WO2008012726A2

WO2008012726A2 - A hot-water supply system

Info

Publication number: WO2008012726A2
Application number: PCT/IB2007/052826
Authority: WO
Inventors: Valagam Raghunathan
Original assignee: Raghavan, Vijaya
Priority date: 2006-07-27
Filing date: 2007-07-16
Publication date: 2008-01-31
Also published as: WO2008012726A3

Abstract

An energy saving hot-water supply system, which comprises a hot-water supply device (1 ) having a hot-water outlet (1 b), a hot-water tap (3) having a shut position and an open position, a piping (5) coupled to the hot-water outlet and having a hot-water pipe (5a) coupled to the hot-water tap, and an arrangement (7) for moving hot water out of hot- water pipe when the hot-water tap is in the shut position.

Description

A HOT-WATER SUPPLY SYSTEM.

FIELD OF THE INVENTION

The invention relates to a hot-water supply system.

BACKGROUND OF THE INVENTION

Hot-water supply systems are known per se. Such a system comprises a heater in which water meant for supplying is heated. The heater is connected to a piping system having a hot-water tap, usually situated at a distant location. In an operational condition the piping system is filled with water supplied by the heater. If the hot-water tap has not been used for some time, the hot water in the piping system is cooled down. Because in most cases the distance between the heater and the hot-water tap is quite long, an annoying consequence of the above described known system is that cold water runs out of the hot-water tap for a considerable time in many situations. This is not only a waste of time, but also a waste of water and energy. As water suitable for consumption, such as drinking water, becomes scarcer due to an ever increasing demand for it, more water will be wasted and energy will be dissipated in this way. A known attempt to solve the above described problem is the use of hot-water circulation systems. A hot-water circulation system has a hot-water heater and a circulation pump for pumping hot water from the heater through a hot-water piping and back to the heater through an additional water piping which runs from a furthest tap or fixture to the heater. This system is capable of providing nearly instant hot water at the tap, but nevertheless wastes a lot of energy because of both the energy required to continuously operate the circulation pump and the energy loss from the continuously moving hot water in the piping system. Even if hot- water circulation systems are provided with timers, the dissipation of energy is considerable. SUMMARY OF THE INVENTION

An object of the invention is to provide a hot-water supply system in which losses of energy are minimal.

This object is achieved by the hot-water supply system according to the invention. The system according to the invention comprises a hot-water supply device having a hot- water outlet, a hot-water tap having a shut position and at least one open position, a piping coupled to the hot-water outlet and having a hot-water pipe coupled to the hot- water tap, and an arrangement for moving hot water through the hot-water pipe in a direction away from the hot-water tap. The hot-water tap may be a tap having a free outlet opening or may be a tap integrated in or connected to a device, such as a dishwasher, washing machine and the like. The hot-water tap may also be part of a tap device having a hot-water tap and a cold-water tap. Moreover, the hot-water tap may be manually or automatically operatable. During use of the hot-water supply system according to the invention the hot water present in the hot-water pipe after closing the tap is removed from this pipe. The removed hot water can be directly or indirectly sent back to the hot-water supply device. Due to the measure applied into the invention the waste of energy in the hot-water pipe is considerably reduced. Another advantage of the fact that no or hardly water remains after usage in the hot-water pipe of the hot-water supply system according to the invention is that freezing problems, if any, relating to the hot-water pipe are automatically avoided. In particular in cold countries this is an important issue as normally specific precaution measures have to be taken in order to prevent freezing. In a practical embodiment of the hot-water supply system according to the invention the hot-water supply device comprises a water heater. The water heater may be a boiler type heater or a reservoirless heater. As energy source gas or electricity may be used.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement is also arranged for moving hot water through the hot-water pipe in a direction towards the hot-water tap. Virtually, the arrangement in this embodiment is able to move hot water coming from the hot-water supply device in the direction of the tap as soon as the tap is opened and to remove the hot water out of the hot-water pipe after closing the tap. In this way an efficient means is created to save energy and water. The time needed for transporting hot water from the hot-water supply device to the hot-water tap, after opening the hot-ware tap, is relatively short because the resistance is small due to absence of water in the hot-water pipe at the moment the hot-water tap opens.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement comprises a pump unit, which is capable of (1 ),in the case that the hot-water tap is in its open position, pumping hot water, supplied by the hot-water supply device, to the hot-water tap via the hot-water pipe and (2), in the case that the hot-water tap is in its shut position, pumping hot-water, present in the hot-water pipe, to a water reservoir. In this embodiment a favourable arrangement is obtained by means of which it is possible to provide a user of the hot-water tap with hot water in a rapid and efficient way after opening of the tap and also to remove the hot water out of the hot-water pipe in a rapid and efficient way. The user may be a person or a device making use of hot water. In a practical embodiment of the hot-water supply system according to the invention the pump unit comprises an electrical pump. Such a pump may be a pump known per se. In certain circumstances the pump unit may comprise another kind of pump, such as a pneumatic or hydraulic pump.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement comprises a valve unit for cooperation with the pump unit. The valve unit may be integrated in the piping and serves for making different connections of the pump unit with the piping. In a practical embodiment of the hot-water supply system according to the invention the valve unit comprises an electromagnetic valve. The electromagnetic valve may be of a kind known per se and preferably includes a solenoid. A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement comprises a controller for controlling the pump unit and/or the valve unit. In this way a well-defined control system is obtained. In a practical embodiment of the hot-water supply system according to the invention the controller comprises a microprocessor. By this measure an accurate controlling is guaranteed.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement comprises a pressure sensor for sensing a pressure in the hot-water pipe and for transmitting a signal relating to the sensed pressure to the controller. During use, the pressure inside the hot-water pipe varies. This varying pressure is detected by the pressure sensor, wherein the pressure sensor sends signals relating to momentary pressure status inside the hot-water pipe to the controller. Preferably, the controller controls all controllable parts of the hot-water supply system on the basis of the sensed pressure.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the arrangement comprises an air inlet valve connected to an air inlet of the hot-water pipe. In this way a connection between the inside of the hot-water pipe and the environs, particularly the open air, can be made when the pressure inside the hot-water pipe is below a certain value below the atmospheric pressure level. Such lower pressure occurs after closing the hot-water tap, during moving the hot water through the hot-water pipe in the direction away from the hot-water tap. After reaching said certain value atmospheric air is allowed to get into the hot-water pipe.

A preferred embodiment of the hot-water supply system according to the invention is characterized in that the pump unit has a pump unit inlet and a pump unit outlet, wherein, in the case that the hot-water tap is in its open position, both the pump unit inlet is connected to the hot-water outlet of the hot-water supply device and the pump unit outlet is connected to a hot-water pipe opening of the hot-water pipe via the valve unit and wherein, in the case that the hot-water tap is in its shut position, both the pump unit inlet is connected to said pipe opening and the pump unit outlet is connected to the water reservoir via the valve unit. In this way a simple, but very accurate and efficient system is obtained. In an practical embodiment of the hot-water supply system according to the invention the valve unit has a first valve and a second valve, each having a first position and a second position, wherein during use, in the case of the open position of the hot- water tap the first valve is in its first position whereby the pump unit inlet is connected to the hot-water outlet and the second valve is its first position whereby the pump unit outlet is connected to the hot-water pipe opening, and wherein during use, in the case of the shut position of the hot-water tap the first valve is in its second position whereby the pump unit inlet is connected to said pipe opening and the second valve is in its second position whereby the pump unit outlet is connected to the water reservoir. In this way a reliable system is obtained.

In a preferred embodiment of the hot-water supply system according to the invention a valve device is provided for connecting the water reservoir to the hot-water supply device. In this water saving embodiment the hot water removed from the hot-water pipe, after closing the hot-water tap, can be brought back to the hot-water supply device. In principle no water needs to be wasted. In a practical embodiment of the hot-water supply system according to the invention the valve device is also arranged for making a connection between the valve unit and the water reservoir. In another practical embodiment of the hot-water supply system according to the invention the valve device is also arranged for making a connection between a cold water pipe and a cold-water inlet of the hot-water supply device. Preferably the valve device is provided with one or more drive solenoids.

In a further embodiment of the hot-water supply system according to the invention the valve device has a first valve element and a second valve element, each having a first position and a second position, wherein during use, in the case of that the first valve element is in its first position the cold water pipe is connected to the cold-water inlet and in the case that the first valve element is in its second position the water reservoir is connected to the cold-water inlet, and wherein during use, in the case that the second valve element is in its first position the valve device makes a connection between the valve unit and the water reservoir and in the case of the second valve member is in its second position the valve device makes a connection between the valve unit and a drain.

In a preferred embodiment of the hot-water supply system according to the invention the controller is arranged for controlling the valve device. In a practical embodiment of the hot-water supply system according to the invention the reservoir is provided with a level sensor for sensing a water level in the water reservoir and for transmitting a signal relating to the sensed water level to the controller.

The hot-water supply system according to the invention is a reliable system by means of which both water and energy can be saved considerably. The system can be easily installed in existing and new buildings.

Embodiments of the hot-water supply device according to the invention are defined in the claims 2 to 19.

The invention also relates to an arrangement for moving hot water through a hot-water pipe. The arrangement according to the invention is specifically meant as an essential subject required in building up the hot-water supply system according to the invention. The arrangement according to the invention is defined in claim 20.

The invention further relates to a use of the hot-water supply system according to the invention. The use according to the invention is defined in claim 21 and has benefits similar to the benefits of the hot-water supply system according to the invention.

The invention further relates to an air inlet valve and a valve unit, both suitable for use in the system according to the invention. The air inlet valve and a valve unit according to the invention are defined in claim 22 and 23, respectively. Both the air inlet valve and the valve unit according to the invention has a reliable and robust construction. Preferably the valve device is identical to the valve unit. The invention further relates to a method of supplying hot water from a hot-water supply device to a hot-water tap via a hot-water pipe. The method according to the invention is defined in claim 24 and has benefits similar to the benefits of the hot-water supply system according to the invention.

With reference to the Claims it is noted that all possible combinations of features mentioned in the Claims are part of the invention. These and other aspects of the invention are apparent from and will be elucidated with reference to the examples described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic disclosure of an embodiment of the hot-water supply system according to the invention.

Figure 2A is a schematic longitudinal section, according to 2B-2B in Figure 2B, of an embodiment of an air inlet valve suitable for use in the hot-water supply system according to the invention.

Figure 2B is schematical top view of the embodiment of Figure 2B. Figure 3A is a schematical longitudinal section of an embodiment of a valve unit suitable for use in the hot-water supply system according to the invention.

Figure 3B is a schematical cross section, according to 3B-3B in Figure 3A, of the embodiment of Figure 3A.

Figure 4 is a schematic disclosure of the embodiment of Figure 1 , being in a normal hot water outlet mode.

Figure 5 is a schematic disclosure of the embodiment of Figure 1 , being in a hot water recovery mode.

Figure 6 is a schematic disclosure of the embodiment of Figure 1 , being in a standby mode. Figure 7 is a schematic disclosure of the embodiment of Figure 1 , being in a turn on- recovery water usage mode. Figure 8 shows a scheme in which pump status of the pumping unit in relation to pressure inside the hot-water pipe as function of time is depicted.

DETAILED DESCRIPTION

The embodiment of the hot-water supply system according to the invention, schematically depicted in Figure 1 , comprises a hot-water supply device 1 , in the form of a water boiler heated by gas or electricity, a hot-water tap 3, and a piping 5. The hot- water supply device 1 , further also mentioned the boiler 1 , is provided with a cold-water inlet 1a and a hot-water outlet 1 b. The piping 5 is mounted to the hot-water outlet 1b and comprises a hot-water pipe 5a, to which the hot-water tap 3 is mounted. The hot-water pipe 5a has a hot-water pipe opening 5a" by means of which the pipe 5a is coupled to another part of the piping 5. The pipe opening 5a" is primarily meant as a hot-water inlet of the hot-water pipe 5a. The hot-water supply system further comprises an arrangement 7 for moving hot water through the hot-water pipe 5a in a direction D1 towards the hot- water tap 3 when the hot-water tap 3 is in an open position, further called the open position, and in a counter direction, i.e. in a direction D2 away from the hot-water tap 3, when the hot-water tap 3 is in its shut position, also called closed position.

The arrangement 7 comprises a pump unit 9 for pumping hot water supplied by the the boiler 1 to the hot-water tap 3 via the hot-water pipe 5a, in the case that the hot-water tap 3 is in the open position, and for pumping water out of the hot-water pipe 5a, in the case that the hot-water tap 3 is in its shut position. The pump unit 9, which may comprise an electrical pump known per se or a variant thereof, has a pump unit inlet 9a and a pump unit outlet 9b. The arrangement 7 further comprises a valve unit 13, which may comprise an electromagnetic valve known per se or a variant thereof. The valve unit 13 has six gates A to F and comprises a first valve 13a and a second valve 13b, wherein the first valve 13a has a first position (A,C) and a second position (B, C) and the second valve 13b has a first position (F, E) and a second position (F, D). In the case of the open position of the hot-water tap 3 the first valve 13a is in its first position (A,C) for connecting the pump unit inlet 9a to the hot-water outlet 1 b, via a part of the piping 5, and the second valve 13b is in its first position (F, E) for connecting the pump unit outlet 9b to the pipe opening 5a", via a part of the piping 5. In the case of the shut position of the hot-water tap 3 the first valve 13a is in its second position (B, C) for connecting the pump unit inlet 9a to the hot-water pipe inlet 5a", via a part of the piping 5, and the second valve 13b is in its second position (F, D) for connecting the pump unit outlet 9b to a water reservoir 11 or the like, via a part of the piping 5. In this embodiment the water reservoir 11 is part of the system according to the invention. Alternatively, the water reservoir may be a separate reservoir, e.g. a reservoir being part of a public system. The arrangement 7 further comprises a controller 15 for controlling the pump unit 9 and the valve unit 13. The controller 15 may comprise a microprocessor known per se or a variant thereof. The arrangement 7 further comprises a pressure sensor 17 for sensing a pressure inside the hot-water pipe 5a and for transmitting signals relating to the detected pressure level to the controller 15. The sensor 17 may be a sensor known per se or a variant thereof. The arrangement 7 further comprises an air inlet valve 19 mounted on an air inlet 5a' in a wall of the hot-water pipe 5a for letting in air into the inside of the pipe 5a. Preferably the air inlet, and thus the air inlet valve, is relatively closely located to the hot- water tap, e.g. at a distance of several centimetres. The pressure sensor is mounted to the hot-water pipe at a suitable location, preferably near to the air inlet valve.

The hot-water supply system according to the invention further comprises a valve device 21 for connecting the water reservoir 11 to the boiler 1 , for making a connection between the valve unit 13 and the water reservoir 11 and for making a connection between a cold-water pipe 23 and the cold-water inlet 1a of the boiler 1. The cold-water pipe may be at least partly a part of the piping. Preferably the pump unit, the valve unit and the valve device are positioned relatively near to the boiler 1 , e.g. within a distance of a few meters. The same preference applies to the water reservoir.

The valve device 21 has six gates G to L and comprises a first valve element 21a and a second valve element 21 b, each having a first position (H, G; L, J, respectively) and a second position (G,I;J,K, respectively). In the case that the first valve element 21a is in its first position (H, G) the cold water pipe 23 is connected to the cold-water inlet 1a, via a part of the piping 5, and in the case that the first valve element 21 a is in its second position (G, I) the water reservoir 11 is connected to the cold-water inlet 1a, via a part of the piping 5. In the case that the second valve element 21b is in its first position (L, J) the valve device 21 makes a connection between the valve unit 13 and the water reservoir 11 , via a part of the piping 5, and in the case that the second valve member 21 b is in its second position (J, K) the valve device 21 makes a connection between the valve unit (13) and a drain 25, via a part of the piping 5. The controller 15 is arranged for controlling the valve device 21. The reservoir 11 is provided with a level sensor 27 for sensing a water level in the water reservoir 11 and for transmitting signals relating to the detected water level in the reservoir 11 to the controller 15. The level sensor 27 comprises a float 27a and two limit switches 27b and 27c. The float is movable in each of the directions d1 and d2. The reservoir 11 is further provided with an air vent 29 and a test unit 31. The air vent 29 serves to relieve of air present inside the reservoir while hot water enters into the reservoir. The test unit 31 can be used to push down the float, if it is stuck.

In Figures 2A and 2B a preferred embodiment 117 of the air inlet valve 17 is shown. The embodiment 117 comprises a housing 101 for mounting to an opening in the wall of the hot-water pipe of the hot-water supply system according to the invention. A movable valve element 103 is arranged inside the housing 101 , wherein the element 103 has a rest position in which it is pushed against a part, particularly a top plate 101a, of the housing 101 by a spring 105 also arranged inside the housing 101. When the pressure inside the housing 101 drops to a certain under pressure the atmospheric pressure overcomes a spring pressure exerted by the spring 105 and an air inlet is formed between the element 103, now being in an activated position, and the plate 101a. The spring pressure may be adjustable.

In Figures 3A and 3B a preferred embodiment 213 of the valve unit 13 is shown. The embodiment 213 comprises a valve housing 201 having six gates A to F, each meant for mounting to a part of the piping of the hot-water supply system according to the invention. A valve body 203 is arranged inside the housing 201 and is translatably mounted along a longitudinal axis a. The valve body 203 comprises two valves 213a and 213b, corresponding to the first valve 13a and the second valve 13b, respectively, in the system shown in Figure 1. In the depicted example the valves 213a and 213b form one integrated unit. The valve unit 213 comprises at least one, e.g. as depicted two solenoid drive units 205, for driving the valve body along the axis a. In the depicted situation the valves 213a and 213b are in a first position, wherein gate A is connected with gate C and wherein gate E is connected with gate F. In another situation the valves 213a and 213b are in a second position, wherein gate B is connected to gate C, and wherein gate D is connected to gate F. It is noted that the valve device 21 depicted in Figure 1 is preferably of a similar construction as the valve unit 213.

With reference to the Figures 1 and 4 to 7 the working principle of the hot-water supply system according to the invention will be elucidated. In a normal hot water outlet mode, wherein the hot-water tap 3 is opened, the pump unit 9 is switched on by the controller 15 and the pump unit instantly sucks hot water from the boiler 1 via a part of the pipeline 5. The hot water passes the gates A and C of the valve unit 13 and reaches the pump unit 9. Then the hot water is instantly delivered to the hot- water tap 3 via the ports F and E of the valve unit 13 and via the hot-water pipe 5a. At the same time cold water enters into the boiler 1 via the gates H and G of the valve device 21. When the tap 3 is closed after usage of hot water, the pressure sensor 17 sends a signal to the controller 15, whereafter the controller 15 immediately switches off the pump unit 9. The hot-water pipe 5 is full of hot water now. After a certain time, which is preferably adjustable, of e.g. a few minutes, the controller 15 activates the valve unit 13 for connecting the gates B and C, and the gates D and F. A new mode has been created, named the hot water recovery mode.

In the hot water recovery mode the controller 15 immediately switches on the pump unit 9, whereby the hot water present in the hot-water pipe 5a is suck via the gates B and C, and delivered to the water reservoir 11 via the gates F and D of the valve unit 13 and the gates J and L of the valve device 21. If the float 27a in the reservoir 11 touches the limit switch 27b, the reservoir 11 is full. Then the level sensor 27 sends a signal to the controller 15 and the controller 15 immediately activates the valve device 21 for connecting the gates I and G, whereby water can flow from the reservoir 11 to the boiler 1 , and the gates J and K, whereby an excess of water coming from the pump unit 9 is delivered through drain 25. Due to sucking the hot water out of the hot-water pipe 5a there occurs a decrease of pressure inside the pipe 5a, whereby this pressure becomes below atmospheric pressure. If the under pressure inside the pipe 5a reaches a certain value the air inlet valve 17 opens and air enters the pipe 5a. This value may be 0.9 bar. The actual values of the pressure inside the pipe 5a value are send to the controller 15 by the pressure sensor 19.

After completing sucking the hot water from the pipe 5a, i.e. the pipe 5a is substantially free of water but filled with air, the controller turns off the pump unit 9. Now a new mode is created, called the standby mode.

In the standby mode, in which mode the tap 3 remains in its closed condition, the pressure inside the pipe 5a is maintained between certain values, in this example between 0.9 and 0.95 bar. If there occurs any minute leakage in the system, particularly in the pipe 5a, there is a risk that the pressure inside the pipe 5a will gradually increase, in this example from 0.9 bar to 0.95 bar. However the pressure sensor 17 sends in that case a signal to the controller15 for immediately starting the pump unit 9 in order to decrease the pressure to the adjusted low level, in this example to 0.9 bar. After reaching that level the controller 15 switches off the pump unit 9. This operation is done repeatedly, if needed, until the hot-water tap 3 is opened.

When the hot-water tap 3 is opened from the standby mode, the pressure inside the hot- water pipe 5a immediately increases from the under pressure, in this example 0.9 bar, to atmospheric pressure by entering atmospheric air through the opened tap 3. The pressure sensor 17 sends a signal related to the new pressure status to the controller 15, which activates the valve unit 13 for connecting the gates A and C and the gates E and F, and switches on the pump unit 9, whereby within seconds hot water can be available at the hot-water tap 3 after opening the tap. There is now reached a mode called the turn on-recovery water usage mode.

In the turn on-recovery water usage mode the controller 15 also activates the valve device 21 for connecting the gates G and I and the gates J and K. Hot water from the boiler 1 immediately reaches the hot-water tap 3 and hot water from the reservoir 11 reaches the boiler 1 via the gates I and H by gravity force. When the float 27a touches the level switch 27c, the level sensor 27 sends a signal to the controller 15, which activates the valve device 21 for connecting the gates H and L and the gates J and K. Thereafter cold water enters the boiler 1. Hot water is continuously coming out of the boiler 1 as long as required. After closing the hot-water tap 3 the system reaches the hot water recovery mode after an adjusted time limit.

For sake of completeness reference is made to the scheme of Figure 8. In this scheme the pump status of the pump unit in relation to the pressure measured by the pressure sensor, i.e. the pressure inside the hot-water pipe, as function of the time is depicted. When after using of hot water the hot-water tap is closed, the pump unit remains active till a set maximum pressure P5 (e.g. 2.0 bar) is achieved. Thereafter the pump unit remains inactive till by one or another reason the pressure reaches a lower pressure P4 (e.g. 1.75 bar), in which case the pump unit increases the pressure to P5. After a set time limit the pump unit starts for pumping hot water out of the hot-water pipe. If a set minimum pressure PO (e.g. 0.9 bar) is reached the pump unit stops. Thereafter the pump unit remains inactive till by one or another reason the pressure reaches a higher pressure P1 (e.g. 0.95 bar), in which case the pump unit decreases the pressure to PO. When the hot-water tap is opened at any moment the pump unit starts for among others pumping water from the hot-water supply device to the hot-water tap. In this situation the pump unit remains active till the pressure P5 is reached. The pump status is fully controlled by the controller. The controller also controls the valve unit and the valve device. The control function of the controller depends on the information sent by the pressure sensor.

While the invention has been illustrated and described in detail in the drawings and foregoing description, illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the description and the claims. In the Claims and the description the word "water" is not restricted to pure water; a mixture of water and another substance, and even another liquid is also covered by the word "water". The word "comprising" does not exclude other elements, and the indefinite article "a" or "an" does not exclude a plurality. Any reference sign in the Claims should not be construed as limiting the scope.

Claims

1. A hot-water supply system comprising

- a hot-water supply device (1 ) having a hot-water outlet (1 b), - a hot-water tap (3) having a shut position and at least one open position,

- a piping (5) coupled to the hot-water outlet and having a hot-water pipe (5a) coupled to the hot-water tap, and

- an arrangement (7) for moving hot water through the hot-water pipe in a direction away from the hot-water tap.

2. The hot-water supply system as claimed in claim 1 , wherein the hot-water supply device comprises a water heater.

3. The hot-water supply system as claimed in claim 1 or 2, wherein the arrangement (7) is also arranged for moving hot water through the hot-water pipe in a direction towards the hot-water tap.

4. The hot-water supply system as claimed in claim 1 , 2 or 3, wherein the arrangement (7) comprises a pump unit (9), which is capable of (1),in the case that the hot-water tap is in its open position, pumping hot water, supplied by the hot- water supply device, to the hot-water tap via the hot-water pipe and (2), in the case that the hot-water tap is in its shut position, pumping hot-water, present in the hot- water pipe, to a water reservoir (11 ).

5. The hot-water supply system as claimed in claim 4, wherein the pump unit comprises an electrical pump.

6. The hot-water supply system as claimed in claim 4 or 5, wherein the arrangement

(7) comprises a valve unit (13) for cooperation with the pump unit.

7. The hot-water supply system as claimed in claim 6, wherein the valve unit comprises an electromagnetic valve.

8. The hot-water supply system as claimed in claim 4 or 5, claim 6 or 7, or claims 4 and 6, wherein the arrangement (7) comprises a controller (15) for controlling the pump unit and/or the valve unit.

9. The hot-water supply system as claimed in claim 8, wherein the controller comprises a microprocessor.

10. The hot-water supply system as claimed in claim 8 or 9, wherein the arrangement (7) comprises a pressure sensor (17) for sensing a pressure in the hot-water pipe and for transmitting a signal relating to the sensed pressure to the controller.

11. The hot-water supply system as claimed in any one of the preceding claims, wherein the arrangement (7) comprises an air inlet valve (19) connected to an air inlet (5a') of the hot-water pipe.

12. The hot-water supply system as claimed in claim 6 or 7, wherein the pump unit has a pump unit inlet (9a) and a pump unit outlet (9b), wherein, in the case that the hot- water tap is in its open position, both the pump unit inlet is connected to the hot- water outlet of the hot-water supply device and the pump unit outlet is connected to a hot-water pipe opening (5a") of the hot-water pipe via the valve unit and wherein, in the case that the hot-water tap is in its shut position, both the pump unit inlet is connected to said pipe opening and the pump unit outlet is connected to the water reservoir via the valve unit.

13. The hot-water supply system as claimed in claim 12, wherein the valve unit has a first valve (13a) and a second valve (13b), each having a first position (A,C; F, E) and a second position (B, C; F, D), wherein, in the case of the open position of the hot-water tap the first valve is in its first position whereby the pump unit inlet is connected to the hot-water outlet and the second valve is its first position whereby the pump unit outlet is connected to the hot-water pipe opening, and wherein, in the case of the shut position of the hot-water tap the first valve is in its second position whereby the pump unit inlet is connected to said pipe opening and the second valve is in its second position whereby the pump unit outlet is connected to the water reservoir.

14. The hot-water supply system as claimed in claim 12, provided with a valve device (21) for connecting the water reservoir to the hot-water supply device.

15. The hot-water supply system as claimed in claim 14, wherein the valve device is also arranged for making a connection between the valve unit and the water reservoir.

16. The hot-water supply system as claimed in claim 14 or 15, wherein the valve device is also arranged for making a connection between a cold water pipe (23) and a cold-water inlet (5a) of the hot-water supply device.

17. The hot-water supply system as claimed in claim 16, wherein the valve device has a first valve element (21a) and a second valve element (21 b), each having a first position (H, G; L, J) and a second position (G, I; L, K), wherein, in the case that the first valve element is in its first position the cold water pipe is connected to the cold- water inlet and in the case that the first valve element is in its second position the water reservoir is connected to the cold-water inlet, and wherein, in the case that the second valve element is in its first position the valve device makes a connection between the valve unit and the water reservoir and in the case that the second valve member is in its second position the valve device makes a connection between the water reservoir and a drain (25).

18. The hot-water supply system as claimed in any one of the claim 14 to 17 in combination with claim 8, wherein the controller is arranged for controlling the valve device.

19. The hot-water supply system as claimed in claim 18, wherein the reservoir is provided with a level sensor (27) for sensing a water level in the water reservoir and for transmitting a signal relating to the sensed water level to the controller.

20. An arrangement (7) for moving hot water through a hot-water pipe (5a) for use in a hot-water supply system as claimed in any one of the preceding claims and as defined in any one of these claims.

21. An use of the hot-water supply system as claimed in any one of the claims 1 to 19.

22. An air inlet valve for use in the hot-water supply system as claimed in any one of the claims 1 to 19, comprising a housing (101 ) and a movable valve element (103) movably arranged in the housing, wherein the valve element has a rest position in which it is pushed against a part (101a) of the housing by a spring (105) and a activated position in which an air inlet is present between the valve element and said plate.

23. A valve unit for use in the hot-water supply system as claimed in any one of the claims 1 to 19, comprising a valve housing (201 ) having six gates (A - F), a valve body (203) movably arranged in the housing and having two valves (213a; 213b), and a drive unit (205) for driving the valves, which valves each have a first position, wherein a first gate (C;E) is connected with a second gate (A;F) and a second position, wherein the first gate (C;E) is connected to another second gate (B;D).

24. A method of supplying hot water from a hot-water supply device to a hot-water tap via a hot-water pipe, comprising the following steps: - pumping hot water through the hot-water pipe in the direction towards the hot- water tap after opening this tap, - pumping hot water out of the hot-water pipe in a counter direction after closing the hot-water tap.

25. The method as claimed in claim 24, comprising the step that water pumped out of the hot-water pipe is direct or indirectly returned to the hot-water supply device.