SK10214Y1 - PTC electric heater - Google Patents

Abstract

The PTC electric heater (100) includes at least two identical rectangular hollow profiles (3) for conducting liquid, each of which is equipped with two connection holes, upper and lower, the upper hole on the hollow profile (3) being connectable to the cold liquid inlet distribution channel with a liquid inlet (1) and the bottom opening on the hollow profile (3) is connectable to the heated liquid outlet distribution channel with a liquid outlet (2), with a PTC heating assembly arranged between each two hollow profiles (3).

Description

Field of technology

The presented technical solution relates to a PTC electric heater of a heat transfer fluid, in particular water or a mixture of water and antifreeze, which is conducted in a closed circuit of a building's heating system. The technical solution relates in particular to an auxiliary (backup) electric heater of a heat transfer fluid in heating systems with a heat pump.

State of the art

Current ecological concepts for heating buildings use heat pump systems, in which heat is extracted from the outside environment. Heat pump systems are often supplemented by another heating source, for example solar heating, an auxiliary gas heater or an auxiliary (backup) electric heater, or a combination of several heating sources.

An auxiliary (backup) electric heater is used in heat pump systems mainly when the heat taken from the outside environment is not sufficient for comfortable heating and/or heating of hot service water, especially in the winter months. At the same time, the electric heater also prevents the heat transfer medium from freezing in extremely unfavorable temperature conditions. In known auxiliary electric heaters, the heating elements are designed as resistance heating elements (rods, spirals) or, more preferably, PTC resistance elements. The heating spiral heats up to a temperature of 850 °C, which can cause overheating of adjacent parts if the temperature of the heating source is not appropriately controlled or monitored. In order to prevent thermal damage caused by the temperatures of these heating sources, which are significantly higher than the temperature of the liquid to be heated, a complex safety concept is required.

Electric heaters with resistance coils are described, for example, in documents EP3910260 A1, EP3869118 A1 and EP3037741 A1.

An alternative to electric heaters with resistance coils are known in the state of the art electric heaters with PTC (Positive Temperature Coefficient) heating elements, the use of which is advantageous mainly due to the fact that the temperature of the heating element does not exceed 300 °C or even less, depending on the specific design of the PTC heating element.

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, which acts on the self-heating of the PTC element due to the passing current. When powered from a constant voltage source, this causes a decrease in the power on the PTC element, which counteracts further temperature growth. The result is simple heating with effective stabilization of the temperature of the heated medium.

Existing PTC liquid heating devices (especially for automotive use) 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. A plurality of channels are provided inside the heating device, some of the channels being used to accommodate the PTC heating elements, while others of the channels are used to pass the liquid.

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

The described solutions do not allow for variability of the device, in particular the simple addition of additional PTC heating elements for the purpose of increasing the device's performance. Another disadvantage is that the entire PTC heating element, except for the wires, is located in the heat exchanger channel and great effort is required to ensure electrical insulation.

An electric backup heater for heat pump systems should provide outputs typically from 5 kW to 12 kW. It is obvious that to achieve the required higher output, it will always be necessary to use multiple PTC heating elements suitably arranged so that the heating energy is transferred as efficiently as possible.

Therefore, another requirement for an electric backup heater is that the design be easily expandable (modular), while ensuring the required waterproofness of the assembly and electrical safety.

In the prior art, a modular PTC electric heater of simple construction is known, described in document SK1082022U1. This PTC heater uses cassette PTC heating elements inserted into the flow channel of the heat exchanger, and therefore does not have ideal flow parameters.

Furthermore, in the prior art, a PTC electric heater with a layered structure is known, as described in document EP4290155A1. Its disadvantage is the round design of the heat exchanger, which does not allow increasing the number of PTC heating assemblies, since when the diameter of the exchanger increases, the unheated area of the exchanger also increases.

The above-mentioned shortcomings of the state of the art are eliminated by the presented technical solution of a PTC electric heater with a PTC layered structure and an integrated liquid distributor, which can be expanded in a simple way.

The essence of the technical solution

The PTC electric heater is made of structurally identical square hollow profiles for conducting liquid, equipped with two connection holes, top and bottom. The top hole on the profile is connectable to the liquid inlet distribution channel (on the top of the heater) with the cold liquid inlet, and the bottom hole is connectable to the outlet distribution channel (on the bottom of the heater) with the heated liquid outlet, the connection is made using plastic connectors.

The profiles are made of metal that conducts heat well, extruded aluminum is a suitable material. Preferably, the cavity of the profile is equipped with ribs to increase the heating surface.

The plastic connectors are T-shaped and are equipped with one clip connection and a seal for a hydraulically tight connection to the hollow profile, and at the same time the plastic connectors are equipped with another clip connection and a seal for creating a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel.

The liquid passes through the cavity of the hollow profile in the direction from the inlet channel to the outlet channel and is heated by a PTC heating assembly arranged between two adjacent (neighboring) hollow profiles.

The PTC heating assembly has a layered structure, known in the prior art.

Each PTC heating assembly in the present technical solution includes two electrodes that are connected to two opposing surfaces of a PTC element. The PTC element is assembled from PTC ceramic plates that are arranged in strips.

The dimensions of the PTC element and their number determine the electrical power of the heater.

An insulating foil (for example, Kapton foil) is inserted between each electrode and the hollow profile for guiding the liquid, which forms the electrical insulation of the PTC and at the same time does not prevent the transfer of heat from the PTC heating assembly to the hollow profile.

Kapton foil is also suitable as a secondary insulation (separation) of conductors, which can withstand high temperatures and electrically insulates the electrodes from the metal hollow profile. The power supply electrical wires are connected to the electrodes in the upper part.

To ensure electrical insulation, the layered PTC heating assembly is surrounded on the outside by a plastic insulating frame, which has holes for passing electrical wires through.

The entire PTC heating assembly is therefore housed in a plastic insulating frame and only the power supply wires exit from it.

The heating of the liquid is carried out by applying voltage (of the appropriate magnitude and polarity) to both wires of the PTC heating assembly, generating heat in the PTC plates and this is transferred through the hollow profile to the liquid.

The liquid heated in the individual hollow profiles is mixed in the outlet distribution channel and is led to the outlet of the heated liquid.

The total power of the electric heater depends on the number and dimensions of the hollow profile and the power of the PTC heating assembly/assemblies. For different volume flows, it is possible to easily assemble a heater of the required power by adding another hollow profile and PTC heating assembly to the heater, while unlike the round design, there are no unheated areas.

One of the plastic connectors in the inlet distribution channel is preferably equipped with a connection for a vent valve.

All hollow profiles and frames surrounding the PTC heating assemblies are fixed together mechanically, for example by means of springs inserted into the formed notches in the profile or by other suitable means.

Mechanical reinforcement of the entire assembly (using springs) ensures its structural properties, good heat transfer and the required electrical power.

Overview of images in drawings

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

The pictures show:

Fig. 1 - view of a PTC electric heater with three hollow profiles and two PTC heating assemblies, Fig. 2 - longitudinal section of the PTC electric heater from Fig. 1, Fig. 3 - PTC electric heater assembly from Fig. 1 in an exploded view with the layers of the PTC heating assembly shown and Fig. 4 - rotated longitudinal section of the PTC electric heater from Fig. 1 with a detail of the plastic frame.

Examples of implementation

The PTC electric heater 100 is made of structurally identical square hollow profiles 3 for conducting liquid, equipped with two connection holes, top and bottom. The top hole on the profile is connectable to the cold liquid inlet distribution channel (on the top of the heater) with liquid inlet 1 and the bottom hole is connectable to the heated liquid outlet distribution channel with liquid outlet 2 (on the bottom of the heater). The connection is made using plastic connecting elements 4, 6. The distribution channels are equipped with blind plugs 5.

The profiles are made of a metal that conducts heat well, extruded aluminum being a suitable material. Preferably, the cavity of the profile is provided with ribs 12 to increase the heating surface.

The plastic connecting elements 4, 6 are T-shaped and are equipped with one connection for a clip 18 and a seal 16 for a hydraulically tight connection to the hollow profile, and at the same time the plastic connecting elements are equipped with another connection for a clip 17 and a seal 15 for creating a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel.

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 heating assembly arranged always between two adjacent (neighboring) hollow profiles.

The PTC heating assembly has a layered structure, known in the prior art.

Each PTC heating assembly in the present technical solution includes two electrodes 8, which are connected to two opposing surfaces of the PTC element 7.

The PTC element 7 is assembled from PTC ceramic plates which are arranged in strips.

The dimensions of the PTC element 7 and their total number in the electric heater 100 determine the power of the heater 100.

An insulating foil 9 (for example, Kapton foil) is inserted between each electrode 8 and the hollow profile 3 for conducting the liquid, which forms the electrical insulation of the electrode 8 and at the same time does not prevent the transfer of heat from the PTC element 7 to the hollow profile 3. Power supply electrical conductors are connected to the electrodes 8 in the upper part.

To ensure electrical insulation, the layered PTC heating assembly is surrounded on the outside by a plastic insulating frame 10, which has openings 14 arranged for the supply electrical conductors.

The heating of the liquid is carried out by applying a voltage (of appropriate magnitude and polarity) to both electrodes 8 in the PTC heating assembly, generating heat in the PTC element 7 and this is transferred via heat exchange with the hollow profiles 3 to the liquid.

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 each PTC heating assembly adjacent to the hollow profile 3.

The liquid heated in the individual hollow profiles 3 is mixed in the outlet distribution channel and is led to the liquid outlet 2.

The total power of the electric heater 100 depends on the number and dimensions of the hollow profile 3 and the electric power of the PTC heating assembly/assemblies, in the exemplary embodiment three hollow profiles 3 and two PTC heating assemblies are used. For different liquid volume flows, it is possible to easily assemble a heater of the required power by adding another hollow profile 3 and another PTC heating assembly to the heater, while in contrast to the round design, no unheated areas are created.

The plastic connecting element 6 in the inlet distribution channel is preferably equipped with a connection 13 for a vent valve.

All hollow profiles and plastic insulating frames surrounding the PTC heating assemblies are fixed together mechanically, for example by means of springs 11 inserted into the formed notches 19 on the hollow profile 3, or in another suitable manner.

Mechanical reinforcement of the entire heater assembly 100 (for example, by means of springs 11) is necessary to ensure tight contact and thus efficient heat transfer, ensuring the structural properties and required electrical performance of the heater 100.

Industrial applicability

The PCT electric heater is advantageously used in heating systems with a heat pump, where it functions as an auxiliary (backup) electric heater for the heat transfer fluid.

List of relational tags

100 PTC electric heater liquid inlet liquid outlet hollow profile connecting element blanking plug connecting element

PTC element electrode insulating foil plastic insulating frame connecting spring ribs connection to air vent hole seal seal clip clip notch

Claims (7)

1. PTC electric heater (100) comprising at least two identical square hollow profiles (3) for conducting liquid, each of which is provided with two connection openings, an upper and a lower one, wherein the upper opening on the hollow profile (3) is connectable to an inlet distribution channel of cold liquid with an inlet (1) of liquid and the lower opening on the hollow profile (3) is connectable to an outlet distribution channel of heated liquid with an outlet (2) of liquid, wherein a PTC heating assembly is arranged between each two hollow profiles (3), characterized in that the distribution channels comprise T-shaped plastic connecting elements (4, 6), each plastic connecting element is provided with a first connection for a clip (18) and a first seal (16) for a hydraulically tight connection to the hollow profile (3), each plastic connecting element (4, 6) is provided with a second connection for a clip (17) and a second seal (15) to create a hydraulically tight inlet distribution channel or a hydraulically tight outlet distribution channel, the plastic connecting element (6) in the inlet distribution channel is equipped with a connection (13) for a vent valve, each hollow profile (3) is made of a metal with good heat conductivity. 2. PTC electric heater (100) according to claim 1, characterized in that the cavity of the hollow profile (3) is provided with ribs (12) to increase the heating surface. 3. PTC electric heater (100) according to any one of the preceding claims, characterized in that each PTC heating assembly comprises two electrodes (8) and a PTC element (7), the electrodes (8) being connected to two opposing surfaces of the PTC element (7) and the PTC element (7) being composed of PTC ceramic plates arranged in strips. 4. PTC electric heater (100) according to claim 3, characterized in that an electrically insulating and heat transfer foil (9) is arranged between each electrode (8) and the hollow module (3) for conducting the liquid, and power supply electric conductors are connected to the electrodes (8) in the upper part. 5. PTC electric heater (100) according to any one of the preceding claims, characterized in that the PTC heating assembly is surrounded on the outside by a plastic insulating frame (10) which has arranged openings (14) for the supply electrical conductors. 6. PTC electric heater (100) according to any one of the preceding claims, characterized in that the hollow profiles (3) and the plastic insulating frames (10) are mechanically connected to each other by means of springs (11) inserted into notches (19) arranged on the hollow profiles (3). 7. A heating system with a heat pump and a closed circuit of a heat transfer fluid, characterized in that the auxiliary electric heater in the closed circuit of the heat transfer fluid is a PTC electric heater (100) according to any one of claims 1 to 6.