EP4269882A1 - Hot water supply system with heat recovery - Google Patents

Abstract

In order to specify a hot water supply system that meets the normative conditions and at least partially reduces or eliminates the mentioned risks, a hot water supply system can have a connection to a fresh water supply for admitting cold drinking water into the hot water supply system, a first heat exchanger for heat transfer of heat from a primary heat transfer medium to the cold one Drinking water, a supply line carrying the heated drinking water, to which at least one consumer is connected, a second heat exchanger for heat recovery by heat transfer of heat from a secondary heat transfer medium to the primary heat transfer medium which is cooled by heat release to the drinking water and a heat transfer medium which transfers flow energy to the primary heat transfer medium - Have pump.

Description

The present invention relates to a hot water supply system with heat recovery.

Heat recovery (WRG for short) absorbs waste heat from an upstream process in order to feed it back into the system at another point, thereby saving energy costs. For efficient heat recovery, the medium to which the waste heat from the upstream process is released should be as cold as possible. This achieves maximum cooling of the medium that gives off the waste heat, which in turn can absorb larger amounts of energy through the upstream process. Examples of upstream processes include: cold storage; industrial processes; general processes that generate wastewater; cooling of server rooms; Freezer cooler from industrial use.

Since heat transfer can only occur from a warmer to a colder medium, it is efficient if the colder medium is kept as cool as possible. This is the reason why operators and planners of hot water supply systems with heat recovery systems now prefer to transfer the heat from the heat recovery heater to the cold water just before the main drinking water heater in the form of a preheating stage. There the cold water is preheated to a certain extent. This has the positive effect that the main drinking water heater can be made smaller because the water no longer has to be heated from approx. 10°C to approx. 60°C, but, for example, only from approx. 35°C to approx. 60° C

Despite this great potential, hot water supply systems with HR are also associated with risks and normative conditions, which are exemplary: According to DVGW W 511, preheating stages must be heated to >60°C at least daily from a volume of >400 l; Preheating stages must be structurally designed in such a way that it is possible to heat them to >60°C daily; Preheating stages create an additional pressure loss in the drinking water pipe; After the preheating stage, the hot water is in a critical temperature range of around 40 °C and is therefore hygienically questionable; During periods of non-use, certain dead pipes with stagnant water arise.

An object of the present invention is to provide a hot water supply system that meets the normative conditions and at least partially reduces or eliminates the risks mentioned.

To solve this problem, the present invention provides a hot water supply system with the features of claim 1.

The hot water supply system according to the present invention has a connection to a fresh water supply for introducing cold drinking water into the hot water supply system. This connection is usually a connection to the public water supply network, although a connection to the public water supply network in the sense of the present invention is in particular an area of a drinking and service water system of a building that communicates directly with the building water meter, however does not yet have a branch that leads to one or more supply lines. The connection regularly corresponds to a point of transfer of drinking water in accordance with Section 3 Paragraph 3 of the Drinking Water Ordinance. The hot water supply network is usually a drinking water installation according to this standard. The hot water supply system according to the present invention is therefore designed in particular as a drinking and service water system for providing warm drinking and service water or at least includes such a drinking and service water system.

To heat the cold drinking water, the hot water supply system has a first heat exchanger for transferring heat from a primary heat transfer medium to the cold drinking water. The drinking water and the primary heat transfer medium are fluidly separated from each other. For this purpose, the first heat exchanger has, for example, a heat-permeable and fluid-impermeable partition wall. This separation prevents contamination of the drinking water by the primary heat transfer medium. The first heat exchanger can in particular be designed as a plate heat exchanger.

The heated drinking water is led through a supply line of the hot water supply system to at least one consumer which is connected to the supply line. The consumers can be connected to the supply line in a variety of ways. For example, several consumers can be connected to the supply line via a flow divider. The connection can just as easily be implemented via a T-piece installation or a ring installation. On the consumer side, the supply line can be designed in sections as a riser line and/or as a floor line. A consumer in the sense of the present invention can in particular be any hot water tapping point in a building, for example a shower or a washbasin. The supply line can be assigned a circulation line for returning drinking water cooling down in the supply line to the first heat exchanger, the circulation line communicating with a circulation pump to generate a preferably constant circulation volume flow. The circulation line generally has a nominal diameter that is at least one step smaller than the supply line.

A heat transfer medium pump is provided to transfer flow energy to the primary heat transfer medium. The primary heat transfer medium is passed through the first heat exchanger through the heat transfer medium pump and corresponding lines.

The hot water supply system has a second heat exchanger for heat recovery. This is intended for the heat transfer of heat from a secondary heat transfer medium to the primary heat transfer medium, which is cooled by heat transfer to the drinking water. The second heat exchanger can be a plate heat exchanger or a heat pump.

The heat from the HRV is therefore first transferred to the primary heat transfer medium and not directly to the drinking water. This means that the heat from the HRV is returned to the system at a point that makes it easier to reduce or eliminate the risk of the drinking water stagnating at a hygienically questionable temperature of, for example, around 40°C. In particular, the primary heat transfer medium preheated by the WRG can be further heated to at least 60 ° C before it is fed to the first heat exchanger to heat the cold drinking water. This means that the cold drinking water can be heated to a specific target temperature without a preheating stage. This target temperature is preferably adjustable. It is particularly preferably in a range from 50°C to 60°C.

According to a preferred development of the present invention, the primary heat transfer medium consists largely or completely of water. The primary heat transfer medium can, for example, be the heating water of a building's heating circuit. More preferably, the hot water supply system has a central heating system with which the primary heat transfer medium can be heated to a temperature that is preferably at least 60 ° C or greater than 60 ° C. The central heating system is preferably a heating system that uses primary energy.

According to a further preferred development of the present invention, the secondary heat transfer medium is a fluid containing waste heat and / or wastewater or gray water, the temperature of the secondary heat transfer medium preferably being at least 35 ° C. More preferably, the temperature of the secondary heat transfer medium is less than 60 ° C. The waste heat can be waste heat from a cooling process and/or from an industrial process and/or from exhaust air. Alternatively or additionally, the secondary heat transfer medium can contain energy from the environment, i.e. the heat present in the ground or in the outside air. Particularly when using a heat pump, it does not necessarily have to be heat recovery in the traditional sense. For the purposes of the present application, a transfer of heat from the environment should preferably also be subsumed under “heat recovery”.

According to a further preferred development of the present invention, the hot water supply system comprises at least one buffer storage for the primary heat transfer medium. The buffer storage is usually dimensioned and designed in such a way that thermal stratification of the primary heat transfer medium occurs automatically within the buffer storage. As a rule, the primary heat transfer medium from the upper area of the buffer storage is used to heat the drinking water. The primary heat transfer medium from the middle and/or lower area of the buffer storage is usually heated to a temperature of at least 60 ° C by a central heating system or an electric heating element of the hot water supply system, whereby it rises to the upper, warmer area in the buffer storage.

According to a further preferred development of the present invention, the hot water supply system comprises at least one main buffer storage connected to the first heat exchanger, which communicates with a central heating system of the hot water supply system in order to keep a part of the primary heat transfer medium at a temperature of at least 60 ° C or higher, at least a secondary buffer storage connected to the second heat exchanger, which holds another part of the primary heat transfer medium for heat recovery, a connecting line between the main buffer storage and the secondary buffer storage for transferring primary heat transfer medium heated by the heat recovery from the secondary buffer storage into the Main buffer storage, and a first return line connecting the first heat exchanger to the secondary buffer storage for returning primary heat transfer medium cooled by heat release to the drinking water from the main buffer storage into the secondary buffer storage. The primary heat transfer medium passes through different stations, whereby it usually heats up from a lowest temperature level in the second heat exchanger and cools down from a highest temperature level in the first heat exchanger. Between these two stations, the primary heat transfer medium is temporarily stored in the buffer storage on the way from the second heat exchanger to the first heat exchanger, the primary heat transfer medium temporarily stored in the main buffer storage being at least partially heated by the heating system to a target temperature for heating the drinking water.

According to a further preferred development of the present invention, the hot water supply system comprises a switching valve provided between the first heat exchanger and the buffer stores for switching between an inlet to the first heat exchanger from the secondary buffer store and an inlet to the first heat exchanger from the main buffer store. In this preferred training, the cold drinking water heated to a preheated temperature level by the recovered heat from the heat exchanger when the inlet to the first heat exchanger from the secondary buffer storage is activated. As a rule, the temperature level of the heat exchanger and therefore also the temperature level of the secondary buffer storage is lower than the target temperature mentioned above between 50°C and 60°C, so that the drinking water temperature is at the preheated temperature level below this range. Usually the temperature of the preheated temperature level is 35°C, 40°C or 45°C, each ± 2.5°C. Due to the lower temperature level of the preheated temperature level, the return temperature of the primary heat transfer medium is also lower, so that on the one hand the efficiency of the heat exchanger increases. On the other hand, the lower temperature level of the WRG is also accompanied by the normative condition mentioned at the beginning that preheating stages with a volume >400 I must be heated to >60°C at least daily. In order to meet this condition, the switching valve can be switched at least once a day in order to activate the inlet to the first heat exchanger from the main buffer storage.

According to a further preferred development of the present invention, the hot water supply system comprises a third heat exchanger for heating the drinking water, which is connected to the supply line in parallel or in series with the first heat exchanger. The third heat exchanger can be a plate heat exchanger. As with the first heat exchanger, the thermal energy for heating the drinking water through the third heat exchanger is also provided by the primary heat transfer medium and preferably from the main buffer storage. This opens up the possibility of heating the drinking water in a cascade manner, with the cascade being triggered when the consumer draws hot water. Due to the hot water extraction, cold drinking water flows into the system via the connection to the fresh water supply and is heated in a first stage of the cascade by the first heat exchanger to a temperature that is, for example, in a range of 50-60 ° C. In the case of a series connection, the drinking water heated by the first heat exchanger is then reheated by the third heat exchanger in a second stage of the cascade to a temperature of, for example, at least 60 ° C and then fed to the consumer. With a parallel connection, the drinking water heated by the first heat exchanger is combined in the second stage of the cascade with the drinking water heated by the third heat exchanger and then fed to the consumer. The flow lines between the buffer storage and the first and third heat exchangers are preferably no longer than 10 m, 15 m, 20 m or 25 m.

According to a further preferred development of the present invention, the hot water supply system comprises a circulation line and a circulation pump assigned to the circulation line for returning anything cooling down in the supply line Drinking water to the third heat exchanger. Heat losses from the warm drinking water in the pipes can be compensated for by the third heat exchanger. This means that even if water is not drawn, warm drinking water at the desired temperature, usually 60°C, can always be available. The circulation flow is usually continuous, so that stagnation of drinking water is reliably avoided. A circulation line usually has a smaller diameter than the upstream supply line leading to the consumer. The third heat exchanger usually operates at a higher temperature level than the first heat exchanger, since the inlet of the third heat exchanger is fed either - in the case of a series connection - the drinking water heated by the first heat exchanger or - in the case of a parallel connection - the warm drinking water returned through the circulation line , whereas the fresh cold drinking water of the fresh water supply system is supplied to the inlet of the first heat exchanger.

According to a further preferred development of the present invention, the hot water supply system comprises a second return line for the primary heat transfer medium connecting the third heat exchanger to the main buffer storage. Since the third heat exchanger usually operates at a higher temperature level, the return temperature of the primary heat transfer medium coming from the third heat exchanger is only slightly lower, so that it is not suitable for heat recovery and can be returned directly to the main buffer storage.

According to a further preferred development of the present invention, the hot water supply system comprises a flushing device assigned to the circulation line or the supply line with a flushing valve for draining drinking water from the hot water supply system. This means that drinking water quality can be guaranteed at all times by opening the flush valve to flush pipe sections with standing water due to longer periods of non-use. The flushed out stale water is replaced by fresh, cold drinking water and heated by the first and/or third heat exchanger. As a rule, the flushing valve is downstream of the first and/or the third heat exchanger in the direction of flow. The flushing device can include several flushing valves.

According to a further preferred development of the present invention, the hot water supply system comprises at least one water temperature sensor, which is assigned to a drinking water outlet of the first heat exchanger, and a control unit for regulating the water temperature of the drinking water heated by the first heat exchanger by controlling the heat transfer medium pump.

According to a further preferred development of the present invention, the control unit is set up in such a way that it controls the heat transfer medium pump in such a way that the The temperature measured by the water temperature sensor corresponds to a setpoint, the setpoint being adjustable.

According to a further preferred development of the present invention, the control unit is set up in such a way that the setpoint corresponds to a reduced hot water temperature value and is raised to a temperature value of at least 60 ° C or greater than 60 ° C at least once per day for a predetermined time or for a predetermined flow rate becomes. A reduced water temperature value is understood to mean in particular a value that is at least 1°C, preferably at least 3°C, 5°C, 10°C or 15°C smaller than 60°C. How often or at what intervals the increase takes place and for how long is preferably variable or adjustable. The duration of the increase can in particular be dependent on consumption or the amount of water flushed out, i.e. it can only be ended, for example, when a certain minimum amount of hot water has been consumed by the consumer or flushed through the flushing device after the increase. As a rule, the hot water supply system includes a flow meter to determine a flow rate.

By lowering the temperature level of the first stage of the cascade, a lower return temperature of the primary heat transfer medium supplied to the secondary buffer storage can be achieved and thus the efficiency of the heat recovery can be increased. The lowering of the temperature level of the first stage of the cascade is preferably achieved with the previously described series connection of the first and third heat exchangers, so that the drinking water in the second stage of the cascade goes from the lowered temperature level to the desired temperature for warm drinking water, usually 60 ° C is heated before it is delivered to the consumer.

According to a further preferred development of the present invention, the control unit controls the switching valve in such a way that the inlet to the first heat exchanger from the main buffer storage is released for the predetermined time or until a predetermined flow rate is reached at an increased temperature and before and after that the inlet is closed the first heat exchanger from the secondary buffer storage is released. In other words, in this preferred development, the heat for the reduced water temperature is provided from the secondary buffer storage and the heat for the temperature value of at least 60 ° C or greater than 60 ° C is provided from the main buffer storage. Alternatively, the heat for both the reduced water temperature and for the temperature value of at least 60°C or greater than 60°C can be provided from the main buffer storage by providing the heat for the temperature value of at least 60°C or greater than 60°C for example from an upper thermal layer and for the lowered water temperature from one underlying thermal layer is provided and / or the primary heat transfer medium cools down for a shorter time on the cold drinking water.

According to a further preferred development of the present invention, the hot water supply system comprises a flushing device control module for initiating a drinking water change by controlling the flushing valve of the flushing device. During such a drinking water change, at least the entire amount of water between the flushing valve and the first heat exchanger is usually exchanged with fresh drinking water. The criteria and/or the interval time and/or the times at which a drinking water change is initiated can preferably be programmed into the flushing device control module. The flushing device control module can be part of the control unit or a higher-level controller, in particular a functional software component of the control unit or the higher-level controller, or can be designed as an independent component, which is preferably designed to be adapted for communication with the control unit or the higher-level controller . As an independent component, it can be provided in a common housing with the control unit or the higher-level controller or separately at another point in the system.

A time-controlled flushing mode can be programmed into the flushing device control module, in which the flushing valve is opened at specific times and/or time intervals for a change in drinking water. For this purpose, the flushing device control module can have a timer that is set to 72 hours, for example.

A warm rinse mode may be programmed into the rinser control module. For example, a drinking water change can be initiated as soon as the setpoint is increased from the reduced temperature value. This allows the water still in the pipes to be drained from the system at a reduced temperature. A stop criterion for the drinking water change in warm flush mode can be generated from the water temperature measured by the temperature sensor. This means that the drinking water change can be completed, for example, when the water temperature measured by the temperature sensor reaches a certain higher target temperature from a lower value.

A heat exchanger flushing mode can be programmed into the flushing device control module, in which a drinking water change is triggered while the changeover valve is set so that the inlet to the first heat exchanger from the secondary buffer storage is activated.

In principle, several flushing modes can be programmed into the flushing device control module. The flushing modes can be implemented interactively with each other. For example, a water change of another mode may cause the timer for the timed mode to reset.

According to a further preferred development of the present invention, the control unit is set up in such a way that the heat transfer medium pump is put out of operation during a cold flushing mode of the flushing device control module. To implement the cold flushing mode, the flushing device preferably comprises at least one flushing valve located upstream of the third heat exchanger in the flow direction. The cold flush mode can be triggered when the consumer stops drawing hot water. In the cold flush mode, the flush valve is opened to exchange the drinking water between the first and third heat exchangers and in the first heat exchanger with fresh cold drinking water. This can prevent the drinking water in the area of the first heat exchanger from developing into a hygienically questionable temperature range after water has been withdrawn by the consumer. Nevertheless, the position of the flushing valve and the specified flow direction ensure that the temperature level of the third heat exchanger, i.e. the second stage of the cascade, remains essentially unaffected. In addition, a backflow preventer can be provided which prevents warm drinking water from flowing back from the second stage of the cascade to the flushing valve. The cold rinse mode can also be triggered without consumption. For example, the control unit can control the heat medium pump to reach the setpoint of, for example, 60 ° C and then trigger the cold flushing mode. This means that the first heat exchanger can be heated to the setpoint temperature at regular intervals, even without the consumer drawing drinking water.

According to a further preferred development of the present invention, the setpoint is set variably and is dependent in particular on a flow temperature of the first heat transfer medium from the secondary buffer storage and/or domestic hot water consumption. For example, the setpoint can be set to be a certain temperature difference ΔT smaller than the flow temperature of the first heat transfer medium supplied from the secondary buffer storage. The temperature difference ΔT can be, for example, 5°C or 10°C. The temperature difference can be adjustable depending on average domestic hot water consumption. For example, the temperature difference can be greater with a higher domestic hot water consumption (e.g. 100 l/min) than with a lower domestic hot water consumption (e.g. 20 l/min). In the event that the flow temperature is greater than 60°C, the setpoint is preferably limited to a maximum of 60°C.

According to a further preferred development of the present invention, the first setpoint is set variably and is dependent in particular on a return temperature of the first heat transfer medium to the secondary buffer storage and/or domestic hot water consumption. The temperature difference ΔT is then usually set so that a maximum cold return temperature is achieved for the primary heat transfer medium.

According to a further preferred development of the present invention, the hot water supply system comprises a disinfection operating mode implemented in the control unit, in which the drinking water is heated to a setpoint of over 60 ° C and drained from the hot water supply system by activating the flushing valve. In the disinfection operating mode, the setpoint is raised to 60°C or higher and the changeover valve, if present, is set for a predetermined time or until a predetermined flow rate is reached at an increased temperature so that the inflow to the first heat exchanger from the main buffer storage is released. You can then switch from the disinfection operating mode back to the previous normal operating mode. For example, the changeover valve can be set again so that the inlet to the first heat exchanger from the secondary buffer storage is released, and the first target temperature can be reduced again. More preferably, the disinfection operating mode can be automatically interrupted by the consumer's consumption of domestic hot water and then continued or canceled and postponed. The disinfection operating mode is particularly preferably followed by one of the rinsing modes.

According to a further preferred development of the present invention, the hot water supply system comprises a data logger for logging the duration, start, stop, date and/or time of a drinking water change by the flushing device and/or the duration, start, stop, date and/or time of an activation of the Disinfection operating mode and/or a flushing volume drained from the hot water supply system during a water change and/or the water temperature measured by a temperature sensor. The data logger is usually connected in terms of data to the control unit and the flushing device control module and/or a higher-level controller.

Fig. 1

eine schematische Darstellung eines ersten Ausführungsbeispiels,

Fig. 2

eine schematische Darstellung eines zweiten Ausführungsbeispiels und

Fig. 3

eine schematische Darstellung eines dritten Ausführungsbeispiels.

Further details and details of the present invention emerge from the following description of exemplary embodiments in conjunction with the drawing. In this show:

Fig. 1

a schematic representation of a first exemplary embodiment,

Fig. 2

a schematic representation of a second exemplary embodiment and

Fig. 3

a schematic representation of a third exemplary embodiment.

Figure 1 schematically represents a hot water supply system. The individual components of this hot water supply system can be provided in a building. The hot water supply system includes a connection 2 to a fresh water supply for admitting cold drinking water. Connection 2 is the point of transfer of drinking water from a water supply system in accordance with the Drinking Water Ordinance. The connection 2 to the fresh water supply is connected via a first line 4 to four first heat exchangers 6 and feeds them with fresh, cold drinking water. The first heat exchangers 6 transfer heat from a primary heat transfer medium P to the cold drinking water. The first heat exchangers 6 can be designed, for example, as plate heat exchangers. By passing through the first heat exchanger 6, the cold drinking water is heated from, for example, 10 ° C to a first temperature level, which can be, for example, in the range of 40 ° C to 60 ° C.

The heated drinking water leaves the first heat exchanger 6 via a second line 10 which is connected to the outlets 8 of the first heat exchanger 6 and which opens into a circulation line 12. The circulation line 12 is connected to four third heat exchangers 14 and communicates with a circulation pump 16, which conveys the heated drinking water in the direction of the third heat exchangers 14. There, further heat is added to the heated drinking water so that it is heated to a second temperature level of preferably at least 60 ° C. The first heat exchangers 6 and the third heat exchangers 14 are therefore connected in series to the supply line 20. Heat from the primary heat transfer medium is also transferred to the drinking water in the third heat exchanger 14. However, the drinking water is already at the warmer first temperature level before it is heated by the third heat exchanger 14.

A supply line 20 is connected to the outlets 18 of the third heat exchanger 14. The supply line 20 leads to a consumer 22, which is connected to the supply line 20 in order to supply it with warm drinking water. The supply line 20, together with the circulation line 12, forms a circuit in which the warm drinking water circulates when not being used by the consumer. Through the circulation and the associated constant heat transfer through the third heat exchanger 18, heat losses from the warm drinking water in the pipes can be compensated for. Due to heat losses in the pipes, the warm drinking water can cool down from 60°C to 55°C, for example.

To drain drinking water from the hot water supply system, a flushing device 24 with a flushing valve 26 is connected to the supply line 20. This means that a drinking water change can be carried out during a longer phase of non-use, with the stale water being drained from the pipes via the flushing valve 26 and replaced with fresh, cold drinking water from connection 2. The flushing valve 26 is assigned a free outlet 28, which drains into a wastewater pipe.

The first heat exchangers 6 are connected by a first flow line 30 to two main buffer stores 32A, 32B, which are filled with the primary heat transfer medium P. From From the first flow line 30, a second flow line 34 branches off, which connects the third heat exchanger 14 to the two main buffer stores 32A, 32B. The first flow line 30 is connected to the uppermost area of the main buffer storage 32A, 32B, ie where the primary heat transfer medium P located therein generally has the highest temperature. The first and second feed lines 30, 34 are preferably as short as possible; for example, a maximum of 20 m long.

In the area of each first heat exchanger 6 or each third heat exchanger 14, the first flow line 30 or the second flow line 34 is assigned a heat transfer medium pump 36 which transfers flow energy to the primary heat transfer medium P. Each of these heat transfer medium pumps 36 is in turn assigned a control unit 38, which is connected in terms of control to the respective heat transfer medium pump 36, the primary heat transfer medium for heating the drinking water being pumped through the heat exchangers 6 and 14 by controlling the heat transfer medium pumps 36. Each outlet 8 of the first heat exchanger 6 and each outlet 18 of the third heat exchanger 14 is assigned a temperature sensor 40, which is connected in terms of data to the control unit 38 of the respective heat exchanger 6 or 14.

The control units 38 are adapted to control the heat transfer medium pump 36 assigned to them in such a way that the temperature measured at the outlet 8 or 18 of the respective heat exchanger 6 or 14 by the temperature sensor 40 corresponds to an adjustable setpoint or reaches this adjustable setpoint. As already indicated above, the control units 38 are generally set so that the control units 38 of the first heat exchangers 6 specify a setpoint in a lower temperature range (e.g. in the range from 40 ° C to 60 ° C) than the control units 38 of the third heat exchangers 6, which usually specify a setpoint of at least 60°C. In particular, the setpoints specified by the control units 38 of the first heat exchanger 6 can be set variably and, for example, be dependent on a flow temperature of the primary heat transfer medium P, a return temperature of the primary heat transfer medium P and / or a hot water consumption rate. The control units 38 can be designed as modules of a higher-level controller, which preferably also includes a flushing device control module 42 for controlling the flushing device 24.

A third feed line 44 is connected to a lower area of the two main buffer stores 32A, 32B. It communicates with a central, primary energy-using heating system 46 of the hot water supply system in order to heat at least part of the primary heat transfer medium P to a temperature of 60 ° C or higher.

In addition to the two main buffer tanks 32A, 32B, the hot water supply system includes a secondary buffer tank 48, which is filled with a part of the primary heat transfer medium P, which is overall at a lower temperature level than the part contained in the main buffer tank 32A, 32B , because the primary heat transfer medium P, which has cooled down on the cold drinking water in the first heat exchangers 6, is returned via a first return line 50 to the lower area of the secondary buffer storage 48. An heat exchanger flow line 52 is connected to the lower area of the secondary buffer storage 48, which communicates with a second heat exchanger 54 to the heat exchanger. Heat is recovered by heat transfer of heat from a secondary heat transfer medium S to the primary heat transfer medium P, which has cooled down by heat transfer to the drinking water. A fluid containing waste heat and/or wastewater or gray water is generally used as the secondary heat transfer medium S. The waste heat can be waste heat from a cooling process and/or from an industrial process.

The primary heat transfer medium P heated by WRG via the second heat exchanger 54 is returned to an upper area of the secondary buffer storage 48 through an WRG return line 56. From there it is passed through a connecting line 58 into the lower areas of the main buffer storage 32A, 32B, where it mixes with warmer primary heat transfer medium P and / or rises and is further heated by the central heating system 46, ultimately returning through the first or the second flow line 30, 34 is supplied to the first or third heat exchangers 6, 14 for heating the drinking water.

Since the third heat exchangers 14 are already fed with a higher drinking water temperature due to the first heating stage by the first heat exchangers 6, less heat must be given off from the primary heat transfer medium to the drinking water in the third heat exchangers 14 in order to achieve the desired temperature for warm drinking water Usually reach 60°C. As a result, the return temperature of the primary heat transfer medium P coming from the third heat exchangers 14 is only slightly lower than the flow temperature of the primary heat transfer medium P directed to the third heat exchangers 14. Therefore, the return of the third heat exchangers 14 is not suitable for the heat exchanger and is via a second return line 60 is returned directly to the main buffer memories 32A, 32B.

The second return line 60 returns the primary heat transfer medium P from the third heat exchangers 14 to the lower regions of the main buffer storage 32A, 32B. There it mixes with warmer or colder primary heat transfer medium P and/or rises and is further heated by means of the central heating system 46, ultimately returning through the first or the second flow line 30, 34 to be supplied to the first or third heat exchangers 6, 14 for heating the drinking water.

A third return line 62 connects the central heating system 46 to the upper areas of the main buffer tanks 32A, 32B.

This in Fig. 2 The hot water supply system shown is the same as the hot water supply system except for one difference Fig. 1 built up. The difference is that the second line 10 is in the hot water supply system Fig. 2 not like the hot water supply system Fig. 1 into the circulation line 12 with the circulation pump 16, but into the supply line 20. At the mouth, the drinking water heated by the first heat exchanger 6 mixes with the drinking water heated by the third heat exchanger 14 and is passed through the supply line 20 to the consumer 22. The drinking water heated by the first heat exchanger 6 is not as in Figure 1 passed through the third heat exchanger 14 before it is passed to the consumer 22. The first heat exchangers 6 and the third heat exchangers 14 are connected in parallel to the supply line 20. Just like with the hot water supply system Figure 1 When the consumer 22 is not in use, the drinking water from the supply line 20 is returned through the circulation line 12 to the third heat exchanger 14.

This in Fig. 3 The hot water supply system shown is the same as the hot water supply system except for one difference Fig. 1 built up. The difference is that in the hot water supply system Fig. 3 A third line 64 is connected between the connecting line 58 and the first flow line 30, the connection of the third line 64 to the first flow line 30 being realized via a switching valve 66 designed as a 3-way valve, which is in the flow direction after the branch of the second Flow line 34 is provided. The higher-level control is connected to the switching valve 66 in terms of control and can set it so that the first heat exchangers 6 are fed by primary heat transfer medium P from the secondary buffer store 48 or so that the first heat exchangers 6 are fed by primary heat transfer medium P from the main buffer stores 32A, 32B are fed. The third heat exchangers 14, however, are independent of the position of the changeover valve 66 and as in the hot water supply system Fig. 1 or Fig. 2 fed by primary heat transfer medium P from the main buffer stores 32A, 32B.

Some special features and control logic for the operation of the hot water supply systems described in connection with the drawing are discussed below as examples. A heating medium should be used as the primary heat transfer medium P.

The hot water supply systems Fig. 1 and 2 are very similar. As already explained, the difference between the two systems lies in the connection of the first and third heat exchanger 6, 14 to the supply line 20 (series connection in Fig.1 and parallel connection in Fig. 2 ). The series connection has the advantage that the smallest withdrawals from the consumer 22, which are not recorded by the first heat exchangers 6, are heated in the third heat exchangers 14 at the latest. However, this advantage creates an additional pressure loss compared to the parallel connection Fig. 2 .

In the hot water supply system Fig. 2 The drinking water heated by the first heat exchangers 6 flows directly into the supply line 20 and mixes there with the drinking water from the third heat exchangers 14 to a mixing temperature. This mixing can result in a brief drop in the desired hot water temperature if, for example, the flow line 30 is not yet at temperature. However, this drop in temperature is negligible if the circulation volume flow is sufficiently large.

How a tap works (explained as an example in Fig. 1):

1. 1. A larger amount of hot water is consumed by the consumer 22, so cold water of approx. 10 ° C flows from the first line 4 through the first heat exchanger 6 and is brought to a higher temperature, for example 50-60 ° C.
2. 2. Since it cannot be ensured that the flow line 30 was already "warm" before the consumer 22 was used, the heated hot water is integrated into the circulation line 12 for reheating through the second line 10.
3. 3. The heating medium, which has cooled down significantly due to the heating of the drinking water (e.g. 35 ° C or colder), is fed into the secondary buffer storage 48 via the first return line 50.
4. 4. The second heat exchanger 54 can then draw the cold return heating medium from the "cold" secondary buffer storage 48 in order to cool the heat from the upstream processes (e.g. 40 ° C or higher).
5. 5. The heating medium heated by heat exchanger rises in the secondary buffer storage 48 and, when the first heat exchanger 6 is under load, is drawn from the secondary buffer storage 48 into the main buffer storage 32A, 32B by the heat transfer medium pumps 36 of the first heat exchanger 6. There it is either sucked in by the central heating system 46 or mixes in the main buffer storage 32A, 32B to a higher temperature, which can be used again for domestic hot water preparation.

How the circulation case works (explained as an example in Fig. 1):

1. 1. When the consumer 22 is not in use, the hot drinking water flows through the circulation line 12 into the third heat exchanger 14 to reheat the circulation volume flow. This happens at a higher temperature level compared to the case described previously. The returning circulation water at, for example, 55°C flows into the third heat exchanger 14 and is heated again to approx. 60 ° C. The heated water then flows back to the consumer 22 via the supply line 20.
2. 2. Since the circulation volume flow is constantly flowing, the second flow line 34 is permanently at temperature. Since the circulation water that cools the heating medium has a temperature level of 55°C, the heating medium can only cool down minimally to this level.
3. 3. The slightly cooled heating medium (around 55 ° C) flows through the second return line 60 into the main buffer storage 32A, 32B and settles there in the appropriate temperature zone. This can then be used again to generate domestic hot water by reheating the central heating system 46.
4. 4. In order to keep the long dead lines hygienic when not in use, a flushing device 24 is provided downstream of the first and third heat exchangers 6, 14 in the direction of flow. When this flushes out water, fresh cold water flows into the system through connection 2.

Special variant reduced hot water temperature in the system according to Fig. 1

In order to be able to achieve an even more effective operation of the second heat exchanger 54, and in order to further cool the return temperature of the first heat exchanger 6 to the secondary buffer storage 48, a reduction in the set hot water temperature (setpoint) of the first heat exchanger 6 to, for example, 50 ° C in combination with flushing measures can be set by the higher-level control. Lowering the set hot water temperature to a minimum of 50°C results in colder return temperatures because the heating medium does not have to heat the hot water as much and can cool down for longer. A high flow temperature is also advantageous in this variant, as this results in an even more cooled return compared to a "colder" flow.

With this more cooled heating medium, the second heat exchanger 54 can release more energy to the heating medium and the secondary buffer storage 48.

This special variant is linked to conditions that were described at the beginning in connection with a preheating stage. Therefore, the first heat exchangers 6 in this special solution are heated to >60°C every day. In addition, in the special variant, a forced flushing of the second line 10 is implemented via the flushing device 24, so that a water change is guaranteed at least every 72 hours via the first heat exchanger 6.

How it works with switching valve 66 (explained as an example in Fig. 3)

The installation variant according to Fig. 3 works on the drinking water side in the same way as the installation variant Fig. 1 . Since this has already been described in advance, only the differences will be discussed below.

In principle, switching the switching valve 66 only changes the temperature level of the heating medium that is supplied to the first heat exchangers 6.

The third heat exchangers 14 remain excluded from the function of the switching valve 66 and function independently of the first heat exchangers 6. Thanks to the switching valve 66, the interconnection meets the requirements of the DVGW worksheet by daily switching between the secondary buffer tank 48 and the main buffer tank 32A, 32B. The first heat exchangers 6 can therefore also be supplied daily with a heating medium > 60 ° C from the main buffer storage 32A, 32B. When switching the switching valve 66 in the direction of the secondary buffer tank 48, the drinking water is preheated to a significantly lower temperature level based on the lower flow temperature of the secondary buffer tank 48. Since the first heat exchangers 6 then only have a "colder" flow medium below 60 ° C available, a special control logic is implemented, which will be described below. With this logic, the control regulates the first heat exchanger 6 so that the setpoint has a certain relationship to the flow temperature of the secondary buffer storage 48. The difference between the actually desired temperature for warm drinking water of approx. 60 ° C and the resulting hot water temperature according to the setpoint is ensured by the reheating of the third heat exchanger 14.

How the tap works with the switching valve 66 in the direction of the secondary buffer tank 48

1. 1. The changeover valve 66 is set so that the first heat exchanger 6 is supplied with heating medium from the secondary buffer storage 48. The flow direction corresponding to this position is referred to in the following text as “flow direction A” or “flow direction A”.
2. 2. The heating medium cooled by the heating of the drinking water is led from the first heat exchangers 6 via the first return line 30 into the secondary buffer storage 48.
3. 3. The second heat exchanger 54 can draw the cold return water from the "cold" secondary buffer storage 48 in order to cool the heat of the upstream processes, for example 40 ° C or higher.
4. 4. Via flow direction A, the waste heat from the upstream processes is then completely sucked back into the first heat exchangers 6 and used for preheating drinking water.

How the tap works: switching valve 66 in the direction of the main buffer tank 32A, 32B

1. 1. Durch eine Regelung der übergeordneten Steuerung erhält das Umschaltventil 66 einen Kontakt oder Impuls die Stellung seiner innenliegenden Kugel zu verändern. Fließrichtung A wird dadurch verschlossen und Fließrichtung B wird geöffnet.
2. 2. Die ersten Wärmeübertrager 6 ziehen nun das hoch temperierte Heizungswasser aus den Haupt-Pufferspeichern 32A, 32B (Strömungsrichtung B) und verwenden dies für die Vorwärmung des kalten Trinkwassers.
3. 3. Aus dem "kalten" Neben-Pufferspeicher 48 zieht sich der zweite Wärmeübertrager 54 das kalte Rücklaufwasser, um die Wärme der vorgelagerten Prozesse bspw. 40°C oder höher daran abzukühlen.
4. 4. Da die Fließrichtung A versperrt ist, strömt das durch die WRG erwärmte Heizungsmedium im Neben-Pufferspeicher 48 auf und wird im Lastfall der ersten Wärmeübertrager 6 durch die Wärmeträgermedium-Pumpen 36 vom Neben-Pufferspeicher 48 in die Haupt-Pufferspeicher 32A, 32B gezogen. Dort wird es entweder von der zentralen Heizanlage 46 angesaugt oder mischt sich im Haupt-Pufferspeicher 32A, 32B auf eine höhere Temperatur, die erneut zur Trinkwarmwasserbereitung verwendet werden kann.
5. 5. Nach einer definierten Zeit oder nach einem definierten Volumen erfolgt erneut ein Impuls und das Umschaltventil 66 verschließt die Strömungsrichtung B und öffnet die Strömungsrichtung A.

Due to the request to heat up a preheating stage daily, the switching valve 66 is switched daily in the direction of the main buffer storage 32A, 32B. The flow direction corresponding to this position is referred to in the following text as “flow direction B” or “flow direction B”.

1. 1. By regulating the higher-level control, the switching valve 66 receives a contact or impulse to change the position of its internal ball. This closes flow direction A and opens flow direction B.
2. 2. The first heat exchangers 6 now draw the high-temperature heating water from the main buffer tanks 32A, 32B (flow direction B) and use this to preheat the cold drinking water.
3. 3. The second heat exchanger 54 draws the cold return water from the "cold" secondary buffer storage 48 in order to cool the heat of the upstream processes, for example 40 ° C or higher.
4. 4. Since the flow direction A is blocked, the heating medium heated by the heat exchanger flows into the secondary buffer tank 48 and, when the first heat exchanger 6 is under load, is drawn from the secondary buffer tank 48 into the main buffer tank 32A, 32B by the heat transfer medium pumps 36 . There it is either sucked in by the central heating system 46 or mixes in the main buffer storage 32A, 32B to a higher temperature, which can be used again for domestic hot water preparation.
5. 5. After a defined time or after a defined volume, a pulse occurs again and the changeover valve 66 closes the flow direction B and opens the flow direction A.

Control logic installation variant according to Fig. 1:

In the special variant, the first heat exchangers 6 are operated with reduced hot water temperatures throughout the day, for example 50 ° C. In order to operate this correctly in accordance with standards, the first heat exchangers 6 must be raised to a hot water temperature of 60°C at least once a day. The interval of how often the increase takes place and the duration of the increase can be variably adjusted by the higher-level control.

1. 1. Regulärer Betrieb der ersten Wärmeübertrager 6 mit abgesenkter Warmwassertemperatur, bspw. 50°C.
2. 2. Ein übergeordneter Befehl geht an die Steuerungseinheiten 38 der ersten Wärmeübertrager 6 zur Anhebung der Warmwassertemperatur (Sollwert) über einen definierten Zeitraum.
3. 3. Da den ersten Wärmeübertragern 6 der "heiße" Vorlauf aus den Haupt-Pufferspeichern 32A, 32B zur Verfügung steht, ist ein Anheben der Warmwassertemperatur ohne weitere Schaltbefehle an zentrale Heizanlage 46 oder andere Bauteile möglich.
4. 4. Nach Ablauf des definierten Zeitraums schaltet ein übergeordneter Befehl die ersten Wärmeübertrager 6 wieder auf die reduzierte Warmwassertemperatur zurück.

In order to implement this hygienically, the following control logic is suggested:

1. 1. Regular operation of the first heat exchanger 6 with a reduced hot water temperature, for example 50 ° C.
2. 2. A higher-level command goes to the control units 38 of the first heat exchanger 6 to increase the hot water temperature (setpoint) over a defined period of time.
3. 3. Since the "hot" flow from the main buffer tanks 32A, 32B is available to the first heat exchangers 6, it is possible to increase the hot water temperature without further switching commands to the central heating system 46 or other components.
4. 4. After the defined period of time has elapsed, a higher-level command switches the first heat exchangers 6 back to the reduced hot water temperature.

Control logic installation variant according to Fig. 3:

The temperature to be achieved after the first heat exchangers 6 in the second line 10 is largely dependent on the available temperature level from the heat exchanger. The temperature can be raised to a maximum of this temperature level by the first heat exchanger 6 at flow path A. However, such a strong increase does not make sense at all, as the heating medium volume flows become very high and the cooling of the heating medium becomes ever smaller. It therefore makes sense to maintain a certain temperature difference between the flow temperature of the secondary buffer storage 48 and the set hot water temperature of the first heat exchanger 6 (setpoint).

• Großer Warmwasserbedarf (100 l/min): Vorlauftemperatur 50°C; Sollwert 40°C; Rücklauftemperatur 20°C.
• Geringer Warmwasserbedarf (20 l/min): Vorlauftemperatur 50°C; Sollwert 45°C; Rücklauftemperatur 20°C.
• Um eine maximal kalte Rücklauftemperatur zu erzielen ist auch ein von der Rücklauftemperatur abhängiger Sollwert denkbar.

The flow temperature of the secondary buffer storage 48 can vary greatly due to a fluctuating temperature level in the heat recovery, which makes it difficult to firmly define a constant temperature as a setpoint. It is therefore proposed to make the setpoint dependent on the flow temperature in flow direction A. E.g.: Setpoint = (flow temperature of flow direction A) -X, where X= 5°C or X=10°C. A volume flow dependency is also conceivable: For example, the value for The following pairs of values are mentioned as an example:

• Large hot water requirement (100 l/min): flow temperature 50°C; Setpoint 40°C; Return temperature 20°C.
• Low hot water requirement (20 l/min): flow temperature 50°C; Setpoint 45°C; Return temperature 20°C.
• In order to achieve a maximum cold return temperature, a setpoint that depends on the return temperature is also conceivable.

Temperature control without consumption

The higher-level control can be set so that the first heat exchangers 6 are heated to at least 60 ° C for disinfection without the consumer tapping or rinsing by the rinsing device. For this purpose, the heat transfer medium pumps 36 are controlled accordingly. The first heat exchangers 6 are heated by the "hot" flow medium and after a certain waiting time by a command rinsed with fresh cold water by a higher-level control system. The cold rinse takes place without heating the cold water. While the heat transfer medium pumps 36 of the first heat exchangers 6 are usually only in operation during consumption or for disinfection, the heat transfer medium pumps 36 of the third heat exchangers 14 are usually in permanent operation in order to ensure a constant circulation flow.

Control logic for warm flushing

During the routine heating of the first heat exchangers 6 to, for example, 60 ° C, a flushing of the flushing device 24 should be able to be triggered at a higher level in order to ensure that, in addition to the first heat exchangers 6, the second line 10 between the first heat exchangers 6 and the third heat exchangers 14 is also heated because it was also operated at a low temperature level.

Cold flush control logic

1. 1. Trinkwasserzapfung durch den Verbraucher endet, die ersten Wärmeübertrager 6 befinden sich auf Temperatur.
2. 2. Ein Befehl des Spüleinrichtungs-Steuerungsmoduls 42 öffnet das Spülventil 26 der Spüleinrichtung 24.
3. 3. Ein Befehl der übergeordneten Steuerung untersagt den Wärmeträgermedium-Pumpen 36 der ersten Wärmeübertrager 6 das Anlaufen trotz eines Volumenstroms, der durch die Spülung über die Geräte strömt.
4. 4. Durch das Öffnen des Spülventils 26 strömt zwangsläufig kaltes Frischwasser durch die erste Leitung 4 über die ersten Wärmeübertrager 6 und die zweite Leitung 10 in die Spüleinrichtung 24 und spült das hygienisch bedenkliche Wasser aus.
5. 5. Nach einem gewissen Volumen, der durch einen Sensor der übergeordneten Steuerung erfasst wird, kommt der Befehl zum Schließen der Spüleinrichtung 24 und Fortsetzen des regulären Betriebes.
6. 6. Die dritten Wärmeübertrager 14 bleiben von dieser Funktion ausgenommen, um die Rückerwärmung des Zirkulationsvolumenstroms sicher zu stellen. Das Spülventil 26 für diese Spülung, kalt, ist daher vorzugsweise in Strömungsrichtung den dritten Wärmeübertrager 14 vorgelagert angeordnet.

In addition to routine heating, it also makes sense to replace the water contents at shorter intervals without heating them first. When rinsing cold, the water contents are exchanged without heating.

1. 1. Drinking water tapping by the consumer ends, the first heat exchangers 6 are at temperature.
2. 2. A command from the flushing device control module 42 opens the flushing valve 26 of the flushing device 24.
3. 3. A command from the higher-level control prohibits the heat transfer medium pumps 36 of the first heat exchanger 6 from starting despite a volume flow that flows over the devices due to the flushing.
4. 4. By opening the flushing valve 26, cold fresh water inevitably flows through the first line 4 via the first heat exchanger 6 and the second line 10 into the flushing device 24 and flushes out the hygienically questionable water.
5. 5. After a certain volume, which is detected by a sensor of the higher-level control, the command comes to close the flushing device 24 and continue regular operation.
6. 6. The third heat exchangers 14 are excluded from this function in order to ensure the reheating of the circulation volume flow. The flushing valve 26 for this cold flushing is therefore preferably arranged upstream of the third heat exchanger 14 in the flow direction.

Control logic for flushing heat exchanger

In the flushing heat exchanger control logic, the higher-level control can be set so that flushing takes place while the first heat exchanger 6 is supplied with "cold" flow medium (flow direction A).

Flushing the circulation line

If the consumer is not being used, it may make sense to also replace the water in the circulation line 12. For this purpose, a flushing valve 26 of the flushing device 24 is connected to the supply line, so that the flushing device can, for example, initiate a time-controlled water change every 72 hours.

So that the hot water temperatures in the downstream pipe network on the consumer side do not collapse, the flushing device 24 should, if possible, flush a constant volume flow from the system, with the incoming cold water being constantly reheated directly by the first heat exchangers 6.

Recording of rinsing and thermal disinfection

After each thermal disinfection or rinsing run, the relevant data should be written to a data logger for later proof of correct operation. These data are preferably: duration of disinfection/rinsing, start! Stop of disinfection/rinsing, date/time of disinfection/rinsing, temperature reached during disinfection/rinsing or switching of the changeover valve, rinsing volume.

Reference symbol list

2

Connection to a fresh water supply

4

first line

6

first heat exchanger

8th

Outlet of the first heat exchanger

10

second line

12

Circulation line

14

third heat exchanger

16

Circulation pump

18

Outlet of the third heat exchanger

20

supply line

22

consumer

24

Flushing device

26

Flush valve

28

free exercise

30

first flow line

32A; 32B

Main buffer memory

34

second supply line

36

Heat transfer medium pump

38

Control unit

40

Temperature sensor

42

Flushing device control module

44

third supply line

46

central heating system

48

Secondary buffer storage

50

first return line

52

WRG supply line

54

second heat exchanger

56

WRG return line

58

connecting line

60

second return line

62

third return line

64

third line

66

changeover valve

P

primary heat transfer medium

S

secondary heat transfer medium

Claims (15)

Hot water supply system, comprising a connection to a fresh water supply (2) for letting cold drinking water into the hot water supply system, a first heat exchanger (6) for transferring heat from a primary heat transfer medium (P) to the cold drinking water, a supply line (4) carrying the heated drinking water, to which at least one consumer (22) is connected, a second heat exchanger (54) for heat recovery by heat transfer of heat from a secondary heat transfer medium (S) to the primary heat transfer medium (P), which has cooled down by heat transfer to the drinking water, and a heat transfer medium pump (36) which transfers flow energy to the primary heat transfer medium (P). Hot water supply system according to claim 1, characterized in that the primary heat transfer medium (P) consists largely or completely of water and can preferably be heated to a temperature by a central heating system (46) of the hot water supply system, which is preferably at least 60 ° C or greater than 60 °C is. Hot water supply system according to claim 1 or 2, characterized in that the secondary heat transfer medium (S) is a fluid containing waste heat and/or wastewater or gray water, the temperature of the secondary heat transfer medium (S) preferably being at least 35°C and less than 60°C . Hot water supply system according to one of claims 1 to 3, characterized by at least one buffer storage (32A, 32B, 48) for the primary heat transfer medium (P). Hot water supply system according to one of the preceding claims, characterized by at least one main buffer store (32A, 32B) connected to the first heat exchanger (6), which communicates with a central heating system (46) of the hot water supply system, to keep a portion of the primary heat transfer medium (P) at a temperature of at least 60 ° C or higher to be ready, at least one secondary buffer store (48) connected to the second heat exchanger (54), which holds another part of the primary heat transfer medium (P) for heat recovery, a connecting line (58) between the main buffer store (32A, 32B) and the secondary buffer store (48) for transferring primary heat transfer medium heated by heat recovery from the secondary buffer store (48) into the main buffer store (32A, 32B), a first return line (50) connecting the first heat exchanger (6) to the secondary buffer storage (48) for returning primary heat transfer medium cooled by heat release to the drinking water from the main buffer storage (32A, 32B) into the secondary buffer storage (48), and preferably a switching valve (66) provided between the first heat exchanger (6) and the buffer stores (32A, 32B, 48) for switching between an inlet to the first heat exchanger (6) from the secondary buffer store (48) and an inlet to the first Heat exchanger (6) from the main buffer tank (32A, 32B). Hot water supply system according to one of the preceding claims, characterized by a third heat exchanger (14) for heating the drinking water, which is connected to the supply line (20) in parallel or in series with the first heat exchanger (6). Hot water supply system according to one of the preceding claims, characterized by a flushing device (24) assigned to the circulation line (12) or the supply line (20) with a flushing valve (26) for draining drinking water from the hot water supply system. Hot water supply system according to one of the preceding claims, characterized by a water temperature sensor (40) which is assigned to a drinking water outlet (8) of the first heat exchanger (6), and a control unit (38) for regulating the water temperature of the drinking water heated by the first heat exchanger (6). by controlling the heat transfer medium pump (36). Hot water supply system according to claim 8, characterized in that the control unit (38) controls the heat transfer medium pump (36) in such a way that the temperature measured by the water temperature sensor (40) corresponds to an adjustable setpoint. Hot water supply system according to claim 9, characterized in that the control unit (38) is set such that the setpoint corresponds to a reduced hot water temperature value and at least once per day for a predetermined time or for a predetermined flow rate to a temperature value of at least 60 ° C or greater than 60°C is raised. Hot water supply system according to claim 10, characterized in that the control unit (38) controls the switching valve (66) so that for the predetermined time or the predetermined flow rate the inlet to the first heat exchanger (6) from the main buffer storage (32A, 32B) is released and before and after the inlet to the first heat exchanger (6) from the secondary buffer storage (48) is released. Hot water supply system according to one of the preceding claims, characterized by a flushing device control module (42) for initiating a drinking water change by controlling the flushing valve (26) of the flushing device (24), the control unit (38) preferably being set up in such a way that the heat transfer medium pump ( 36) is put out of operation for the duration of the open position of the flushing valve (26). Hot water supply system according to one of the preceding claims, characterized in that the setpoint is set variably and in particular depends on a) a flow temperature of the first heat transfer medium from the secondary buffer storage (48) and / or a domestic hot water consumption and / or b) on a return temperature of the first Heat transfer medium to the secondary buffer storage (48) and/or domestic hot water consumption. Hot water supply system according to one of the preceding claims, characterized by a disinfection operating mode implemented in the control unit (38), in which the drinking water is heated to a temperature of over 60 ° C and drained from the hot water supply system by activating the flushing valve (26). Hot water supply system according to one of the preceding claims, characterized by a data logger for logging the duration, start, stop, date and / or time of a drinking water change by the flushing device and / or an activation of the disinfection operating mode and / or a drained from the hot water supply system during a water change Rinsing volume and/or the water temperature measured by a temperature sensor.

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