A method and a device for damping temperature peaks FIELD OF THE INVENTION AND PRIOR ART The present invention relates to a method for damping tem- perature peaks of the water in a water conduit for tap hot-water, which water conduit is supplied with said water from a heat ex- changer that is adapted to heat the water so as to provide tap hot-water. The invention further relates to a device for damping temperature peaks of the water in a water conduit for tap hot- water. The invention also relates to a system for providing tap hot-water, comprising a heat exchanger for heating water and a water conduit connected to this heat exchanger for conducting the heated water to one or several tapping points.

In a system for providing tap hot-water where the hot-water is heated in a heat exchanger and conducted to an opened hot- water tap at a tapping point without intermediate storage in a storage tank, it will normally take some time, at least a couple of seconds, before the automatic control device of the system has managed to set the correct hot-water temperature. The control device normally comprises one or several sensors, which give a signal to the heat exchanger to start heating the hot-water when the hot-water tap is opened. When the hot-water tap has been opened, the water that has been located in the water conduit

between the heat exchanger and the hot-water tap will first flow out through the hot-water tap. This water may be cold or luke- warm depending on how long the water has been standing still in the water conduit. Thereafter, the water volume that was standing still in the heat exchanger before the opening of the hot-water tap will flow out. This water volume will then be followed by hot-water that has been heated under continuous flow through the heat exchanger and that gradually assumes the temperature set by the control device. When the heat exchanger for instance is connected to a district heating pipeline and on its primary side is supplied with hot district heating water from a district heating plant, a water volume that is standing still on the secondary side of the heat exchanger may through the heat transfer from the generally very hot district heating water reach such a high temperature, normally up to about 80°C, that there is a risk for scalding when this hot water volume later on flows out of a hot-water tap at a tapping point. This scalding may cause personal injuries of more or less serious character even though the hot water volume flows out of the hot-water tap only during a very short period of time of one or a couple of seconds.

There is consequently a need of damping temperature peaks in a hot-water conduit caused by a hot water volume that has been standing still in a heat exchanger. Also temperature peaks caused in other ways, in the form of heat peaks as well as cold peaks, may have to be dampened of the tap hot-water in order to enhance the security and the comfort for those who use tap hot-water from a system of the type in question.

OBJECT OF THE INVENTION The object of the present invention is to make possible a simple and reliable damping of temperature peaks of the water in a water conduit for tap hot-water.

SUMMARY OF THE INVENTION According to the invention, said object is achieved by means of a method according to claim 1, a device according to claim 5 and a system according to claim 9.

The inventive solution implies that the water after the heating in a first heat exchanger is conducted through a second heat ex- changer, the water in this second heat exchanger being con- ducted through a first flow circuit and thereafter through a second flow circuit that is in heat transferring relation to the first flow circuit so as to make possible exchange of heat between water flowing in the different flow circuits. A first water volume that has been standing still in the first exchanger and thereby reached a very high temperature will with the inventive solution, during the passage through the second heat exchanger, transfer heat to a cooler second water volume located in front of the first water volume in the water conduit, whereby the temperature of said first water volume is reduced whereas the temperature of said second water volume is increased. Consequently, a damp- ing of the temperature peak caused by said first water volume is hereby achieved. The inventive solution will work completely automatically and does not require any control device or moni- toring device in order to achieve the desired temperature damping. The inventive solution is consequently very simple and reliable and may furthermore be implemented by joining a modi- fied conventional heat exchanger, which has been modified in a simple manner, to the water conduit between an existing heat exchanger in a hot-water system and the tapping points, whereby the inventive solution is possible to implement at low cost.

According to a preferred embodiment of the invention, the two flow circuits of the second heat exchanger are connected in par- allel-flow, which increases the intended damping effect as com-

pared to a case where the flow circuits of the second heat ex- changer-are connected in contra-flow.

Further preferred embodiments of the invention will appear from the dependent claims and the subsequent description.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will in the following be more closely described by means of embodiment examples, with reference to the appended drawings. It is shown in: Fig 1 a circuit diagram illustrating a system according to the present invention connected to a heat source, Fig 2 a schematical illustration of an inventive device accord- ing to a first embodiment, as seen in a cut lateral view, Fig 3 a schematical illustration of an inventive device accord- ing to a second embodiment, as seen in an exploded view, Fig 4 a schematical illustration of an inventive device accord- ing to a third embodiment, as seen in a cut lateral view, and Fig 5 a diagram illustrating heat curves for tap hot-water in a hot-water system of conventional type and a corre- sponding system provided with a device according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Fig 1 illustrates a system according to an embodiment of the present invention intended for providing tap hot-water in a building 2, such as for instance in a residential property in the

form of a detached house or a multi-family. house. The system 1 comprises a heat exchanger 3 for heating water and a water conduit 4 connected to this heat exchanger 3 for conducting the heated water to one or several tapping points 5, for instance in the form of hot-water taps. The heat exchanger 3 has its primary circuit connected to a heat source 6, from which a heat-carrying medium is supplied to the inlet 7a of the primary circuit via a supply conduit 8. The outlet 7b of the primary circuit of the heat exchanger is connected to a return conduit 9, which conducts the heat-carrying medium back to the heat source 6. The-heat source 6 is for instance a district heating plant, in which case said heat-carrying medium is district heating water. The heat ex- changer 3 has at least one secondary circuit 10, the inlet 11 a of which is connected to a cold-water conduit 12 and the outlet 11b of which is connected to the above-mentioned hot-water conduit 4. The heat exchanger 3 is consequently adapted to heat the water supplied via the cold-water conduit to a suitable tempera- ture by means of the heat from the heat-carrying medium in the primary circuit. The control of the heat exchanger 3 and thereby of the temperature of the hot-water in the hot-water conduit 4 is accomplished by means of conventional and here not shown control equipment. In a system of the type here in question, the heat exchanger 3 will normally also comprise a further secon- dary circuit for generation of heat to a heating system for heat- ing of for instance indoor air. The inlet and the outlet of such a further secondary circuit are in Fig 1 indicated with 13a and 13b, respectively.

According to the present invention, the system further comprises a device in the form of a heat exchanger 14 arranged in the hot- water conduit 4 downstream the above-mentioned first heat ex- changer 3. This second heat exchanger 14 is designed to damp occasional temperature peaks in the hot-water conduit 4. The second heat exchanger 14 comprises a first flow circuit 15a and a second flow circuit 15b that is in heat transferring relation to the first flow circuit 15a so as to make possible exchange of

heat between water flowing in the different flow circuits 15a, 15b. The second flow circuit 15b is connected in series with the first flow circuit 15a, i. e : the outlet of the first flow circuit 15a is connected to the inlet of the second flow circuit 15b, so that a water volume that flows into the second heat exchanger 14 from the water conduit 4 first will pass through the first flow circuit 15a and exchange heat with the water volume in front thereof, which at that moment is located in the second flow circuit 15b, so as to thereafter pass through the second flow circuit 15b and exchange heat with the water volume located behind thereof, which at that moment is located in the first flow circuit 15a.

Consequently, the temperature of the water in the second flow circuit 15b will be affected by the temperature of the water in the first flow circuit 15a and vice versa. A first water volume that has been standing still in the first heat exchanger 3 and thereby reached a very high temperature will during the flowing through the first flow circuit 15a transfer heat to a cooler second water volume that is located in front of the first water volume and simultaneously is flowing through the second flow circuit 15b, whereby the temperature of said first water volume is reduced whereas the temperature of said second water volume is increased. During the subsequent flowing through the second flow circuit 15b, said first water volume will transfer heat to a cooler third water volume that is located behind the first water volume and simultaneously is flowing through the first flow circuit 15a, whereby the temperature of said first water volume is further reduced.

The second heat exchanger 14 has its inlet 18a connected to the secondary circuit outlet 11b of the first heat exchanger 3 and its outlet 18b connected to the tapping points 5. The first and second flow circuits 15a, 15b can be considered to consti- tute the primary circuit and the secondary circuit, respectively, of the second heat exchanger, and a water volume that flows into the second heat exchanger 14 via the inlet 18a will conse-

quently in turn pass through the primary circuit 15a and the sec- ondary circuit 15b.

The two flow circuits 15a, 15b are suitably connected in parallel- flow, which implies that the two flow circuits 15a, 15b are so ar- ranged that they conduct the water in the same or at least es- sentially the same direction in the area where they are in heat transferring relation to each other.

The second heat exchanger 14 is suitably of recuperative type, i. e. it is suitably so designed that the water flows through one of the flow circuits without being mixed with the water that is lo- cated in the other flow circuit.

If so considered appropriate, valve members 25,26 may be ar- ranged in the hot-water conduit 4 upstream and downstream, respectively, the second heat exchanger 14.

A first embodiment of the inventive device is shown in Fig 2. The device has here the form of a heat exchanger 14'specially de- signed for the purpose in question, which heat exchanger com- prises a first flow circuit 15a and a second flow circuit 15b that is in heat transferring relation to the first flow circuit 15a. The device 14'has an inlet 18a, which is connected to the inlet 16a of the first flow circuit. The outlet 16b of the first flow circuit is connected to the inlet 17a of the second flow circuit via a con- nection conduit 21, and the outlet 17b of the second flow circuit is in its turn connected to the outlet 18b of the device. The two flow circuits 15a, 15b are here connected in parallel-flow so that the water will flow in the same directions in the two flow circuits.

The second flow circuit 15b is separated from the first flow cir- cuit 15a by an internal wall 19 of the heat exchanger 14', the heat transfer between the water in the different flow circuits be- ing effected through this wall 19. This wall 19 is consequently to be of a material with a good capacity of heat transmission. The connection conduit 21 is separated from the second flow circuit

15b by an internal wall 27 of the heat exchanger 14'. This wall 27 should be of a material with a good insulating capacity in or- der to avoid heat transfer between the water in the connection conduit 21 and the water in the second flow circuit 15b. The connection circuit 21 is here arranged in the interior of the heat exchanger 14'. The two flow circuits 15a, 15b and the connec- tion conduit 21 between these flow circuits are here separated from the surroundings by the external walls 20 of the heat exchanger 14'.

A second embodiment of the inventive device is shown in Fig 3.

The device has here the form of a plate heat exchanger 14", which comprises a first flow circuit 15a and a second flow circuit 15b that is in heat transferring relation to the first flow circuit 15a. The device 14"has an inlet 18a, which is connected to the inlet 16a of the first flow circuit. The outlet 16b of the first flow circuit is connected to the inlet 17a of the second flow circuit via a conduit 21, and the outlet 17b of the second flow circuit is in its turn connected to the outlet 18b of the device. The respective flow circuit 15a, 15b comprises several plate-shaped channels arranged in parallel, each of which is arranged between two adjacent plate elements 22. The plate elements are so designed that the channels of the two flow circuits are alternate in relation to each other, every second channel belonging to the first flow circuit 15a and the other channels belonging to the second flow circuit 15b. Consequently, heat is transferred between the two flow circuits through the plate elements 22, which consequently are to be of a material with a good capacity of heat transmission. The two flow circuits 15a, 15b are here connected in parallel-flow, so that the water flows in the same direction in all channels. A device 14"according to the embodiment illustrated in Fig 3 can be formed by a series connection of the primary circuit 15a and the secondary circuit 15b of a con- ventional plate heat exchanger, for instance by means of an external conduit 21 as illustrated in Fig 3.

A third embodiment of the inventive device is shown in Fig 4.

The device has here the form of a tube heat exchanger 14"', which comprises a first tube-shaped flow circuit 15a and a sec- ond tube-shaped flow circuit 15b that is in heat transferring re- lation to the first flow circuit 15a. The second flow circuit 15b is here coaxially arranged about the first flow circuit 15a. The de- vice 14"'has an inlet 18a, which is connected to the inlet 16a of the first flow circuit. The outlet 16b of the first flow circuit is connected to the inlet 17a of the second flow circuit via a con- duit 21, and the outlet 17b of the second flow circuit is in its turn connected to the outlet 18b of the device. Heat is transferred between the two flow circuits through the tube-shaped partition wall 24 that separates these flow circuits, which partition wall consequently is to be of a material with a good capacity of heat transmission. The two flow circuits 15a, 15b are here connected in parallel-flow, so that the water will flow in the same directions in the two tube-shaped flow circuits. A device 14"'according to the embodiment illustrated in Fig 4 may be formed by a series connection of the primary circuit 15a and the secondary circuit 15b of a conventional tube heat exchanger, for instance by means of an external conduit 21.

The dimensions of the inventive device 14 are adapted from case to case depending on the design of the system in which the device is to be included and the temperature damping that needs to be achieved. The damping effect is inter alia affected by the volume of the connection conduit 21 between the two flow circuits 15a, 15b and an adaptation of the damping effect is possible to achieve by a suitable choice of this volume.

The inventive system 1 is with advantage a so called district heating substation intended to be installed in a building, such as a residential property in the form of a detached house or a multi- family house, in order to provide tap hot-water in the building and where appropriate heat to a heating system for heating in- door air. In this case, the primary circuit of the first heat ex-

changer 3 is adapted to be supplied with district heating water from a district heating plant. The system 1 may however be con- nected to any kind of heat source capable of supplying a heat- carrying medium of a temperature sufficiently high for the pur- pose in question to the primary circuit of the first heat exchanger 3.

A system 1 of the type in question may be provided with a de- vice 14 according to the present invention for damping tem- perature peaks already when the system is installed, but it is also possible to supplement an existing and installed system with such a device 14 afterwards. If so considered appropriate, the system can be provided with two or several second heat ex- changers 14 connected in series in the water conduit 4 between the first heat exchanger 3 and the respective tapping point 5.

The inventive device 14 is of course only capable of damping an occasional temperature peak of the hot-water delivered from the first heat exchanger 3. In case of a continuous feeding of water of a certain temperature from the first heat exchanger 3, the water that is flowing out through a water tap at a tapping point connected to the first heat exchanger will at last assume essen- tially this temperature.

Practical tests have shown that a damping that is satisfactory in this connection is achieved of the temperature of a water volume that with an initial temperature of about 80°C is fed through a device according to the invention. A diagram with heat curves from such a test is shown in Fig 5. The diagram has a first heat curve A, shown in dashed line, for the hot-water at a tapping point connected to a district heating substation of conventional type without a device according to the invention, and a second heat curve B, shown in continuous line, for the hot-water at a tapping point connected to a corresponding district heating sub- station provided with a device 14"according to the embodiment illustrated in Fig 3 joined to the hot-water conduit between the

district heating substation and the tapping point. In both cases, the hot-water conduit is supplied with hot-water of essentially the same temperature. As appears from this diagram, the hot- water will in the first-mentioned case (heat curve A) briefly as- sume a temperature of about 78°C resulting in a risk of scalding, whereas the highest water temperature in the last-mentioned case (heat curve B) is about 61°C. In the last-mentioned case, the existing temperature peak has been dampened to such a level that there is no longer any risk of scalding.

The invention is of course not in any way restricted to the pre- ferred embodiments described above, on the contrary many possibilities to modifications thereof should be apparent to a person skilled in the art without departing from the basic idea of the invention as defined in the appended claims.