Heat exchanger for a heat pump, method for defrosting a heat exchanger, heat pump, computer program product and use of an electrically conductive coating

Abstract

The invention relates to a heat exchanger (9) for a heat pump (1), configured for heat exchange with ambient air (14) and comprising a refrigerant line (19) which has at least a portion of an electrically non-conductive coating (15) on which at least a portion of an electrically conductive coating (16) is applied. The electrically conductive coating (16) can be used as a resistance heater for defrosting the heat exchanger. Furthermore, a method for defrosting the heat exchanger (9), a heat pump (1), a computer program (13), and the use of an electrically conductive coating (16) are proposed.

Description

[0001] The invention relates to a heat exchanger for a heat pump, a method for de-icing a heat exchanger, a heat pump, a computer program product and the use of an electrically conductive coating.

[0002] The invention addresses the problem of icing in the heat exchanger of a heat pump that extracts heat from the ambient air. The heat exchanger can be connected to an evaporator of an air-source heat pump. Under normal operating conditions, this evaporator extracts heat from the ambient air and makes it available for heating a building and / or for heating domestic hot water. Ambient air is always understood here to mean outside air, even if the evaporator or heat exchanger itself is located inside a building, for example, a frost-free installation room. In such a case, the evaporator or heat exchanger is still exposed to outside air, which is guided through suitable flow paths. The invention further relates to a computer program for carrying out a method for defrosting an evaporator or heat exchanger of an air-source heat pump.

[0003] In normal operation, the evaporator of an air-source heat pump is circulated through its interior by a very cold refrigerant, whose temperature is significantly lower than that of the ambient air. Heat is extracted from the ambient air, which the refrigerant absorbs and evaporates. In particular, parts of the evaporator's outer surface can reach temperatures below the freezing point of water. This also applies to other heat exchangers that use, for example, brine as a heat transfer medium.

[0004] This causes moisture from the air (water vapor) to condense and freeze on these parts, forming water ice. As this ice thickens, it impedes heat exchange and can even lead to mechanical damage to the evaporator or heat exchanger. Therefore, it is common practice to defrost iced-up evaporators or heat exchangers as needed or periodically. For example, a heat pump can be operated in reverse (then functioning like an air conditioner or refrigerator), heating the inner surface of the evaporator (which then acts as a condenser) and thus melting the ice on its outer surface. The ice transforms into liquid water, which drips off and can be drained away.However, icing on evaporators or heat exchangers exposed to ambient air occurs particularly at high relative humidity and corresponding temperatures, for example, in a temperature range of 0°C to 6°C and high relative humidity. This makes defrosting difficult, and unfavorable wind conditions (direction and speed of the wind are important parameters) can cause further problems. It is also known to use additional, usually electrically operated, auxiliary heating devices for defrosting. Icing of the heat exchanger can occur particularly on the fins of the heat exchanger through which the ambient air flows, or also on any air inlet grille of the heat exchanger that may be located upstream of the heat exchanger in the direction of the ambient airflow. Such a method for defrosting a heat exchanger of a heat pump or similar system is described below.An air inlet grille is described, for example, in EP 4 212 786 A1.

[0005] A disadvantage of such methods is that, due to the reversal of the refrigeration cycle, a significant amount of time is required to introduce heat into the heat exchanger. Additionally, when returning to normal operation, the heat extracted for defrosting must be re-injected before a heat demand can be met.

[0006] WO 2014 / 083 066 A2 proposes a method to avoid the aforementioned disadvantages by applying an electric current to the heat exchanger tubes, causing them to act as resistance heaters. To electrically decouple the heat exchanger from the air conditioning unit, insulating sleeves are provided at the inlet and outlet of the heat exchanger, electrically isolating the refrigerant circuit within the heat exchanger area. A disadvantage is that installing these insulating sleeves is complex and increases the risk of refrigerant circuit leaks.

[0007] The object of the present invention is therefore to at least partially alleviate the problems described with reference to the prior art. In particular, the invention is intended to provide a heat exchanger, a method for defrosting a heat exchanger, a heat pump, a computer program, and an application that enable particularly efficient defrosting of a heat pump's heat exchanger, while minimizing the manufacturing effort for the heat exchanger. Furthermore, the refrigeration circuit of the heat pump is intended to exhibit a low risk of leakage.

[0008] These problems are solved by the features of the independent claims. Further advantageous embodiments of the solution proposed here are specified in the independent claims. It should be noted that the features listed in the dependent claims can be combined with one another in any technologically meaningful way and define further embodiments of the invention. Furthermore, the features specified in the claims are further specified and explained in the description, which also presents further preferred embodiments of the invention.

[0009] To solve the problem, a heat exchanger for a heat pump is proposed, designed for heat exchange with ambient air. The heat exchanger comprises a refrigerant line, at least partially coated with an electrically non-conductive coating, and at least partially coated with an electrically conductive coating.

[0010] A heat pump can be a familiar type of heat pump used for heating or cooling a building or for providing hot water. The heat pump is designed to extract heat from the ambient air and transport it through a refrigerant circuit, making it usable. Within this circuit, a refrigerant circulates in the refrigerant line, absorbing heat in an evaporator and releasing it in a condenser. The phase transition of the refrigerant between the evaporator and condenser is controlled by a compressor and an expansion valve. When the heat pump is operating in heating mode, the evaporator extracts heat from the ambient air and makes it available for use within the building via the condenser.For this purpose, a further heat exchanger, operatively connected to the condenser, can transfer the heat, for example, to a heat transfer fluid circulating in a heating circuit or to a heat storage device, such as a hot water storage tank or a buffer tank. The evaporator can be operatively connected to, or even be part of, a heat exchanger as proposed here.

[0011] The refrigerant line in the area of ​​the heat exchanger, which is designed for heat exchange with ambient air, is designed to have at least a partially non-conductive coating. An electrically conductive coating is applied at least partially to this non-conductive coating. Consequently, the electrically conductive coating can be used as a resistance heater for defrosting the heat exchanger. The non-conductive coating serves to electrically decouple the resistance heater, or the conductive coating, from the heat exchanger and thus from the heat pump. This ensures that the current flow of the resistance heater remains limited to the coating and therefore to the area to be defrosted.

[0012] The heat exchanger can have a large number of fins to increase the surface area available for heat exchange. These fins can be in thermally conductive contact with a refrigerant line of the evaporator through which the refrigerant flows. The fins can also have at least a portion of an electrically non-conductive coating and, on top of this, at least a portion of an electrically conductive coating, so that the fins can also be electrically heated.

[0013] The fins, refrigerant lines, or heat exchanger can be subjected to airflow from a fan or blower to facilitate heat exchange with the ambient air. The ambient air flowing into the heat exchanger can be supplied through an air inlet grille, which may be part of a housing containing the heat exchanger. The heat exchanger can, for example, be part of the outdoor unit of a heat pump. The air inlet grille, or the areas or components around it, can also have at least a partially non-conductive coating, onto which an electrically conductive coating is applied, so that the air inlet grille can also be electrically heated for defrosting.

[0014] Due to heat extraction, the ambient air flowing through the heat exchanger can condense, and the condensate (water) can accumulate on the refrigerant lines, the fins of the heat exchanger, or the air inlet grille, potentially freezing. As icing progresses, the flow of ambient air through the heat exchanger, and thus the heat exchange itself, can be restricted.

[0015] The electrically non-conductive coating can be any coating that is electrically non-conductive or non-leading and remains permanently mechanically stable on the refrigerant line, fins, or air inlet grille at the temperatures occurring at the heat exchanger. The electrically non-conductive coating can prevent leakage currents and / or short circuits when the electrically conductive coating is energized during a defrosting process.

[0016] According to one embodiment, the refrigerant line can be made of aluminum, and the electrically non-conductive coating can be an anodized coating. Anodizing is a process for creating a protective oxide layer on aluminum by means of anodic oxidation. An anodized protective layer can have a thickness of 5 to 25 micrometers, which ensures reliable decoupling of the conductivity of the electrically conductive coating from the non-conductive coating of the refrigerant line, the fins, and / or the air inlet grille. An anodized coating is electrically non-conductive and also has excellent adhesion properties over a very wide temperature range.

[0017] An insulating coating, being electrically non-conductive, does not conduct (practically) any electric current and is often used or referred to as corrosion protection. Plastic coatings applied, for example, by fluidized bed sintering or electrostatic powder spraying are such electrically non-conductive coatings that can also be used for the present invention. Suitable plastic coatings include, for example, fluoropolymers or polyamides, polyacrylates, resins such as epoxides, and / or polyurethanes.

[0018] In addition to polymer coatings, elastomers, such as styrene-rubber copolymers, can also be used as electrically non-conductive coatings. Coating with glass or silicates is another possibility. A silicone coating can also be applied or provided as an electrically insulating layer.

[0019] The electrically conductive coating can be any coating that possesses sufficient electrical conductivity for resistance heating. For example, the electrically conductive coating can be a metallic coating applied by dipping and / or vapor deposition. The electrically conductive coating can be applied to all or part of the surface of the electrically non-conductive coating. It is also possible for the electrically non-conductive coating to be in the form of a strip that forms part of the circumference of the refrigerant line. Electrically conductive coatings such as copper plating, gold plating, and / or silver plating are also conceivable.

[0020] The electrically conductive coating can begin at a first point and end at a second point on the refrigerant line and / or a fin of the heat exchanger and / or the air inlet grille. Electrical contact can then be established at both points. This electrical contact can be made in any desired manner, but it should be stable over the long term with respect to the temperatures encountered during heat exchanger operation. For example, electrical contact can be achieved using a sleeve and / or adhesive. The first and second points can be connected to an electrical voltage source via this electrical contact, which applies a suitable voltage to these points for defrosting.The voltage source can, for example, be connected to a control and regulating unit of a heat pump that includes the heat exchanger and performs a defrosting process.

[0021] For electrical contacting, well-known methods can be used. Suitable options are listed below as examples.

[0022] A detachable electrical connection can be selected from the following group: connectors, possibly with spring contacts and cable lugs; terminals, for example push-in terminals, screw terminals (detachable screw connection of solid copper wires)

[0023] A conditionally detachable electrical connection can be selected from the following group: soldering; soldering (threading technique, free wiring), wire wrapping technique (winding, also "wrapping"); insulation displacement connectors; press-fit contacts; connections using press-fit technology.

[0024] A permanent electrical connection can be selected from the following group: welds; bond connections (cold pressure welding); adhesive connections (with conductive adhesive); press connections; crimp connectors; rivet connections; butt connectors (cable lugs, crimp sleeves, crimping, solder connectors), splicing.

[0025] According to one embodiment, the electrically conductive coating can be a coating made of an electrically conductive polymer. A coating made of an electrically conductive polymer is easy to apply and exhibits particularly long-term adhesion within the relevant temperature range.

[0026] Electrically conductive polymers include extrinsically conductive polymers, which derive their conductivity from the addition of conductive materials such as metallic particles (e.g., aluminum flakes) or conductive non-metallic materials (e.g., carbon black). The conductivity of intrinsically conductive polymers is achieved through conjugated double bonds, which allow the free movement of charge carriers in the doped state.

[0027] Examples of extrinsically conductive polymers suitable for use within the scope of the invention are listed below: thermoplastic polymers with conductive fillers, such as carbon or metal chips or particles, such as aluminum, copper, or iron. Suitable thermoplastics include, for example, acrylonitrile butadiene styrene (ABS), polyamides (PA), polylactic acid (PLA), polymethyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyetheretherketone (PEEK), and polyvinyl chloride (PVC). The most commonly used thermoplastics are polyolefins, such as polyethylene and polypropylene.

[0028] Suitable intrinsically conductive polymers can be, for example, electrically conductive polymers from the polyaniline (PAni), polythiophene, and / or polypyrrole groups. A suitable representative from the polythiophene group is, for example, poly-3,4-ethylenedioxythiophene (PEDOT) with polystyrenesulfonate (PSS) as a counterion. Doped polyethyne can also be used within the scope of the invention. Other examples of electrically self-conducting polymers are polyacetylene, polyparaphenylene, and polypyrrole.

[0029] The coating with an electrically conductive polymer can be applied, for example, using an immersion process. Other suitable technical methods include fluidized bed sintering, electrostatic powder spraying (which is of minor importance here, as tribological properties of the coating are not required), and / or plastic flame spraying.

[0030] In particular, a coating is a plastic-like layer. A distinction can be drawn between whether a reaction or cross-linking of the coating takes place (automotive clear coat) or whether a plastic simply melts and solidifies on the surface (fluidized sintering with thermoplastics), although the transitions are fluid. As a rule, plastic coatings have significantly greater layer thicknesses than conventional paints.

[0031] Polymer coating is typically achieved through powder coating or dipping (immersion coating). Other options include wet painting, vacuum coating, or thermal spraying.

[0032] The layer thickness to be set depends on the electrical power to be transmitted and can be set if the electrical power is known.

[0033] According to one embodiment, the heat exchanger can have at least one sensor for detecting icing of the heat exchanger, its fins, and / or an air inlet grille. The sensor can be any sensor suitable for detecting icing. A large number of such sensors are known from the prior art.

[0034] According to one embodiment, the sensor for detecting icing of the heat exchanger can be a caloric sensor.

[0035] The caloric sensor can detect a heat transfer from at least one first heating element of the caloric sensor to at least one temperature sensor of the caloric sensor or from the caloric sensor, or a first heating element of the caloric sensor, to the environment according to a caloric measurement principle.

[0036] The underlying principle of the caloric sensor is that the heat transfer is significantly dependent on the surrounding medium, thus enabling the identification of the environment. Specifically, the measured heat transfer can determine whether the surrounding medium is air, condensate (water), or ice. Therefore, the caloric sensor can utilize a heat source to facilitate heat transfer. The sensor's advantage lies particularly in determining the dew point or detecting incipient icing, for example, on a test surface within / on the sensor that possesses the same thermodynamic properties as the heat exchanger fin within the air duct. Due to the short distance and identical thermodynamic conditions, combined with very low thermal mass, real-time detection of (incipient) icing is possible.For this purpose, it is advantageous if the caloric sensor has a low heat capacity and therefore low thermal inertia.

[0037] In the context of this document, a temperature sensor can refer to a sensor that provides an electrical signal as a measure of temperature. In principle, any temperature sensor can be used to implement the present invention, for example, resistance-based temperature sensors such as NTC thermistors or PTC thermistors. Alternatively, more complex thermocouples can also be used.

[0038] According to one embodiment, one or more caloric sensors can be arranged on the heat exchanger and / or the air inlet grille. In particular, one or more caloric sensors can be arranged on fins of the heat exchanger and / or the air inlet grille, distributed across the available flow cross-section of the heat exchanger, thus advantageously enabling the detection of local or partial icing of the heat exchanger.

[0039] According to one embodiment, at least one caloric sensor and at least one additional temperature sensor can be distributed across the flow cross-section. In this way, (partial) icing can be detected from the signal of an additional temperature sensor in conjunction with the signal of the caloric sensor. Specifically, a caloric sensor and an additional temperature sensor can be located centrally in the flow cross-section, and an additional temperature sensor can be positioned in each of the outer regions of the flow cross-section (for example, geodesically at the top, bottom, and on both sides). An additional temperature sensor can be configured to detect an absolute temperature signal.

[0040] According to one embodiment, at least one caloric sensor can be arranged on a substrate exhibiting the lowest possible thermal conductivity and heat capacity. The substrate can be understood as a base plate on which the caloric sensor is mounted, and which, due to its low thermal conductivity and heat capacity, facilitates the detectable heat transfer within the caloric sensor. The thermal conductivity and heat capacity can each be below a certain threshold. This threshold can specify a thermal conductivity that results in only negligible heat transfer to the substrate and thus to the mounting of the caloric sensor, and consequently, only a negligible influence on the detection of heat transfer to or from the surrounding medium. Furthermore, the substrate should exhibit the most consistent possible behavior towards water, meaning that exposure to water should not cause any changes (e.g., swelling) to the substrate.For example, glass can be a suitable material for the substrate.

[0041] According to one embodiment of the caloric sensor, the substrate can form an extension of a fin of the heat exchanger or the air inlet grille. The substrate can then serve as a thermally conductive connection to the fin. Advantageously, in this embodiment, the flow conditions are identical to those of a fin. Furthermore, this embodiment advantageously allows the determination of an icing or condensation rate (or gradient) by repeatedly drying the caloric sensor.

[0042] According to one embodiment, the at least one caloric sensor can comprise at least one second heating element configured to remove condensate and / or ice deposited on the caloric sensor by applying heat. For example, the at least one second heating element can be arranged on the side of the heating element facing away from the caloric sensor. After detecting condensate or ice, the at least one second heating element can remove it, thus restoring the detection capability of the caloric sensor. Alternatively or cumulatively, operating the at least one first heating element at an increased heating power can also contribute to the removal of deposited condensate and / or ice.

[0043] The at least one first or second heating element of the caloric sensor can, in particular, be a resistance-based electrical heating element that can convert electrical current into heat.

[0044] According to one embodiment, the caloric sensor can comprise one or more first heating elements arranged adjacent to at least one temperature sensor, forming at least one gap between the first heating element and the temperature sensor. Condensation and / or ice can accumulate in this gap. The accumulation of condensation and / or ice in the gap can significantly increase its thermal conductivity, leading to a detectable increase in the heat flow / heat transfer from the first heating element to the temperature sensor. This increase in heat flow would then be detectable by an increase in the temperature of the temperature sensor. With such an embodiment, high accuracy can be achieved at a defined, small, and constant distance between the first heating element and the temperature sensor, particularly when mounted on a substrate.

[0045] For example, in the case of the caloric sensor, an arrangement of one, two, or four square heating elements equidistant from a centrally located temperature sensor would be possible. Alternatively, a heating element with a circular cutout could enclose a circular temperature sensor. A suitable distance between the first heating element and the temperature sensor has proven to be between 0.02 millimeters and 2 millimeters, or even up to 5 millimeters, depending on the specific design of the caloric sensor. The 0.02 millimeter distance may be suitable, for example, for integration on a chip, while 2 millimeters is suitable for a design using discrete SMD (Surface Mounted Device) or THT (Through-Hole Technology) components, such as on a PCB (Printed Surface Board). High thermal conductivity or a high heat capacity of the substrate can facilitate the detection of icing or other conditions.Condensation is made more difficult due to an additional thermal path beyond the heat transfer being measured. This can negatively reduce the sensitivity of the detection.

[0046] According to one embodiment of the caloric sensor, the first heating element and the temperature sensor can also be integrated into a single component. In this case, a resistance-based temperature sensor can be energized with an electric current, and its resistance can be measured as a measure of the temperature. If water or ice accumulates on the sensor, increased heat transfer to the surroundings can lead to a lower temperature reading. For this purpose, small SMD (Surface Mount Device) resistors (especially those with an edge length of less than 5 millimeters, preferably less than 2 millimeters) have proven effective. An SMD resistor is a conductive electronic component for surface mounting that has conductive edges for contact on at least two sides.Examples of suitable SMD resistors include an SMD resistor with the code 03015 with a size of 0.3 millimeters [mm] x 0.15 mm or with the code 0201 and a size of 0.25 mm x 0.125 mm.

[0047] According to one embodiment, at least one sensor for detecting icing is an optical sensor comprising at least one transmitter for emitting radiation and at least one receiver (detector) for detecting the radiation emitted by the transmitter. The optical sensor is further configured to detect water in liquid or solid form that is present in or along the path of the radiation emitted by the transmitter.

[0048] The transmitter of the optical sensor can be configured to emit electromagnetic radiation (waves) in the visible light (VIS) range (visible to the human eye) and / or in the infrared range. The wavelength of the visible light (VIS) can be in the range of 350 nanometers to 650 nanometers, and that of the infrared radiation in the range of 650 nanometers to 7 micrometers. The invention can also be used with a transmitter that can be configured to emit electromagnetic radiation (waves) in the ultraviolet (UV) range with a wavelength of 230 nanometers to 350 nanometers.

[0049] The at least one optical sensor can be thermally coupled to a region of the heat exchanger, such as a fin or the air inlet grille, in an ideally thermally compatible manner. This means that the surface of the optical sensor should exhibit the same behavior towards adhering water (in liquid or solid form) as the region of the heat exchanger. This can particularly affect thermal conductivity and heat capacity.

[0050] Furthermore, the at least one optical sensor can be arranged on or within a lamella in such a way that the same thermodynamic conditions for water deposition exist as on the lamella itself. For this purpose, the optical sensor can, for example, be integrated into a lamella so that its (detection) surface forms a plane with the lamella.

[0051] According to one embodiment, one or more optical sensors can be arranged on the heat exchanger. In particular, one or more optical sensors can be arranged on fins of the heat exchanger and / or the air inlet grille, distributed across the available flow cross-section of the heat exchanger, thus advantageously enabling the detection of local or partial icing of the heat exchanger.

[0052] According to a simple embodiment of the optical sensor, a transmitter can be geodetically positioned on the underside of a fin of the heat exchanger or air inlet grille, and a receiver on the upper side of an adjacent fin, such that radiation emitted by the transmitter can be detected by the receiver. The arrangement of transmitter and receiver can also be reversed. This simple embodiment thus makes it possible to detect water trapped between the transmitter and receiver; in particular, water trapped on the upper or lower side of a fin can be detected in liquid or solid form.

[0053] According to one embodiment, at least one optical sensor and at least one additional temperature sensor can be distributed across the flow cross-section. In this way, icing can be detected from the signal of an additional temperature sensor in conjunction with the ambient medium determined by the optical sensor. Specifically, an optical sensor and an additional temperature sensor can be located centrally in the flow cross-section, and an additional temperature sensor can be located in each of the outer regions of the flow cross-section (for example, geodetically at the top, bottom, and on both sides). An additional temperature sensor can be configured to detect an absolute temperature signal.

[0054] According to one embodiment, the at least one optical sensor can include at least one heating element configured to remove condensate and / or ice deposited on the optical sensor by applying heat. For example, the at least one heating element can be arranged on the side of a fin facing away from the optical sensor or directly on the optical sensor. After detecting condensate or ice, the at least one heating element can remove it and thus restore the optical sensor's detection capability.

[0055] The at least one heating element of the optical sensor can, in particular, be a resistance-based electrical heating element that can convert electrical current into heat.

[0056] The optical sensor's at least one transmitter can be any transmitter capable of emitting the aforementioned electromagnetic radiation. For example, the transmitter could be a lighting device, such as a light-emitting diode (LED, COB LED, or infrared LED). The transmitter can utilize electrical energy for this purpose. The transmitter can also include a collimation device, particularly a collimation lens, which aligns the emitted radiation(s) parallel to each other. The collimation device could, for example, be a gradient-index lens (GRIN). Such lenses have a variable refractive index, which allows for arc-shaped deflection of a beam and thus advantageously enables a flat lens design for radiation collimation.

[0057] The optical sensor's at least one receiver (detector) can be a device for receiving the radiation emitted by the transmitter. The receiver can generate an electrical signal that allows the intensity of the radiation reaching the receiver to be determined. Photodiodes, such as PIN diodes, can be used for this purpose. It is understood that the receiver should be tuned to the radiation emitted by the transmitter. The receiver can also include a collimating lens that focuses incident parallel radiation onto a detection surface of the receiver. The aforementioned GRIN lenses can also be used for this purpose.

[0058] According to one embodiment of the optical sensor, the at least one optical sensor can comprise a mirror, and the receiver can detect a reflection of the radiation emitted by the transmitter. The mirror can be a known mirror for reflecting visible light and / or IR or UV radiation, for example, a metallic surface. The transmitter can emit the radiation at an angle of incidence onto the mirror, and the receiver can be arranged, in particular, at the angle of reflection. For example, the mirror could be located on a (geodesically oriented upward-facing) surface of a lamella, and the transmitter and receiver could be located on the underside of a lamella positioned above it. When water in liquid or solid form adheres to the mirror, its reflectivity is weakened, and the incident radiation is scattered in various directions. This reduces the intensity of the radiation reaching the receiver to a detectable level.

[0059] According to one embodiment, the optical sensor can be configured to detect a change in total internal reflection at an optical interface during the transition from an optically denser medium, having a refractive index greater than 1, to an optically less dense medium (here, the surrounding medium) with a lower refractive index. In this case, the radiation (light) has a lower propagation speed in the optically denser medium than in the optically less dense medium (the surrounding medium). For this purpose, the optical interface is arranged and oriented such that water in liquid or solid form can adhere to it during operation of the heat exchanger. Thus, the reflection behavior of the optical interface changes depending on the surrounding medium. In this way, radiation striking the optical interface can be reflected back into the optically denser medium.In the optically less dense medium (the surrounding medium), a surface-guided radiation wave can be generated at the optical interface. If water in solid and / or liquid form is present at the optical interface, this leads to scattering of the surface-guided radiation wave, resulting in a measurable attenuation of the radiation reflected at the optical interface. In particular, the emitter can direct the radiation onto the optical interface at an angle of incidence greater than the critical angle for total internal reflection. The angle of incidence here refers to the angle that the incident radiation makes with a normal (here, the normal to the mirror surface). The critical angle for total internal reflection can be calculated using the law of refraction, given the refractive indices of the two media adjacent to the optical interface.

[0060] According to one embodiment of the optical sensor, the optical interface can be formed by a geometric body and the surrounding medium. The geometric body can, in particular, consist of a transparent, light-transmitting material, such as glass, plastic, mineral, or semiconductor material.

[0061] According to one embodiment of the optical sensor, the geometric body can have the form of a prism, a half-cylinder, a hemisphere, or a spherical or aspherical lens. Advantageously, the geometric shape of the body can have an axis of symmetry with respect to the input and output coupling of the radiation.

[0062] According to one embodiment of the optical sensor, the optical interface on the side facing the surrounding medium can have a coating that promotes homogeneous wetting of the optical interface. The coating can exhibit the property of a small contact angle between water and the coating film. The coating can thus improve the wetting of the sensor or the optical interface. For example, droplet formation on the optical interface can reduce the contact area (of ice or condensate with the optical interface) and therefore only cause partial disturbance of the surface waves, resulting in a lower modulation of the intensity to be detected. Thus, a hydrophilic coating can improve the response behavior of the optical sensor. Such hydrophilic nanocoatings are known from the prior art, and a suitable one can be selected.

[0063] According to one embodiment of the optical sensor, the optical interface can include a reflective region, and a first receiver can detect radiation reflected at the optical interface, while a second receiver can detect radiation reflected at the reflective region. The reflective region is defined as a portion of the optical interface where it acts as a mirror. This reflective region can be formed, in particular, by applying a metallic coating, for example, by vapor deposition. This embodiment advantageously allows for the detection of intensity fluctuations from the transmitter by evaluating the signals received by the first and second receivers. These intensity fluctuations can be caused, for example, by aging or by contamination of the transmitter.In other words, radiation detected by the second receiver that was reflected at the specular area can be considered a reference signal, allowing for higher sensitivity in the evaluation of the signal reflected at the optical interface.

[0064] According to one embodiment of the optical sensor, a polarizing filter can be configured to polarize at least a portion of the radiation from the at least one transmitter. For this purpose, the polarizing filter can be positioned, in particular, in the beam path between the transmitter and the optical interface. Advantageously, polarized light allows for differentiation between water in liquid or solid phase at the optical interface. Liquid water does not exhibit polarizing properties for radiation (especially visible light). In contrast, the polarization of the incident light is altered / rotated when ice forms. This results in partial contrast modulations as an interaction between polarized radiation (light) and the crystalline ice, causing a detectable reduction in intensity along the polarized light's path.For this design, a coating as described above, which ensures homogeneous wetting of the interface, is helpful, as it can also promote homogeneous crystal formation at the optical interface. In conjunction with the polarizing properties of the optical interface (Fresnell reflection with different reflectances for s- and p-polarized light), the polarization caused by the ice at the optical interface can lead to a noticeable improvement in contrast and thus enable differentiation between the liquid and solid phases of the water deposited at the optical interface.

[0065] According to one embodiment of the optical sensor, a second polarization filter can be arranged between the optical interface and the receiver. This second polarization filter (polarizer) can be considered an analyzer positioned in front of the receiver and, depending on the polarization setting, minimizes the radiation reflected from the optical interface in an undisturbed state (no condensate). Depending on the condensate and its phase, the detectable intensity or its contrast at the receiver can increase (inverse detection behavior).

[0066] Both linear and circular polarizers (polarizing filters) can be used for this purpose.

[0067] According to one embodiment of the optical sensor, a first receiver can detect radiation from a transmitter reflected at the optical interface, a second receiver can detect radiation from a transmitter reflected at a specular area of ​​the optical interface, and a third receiver can detect polarized radiation reflected at the optical interface. In particular, the radiation from a transmitter can be divided into three beam ranges to avoid transmitter-related intensity differences. This embodiment enables particularly sensitive detection by capturing the reference signal reflected at the specular area and, furthermore, by detecting the polarized radiation reflected at the optical interface, allows for differentiation as to whether water is present in liquid or solid form at the optical interface.For this purpose, the first, second and third receivers can be arranged directly adjacent to each other, so that their detection surfaces lie largely in one plane.

[0068] According to one embodiment of the optical sensor, the at least one transmitter can couple the radiation directly into the optically denser medium, and the receiver can couple radiation directly out of the optically denser medium. In other words, the at least one transmitter and / or the at least one receiver can be connected to the geometric body in such a way that radiation emitted by the transmitter is directly coupled into the geometric body and directly coupled out of the geometric body by the receiver. "Directly" here means that there is no gap between the transmitter or receiver and the optical body that is accessible to an surrounding medium, thus preventing the effects of contamination. For this purpose, the transmitter, receiver, a collimation device, and / or a polarizing filter can be connected to the geometric body, for example, by being cemented or glued in place.Furthermore, this design allows for a very compact construction of an optical sensor for the heat exchanger.

[0069] According to one embodiment, an optical sensor for the heat exchanger can be manufactured using a MEMS (micro-electro-mechanical systems) or MOEMS (micro-opto-electro-mechanical systems) process. This advantageously allows for a particularly small, monolithic optical sensor design. A MEMS or MOEMS process is based on semiconductor technology and enables the production of a miniaturized, monolithic optical sensor for the heat exchanger proposed here.

[0070] It is understood that at least one optical sensor can be combined with at least one caloric sensor to detect icing on a heat exchanger proposed here.

[0071] According to another aspect of the invention, a method for de-icing a heat exchanger of a heat pump proposed here is also proposed, comprising the following steps: a) Detecting icing of the heat exchanger, b) Applying an electric current to the electrically conductive coating if, in step a), icing of the heat exchanger was detected.

[0072] Steps a) and b) of the procedure can be performed at least once in the specified order. In particular, step b) can be performed each time the condition of step a) is met. The procedure serves for the rapid and efficient defrosting of a heat exchanger of a heat pump, which is designed for heat exchange with ambient air.

[0073] According to step a), icing of the heat exchanger can be detected. This detection can be carried out in any number of ways. For example, the performance of a fan designed to circulate air through the heat exchanger can be used. Icing of the heat exchanger can reduce its airflow, resulting in a characteristic change in the fan's performance. Another possibility is to monitor the supply and return temperatures of the refrigerant at the heat exchanger to detect a reduction in heat exchange and thus icing.

[0074] Alternatively or additionally, icing of the heat exchanger can also be detected by sensors. For this purpose, a caloric sensor and / or an optical sensor, as described here, can be used.

[0075] According to step b), if icing of the heat exchanger was detected in step a), it can be defrosted. For this purpose, an electrical voltage can be applied to the first and second points of the electrically conductive coating of the refrigerant line, a fin of the line, and / or the air inlet grille using a voltage source. This voltage causes an electric current to flow, resulting in targeted heating and thus defrosting. Step b) can be carried out for a predetermined duration. This duration can also be adjusted based on a prior assessment of the icing. This assessment can be performed, for example, during the icing detection in step a), such as by evaluating the increase in the heat exchanger fan's output.Alternatively or cumulatively, a sensor can be used to detect icing, confirm that complete / sufficient de-icing has occurred, and then the execution of step b) can be terminated.

[0076] According to one embodiment of the method, the flow of refrigerant through the heat exchanger can be interrupted during step b). A continuous flow of refrigerant through the heat exchanger causes the heat introduced by the resistance heating of the electrically conductive layer to be dissipated, thereby extending the defrosting time. For example, the compressor can be switched off and / or the expansion valve closed. In addition, a fan that causes flow through the heat exchanger can be switched off to prevent or reduce the heat dissipation from the electrically conductive coating. The invention is particularly applicable to heat pumps in which a further refrigeration or brine circuit is interposed between the refrigeration circuit and the heat exchanger.In such systems, a circulation unit of the additional refrigeration or brine circuit can be deactivated according to one design. The aim is to prevent or significantly reduce heat loss from the heat exchanger in order to avoid unnecessarily extending the time required for defrosting.

[0077] According to another aspect of the invention, a heat pump is also proposed, comprising a heat exchanger as proposed herein. The heat pump can be configured, in particular, for supplying heat to a building, i.e., for providing heating and / or hot water. The heat exchanger proposed herein can be operatively connected to an evaporator and configured to extract heat from the ambient air. For this purpose, it can be located in an outdoor unit of the heat pump. The heat pump system can include a control unit configured to carry out a method proposed herein. For this purpose, the control unit can have and / or be equipped with a processor for data processing. Furthermore, the control unit can have or access a memory on which data for carrying out a method proposed herein is stored or is stored.

[0078] In addition, a computer program product is proposed, comprising commands that cause a heat pump proposed herein to carry out a procedure presented here in a fully automated manner. In other words, this specifically concerns a computer program (product) comprising commands that, when executed by a computer, cause it to perform a procedure proposed here. The computer program can, in particular, be executed on a control unit of a heat pump proposed herein.

[0079] Another aspect is the proposal for a computer-readable storage medium on which a computer program product proposed here is stored.

[0080] According to a further aspect of the invention, the use of an electrically conductive coating for resistance heating is proposed for defrosting a heat exchanger of a heat pump. The electrically conductive coating can be arranged, in particular, on a refrigerant line, a fin connected to the refrigerant line, and / or an air inlet grille of the heat exchanger. Furthermore, the electrically conductive coating can be applied to an electrically non-conductive coating.

[0081] It should be noted as a precaution that the numerical terms used here ("first", "second", etc.) primarily serve (only) to distinguish between several similar objects, quantities, or processes, and thus do not necessarily dictate any dependency and / or sequence between these objects, quantities, or processes. Should a dependency and / or sequence be required, this is explicitly stated here, or it will be obvious to a person skilled in the art upon studying the specific configuration described. Where a component can occur multiple times ("at least one"), the description of one of these components may apply equally to all or some of the multiple components, but this is not mandatory.

[0082] The details, features, and advantageous designs discussed in connection with the heat exchanger can also occur in the heat pump, computer program product, and application presented here, and vice versa. In this respect, full reference is made to the explanations provided therein for a more detailed characterization of the features.

[0083] This document describes a heat exchanger for a heat pump, a method for defrosting a heat exchanger, a heat pump, a computer program, and an application that at least partially solves the problems described with reference to the prior art. In particular, the heat exchanger, the method, the computer program, and the application contribute to enabling rapid defrosting that is independent of the heat pump's operating state. Particularly advantageous is the ability to detect icing at such an early stage using sensors, thus requiring only a very short defrosting process that minimally affects the normal operation of the heat exchanger or heat pump. Any potential reduction in user comfort due to the process can be advantageously kept to a barely perceptible or imperceptible level. Furthermore, the invention can be implemented using simple manufacturing methods.

[0084] The invention and its technical context are explained in more detail below with reference to the accompanying figures. It should be noted that the invention is not intended to be limited by the exemplary embodiments shown. In particular, unless explicitly stated otherwise, it is also possible to extract partial aspects of the situations described in the figures and combine them with other components and findings from the present description. It should be emphasized that the figures, and especially the depicted dimensions, are only schematic. They show: Fig. 1: a heat pump proposed here, Fig. 2: a refrigerant line of a heat exchanger proposed here, and Fig. 3: a heat exchanger proposed here.

[0085] Fig. Figure 1 shows an exemplary and schematic representation of a heat pump 1 presented here for supplying a building 7 with thermal energy. The heat pump 1 can comprise an outdoor unit 6, which extracts heat from the ambient air, and an indoor unit 8 for transferring the absorbed heat into the building 7. A refrigerant can be circulated in a refrigeration circuit 12, which can evaporate in an evaporator 3 of the refrigeration circuit 16 and liquefy in a condenser 4 of the refrigeration circuit 12. Furthermore, a compressor 2 and an expansion valve 5 can be provided in the refrigeration circuit 12, with the compressor 2 being driven by an electric motor. The expansion valve 5 can have an adjustable opening width, which can be controlled by a motor, for example, a stepper motor.The refrigerant can be transported in refrigeration circuit 12 in a recirculation direction 11 from the evaporator 3 via the compressor 2 to the condenser 4 and then via the expansion valve 5 back to the evaporator 3. Refrigeration circuit 12 comprises a refrigerant line 19, which has a first point 17 in the region of an inlet of the heat exchanger 9 and a second point 18 in the region of an outlet of the heat exchanger 9. The inlet and outlet of the heat exchanger 9 refer to the refrigerant recirculation direction 11. The first point 17 and the second point 18 define a section of the refrigerant line 19 that may be affected by icing during normal operation of the heat pump 1. It should be noted for clarification that the representation of the refrigerant line 19 in the region of the heat exchanger 9 is greatly simplified and is usually arranged in a meandering or other planar shape.Furthermore, the refrigerant line 19 can include fins (not shown here) that increase the surface area available for heat exchange. The heat exchanger 9 is designed for heat exchange with ambient air 14. For this purpose, the heat exchanger 9 can include a fan (not shown here) designed to circulate ambient air 14 through the heat exchanger 9. The refrigerant line 19 can be made of aluminum. The heat pump 1 includes a control unit 10, designed to regulate and control the operation of the refrigeration circuit 12. The control unit 10 is also designed to execute a procedure proposed here. For this purpose, a computer program 13, which causes the control unit 10 to execute the heat pump 1 as proposed here, can be stored in a memory of the control unit 10.

[0086] In the section of the refrigerant line 19 from the first point 17 to the second point 18, the refrigerant line 19 has an electrically non-conductive coating 15. In this example, this can be an anodized layer, i.e., an aluminum oxide layer (Al₂O₃). An electrically conductive coating 16 can be applied to the electrically non-conductive coating 15. In this example, it consists of an electrically conductive polymer. The heat pump 1 also includes a voltage source 21, which can be controlled by the control unit 10. The voltage source 21 is electrically connected to the electrically conductive coating 16 at the first point 17 and at the second point 18, so that a voltage can be applied which generates a current flow in the electrically conductive coating 16 and thus causes the electrically conductive coating 16 to heat up.

[0087] Fig. Figure 2 shows an exemplary and schematic cross-section of the refrigerant line 19 in the area from the first point 17 to the second point 18. The refrigerant can circulate inside the refrigerant line 19. The electrically non-conductive coating 15 is applied to the refrigerant line 19, which electrically decouples the refrigerant line 19 from the electrically conductive coating 16 applied to the electrically non-conductive coating 15.

[0088] Fig.Figure 3 shows an exemplary and schematic representation of the heat exchanger 9. The refrigerant line 19 with the electrically non-conductive coating 15 and the electrically conductive coating 16 arranged on it can be routed in a meandering pattern within the heat exchanger 9 and form a heat exchange surface. The voltage source 21 is electrically connected to the electrically conductive coating 16 and can introduce a heating current into it. A flow of ambient air 14 can be effected by a fan (not shown here).

[0089] According to step a) of the method proposed here, icing of the heat exchanger 9 can be detected by the control unit 10. This can be done in particular by means of the sensor 20. Alternatively or cumulatively, other signals can also be used for this purpose, for example, the power output of the blower that supplies the heat exchanger 9 with ambient air 14, or a control signal for the blower.

[0090] If icing of the heat exchanger 9 is detected in step a), step b) of the procedure, namely de-icing of the heat exchanger 9, can be carried out. For this purpose, the control unit 10 can send a control signal to the voltage source 21, which then applies a heating voltage to the electrically conductive coating 16. The heating voltage generates an electric current that heats the electrically conductive coating 16. The heat introduced in this process de-ices the heat exchanger 9. Step b) can be terminated as soon as the sensor 20 no longer detects icing of the heat exchanger 9.

[0091] The procedure can be carried out continuously or permanently during the operation of heat pump 1. Reference symbol list 1 heat pump 2 compressors 3 evaporators 4 liquefiers 5 Expansion valve 6 Outdoor part 7 buildings 8 Inner part 9 heat exchangers 10 Control and monitoring unit 11. Direction of circulation 12 refrigeration circuit 13 Computer program product 14 Ambient air 15 electrically non-conductive coating 16 electrically conductive coating 17 first point 18 second point 19 Refrigerant line 20 Sensor 21 Voltage source QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 4 212 786 A1

[0004] WO 2014 / 083 066 A2

[0006]

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