the hollow heating module.

At least one heat-generating PTC heating assembly is arranged on the outer surfaces of the hollow heating module, each PTC heating assembly including a flexible metal electrical conductor for applying electrical voltage and pressing the PTC assembly against the concentric wall and also against the heating module.

The flexible conductor ensures tight contacts between the individual layers of the PTC heating assembly. Using a flexible electrical wire, the entire PTC heating assembly is pressed to the hollow heating module on one side and to the plastic concentric wall on the other side. Basically, no pressing or gluing is necessary to ensure good contact of all layers of the PTC heating assembly with each other and also to ensure good contact with the heating module and the plastic concentric wall.

The heating of the liquid is done by applying a voltage (of suitable magnitude and polarity) to both leads of the PTC heating assembly, generating heat in the PTC plates, and this is transferred through the hollow heating module to the liquid.

In a preferred embodiment, the electrically conductive body of the hollow heating module is used as the second electrical conductor.

Overview of images on drawings

The technical solution will be explained using, but not limited to, pictures.

These depict:

fig. 1 - Electric PTC liquid heater - exploded view

fig. 2 - PTC heating assembly layers - in exploded view

fig. 3 - Illustration of a hollow heating element and its cross-section

fig. 4 - Cross-section of the assembled PTC electric heater, with detail of the PTC heating assembly inserted in the installation cavity

fig. 5 - Connection diagram of three-phase electric voltage to PTC heating assemblies - connection example

Implementation examples

Example 1

In fig. 1 shows an electric heater according to the presented technical solution. This includes a plastic tank for liquid consisting of an upper cylindrical part 1 and a lower conical part 2, which are watertightly connected to each other by a screw connection of flanges 24 and 25 and a gasket 22. Inside the plastic tank is arranged a substantially cylindrical plastic concentric wall 5 defining an internal circulation channel 31 for conducting the liquid intended for heating and the external circulation channel 32 for the removal of the heated liquid, which is simultaneously freed of solid impurities. The external circulation channel 32 is arranged between the concentric wall 5 and the cylindrical part of the cover 1, while the external circulation channel 32 is connected to the outlet 4 of the heated liquid. In the lower conical part 2 of the tank, there is a space for the settling of solid impurities, which are separated from the liquid stream by hitting obstacles and fall into the area with the lowest flow speed. The conical part 2 of the tank has a connection for connecting the drain valve 7, which is used to remove settled dirt from the heater.

Furthermore, the electric heater includes a hollow heating module 6 (shown in Fig. 3 and Fig. 1) arranged in the internal circulation channel 31 (along the axis of the upper cylindrical part of the water tank). The heating module 6 is equipped with a connection socket 61 with an external thread for the input of the liquid intended for heating to the heater, a continuous cavity for conducting and heating this liquid and a connection socket 62 with an internal thread for the output of the heated water.

The hollow heating module 6 is watertightly connected to the heater tank by means of a connecting nut 21, a connecting neck 62 and O-rings 23.

The hollow heating module 6 and its cross-section is shown in fig. 3. On its outer surface, it has arranged surfaces 64 bounded by protrusions 63. On its inner surface, in the continuous cavity 65, it has advantageously arranged ribs 66 to increase the heating surface.

The concentric plastic wall 5 has a pair of protrusions 51 arranged on its inner surface, facing the inner circulation channel 31, which are shaped so that the protrusions 63 arranged on the outer surface of the hollow heating module 6 fit between these protrusions 51. The detail of the arrangement is shown in Fig. Fig. 4. Pairs of protrusions 51 are arranged to shapely connect the protrusions 63, which are arranged on the outer surface of the hollow heating module 6.

After inserting the hollow heating module 6 into the internal circulation channel 31, installation gaps 19 are created between the plastic concentric wall 5 and the surfaces 64 of the hollow heating module 6 for inserting at least one PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6. The given example allows the use of up to six PTC heating assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6, the number of assemblies is not limited by this number (in other embodiments).

Each PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 in the presented technical solution includes two electrical conductors 11, 15, the first electrical conductor 11 and the second electrical conductor 15, which are connected to two opposite surfaces of the PTC layer 13. PTC layer 13 is assembled from PTC plates, while a graphite pad 12, 14 is inserted between the PTC layer 13 and each electrical conductor 11, 15 to improve the electrical and thermal conductivity. The pad 12, 14 can be glued with electrically conductive glue, its task is to ensure the contact between the PTC layer 13 and the electric conductor 11, 15, the pad 12, 14 eliminates any unevenness on both materials at the point of their contact.

In the presented solution, a spring is used as the first electrical conductor 11, for example a shaped electrically conductive elastic band. The first electric conductor 11 rests on the concentric wall 5 with its flexible part.

Between the second electric conductor 15 and the hollow heating module 6, an electrically insulating film 16 (for example Kapton film) is applied, which forms insulation for the second electric conductor 15 and at the same time does not prevent the transfer of heat from the PTC heating assembly to the hollow heating module 6.

At least one heat-generating PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 is arranged on the outer surfaces 64 of the hollow heating module, and each PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 includes a flexible metal electrical conductor 11 to supply the electric voltage and to press the PTC assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 to the concentric wall 5 and also to the heating module 6.

Basically, no pressing or gluing is necessary to ensure good contact of all PTC layers of the heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 with each other and also to ensure good contact with the heating module 6 and the plastic concentric wall 5.

At the same time, a pair of protrusions 51 shaped connected to a protrusion 63 is shaped connected to isolate the electrically conductive parts of the PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6.

After inserting the PTC heating assembly into the installation gap 19, there remains an unfilled, free space in it, usually filled with air. To improve the insulating properties, in an advantageous embodiment, the free space between the first electric conductor 11 and the concentric wall 5 and in the installation gap 19 is filled with thermally conductive and at the same time electrically insulating filling material.

The heating of the liquid is carried out in such a way that by applying a voltage (of suitable size and polarity) to the electrical contacts 17, 18 of the conductors 11, 15 of the PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6, heat is generated in the PTC layer, and this heat is transferred through the hollow heating module 6 to the liquid in the internal circulation channel 31. The ribs 66 are arranged to increase the heating surface.

The plastic concentric wall 5 is also partially heated and this heat is transferred to the liquid in the external circulation channel 32. The generated heat is therefore used in the presented solution as efficiently as possible and the heated liquid is freed of solid impurities before exiting the heater.

The electric heater is preferably used as an electric back-up heater in systems with a heat pump, for heating a less pure liquid, possibly also containing glycol.

In fig. 5 is an exemplary diagram of the Y-connection of the three-phase voltage to the connection contacts 17, 18 of the electrical conductors 11 and 15 of the PTC heating assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6. The phase voltage L2 is connected to the contacts 17 of the first electric conductor 11 of the heating assemblies PTC1 and PTC2, the phase voltage L3 is connected to the contacts 17 of the first electric conductor 11 of the heating assemblies PTC3 and PTC4, and the phase voltage L1 is connected to the contacts 17 of the first electric conductor 11 of the heating assemblies PTC5 and PTC 6. Contacts 18 of the second electrical conductor 15 on all heating assemblies PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 are connected to zero potential.

The electrical connections may be different according to the requirements for heating power.

The electric PTC heater integrates the function of a filter of solid impurities, solid impurities are separated from the liquid stream by impacts on the ribs 66 arranged in the continuous cavity 65 of the hollow heating module 6 and settle in the conical part 2 of the tank. A drain valve 7 is connected to the tank to drain dirt.

Example 2 (not shown)

In the second embodiment of the technical solution, the electrically conductive body of the hollow heating module 6 is used as the second electrical conductor 15.

In this case, the PTC heating assembly PTC1, PTC2, PTC3, PTC4, PTC5, PTC6 includes the first electrical conductor 5 11, the PTC layer 13 and the graphite pads 12, 14, and the conductive surface of the hollow heating module 6 as the second electrical conductor 15.

Such an arrangement is suitable for use in a pure water flow heater, as a mandatory part of flow heaters is a water conductivity measurement module and also other safety measures.

The electric PTC heater for heating liquids according to the presented technical solution is intended for heating 10 liquids circulating mainly in the heating circuits of residential buildings. Compared to systems based on resistance wire heating, PTC electric heaters provide many advantages and simplify heating control.

Claims (7)

CLAIMS FOR PROTECTION 1. An electric liquid heater, comprising a plastic container for liquid consisting of an upper cylindrical part (1) and a lower conical part (2), connected to each other in a watertight manner, while inside the plastic container a substantially cylindrical plastic concentric wall (5) defining the internal circulation is firmly arranged a channel (31) and an external circulation channel (32), wherein the external circulation channel (32) is connected to the outlet (4) of the heated liquid; heating module (6), wherein the heating module (6) is equipped with a connection socket (61) for supplying the liquid intended for heating, a continuous cavity (65) for conducting the liquid intended for heating and external surfaces (64), characterized in that the hollow the heating module (6) is arranged in the internal circulation channel (31), at least one PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) generating heat is arranged on the outer surfaces (64) of the heating module (6). each PTC heater assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) includes a flexible metal electrical conductor (11) to apply electrical voltage and to press the PTC heater assembly to the concentric wall (5) and to the heater module (6). 2. Electric liquid heater according to claim 1, characterized in that the PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) is assembled as a layered structure from layers of the first flexible electric conductor (11), the first graphite pad (12) ), layers of PTC plates (13), second graphite pad (14), second electrical conductor (15) and electrical insulator (16). 3. Electric liquid heater according to claim 1, characterized in that the PTC heating assembly (PTC1, PTC2, PTC3, PTC4, PTC5, PTC6) is assembled as a layered structure from the layers of the first flexible electric conductor (11), the first graphite pad (12) ), PTC plates (13) and the second graphite pad (14) and the heating module (6) is connected as a second electrical conductor. 4. An electric liquid heater according to any one of the preceding claims, characterized in that the hollow heating module (6) has arranged surfaces (64) defined by protrusions (63) on its outer surface and has arranged ribs (66) in the continuous cavity (65) increasing the heating surface. 5. An electric liquid heater according to any one of the preceding claims, characterized in that the concentric plastic wall (5) has on its inner surface, directed into the internal circulation channel (31), arranged pairs of protrusions (51) for shape connection with the protrusions (63) ), which are arranged on the outer surface of the hollow heating module (6). 6. Electric liquid heater according to any one of the preceding claims, characterized in that between the hollow heating module (6) and the plastic concentric wall (5) installation gaps (19) are arranged for the insertion of at least one PTC heating assembly (PTC1, PTC2, PTC3 , PTC4, PTC5, PTC6). 7. An electric liquid heater according to any one of the preceding claims, characterized in that the free space between the first electric conductor (11) and the concentric wall (5) in the installation gap (19) is filled with a thermally conductive and electrically insulating filling material.