Frost protection for a monoblock heat pump

Abstract

A frost protection system for a condenser heat exchanger (210) of a monoblock heat pump (200) of a central heating system is proposed, comprising the following components: an outside temperature sensor (285), an accumulator (270), means for detecting a power failure, a bypass line (260) running parallel to a section of the supply line (240) or the return line (245), and a pump (265) for pumping water used for heating through the bypass line (260), which is driven by the accumulator (270). If the power supply fails and the outside temperature is low enough to pose a risk of frost, the system ensures that warm water from the heating circuit flows through the condenser heat exchanger (210), thereby preventing frost damage to the condenser heat exchanger (210). The system is particularly suitable as a retrofit kit for existing central heating systems with monoblock heat pump (200).

Description

Field of the invention

[0001] The invention relates to a frost protection system for a monoblock heat pump connected to a central heating system, as well as a method for operating the same, a corresponding central heating system and a computer program. State of the art

[0002] Heat pumps for central heating systems are usually electrically powered. Electricity suppliers often reserve the right to interrupt the power supply to heat pumps for periods of up to several hours to ensure the stability of the power grid. Even in cases where this is not practiced, there is a risk of power outages. In the cold season, this can lead to the temperature in the condenser heat exchanger of a monoblock heat pump dropping so low that the water in the heating circuit freezes. Given the complex design of these heat exchangers in modern heat pumps, this can easily cause significant property damage. Task

[0003] The object of the invention is to provide frost protection systems and methods for operating the same which prevent frost damage to the condenser heat exchanger of a monoblock heat pump. Solution

[0004] This problem is solved by the subject matter of the independent claim. Advantageous developments of the subject matter of the independent claim are characterized in the subclaims. The wording of all claims is hereby incorporated by reference into this description.

[0005] The use of the singular shall not exclude the plural, and this shall also apply in the reverse sense unless otherwise disclosed.

[0006] To solve this problem, a frost protection system is proposed for a condenser heat exchanger of a monoblock heat pump connected to a central heating system. The central heating system has a heating circuit for water used for heating. The heat pump has a refrigerant circuit, with the condenser heat exchanger serving to transfer energy between the heat pump's refrigerant and the water used for heating from the heating circuit. The heating circuit is connected to the condenser heat exchanger via a supply line and a return line. The frost protection system has the following components: an outside temperature sensor, a storage tank for electrical energy, means for detecting a power failure, a bypass line connected in such a way that it runs parallel to a section of the supply line or the return line, and a pump for pumping water used for heating through the bypass line. The pump is powered by electrical energy from the storage tank.

[0007] The storage device for electrical energy is typically a rechargeable accumulator or a battery. This preferably provides a voltage of 12V, for example. The pump is an electrically operated circulating pump, designed just powerful enough to allow a small flow through the condenser heat exchanger to prevent the water there from freezing. If the power supply to the central heating system and heat pump fails and the outside temperature sensor registers a temperature low enough to pose a risk of frost, e.g., below 2°C or 4°C, the frost protection system ensures that (still warm) water from the return of the heating circuit continues to flow through the condenser heat exchanger. This prevents frost damage to the condenser heat exchanger.

[0008] Preferably, the heating circuit includes a buffer tank that stores sufficient hot water, especially for situations where the central heating or heat pump is interrupted during cold weather. In such a case, the bypass line and pump are preferably installed so that hot water from this buffer tank can be pumped through the condenser heat exchanger.

[0009] The described frost protection system is particularly suitable as a retrofit kit for existing central heating systems with monoblock heat pumps.

[0010] The electrical energy storage system can be charged using the regular power connection used to power the heating system. However, if available, alternative charging options can also be provided, particularly those that are independent of the power grid, such as a photovoltaic system and / or a generator installed on the building being heated.

[0011] By installing a backflow preventer in the section of the flow line or the return line to which the bypass line acts as a bypass line and is connected in parallel, the requirements on the performance of the circulation pump can be kept as low as possible.

[0012] The heating circuit of the central heating system preferably has a buffer storage tank. Other storage tanks, tanks, or similar may of course also be present, for example a storage tank with a heat exchanger for a hot water supply. These storage tanks can be arranged in different ways, e.g., parallel or in series with the radiators of the heating circuit, whereby different valves can be provided to enable operation of the central heating system with and / or without a buffer storage tank, for example, depending on the current heat demand of the building. In this case, the bypass line is preferably arranged on the return line of the heating circuit of the central heating system downstream of the buffer storage tank. This ensures that, in the event of a power failure and cold outside temperatures, as already described, the pump pumps, in particular, warm water from the buffer storage tank through the condenser heat exchanger.

[0013] The frost protection system can provide protection against frost damage even during extended power outages and / or shutdowns if it also includes a first shut-off valve in the supply line, a second shut-off valve in the return line, at least one actuator for actuating the two shut-off valves, means for determining the fill level of the electrical energy storage, and a controller. The controller is coupled to the outside temperature sensor, the means for detecting a power outage, the means for determining the fill level of the electrical energy storage, and the at least one actuator.

[0014] The controller can, for example, be a computing unit, control electronics, a digital signal processor (DSP), a microcontroller, a computer, or a plurality of these in a network with corresponding programming. The programming can be implemented, for example, within a fixed circuit arrangement of the computing unit, control electronics, the DSP, and / or the microcontroller or using field-programmable gate arrays (FPGAs).

[0015] This frost protection system can react if the water level in the electrical energy storage tank drops so low that continuous safe operation of the pump is no longer guaranteed. In this case, the shut-off valves would close, allowing the water-carrying part of the condenser heat exchanger to be drained to prevent frost damage without having to drain the entire central heating hot water circuit.

[0016] Draining the condenser heat exchanger is made easier if a drain valve is provided to drain the water used for heating from the condenser heat exchanger. This is preferably located at the lowest point. Alternatively, a design in which the drain valve is combined with one of the previously mentioned shut-off valves is also possible.

[0017] Draining the condenser heat exchanger is further facilitated by the presence of an aerator for venting a water line in the condenser heat exchanger. This is preferably located at the highest point of the heat exchanger.

[0018] The most complete emptying of the condenser heat exchanger can be achieved by using a gas cartridge to blow out the water used for heating from the condenser heat exchanger. This is filled with compressed air or, preferably, an inert gas such as nitrogen. Due to lower costs, CO 2 particularly preferred. If the condenser heat exchanger needs to be completely drained, the control system not only opens the drain valve, but also opens this gas cartridge, which empties it and blows out the condenser heat exchanger.

[0019] To solve the problem, a method for operating the antifreeze system described above is also proposed.

[0020] Individual method steps are described in more detail below. In a preferred variant of the invention, the steps are performed in the order specified. However, the steps do not necessarily have to be performed in the order specified, and the method to be described may also include additional, unmentioned steps.

[0021] The procedure includes the following step: If the outside temperature sensor detects an outside temperature below a first predefined threshold, and if the power failure detection system detects a power failure, the pump pumps water used for heating through the bypass line. The first predefined threshold is a temperature above which there is a significant risk that the water in the condenser heat exchanger could freeze without flow. This first predefined threshold can, for example, be in the range between 2 °C and 4 °C. The water used for heating is usually much warmer, so the operation of the pump prevents the condenser heat exchanger from freezing. This is especially true if the water is supplied from a buffer tank, as it then usually has a temperature that is only just below the flow temperature during regular heating operation.

[0022] In case of prolonged power outages or interruptions, it is advantageous if the procedure for operating the frost protection system described above includes the following steps: If the outside temperature sensor detects an outside temperature below a first predetermined threshold, and if the means for detecting a power failure detects a power failure, and if the means for determining the fill level of the electrical energy storage device detects a fill level below a second predetermined threshold, the controller controls the at least one servomotor such that the at least one servomotor blocks the supply line by means of the first shut-off valve in the supply line and the return line by means of the second shut-off valve in the return line. In this case, the controller also allows the water used for heating to drain from the condenser heat exchanger. As the second predetermined threshold, a fill level of the electrical energy storage device must be selected that still briefly allows the servomotor to be actuated to shut off the shut-off valves.This process ensures that, in the event of a prolonged power outage during cold weather, the condenser heat exchanger of the monoblock heat pump is protected from frost damage. If the level of the electrical energy storage tank drops to such an extent that continued operation of the pump can no longer be guaranteed, the shut-off valves are closed and the water-carrying part of the condenser heat exchanger is drained.

[0023] Without this measure, the pump could stop working when the condenser heat exchanger is filled with water, which could then suffer frost damage.

[0024] Alternatively or additionally, the method for operating the frost protection system already described, if at least a second temperature sensor is provided on the return line and / or on the buffer tank, may comprise the following steps: If the outside temperature sensor detects an outside temperature below a first predetermined threshold, and if the means for detecting a power failure detects a power failure, and if the second temperature sensor detects a temperature below a third predetermined threshold, the controller controls the at least one actuator such that the at least one actuator blocks the supply line by means of the first shut-off valve in the supply line and the return line by means of the second shut-off valve in the return line. In addition, the controller allows the water used for heating to drain from the condenser heat exchanger. The third predetermined threshold should be a temperature just above the first predetermined threshold, e.g. 6 °C.If, as a result of a prolonged power outage, the temperature of the water used for heating drops so low that freezing of the condenser heat exchanger can no longer be ruled out despite continued flow, the shut-off valves are closed and the water-carrying part of the condenser heat exchanger is emptied.

[0025] The task is further solved by a central heating system with a monoblock heat pump, which has a frost protection system as already described.

[0026] The object is also achieved by a computer program comprising instructions which cause the control of the frost protection system described above to carry out the method steps described above.

[0027] A computer-readable medium on which the computer program just described is stored also solves the problem.

[0028] Further details and features will become apparent from the following description of a preferred embodiment in conjunction with the figures. The respective features can be implemented individually or in combination with one another. The possibilities for solving the problem are not limited to the embodiment. For example, range specifications always include all intermediate values ​​(not mentioned) and all conceivable subintervals.

[0029] An exemplary embodiment is shown schematically in the figures. Identical reference numerals in the individual figures denote identical or functionally identical elements, or elements that correspond to one another in terms of their functions. In detail: Fig. 1 a schematic representation of an air / water compression heat pump (state of the art); and Fig. 2 a schematic representation of part of a central heating system with an air / water compression heat pump in monoblock design with a frost protection system for the condenser heat exchanger.

[0030] Based on Fig. 1 will first explain the general functioning of a known heating system with a heat pump 100. The direction in which the refrigerant (e.g., propane, R-290) circulates in the refrigerant circuit is indicated by an arrow 102. The gaseous refrigerant is compressed by the compressor 105, which causes a temperature increase. In modern heat pumps, the refrigerant can, for example, reach a temperature of over 70 °C in this way. The compressor 105 is usually electrically driven. The warm, gaseous refrigerant flows, driven by the compressor 105, into the condenser heat exchanger 110. There, the refrigerant transfers heat to the hot water circuit 115 of the heating system. The flow direction of the heating circuit is indicated by arrows 116 and 117. The compressed gas cools slightly and then condenses at a constant temperature.The water in the heating system's hot water circuit absorbs the heat released during condensation and can thus be heated to up to 70°C (flow temperature). The now liquid refrigerant flows on to the expansion valve 120, where it expands and cools significantly, typically to a temperature of around -30°C. The cold refrigerant flows on to the evaporator heat exchanger 125. There, heat from, for example, the ambient air is transferred to the refrigerant. A fan is usually present for this purpose. The refrigerant evaporates here at a constant temperature. Afterward, the refrigerant typically has a temperature of between 0 and 10°C. It then flows on to the compressor 105.

[0031] In Fig. Figure 2 shows a heating system with a monoblock heat pump 200 equipped with an antifreeze system for the condenser heat exchanger 210.

[0032] In the monoblock heat pump 200, all components of the heat pump, i.e. the compressor 205, the condenser heat exchanger 210, the expansion valve 220, and the evaporator heat exchanger 225 with fan, are housed in a machine housing located outside the building to be heated. An exterior wall 230 of the building is Fig. 2 indicated.

[0033] The supply line 240 and the return line 245 of the central heating system are connected to the condenser heat exchanger 210. A main pump 250 drives the heating circuit. This main pump is in Fig. 2 is attached to the flow line 240, but can of course also be provided elsewhere, e.g., on the return line 245. The flow direction of the heating circuit is indicated by arrows 216 and 217.

[0034] A buffer tank 255 is arranged between the flow line 240 and the return line 245. In Fig. 2, the buffer tank 255 is arranged parallel to the heating elements of the building (not shown), but in other designs it can also be connected in series or even not be present at all. Preferably, valves, e.g., directional control valves, are arranged at the connections of the buffer tank 255, which can be switched depending on the operating requirements of the heating system. For reasons of simplification, these are shown in Fig. 2 not shown. Depending on whether, for example, the central heating system is also intended to provide hot water for the building, additional tanks, storage tanks, or similar may be provided.

[0035] Downstream of the buffer tank 255 on the return line 245, a bypass or bypass line 260 is arranged. A pump 265, preferably an electric circulating pump, is arranged on this bypass line 260. It is supplied with electrical energy not from the normal power supply, but from an electrical energy storage device, preferably an accumulator 270. Typically, the accumulator 270 provides a voltage of 12 V. The circulating pump 265 is preferably designed to be just powerful enough to ensure a minimum flow through the condenser heat exchanger 210, which is just sufficient to prevent it from freezing. Parallel to the bypass line 260, a backflow preventer 275 is located in the return line to ensure the desired flow direction.

[0036] The circulation pump 265 is preferably connected to a controller 280. This controller is in turn connected to an outside temperature sensor 285, as well as, if necessary, to means for detecting a power failure and / or means for determining the filling level of the accumulator 270 (both not shown). These connections can be realized, for example, by cables which are Fig.2 are shown as dotted lines. Alternatively, wireless connections, e.g. via infrared or radio signals, are also conceivable. In the embodiment shown, the control system 280 is arranged in a box which can be mounted on the building wall 230, in particular if the described frost protection system has been retrofitted. In other embodiments, the control system can, for example, be integrated into the existing heating control system. Thus, if there is a power failure and the outside temperature is so low that freezing of the condenser heat exchanger 210 cannot be ruled out, the control system can activate the circulation pump 265, which ensures that warm water, e.g. from the buffer tank 255, flows through the condenser heat exchanger 210 and thus prevents freezing.

[0037] If present, the means for determining the fill level of the accumulator 270 allow for additional precautionary measures to be taken if the power outage lasts longer in cold weather. For this purpose, a first shut-off valve 290 is provided on the supply line 240, and a second shut-off valve 295 is provided on the return line 245. These shut-off valves are preferably located as close as possible to the condenser heat exchanger 210 of the heat pump. They are actuated by at least one actuator (not shown). If the filling level of the accumulator 270 drops to such an extent that continuous operation of the circulation pump 265 can no longer be reliably guaranteed, the controller 280 activates at least one servomotor and blocks the flow line 240 and the return line 245 by means of the shut-off valves 290, 295, whereby the condenser heat exchanger 210 is separated from the heating circuit of the central heating system.The water-carrying part of the condenser heat exchanger 210 is then drained via a drain valve 299, preventing frost damage. For this purpose, a gas cartridge (not shown) containing, for example, CO can also be connected to the condenser heat exchanger 210. 2 (preferred) or nitrogen or (less preferred) compressed air. It is opened when the condenser heat exchanger 210 is to be emptied. The gas under pressure in the gas cartridge then blows out the condenser heat exchanger 210, ensuring complete emptying. GlossaryBypass, bypass line

[0038] The term bypass or bypass line refers to a bypass line in a technical system, e.g. to bypass check valves, to relieve the load on large ball valves to reduce the actuating force required to open them, to increase the return temperature in heating systems or to reduce the line pressure when using unregulated pumps or fans (according to https: / / de.wikipedia.org / wiki / Bypass). Heating circuit

[0039] The heating circuit is the hot water circuit of a central heating system. refrigerant

[0040] According to DIN EN 378-1:2021-06, paragraph 3.7.1, a refrigerant is defined as "a fluid used for heat transfer in a refrigeration system, which absorbs heat at low temperature and low pressure and releases heat at higher temperature and higher pressure, usually resulting in changes of state of the fluid." According to DIN 8960:1998-11, paragraph 3.1, a refrigerant is defined as "a working medium which, in a refrigeration process, absorbs heat at low temperature and low pressure and releases heat at higher temperature and higher pressure." The definitions according to DIN refer to compression refrigeration machines. A change of state within the meaning of the standard refers to a change in the physical state. (According to https: / / de.wikipedia.org / wiki / K%C3%A4Itemittel.) Air-water heat pump

[0041] Air-to-water heat pumps extract heat from exhaust air or outside air, less commonly with preheating through geothermal heat exchangers, facade collectors, or similar. Heat is released via water-based heating systems. Monoblock heat pump, monoblock design for heat pumps

[0042] A monoblock heat pump is a compact design in which all refrigerant-loaded components (evaporator heat exchanger, compressor, condenser heat exchanger, expansion valve) and the air blower are housed in a single machine housing, usually installed outdoors. Since the refrigerant circuit is created and filled at the factory, only a connection to the heating system's water pipes is required. Backflow preventer

[0043] Backflow preventers allow flow through pipes, valves, and pumps in only one direction. They close automatically when the flow direction is reversed and reopen automatically when the flow direction is permitted. There are a variety of valve types that prevent backflow, including check valves, non-return valves, and ball valves. (According to https: / / de.wikipedia.org / wiki / R%C3%BCckflussverhinderer)Return

[0044] See lead time. Circulation pump

[0045] In a hot water heating system, a circulation pump transports the heated heat transfer medium (i.e., water) to the radiators or house connection stations in a closed circuit and simultaneously recirculates the cooled water from the return line for reheating in the boiler, heat pump, or buffer tank. Radial centrifugal pumps are typically used. (According to https: / / de.wikipedia.org / wiki / Umw%C3%A4lzpumpe_(Heiztechnik))Feed

[0046] In a hot water heating system, the pipes from the heat source (e.g., a boiler) to the radiators or heat consumers are referred to as the supply line; the pipes from the radiators back to the heat source are referred to as the return line. The temperature difference between the supply and return lines is referred to as the spread. heat pump

[0047] A heat pump is a combined heat and power machine that, through the application of technical energy, absorbs thermal energy from a reservoir at a lower temperature (usually the environment) and transfers it—along with the drive energy—as useful heat at a higher temperature to a system to be heated. Heat pumps can therefore be used for heating purposes, e.g., for heating buildings.

[0048] In this case, only air / water compression heat pumps are of interest.

[0049] Compression heat pumps utilize the physical effect of evaporation enthalpy. Driven by a compressor, a refrigerant circulates in a circuit, alternating between liquid and gaseous states.

[0050] The cycle that takes place in such a heat pump can be formed from the following steps: Compression: The gaseous refrigerant is compressed in the (usually electrically driven) compressor, heating the gas. The compressor's discharge pressure is regulated so that the corresponding saturated steam temperature is several degrees above the heat sink temperature. In heating systems, this is the flow temperature. Condensation: The hot, compressed gas transfers its heat to the water in the heating system in the condenser heat exchanger. The compressed and superheated gas initially cools slightly (gas superheating) until it reaches a temperature corresponding to the saturated vapor pressure. The refrigerant then condenses (liquefies) at a constant temperature. Expansion: As it passes through the expansion valve, a throttle, the liquid refrigerant expands. It largely evaporates, cools, and is then fed to the evaporator. Evaporation: The evaporator is the second heat exchanger, where heat from the ambient air (or, for example, the ground) is transferred to the refrigerant at a low temperature. The refrigerant evaporates at a constant temperature. The pressure in the evaporator is regulated by the expansion valve so that the temperature of the gas in the evaporator remains below the ambient temperature. The temperature of the heat source must always be higher than the evaporation temperature of the refrigerant. (According to https: / / de.wikipedia.org / wiki / W%C3%A4rmepumpe)Heat exchanger

[0051] A heat exchanger is a device that transfers thermal energy from one material stream to another.

[0052] For good efficiency, the component separating the media must have good thermal conductivity and a large surface area. Turbulent flow is beneficial for good heat transfer. This occurs primarily at high Reynolds numbers. Therefore, the flow velocity should be as high as possible and the viscosity of the media low. However, high velocity and a large wetted surface also require a high energy input to pump the media through the heat exchanger.

[0053] In heat exchangers where one medium is a liquid and the other is a gas, the heat capacities per volume of the media differ greatly. Much more gas must flow through than liquid, and the heat transfer area on the gas side must be increased. This is often achieved by fins or plates, for example, in high-temperature radiators, the cooling coils at the back of a refrigerator or air conditioner, or the radiator of a car. central heating system

[0054] A central heating system (collective heating) has a central heating point and supplies one or more rooms or buildings with water (liquid or vapor) as a carrier medium. In this case, this always refers to a hot water heating system. Reference symbol 100 heat pump 102 Flow direction of the refrigerant 105 compressors 110 Condenser heat exchanger 115 Heating water circuit 116 Flow direction of the heating circuit in the flow 117 Flow direction of the heating circuit in the return 120 expansion valve 125 evaporator heat exchanger with fan 200 monoblock heat pump 205 compressors 210 Condenser heat exchanger 216 Flow direction of the heating circuit in the flow 217 Flow direction of the heating circuit in the return 220 expansion valve 225 Evaporator heat exchanger with fan 230 building exterior wall 240 flow line 245 Return line 250 main pump 255 buffer storage 260 Bypass line 265 (Circulation) pump 270 storage for electrical energy, accumulator 275 backflow preventers 280 Control 285 Outside temperature sensor 290 first shut-off valve 295 second shut-off valve 299 drain valve cited literature

[0055] cited non-patent literature DIN EN 378-1:2021-06 DIN 8960:1998-11 QUOTES CONTAINED IN THE DESCRIPTION

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

[0000] https: / / de.wikipedia.org / wiki / Bypass

[0038] DIN EN 378-1:2021-06 [0040, 0055] DIN 8960:1998-11 [0040, 0055]

Claims

[1] Antifreeze system for a condenser heat exchanger (210) of a monoblock heat pump (200) connected to a central heating system; 1.1.1 the central heating system comprises a heating circuit for water used for heating; 1.1.2 wherein the heat pump (200) has a refrigerant circuit; 1.1.3 wherein the condenser heat exchanger (210) serves to transfer energy between the refrigerant of the heat pump and the water from the heating circuit used for heating; 1.1.4 wherein the heating circuit is connected to the condenser heat exchanger (210) via a flow line (240) and a return line (245); wherein the frost protection system comprises the following components: 1.2 an outside temperature sensor (285); 1.3 a storage device for electrical energy (270); 1.4 Means of detecting a power failure; 1.5 a bypass line (260) connected in such a way that it runs parallel to a section of the supply line (240) or the return line (245); and 1.6 a pump (265) for pumping water used for heating through the bypass line (260); 1.6.1 wherein the pump (265) is operated with electrical energy from the storage device (270). [2] Antifreeze system according to the preceding claim, characterized by that a backflow preventer (275) is arranged in the section of the flow line (240) or the return line (245) to which the bypass line (260) is connected in parallel. [3] Frost protection system according to one of the preceding claims, wherein the heating circuit of the central heating system comprises a buffer storage (255), characterized by that the bypass line (260) is arranged on the return line (245) of the heating circuit of the central heating system downstream of the buffer storage tank (255). [4] Antifreeze system according to one of the preceding claims, characterized by 4.1 a first shut-off valve (290) in the supply line; 4.2 a second shut-off valve (295) in the return line; 4.3 at least one servomotor for operating the two shut-off valves (290, 295); 4.4 means for determining a filling state of the storage (270) for electrical energy; and 4.5 a controller (280); 4.5.1 wherein the controller (280) is coupled to the outside temperature sensor (285), the means for detecting a power failure, the means for determining a filling state of the storage (270) for electrical energy and the at least one servo motor. [5] Antifreeze system according to the immediately preceding claim, characterized by a drain valve (299) for draining the water used for heating from the condenser heat exchanger (210). [6] Antifreeze system according to one of the two immediately preceding claims, characterized by an aerator for ventilating a water-carrying line of the condenser heat exchanger (210). [7] Antifreeze system according to one of the three immediately preceding claims, characterized by a gas cartridge for blowing out the water used for heating from the condenser heat exchanger (210). [8] A method for operating the antifreeze system according to any one of the preceding claims, comprising the following step: 8.1.1 if the outside temperature sensor (285) detects an outside temperature below a first predetermined threshold, and 8.1.2 if the means for detecting a power failure detect a power failure, 8.2 then the pump (265) pumps water used for heating through the bypass line (260). [9] A method for operating the antifreeze system according to any one of claims 4 to 7, comprising the following steps: 9.1.1 if the outside temperature sensor (285) detects an outside temperature below a first predetermined threshold, and 9.1.2 if the means for detecting a power failure detect a power failure, and 9.1.3 if the means for determining the filling level of the storage device (270) for electrical energy detect a filling level below a second predetermined threshold, 9.2 then, the controller (280) controls the at least one servomotor in such a way that the at least one servomotor blocks the supply line (240) by means of the first shut-off valve (290) in the supply line (240) and the return line (245) by means of the second shut-off valve (295) in the return line (245); and 9.3 the control (280) additionally allows the water used for heating to flow out of the condenser heat exchanger (210). [10] Method for operating the antifreeze system according to one of claims 4 to 7, 10.1, wherein at least one second temperature sensor is provided on the return line (245) and / or on the buffer tank (255), comprising the following steps: 10.2.1 if the outside temperature sensor (285) detects an outside temperature below a first predetermined threshold, and 10.2.2 if the means for detecting a power failure detect a power failure, and 10.2.3 if the second temperature sensor detects a temperature below a third predetermined threshold, 10.3 then the controller (280) controls the at least one servomotor in such a way that the at least one servomotor blocks the supply line (240) by means of the first shut-off valve (290) in the supply line (240) and the return line (245) by means of the second shut-off valve (295) in the return line (245); and 10.4 the control (280) additionally allows the water used for heating to flow out of the condenser heat exchanger (210). [11] Central heating system with a monoblock heat pump (200), characterized by an antifreeze system according to any one of the preceding antifreeze system claims 1 to 7. [12] Computer program comprising instructions which cause the control of the antifreeze system according to one of the preceding antifreeze system claims 4 to 7 to carry out the method steps according to one of the preceding method claims 8 to 10. [13] A computer-readable medium on which the computer program according to the immediately preceding claim is stored.

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