Safety shut-off for heat pump system

Abstract

The invention relates to a safety system for a heat pump system and to a method for operating the safety system. The problem underlying the invention is that a potentially combustible refrigerant can enter the secondary circuit via the corresponding heat exchanger. The safety system according to the invention comprises a control module which is coupled to one or more sensors which detect the cause of the safety shut-off and which are provided in the secondary circuit. The sensors allow gas to be detected in the secondary circuit directly or using variables which suggest the presence of gas. According to the invention, when gas is present in the secondary circuit, the flow through the secondary circuit is reduced by correspondingly controlling the circulating pump. Thus, gaseous refrigerant is prevented from entering the building.

Description

[0001] Safety shutdown for heat pump system

[0002] The invention relates to a security system for a heat pump system and a method for operating the security system.

[0003] The invention is based on the problem that potentially flammable refrigerant can enter the secondary circuit via the corresponding heat exchanger. A secondary circuit is understood here to be a hydraulic circuit, in particular a water circuit, to which the refrigeration circuit releases heat or absorbs heat from it. An example of such a secondary circuit is a heating circuit in heat pump systems that operate as heating systems.

[0004] The safety system according to the invention comprises a control module coupled to one or more sensors located in the secondary circuit that detect the cause of the safety shutdown. The sensors enable the detection of gas in the secondary circuit directly or via variables that indicate the presence of gas. According to the invention, if gas is present in the secondary circuit, the flow through the secondary circuit is reduced or prevented by controlling the circulation pump accordingly. This prevents the gaseous refrigerant from entering the secondary circuit.

[0005] Heat pump systems used for heating have a primary circuit for carrying a refrigerant and a secondary circuit – the actual heating circuit – for carrying the corresponding heat transfer medium – usually a heating medium with water as its main component. Heat is transferred between the refrigerant and the heating medium via a heat exchanger. This solution is also applicable to refrigeration systems, although the terms commonly used for heat pumps are used here.However, when using flammable refrigerants, particularly hydrocarbons such as C3H8 (R290, propane), there is the problem that a defect, for example a general defect, corrosion or a defect caused by freezing water (heating medium), in the heat exchanger, which is designed as a plate heat exchanger, for example, can cause gaseous refrigerant to enter the secondary circuit, in particular a heating area of ​​the secondary circuit, which can then reach a house heated with the heat pump system via the distribution system of the secondary circuit and escape there via automatic vent valves, safety valves or drain valves.

[0006] If a flammable refrigerant, such as propane, is used, an ignitable mixture can form with the room air, which then poses a danger to the house and its occupants.

[0007] It is known from the prior art that a gas separator with automatic vent and a safety valve in the flow line are present in the secondary circuit of a heat pump system in order to safely remove flammable refrigerant entering the secondary circuit before a secondary medium flowing through the secondary circuit, in particular water, together with the refrigerant contained therein, reaches the living areas and thus prevent the refrigerant from escaping into the living areas of the house.

[0008] The safety valve for blowing off the refrigerant is dimensioned in such a way that this safety discharge valve in the secondary circuit responds before any other safety valves that may be installed and therefore opens approximately 0.5 bar below the opening pressure of the other safety valves.

[0009] Especially when using propane gas as the refrigerant, multiple valves / vents may be provided, for example, in a supply and return line of the secondary circuit. In some cases, a microbubble separator is also used, which may include an automatic vent.

[0010] The disadvantage of these solutions is that, despite the installed vent valves and drain valves, a dangerous amount, i.e., over 150 g of flammable refrigerant, can enter the secondary circuit – in other words, the heating circuit – unnoticed and thus ultimately into the rooms to be heated. Therefore, additional drain valves and open automatic vents can allow flammable refrigerant to escape directly into living spaces or utility rooms of the house, where an ignitable gas mixture can form. Document US 2014196483 A1 proposes that, if a leak detection device detects a leak due to a pressure increase, a control system on both sides of the intermediate heat exchanger closes valves arranged in the secondary circuit to prevent the refrigerant from passing beyond the valves into the secondary circuit. A pressure sensor arranged in the flow of the secondary circuit is provided as the leak detection device.

[0011] From US 2019346191 A1 it is known that an appropriately configured pressure regulating valve interrupts the flow of the fluid when the pressure of the fluid in the secondary circuit after the intermediate heat exchanger increases.

[0012] US 2020080757 A1 discloses another solution for a refrigerant leak in the heat transfer circuit. When a refrigerant leak detection device detects a refrigerant leak in the heat transfer circuit, a valve arrangement switches the primary circuit so that the evaporator functions as a condenser and the condenser as an evaporator.

[0013] Even these state-of-the-art solutions cannot satisfactorily resolve the problem. In particular, closing the valves in the secondary circuit prevents the degassing of the heat transfer fluid from continuing, resulting in a complete failure of the heating system.

[0014] The starting point of the invention is a heat pump system, wherein the heat pump system comprises a primary circuit for carrying a coolant and a secondary circuit for carrying a heating medium liquid.

[0015] As is typical for heat pump heating systems, the primary circuit comprises a heat source / refrigerant heat exchanger, a compressor, a refrigerant / heating medium heat exchanger, and at least one expansion device, preferably two expansion devices. The refrigerant / heating medium heat exchanger is integrated into the primary circuit via the primary side.

[0016] The secondary circuit comprises the secondary side of the refrigerant-heating medium heat exchanger, a gas separator with a vent valve and / or a safety relief valve, a circulation pump, and the heat consumer, such as radiators and heat exchangers in storage tanks. The invention is based on the problem that a leak in the refrigerant-heating medium heat exchanger can allow refrigerant to enter the secondary circuit, i.e., the heating circuit. Since the heating circuit is generally operated at a significantly lower pressure, the refrigerant evaporates during the transfer, thus forming gas bubbles. If the refrigerant is flammable, such as propane, this gas can escape, particularly at vent valves, and thus pose a fire or explosion hazard.

[0017] The aim underlying the present invention is therefore to reduce, in the event that flammable refrigerant enters the secondary circuit and can thus enter the heating system of a house, to a non-critical amount by separation from the liquid heating medium or, if the separation is not sufficient, to reduce the circulation of the heating medium and, if necessary, to prevent it.

[0018] According to the invention, it is therefore provided that the security system comprises a control module and at least one sensor coupled to the control module, wherein the at least one sensor is arranged in the secondary circuit and is designed to directly or indirectly detect gas in the secondary circuit and the control module is designed to control at least one circulation pump of the secondary circuit in such a way that if the amount of gas exceeds a predefined threshold value or if gas is detected by the control module on the basis of the data of the at least one sensor in the heating medium liquid of the secondary circuit, the power of the circulation pump is reduced - possibly down to zero.

[0019] The detection of the gaseous refrigerant is based on the recorded sensor data, which, based on a physical reference, suggest the presence of the gas in the heating medium fluid of the secondary circuit.

[0020] By reducing the power of the circulation pump and thus the flow rate in the secondary circuit, the amount of gas conveyed through the secondary circuit with the water flow can be reduced or even eliminated altogether. With a reduced pump power, the gas is separated in the gas separator and removed from the secondary circuit via the automatic vent valve or the safety drain valve just as efficiently as with a higher flow rate through the secondary circuit. Accordingly, effective degassing of the secondary circuit can be achieved in a beneficial manner.Accordingly, after detecting or determining a gaseous refrigerant in the area of ​​the sensor by exceeding a value related to a quantity of gas in the liquid of the secondary circuit, the further transport of gaseous refrigerant in the secondary circuit can be prevented, so that the part of the secondary circuit in which no refrigerant is (yet) present remains free of flammable refrigerant.

[0021] The safety system according to the invention for a heat pump system thus advantageously makes it possible to effectively prevent the refrigerant gas bubbles from being carried along in the heating system in the event of a leak in the refrigerant-heating medium heat exchanger and insufficient gas separation and discharge by means of a vent valve and / or a safety discharge valve.

[0022] The control module is advantageously integrated into the control unit of the heat pump system. The control module can also be designed to retrofit the heat pump system with the safety system according to the invention.

[0023] The heat source is not limited in the invention and can include air, brine, water, or other heat sources. Accordingly, the heat source-refrigerant heat exchanger is designed as a suitable heat exchanger, for example, as an air-refrigerant heat exchanger in the case of air as the heat source or as a brine-refrigerant heat exchanger in the case of brine as the heat source, without being limited thereto.

[0024] Features of advantageous embodiments of the invention are defined in particular in the subclaims, wherein further advantageous features, embodiments and configurations can also be gathered by the person skilled in the art from the above explanations and the following discussion.

[0025] Preferably, the at least one sensor of the security system according to the invention is a gas sensor, a pressure sensor, a temperature sensor and / or a volume flow sensor, in particular a vortex volume flow sensor.

[0026] Gas sensors can diagnose the presence of gas in the secondary circuit and provide immediate and therefore clear evidence of gaseous refrigerant. Pressure sensors can detect elevated pressure in the secondary circuit. However, gaseous refrigerant is removed from the secondary circuit through the vent valve, preferably located in the upper area of ​​the gas separator, or the quick vent. Therefore, pressure fluctuations, in particular, can indicate that gaseous refrigerant has entered the secondary circuit.

[0027] By arranging the sensors in or immediately after the gas separator, it can be advantageously determined whether refrigerant has entered the area of ​​the secondary circuit after the gas separator or whether there is a risk that refrigerant gas will enter the secondary circuit.

[0028] Temperature fluctuations detected by temperature sensors or volume flow fluctuations detected by volume flow sensors can also indicate the presence of gas in the secondary circuit.

[0029] The sensors mentioned can therefore be used to detect irregularities in the secondary circuit, which in particular suggest the presence of gas bubbles and thus the penetration of gaseous refrigerant into the secondary circuit.

[0030] A further solution to the inventive problem is provided by arranging the corresponding circulation pump in the flow line of the secondary circuit, preferably immediately after the heat exchanger, in a heat pump system comprising a primary circuit for conveying a refrigerant and a secondary circuit for conveying a heating medium. If gas were to enter the secondary circuit, refrigerant gas would enter the circulation pump, thus preventing circulation of the heating medium and thus advantageously preventing further transport of the refrigerant gas into the secondary circuit.

[0031] Preferably, the safety system for a heat pump system is designed in such a way that the features of the safety system explained above are combined. Accordingly, the sensory detection of the effects of refrigerant gas ingress and the suppression of secondary circuit circulation by the arrangement of the circulation pump in the event of refrigerant gas ingress complement each other advantageously to minimize the risk of explosion due to flammable refrigerant gas in the secondary circuit.

[0032] The invention further provides a heat pump system comprising a safety system as described above. Accordingly, the heat pump system has the advantages of the safety system according to the invention. According to a preferred embodiment of the invention, the heat pump system comprises a check valve arranged in the return line of the secondary circuit upstream of the evaporator. When the circulation pump is switched off, the check valve prevents refrigerant gas from entering the secondary circuit in the opposite direction to the circulation direction.

[0033] The heat pump system is preferably coupled with an auxiliary heater. The auxiliary heater, for example, an electric one, can be activated together with the circulation pump as needed if no gas has been detected or identified by at least one sensor and the control module in the secondary circuit. This ensures that the auxiliary heater is not damaged by the refrigerant gas. The auxiliary heater can preferably be activated after a buffer time of, for example, 30 minutes has elapsed to increase safety.

[0034] The invention further provides a method for operating a safety system described above for a heat pump system specified above. According to the invention, gas in the secondary circuit is detected by the at least one sensor in short time cycles, or if the sensor data detected by the at least one sensor in short time cycles suggest the presence of gas in the secondary circuit, the sensor data is forwarded to the control module and evaluated in the control module in such a way that any gas present in the secondary circuit is directly measured or indirectly detected.

[0035] The direct measurement is performed using a gas sensor. The indirect determination of the presence or absence of gas is made based on the sensor data acquired by pressure sensors, temperature sensors, or volume flow sensors. These data, due to deviations from data that would normally indicate normal operation, may indicate a malfunction due to the presence of gas in the secondary circuit.

[0036] In the event of gas being detected by a sensor or gas being detected in the heating medium fluid of the secondary circuit, the control module is designed to control the circulation pump in such a way that the performance of the circulation pump is reduced.

[0037] Accordingly, the method according to the invention reduces the entry of refrigerant gas into the secondary circuit by reducing the circulation pump output. Accordingly, the risk of explosions due to flammable refrigerant leakage in areas within buildings is significantly reduced. Preferably, if the measured gas quantity exceeds a predefined threshold or gas is detected by the at least one sensor and the control module, the output of the circulation pump is initially reduced to 50%. This drastic reduction enables the gas separator arranged in the supply line to completely separate the incoming gas. If gas is still present in the secondary circuit based on the sensor data, the output of the circulation pump is initially reduced to 25% and, if the need persists, to 10%.

[0038] Ultimately, the circulation pump's output is reduced to zero if the conditions remain the same. The gradual reduction in flow through the secondary circuit allows the refrigerant gas to be removed through the gas separator and the corresponding safety or vent valves. At the same time, the heat pump can advantageously continue to operate at reduced output in many cases.

[0039] The method is preferably characterized in that gas is detected in the secondary circuit when the measured data from the pressure sensor, the temperature sensor, and / or the volume flow sensor rises above a limit value stored in the control module, or when there is a brief fluctuation in the measured data from the pressure sensor, the temperature sensor, and / or the volume flow sensor that exceeds a fluctuation limit. If gas is detected in this way, the control module reduces the power of the circulation pump.

[0040] In addition to the direct detection of refrigerant gas in the secondary circuit by a gas sensor, an increase in the measured data from the pressure sensor, temperature sensor, and / or volume flow sensor, but especially fluctuations in these measured data, can indicate the presence of refrigerant gas in the secondary circuit. The control module detects the presence of gas accordingly.

[0041] As a result, the control module controls the circulation pump in the manner described above. By indirectly detecting refrigerant gas in the secondary circuit, existing sensors can also be advantageously used to activate the safety system according to the invention.

[0042] The present invention is further illustrated and explained below with reference to exemplary embodiments shown in the figures. Figure 1 shows a hydraulic circuit diagram illustrating the safety system according to the invention for a heat pump system.

[0043] In the accompanying drawing and the explanations to this drawing, corresponding or related elements are marked with corresponding reference symbols where appropriate.

[0044] Fig. 1 shows a hydraulic circuit diagram to illustrate a first embodiment of the heat pump system 100 according to the invention.

[0045] The heat pump system 100 comprises a primary circuit 110 and a secondary circuit 120, which is designed as a heating circuit 120.

[0046] The heat pump system 100 is designed in such a way that the primary circuit 110 comprises a heat source-refrigerant heat exchanger 111, for example in the form of an evaporator 111, a compressor 112, a refrigerant-heating medium heat exchanger 113, for example in the form of a condenser, and an expansion device 114, for example in the form of a two-stage throttle device on both sides of a refrigerant collector 117 which is then at an intermediate pressure.

[0047] The heat source-refrigerant heat exchanger 111 may be an air-refrigerant heat exchanger in the case of an air heat pump or a differently designed heat exchanger in the case of a differently designed heat source, for example when using water or brine as the heat source.

[0048] Furthermore, a refrigerant circuit reversing device 115, designed as a 4-way valve, is arranged in the primary circuit 110. Accordingly, the refrigerant flows through the refrigerant-heating medium heat exchanger 113 on the primary side, where it changes from the gaseous to the liquid state (condensation).

[0049] The heating circuit 120 comprises the secondary side of the refrigerant-heating medium heat exchanger 113, in which the heating medium is heated, a gas separator 121 and a circulation pump 124. A quick vent valve 122 and a safety drain valve 123 are arranged on the gas separator 121.

[0050] Gas can potentially accumulate in the gas separator 121, which is located downstream of the refrigerant-to-heating medium heat exchanger 113 in the flow direction. This gas can then escape via the automatic quick vent 122 located in the upper area. The safety relief valve 123 opens when the pressure in the heating circuit 120 equals or exceeds a pressure limit value of the safety relief valve 123 for opening. Since the safety relief valve 123 is also located in the upper area of ​​the gas separator 121, gas is also released first when it opens. Other designs of the gas separator 121 are also possible.

[0051] The invention is based on the problem that, if the refrigerant-heating medium heat exchanger 113 is leaking, liquid refrigerant can enter the heating circuit 120. Since the heating circuit 120 is generally operated at a significantly lower pressure, the refrigerant evaporates upon entering the heating circuit 120, thus forming gas bubbles. If the refrigerant is flammable, such as propane, this gas can escape, particularly in automatic venting systems, and thus pose a fire or explosion hazard.

[0052] The safety system according to the invention for a heat pump system 100 serves, in the event of a leak in the refrigerant-heating medium heat exchanger 113 and insufficient gas separation and discharge by means of quick vent 122 and safety discharge valve 123, to prevent the gas bubbles from being carried along in the heating system 120 as completely as possible.

[0053] According to the invention, the security system comprises a control module 130 and at least one sensor 131, 132, 133, 134 coupled to the control module 130, wherein the at least one sensor 131, 132, 133, 134 is arranged in the secondary circuit 120 and is designed to directly or indirectly detect gas in the heating circuit 120 and the control module 130 is designed to control at least one circulating pump 124 of the heating circuit 120 such that the power of the circulating pump 124 is reduced if the amount of gas exceeds a predefined threshold value or if the control module 130 detects gas in the heating medium liquid of the heating circuit 120 based on the data of the at least one sensor 131, 132, 133, 134.

[0054] A sensor 131 configured as a gas sensor can directly detect the amount of gas present in the heating fluid. As soon as this gas quantity exceeds a threshold value stored in the control module 130, the power of the circulation pump 124 is reduced—possibly to zero.

[0055] Sensors 132, 133, 134 can measure variables that, based on a physical reference, suggest that gas is present in heating circuit 120, particularly in the area of ​​the respective sensor 132, 133, 134. These variables are, in particular, the pressure, temperature, and volume flow in heating circuit 120. Accordingly, pressure sensors 132, temperature sensors 133, and / or volume flow sensors 134 can be provided as sensors 132, 133, 134.

[0056] Thus, based on data determined by sensors 132, 133, 134, control module 130 indirectly determines that gas is present in heating circuit 120.

[0057] Even if gas is detected in the heating circuit 120, the power of the circulation pump 124 is reduced - if necessary to zero.

[0058] According to the invention, it is provided that in the event of an existing or likely refrigerant transfer into the heating circuit 120 as determined by sensor data evaluation, the power of the circulation pump 124 of the heating circuit 120 is reduced, preferably in stages.

[0059] Due to the reduced power of the circulation pump 124, the flow in the gas separator 121 is reduced, so that more gas, in the best case all of the gas, can be separated in the gas separator 121.

[0060] By reducing the flow rate, for example, initially to half the flow rate, more refrigerant can be separated in the gas separator 121 due to the lower flow velocity, thus preventing refrigerant bubbles from entering the living area of ​​the heating circuit. This advantageously and effectively prevents the formation of an explosive or flammable mixture due to the refrigerant escaping through automatic vents in the living area.

[0061] According to the invention, the further entrainment of the refrigerant gas in the heating circuit 120 is thus effectively prevented and accordingly the risk of fire or explosion is advantageously considerably reduced.

[0062] At the same time, heating operation can be maintained.

[0063] If necessary, the power of the circulation pump 124 can or must be reduced to zero if gas continues to be detected or detected in the heating circuit 120.

[0064] Furthermore, an auxiliary heater 127, such as an electric heater, is provided in heating circuit 120. This heater can be activated as needed via control module 130 if, based on sensor data, there is no refrigerant gas in heating circuit 120. Activation of auxiliary heater 127 may be necessary if the heat pump heater fails or if the heating capacity of heat pump system 100 is insufficient due to a reduction in circulation pump capacity.

[0065] List of reference symbols

[0066] 100 heat pump system

[0067] 110 Primary circuit

[0068] 111 Refrigerant-to-air heat exchanger

[0069] 112 compressors

[0070] 113 Refrigerant-heating medium heat exchanger

[0071] 114 Expansion device, throttle device

[0072] 115 refrigeration circuit reversing device

[0073] 120 Secondary circuit, heating circuit

[0074] 121 gas separators

[0075] 122 vent valve, quick vent, automatic vent

[0076] 123 Safety drain valve

[0077] 124 Circulation pump

[0078] 125 heating consumers

[0079] 126 check valve

[0080] 127 Additional heating

[0081] 130 Control module

[0082] 131 sensor, gas sensor, gas detector

[0083] 132 Sensor, pressure sensor

[0084] 133 Sensor, temperature sensor

[0085] 134 Sensor, volume flow sensor, flow meter

[0086] 135 Control line

[0087] VL flow

[0088] RL return

[0089] P Circulation pump power no

[0090] + yes

Claims

Claims 1 . A safety system for a heat pump system (100), wherein the heat pump system (100) comprises a primary circuit (110) for carrying a refrigerant and a secondary circuit (120) for carrying a heating medium fluid, - wherein the primary circuit (110) comprises a heat source-refrigerant heat exchanger (111), a compressor (112), a refrigerant-heating medium heat exchanger (113) and at least one expansion device (114), preferably two expansion devices, and the refrigerant-heating medium heat exchanger (113) is integrated into the primary circuit (110) with a primary side, and the secondary circuit (120) comprises the refrigerant-heating medium heat exchanger (113) integrated with a secondary side, a gas separator (121) with a vent valve (122) and / or a safety drain valve (123) and a circulation pump (124), - wherein the security system comprises a control module (130) and at least one sensor (131, 132, 133, 134) coupled to the control module (130), - wherein the at least one sensor (131, 132, 133, 134) is arranged in the secondary circuit (120) and is designed to directly or indirectly detect gas in the secondary circuit (120), and the control module (130) is designed to control the at least one circulating pump (124) of the secondary circuit (120) such that the power of the circulating pump (124) is reduced if the amount of gas in the heating medium liquid of the secondary circuit (120) detected by the sensor (131) exceeds a predefined threshold value, or if the amount of gas in the heating medium liquid of the secondary circuit (120) is detected by the control module (130) on the basis of the data of the at least one sensor (132, 133, 134).

2. Safety system for a heat pump system (100) according to claim 1, wherein the at least one sensor (131, 132, 133, 134) is a gas sensor (131), a pressure sensor (132), a temperature sensor (133) and / or a volume flow sensor (134), in particular a vortex volume flow sensor.

3. Safety system for a heat pump system (100) according to one of the preceding claims, wherein the at least one sensor (131, 132, 133, 134) is arranged in or after the gas separator (121).

4. Safety system for a heat pump system (100), wherein the heat pump system (100) comprises a primary circuit (110) for conducting a coolant and a secondary circuit (120) for conducting a heating medium and a circulating pump (124) is arranged in the secondary circuit (120), wherein the circulating pump (124) of the secondary circuit (120) is arranged downstream of the coolant-heating medium heat exchanger (113) in a flow line (VL) of the secondary circuit (120) in the flow direction of the secondary circuit (120).

5. A security system for a heat pump system (100) according to any one of claims 1 to 3 and claim 4.

6. Heat pump system (100) with a security system according to one of claims 1 to 5.

7. Heat pump system (100) according to claim 6, wherein the heat pump system (100) further comprises a check valve (127) arranged in the return line (RL) of the secondary circuit (120) in the flow direction of the secondary circuit (10) upstream of the refrigerant-heating medium heat exchanger (113).

8. Heat pump system (100) according to claim 6 or 7, wherein the heat pump system (100) is coupled to an additional heater (127) and the additional heater (127) can be switched on if no gas is detected or determined in the secondary circuit (120) by the control module (130).

9. A method for operating a security system for a heat pump system (100) according to one of claims 1 to 7, - wherein gas in the secondary circuit (120) is detected by the at least one sensor (131) in short time cycles or the quantities / sensor data detected by the at least one sensor (131, 132, 133) in short time cycles suggest the presence of gas in the secondary circuit (120), - the sensor data are forwarded to the control module (130) and evaluated in the control module (130) in such a way that gas present in the secondary circuit (120) is directly measured or indirectly detected and, if gas is measured or gas is detected in the heating medium fluid of the secondary circuit (120), the control module controls the circulation pump (124) in such a way that the power of the circulation pump (124) is reduced.

10. The method according to claim 9, wherein - in the event of a measured gas quantity or detected gas exceeding a predefined threshold value by means of the at least one sensor (131, 132, 133, 134) and the control module (130), the power of the circulation pump (124) is initially reduced to 50% by means of control by the control module (130), - in the event of a further measured gas quantity (M) exceeding a predefined threshold value or gas detected by means of the at least one sensor (131, 132, 133, 134) and the control module (130), the power of the circulation pump (124) is reduced to 25% by means of control by the control module (130), - in the event of a further measured gas quantity exceeding a predefined threshold value or gas detected by means of the at least one sensor (131, 132, 133, 134) and the control module (130), the power of the circulation pump (124) is reduced to 10% by means of control by the control module (130), - in the event of a further measured gas quantity exceeding a predefined threshold value or detected gas by means of the at least one sensor (131, 132, 133, 134) and the control module (130), the power of the circulation pump (124) is reduced to zero by means of control by the control module (130) and - if the power of the circulation pump (124) has been reduced, in each case if no further measured gas quantity exceeds a predefined threshold value or if no gas is detected by means of the at least one sensor (131, 132, 133, 134), the power of the circulation pump (124) is gradually increased by means of control by the control module (130).

11. Method according to one of claims 9 or 10, wherein an increase in the measured data of the pressure sensor (131), the temperature sensor (132) and / or the volume flow sensor (133) above a limit value or a short-term fluctuation in the measured data of the pressure sensor (131), the temperature sensor (132) and / or the volume flow sensor (133) exceeding a fluctuation limit value determines the presence of gas in the secondary circuit (120) and thus the reduction in the power of the circulation pump (124) takes place via the control module (130).

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