A HEAT EXCHANGER ARRANGEMENT AND METHOD FOR CONTROL OF A FLUID THROUGH A HEAT EXCHANGER ARRANGEMENT

Abstract: A plate heat exchanger (6) comprising plates (8) with port holes forming port channels (15, 16), where some passages are part of a set of tap-water passages (22) communicating with two of said port channels. A disc (12), with an opening (25), divides one (16) of the tap-water port channels into a first and a second part, such that the tap-water passages (22) are divided into at least two, serially connected, groups. An elongated temperature sensor (26) extends through the disc (12), substantially closing the opening (25). In this way, the temperature sensor may sense two different tap-water temperatures, i.e. the temperatures in the respective parts of the divided port channel, and actuate a valve, controlling the flow of a primary fluid, to an extent representative of the temperatures in both port channels.

Description: A heat exchanger arrangement and method for control of a fluid through a heat exchanger arrangement The present invention relates to a heat exchanger arrangement for heating of tap water by means of a primary fluid comprising a plate heat exchanger, which comprises a plate package of heat exchanger plates, which are provided with port holes forming port channels in the plate package and between which there is delimited heat exchange passages, some of which are part of a set of tap water passages arranged to be flown through by tap water and others are part of a set of primary passages arranged to be flown through by the primary fluid. The heat exchanger arrangement further comprises a valve arranged to control a flow of the primary fluid through said primary passages and an elongated temperature sensor arranged to actuate said valve. In the plate heat exchanger at least one of said tap water passages communicates with two first of the said port channels and at least one of said primary passages communicates with two other of said port channels. A flow actuating means divides one of said two first port channels in a first and a second part and said set of tap water passages are divided into at least two groups connected in series, in which groups the tap water passages are connected in parallel. The invention also comprises a method for control of a fluid of primary fluid through a heat exchanger arrangement arranged for heating of tap water by means of the primary fluid and comprising a plate heat exchanger and a valve according to the above description and at least one temperature sensor for actuating the valve. A heat exchanger arrangement of the said kind may form a part of a unit for heating of tap water in a house, alternatively a flat. The primary fluid, by means of which the tap water is heated, may consist of for example district heating water or water, which has been heated in an oil or gas heated central heater. When the tap water is mentioned in the following it means tap water which is heated or has been heated in the heat exchanger arrangement. Further there is meant by the expression tapping, tapping of tap water which has been heated in the heat exchanger arrangement. Said valve is arranged to control the flow of the primary fluid through the primary passages in the plate heat exchanger in dependence of the actual temperature of the tap water. The elongated temperature sensor, which senses the temperature of the tap water, may be filled with a substance, which makes a pressure inside the temperature sensor to change in dependence of the temperature to which the same is exposed. The temperature sensor is in such a case connected to the valve by means of a thin so called capillary tube, through which variations in pressure within the temperature sensor are transferred to the valve, which in its turn actuates the flow of primary fluid through the heat exchanger arrangement. The valve may be of a kind which is adjustable between two different starting points, one for each of two operation cases for the heat exchanger arrangement, and adjustable from each of these two starting points. With starting point there is meant a setting for achieving a specific tap water temperature at certain determined operation conditions, as a certain pressure and a certain temperature of the primary fluid. One operation case is intended for tapping and the other operation case is intended for breaks in the tapping, at which in the later case the stationary tap water in the plate heat exchanger shall be uept at a certain desired temperature. The valve shall control the flow of primary fluid in dependence of the actual tap water temperature. Up to now valves used in heat exchanger arrangements of the described kind are relatively costly and it is therefore desirable that simpler and less expensive valves could be used. Consequently, it is desirable that a control of a valve shall be possible in both the operation cases mentioned above from one and the same starting point for the valve. In order that such a simpler valve could be used and a good control of the primary fluid shall be obtained it is necessary that the temperature sensor is actuated rapidly when an operation case for the heat exchanger arrangement is changed. The temperature sensor is as has been mentioned arranged for sensing the tap water temperature and therefore it rapidly senses changed operation conditions for tapping. However, the temperature sensor may be so arranged that it cannot sense the tap water temperature in the plate heat exchanger with sufficient accuracy just when the tapping is ended and during breaks in the tapping. If the temperature sensor is arranged in an unsuitable place in the heat exchanger arrangement, the flow of primary fluid will not be controlled sufficiently rapidly by the valve, at which the stationary tap water in the plate heat exchanger may be heated to a temperature close to the temperature of the primary fluid. District heating water may for example have a temperature of 65-90 degrees C. At that a large part of the heat energy in the primary fluid goes to waste. When tapping starts again there is a large risk for scald and if the tap water contains lime there may be lime deposits on the heat exchanger plates. It has earlier been proposed that a temperature sensor shall be actuated both by the tap water and the primary fluid at which the problems men- tioned above may be avoided. For example each of the Danish patent application 8803153 and the Danish patent publication DK 171519 B1 describe a separate heat exchanger arranged to actuate an elongated temperature sensor. To use a separate heat exchanger to actuate the temperature sensor is, however, both space and cost demanding. EP 608 195 B1 describes a plate heat exchanger in a heat exchanger arrangement of the kind described above. The heat exchange passages in the plate heat exchanger are divided into two groups, in which one group of heat exchange passages are arranged to be flown through by tap water and district water in so called diagonal flow and the second group of heat exchange passages are arranged to be flown through in so called parallel flow. Further, there is a flow actuating means in the shape of a special plate arranged between the groups. The plate divides a first port channel into two parts and is provided with a tube extending through one of the port channel parts. A first part of the first port channel is flown through by tap water and a second part of the same is flown through by district water. In the first port channel part and in the tube a temperature sensor extends for simultaneous sensing of the temperature of the tap water and of the district water. In a plate heat exchanger according to EP 608 195 B1 three kinds of different heat exchange plates must be used in order to achieve a diagonal flow and a parallel flow. This is of disadvantage as regards the costs. Further, the said tube must be connected with the special plate between the groups in a fluid tight manner such that tap water and district heating water in the respective parts of the first port channel shall not mix. This also implies extra costs for producing the plate heat exchanger. The aim of the invention is to solve the problem mentioned above with a bad control of the temperature of the tap water in a heat exchanger arrangement of the kind mentioned in the introduction and to avoid problems connected with tightening of a connection between a tube and a plate in a plate heat exchanger according to EP 608 195 B1. This aim may according to the present invention be achieved in that the tap water passages in both said groups communicate with said two first port channels, that the said flow actuating means is provided with an opening and that the said elongated temperature sensor extends through the said opening in such a way that it is situated in both of the mentioned port channels first and second parts and substantially closes the opening. According to the invention the temperature sensor extends into a port channel which is arranged to be flown through only by tap water. Therefore it is not necessary that it is completely tight around the temperature sensor in the opening in the flow actuating means. The temperature sensor is with this arrangement arranged to give a signal which is representative for both a temperature of the tap water in the first part of the port channel and a temperature of the tap water in the second part of the port channel. Such a so called representative temperature is lower than the outlet temperature of the tap water, which means that when the tapping is discontinued the valve will close the flow of the primary fluid more rapidly than if the temperature sensor was arranged to feel the outlet temperature of the tap water. During breaks in the tapping the stationary tap water in the port channel around the temperature sensor is heated by the primary fluid in the primary passages, at which the temperature sensor is actuated. In such cases the present invention is of advantage in that the flow of the primary fluid may be kept very low, which makes a good energy economy possible. Further, the temperature in the plate heat exchanger may be kept at a low level, at which lime is not deposited on the heat exchanger plates and from which the tap water easily may be heated to a desired outlet temperature when tapping starts. In a preferred embodiment of the invention a further flow actuating means divides a second of said two first port channels into two parts, at which the said set of tap water passages is divided into three groups connected in series. With advantage said first part of said first port channel is arranged to be flown through by tap water, which already has passed at least one of said groups of tap water passages connected in series. In contrast to the first mentioned embodiment, in which the first part of said one port channel is flown through by unheated tap water, the said one port channel is flown through in its first part by tap water with a temperature which is higher than the inlet temperature of the tap water in the second mentioned embodiment. The so called representative temperature will therewith be higher than in the first mentioned embodiment, which is of advantage among all for the accuracy of the control of the valve and for setting the starting point of the valve. According to two further embodiments of the invention also said set of primary passages is divided into two, alternatively three, groups con- nected in series. If the heat exchanger plates in the plate heat exchanger are mainly rectangular and said port holes are situated in the corner parts of the heat exchanger plates, at which port holes forming said two first port channels are situated at the same side of the respective heat exchanger plates, all the heat exchanger passages in the plate heat exchanger are arranged to be flown through in a so called parallel flow manner. Such a plate heat exchanger may be manufactured of heat exchanger plates of a single kind, which is of advantage in view of the expenses. Alternatively, the port holes forming said two first port channels may be arranged in diagonally opposite corner parts of the respective heat exchanger plates, at which all the heat exchanger passages in the plate heat exchanger are arranged to be flown through in so called diagonal flow manner. Such a plate heat exchanger may be manufactured of heat exchanger plates of only two kinds. The method according to the invention is characterised in that the temperature of the tap water is sensed on at least two different places in the plate heat exchanger by one or several temperature sensors and in that the flow of primary fluid through said primary passages is controlled by said valve based on the sensed values of the temperature of the tap water. By sensing the temperature of the tap water on two different places in the plate heat exchanger different values of the temperature of the tap water may be used for actuating the valve. According to the method one, two or several separate temperature sensors may be used for sensing the tap water temperature as has been mentioned. When only one temperature sensor is used it is preferably of said mentioned elongated kind. If several temperature sensors are used, these may consist of electrical temperature sensors as thermistors or thermoelement, for example such in which the resistance is changed in dependence of the temperature they are subjected to. These electrical sensors may be arranged on one or both sides of the flow actuating means. In a heat exchanger arrangement comprising a plate heat exchanger, in which said tap water passages in both said groups communicate with said two first port channels, the temperature of the tap water may be sensed in the first and second part of said one of the two first port channels. This is possible also with a single preferably elongated temperature sensor. When two or several separate temperature sensors are used the tap water temperature may be sensed in at least one of said tap water passages or in a port channel which is not in line with said one of the two first port channels. With advantage the temperature of the tap water may be sensed after it at least partly has been flown through at least one of said groups of tap water passages connected in series. The invention shall be described further with reference to the attached drawing, on which fig. 1 shows a unit for heating of tap water, comprising a heat exchanger arrangement according to an embodiment of the invention, and fig. 2-4 schematically show two different plate heat exchangers for heat exchanger arrangements according to the invention. Fig. 1 shows a unit 1 for heating tap water. The unit 1 comprises a heat exchanger arrangement 2 with a plate heat exchanger 3 and a valve 4, which is connected to an elongated temperature sensor by way of a capillary tube 5. In the heat exchanger arrangement 2 the tap water is heated by a primary fluid, at which the actual heat exchange takes place in the plate heat exchanger 3. The elongated temperature sensor is filled with for example carbon dioxide and is arranged within the plate heat exchanger in such a way that it reacts to a representative tap water temperature based on the tap water temperature in different parts of the plate heat exchanger 3. When the temperature sensor is subjected to different temperatures the pressure within the temperature sensor is changed and these changes in pressure are transferred by way of the capillary tube to the valve 4, which actuates a flow of the primary fluid through the plate heat exchanger 3. Depending on which representative temperature of the tap water which the temperature sensor reacts to the valve 4 will increase or diminish the flow of primary fluid. In order to obtain a suitable outlet temperature of the tap water during existing operation conditions, for example 55 degrees C, at a certain flow of tap water, the valve 4 is provided with means for adjustment of its starting position. A certain flow of tap water during a specific operation condition corresponds to a certain temperature of the tap water which leaves the plate heat exchanger. The flow of tap water through the heat exchanger arrangement and the plate heat exchanger is determined by the need at the tap points which the unit 1 provides with tap water. In fig 2 and 3 there is shown a possible embodiment of a plate heat exchanger 6 for a heat exchanger arrangement according to the invention. The plate heat exchanger 6 comprises a plate package 7 of heat exchanging plates 8 provided with a press pattern of grooves and ridges, two end plates 9, 10 and flow actuating means in the shape of discs 1 1 , 12. Each heat exchanger plate 8 is rectangular and in its corner parts provided with port holes 13, 14 forming port channels in the plate package 7. Two of the port channels 15, 16 are shown in fig 3. Exactly in front of the two port channels 15, 16 there are connection flanges 17-20 for connection to tubes, which lead the tap water and the primary fluid to and from the plate heat exchanger 6 when this is a part of a heat exchanger arrangement. Between the heat exchanger plates 8 there is formed a set of primary passages 21 and a set of tap water passages 22 which each communicate with two of the port channels. The primary passages 21 are arranged to be flown through by primary fluid and the tap water passages 22 are arranged to be flown through by tap water. Each of the sets of passages 21 and 22 is divided into two groups connected in series by means of the discs 11 , 12, which are arranged in the port channels 15, 16. Within each groups the passages 21 and 22 are connected in parallel, respectively. During tapping primary fluid flows into the plate heat exchanger 6 through the connection flange 17 and a first part of the port channel 15. The primary fluid flows on by way of the first group of primary passages 21 to a part 23 of the plate heat exchanger 6 which is shown in fig 2. By way of a port channel, not shown, in this part 23 of the heat exchanger the primary fluid flows into the second group of primary passages 21 and from there by way of a second part of the port channel 15 and the connection flange 18 out from the plate heat exchanger 6. In a corresponding way the tap water flows into the plate heat exchanger 6 through the connection flange 19 and by way of a first part of the port channel 16 into the first group of tap water passages 22. In a part 24 of the plate heat exchanger 6, which is shown in fig. 2, the tap water flows through a not shown port channel further into the second group of tap water passages 22 and by way of a second part of the port channel 16 and the connection flange 20 out from the plate heat exchanger 6. The disc 12 is provided with an opening 25, which has a diameter which corresponds to an outer diameter of a temperature sensor 26 which extends in the port channel 16 through the opening 25. The temperature sensor 26 mainly closes the opening 25, such that the disc 12 retains its flow actuating function. A little leakage of tap water through the opening 25 around the temperature sensor 26 may be accepted since the port channel 16 on both sides of the disc 12 is filled with tap water. When tapping the tap water in the first part of the port channel 16 has not been heated by the primary fluid. The tap water in the second part of the port channel 16 has flown through all tap water passages 22 and has been heated to the outlet temperature of the tap water. During tapping the temperature sensor 26 will consequently feel two different temperatures, i.e. the inlet and outlet temperature of the tap water, and at that react to a so called representative temperature. Such a representative temperature does not necessarily consist of the mean temperature between the inlet and outlet temperature of the tap water. During breaks in the tapping the stationary tap water and primary fluid in the plate heat exchanger 6 will cool down. The lowering of the temperature of the tap water will be sensed by the temperature sensor 26, at which the valve 4 in the heat exchanger arrangement is opened such that primary fluid again starts to flow through the primary passages 21 and heats the stationary tap water in the tap water passages 22. The primary fluid, which flows through the plate heat exchanger, heats also the stationary tap water in the port channel 16 until the representative temperature is so high that the temperature sensor 26 forces the valve 4 to close. The tap water in the first part of the port channel 16 has at that a temperature which is higher than the normal inlet temperature of the tap water and the tap water in the second part of the port channel 16 has a temperature which is lower than the normal outlet temperature of the tap water during tapping. In stead of the elongated temperature sensor 26 shown in fig. 3, one may, within the scope of the invention use electrical temperature sensors. These may be used on one side of the disc 25 or on both sides of the same. If electrical sensors are used there is of course no opening in the disc 25. It is possible to sense the temperature either at some selected points or to arrange a number of sensors in the tap water passage. Fig. 4 shows schematically the flow path for tap water through a plate heat exchanger 3 according to fig 1 , comprising several usual heat exchanger plates 27 and two specially designed heat exchanger plates 28, 29, which serve as flow actuating means in that they have fewer than four port holes. The heat exchanger plates 27 - 29 and the two end plates 30, 31 form a plate package 32. The heat exchanger plates 27 - 29 abut each other around the port holes such that a set of tap water passages 33 and a set of primary passages 34 are formed between the heat exchanger plates 27 - 29. Four port channels 35 - 38 extend into the plate package 32, of which three 35 - 37 are seen in fig. 4. A broken line 39 symbolises the flow path of the tap water through the plate package 32. At the heat exchanger plate 28 the port channel 35 is divided into two parts and at the heat exchanger plate 29 the port channel 36 is divided into two parts in that the heat exchanger plates 28 and 29 are not provided with port holes straight in front of the respective port channels 35 and 36. By this division of the port channels 35 and 36 the tap water passages 33 are divided into three groups 40 of tap water passages connected in series. The heat exchanger plate 29 and an adjacent heat exchanger plate are provided with openings 41 around which these two heat exchanger plates tightly lie close to are each other. Through the openings 41 a temperature sensor is arranged to extend into the port channel 36 mainly closing the openings 41. A dotted line 42 shows the flow direction of the primary fluid through the plate package 32. Also each of the port channels 37 and 38 are divided into two parts by the heat exchanger plates 28 and 29, which lack port holes straight in front of these two port channels. At that also the primary passages 34 are divided into three groups 43 connected in series. Several variations of the invention are possible within the scope of the following claims. Thus the heat exchanger passages for the primary fluid does not need to be divided into the same number of groups as the heat exchanger passages for the tap water but may for example be part of a single group, within which all heat exchanger passages are connected in parallel. The number of heat exchanger plates may be more or less than what has been shown in fig. 2 - 4. The heat exchanger plates may be permanently joined to each other in abutting points between the heat exchanger plates for example by soldering, welding or gluing. Alternatively, packages may be arranged between the heat exchanger plates, at which these must be kept together, for example by means of bolts and nuts. In fig. 4 there is seen that the temperature sensor may be arranged in a port channel 36, in which the temperature sensor is arranged to be surrounded only by heated tap water, i.e. the temperature sensor is not surrounded by not heated tap water. Further the temperature sensor may not need to be arranged to extend such that it extends equally long on both sides of the flow actuating means but may extend to a longer part in one part of the first port channel than in another part of the same. Depending on how the heat exchanger plates with four port holes are pressed around the port holes and how the heat exchanger plates with fewer than four port holes, which make up the flow actuating means, are pressed in the parts which divide a port channel into two parts, two tap water passages, alternatively two primary passages, in the plate heat exchanger may be arranged close to each other on each side of a heat exchanger plate forming a flow actuating means. The heat exchanger plates may be formed by a single plate but may alternatively be formed of a double plate such that the heat exchanger plate consists of two mainly identical plate elements abutting each other in a tight manner. Such plate elements are only connected to each other at certain places such that there is formed between the plate elements a thin space which communicates with the surroundings of the plate heat exchanger. A leakage through one of the plate elements may be indicated outside the plate heat exchanger before both plate elements in a heat exchanger plate have burst. At that there is avoided a mixture of tap water and primary fluid. In that the plate heat exchanger according to the invention in its heat exchanging part may be constructed of only heat exchanger plates, i.e. no further means, which are arranged between the tap water and the primary fluid are necessary, the invention shows great advantages in relation to the prior art as described above. For example it is difficult to produce a plate heat exchanger as described in EP 608 195 B1 to a reasonable cost with both heat exchanger plates of double plate and the said tube for the temperature sensor consisting of double tube elements. Such a tube of double tube elements with a space therebetween, which communicates with the surrounding of the plate heat exchanger is necessary to indicate a leakage through the tube such that mixing of the tap water with primary fluid may be avoided. If several separate, i.e. electrical, temperature sensors are used for sensing the tap water temperature these may actuate the valve by way of a separate control unit.

Claims: Claims 1. A heat exchanger arrangement for heating tap water by means of a primary fluid comprising a plate heat exchanger (3; 6) comprising a plate package (7; 32) of heat exchanger plates (8; 27), which are provided with port holes (13,14) forming port channels (15,16; 35-38) in the plate package (7; 32) and between which heat exchange passages are formed, of which some are part of a set of tap water passages (22; 23) intended to be flown through by tap water and others are part of a set of primary passages (21 ; 34) adapted to be flown through by the primary fluid, a valve (4) arranged for control of a flow of the primary fluid through said primary passages (21 ; 34), and an elongated temperature sensor (26) to influence said valve (4), at which in said plate heat exchanger (3; 6) at least one of said tap water passages (22; 33) communicates with two first of the said port channels (16; 35; 36) and at least one of the said primary passages (21 ; 34) communicates with two other of said port channels (15; 37, 38), a flow actuating means (12; 29) divides one of said two first port channels (16; 36) into a first and a second part and said set of tap water passages (22; 33) are divided into at least two groups (40) connected in series, in which groups the tap water passages (22; 33) are connected in parallel, c h a r a c t e r i s e d i n that tap water passages (22; 33) in both said groups (40) communicate with said first two port channels (16; 35; 36), - that said flow actuating means (12; 29) are provided with an opening (25; 41 ), and that said elongated temperature sensor (26) extends through the said opening (25; 41 ) such that it is situated in both the first and second part of the said port channel (16, 36) and to a considerable extent closes the openings (25; 41 ). 2. A heat exchanger arrangement according to claim 1 , in which a further flow actuating means (28) divides a second (35) of said two first port channels (35, 36) into two parts, at which said set of tap water passages (33) are divided into three groups (40) connected in series. 3. A heat exchanger arrangement according to claim 2, in which said first part of said one port channel (36) is adapted to be flown through by tap water, which has flown through at least one of said groups (40) of tap water passages connected in series. 4. A heat exchanger arrangement according to any of the preceding claims, wherein said set of primary passages (21 ; 34) are divided into at least two groups (43) connected in series, in which groups the primary passages (21 ; 34) are connected in parallel. 5. A heat exchanger arrangement according to claim 4, wherein said set of primary passages (34) are divided into three groups (43) connected in series. 6. A heat exchanger arrangement according to any of the preceding claims, wherein said heat exchanger plates (8; 27) are mainly rectangular and said port holes (13,14) are situated in the corner parts of the heat exchanger plates (8; 27), wherein port holes forming said two first port channels (16; 35, 36) are situated at the same side of the respective heat exchanger plates (8; 27). 7. A heat exchanger arrangement according to any of the claims 1-5, wherein the said heat exchanger plates (8; 27) are mainly rectangular and said port holes (13,14) are situated in the corner parts of the heat exchanger plates (8; 27), at which port holes forming the said two first port channels are situated in diagonally opposite corner parts of the respective heat exchanger plates (8; 27). 8. A method for control of a flow of primary fluid through a heat exchanger arrangement for heating tap water by means of said primary fluid, comprising a plate heat exchanger comprising a plate package of heat exchange plates, which are provided with port holes forming port channels in the plate package and between which heat exchange passages are delimited, wherein some are part of a set of tap water passages arranged to be flown through by tap water and others are part of a set of primary passages arranged to be flown through by the primary fluid, a valve is arranged to control said flow of the primary fluid, and at least one temperature sensor to actuate said valve, wherein in said plate heat exchanger - at least one of said tap water passages communicates with two first of said port channels and at least one of said primary passages communicates with two other of said port channels, a flow actuating means divides one of the said two first port channels into a first and a second part, and said set of tap water passages is divided into at least two groups connected in series, within which group the tap water passages are connected in parallel, wherein the temperature of the tap water is sensed at at least two different places in said plate heat exchanger by at least said temperature sensor, said flow of primary fluid through said primary passages is controlled by said valve based on the sensed values of the temperature of the tap water. 9. A method according tc claim 8, in which the temperature of the tap water is sensed by at least two separate temperature sensors. 10. A method according to any of claims 8 and 9 in a heat exchanger arrangement comprising a plate heat exchanger, in which said tap water passages in both the said groups communicate with said two first port channels, at which the temperature of the tap water is sensed in said first and second part of said one of the two first port channels. 11. A method according to claim 9, in which the temperature of the tap water is sensed in at least one of said tap water passages. 12. A method according to any of claims 8-11 , in which the temperature of the tap water is sensed after having passed at least one of said groups of tap water passages connected in series.

Inventors: ENGSTROEM ANDERS, HELIN PEROLA MAGNUS, ENGSTROEM, ANDERS, HELIN, PEROLA, MAGNUS
Applicants: ALFA LAVAL AB, ENGSTROEM ANDERS, HELIN PEROLA MAGNUS, ENGSTROEM, ANDERS, HELIN, PEROLA, MAGNUS
Application year: 2000
Main classification: F28F27
IPC codes: F24D19, F28D9, F28F27