Safety device for heat pump device and heat pump device

Abstract

The present invention relates to a safety device for a reversible heat pump device (10) with a refrigerant circuit coupled to a heat transfer circuit (20) via a first heat exchanger (13). The safety device comprises a first pressure switch for monitoring the pressure of a refrigerant in the refrigerant circuit of the heat pump device (10) and a temperature switch for monitoring the temperature of the refrigerant in the refrigerant circuit of the heat pump device (10). The first pressure switch comprises a first switch (S1) configured to open when the refrigerant pressure is less than a first predetermined pressure limit. The temperature switch comprises a second switch (S2) configured to open when the refrigerant temperature exceeds a predetermined temperature limit.The first switch (S1) is arranged in parallel to the second switch (S2), so that the power supply to the heat pump device (10) is interrupted if the first switch (S1) and the second switch (S2) are open.

Description

[0001] The present invention relates to a safety device for a reversible heat pump device and to a reversible heat pump device.

[0002] Heat pumps are characterized by their high efficiency and can therefore be particularly attractive for heating and / or cooling a building from both an ecological and economic perspective. Heating with ambient heat is climate-friendly. Furthermore, many energy suppliers have been offering special heat pump tariffs for several years now, which are financially more attractive than a standard electricity tariff.

[0003] A heat pump of this type has a refrigerant circuit. R290 (propane), for example, can be used as the refrigerant. Since propane is flammable, any unintentional leakage must be prevented.

[0004] In a heat pump's refrigerant circuit, the refrigerant absorbs heat from the surrounding medium and evaporates during heating operation. Accordingly, this heat exchanger is referred to as an evaporator during heating operation. One possible cause of malfunctions in heat pumps is the formation of an ice layer on the evaporator due to moisture in the ambient air, which impedes heat transfer. This ice layer then typically needs to be removed through a defrosting process.

[0005] Furthermore, a heat pump of this type has an additional heat exchanger, often designed as a plate heat exchanger. In heating mode, this plate heat exchanger is also referred to as a condenser. Here, heat is transferred from the refrigerant, compressed by a compressor, to a heat transfer medium in a heating circuit, with the refrigerant changing from a gaseous to a liquid state.

[0006] During defrosting or cooling operation of the heat pump, the cycle is reversed. The condenser (plate heat exchanger) becomes the evaporator, and vice versa. Consequently, low temperatures can occur at the plate heat exchanger. Since the heat transfer medium is usually water, it is essential to prevent the temperature from dropping below freezing to avoid a refrigerant leak in the plate heat exchanger caused by the heat transfer medium in the heating circuit freezing.

[0007] A safety system for refrigeration compressors in refrigeration systems is disclosed in German patent application DE 10 2007 052 ​​532 A1. This computer-controlled safety system monitors the operating conditions of the refrigeration system. Among other things, it simultaneously monitors and evaluates the status of a high-pressure safety limiter and a high-pressure switch. Each safety device in the refrigeration system influences the function of the refrigeration compressor(s). In the event of a malfunction, the high-pressure safety limiter immediately shuts off the compressor, and automatic reset is not possible. The high-pressure switch immediately shuts off the compressor in the event of a malfunction, and multiple automatic resets are possible. The safety system can be used in all refrigeration systems with at least one refrigeration compressor, including heat pumps, drying systems, ice machines, and dehumidification systems with one or more compressors.

[0008] DE 10 2020 112 376 A1 discloses a heat pump system with a plate heat exchanger and a low-pressure switch arranged on the plate heat exchanger, which is intended to switch off the compressor of the heat pump system when a predetermined low-pressure cut-off level is reached or undershot.

[0009] However, the known safety devices can lead to the heat pump shutting down unintentionally under certain conditions. This can be prevented, for example, by monitoring the operation with a complex control system.

[0010] Based on the state of the art, an improved safety device for a reversible heat pump device is to be provided, which is particularly simple in design and which, in addition to preventing the heat transfer medium from freezing on the heat exchanger, can also prevent the heat pump device from being switched off unintentionally during heating or defrosting operation.

[0011] The problem is solved by a safety device according to claim 1 or claim 2 and by a heat pump device according to claim 3. Preferred embodiments are the subject of the dependent claims, the drawings and the following description of exemplary embodiments.

[0012] The safety device according to a first aspect of the invention comprises a first pressure switch and a temperature switch.

[0013] The first pressure switch is configured to monitor the refrigerant pressure in the refrigerant circuit of the heat pump device. In other words, the first pressure switch measures the refrigerant pressure in the refrigerant circuit or in a line (e.g., supply or return) of the refrigerant circuit. The first pressure switch includes a first switch that is configured to open when the measured refrigerant pressure is less than a predefined first pressure limit. The first pressure switch can therefore also be referred to as a low-pressure switch.

[0014] The first pressure limit can be specified depending on characteristic parameters of the heat pump device used. It can depend, in particular, on the design and dimensioning of the heat pump device. Furthermore, the first pressure limit can depend on characteristic properties of the refrigerant used, such as its evaporation pressure. The first pressure limit is specifically set to prevent the heat transfer medium from freezing in the heating circuit and is therefore based on the freezing point of the heat transfer medium, which is usually water.

[0015] For example, if water is used as the heat transfer medium (freezing point 0°C) and propane as the refrigerant (evaporation temperature 0°C), the first pressure limit corresponds to the evaporation pressure of propane, which is 4.71 bar(a). The pressure switch is configured accordingly so that the first switch opens when the measured pressure is ≤ 4.71 bar(a). The pressure switch is positioned in the refrigerant circuit in such a way that the first switch is not expected to open during normal heating operation, as a higher pressure always prevails at that point.

[0016] The temperature switch is configured to monitor the temperature of the refrigerant in the refrigerant circuit of the heat pump device. In other words, the temperature switch measures the temperature of the refrigerant in the refrigerant circuit or in a line (e.g., supply or return) of the refrigerant circuit. The temperature switch includes a second switch that is configured to open when the refrigerant temperature exceeds a predefined temperature limit. The temperature switch can therefore also be referred to as a safety temperature switch.

[0017] The temperature switch is preferably located near the second heat exchanger. Depending on the operating state of the heat pump, the temperature switch at this location measures approximately the evaporation temperature (heating mode) or the condensation temperature (cooling mode) of the refrigerant. The temperature switching point, i.e., the temperature limit, is selected to be characteristic of stable cooling operation. For example, the initial phase of a defrost cycle in the heat pump is considered unstable cooling operation. The temperature limit generally depends on the design and dimensioning of the heat pump and must therefore be determined through testing. The temperature limit is selected so that it is not reached during normal operation (heating mode) of the heat pump.

[0018] A safety device according to a second aspect of the present invention comprises a second pressure switch instead of the temperature switch. The position of the second pressure switch can correspond to the position of the temperature switch.

[0019] The second pressure switch is configured like the first pressure switch to monitor the refrigerant pressure in the refrigerant circuit of the heat pump device. In other words, the second pressure switch measures the refrigerant pressure in the refrigerant circuit or in a line (e.g., supply or return) of the refrigerant circuit. The second pressure switch includes a secondary switch that is configured to open when the measured refrigerant pressure exceeds a predefined second pressure limit.

[0020] The second pressure limit is determined by the condensing pressure of the refrigerant during cooling operation of the heat pump unit. If the refrigerant pressure at the second pressure switch is higher than the second pressure limit, it can be assumed that the heat pump unit is not in the initial phase of a defrost cycle, but rather in stable cooling operation. The second pressure limit generally depends on the design and dimensioning of the heat pump unit and must therefore be determined through testing.

[0021] The first switch is arranged in parallel to the second switch, so that if both the first and second switches are open, the power supply to the heat pump device is interrupted.

[0022] The first pressure switch, the second pressure switch, and the temperature switch are preferably safety-related switching devices that, upon reaching, falling below, or exceeding their respective limit values, can open a (preferably electromechanical) switch, in particular to interrupt the power supply to the compressor and thus shut down the heat pump device. All or some of the three switching devices can preferably be self-resetting, so that the corresponding switches close again as soon as the respective limit value is again fallen below or exceeded.

[0023] The first pressure switch may preferably have an automatic (self-resetting) and / or a manual reset device. The temperature switch may preferably only have an automatic reset device. The second pressure switch may particularly preferably only have an automatic reset device.

[0024] The preferred safety-related switching devices described here can preferably be implemented without a control or regulating device and are preferably not connected to any control or regulating device of the heat pump system. Therefore, no complex and potentially fault-prone electronic components are necessary to shut down the heat pump system. Only the opening of both parallel-connected switches is required to interrupt the power supply. Thus, due to the simple design using basic electromechanical components, a high reliability of the safety shutdown by the safety device can be ensured.

[0025] A reversible heat pump device according to the invention for heating and / or cooling a building comprises a safety device according to one aspect of the present invention.

[0026] The heat pump device further comprises a refrigerant circuit in which a refrigerant circulates, a compressor arranged in the refrigerant circuit for compressing the refrigerant, a four-way valve for effecting a reversal of the cycle, a first heat exchanger for coupling the refrigerant circuit with a heat transfer circuit in which a heat transfer medium circulates, an expansion valve in the refrigerant circuit for expanding the refrigerant, and a second heat exchanger for transferring heat from an ambient medium to the refrigerant or vice versa.

[0027] Furthermore, the heat pump device may include a manifold, an internal heat exchanger, an additional expansion valve, and pressure and temperature sensors. Since these components are not necessary to explain the safety device, they will not be described in detail below.

[0028] The temperature switch or the second pressure switch is preferably arranged between the expansion valve and the second heat exchanger. Alternatively, the temperature switch or the second pressure switch can be arranged between the second heat exchanger and the four-way valve. In other words, the temperature switch or the second pressure switch is preferably arranged in the flow or return line of the second heat exchanger.

[0029] According to a preferred embodiment, the first heat exchanger is a plate heat exchanger.

[0030] Preferably, the first pressure switch is arranged between the first heat exchanger and the expansion valve. In an alternative embodiment, the first pressure switch can also be arranged between the four-way valve and the first heat exchanger. In other words, the first pressure switch can be located in the supply or return line of the first heat exchanger to measure a characteristic refrigerant pressure at the first heat exchanger. In particular, the first pressure switch can thus activate when a refrigerant evaporation pressure is reached at the first heat exchanger (cooling operation).

[0031] A heat pump system according to the invention comprises a heat transfer medium. The heat transfer medium transports heat for heating or cold for cooling the building. For example, water circulating in a heating circuit of the building can be used as the heat transfer medium for heating. Alternatively or additionally, air circulating, for example, in an open circuit, can be used for cooling or heating. The heat pump system can thus be a component of a heating, ventilation, air conditioning, and / or refrigeration system (HVAC system).

[0032] In a preferred embodiment, the heat pump system can be designed for both cooling and heating the building. Accordingly, separate heating circuits or cooling lines and / or ventilation ducts can be provided for suitable heat transfer media. The heating circuits or cooling lines and / or ventilation ducts can include a circulation device suitable for the respective heat transfer medium, for example, a pump and / or a fan.

[0033] The heat pump device preferably includes a control unit for regulating and / or controlling the heat pump device. In the following, the term "regulating" is used for both control and regulating processes. The control unit can output corresponding control signals to the heat pump device, in particular to the compressor of the heat pump device, via a suitable interface and suitable signal lines.

[0034] The control unit may have an interface for outputting information. In particular, this interface may enable the transmission of a message to a mobile device belonging to a user or operator of the heat pump system. Additionally or alternatively, the control unit may have a display device, such as a screen, for outputting information, for example, an error message.

[0035] The interface between the control system and the user or operator for outputting messages can generally be understood as a human-machine interface (HMI), through which the user or operator can preferably also input data. In a preferred implementation, the HMI can be an application ("app") on the user's or operator's mobile device. The cloud or server can also be used as an interface. This allows access to data in the cloud or on the server, particularly via a web browser, which can also enable control system interventions. BRIEF DESCRIPTION OF THE FIGURES

[0036] Further advantageous embodiments are described in more detail below with reference to an exemplary embodiment shown in the drawings, to which, however, the invention is not limited.

[0037] They show schematically: Figure 1 Fig. 1 illustrates a heat pump device according to an exemplary embodiment. Figure 2 Fig. 2 illustrates a safety device with two switching devices connected in parallel. Figure 3 Figs. 3a to 3d Illustrate the states of the safety device for different operating states of the heat pump device. DETAILED DESCRIPTION OF THE INVENTION USING EXAMPLES OF EXECUTION

[0038] In the following description of a preferred embodiment of the present invention, the same reference numerals denote identical or comparable components.

[0039] Fig. 1Figure 1 shows a simplified representation of an embodiment of a heat pump device 10 according to the invention for heating and / or cooling a building or a part thereof. The heat pump device 10 comprises a compressor 11, a four-way valve 12, a first heat exchanger 13, an expansion valve 14, and a second heat exchanger 15. Other optional components are not shown. The arrows illustrate the direction in which the refrigerant circulates through the refrigerant circuit during heating operation of the heat pump device 10. By actuating the four-way valve 12, a reversal of the cycle can be effected to operate the heat pump device 10, for example, in cooling or defrosting mode.

[0040] The first heat exchanger 13 serves to transfer heat between the refrigerant in the refrigerant circuit and a heat transfer medium in a heating circuit 20 of the building.

[0041] The operating principle of the heat pump device 10 corresponds to the known operating principle of a heat pump. In heating mode, the first heat exchanger 13 serves as a condenser and the second heat exchanger 15 serves as an evaporator. In cooling mode, the first heat exchanger 13 serves as an evaporator and the second heat exchanger 15 serves as a condenser. A plate heat exchanger is preferably used as the first heat exchanger 13. By monitoring the evaporation pressure at the plate heat exchanger, freezing of the heat transfer medium in the plate heat exchanger can be prevented.

[0042] Fig. 2 illustrates a circuit diagram of the safety device according to the invention, consisting of a first pressure switch and a temperature switch or of a first pressure switch and a second pressure switch, each of which is assigned to a first switch S1 and a second switch S2.

[0043] By connecting the two switches S1 and S2 in parallel, a power supply is established between points 1 and 2 in Fig. 2 The circuit is only interrupted when both switches S1 and S2 are open. As long as the circuit between points 1 and 2 is closed, the heat pump device 10 (in particular the compressor 11) is supplied with power.

[0044] The following will be based on Fig. 3 explains under what conditions the power supply to the heat pump device can be interrupted. Fig. 3 corresponds to the design of the safety device with a low-pressure switch (first pressure switch with first switch S1) and a safety temperature switch (temperature switch with second switch S2).

[0045] Figs. 3a to 3d A total of eight diagrams are shown, each presented in pairs. The two diagrams in Fig. 3aThis concerns the case where the heat pump device 10 is operated in heating mode. The temperature limit is selected such that no exceedance of the temperature limit is expected during heating operation. Since the temperature switch is located in the flow line to the second heat exchanger 15 and after the expansion valve 14, the temperature of the refrigerant at this point is always low during heating operation and is, for example, in the range of -20 to +30°C.

[0046] The pressure switch (low-pressure switch) is located in the return line of the first heat exchanger 13 and thus measures the refrigerant pressure at the condenser during heating operation. It is possible for the pressure to drop below the first pressure limit, causing the first switch S1 to open (top right in the diagram). Fig. 3 However, since the second switch S2 of the temperature switch remains closed, the power supply is not interrupted.

[0047] The two circuit diagrams in Fig. 3bThis concerns the initial phase of a defrost cycle. In contrast to the heating cycle, which in Fig. 3a As depicted, a cycle reversal has thus occurred. In the initial phase, the temperature remains below the temperature limit. Switch S2 therefore remains closed. Even if the pressure at the first pressure switch falls below the first pressure limit (right image), the power supply is not interrupted.

[0048] Thus, by connecting the first pressure switch in parallel with the temperature switch, an unintentional shutdown of the heat pump device 10 can be prevented.

[0049] The two diagrams in Fig. 3c This illustrates operation after the initial defrosting phase. The temperature at the temperature switch has risen above the temperature limit. If the pressure at the first pressure switch also falls below the pressure limit, the power supply to the heat pump device 10 is interrupted (right image).

[0050] The two diagrams in Fig. 3d This illustrates a cooling operation. The temperature at the temperature switch can rise above the temperature limit. If the pressure at the first pressure switch also falls below the pressure limit, the power supply to the heat pump device 10 is interrupted (right image). This prevents the plate heat exchanger (first heat exchanger) from freezing.

[0051] One of the Figs. 3a to 3d A corresponding representation of the operating states for the implementation of the safety device with a first pressure switch (low-pressure switch) and a second pressure switch is obtained by replacing the temperature switch with the second pressure switch. Instead of a temperature limit, a second pressure limit is then used, and the second switch S2 opens when the second pressure limit is reached or exceeded.

[0052] Determining the pressure limit can be done analogously to determining the temperature limit, since pressure and temperature in the wet vapor and liquid regions of the refrigerant are more or less directly related. In other words, the pressure limit can be determined based on the physical properties of the respective refrigerant.

[0053] The features disclosed in the foregoing description, the claims and the drawings can be important for the realization of the invention in its various embodiments, both individually and in any combination. REFERENCE MARK LIST

[0054] 10 Heat pump device 11 Compressor 12 Four-way valve 13 First heat exchanger 14 Expansion valve 15 Second heat exchanger S1 First switch S2 Second switch

Claims

1. Safety device for a reversible heat pump device (10) with a refrigerant circuit coupled to a heat transfer circuit (20) via a first heat exchanger (13), the safety device comprising: a first pressure switch for monitoring a pressure of a refrigerant in the refrigerant circuit of the heat pump device (10), wherein the first pressure switch comprises a first switch (S1) configured to open when the pressure of the refrigerant is less than a first predetermined pressure limit; a temperature switch for monitoring a temperature of the refrigerant in the refrigerant circuit of the heat pump device (10), wherein the temperature switch comprises a second switch (S2) configured to open when the temperature of the refrigerant is greater than a predetermined temperature limit;wherein the first switch (S1) is arranged in parallel to the second switch (S2) such that the power supply to the heat pump device (10) is interrupted if the first switch (S1) and the second switch (S2) are open.

2. Safety device for a reversible heat pump device (10) with a refrigerant circuit coupled to a heat transfer circuit (20) via a first heat exchanger (13), the safety device comprising: a first pressure switch for monitoring the pressure of a refrigerant in the refrigerant circuit of the heat pump device (10), the first pressure switch comprising a first switch (S1) configured to open when the pressure of the refrigerant is less than a first predetermined pressure limit; a second pressure switch for monitoring the pressure of the refrigerant in the refrigerant circuit of the heat pump device (10), the second pressure switch comprising a second switch (S2) configured to open when the pressure of the refrigerant is greater than a second predetermined pressure limit;wherein the first switch (S1) is arranged in parallel to the second switch (S2) such that the power supply to the heat pump device (10) is interrupted if the first switch (S1) and the second switch (S2) are open.

3. Safety device according to claim 1 or 2, wherein the first pressure switch has an automatic reset device and / or a manual reset.

4. Safety device according to one of claims 1 to 3, wherein the temperature switch has an automatic reset device.

5. Safety device according to one of claims 1 to 4, wherein the second pressure switch has an automatic reset device.

6. Reversible heat pump device (10) for heating and / or cooling a building, wherein the heat pump device (10) comprises: a refrigerant circuit in which a refrigerant circulates; a compressor (11) arranged in the refrigerant circuit for compressing the refrigerant; a four-way valve (12) for effecting a reversal of the circuit; a first heat exchanger (13) for coupling the refrigerant circuit with a heat transfer circuit (20) in which a heat transfer medium circulates; an expansion valve (14) in the refrigerant circuit for expanding the refrigerant; a second heat exchanger (15) for transferring heat from an ambient medium to the refrigerant or vice versa; and a safety device according to any one of claims 1 to 5.

7. Heat pump device (10) according to claim 6, wherein the temperature switch or the second pressure switch is arranged between the expansion valve (14) and the second heat exchanger (15).

8. Heat pump device (10) according to claim 6 or 7, wherein the first heat exchanger (13) is a plate heat exchanger; and the first pressure switch is arranged between the first heat exchanger (13) and the expansion valve (14).

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