Hot water supply system with heat recovery

Abstract

To specify a hot water supply system that meets the normative conditions and at least partially reduces or eliminates the aforementioned risks, a hot water supply system may include a connection to a fresh water supply for introducing cold drinking water into the hot water supply system, a first heat exchanger for transferring heat from a primary heat transfer medium to the cold 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 transferring heat from a secondary heat transfer medium to the primary heat transfer medium which has cooled down by releasing heat to the drinking water, and a heat transfer medium pump that transfers flow energy to the primary heat transfer medium.

Description

[0001] The present invention relates to a hot water supply system with heat recovery.

[0002] In heat recovery (HR), waste heat from an upstream process is captured and fed back into the system at another point, thereby saving energy costs. For efficient HR, the medium to which the waste heat from the upstream process is transferred should be as cold as possible. This ensures maximum cooling of the medium releasing the waste heat, allowing it to then absorb larger amounts of energy from the upstream process. Examples of upstream processes include: cold storage facilities; industrial processes; general processes that generate wastewater; server room cooling; and industrial freezers.

[0003] Since heat transfer can only occur from a warmer to a colder medium, it is efficient to keep the colder medium as cool as possible. This is why operators and planners of hot water supply systems with heat recovery now prefer to transfer the heat from the heat recovery unit to the cold water just before the main domestic hot water heater in the form of a preheating stage. There, the cold water is preheated to a certain degree. This has the positive effect that the main domestic hot water heater can be smaller, because the water no longer needs to be heated from approximately 10°C to approximately 60°C, but, for example, only from approximately 35°C to approximately 60°C.

[0004] Despite this great potential, hot water supply systems with heat recovery also involve risks and regulatory requirements, such as: According to DVGW W 511, preheating stages with a volume >400 l must be heated to >60°C at least daily; preheating stages must be structurally designed to allow for daily heating to >60°C; preheating stages create an additional pressure loss in the drinking water line; after the preheating stage, the hot water is in a critical temperature range around 40°C and is therefore hygienically questionable; during periods of non-use, certain dead legs with stagnant water develop.

[0005] A hot water supply system with the features of the preamble of claim 1 is known from document DE 10 2019 000 430 A1.

[0006] One object of the present invention is to provide a hot water supply system that meets the normative requirements and at least partially reduces or eliminates the aforementioned risks.

[0007] To solve this problem, the present invention provides a hot water supply system with the features of claim 1.

[0008] 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 generally a connection to the public water supply network, whereby, for the purposes of the present invention, a connection to the public water supply network is defined in particular as a section of a building's drinking and service water system that communicates directly with the building's water meter but does not yet have a branch leading to one or more supply lines. This connection typically corresponds to a point of transition from drinking water to domestic water as defined in 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 hot drinking and service water or comprises at least such a drinking and service water system.

[0009] To heat the cold drinking water, the hot water supply system includes 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 fluidically separated. For this purpose, the first heat exchanger has, for example, a thermally permeable and fluid-impermeable partition. This separation prevents contamination of the drinking water by the primary heat transfer medium. The first heat exchanger can be designed, in particular, as a plate heat exchanger.

[0010] The heated drinking water is conveyed through a supply line of the hot water supply system to at least one consumer connected to the supply line. The connection of consumers to the supply line can be implemented in various ways. For example, several consumers can be connected to the supply line via a flow divider. The connection can also be achieved via a T-junction or a ring main. At the consumer end, the supply line can be configured, at least in sections, as a riser and / or as a floor-level supply line. A consumer within the meaning of the present invention can be, in particular, any hot water outlet in a building, e.g., a shower or a washbasin.The supply line can be connected to a circulation line for returning potable water that cools down in the supply line to the first heat exchanger, wherein the circulation line communicates with a circulation pump to generate a preferably constant circulation flow rate. The circulation line typically has a nominal diameter that is at least one nominal diameter step smaller than that of the supply line.

[0011] A heat transfer pump is provided to transfer flow energy to the primary heat transfer medium. The primary heat transfer medium is circulated through the first heat exchanger by the heat transfer pump and corresponding pipes.

[0012] For heat recovery, the hot water supply system has a second heat exchanger. This is designed to transfer heat from a secondary heat transfer medium to the primary heat transfer medium, which has cooled down by releasing heat into the drinking water. The second heat exchanger can be a plate heat exchanger or a heat pump.

[0013] The heat from the heat recovery system (HRS) is therefore first transferred to the primary heat transfer medium and not directly to the potable water. This means the heat from the HRS is returned to the system at a point that makes it easier to reduce or eliminate the risk of the potable water stagnating at a hygienically unsafe temperature of, for example, approximately 40°C. In particular, the primary heat transfer medium, preheated by the HRS, can be further heated to at least 60°C before being fed to the first heat exchanger to heat the cold potable water. This allows the cold potable water to be heated to a specific target temperature without a preheating stage. This target temperature is preferably adjustable and is most preferably in the range of 50°C to 60°C.

[0014] According to a preferred embodiment of the present invention, the primary heat transfer medium consists mostly or entirely 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 includes 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 primary energy-utilizing heating system.

[0015] According to a further preferred embodiment of the present invention, the secondary heat transfer medium is a fluid containing waste heat and / or wastewater or greywater, wherein the temperature of the secondary heat transfer medium is preferably 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 ambient air. Particularly when using a heat pump, this does not necessarily have to be heat recovery in the conventional sense. For the purposes of this application, the transfer of heat from the environment is also preferably to be subsumed under "heat recovery".

[0016] According to a further preferred embodiment of the present invention, the hot water supply system comprises at least one buffer storage tank for the primary heat transfer medium. The buffer storage tank is typically dimensioned and designed such that thermal stratification of the primary heat transfer medium occurs automatically within the tank. Generally, the primary heat transfer medium from the upper part of the buffer storage tank is used to heat the domestic hot water. The primary heat transfer medium from the middle and / or lower part of the buffer storage tank 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, causing it to rise to the upper, warmer part of the buffer storage tank.

[0017] According to the invention, the hot water supply system comprises at least one main buffer storage tank connected to the first heat exchanger, which communicates with a central heating system of the hot water supply system in order to keep a portion of the primary heat transfer medium at a temperature of at least 60°C or higher, at least one secondary buffer storage tank connected to the second heat exchanger, which holds another portion of the primary heat transfer medium for heat recovery, a connecting line between the main buffer storage tank and the secondary buffer storage tank for transferring primary heat transfer medium heated by heat recovery from the secondary buffer storage tank to the main buffer storage tank, and a first return line connecting the first heat exchanger to the secondary buffer storage tank for returning primary heat transfer medium cooled by heat transfer to the drinking water from the main buffer storage tank to the secondary buffer storage tank.The primary heat transfer medium passes through different stages, typically heating up from a lowest temperature level in the second heat exchanger and cooling down from a highest temperature level in the first heat exchanger. Between these two stages, the primary heat transfer medium is temporarily stored in buffer storage tanks on its way from the second to the first heat exchanger. The heating system then heats at least part of the primary heat transfer medium stored in the main buffer storage tank to a target temperature for heating the domestic hot water.

[0018] According to a further preferred embodiment of the present invention, the hot water supply system comprises a diverter valve located between the first heat exchanger and the buffer storage tanks for switching between an inlet to the first heat exchanger from the secondary buffer storage tank and an inlet to the first heat exchanger from the main buffer storage tank. In this preferred embodiment, the cold drinking water is heated to a preheated temperature level by the recovered heat from the heat recovery system when the inlet to the first heat exchanger from the secondary buffer storage tank is activated. Typically, the temperature level of the heat recovery system, and thus also the temperature level of the secondary buffer storage tank, is lower than the aforementioned target temperature of between 50°C and 60°C, so that the drinking water temperature at the preheated temperature level is below this range.The temperature of the preheated temperature level is typically 35°C, 40°C, or 45°C, within a tolerance of ± 2.5°C. The lower temperature of the preheated temperature level also results in a lower return temperature of the primary heat transfer medium, thus increasing the efficiency of the heat recovery system. However, this lower temperature level also fulfills the aforementioned regulatory requirement that preheating stages with a volume greater than 400 liters must be heated to >60°C at least daily. To meet this requirement, the diverter valve can be switched at least once a day to activate the flow from the main buffer tank to the first heat exchanger.

[0019] According to a further preferred embodiment 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 by the third heat exchanger is provided by the primary heat transfer medium and preferably from the main buffer storage tank. This allows for cascade heating of the drinking water, with the cascade being triggered by the consumer drawing hot water.Due to hot water draw-off, cold drinking water flows into the system via the connection to the fresh water supply and is heated in the first stage of the cascade by the first heat exchanger to a temperature, for example, in the range of 50-60°C. In a series connection, the drinking water heated by the first heat exchanger is then further heated by the third heat exchanger in a second stage of the cascade to a temperature of, for example, at least 60°C and then supplied to the consumer. In a parallel connection, the drinking water heated by the first heat exchanger is combined with the drinking water heated by the third heat exchanger in the second stage of the cascade and then supplied to the consumer. Preferably, the supply lines between the buffer storage tanks and the first and third heat exchangers are no longer than 10 m, 15 m, 20 m, or 25 m.

[0020] According to a further preferred embodiment of the present invention, the hot water supply system comprises a circulation line and a circulation pump associated with the circulation line for returning drinking water that cools down in the supply line to the third heat exchanger. Heat losses of the hot drinking water in the pipes can thus be compensated for by the third heat exchanger. This ensures that hot drinking water at the desired temperature, typically 60°C, is always available, even when no water is being drawn. The circulation flow is generally continuous, thus reliably preventing stagnation of drinking water. A circulation line typically has a smaller diameter than the upstream supply line leading to the consumer.Typically, the third heat exchanger operates at a higher temperature level than the first heat exchanger, since the inlet of the third heat exchanger is supplied with either – in the case of series connection – the drinking water heated by the first heat exchanger or – in the case of parallel connection – the warm drinking water returned via the circulation line, whereas the inlet of the first heat exchanger is supplied with the fresh cold drinking water from the fresh water supply system.

[0021] According to a further preferred embodiment 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 tank. Since the third heat exchanger typically operates at a higher temperature level, the return temperature of the primary heat transfer medium coming from the third heat exchanger is only slightly reduced, so that it is not suitable for heat recovery and can be returned directly to the main buffer storage tank.

[0022] According to a further preferred embodiment of the present invention, the hot water supply system comprises a flushing device associated with the circulation line or the supply line, including a flushing valve for draining drinking water from the hot water supply system. This ensures the drinking water quality at all times by allowing sections of pipe containing stagnant water due to prolonged periods of non-use to be flushed by opening the flushing valve. The flushed-out stagnant water is replaced with fresh, cold drinking water and heated by the first and / or the third heat exchanger. Typically, the flushing valve is located downstream of the first and / or the third heat exchanger in the direction of flow. The flushing device can include multiple flushing valves.

[0023] According to a further preferred embodiment of the present invention, the hot water supply system comprises at least one water temperature sensor 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.

[0024] According to a further preferred embodiment of the present invention, the control unit is configured to control the heat transfer medium pump in such a way that the temperature measured by the water temperature sensor corresponds to a setpoint, wherein the setpoint is adjustable.

[0025] According to a further preferred embodiment of the present invention, the control unit is configured such that the setpoint corresponds to a reduced hot water temperature and is raised to a temperature of at least 60°C or higher at least once a day for a predetermined time or flow rate. A reduced water temperature is understood here to be, in particular, a value that is at least 1°C, preferably at least 3°C, 5°C, 10°C, or 15°C lower than 60°C. The frequency and duration of the temperature increase are preferably variable or adjustable. The duration of the increase can, in particular, depend on consumption or the amount of water flushed out, i.e., it can, for example, only end when a certain minimum amount of hot water has been consumed by the user or flushed through the flushing device after the temperature increase.The hot water supply system typically includes a flow meter to determine the flow rate.

[0026] Lowering the temperature level of the first stage of the cascade allows for a lower return temperature of the primary heat transfer medium supplied to the secondary buffer storage tank, thus increasing the efficiency of the heat recovery system. This reduction in the temperature level of the first stage of the cascade is preferably achieved using the previously described series connection of the first and third heat exchangers, so that the potable water in the second stage of the cascade is heated from the reduced temperature level to the desired temperature for hot water, typically 60°C, before being supplied to the consumer.

[0027] According to a further preferred embodiment of the present invention, the control unit controls the diverter valve such that, for a predetermined time or until a predetermined flow rate is reached at the increased temperature, the inlet to the first heat exchanger from the main buffer storage tank is enabled, and before and after this period, the inlet to the first heat exchanger from the secondary buffer storage tank is enabled. In other words, in this preferred embodiment, the heat for the reduced water temperature is supplied from the secondary buffer storage tank, and the heat for the temperature value of at least 60°C or greater than 60°C is supplied from the main buffer storage tank.Alternatively, the heat for both the reduced water temperature and the temperature value of at least 60°C or greater than 60°C can be provided from the main buffer storage tank 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 reduced water temperature from a lower thermal layer and / or by ensuring that the primary heat transfer medium cools down for a shorter time against the cold drinking water.

[0028] According to a further preferred embodiment of the present invention, the hot water supply system comprises a flushing device control module for initiating a drinking water exchange by actuating the flushing device's flushing valve. During such a drinking water exchange, typically at least the entire volume of water between the flushing valve and the first heat exchanger is replaced with fresh drinking water. The criteria and / or the interval time and / or the times at which a drinking water exchange is initiated are preferably programmable into the flushing device control module.The flushing system control module can be part of the control unit or a higher-level control system, in particular a functional software module of the control unit or the higher-level control system, or it can be designed as a standalone component, preferably adapted for communication with the control unit or the higher-level control system. As a standalone component, it can be housed in a common enclosure with the control unit or the higher-level control system, or separately located elsewhere in the system.

[0029] The flushing system control module can be programmed with a time-controlled flushing mode, in which the flushing valve is opened at specific times and / or intervals to exchange the drinking water. For this purpose, the flushing system control module can have a timer that is set, for example, to 72 hours.

[0030] A hot flush mode can be programmed into the flushing system control module. For example, a drinking water exchange can be initiated as soon as the setpoint temperature rises above the reduced value. This allows the water still in the pipes at the reduced temperature to be drained from the system. A stop criterion for the drinking water exchange in hot flush mode can be generated from the water temperature measured by the temperature sensor. This means, for example, that the drinking water exchange can be terminated when the water temperature measured by the temperature sensor reaches a specific higher target temperature after starting from a lower value.

[0031] The flushing device control module can have a WRG flushing mode programmed in which a drinking water exchange is triggered while the diverter valve is set so that the supply to the first heat exchanger from the secondary buffer storage tank is activated.

[0032] In principle, several flushing modes can be programmed into the flushing system's control module. These flushing modes can be implemented to interact with each other. For example, a water change in another mode can reset the timer for the time-controlled mode.

[0033] According to a further preferred embodiment of the present invention, the control unit is configured such that the heat transfer medium pump is deactivated during a cold flush mode of the flushing device control module. To implement the cold flush 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 by the consumer stopping hot water withdrawal. In cold flush mode, the flushing valve is open to replace the potable water between the first and third heat exchangers and within the first heat exchanger with fresh, cold potable water. This prevents the potable water in the area of ​​the first heat exchanger from rising to a hygienically unsafe temperature range after water withdrawal by the consumer.Nevertheless, the position of the flushing valve and the predetermined flow direction ensure that the temperature level of the third heat exchanger, i.e., the second stage of the cascade, remains essentially unaffected. Additionally, a non-return valve can be provided to prevent warm drinking water from flowing back from the second stage of the cascade to the flushing valve. The cold flushing mode can also be triggered without any water consumption. For example, the control unit can activate the heat pump to reach the setpoint temperature of, say, 60°C and then trigger the cold flushing mode. This allows the first heat exchanger to be heated to the setpoint temperature at regular intervals, even without any drinking water being drawn by the consumer.

[0034] According to a further preferred embodiment of the present invention, the setpoint is variably adjusted and, in particular, depends on the supply temperature of the first heat transfer medium from the secondary buffer storage tank and / or the domestic hot water consumption. For example, the setpoint can be set lower than the supply temperature of the first heat transfer medium supplied from the secondary buffer storage tank by a specific temperature difference ΔT. The temperature difference ΔT can be, for example, 5°C or 10°C. The temperature difference can be adjustable depending on the average domestic hot water consumption. For example, the temperature difference can be greater with higher domestic hot water consumption (e.g., 100 l / min) than with lower domestic hot water consumption (e.g., 20 l / min). In the event that the supply temperature should be greater than 60°C, the setpoint is preferably limited to a maximum of 60°C.

[0035] According to a further preferred embodiment of the present invention, the first setpoint is variably adjusted and, in particular, depends on the return temperature of the first heat transfer medium to the secondary buffer storage tank and / or on domestic hot water consumption. The temperature difference ΔT is then generally set so that a maximally low return temperature for the primary heat transfer medium is achieved.

[0036] According to a further preferred embodiment 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 above 60°C and drained from the hot water supply system by actuating the flushing valve. In disinfection operating mode, the setpoint is raised to 60°C or higher, and the diverter valve, if present, is set for a predetermined time or until a predetermined flow rate is reached at the raised temperature, such that the inlet to the first heat exchanger from the main buffer storage tank is enabled. Subsequently, the system can switch back from disinfection operating mode to the previous normal operating mode.For example, the diverter valve can be set again so that the supply to the first heat exchanger from the secondary buffer tank is enabled, and the first setpoint temperature can be lowered again. Preferably, the disinfection operating mode can be automatically interrupted by domestic hot water consumption and then resumed or aborted and postponed. Particularly preferably, one of the flushing modes follows the disinfection operating mode.

[0037] According to a further preferred embodiment of the present invention, the hot water supply system comprises a data logger for recording the duration, start, stop, date, and / or time of a drinking water exchange by the flushing device, and / or the duration, start, stop, date, and / or time of an activation of the disinfection operating mode, and / or the flushing volume drained from the hot water supply system during a water exchange, and / or the water temperature measured by a temperature sensor. The data logger is typically connected to the control unit and the flushing device control module, and / or a higher-level control system.

[0038] Further details and specifics of the present invention will become apparent from the following description of exemplary embodiments in conjunction with the drawing. The drawing shows: Fig. 1 is a schematic representation of a first embodiment, Fig. 2 is a schematic representation of a second embodiment and Fig. 3 is a schematic representation of a third embodiment.

[0039] Figure 1Figure 1 schematically represents a hot water supply system. The individual components of this hot water supply system can be located within a building. The hot water supply system includes a connection 2 to a fresh water supply for the introduction of cold drinking water. Connection 2 is the point of transition from drinking water in a water supply system, as defined by the Drinking Water Ordinance. Connection 2 to the fresh water supply is connected via a first line 4 to four first heat exchangers 6, which are supplied 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, for example, be designed as plate heat exchangers. By passing through the first heat exchangers 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.

[0040] The heated drinking water leaves the first heat exchangers 6 via a second line 10 connected to the outlets 8 of the first heat exchangers 6, which leads 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 pumps the heated drinking water towards the third heat exchangers 14. There, the heated drinking water receives further heat, 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, before being heated by the third heat exchangers 14, the drinking water is already at the warmer first temperature level.

[0041] 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 to provide it with hot drinking water. The supply line 20, together with the circulation line 12, forms a circuit in which the hot drinking water circulates when not in use by the consumer. This circulation, and the associated continuous heat transfer through the third heat exchanger 18, compensates for heat losses of the hot drinking water in the pipes. These heat losses can cause the hot drinking water to cool down, for example, from 60°C to 55°C.

[0042] 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 allows a drinking water exchange to be carried out during a longer period of non-use, whereby the stagnant water is drained from the pipes via the flushing valve 26 and replaced with fresh, cold drinking water from connection 2. The flushing valve 26 is connected to a free outlet 28, which drains into a wastewater pipe.

[0043] The first heat exchangers 6 are connected by a first supply line 30 to two main buffer tanks 32A, 32B, which are filled with the primary heat transfer medium P. A second supply line 34 branches off from the first supply line 30 and connects the third heat exchangers 14 to the two main buffer tanks 32A, 32B. The first supply line 30 is connected to the uppermost section of the main buffer tanks 32A, 32B, i.e., where the primary heat transfer medium P contained therein typically has the highest temperature. The first and second supply lines 30, 34 are preferably as short as possible; for example, a maximum length of 20 m.

[0044] In the area of ​​each first heat exchanger 6 and each third heat exchanger 14, a heat transfer medium pump 36, which transfers flow energy to the primary heat transfer medium P, is assigned to the first supply line 30 and the second supply line 34, respectively. Each of these heat transfer medium pumps 36 is in turn assigned a control unit 38, which is connected to the respective heat transfer medium pump 36 for control purposes. By controlling the heat transfer medium pumps 36, the primary heat transfer medium is pumped through the heat exchangers 6 and 14 to heat the drinking water. 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 to the control unit 38 of the respective heat exchanger 6 and 14 for data transmission.

[0045] The control units 38 are designed to control their associated heat transfer medium pump 36 such that the temperature measured by the temperature sensor 40 at the outlet 8 or 18 of the respective heat exchanger 6 or 14 corresponds to or reaches an adjustable setpoint. As already indicated above, the control units 38 are generally set such that the control units 38 of the first heat exchanger 6 specify a setpoint in a lower temperature range (e.g., in the range of 40°C to 60°C) than the control units 38 of the third heat exchanger 6, which typically specify a setpoint of at least 60°C.In particular, the setpoints specified by the control units 38 of the first heat exchangers 6 can be variably adjusted and may depend, for example, 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 control system, which preferably also includes a flushing device control module 42 for controlling the flushing device 24.

[0046] A third flow line 44 is connected to a lower section of the two main buffer storage tanks 32A, 32B. It communicates with a central heating system 46 of the hot water supply system that uses primary energy in order to heat at least part of the primary heat transfer medium P to a temperature of 60°C or higher.

[0047] In addition to the two main buffer tanks 32A and 32B, the hot water supply system includes a secondary buffer tank 48, which is filled with a portion of the primary heat transfer medium P. This portion is at a lower temperature than the portion contained in the main buffer tanks 32A and 32B because the primary heat transfer medium P, cooled by the cold drinking water in the first heat exchangers 6, is returned to the lower section of the secondary buffer tank 48 via a first return line 50. A heat recovery supply line 52 is connected to the lower section of the secondary buffer tank 48 and communicates with a second heat exchanger 54 for heat recovery. Heat is recovered through heat transfer from a secondary heat transfer medium S to the primary heat transfer medium P, which has been cooled by releasing heat to the drinking water.The secondary heat transfer medium S is typically a fluid containing waste heat and / or wastewater or greywater. This waste heat can originate from a cooling process and / or an industrial process.

[0048] The primary heat transfer medium P, heated via the second heat exchanger 54 by heat recovery, is returned to an upper section of the secondary buffer storage tank 48 via a heat recovery return line 56. From there, it is routed through a connecting line 58 to the lower sections of the main buffer storage tanks 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, before finally being supplied again via the first or second supply line 30, 34 to the first or third heat exchangers 6, 14 for heating the domestic hot water.

[0049] Since the third heat exchangers 14 are already supplied with a higher potable water temperature due to the first heating stage by the first heat exchangers 6, less heat needs to be transferred from the primary heat transfer medium to the potable water in the third heat exchangers 14 to reach the desired temperature for hot potable water, typically 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 supply temperature of the primary heat transfer medium P leading to the third heat exchangers 14. Therefore, the return flow from the third heat exchangers 14 is not suitable for heat recovery and is routed directly back to the main buffer tanks 32A and 32B via a second return line 60.

[0050] The second return line 60 carries the primary heat transfer medium P from the third heat exchangers 14 back to the lower sections of the main buffer storage tanks 32A, 32B. There it mixes with warmer or colder primary heat transfer medium P and / or rises and is further heated by the central heating system 46, in order to finally be supplied again via the first or second supply line 30, 34 to the first or third heat exchangers 6, 14 for heating the domestic hot water.

[0051] A third return line 62 connects the central heating system 46 with the upper areas of the main buffer storage tanks 32A, 32B.

[0052] The in Fig. 2 The depicted hot water supply system is, with one difference, identical to the hot water supply system from Fig. 1 constructed. The difference lies in the fact that the second line 10 in the hot water supply system is after Fig. 2not like the hot water supply system after Fig. 1 The drinking water does not flow into the circulation line 12 with the circulation pump 16, but rather into the supply line 20. At the outlet, the drinking water heated by the first heat exchangers 6 mixes with the drinking water heated by the third heat exchangers 14 and is conveyed to the consumer 22 via the supply line 20. The drinking water heated by the first heat exchangers 6 is therefore not heated as in the first heat exchanger 6. Figure 1 The water is routed through the third heat exchanger 14 before being directed to the consumer 22. The first heat exchanger 6 and the third heat exchanger 14 are thus connected in parallel to the supply line 20. This is the same as in the hot water supply system according to... Figure 1 When the consumer 22 is not in use, the drinking water from the supply line 20 is returned to the third heat exchanger 14 via the circulation line 12.

[0053] The in Fig. 3The depicted hot water supply system is, with one difference, identical to the hot water supply system from Fig. 1 constructed. The difference lies in the fact that in the hot water supply system after Fig. 3A third line 64 is connected between the connecting line 58 and the first supply line 30. The connection of the third line 64 to the first supply line 30 is realized via a diverter valve 66 designed as a 3-way valve, which is located downstream of the branch of the second supply line 34 in the flow direction. The higher-level control system is connected to the diverter valve 66 and can position it so that the first heat exchangers 6 are supplied with primary heat transfer medium P from the secondary buffer storage tank 48, or so that the first heat exchangers 6 are supplied with primary heat transfer medium P from the main buffer storage tanks 32A and 32B. The third heat exchangers 14, on the other hand, are supplied independently of the position of the diverter valve 66 and as in the hot water supply system according to Fig. 1 or Fig. 2 supplied by primary heat transfer medium P from the main buffer storage tanks 32A, 32B.

[0054] The following section discusses some exemplary features and control logics for the operation of the hot water supply systems described in conjunction with the drawing. A heating medium is to be used as the primary heat transfer medium P.

[0055] The hot water supply systems made of 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 exchangers 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 minute heat withdrawals from the consumer 22, which are not covered by the first heat exchangers 6, are heated at the latest in the third heat exchangers 14. However, this advantage generates an additional pressure loss compared to the parallel connection according to [reference]. Fig. 2 .

[0056] In the hot water supply system according to 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 mixed temperature. This mixing can cause a brief drop in the desired hot water temperature if, for example, the supply line 30 is not yet at temperature. However, this temperature drop is negligible if the circulation flow rate is sufficiently high. How a dispensing valve works (example shown in Fig. 1):

[0057] 1. Consumer 22 uses a larger quantity of hot water, so cold water at approximately 10°C flows from the first line 4 through the first heat exchanger 6 and is heated to a higher temperature, e.g., 50-60°C. 2. Since it cannot be guaranteed that the supply line 30 was already warm before consumer 22 was used, the heated hot water is fed into the circulation line 12 via the second line 10 for further heating. 3. The heating medium, which has cooled considerably due to the heating of the drinking water (e.g., 35°C or lower), is routed via the first return line 50 to the secondary buffer tank 48. 4. The second heat exchanger 54 can then draw the cold return heating medium from the "cold" secondary buffer storage tank 48 in order to cool the heat from the upstream processes (e.g., 40°C or higher). 5.The heating medium, heated by the heat recovery system, rises in the secondary buffer tank 48 and, when the first heat exchangers 6 are operating, is drawn from the secondary buffer tank 48 into the main buffer tanks 32A and 32B by the heat transfer medium pumps 36 of the first heat exchangers 6. There, it is either drawn in by the central heating system 46 or mixes in the main buffer tanks 32A and 32B to a higher temperature, which can then be used again for domestic hot water preparation. How a circulation system works (example shown in Fig. 1):

[0058] 1. When consumer 22 is not in use, the domestic hot water flows through the circulation line 12 into the third heat exchangers 14 to reheat the circulating flow. This occurs at a higher temperature than in the previously described case. The returning circulating water, for example at 55°C, flows into the third heat exchangers 14 and is reheated to approximately 60°C. The heated water then flows back to consumer 22 via the supply line 20. 2. Since the circulating flow is constant, the second supply line 34 is permanently at temperature. Because the circulating water, which cools the heating medium, has a temperature of 55°C, the heating medium can only cool down minimally to this level. 3.The slightly cooled heating medium (around 55°C) flows through the second return line 60 into the main buffer storage tanks 32A and 32B, where it stratifies into the appropriate temperature zone. This can then be reused for domestic hot water production by reheating the central heating system 46. 4. To ensure the long dead legs remain hygienically clean during periods of non-use, a flushing device 24 is provided downstream of the first and third heat exchangers 6 and 14 in the direction of flow. When this device 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

[0059] To achieve even more efficient operation of the second heat exchanger 54 and to further cool the return temperature of the first heat exchanger 6 to the secondary buffer tank 48, the setpoint temperature of the first heat exchanger 6 can be lowered to, for example, 50°C in combination with flushing measures via the higher-level control system. Lowering the setpoint temperature of the first heat exchanger 6 to a minimum of 50°C results in lower return temperatures, as the heating medium does not have to heat the hot water as much and can cool down from it for a longer period. A high supply temperature is also advantageous with this configuration, as it results in a comparatively cooler return temperature compared to a "colder" supply temperature.

[0060] With this more significantly cooled heating medium, the second heat exchanger 54 can again transfer more energy to the heating medium and the secondary buffer storage tank 48.

[0061] This special variant is subject to conditions that were described at the beginning in connection with a preheating stage. Therefore, in this special solution, the first heat exchangers 6 are heated to >60°C daily. In addition, this special variant implements forced flushing of the second line 10 via the flushing device 24, thus guaranteeing a water exchange at least every 72 hours through the first heat exchangers 6. Functioning of the switching valve 66 (explained using Fig. 3 as an example)

[0062] The installation variant according to Fig. 3 It works on the drinking water side in the same way as the installation variant according to Fig. 1 Since this has already been described, only the differences will be discussed below.

[0063] In principle, switching the diverter valve 66 only changes the temperature level of the heating medium that is supplied to the first heat exchangers 6.

[0064] The third heat exchangers 14 remain excluded from the function of the diverter valve 66 and operate independently of the first heat exchangers 6. The diverter valve 66 ensures that the system meets the requirements of the DVGW (German Technical and Scientific Association for Gas and Water) worksheet by switching daily between the secondary buffer tank 48 and the main buffer tanks 32A, 32B. This allows the first heat exchangers 6 to be supplied daily with a heating medium > 60°C from the main buffer tanks 32A, 32B. When the diverter valve 66 switches towards the secondary buffer tank 48, the potable 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.Using this logic, the control system regulates the first heat exchangers 6 so that the setpoint assumes a specific ratio to the flow temperature of the secondary buffer storage tank 48. The difference between the desired temperature for hot drinking water of approximately 60°C and the actual hot water temperature set according to the setpoint is ensured by the reheating of the third heat exchangers 14. Function of the dispensing process at the changeover valve 66 towards the secondary buffer tank 48

[0065] 1. The diverter valve 66 is positioned so that the first heat exchangers 6 are supplied with heating medium from the secondary buffer tank 48. The flow direction corresponding to this position is referred to in the following text as "flow direction A" or "flow direction A". 2. The heating medium, cooled by the heating of the domestic hot water, is routed from the first heat exchangers 6 via the first return line 30 into the secondary buffer tank 48. 3. The second heat exchanger 54 can draw the cold return water from the "cold" secondary buffer tank 48 to cool the heat from the upstream processes, e.g., to 40°C or higher. 4. Via flow direction A, the waste heat from the upstream processes is then completely drawn back into the first heat exchangers 6 and used for preheating the domestic hot water. Function of the dispensing process at diverter valve 66 towards main buffer tank 32A, 32B

[0066] Due to the requirement to heat a preheating stage daily, the diverter valve 66 is switched daily towards the main buffer storage tank 32A, 32B. The flow direction corresponding to this position is referred to in the following text as "flow direction B". 1. The higher-level control system sends a signal or impulse to the diverter valve 66, causing it to change the position of its internal ball. This closes flow direction A and opens flow direction B. 2. The first heat exchangers 6 now draw the high-temperature heating water from the main buffer tanks 32A and 32B (flow direction B) and use it to preheat the cold domestic hot water. 3. The second heat exchanger 54 draws the cold return water from the "cold" secondary buffer tank 48 to cool the heat from the upstream processes, e.g., 40°C or higher. 4. Since the flow direction A is blocked, the heating medium heated by the heat recovery system flows into the secondary buffer storage tank 48 and, in the case of load of the first heat exchangers 6, is drawn from the secondary buffer storage tank 48 into the main buffer storage tanks 32A, 32B by the heat transfer medium pumps 36.There, it is either drawn in by the central heating system 46 or mixed in the main buffer storage tank 32A, 32B to a higher temperature, which can then be used again for domestic hot water preparation. 5. After a defined time or volume, another impulse is triggered and the diverter valve 66 closes flow direction B and opens flow direction A. Control logic installation variant according to Fig. 1:

[0067] In the special variant, the first heat exchangers 6 operate with reduced hot water temperatures throughout the day, e.g., 50°C. To ensure correct operation according to standards, the first heat exchangers 6 must be raised to a hot water temperature of 60°C at least once a day. The frequency and duration of this heating cycle are variably adjustable via the higher-level control system.

[0068] To implement this in a hygienically sound manner, the following rule logic is proposed: 1. The first heat exchangers 6 operate normally with a reduced hot water temperature, e.g., 50°C. 2. A higher-level command is sent to the control units 38 of the first heat exchangers 6 to raise the hot water temperature (setpoint) for a defined period. 3. Since the first heat exchangers 6 have access to the "hot" flow from the main buffer storage tanks 32A and 32B, raising the hot water temperature is possible without further switching commands to the central heating system 46 or other components. 4. After the defined period 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:

[0069] The target temperature after the first heat exchangers 6 in the second line 10 depends significantly on the available temperature level from the heat recovery system. The temperature can be raised to this level by the first heat exchangers 6 in flow path A. However, such a large increase is not advisable, as it results in very high flow rates for the heating medium and reduces the cooling of the heating medium. Therefore, it is beneficial to maintain a certain temperature difference between the flow temperature of the secondary buffer tank 48 and the setpoint temperature of the first heat exchangers 6.

[0070] The flow temperature of the secondary buffer tank 48 can vary considerably due to fluctuating temperature levels in the heat recovery system, making it difficult to define a constant temperature as the setpoint. Therefore, it is proposed to make the setpoint dependent on the flow temperature in flow direction A. For example: Setpoint = (Flow temperature in flow direction A) - X, where X = 5°C or X = 10°C. A flow rate dependency is also conceivable: For example, the value for X could be higher if a high hot water demand is expected and lower if lower hot water consumption is expected. The following pairs of values ​​are given as examples: High hot water demand (100 l / min): Flow temperature 50°C; setpoint 40°C; return temperature 20°C. Low hot water demand (20 l / min): Flow temperature 50°C; setpoint 45°C; return temperature 20°C. To achieve the lowest possible return temperature, a setpoint dependent on the return temperature is also conceivable. Temperature control without consumption

[0071] The higher-level control system can be configured to heat the first heat exchangers 6 to at least 60°C for disinfection without any draw-off by the consumer or flushing by the flushing device. For this purpose, the heat transfer medium pumps 36 are controlled accordingly. The first heat exchangers 6 are heated by the "hot" supply medium and, after a specific waiting period, are flushed with fresh cold water by a command from the higher-level control system. This cold flushing 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 generally in continuous operation to ensure a constant circulation flow. Control logic flush warm

[0072] 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 in a higher-level manner 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, since it was also operated at a low temperature level. Control logic: cold flush

[0073] In addition to routine heating, it is also advisable to replace the water at shorter intervals without preheating it. When flushing with cold water, the water is replaced without heating. 1. Drinking water draw-off by the consumer ends; the first heat exchangers 6 are at temperature. 2. A command from the flushing unit control module 42 opens the flushing valve 26 of the flushing unit 24. 3. A command from the higher-level control unit prevents the heat transfer medium pumps 36 of the first heat exchangers 6 from starting, despite a flow rate passing through the units during flushing. 4. By opening the flushing valve 26, cold fresh water inevitably flows through the first line 4, over the first heat exchangers 6, and through the second line 10 into the flushing unit 24, flushing out the hygienically questionable water. 5. After a certain volume, detected by a sensor of the higher-level control unit, a command is issued to close the flushing unit 24 and resume regular operation. 6. The third heat exchangers 14 remain excluded from this function in order to ensure the reheating of the circulating volume flow.The flushing valve 26 for this cold flushing is therefore preferably arranged upstream of the third heat exchanger 14 in the direction of flow. Control logic flushing WRG

[0074] In the control logic for flushing the heat recovery system, the higher-level control can be set so that flushing takes place during the supply of the first heat exchanger 6 with "cold" supply medium (flow direction A). Flushing the circulation line

[0075] If the consumer is not in use, it may be useful 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 exchange every 72 hours.

[0076] To prevent the hot water temperatures in the downstream pipe network on the consumer side from collapsing, the flushing device 24 should flush a constant volume flow from the system, whereby the incoming cold water is directly and constantly reheated by the first heat exchangers 6. Documenting the rinsing and thermal disinfection processes

[0077] After each thermal disinfection cycle or flushing procedure, the relevant data should be recorded on a data logger for later verification of correct operation. This data preferably includes: duration of disinfection / flushing, start / stop of disinfection / flushing, date / time of disinfection / flushing, temperature reached during disinfection / flushing or switching of the diverter valve, and flushing volume. Reference symbol list

[0078] 2 Connection to a fresh water supply 4 First line 6 First heat exchanger 8 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 Flushing valve 28 Free outlet 30 First flow line 32A; 32B Main buffer tank 34 Second flow line 36 Heat transfer medium pump 38 Control unit 40 Temperature sensor 42 Flushing device control module 44 Third flow line 46 Central heating system 48 Secondary buffer tank 50 First return line 52 Heat recovery flow line 54 Second heat exchanger 56 Heat recovery return line 58 Connecting line 60 Second return line 62 Third return line 64 Third line 66 Diverter valve P Primary heat transfer medium S Secondary heat transfer medium

Claims

1. A hot-water supply system, comprising: a connection to a freshwater supply (2) for admitting 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 (20) carrying the heated drinking water having at least one user (22) connected thereto, a second heat exchanger (54) for heat recovery by heat exchange from heat of a secondary heat transfer medium (S) to the primary heat transfer medium (P) cooled by heat transfer to the drinking water, and a heat transfer medium pump (36) transferring flow energy to the primary heat transfer medium (P); characterized by at least one main buffer storage (32A, 32B) connected to the first heat exchanger (6) and communicating with a central heating installation (46) of the hot-water supply system for holding at least part of the primary heat transfer medium (P) at a temperature of at least equal to 60°C or higher, at least one auxiliary buffer storage (48) connected to the second heat exchanger (54) holding another part of the primary heat transfer medium (P) for heat recovery, a connecting line (58) between the main buffer storage (32A, 32B) and the auxiliary buffer storage (48) for transferring the primary heat transfer medium heated by the heat recovery from the auxiliary buffer storage (48) to the main buffer storage (32A, 32B), and a return line (50) connecting the first heat exchanger (6) to the auxiliary buffer storage (48) for returning the primary heat transfer medium cooled by heat transfer to the drinking water from the main buffer storage (32A, 32B) to the auxiliary buffer storage (48).

2. The hot-water supply system according to claim 1, characterized in that the primary heat transfer medium (P) largely or completely consists of water.

3. The hot-water supply system according to claims 1 or 2, characterized in that the secondary heat transfer medium (S) is a fluid including exhaust heat and / or wastewater or grey water, wherein the temperature of the secondary heat transfer medium (S) is preferably at least 35°C and less than 60°C.

4. The hot-water supply system according to anyone of the preceding claims, characterized by a switching valve (66) provided between the first heat exchanger (6) and the buffer storages (32A, 32B, 48) for switching between an inlet into the first heat exchanger (6) from the auxiliary buffer storage (48) and an inlet into the first heat exchanger (6) from the main buffer storage (32A, 32B).

5. The hot-water supply system according to anyone of the preceding claims, characterized by a third heat exchanger (14) for heating the drinking water that is connected to the supply line (20) parallel or in line to the first heat exchanger (6).

6. The hot-water supply system according to anyone of the preceding claims, characterized by a flushing unit (24) including a flush valve (26) allocated to the circulation line (12) or the supply line (20) for discharging drinking water from the hot-water supply system.

7. The hot-water supply system according to anyone of the preceding claims, characterized by a water temperature sensor (40), allocated to a drinking water outlet (8) of the first heat exchanger (6), and a controller (38) for controlling the water temperature of the drinking water heated by the first heat exchanger (6) by driving the heat transfer medium pump (36).

8. The hot-water supply system according to claim 7, characterized in that the controller (38) controls the heat transfer medium pump (36) such that the temperature measured by the water temperature sensor (40) complies with an adjustable set value.

9. The hot-water supply system according to claim 8, characterized in that the controller (38) is configured such that the set value corresponds to a lowered value of the water temperature that is increased to a temperature value of at least 60°C or above 60°C at least once a day for a predetermined period or a predetermined flow rate.

10. The hot-water supply system according to claim 9, characterized in that the controller (38) controls the switching valve (66) such that the inflow into the first heat exchanger (6) from the main buffer storage (32A, 32B) is enabled for said predetermined period or said predetermined flow rate, wherein before and after that the inflow into the first heat exchanger (6) from the auxiliary buffer storage (48) is enabled.

11. The hot-water supply system according to anyone of claims 6 to 10, characterized by a flushing unit control module (42) for initiating an exchange of drinking water by driving the flushing valve (26) of the flushing unit (24), wherein the controller (38) preferably is configured such that the heat transfer medium pump (36) is deactivated during the opening time of the flushing valve (26).

12. The hot-water supply system according to anyone of claims 7 to 11, characterized in that the set value is variably adjusted and in particular depends on a) an inlet temperature of the first heat transfer medium from the auxiliary buffer storage (48) and / or a consumption of hot drinking water and / or on b) a return temperature of the first heat transfer medium to the auxiliary buffer storage (48) and / or a consumption of hot drinking water.

13. The hot-water supply system according to anyone of the preceding claims, characterized by a disinfection mode implemented in the controller (38) for heating the drinking water up to a temperature above 60°C and discharging the same from the hot-water supply system by driving the flushing valve (26).

14. The hot-water supply system according to anyone of the preceding claims, characterized by a data logger for logging the duration, start, stop, date and / or time of an exchange of drinking water by the flushing unit and / or an activation of the disinfection mode and / or a flushing amount discharged from the hot-water supply system during an exchange of water and / or the water temperature measured by the temperature sensor.

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