PTC electric heater

Abstract

The PTC electric heater (100) comprises at least two identical square hollow profiles (3) for conducting liquid, each provided with two connection openings, an upper and a lower one, wherein the upper opening on the hollow profile (3) is connectable to a distribution channel for the inlet of cold liquid with a liquid inlet (1) and the lower opening on the hollow profile (3) is connectable to a distribution channel for the outlet of heated liquid with a liquid outlet (2), wherein a PTC heating unit is arranged between each of the two hollow profiles (3).

Description

[0001] The technical solution presented relates to a PTC electric heater for a heat transfer fluid, in particular water or a mixture of water and antifreeze, which is run in a closed circuit of a building's heating system. The technical solution relates in particular to an electric auxiliary heater for the heat transfer fluid in heat pump heating systems.

[0002] Current environmentally friendly building heating concepts use heat pump systems that extract heat from the environment. Heat pump systems are typically supplemented by an additional heat source—e.g., solar thermal energy, gas-fired auxiliary heating, electric auxiliary heating, or a combination of several heat sources.

[0003] Electric auxiliary heating is used in heat pump systems primarily when the heat extracted from the outside air is insufficient for comfortable heating and / or hot water production, especially in the winter months. At the same time, the electric heater also prevents the heat transfer medium from freezing under extremely unfavorable temperature conditions. In conventional electric auxiliary heaters, the heating elements are designed as resistance heating elements (rods, coils) or, preferably, as PTC resistance elements. The heating coil is heated to a temperature of up to 850°C, which can lead to overheating of adjacent components if the temperature of the heat source is not appropriately regulated or monitored. To avoid thermal damage caused by the temperatures of these heat sources, which are significantly higher than the temperature of the fluid to be heated, a costly safety concept is required.

[0004] Electrical resistance heaters are described, for example, in documents EP3910260 A1, EP3869118 A1 and EP3037741 A1.

[0005] An alternative to electrical resistance heaters is the modern electrical PTC heater (Positive Temperature Coefficient), the use of which is particularly advantageous because the temperature of the heating element does not exceed 300°C, or even less, depending on the design of the PTC heating element.

[0006] PTC elements are electrically conductive at low temperatures, but after reaching a certain temperature threshold, their electrical conductivity drops sharply. Therefore, as the temperature of a PTC element rises, its resistance increases. Negative feedback is used, which kicks in when the PTC element is actually heated due to the current flowing through it. When powered by a constant voltage source, this causes a power drop across the PTC element, which counteracts any further temperature increase. This results in simple heating with effective temperature stabilization of the heated medium.

[0007] Existing PTC liquid heaters (particularly for automotive use) typically comprise a PTC heating element with a heat transfer structure that is typically very complex, resulting in disadvantages such as low heat transfer rates and uneven heat transfer. Several channels are provided inside the heater, some of which house the PTC heating elements, while others are used for fluid flow.

[0008] An example of such a device is the solution described in document EP3001118 A1.

[0009] The solutions described do not allow for any device variability, especially the simple addition of additional PTC heating elements to increase the device's performance. Another disadvantage is that the entire PTC heating cell, with the exception of the wires, is located in the heat exchanger channel, making electrical insulation very difficult.

[0010] The electric auxiliary heater for heat pump systems is typically designed for outputs of 5 kW to 12 kW. To achieve the required higher output, multiple PTC heating elements must always be used, arranged to transfer the heat energy as efficiently as possible.

[0011] A further requirement for an additional electric heater is that the construction must be easily expandable (modular) and at the same time the required watertightness of the assembly and electrical safety must be guaranteed.

[0012] A modular PTC electric heater of simple design is known from the prior art, described in document SK1082022 U1. This PTC heater uses cartridge PTC heating elements embedded in the flow channel of a heat exchanger and therefore does not exhibit ideal flow parameters.

[0013] Furthermore, a PTC electric heater with a layered structure, described in EP4290155A1, is known in the prior art. Its disadvantage is the circular design of the heat exchanger, which prevents an increase in the number of PTC heating elements, since the unheated surface area of ​​the heat exchanger also increases with the diameter of the heat exchanger.

[0014] The aforementioned deficiencies of the state of the art are eliminated by the present technical solution of a PTC electric heater with PTC layer structure and with integrated liquid distributor, which can be easily expanded.

[0015] The PTC electric heater consists of structurally identical square hollow profiles for conducting fluids, each equipped with two connection holes (top and bottom). The upper hole of the profile can be connected to the distribution channel for the fluid inlet (on the top of the heater) with the inlet for cold fluid, and the lower hole can be connected to the distribution channel for the outlet (on the bottom of the heater) with the outlet for heated fluid. The connection is made with plastic plugs.

[0016] The profiles are made of a metal with good heat conductivity, with extruded aluminum being a suitable material. The profile cavity is preferably provided with ribs to increase the heating surface.

[0017] The plastic fittings are T-shaped and provided with a clip connection and seal for a hydraulically tight connection to the hollow profile. At the same time, the plastic fittings are provided with another clip connection and seal to form a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel.

[0018] The liquid flows through the hollow profile in the direction from the inlet channel to the outlet channel and is heated by a PTC heater arranged between two adjacent hollow profiles.

[0019] The PTC heating unit has a layered structure known from the prior art. Each PTC heating unit in the present technical solution comprises two electrodes connected to two opposite surfaces of the PTC element. The PTC element consists of PTC ceramic discs arranged in strips.

[0020] The dimensions of the PTC elements and their number determine the electrical power of the heater.

[0021] An insulating foil (e.g. Kapton foil) is inserted between each electrode and the hollow profile to conduct the liquid, which forms the electrical insulation of the PTC but does not prevent the heat transfer from the PTC heating unit to the hollow profile.

[0022] Kapton foil is also suitable as secondary insulation (decoupling) for conductors, withstanding high temperatures and electrically insulating the electrodes from the hollow metal profile. The electrodes are connected to the electrical wires at the top.

[0023] To ensure electrical insulation, the laminated PTC heating unit is surrounded on the outside by an insulating plastic frame that has holes for the electrical wires to pass through.

[0024] The entire PTC heating unit is therefore housed in an insulating plastic frame, and only the power supply wires are exposed.

[0025] The liquid is heated by applying a voltage (of appropriate strength and polarity) to the two wires of the PTC heating unit to generate heat in the PTC wafers, which is transferred through the hollow profile into the liquid.

[0026] The liquid heated in the individual hollow profiles is mixed in the outlet distribution channel and directed to the outlet of the heated liquid.

[0027] The total output of the electric heater depends on the number and dimensions of the hollow profile and the power of the PTC heating unit / PTC replacement. For different flow rates, a heater with the desired power can be easily assembled by adding an additional hollow profile and a PTC heating unit to the heater. Unlike the round design, there are no unheated areas.

[0028] One of the plastic nozzles in the inlet manifold is preferably provided with a connection for a vent valve

[0029] All hollow profiles and frames surrounding the PTC heaters are mechanically connected to each other, e.g., by springs inserted into the profile recesses or by other suitable means.

[0030] The mechanical stiffening of the entire assembly (by springs) ensures its structural properties, good heat transfer and the required electrical performance.

[0031] The technical solution is explained with the help of images, but is not limited to them.

[0032] The pictures show: Fig. 1 - View of the PTC electric heater with three hollow profiles Fig. 2 - Longitudinal section through the PTC electric heater from Fig. 1 Fig. 3 - PTC electric heating assembly made of Fig. 1 in exploded view with PTC heating assembly layers shown Fig. 4 - rotated longitudinal section of the PTC electric heater from Fig. 1 with detail of the plastic frame

[0033] The PTC electric heater 100 consists of structurally identical square hollow profiles 3 for conducting fluid, provided with two connection openings, one at the top and one at the bottom. The upper opening of the profile can be connected to a distribution channel for the inlet of cold fluids (located on the top of the heater) with a fluid inlet 1, and the lower opening can be connected to a distribution channel for the outlet of heated fluids with a fluid outlet 2 at the bottom of the heater. The connection is made with plastic closures 4, 6. The distribution channels are provided with plugs 5.

[0034] The profiles are made of a metal with good heat conductivity, with extruded aluminum being a suitable material. The profile cavity is preferably provided with 12 ribs to increase the heating surface.

[0035] The plastic connecting elements 4, 6 are T-shaped and provided with a clamp connection 18 and a seal 16 for hydraulically tight connection to the hollow profile; at the same time, the plastic connecting elements are provided with an additional clamp connection 17 and a seal 15 for forming a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel.

[0036] The liquid passes through the cavity of the hollow profile 3 in the direction from the inlet distribution channel to the outlet distribution channel and is heated by a PTC heater, which is always arranged between two adjacent (neighboring) hollow profiles.

[0037] The PTC heating unit has a layered structure known from the prior art. Each PTC heating unit in the present technical solution comprises two electrodes 8 connected to two opposite surfaces of the PTC element 7. The PTC element 7 is constructed from strip-like PTC ceramic plates. The dimensions of the PTC element 7 and the total number of PTC elements in the electric heater 100 determine the power of the heater 100.

[0038] An insulating film 9 (e.g., a Kapton film) is inserted between each electrode 8 and the liquid-conducting hollow profile 3. This film provides electrical insulation for the electrode 8 while simultaneously not preventing heat transfer from the PTC element 7 to the hollow profile 3. The power supply lines are connected to the top of the electrodes 8. To ensure electrical insulation, the PTC layer heating assembly is externally surrounded by an insulating plastic frame 10, which has openings 14 for electrical power cables. The liquid is heated by applying a voltage (of suitable strength and polarity) to the two electrodes 8 in the PTC heating unit to generate heat in the PTC element 7, which is transferred to the liquid through heat exchange with the hollow profiles 3.The fluid flows through the cavity of the hollow profile 3 in the direction from the inlet distribution channel to the outlet distribution channel and is heated by each PTC heating unit adjacent to the hollow profile 3. The fluid heated in the individual hollow profiles 3 is mixed in the outlet distribution channel and directed to the fluid outlet 2.

[0039] The total output of the electric heater 100 depends on the number and dimensions of the hollow profile 3 and the electrical output of the PTC heating assembly(s). In the exemplary embodiment, three hollow profiles 3 and two PTC heating assemblies are used. For different fluid flow rates, a heater with the desired output can be easily assembled by adding another hollow profile 3 and another PTC heating assembly. Unlike the circular design, this creates no unheated areas.

[0040] The plastic connection element 6 in the inlet manifold duct is preferably provided with a connection 13 for a vent valve. All hollow profiles and the plastic insulation frames surrounding the PTC heaters are mechanically connected to each other, e.g., by means of springs 11 inserted into the shaped recesses 19 of the hollow profile 3, or by other suitable means.

[0041] Mechanical stiffening of the entire heater assembly 100 (e.g., by springs 11) is required to ensure close contact and thus efficient heat transfer and to ensure the structural properties and desired electrical performance of the heater 100.

[0042] The PCT electric heater is advantageously used in heating systems with heat pumps, where it takes on the function of an additional electric heater for the heat transfer fluid. List of reference symbols

[0043] 100PTC Electric Heater 1Liquid Inlet 2Liquid Output 3Hollow Profile 4Connecting Element 5Plug 6Connecting Element 7PTC Element 8Electrode 9Insulating Foil 10Plastic Insulating Frame 11Connecting Spring 12Ribs 13Connection for Vent Valve 14Hole 15Seal 16Seal 17Clip 18Clip 19Notch

Claims

1. An electric PTC heater (100) comprising at least two identical square hollow profiles (3) for conducting liquid, each of the profiles being provided with two connection openings, an upper and a lower one, wherein the upper opening on the hollow profile (3) is connectable to a distribution channel for the inlet of cold liquid with a liquid inlet (1) and the lower opening on the hollow profile (3) is connectable to a distribution channel for the outlet of heated liquid with a liquid outlet (2), wherein a PTC heating arrangement is arranged between each of the two hollow profiles (3), characterized in thatthe distribution channels have T-shaped plastic connecting elements (4, 6), each plastic connecting element is provided with a first clamp connection (18) and a first seal (16) for hydraulically tight connection to the hollow profile (3), each plastic connecting element (4, 6) is provided with a second clamp connection (17) and a second seal (15) in order to form a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel, a plastic connector (6) in the inlet distribution channel is provided with a connection (13) for a vent valve, each hollow profile (3) is made of a heat-conducting metal.

2. Electric PTC heater (100) according to claim 1, characterized in that the hollow profile cavity (3) is provided with ribs (12) in order to increase the heating surface.

3. Electric PTC heater (100) according to one of the preceding claims, characterized in thateach PTC heating assembly comprises two electrodes (8) and a PTC element (7), wherein the electrodes (8) are connected to two opposite surfaces of the PTC element (7) and the PTC element (7) is composed of PTC ceramic plates arranged in strips.

4. Electric PTC heater (100) according to claim 3, characterized in that an electrically insulating and heat-transferring foil (9) is arranged between each electrode (8) and the hollow module (3) for conducting the liquid, and electrical power supply wires are connected to the electrodes (8) at the top of the electrodes (8).

5. Electric PTC heater (100) according to one of the preceding claims, characterized in that the PTC heating assembly is surrounded on the outside by an insulating plastic frame (10) in which openings (14) for the electrical power wires are arranged.

6. Electric PTC heater (100) according to one of the preceding claims, characterized in thatthe hollow profiles (3) and the plastic insulating frames (10) are mechanically connected to one another by means of springs (11) which are inserted into notches (19) arranged on the hollow profiles (3).

7. Heating system with heat pump and closed heat transfer circuit, characterized in that the additional electric heater in the closed circuit of the heat transfer fluid is an electric PTC heater (100) according to one of claims 1 to 6.

8. Electric PTC heater (100) with at least two identical square hollow profiles (3) for conducting liquid, each of the profiles being provided with two connection openings, an upper and a lower one, wherein the upper opening on the hollow profile (3) is connectable to a distribution channel for the inlet of cold liquid with a liquid inlet (1) and the lower opening on the hollow profile (3) is connectable to a distribution channel for the outlet of heated liquid with a liquid outlet (2), wherein a PTC heating arrangement is arranged between each of the two hollow profiles (3), characterized in thatthe distribution channels comprise T-shaped plastic closures (4, 6), Each plastic connecting element is provided with a first clamp connection (18) and a first seal (16) for hydraulically tight connection to the hollow profile (3), each plastic connecting element (4, 6) is provided with a second clamp connection (17) and a second seal (15) in order to form a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel, the plastic connecting element (6) in the inlet distribution channel is provided with a connection (13) for the vent valve, Each hollow profile (3) is made of a metal with good heat conduction.

9. Electric PTC heater (100) according to claim 1, characterized in that the hollow profile cavity (3) is provided with ribs (12) to increase the heating surface.

10. PTC electric heater (100) according to one of the preceding claims, characterized in thatEach PTC heating assembly comprises two electrodes (8) and a PTC element (7), wherein the electrodes (8) are connected to two opposite surfaces of the PTC element (7) and the PTC element (7) is composed of PTC ceramic plates arranged in strips.

11. Electric PTC heater (100) according to claim 3, characterized in that An electrically insulating and heat-transferring foil (9) is arranged between each electrode (8) and the hollow liquid-conducting module (3), and electrical supply lines are connected to the electrodes (8) at the top.

12. PTC electric heater (100) according to one of the preceding claims, characterized in that The PTC heating unit is surrounded on the outside by an insulating plastic frame (10) in which holes (14) for the electrical supply lines are arranged.

13. PTC electric heater (100) according to one of the preceding claims, characterized in thatthe hollow profiles (3) and the plastic insulating frames (10) are mechanically connected to one another by springs (11) which are inserted into notches (19) arranged on the hollow profiles (3).

14. Heating system with heat pump and closed heat transfer circuit, characterized in that the additional electric heater in the closed circuit of the heat transfer fluid is an electric PTC heater (100) according to one of claims 1 to 6.

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