Refrigerant separation in heating circuit

Abstract

Installation of a heat pump in a building, the installation comprising: a heat pump operated with a flammable refrigerant (11), wherein the heat pump is located in a casing (9) and the casing is located in a building, in the casing (9) of the heat pump an internal heat exchanger (1) which is connected to the flammable refrigerant (11) on one side and to the heating circuit water (10) on the other side, in the casing (9) of the heat pump a refrigerant / air separator (2) which is arranged downstream in the heating circuit behind the internal heat exchanger (1), in the casing (9) of the heat pump a safety valve (4) which is arranged downstream in the heating circuit behind the refrigerant / air separator (2), a heating circuit pump (5) which is arranged downstream in the heating circuit behind the safety valve (4), at least one heating consumer (8) with a hot water supply and a hot water return,A further safety valve (6) is located between the hot water inlet and the heating circuit pump (5), and a water expansion tank (7) is located between the hot water return and the internal heat exchanger (1), wherein the safety valve (4) in the heat pump housing (9) has a lower opening pressure than the safety valve (6) between the heating circuit pump (5) and the heat consumer (8), and the difference in opening pressure is set to be greater than the pressure difference due to the geodetic height of the water column between the two safety valves (4, 6).

Description

[0001] The invention relates to the separation of refrigerant that has leaked from a heat pump's refrigeration circuit into a heating circuit. Such leaks are extremely rare, but can have serious consequences if the refrigerant is flammable. Since it became known that the existing safety refrigerants are extremely harmful to the climate when released into the environment, flammable refrigerants are frequently used as replacements.

[0002] These refrigerants have very good thermodynamic properties and allow for highly efficient operation. Examples include R290, R600a, R1270, R32, and R441a. However, they must be operated at a higher pressure than previous refrigerants, which can lead to a situation where, in the event of a leak in the condenser heat exchanger, which transfers heat from the refrigerant to the heating circuit, refrigerant can enter the heating circuit, which typically operates at a lower pressure and consists primarily of water.

[0003] This can go unnoticed for a long time if the leak is small. In such a case, the loss of refrigerant in the refrigerant circuit is hardly noticeable, and a pressure increase in the heating circuit is also barely observable. Such a leak becomes noticeable at the air separator of the heating circuit, which in such cases often has a separating device for air and gaseous refrigerant and is designed as a vent valve. A number of suitable designs exist in the prior art, which a specialist can access.

[0004] If refrigerant enters the heating circuit due to a leak, but cannot be completely released at the vent valve of the refrigerant / air separator, the refrigerant accumulates in the heating circuit. This resulting refrigerant buildup then displaces the heating water.

[0005] If the heat pump is installed at the top of the building to be heated, i.e., above the heating circuit installations, the refrigerant / air separator and the safety valve in the heat pump form the highest point of the building's heating circuit installation. The geodetic pressure difference between the safety valve in the heat pump and other safety valves in the building's heating circuit installation is reduced by the accumulation of refrigerant.

[0006] To prevent refrigerant from being transported into the heating circuit hydraulics along with the heating water, the circulation of the heating water must be stopped in such a case. According to the invention, this is achieved by arranging the heating pump directly downstream of the refrigerant / air separator and the safety valve in the direction of flow. If the refrigerant accumulation reaches the pump and fills the pump housing with gas, it is no longer possible to pump heating water, since heating pumps are centrifugal pumps and cannot pump gas.

[0007] The gaseous refrigerant continues to expand, displacing the heating water between the heat pump's safety valves and the building's heating circuit. The opening pressure of the safety valve in the heat pump is lower than the opening pressure of the other safety valves in the building's heating circuit. If there are multiple heat generators in the building's heating circuit, additional safety valves are required. This eliminates the geodetic pressure difference between the safety valves in the building's heating circuit and those in the heat pump. The displaced water is forced into an expansion vessel, which is always present in a heating system.

[0008] This leads to a pressure increase throughout the building's heating circuit until the lower opening pressure of the safety valve in the heat pump is reached, at which point the safety valve opens. The refrigerant then escapes from the heating system at a defined point within the heat pump and can be safely discharged or collected as described. It is quite possible that another safety valve in the building's heating circuit will open first, releasing heating water and further reducing the geodetic pressure difference. If other safety valves in the building's heating circuit open, only heating water, not refrigerant, can escape from them.

[0009] Therefore, if multiple safety valves are present in the building's heating circuit, it must be ensured that the safety valve located in the heat pump housing and equipped with a gaseous refrigerant separator opens. This is achieved as described above. Relevant state-of-the-art technology exists for this purpose, but it does not take into account the influence of geodetic height.

[0010] EP 3 351 868 B1 describes a heat pump device with a refrigeration circuit and a fluid circuit configured as a heating circuit, including the usual components and safety valves. Care is taken to ensure that, in the event of a refrigerant leak, the refrigerant can only escape within the refrigeration circuit casing. For this purpose, a pressure regulating valve is provided in the heating circuit between the condenser and the radiator, which stops the flow in the event of a pressure increase. Furthermore, a safety valve can be provided between the condenser outlet and the pressure regulating valve, and a vent valve can be provided between the pressure regulating valve and the radiator. The geodetic height is irrelevant.

[0011] German patent DE 10 2020 103 743 A1 describes a heat pump system in which, viewed in the direction of flow of the heating circuit medium, a non-return valve is installed downstream of the heating circuit pump and a safety valve is installed downstream of the heat exchanger in the primary circuit. This prevents backflow into the secondary circuit in the event of a leak and allows for venting in the direction of flow if the pressure increases. DE 10 2020 103 743 A1 does not specify the static head, additional safety valves, or the corresponding positioning of all these measures.

[0012] DE 10 2019 123 513 A1 describes a heat pump system with a refrigeration circuit and a fluid circuit configured as a heating circuit, including the usual components and safety valves. On the suction side of the heating circuit, a safety valve and air vents are provided for the circulation pump. On the discharge side, following the circulation pump, a first flow control device is installed in the supply line of the heating system, and another in the return line. Specifically, these flow control devices are a pressure reducer and a check valve. The geodetic height is irrelevant in this context.

[0013] EP 3 822 545 A1 describes a heat pump in which a refrigerant flows through the primary side of a heat exchanger and a heating circuit medium flows through the secondary side. The pressure of the heating circuit medium is measured, and valves are provided in both the return and supply lines of the heating circuit to interrupt the circuit. Such an interruption occurs when the pressure in the heating circuit exceeds a predetermined value.

[0014] DE 10 2020 103 743 A1 describes a heat pump system with a heat pump circuit and a heating circuit, in which a heating circuit pump is arranged on the return side and, downstream but before entering the condenser heat exchanger, a check valve is arranged, and where the check valve prevents backflow to the pump. On the heating circuit supply side, a degassing device is provided directly after the heat exchanger in the heating circuit to separate gaseous refrigerant that has entered the heating circuit in the event of a leak.

[0015] WO 2018 / 154628 A1 describes a split air conditioning system with an indoor unit and an outdoor unit. The outdoor unit contains the complete refrigerant circuit and is connected to a heat transfer circuit that is linked to the indoor unit. The return line of the heat transfer fluid from the indoor unit has a circulation pump located outdoors, and a gas separator is installed in the heat transfer fluid supply line to the indoor unit. If gaseous refrigerant from the refrigerant circuit enters the heat transfer circuit due to a leak, it is separated there and vented outdoors.

[0016] US patents 10,663,179 B2 and 10,393,413 B2 describe heat pumps with a refrigeration cycle that uses a flammable refrigerant. Any refrigerant that may leak is vented into the installation room by a fan.

[0017] The invention solves the problem by installing a heat pump in a building, wherein the installation includes A heat pump operated with a flammable refrigerant, wherein the heat pump is housed in an enclosure and the enclosure is located in a building, the enclosure of the heat pump contains an internal heat exchanger connected to the flammable refrigerant on one side and to the heating circuit water on the other side, the enclosure of the heat pump contains a refrigerant / air separator located downstream of the internal heat exchanger in the heating circuit, the enclosure of the heat pump contains a safety valve located downstream of the refrigerant / air separator in the heating circuit, a heating circuit pump located downstream of the safety valve in the heating circuit, at least one heating consumer with a hot water supply and a hot water return, a further safety valve between the hot water supply and the heating circuit pump, and a water expansion tank between the hot water return and the internal heat exchanger.where the safety valve in the heat pump housing has a lower opening pressure than the safety valve between the heating circuit pump and the heat consumer, and the difference in opening pressure is greater than the pressure difference due to the geodetic height of the water column between the two safety valves.

[0018] This installation is particularly suitable for outdoor air-to-water heat pumps, which are often installed on the roof of a building or an extension, such as a garage. The heating circuit pump should be located directly after the safety valve and the refrigerant / air separator, ideally also within the heat pump housing. It goes without saying that in systems with multiple building heating circuits, each heating circuit has its own heating circuit pump, with the above description applying analogously.

[0019] If several safety valves are used in the heating circuit, the above-described relationship between the opening pressures applies in pairs to the opening pressure of the safety valve in the heat pump housing and the respective safety valve in the heating circuit.

[0020] This is preferably used when the heat pump is located at the top of the building or on top of the building, for example in an attic or a

[0021] Flat roofs as part of a retrofit measure, and thus above the consumers, such as underfloor heating systems on floors below. However, the invention is not limited to this application. It is also applicable if the heat pump has a summer switchover to chilled water, which is circulated through the underfloor heating pipes instead of hot water or is used in chilled ceilings.

[0022] The invention is described by means of Fig. 1and explained in more detail in Table 1. It shows: Fig. 1 a schematic representation of a heat pump installation, Fig. 2 A schematic representation of a heat pump installation with a second heat generator, Table 1 a comparison of the resulting pressures.

[0023] Fig. 1Figure 1 shows a schematic representation of an exemplary heat pump installation with an internal heat exchanger 1, through which flammable refrigerant 11 flows on one side and heating water 10 on the other. Only the simplified heating circuit is considered here; this circuit can also be operated as a cooling water circuit if the heat pump has a corresponding switch for summer operation. In this configuration, the heating circuit water 10, coming from the internal heat exchanger 1, is first directed into the refrigerant / air separator 2, where air is separated along with gaseous refrigerant and discharged via the vent valve 3 if a leak has occurred in the refrigerant / air separator. This separation may be incomplete in the event of a leak.

[0024] The heating circuit water then flows past the safety valve 4 in the heat pump. The further treatment of the vented gases and any substances that may have accumulated in the safety valve 4 is not shown; this treatment varies depending on the installation, environment, and design of the heat pump and is not discussed here. Both the vent valve and the safety valve are located in the housing 9 of the heat pump. The downstream heating circuit pump 5 can also be located inside the housing 9 of the heat pump, as shown here, but it can also be positioned elsewhere, upstream of the heat users. It is advantageous if, in the event of a leak, the gaseous refrigerant fills the pump housing as quickly as possible, thus preventing the pumping of heating water.

[0025] Between the heating circuit pump 5 and the heat exchanger of the heating consumer 8 of the heating circuit is the safety valve 6, which protects the downstream heat exchangers, usually underfloor heating systems, from pressure overload. Before the heating circuit water is returned to the internal heat exchanger 1, the volume equalization due to the thermal expansion of the heating circuit water takes place in the expansion tank 7.

[0026] Fig. 1 It also shows the position of the pressure stages p1 to p6, which are to be expected in this simplified but typical heating circuit.

[0027] Fig. 2 Figure 1 shows a schematic representation of an exemplary heat pump installation with a second heat generator, in this example an electric auxiliary heater 12. This is arranged between the safety valve 4 of the heat pump and the safety valve 6 of the building heating circuit at the lowest point between the two safety valves.

[0028] Table 1 shows the pressure curves in the water of the heating circuit for the [unclear text]. Fig. 1 The illustrated embodiment is shown in column 1 under normal circumstances and in column 2 in advanced leakage cases. Table 1 Pressure bar ü normal bar ü leck p1 1,3 2,5 p2 1,3 2,5 p3 1,9 2,5 p4 2,4 2,5 p5 1,9 2,5 p6 1,4 2,5

[0029] In this case, the leak pressurizes the entire heating circuit. This pressure depends on the conditions in the internal heat exchanger and the temperature of the flammable refrigerant; it could also increase. The gaseous refrigerant causes heating circuit water to be forced into the expansion vessel 7 until a first safety valve opens. Pumping by the heating circuit pump 5 ceases as soon as the gaseous refrigerant reaches the pump. Before it can then reach the heating consumers 8 of the heating circuit, safety valve 4 must open. However, safety valve 6 must not open until geodetic pressure equalization has occurred. This is achieved by requiring safety valve 4 to open at a lower pressure than safety valve 6.

[0030] The difference in the geodetic height of the two safety valves must be taken into account. Under normal operating conditions, in addition to the dynamic pressure difference due to flow pressure losses and the compensation provided by the heating circuit pump, the respective static pressure of the water column also acts as pressure at the safety valve. In this case, that is the pressure difference between pressures p5 and p6 and p1 and p5, here 0.5 to 0.6 bar, which corresponds approximately to two floors. If both safety valves were set to the same pressure, the lower valve would always open first.

[0031] Since this is undesirable here, the pressure difference due to the geodetic height must be taken into account when selecting the safety valves and their opening pressure. Therefore, the two safety valves must also differ in normal operation. In this example, safety valve 4 is to be set to an opening pressure between 2 and 2.4 bar g, and safety valve 6 to an opening pressure of 3 bar g, i.e., at least 0.6 bar higher than the safety valve in the heat pump. This requirement is to be eliminated by the installation. This allows for height differences of up to 15 meters, whereby a minimum pressure must be maintained at the heating pump to prevent cavitation. The opening pressure of the safety valve in the heat pump is chosen to be as high as possible, but, taking tolerances into account, lower than the opening pressure of the safety valve in the building's heating circuit.This makes it possible to use identical devices in other installations where the heat pump forms the lowest point in the heating system. Reference symbol list

[0032] 1 Internal heat exchanger 2 Refrigerant / air separator 3 Refrigerant / air separator vent valve 4 Safety valve in the heat pump 5 Heating circuit pump 6 Safety valve in the heating circuit 7 Expansion vessel 8 Heating consumer 9 Heat pump housing 10 Heating circuit water 11 Refrigerant 12 Electric auxiliary heater p1 Pressure at the refrigerant / air separator p2 Pressure at the safety valve in the heat pump p3 Pressure after the heating circuit pump p4 Pressure at the safety valve in the heating circuit p5 Pressure at the expansion vessel p6 Pressure at the inlet of the internal heat exchanger Δp Differential pressure of safety valves 4 and 6

Claims

1. Installation of a heat pump in a building, wherein the installation comprises - a heat pump operated with a combustible refrigerant (11), wherein the heat pump is located in a housing (9) and the housing is located in a building, - an internal heat exchanger (1) in the housing (9) of the heat pump, which is connected to the flammable refrigerant (11) on one side and to the heating circuit water (10) on the other side, - a refrigerant / air separator (2) in the housing (9) of the heat pump, which is arranged on the outlet side in the heating circuit behind the internal heat exchanger (1), - a safety valve (4) in the housing (9) of the heat pump, which is arranged downstream in the heating circuit behind the refrigerant / air separator (2), - a heating circuit pump (5) which is arranged downstream in the heating circuit behind the safety valve (4), - at least one heating consumer (8) with a hot water inlet and a hot water return, - a further safety valve (6) between the hot water inlet and the heating circuit pump (5), - between the hot water return and the internal heat exchanger (1), a water expansion tank (7), wherein the safety valve (4) in the heat pump housing (9) has a lower opening pressure than the other safety valve (6) between the heating circuit pump (5) and the heating consumer (8), and the difference in opening pressure is greater than the pressure difference due to the geodetic height of the water column between the two safety valves (4, 6).

Images