DE112013001269B4 - Method for operating a hot water supply system and hot water supply system for carrying out the method - Google Patents

Abstract

Method for operating a hot water supply system (10a-d'), in which method fresh water is supplied to the hot water supply system (10a-d) via a cold water inlet (17), the supplied fresh water is heated and the hot water produced is supplied to one or more consumers (21) via a hot water pipe (28), wherein the hot water is produced with a predetermined hot water volume (V) and is kept ready for consumption, characterized in that in order to avoid harmful bacteria concentrations in the hot water volume (V), hot water from the hot water volume is replaced by fresh water to a sufficient extent,
wherein, taking into account the amount of hot water drawn by the consumers (21), the entire hot water volume (V) is completely replaced by fresh water in a predetermined period of time, wherein the withdrawal of hot water from the hot water volume (V) by the consumers (21) is monitored, and that additionally hot water is replaced by fresh water if the consumption of hot water is not sufficient to completely replace the entire hot water volume (V) with fresh water in the predetermined period of time,
and wherein, in order to additionally replace hot water with fresh water, hot water is specifically drained from the hot water volume (V).

Description

TECHNICAL AREA

The present invention relates to the field of hot water supply. It relates to a method for operating a hot water supply system according to the preamble of claim 1.

It also concerns a hot water supply system for carrying out the procedure.

STATE OF THE ART

It has been known for decades that under certain conditions bacteria can develop in hot water supply systems that can cause health problems for hot water consumers. These harmful bacteria include so-called legionella. The best-known type of legionella is Legionella pneumophila, which also causes most cases of legionella disease. This legionella multiplies at temperatures between about 25°C and 45°C, with the optimal temperature for growth being around 36°C. At temperatures above 55°C, the legionella begins to die. This process is faster the higher the temperature is above 55°C. In contrast, at temperatures from drinking water to around 15°C (cold water), legionella does not multiply significantly. Under these cold water conditions, the number of legionella bacteria, which are practically always present in the water, is below a level that is a concern for humans.

Legionella is mainly transmitted through the lungs when inhaling fine water droplets contaminated with Legionella, such as those produced when showering. Transmission of Legionella through drinking water or washing with water is, however, rather unlikely.

Various proposals have been made in the past as to how the health risks posed by bacteria, especially Legionella, in hot water supply systems can be reduced, eliminated or completely avoided. These include, for example, thermal, chemical or radiation-based killing of the bacteria.

The publication DE 199 32 436 A1 discloses a hot drinking water pipe system with at least one drinking water heater/storage tank for hot drinking water, a cold drinking water pipe for supplying cold drinking water to the tank, a pipe system which forms a closed circulation circuit with the tank, consisting of an output line connected to the tank with at least one tap for withdrawing hot drinking water and an input line connected to the output line and the tank for returning the hot drinking water not withdrawn to the tank, at least one pump device for circulating the hot drinking water in the circulation circuit and at least one heat exchanger connected to a heating circuit for heating the cold drinking water supplied through the cold drinking water pipe and for maintaining the hot drinking water temperature in the circulation circuit. In an arrangement known as a legionella circuit, the inlet line has at least one branch with at least one branch line, wherein the inlet line is connected in the middle area of the tank just above the heat exchanger, the cold drinking water line is connected below the inlet line in the lower area of the tank, the branch line is connected below the cold drinking water line at the bottom of the tank and a first balancing valve is arranged in the inlet line after the branch in the direction of flow and a second balancing valve is arranged in the branch line. As a result, the circulation temperature in the entire pipe network is kept at such a level that the hot water is largely free of microorganisms, in particular legionella, and that the tank is thermally disinfected of microorganisms at regular intervals over a relatively short period of time by an increased circulation temperature in a largely shortened pipe branch.

The publication EP 1 094 279 A2 describes a storage boiler system having a hot water reservoir, a heating device for heating water, a cold water supply connected to the storage boiler system and supplying it with cold tap water, a tap connected to the reservoir for dispensing hot water from the reservoir. Means are provided in the reservoir for moving water from a lower region of the reservoir to another region of the reservoir.

The publication DE 36 29 532 A1 discloses a device with a water heater, a tap connected to the latter and a shower line with a shower head connected to the latter, wherein a drain valve is provided with which the shower line can be drained.

From the publication DE 38 32 837 A1 A pipe arrangement for hot water supply is known in which a hot water pressure pipe from a water heater to a tap fitting and an outlet line from the tap fitting to a tap point and a cold water line is connected to the tap fitting. A flush valve is provided on the tap fitting, which is on the one hand connected to the cold water line and on the other hand connected to the hot water pressure line and/or the outlet line.

The publication EP 0 296 630 A1 shows a hot water heater with a storage tank through which water flows, with a cold water inlet in the lower tank area and a hot water outlet in the upper tank area, and with a heating element arranged in the storage tank. A cold water outlet is provided in the lower tank area.

The publication WO 02/ 040 906 A1 describes a method for reducing bacterial growth in a water mixer comprising a cold water supply line, a hot water supply line and a mixing chamber. The mixing chamber of the mixer and the consumer line are emptied of hot water or mixed water after consumption, the mixer is supplied with additional cold water to lower the temperature in the mixer and the consumer line, and the supplied cold water is then drained from the mixer and the consumer line. The publication FR 2 876 178 A1 discloses a device with bypass valves for the passage of cold and hot water from hot water and cold water supply lines to cold and hot water chambers. A mixing chamber mixes the cold and hot water. The mixed water is output through a solenoid valve which is opened by an electrical pulse from a 6-volt lithium battery when appropriate information is detected by a detection unit and which is closed by another pulse when a certain condition is reached. A similar solution is known from WO 01/61224 A1 known.

The publication FR 2 891 169 A1 finally discloses an automatic shower flushing system consisting of a solenoid valve installed in a bypass line between the hot water supply line and the mixer unit and the shower head. The valve is opened, for example, twice a day for 10 minutes by a central control or a timer to prevent the accumulation of stagnant water and to reduce or avoid the possibility of spreading Legionnaires' disease.

The publication DE 38 38 476 A1 relates to a method for operating a storage water heater with at least temporary heating of the domestic water to higher temperatures of around 65° - 85°C.

The publication EN 10 2006 032 048 A1 relates to a method for operating a drinking water system with a hot water pipe, which comprises a circulation circuit with a return line. The circulation circuit is closed via a three-way valve located in a first position and arranged in a return line of the circulation circuit, which is opened in a second position to flush the return line, wherein the three-way valve has a drive for actuating the three-way valve, which is controlled by a controller.

The publication EP 2 224 176 A1 relates to a heating device with a basin with a cold water inlet connected to a cold water supply and a hot water outlet. The basin contains a main heating unit and an additional heating unit arranged above the main heating unit. A heat exchanger is arranged between the main heating unit and the additional heating unit. The heat exchanger comprises an inlet connected to the cold water inlet and an outlet connected to the hot water outlet via a main mixing valve located on the hot water outlet. The problem with all known solutions is that they are either limited to the hot water boiler or only to the supply lines to the consumer (particularly to the shower). In addition, these solutions usually require additional fittings and lines, some of which are complex and some of which are not suitable for retrofitting.

In fact, however, large bacterial populations develop not only in certain parts of a hot water system, but in all parts where the right growth conditions, especially growth temperatures, prevail.

DESCRIPTION OF THE INVENTION

It is therefore an object of the invention to provide a hot water system and a method for operating it, with which the health hazard posed by bacteria such as legionella can be safely excluded in a simple manner without chemicals, radiation or temperature increases. These and other objects are achieved by the features of claims 1 and 6.

The subject of the invention is a method for operating a hot water supply system, in which method fresh water is supplied via a cold water inlet of the hot water supply system. supplied, the supplied fresh water is heated and the generated hot water is supplied to one or more consumers via a hot water pipe, whereby the hot water is generated with a predetermined hot water volume and kept ready for consumption. To avoid harmful bacterial concentrations, in particular legionella, in the hot water volume, a sufficient amount of hot water from the hot water volume is replaced by fresh water.

According to the invention, taking into account the amount of hot water taken by the consumers, the entire hot water volume is completely replaced by fresh water in a predetermined period of time. According to the invention, the withdrawal of hot water from the hot water volume by the consumers is monitored and additional hot water is replaced by fresh water if the consumption of hot water is not sufficient to completely replace the entire hot water volume with fresh water in the predetermined period of time.

According to the invention, hot water is specifically drained from the hot water volume to additionally replace hot water with fresh water. One embodiment is characterized in that the hot water is drained from the hot water volume via a valve present at a consumer.

Likewise, the hot water can also be drained from the hot water volume via a specially provided valve.

In particular, the valve for draining the hot water is designed as a controllable valve, whereby the targeted draining of the hot water is controlled by a controller.

Yet another embodiment of the method according to the invention is characterized in that the control system controls the valve in accordance with the time-dependent hot water consumption.

The hot water supply system according to the invention for carrying out the method comprises first means for heating and storing a hot water volume, a cold water inlet which is connected to the first means, and connection means via which one or more hot water consumers can be connected or are connected to the first means. It is characterized in that a controllable valve for the controlled discharge of hot water from the hot water volume is connected to the first means, and that a control is provided which controls the controllable valve.

According to an embodiment of the hot water supply system according to the invention, the controllable valve is assigned to a consumer.

The controllable valve can also be a separate outlet valve. Another embodiment of the hot water supply system according to the invention is characterized in that second means are provided for monitoring the hot water consumption from the hot water volume, and that the second means are connected to the control system.

In particular, the second means comprise a flow meter which is arranged between the cold water inlet and the first means.

A further embodiment is characterized in that the first means comprise a hot water circuit with a circulation pump.

The hot water circuit can have a heat exchanger which is arranged in a hot water tank.

However, it is also conceivable that a hot water tank is part of the hot water circuit.

A further embodiment of the invention is characterized in that the first means comprise a hot water pipe interacting with a hot water storage tank.

The hot water pipe can be connected directly to an outlet of the hot water tank.

However, it is also conceivable that the hot water pipe is connected to the hot water tank via a heat exchanger.

BRIEF EXPLANATION OF THE FIGURES

• 1 ein stark vereinfachtes Schema einer Warmwasserversorgungsanlage gemäß einem Ausführungsbeispiel der Erfindung, mit einem Warmwasserkreislauf, der über einen Wärmetauscher an einen Warmwasserspeicher thermisch angekoppelt ist (Durchlauferhitzer-Prinzip);
• 2 ein stark vereinfachtes Schema einer Warmwasserversorgungsanlage gemäß einem anderen Ausführungsbeispiel der Erfindung, mit einer einfachen Warmwasserleitung, die über einen Wärmetauscher an einen Warmwasserspeicher thermisch angekoppelt ist (Durchlauferhitzer-Prinzip);
• 3 ein stark vereinfachtes Schema einer Warmwasserversorgungsanlage gemäß einem weiteren Ausführungsbeispiel der Erfindung, mit einem Warmwasserkreislauf, in den ein Warmwasserspeicher eingeschaltet ist (Frischwasser-Speichersystem); und
• 4 ein stark vereinfachtes Schema einer Warmwasserversorgungsanlage gemäß einem noch anderen Ausführungsbeispiel der Erfindung, mit einer einfachen Warmwasserleitung, in die ein Warmwasserspeicher eingeschaltet ist (Frischwasser-Speichersystem).

The invention will be explained in more detail below using exemplary embodiments in conjunction with the drawing. They show:

• 1 a highly simplified diagram of a hot water supply system according to an embodiment of the invention, with a hot water circuit which is thermally coupled to a hot water storage tank via a heat exchanger (instantaneous water heater principle);
• 2 a highly simplified scheme of a hot water supply system according to a another embodiment of the invention, with a simple hot water pipe which is thermally coupled to a hot water tank via a heat exchanger (instantaneous water heater principle);
• 3 a highly simplified diagram of a hot water supply system according to a further embodiment of the invention, with a hot water circuit into which a hot water storage tank is connected (fresh water storage system); and
• 4 a highly simplified diagram of a hot water supply system according to yet another embodiment of the invention, with a simple hot water pipe into which a hot water storage tank is connected (fresh water storage system).

WAYS OF IMPLEMENTING THE INVENTION

The present invention is based on the situation that in the drinking, service or fresh hot water sector, under certain conditions (low water consumption, water temperature between 25-45°C), legionella contamination in the drinking hot water is likely to occur, which can lead to illness or even death in the consumer.

• Eine Art von System hat sehr viel Wasserinhalt, da das Brauchwarmwasser in einem Brauchwarmwasser-Speicher gespeichert wird.

In many industrialized countries (such as Switzerland or Germany), to prevent this risk, the water is periodically heated to over 60°C in order to kill the legionella bacteria (see the legionella circuit mentioned at the beginning). However, this heating of the water requires a lot of energy and is not always successful (for example, in pipes or volumes where there is no flow, or when the connected shower heads are not flowing through, etc.). In this context, one can basically distinguish between two types of domestic hot water preparation systems:

• One type of system has a lot of water capacity because the domestic hot water is stored in a domestic hot water tank.

The other type of system has relatively little water content, since the domestic hot water is heated in a continuous flow heater process and the heat energy is stored in a closed circuit (fresh water module technology).

The new solution described below is basically suitable for both systems, but has particularly many advantages in connection with the fresh water module technology.

Legionella bacteria have so far been combated primarily by raising the water temperature to >60°C. Furthermore, the view is taken, particularly in connection with the associated standards, that water should/must always flow. Hot water pipes through which water is not or only rarely flowed should be avoided if possible.

The present invention, on the other hand, is based on a solution approach that does not focus on thermally combating bacteria by continuously or periodically heating the fresh water, but rather on "diluting" the fresh water. Of course, heating can also be combined with this dilution.

During dilution, the aim is to ensure that the contents of a hot water network, including any storage volume contained therein (hereinafter also referred to as hot water volume V), are used up within a period of approx. 8 hours (preferably 4 hours) and that new, fresh water flows into the network or volume (no standing water in the network or volume over a period of >8h or 4h).

For a fresh water storage system with a 5000-litre hot water tank and a network capacity of approx. 200 litres ( 3 , 4 ) approximately 5200 litres of water would have to be consumed or passed through every 4-8 hours.

With a fresh water module technology based on the instantaneous water heater principle ( 1 , 2 ) only the net content of approx. 200 liters needs to be used or passed through every 4-8 hours.

In a temperature range that is ideal for Legionella (approx. 25°C-50°C), the number of Legionella bacteria doubles significantly to a level that is harmful or even fatal to humans.

However, with "dilution" (through guaranteed water consumption) every 4-8 hours - as new research results show - the number of legionella bacteria can never reach a concentration that is harmful to humans. With regard to the consumption situation, a distinction can be made in particular between old and new buildings, residential buildings, hospitals, retirement homes, industrial and commercial buildings, sports facilities, hotels, etc., large and small buildings with one or more supply lines (branch lines) and/or with or without circulation lines (hot water circuit) across all or just some of the taps. Some of these buildings (branch lines, taps) are used regularly and the required dilution can be achieved automatically with professional planning, especially with the instantaneous water heater system.

Other properties have parts of the building that may not be used periodically or for a longer period of time. are needed, for example “cold beds” in holiday homes, conversions in buildings, sports facilities during the holiday season, hotels in the off-season, older existing properties, etc.

In order to save energy on the one hand and to improve hygiene on the other hand (flow through the taps such as shower heads, etc.), the idea of the invention is to work with the forced (controlled) "dilution" of the legionella where necessary and/or sensible by draining the coldest possible water from the hot water volume and simultaneously adding cold fresh water.

• • Berechnen des Inhalts des Warmwassersystems (WarmwasserVolumen) und automatisches, periodisches Ablassen bei den richtigen, wichtigen, oder allen Zapfstellen, bis der Wasserinhalt erneuert und oder die nötige Verdünnung erreicht ist (gesteuert z.B. über die Zeit, oder spezielle Messsysteme);
• • Ablassen über die Zirkulationsleitung (die Zapfstellen werden dabei allerdings nicht durchströmt, dies ist aber einfacher und entspricht auch dem Stand der Technik bei der „Wärmevernichtung“);
• • Das zeitliche oder periodische Ablassen von möglichst kaltem Frischwasser auf der Warmwasserseite kann mittels festen Zeiten (z.B. alle 8 Stunden 2 Minuten öffnen der entsprechenden Entleerungsstellen) oder automatisch mit angepassten Zeitintervallen über Temperatur und/oder Volumenstromerfassung gesteuert werden (Zum Beispiel bei einer Sportanlage bei Duschen während der Saison nie und während den Ferien periodisch).
• • Dabei können in einem Objekt jeweils auch nur einzelne Stränge „verdünnt“ werden, wenn die anderen Stränge durch die Benutzung genügend „Verdünnung“ erfahren.
• • Dadurch, dass die Verdünnung mit kaltem Wasser erfolgen kann, braucht diese Art der Legionellen-Bekämpfung weniger Energie und der Nachteil der Temperaturabkühlung in den durch die Legionellen-Bekämpfung „heißen“ Leitungen (>60°C, welche unter Umständen auf Raumtemperatur auskühlen und somit wieder den kritische Wachstumsbereich für Legionellen durchlaufen welcher zu einer großen Legionellen-Zunahme führt) fällt weg,
• • Werden die Zapfstellen bei der „Verdünnung“ mit einbezogen, gibt es genügend Systeme auf dem Markt mit automatischen Öffnungsmechanismen, welche man einsetzen kann (automatische Wasserspender mit Beendigung, etc. wie Zeit- Geldautomaten bei Duschen auf Campingplätzen oder auf öffentlichen WC das hinhalten der Hand, dann fließt das Wasser und wenn man die Hand wegzieht, schließt die Zapfstelle, Wasserventile, etc.).
• • Die Erfindungsidee ist also die, dass durch „Verdünnung“ die Stellen „verdünnt“ werden, welche gefährdet sind und dies mit dem geringstmöglichen Energie- und Wasserbedarf und dadurch die Legionellen-Gefährdung beseitigt wird, und dass - wenn notwendig - auch das gesamte Warmwasser-Volumen „verdünnt“ wird.

The following options are available individually or in combination:

• • Calculating the content of the hot water system (hot water volume) and automatically, periodically draining it at the correct, important or all taps until the water content is renewed and/or the required dilution is achieved (controlled e.g. by time or special measuring systems);
• • Draining via the circulation line (the taps are not flowed through, but this is simpler and also corresponds to the state of the art in “heat destruction”);
• • The timed or periodic drainage of fresh water, which is as cold as possible, on the hot water side can be controlled using fixed times (e.g. opening the corresponding drainage points for 2 minutes every 8 hours) or automatically with adjusted time intervals via temperature and/or volume flow measurement (for example, in a sports facility with showers, never during the season and periodically during the holidays).
• • In an object, only individual strands can be “diluted” at a time if the other strands experience sufficient “dilution” through use.
• • Because the dilution can be carried out with cold water, this type of Legionella control requires less energy and the disadvantage of the temperature cooling in the pipes that are “hot” due to the Legionella control (>60°C, which may cool down to room temperature and thus pass through the critical growth area for Legionella again, which leads to a large increase in Legionella) is eliminated.
• • If the taps are included in the "dilution", there are enough systems on the market with automatic opening mechanisms that can be used (automatic water dispensers with a shut-off function, etc. such as time-controlled cash machines at showers on campsites or in public toilets; you hold your hand out, then the water flows and when you pull your hand away, the tap closes, water valves, etc.).
• • The idea behind the invention is that by “dilution” the areas that are at risk are “diluted” and this is done with the lowest possible energy and water consumption, thus eliminating the risk of legionella, and that - if necessary - the entire hot water volume is also “diluted”.

1 shows a highly simplified diagram of a hot water supply system according to an embodiment of the invention. The water supply system 10a of the 1 comprises a closed hot water circuit 15 in which the hot water circulates by means of a circulation pump 16 (or by gravity). The hot water circuit 15 is thermally coupled to a hot water tank 12 via a heat exchanger 14 (instantaneous water heater principle), the water content of which is heated by a heating device 11 via a further heat exchanger 13.

Warm water can be taken from the hot water circuit 15 via a storage line 30 and directed to a tap, which in the example shown is a shower. Of course, further taps of this or another type can be connected to the hot water circuit 15. Cold water is supplied to the hot water circuit 15 via a cold water connecting line 18 from a cold water inlet 17, which replaces the warm water taken from the hot water circuit 15 via the storage line 30. At the same time, a cold water line 20 leads from the cold water inlet 17 to the tap, so that the desired water temperature can be achieved at the shower by a mixture of warm water and cold water, which is adjusted by a warm water valve 22 and a cold water valve 23.

In the 1 In the example shown, the hot water volume V is essentially equal to the content of the hot water circuit 15. The controllable dilution of the hot water volume by cold fresh water described above is achieved in this example by arranging a controllable outlet valve 29 on the hot water circuit 15, which can be opened by a control 24 via a control line 27 in order to allow hot water to flow out of the hot water circuit 15 or the hot water volume in a targeted manner. The hot water flowing through the outlet The hot water leaking out of valve 29 is simultaneously replaced by cold water, which flows into the hot water circuit 15 via the cold water connecting line 18. In this way, the hot water volume V can be completely replaced within a predetermined period of time, controlled by the control system 24, with the bacteria or legionella contained therein also being removed from the system along with the exchanged water. This procedure allows the bacterial population in the hot water system to be controlled and kept at a low and therefore harmless level.

When replacing the hot water, the heating of the water in the hot water tank 12 by the heating device (e.g. by means of a charging pump (not shown)) can generally be interrupted in order to avoid unnecessary energy loss due to the escaping hot water.

Since this water exchange or “dilution” takes place via the existing pipes of the system, practically no structural changes to the system are necessary if the bacterial infestation is to be combated in the proposed manner. In the example of the 1 In addition to the control 24, only the outlet valve 29 would have to be provided, which can be arranged at any point in the hot water circuit 15. In the simplest case, however, as in 4 indicated by the dashed control line 27' - the hot water valve 22 of the tap (shower) can be designed as a controllable valve and can be forcibly opened by the control 24 for the purposes of "dilution". In this case, the structural changes are limited to the installation of the control 24.

The control 24 can control the dilution process, for example, by means of a timer that ensures that the water in the hot water system is exchanged within a predetermined period of time. However, such a greatly simplified procedure would not take into account that sufficient exchange can also be achieved through normal operation at the tap (shower). In order to avoid unnecessary water losses in this respect, 1 a flow meter must be installed in the cold water connecting line 18, which indicates to the control system 24 to what extent and at what intervals hot water from the hot water circuit 15 or the hot water volume V has been exchanged for fresh water from the cold water inlet 17.

If the control 24 determines from the data of the flow meter 19 that only half of the hot water volume V has been replaced by cold fresh water over a period of, for example, 4 or 8 hours, the control 24 can open the outlet valve 29 to further dilute the hot water volume.

The same procedure can also be applied in a hot water supply system 10b, as shown in 2 is reproduced. In this case, instead of the hot water circuit, a simple hot water pipe 28 is led to the tap, with a heat exchanger 14 being inserted into the hot water pipe 28, which in turn is located in the hot water tank 12. The hot water volume V in this case is the volume of the hot water pipe 28 from the inlet on the hot water tank 12 to the outlet valve 29.

As already mentioned above, a significantly larger volume of hot water V must be exchanged or diluted if the content of the hot water tank 12 is part of the hot water circuit 15 (hot water supply system 10c in 3 ) or is inserted into the hot water pipe 28 (hot water supply system 10d in 4 ). In both of these cases, the replacement or dilution affects not only individual pipes but also the contents of the hot water tank 12 itself, which leads to higher water losses in the case of forced dilution.

List of reference symbols

10a-d

Hot water supply system

11

Heating device

12

Hot water tank

13,14

Heat exchanger

15

Hot water circuit

16

Circulation pump

17

Cold water inlet

18

Cold water connection line

19

Flowmeter

20

Cold water pipe

21

consumer

22

Hot water valve

23

Cold water valve

24

steering

25

Hot water flow

26

Hot water return

27.27'

Control line

28

Hot water pipe

29

Outlet valve

30

Discharge line

V

Hot water volume

Claims (16)

Method for operating a hot water supply system (10a-d'), in which method fresh water is supplied to the hot water supply system (10a-d) via a cold water inlet (17), the supplied fresh water is heated and the hot water produced is supplied to one or more consumers (21) via a hot water pipe (28), wherein the hot water is produced with a predetermined hot water volume (V) and is kept ready for consumption, characterized in that in order to avoid harmful bacteria concentrations in the hot water volume (V), a sufficient amount of hot water from the hot water volume is replaced by fresh water, wherein, taking into account the amount of hot water withdrawn by the consumers (21), the entire hot water volume (V) is completely replaced by fresh water within a predetermined period of time, wherein the withdrawal of hot water from the hot water volume (V) by the consumers (21) is monitored, and that additionally hot water is replaced by fresh water if the consumption of hot water is not sufficient to cover the entire To completely replace the hot water volume (V) with fresh water within the specified period of time, and to additionally replace hot water with fresh water, hot water is specifically drained from the hot water volume (V). Procedure according to Claim 1 , characterized in that the hot water is drained from the hot water volume (V) via a valve provided at a consumer (21). Procedure according to Claim 1 , characterized in that the hot water is drained from the hot water volume (V) via a valve specially provided for this purpose. Procedure according to Claim 2 or 3 , characterized in that the valve for draining the hot water is designed as a controllable valve, and that the targeted draining of the hot water is controlled by a control (24). Procedure according to Claim 4 , characterized in that the control (24) controls the valve according to the time-dependent hot water consumption. Hot water supply system (10a-d) for carrying out the method according to one of the Claims 1 - 5 , comprising first means (12, 14, 15, 28) for heating and storing a hot water volume (V), a cold water inlet (17) which is connected to the first means (12, 14, 15, 28), and connection means via which one or more hot water consumers (21) are connected to the first means (12, 14, 15, 28), wherein a controllable valve for the controlled discharge of hot water from the hot water volume (V) is connected to the first means (12, 14, 15, 28), and that a control (24) is provided which controls the controllable valve, wherein the hot water supply system (10a-d) is designed such that, in order to avoid harmful bacteria concentrations in the hot water volume (V), hot water from the hot water volume is replaced by fresh water to a sufficient extent, taking into account the amount of hot water withdrawn from the consumers (21), the entire hot water volume (V) is completely replaced by fresh water within a predetermined period of time, wherein the withdrawal of hot water from the hot water volume (V) by the consumers (21) is monitored, and wherein additional hot water is replaced by fresh water if the consumption of hot water is not sufficient to completely replace the entire hot water volume (V) with fresh water within the predetermined period of time, and wherein hot water is specifically drained from the hot water volume (V) for the additional replacement of hot water with fresh water. Hot water supply system (10a-d) according to Claim 6 , characterized in that the controllable valve is assigned to a consumer (21). Hot water supply system (10a-d) according to Claim 6 , characterized in that the controllable valve is a separate outlet valve (29). Hot water supply system (10a-d) according to one of the Claims 6 - 8th , characterized in that second means (19) are provided for monitoring the hot water consumption from the hot water volume (V), and that the second means (19) are connected to the control (24). Hot water supply system (10a-d) according to Claim 9 , characterized in that the second means comprise a flow meter (19) which is arranged between the cold water inlet (17) and the first means (12, 14, 15, 28). Hot water supply system (10a-d) according to one of the Claims 6 - 10 , characterized in that the first means (12, 14, 15, 28) comprise a hot water circuit (15) with a circulation pump (16). Hot water supply system (10a-d) according to Claim 11 , characterized in that the hot water circuit (15) has a heat exchanger (14) which is arranged in a hot water tank (12). Hot water supply system (10a-d) according to Claim 11 , characterized in that a hot water storage tank (12) is part of the hot water circuit (15). Hot water supply system (10a-d) according to one of the Claims 6 - 10 , characterized in that the first means (12, 14, 15, 28) comprise a hot water pipe (28) cooperating with a hot water tank (12). Hot water supply system (10a-d) according to Claim 14 , characterized in that the hot water pipe (28) is directly connected to an outlet of the hot water tank (12). Hot water supply system (10a-d) according to Claim 14 , characterized in that the hot water pipe (28) is coupled to the hot water tank (12) via a heat exchanger (14).