The invention relates to a tap water preparing device according to the preamble of Claim 1. The invention furthermore relates to a method for a tap water preparing device according to Claim 15.

Prior art

Tap water preparing devices for heating cold tap water (drinking water) in order to be used for hygiene purposes are generally known and are mainly used in three forms:

• Central-heating boilers, in which cold tap water is heated in a heat exchanger through the combustion of gas or oil.

• Electrically heated boiler tanks, in which the cold tap water is heated using electrical heating elements.

· Heat delivery sets often used in district heating, wherein the cold tap water is heated in a heat exchanger using hot water from the heating network.

For hygiene purposes, the temperature of warm tap water only needs to be 40°C to 45°C. However, in this temperature range, there is a strong development of the Legionella bacteria. In order to prevent contamination with this bacteria, the tap water in the tap water preparing devices is heated to a temperature of approximately 55°C to approximately 60°C, so that the bacteria dies. However, producing such a high temperature leads to considerable energy losses during generation, transport and storage of the tap water.

It is therefore an object of the invention to provide a tap water preparing device and a method therefor which overcome this drawback.

Summary of the invention

The object is achieved by a tap water preparing device for heating cold tap water to warm tap water, comprising a heat exchanger, a supply connection for cold tap water in a primary circuit of the heat exchanger, a delivery connection for warm tap water from the primary circuit of the heat exchanger, a sensor for determining flow of water through the delivery connection, and a heat source for heating the incoming tap water, wherein the heat source is located in the heat exchanger, characterized in that the tap water preparing device is provided with cooling means for controllably cooling the heat exchanger and the tap water located in the primary circuit, wherein the cooling means are configured to cool the heat exchanger and the tap water located in the primary circuit to a temperature of 25°C or lower.

As a result of the fact that the heat exchanger and the volume of cold tap water that this heat exchanger contains are cooled down again within a short time after the production of warm tap water to a temperature at which the Legionella bacteria no longer multiplies, it is no longer necessary to heat the heat exchanger to 55°C-60°C in order to kill the Legionella bacteria. In order to ensure that, under practical circumstances, no unacceptable multiplication of this bacteria takes place while the tap water is at a standstill in the heat exchanger, the heat exchanger and the tap water located therein are actively cooled to a temperature at which the growth of Legionella practically comes to a stop. According to current scientific insights, such a temperature is 25°C or lower. The person skilled in the art will understand that the setting of the temperature may depend on, for example, the quality of the cold tap water or the material used for the heat exchanger.

Instead of the usual relatively high temperature of 55°C to 60°C, a heating temperature of the heat exchanger of approximately 40°C to approximately 45°C is sufficient. Such a relatively low temperature can be generated with much higher efficiency than the high temperatures of 55°C to 60°C which are common in the prior art.

As the heat exchanger and the tap water located therein are cooled to a temperature of approximately 25°C or lower after the production of warm tap water, it is no longer necessary to also heat the heat exchanger during the period in which no warm tap water is produced in order to prevent the development of the Legionella bacteria.

The resulting prevention of heat losses can quickly lead to a 10-20% reduction in the total energy consumption.

In addition, the invention relates to a method for a tap water preparing device for heating cold tap water to warm tap water, comprising a heat exchanger, a supply connection for cold tap water in a primary circuit of the heat exchanger, a delivery connection for warm tap water from the primary circuit of the heat exchanger, and a heat source for heating the incoming tap water in the primary circuit, wherein the heat source is located in the heat exchanger, wherein the method comprises:

allowing tap water to flow through the primary circuit of the heat exchanger; heating the flowing tap water to warm tap water in the primary circuit of the heat exchanger;

interrupting the flow so that tap water no longer flows;

subsequently cooling the heat exchanger and warm tap water located in the primary circuit of the heat exchanger to a temperature equal to or lower than 25°C.

Advantageous embodiments are defined by the dependent claims.

Further features, possible applications and advantages of the invention are apparent from the following description of exemplary embodiments of the invention. Brief description of the drawing

The invention will be described in more detail below with reference to a number of drawings which show a few exemplary embodiments. The drawings are only intended for illustrative purposes and should not be interpreted as limiting the inventive concept which is defined by the attached claims.

In the drawing:

Figure 1 diagrammatically shows a tap water preparing device according to an embodiment;

Figure 2 diagrammatically shows a tap water preparing device according to a further embodiment;

Figure 3 diagrammatically shows a tap water preparing device according to an embodiment; and

Figure 4 diagrammatically shows a tap water preparing device according to an embodiment.

In the description below, the same reference numerals in each case denote identical or similar components in the figures.

Description of embodiments

Figure 1 diagrammatically shows a tap water preparing device according to an embodiment.

The warm tap water preparing device 100 shown in the figure comprises a heat exchanger 1, a connection to a supply pipe 2 with cold tap water, a connection to a delivery pipe 7 to a warm tap water delivery point, a sensor 3 to detect the shut-off or flow S of the warm tap water, a control unit 4, an inlet 6 of hot circulating water, a valve 5 in the inlet with hot circulating water, an outlet 8 of the circulating water, a branch pipe 9 in the delivery pipe and a valve 10 in the branch pipe.

In the heat exchanger, a primary circuit is provided for tap water to pass through and a secondary circuit of hot circulating water, for example originating from district heating, is used as heat source for heating the tap water. In the secondary circuit, the circulating water is fed in via inlet 6 and discharged through outlet 8.

When warm water is required, the water in the delivery pipe 7 starts flowing towards the warm tap water delivery point, while at the same time cold tap water is supplied from inlet pipe 2. The sensor 3 which is connected to the control unit 4 (indicated by the dashed line between sensor 3 and control unit 4) detects said flow S. On the basis of the sensor detection, the control unit 4 opens the valve 5 in the inlet 6 of hot circulating water (denoted by the dashed line between valve 5 and control unit 4). As a result, hot water of for example 50°C flows from the inlet 6 of hot circulating water through the heat exchanger 1 as a heating flow.

In the heat exchanger 1, the primary circuit with cold tap water is heated to

approximately 45°C by thermal coupling with the heating flow in the secondary circuit of hot circulating water. At the same time, the circulating water is cooled to 20°C to 40°C and flows back through outlet 8.

When no more warm tap water is required, the flow of tap water through the inlet pipe 2 and delivery pipe 7 stops. The control unit 4 closes the valve 5 in the inlet 6 of hot circulating water on the basis of the detection of the sensor 3, as a result of which the supply of hot circulating water stops. The control unit 4 is connected to the valve 10 in the branch pipe 9, denoted by the dashed line between valve 10 and control unit 4. After a predetermined waiting time, the control unit 4 opens the valve 10 in the branch pipe during a cooling period, in which cold tap water flows through the heat exchanger 1 and thus cools the heat exchanger 1 and the tap water located therein to a temperature of 25°C or lower, at which there is no longer unacceptable development of the

Legionella bacteria. The tap water used for the cooling is discharged to an outlet 11. The control unit 4 is provided with a time control for determining at least the waiting time and optionally the cooling period.

The waiting time can be determined, on the one hand, to prevent the need for unnecessary cooling and heating of the tap water in the event of repeatedly tapping heated water at short intervals and, on the other hand, to prevent unacceptable development of Legionella from taking place, which is dependent on the temperature of the tap water in the heat exchanger and, inter alia, on the water quality of the incoming cold tap water.

Under practical circumstances, the waiting time could be selected to be, for example, between 15 minutes and approximately 90 minutes. Existing norms for cooling warm water in a warm water delivery pipe may also be taken into account. In the Netherlands, for example, this is subject to a norm that the stationary water in the delivery pipe is cooled to 25°C after 45 minutes.

In an embodiment, the control unit 4 comprises a time relay for controlling said waiting time and, optionally, the cooling period.

Figure 2 diagrammatically shows a tap water preparing device 101 according to a further embodiment.

In this further embodiment, the tap water preparing device 101 additionally comprises a temperature sensor 12 which is connected to the control unit 4 in order to transmit a temperature signal, denoted by the dashed line between temperature sensor 12 and control unit 4. The temperature sensor 12 is configured to measure the temperature of the heat exchanger 1 and the volume of tap water that it contains.

After the flow of warm tap water in the delivery pipe 7 stops, the valve 10 in the branch pipe 9 is opened by the control unit 4 after the predetermined waiting time. Under the control of the control unit 4, the valve 10 in the branch pipe 9 closes again when the temperature of the heat exchanger 1 and the volume of tap water that it contains has decreased to a set temperature, 25°C or lower, detected by the temperature sensor. Figure 3 diagrammatically shows a tap water preparing device according to an embodiment.

The warm tap water preparing device 102 shown in the figure comprises a heat exchanger 1, a connection to an inlet pipe 2 with cold tap water, a connection to a delivery pipe 7 to a warm tap water delivery point, a sensor 3 to detect the shut-off or flow S of the warm tap water, a control unit 4, an inlet 6 of hot circulating water, a valve 5 in the inlet with hot circulating water, an outlet 8 of the circulating water. In this case, an external cooling body 13 which is thermally coupled to the heat exchanger 1 is provided as cooling means. In this embodiment, no tap water is thus used as coolant. In this case, heat is removed by dissipation from the cooling body 13 to the surroundings. After the flow of warm tap water in the delivery pipe 7 stops, the cooling body 13 removes heat to the surroundings, for example the ambient air. As a result, the heat exchanger 1 and the volume of tap water it contains are cooled.

To promote the cooling, a fan 14 may be provided in order to create an air flow around the cooling body 13. The fan 14 is connected to the control unit 4, as denoted by the dashed line between fan 14 and control unit 4. The fan 14 is started by the control unit 4 at a predetermined time after stopping the flow of warm tap water in delivery pipe 7, on the basis of the detection of the flow sensor 3.

In this embodiment, too, the tap water preparing device 102 may be provided with a temperature sensor 12 for measuring the temperature of the heat exchanger and the tap water located therein. The temperature sensor is connected to the control unit as has already been explained with reference to Figure 2.

Figure 4 diagrammatically shows a tap water preparing device 103 according to an embodiment.

In this embodiment, the heating medium is not hot water, but refrigerant.

The secondary circuit of the heat exchanger 1 is connected to an inlet 15 with hot, liquid or gaseous refrigerant at high pressure and an outlet 16 with liquid refrigerant at high pressure. In the secondary circuit, the inlet 15 and outlet 16 are connected to one another.

The secondary circuit or the inlet 15 with liquid or gaseous refrigerant at high pressure has a branch to an outlet pipe 17 for gaseous refrigerant at low pressure. The outlet pipe 17 for gaseous refrigerant is connected to a (vacuum) compressor (not shown) for achieving a low pressure in the outlet pipe 17.

A first shut-off valve 18, second shut-off valve 19 and third shut-off valve 20, respectively, are accommodated in each of the inlet 15, outlet 16 and outlet pipe 17 for refrigerant. The first, second and third shut-off valves 18, 19, 20 are each connected to the control unit 4 as denoted by the respective dashed lines between first, second and third shut-off valve 18, 19, 20 and control unit.

At rest, all three shut-off valves 18, 19, 20 in the refrigerant-conducting pipes 15, 16, 17 are closed.

When warm water is required, the water in the pipe starts flowing towards the tap water delivery point 7, while at the same time cold tap water is supplied to the primary circuit of the heat exchanger 1 from supply pipe 2. The sensor 3 detects this flow S and the control unit 4 opens the first shut-off valve 18 and second shut-off valve 19. As a result, liquid or gaseous refrigerant at high pressure flows from the inlet 15 for high- pressure liquid or gaseous refrigerant through the secondary circuit of the heat exchanger 1 to the outlet 16 for liquid refrigerant. In the primary circuit of the heat exchanger 1, the cold tap water is heated to approximately 45°C, while at the same time gaseous refrigerant supplied to the secondary circuit of the heat exchanger condenses (and the formed condensate cools) or the supplied liquid refrigerant cools. The resulting cooled, liquid refrigerant flows towards outlet 16.

In any case, the pressure prevailing in the secondary circuit for the gaseous refrigerant at high pressure corresponds in this step to the condensation pressure associated with the condensation temperature of the refrigerant used.

When no more warm tap water is required, the flow of warm tap water into the delivery pipe 7 stops. The control unit 4 closes the first and second shut-off valves 18 and 19, as a result of which the supply of refrigerant at high pressure stops, while refrigerant at high pressure which is present in the secondary circuit comes to a halt. After a predetermined time, the control unit 4 opens the third shut-off valve to the outlet pipe 17 for gaseous refrigerant at low pressure, as a result of which the pressure of the refrigerant in the secondary circuit of the heat exchanger 1 drops. Due to the drop in the pressure of the refrigerant in the secondary circuit of the heat exchanger 1, the liquid refrigerant present in the secondary circuit begins to evaporate causing heat to be extracted from the heat exchanger 1 and the volume of tap water it contains, as a result of which the temperature drops further.

If the temperature has dropped sufficiently as measured, for example, by the temperature sensor 12 or as determined by the duration, the third shut-off valve 20 can be closed by the control unit 4.

By using an outlet pipe 17 for low-pressure gaseous refrigerant, the heat exchanger 1 and the volume of water that the primary circuit of the heat exchanger contains can be cooled to a temperature which is lower than both the ambient temperature and the temperature of the cold tap water which is fed in. This slows the development of the Legionella bacteria yet further.

Various refrigerants can be used, as will be known to the person skilled in the art. Mentioned by way of example are: R134A, R410A, carbon dioxide (C0 ₂ ), R1234 and water (H2O), but the refrigerants are not limited to these examples. It should be noted that hot air (combustion gases) or an electrical heating element is also possible as an alternative heat source in addition to hot circulating water or refrigerant. The person skilled in the art will understand that such heat sources can be used in a similar way to the hot circulating water or the refrigerant. The person skilled in the art will also understand that the invention can be used in the same way as described above in the event that these alternative heat sources are used.

Alternative and equivalent embodiments of the present invention are conceivable without departing from the inventive concept, as will be clear to the specialist in the field. In this case, all the features which have been described or illustrated are in themselves or in any combination the subject matter of the invention, irrespective of whether they are summarized in the claims or referred back to and likewise irrespective of how they are phrased or represented in the description or in the drawing, respectively. The inventive concept is only limited by the attached claims.