EP3084316B1

EP3084316B1 - Heat exchanger apparatus

Info

Publication number: EP3084316B1
Application number: EP14821605.4A
Authority: EP
Inventors: Carsten NØRGÅRD
Original assignee: EC Power AS
Current assignee: EC Power AS
Priority date: 2013-12-20
Filing date: 2014-12-18
Publication date: 2020-04-22
Anticipated expiration: 2034-12-18
Also published as: WO2015091778A1; GB201322670D0; GB2522404A; GB2522404B; EP3084316A1

Description

The present invention relates to a heat exchanger apparatus and more particularly, but not exclusively, to an apparatus of the type used as part of an industrial or domestic central heating arrangement.
In a domestic or industrial central heating arrangement or installation, the components of the system i.e. the heat source, pumps, heat exchangers and the like, are fluidly connected together by means of pipes or conduits. The pipes are generally arranged to communicate hot or cold water between the components of the system such as from a heat source, via pumps, to one or a series of radiators.
In conventional arrangements these components are connected by a series of pipes which have been pre-formed, or bent, into the required geometry. The pipes are generally formed using specialist equipment so as to fluidly connect the various components together and to provide the required flow path(s) between components.
In these conventional arrangements the space required between the components of the heating system can be considerable as a result of the limit of radius of curvature which can be achieved for a given pipe diameter. In many applications it is in fact essential that the amount of space used is minimal and that the components (e.g. pumps, valves and the like) are situated as close together as possible. This is particularly the case in applications where an installation is required to be contained within a defined space or in a casing such as a combined heat and power unit (CHP).
Typical CHP systems generally comprise a motor/generator set, a heat storage unit, a boiler and a heat pump which are required to consume as small a space as possible. The heat (and electrical) source, together with the heat exchangers, pumps, valves and associated interconnections are often all contained within a single casing and it is desirable to minimise the size of the casing and thereby the overall space which the unit consumes.
One means to minimise the space consumed by the connections between components within such an installation is to use a manifold or distributor arrangement. A manifold can be used as a common conduit to which a number of components can be connected, thereby allowing fluid to flow between inlet and outlet ports along the manifold and between respective components. This does not however provide for specific flow paths between components.
An example of a distributor for providing a space saving arrangement can be seen in WO2007/066135 . This distributor allows for a space saving in the components used to create the required flow paths from various inputs and outputs in the installation. However, this distributor is arranged to receive fluid after heat exchange has occurred and it does not provide any improvement in the arrangement of the heat exchanger and related parts, such as pumps and the associated pipework. The heat exchanger apparatus will include a heat exchanger with primary and secondary circuits, a pump for each of the primary and secondary circuits, and associated valves for control of the flow. It is important in many situations to use a heat exchanger since it is necessary to separate systems with different pressures. For example, where the heat is obtained by cooling an engine in a combined heat and power device then the coolant circuit may have a maximum pressure that is not much higher than 1 bar. In contrast, a heating system for a building can have a design pressure of 3 bar or even up to 6 bar in tall buildings. There is hence a need for an efficient installation design that can include a heat exchanger.
An example of a heat exchanger system used in the context of CHP devices is found in WO 2005/036060 . Figure 1 of that document, which is identical to Figure 1 herein, shows a known heat exchanger arrangement, which is commonplace. A heat exchanger 11 has a primary side and secondary side. The primary side has an input 20 and an output 19. The secondary side has an input 18 and an output 21. Fluid such as water flows from a heat source 13, for example a boiler or engine, through the heat exchanger primary side and back to the heat source 13 again. This forms a primary circuit 23. On the secondary side, fluid such as water flows from a heat load 14, for example a space heating system such as a radiator system, through the secondary side of the heat exchanger and back to the load 14. This forms the secondary circuit 22. Heat is thereby transferred to the secondary circuit 22 from the primary circuit 23. Movement of fluid through the heat exchanger circuits is controlled by a primary side pump 10 and secondary side pump 7. The actual temperature of the water in the secondary circuit 22 is a function of the temperature differential between the two circuits, the thermal efficiency of the design of the heat exchanger 11, and the mass flow rate of the circuits and of the degradation of the heat exchanger.
In WO 2005/036060 refinements are proposed to improve the control of heat exchange by the use of valves controlled based on temperature measurements. However, there is no discussion of refinements based on the physical layout of the system and no suggestion that improvements in this area might be beneficial. Instead the system uses conventional pipework connections, for example as fitted by a plumber. These are known to be reliable and effective. The circular shape of pipes is well suited to containing and directing fluid flowing under pressure.
DE 202008003349 U1 discloses a domestic water heater comprising a plate heat exchanger, oriented at an angle to the vertical to avoid cold water flowing to a hot water tap. EP 2 413 046 A1 discloses a domestic water heater comprising a heat exchanger showing all features of the preamble of independent claim 1.
Viewed from a first aspect, the invention provides a heat exchanger apparatus comprising: a heat exchanger, the heat exchanger having a primary side and a secondary side, the secondary side having connections for a secondary side inlet and a secondary side outlet, and the primary side having a connection for a primary side inlet, wherein a first end of the heat exchanger has the connection for the primary side and one connection for the secondary side, and wherein a second end of the heat exchanger has the other connection for the secondary side; a primary circuit pump for propelling fluid through a primary circuit from the primary side inlet to a primary side outlet; a secondary circuit pump for propelling fluid through the secondary side of the heat exchanger and a through a secondary circuit connected thereto from the secondary side inlet to the secondary side outlet; and a secondary side manifold arrangement for connecting the secondary pump to the heat exchanger and to the secondary circuit; wherein both the primary pump and the secondary pump are arranged in parallel with the line between the first end and the second end of the heat exchanger and each of the pumps have a pump inlet and pump outlet with inlet and outlet flow directions generally parallel to the line between the first end and the second end of the heat exchanger; characterised in that the primary side of the heat exchanger has a connection for a the primary side outlet, and the second end of the heat exchanger has the other connection for the primary side; in that the heat exchanger apparatus further comprises a primary side manifold arrangement for connecting the primary pump to the heat exchanger and to the primary circuit; in that the primary circuit pump is for propelling fluid through the primary side of the heat exchanger to which the primary circuit is connected; and in that the primary and secondary manifold arrangements each connect one connector of one side of the heat exchanger to an inlet or outlet of the respective primary or secondary pump, connect the second connector of said one side of the heat exchanger to the respective primary or secondary circuit, and connect the respective primary or secondary circuit to the other of the inlet or outlet of the respective primary or secondary pump.
In this arrangement the pumps are placed parallel with the heat exchanger and with a line between the two ends of the heat exchanger. This provides a compact arrangement since the 'length' of the pump can be fitted alongside and within the 'length' of the heat exchanger. Typically the heat exchanger will be longer in one dimension than another, and this longest dimension will be between the two ends, which means that the proposed arrangement allows maximum space for the pumps whilst keeping the space required by the whole apparatus to a minimum. This layout can be understood from Figures 2 to 9, which show example arrangements. It is to be contrasted with known layouts, as shown in Figure 1 and WO 2005/036060 , where the pump is perpendicular to the heat exchanger rather than in parallel with it. The reason for this prior art arrangement is that the pumps are placed with the inlet and/or outlet aligned with the direction of flow for connections to the heat exchanger, which have a flow direction perpendicular to the heat exchanger.
It will be appreciated that numerous arrangements for the orientations of the pumps and heat exchanger are possible within this general arrangement. Provided that the pumps are in parallel with the heat exchanger orientation then the invention is not particularly restricted to any given arrangement, although as noted above it can be advantageous to connect the pump(s) to the cold end of the heat exchanger. In one example arrangement connect the pump(s) to the cold end of the heat exchanger. In one example arrangement the layout is as follows: the primary side outlet of the heat exchanger is at the top of the heat exchanger, which is in use vertically oriented, and this is connected by a first part of the primary side manifold arrangement to the primary circuit pump; the outlet of the primary circuit pump connects via the second part of the primary side manifold to the return for the primary circuit; the second part of the primary side manifold also connects the primary circuit flow to the heat exchanger primary side inlet; the secondary side inlet of the heat exchanger is at the top of the heat exchanger and this is connected by the first part of the secondary side manifold arrangement to the outlet of the secondary circuit pump; the second part of the secondary side manifold arrangement includes a feedback conduit connecting the secondary side outlet of the heat exchanger to the inlet of the secondary circuit pump; and the second part of the secondary side manifold arrangement also connects the secondary side outlet of the heat exchanger to the return for the secondary circuit, and connects the secondary circuit flow to the inlet of the secondary circuit pump; wherein a three-way valve controls the flow through the feedback conduit.
The manifold arrangement for one circuit (for one side of the heat exchanger) may be split into two parts, one part forming a coupling between the pump and the heat exchanger, and a second part forming couplings between the pump and the circuit and between the circuit and the heat exchanger. Preferably this second part of the manifold comprises connectors for coupling to the circuit, with the connectors being aligned and facing in the same direction. In preferred embodiments the connectors face away from the pump and are parallel with the line between the two ends of the heat exchanger. In the common situation where the line between the two ends of the heat exchanger is vertical then the connectors will be aligned with the vertical, and may for example be facing downwards.
Typically the heat exchanger connections will exit the heat exchanger in a direction perpendicular to the direction between the two ends of the heat exchanger. In this instance the manifold arrangement preferably acts to redirect the flow direction so that it is parallel with the direction between the two ends of the heat exchanger and aligned with the flow direction for the relevant on-going connection point at the pump or at the circuit. For example, the flow direction from an outlet of the primary side for the heat exchanger may be turned by the manifold so that it is aligned with the inlet of the primary side pump.
Preferably the manifold arrangement is a cast and/or machined manifold. Thus, the manifold is preferably not formed by conventional plumbing. Instead it may be a custom part specifically designed to form the required connections between the heat exchanger, the pump and the circuit. This allows for the design of the parts to be set prior to final assembly, which makes installation and final assembly of the heat exchanger apparatus far simpler. Since final assembly often occurs on site, where connections are made with existing heat sources and heat loads, then this can be a big advantage in terms of reduced time and reduced complexity, and hence reduced costs for the end user. In the cast and/or machined manifold the flow paths may have a circular geometry. This allows for the advantages of the circular shape of the flow paths to be maintained despite the fact that conventional plumbing is not used.
The heat exchanger may be an opposed (counter) flow heat exchanger, wherein the primary side and secondary side have flow directions that are in parallel but in opposite directions. That is to say, the first end of the heat exchanger will have an inlet for one side of the heat exchanger and an outlet for the other side, whereas the second end of the heat exchanger will have an outlet for the one side and an inlet for the other side. This means that the direction between the two ends of the heat exchanger is also the direction of fluid flow within the heat exchanger, with fluid flowing on one side from the first end to the second end and on the other side in from the second end to the first end. In this arrangement one end of the heat exchanger will be a hot end, with maximum temperature on both sides, and the other end of the heat exchanger will be a cold end, with the minimum temperature on both sides. Typically the primary side is designated as the side connected to the heat source, and hence the heat exchanger in this arrangement may have a primary side inlet connected to the heat source at the hot end, a primary side outlet returning cooled flow to the primary circuit at the cold end, a secondary side inlet receiving flow from the secondary circuit at the cold and, and a secondary side outlet returning heated flow to the heat load on the secondary circuit at the cold end.
In an alternative arrangement, the heat exchanger may be a cross flow heat exchanger. Some heat exchangers, such as brazed plate heat exchangers, do not provide a perfect counter flow but instead have a cross flow, although they can have a similar effectiveness to counter flow heat exchangers. The heat exchanger of the first aspect hence may be a brazed plate heat exchanger. This type of heat exchanger also has first and second ends with connections grouped in pairs at each end.
The heat exchanger may be oriented, in use, so that the direction between the first and second end is generally vertical and the hot end is at the top of the heat exchanger. This arrangement is often used in prior art systems since the flow through the heat exchanger is not disturbed by natural convection. However, in contrast to this typical prior art arrangement, in some preferred embodiments the heat exchanger apparatus is arranged, in use, so that the cold end is at the top of the heat exchanger. This allows for the pump to be at the cold part of the circuit that it drives. This is a particular advantage for higher temperature systems, as well as for high flow systems. It has been found that in such systems the effects of natural convection can be ignored.
It may be preferred for the pump to be at the cold part of the circuit, and hence in some embodiments the heat exchanger apparatus may be arranged so that the pump is at the cold part of the circuit. With this arrangement, when there are similar pump and manifold arrangements on both sides, then since the cold water from primary and secondary sides will generally be connected to the same end of the heat exchanger (for counter flow) then the pumps will also be connected to the same (cold) end. Then, when the pumps are mounted parallel to the heat exchanger, the other end of the pumps will get close to the other connections of the heat exchanger. Thus all four connections are now close together and can be oriented in the same direction. This provides an effective and compact arrangement.
The apparatus may include a feedback conduit connecting the inlet and outlet of the heat exchanger and a three-way valve for controlling the flow through and within the manifold arrangement. With the use of this valve the first aspect preferably references a pump and manifold on the secondary side, with the three-way valve being coupled to the manifold arrangement on the secondary side to control the flow through a feedback conduit on the secondary circuit. The feedback conduit may be formed as a part of the manifold arrangement. The feedback conduit may allow for the inlet and outlet of the pump to recycle all or a part of the secondary flow through the heat exchanger without the flow passing through the secondary circuit. It is particularly preferred for this three-way valve to be controlled based on indications of the temperature on the primary side of the heat exchanger, for example in accordance with the control arrangement described in WO 2005/036060 . In this way the feedback conduit on the secondary circuit can advantageously be used to control the temperature of the primary circuit. The three-way valve may advantageously be mounted in line with the secondary circuit pump, i.e. with an inlet or an outlet of the valve connecting to the inlet or outlet of the pump as well as to the circuit and the feedback conduit. This location for the valve allows for the most compact arrangement for the heat exchanger apparatus.
In some preferred implementations the heat exchanger apparatus is used with a combined heat and power device, with the heat exchanger transferring heat from a primary circuit which is the cooling circuit of the combined heat and power device to a secondary circuit connected to a heat load. For example the heat load may be a hot water storage system and/or a space heating system.
Certain preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

Figure 1 shows a prior art heat exchanger layout;
Figure 2 is a diagram of a preferred embodiment of a heat exchanger apparatus;
Figures 3 to 6 show various alternative layouts for the orientation of flow paths in the heat exchanger and for location of a three-way valve that, in preferred embodiments, controls the flow through the heat exchanger;
Figure 7 shows a heat exchanger apparatus in a system with an expansion vessel, a combined heat and power device as the heat source; and a hot water storage device as the heat load; and
Figures 8 and 9 are non-schematic views of a heat exchanger apparatus and expansion tank, where the relative sizes of the pumps, heat exchanger and manifolds can be seen.

The prior art arrangement of Figure 1 is explained above. Figure 2 shows an embodiment incorporating the proposed new heat exchanger apparatus. It will be understood that there is a significant difference in the orientation and location of the pumps for the two circuits 22, 23 for the arrangement of Figure 2 compared to that of Figure 1. There are also significant changes in the manifold arrangement that forms the connections for the primary and secondary circuits. In the arrangement of Figure 2 the primary circuit pump 10 and the secondary circuit pump 7 are in parallel with the heat exchanger 11. The flow direction between the inlet and outlet for the pumps 7, 10 is in parallel with the flow direction between the inlets 18, 20 and outlets 19, 21 of the heat exchanger. In the orientation shown in the Figure the flow direction is vertical in each case.
The system of Figure 2 communicates heat between a primary circuit 23 and a secondary circuit 22 through the heat exchanger 11. It consists of two pumps 7, 10, one heat exchanger 11, two lower manifold arrangements 6, 12 with internal and external connections 1, 2, 3, 4, joining the pumps 7, 10, heat exchanger 11 and return/flow for the two circuits 22, 23, and also two upper manifold arrangements, 8, 9 with internal connections between the pumps 7, 10 and the heat exchanger.
The heat exchanger 11 is of a type where the connections 18, 19, 20, 21 are grouped in pairs, and where each group of connections has one connection of the primary circuit and one of the secondary circuit. In this case the primary side outlet 19 and secondary side inlet 18 are at one end of the heat exchanger 11 and at the other end we find the primary side inlet 20 and secondary side outlet 21. This type of configuration is common for plate heat exchangers, and thus the heat exchangers described herein may be plate heat exchangers.
The lower primary side manifold 12 is mounted to primary side inlet 20 of the heat exchanger 11 and provides a connector 2 to join to the primary circuit flow and a connector 1 to join to the primary circuit return. The primary circuit return is joined to the outlet of the pump 10 and the inlet of the pump 10 is connected by the upper primary side manifold part 9 to the primary side outlet 19 from the heat exchanger 11. The manifold 12 is elongate and mounted basically perpendicular to the heat exchanger 11. In the preferred arrangement the heat exchanger 11 is positioned vertically and the manifold 12 horizontally on the lower set of connections from the heat exchanger. A similar arrangement is used for the secondary side lower manifold 6, which has a connector 3 to join to the secondary circuit return and a connector 4 to join to the secondary circuit flow. The secondary circuit flow is joined via the connector 4 to the inlet of the secondary circuit pump 7 and the secondary circuit return is joined via the connector 3 to the secondary side outlet 21 of the heat exchanger 11. The upper secondary side manifold part 8 couples the secondary circuit pump 7 to the inlet 18 for the secondary side of the heat exchanger 11. The lower manifolds 6, 12 together hold all of the external connections 1-4 to the heat source 13 (primary circuit 23) and heat load 14 (secondary circuit 22).
One pump 10 is mounted on the manifold to the left of the heat exchanger 11; the other pump 7 is mounted to the right. Both pumps 7, 10 are mounted in parallel with the heat exchanger 11. This results in a compact arrangement for the heat exchanger apparatus. With a vertical arrangement for the heat exchanger 11, one pump will pump upwards, the other downwards. This provides the counter flow in the heat exchanger 11.
The connections 1, 2, 3, 4 on the manifolds 6, 12 are close together and aligned facing in the same direction. They are hence easily accessible for coupling the heat exchanger apparatus to the heat source and heat load circuits. The installer can provide suitable pipework in advance for the required connections, and final assembly/installation of the heat exchanger apparatus is made simple since it is just necessary to join the connectors 1, 2, 3, 4 to the respective circuits, and possibly also to join the manifolds to the pumps and heat exchanger. Later maintenance is also made more straightforward, since the manifold arrangement allows for easy disconnection and removal of the heat exchanger apparatus, to permit replacement of one of the pumps 7, 10 or the heat exchanger 11.
Note that although in this example the primary circuit is shown on the left and the secondary circuit on the right, with the cold end of the heat exchanger at the top, the invention is not limited to this and in fact the primary loop and the secondary loop could be switched. Conventionally the heat exchanger 11 might be hot at the top and cold at the bottom. The heat exchanger 11 is normally used such that the hot water from the heat source 13 enters at the top of the heat exchanger 11 and leaves as cooled water at a lower connection of the heat exchanger 11. Then the cold return water of the heat load 14 enters at a lower connection and after being heated it leaves at the top of the heat exchanger 11. Especially for heat exchangers 11 used where the flow is sometimes slow, this is important since the flow through the heat exchanger 11 is then not disturbed by natural convection.
In some preferred embodiments a feedback conduit is provided in the lower secondary side manifold part 6 and a three-way valve 5 is used on the secondary circuit 22 to control feedback of fluid from the secondary circuit pump outlet through the secondary side inlet 18 of the secondary side of the heat exchanger 11. This can be used to control the temperature on the primary circuit 23. Figures 3 to 6 illustrate four different possible ways to build the three-way valve 5 into the manifold 6.
In Figure 3, the three-way valve 5 is a mixing valve that mixes the heated water from the heat exchanger 11 with the cold return water from the heat load 14. The outlet from the three--way valve 5 is into the pump 7. Thus, the valve 5 can divert flow from the heat exchanger outlet 21 back into the pump 7 in order to recirculate water on the secondary side of the heat exchanger 11 and control primary side temperature.
In Figure 4, the three-way valve 5 is a diverter valve fed with heated water from the pump 7. The water can be diverted between the hot flow to the heat load 14 and the hot water to be mixed with the cold return before entering the heat exchanger 11. The valve 5 can hence couple the outlet from the pump 7 to the inlet 18 for the secondary side of the heat exchanger. Again this allows for recirculation on the secondary side.
The arrangement of Figure 5 again uses a diverter valve as the three-way valve 5. In this case it is fed by heated water from the heat exchanger 11. The water can be diverted between the hot flow to the heat load 14 and the hot water to be mixed with the cold return before entering the pump 7. When flow is diverted via the feedback conduit in the manifold 6 then it can recirculate on the secondary side to control the primary side temperature.
The final alternative shown in Figure 6 has a three-way valve 5 as a mixing valve that mixes the heated water from the pump 7 with the cold return water from the heat load 14. The outlet from the valve 5 is into the heat exchanger 11.
Of these four alternatives the layout of Figure 3 and Figure 4 are preferred on the basis that the valve 5 is positioned far from the heat exchanger 11. This allows more space for the valve 5, and maintains the advantage of a compact arrangement- especially when a valve actuator is placed on top of the manifold as in the preferred arrangement of Figures 8 and 9, which is discussed below. In the less preferred arrangements of Figures 5 and 6 the valve actuator may take up the same horizontal space as the heat exchanger 11, and hence the manifold arrangement has to be extended compared to that of Figures 3 and 4.
In high temperature systems it is furthermore preferable to place pumps at as cold a location as possible. This will help maintain the best operating conditions for the pump as well as ensuring that the distance from the boiling point of the water and the pressure that the pump provides is appropriate for the pump. Therefore the pump on the primary circuit, that is the hottest, should be placed after the cooling through the heat exchanger. For this reason the layout of Figure 3 is most preferred, although it will be appreciated that this might not apply for all systems.
It will be seen that the layout of Figure 3 does not follow the conventional rule that heat exchangers should be oriented with the highest temperatures at the top. However, it has been found that the effects of convection flow can be ignored when the heat exchanger has high flow rates and high temperatures, which is the case when the heat exchanger apparatus is used for heat exchanger with a combined heat and power device as shown in Figure 7, which is one possible use for this apparatus.
In Figure 7, as well as a combined heat and power unit 13 as an example of a heat source, and a hot water storage device 14 as an example of a heat load, the heat exchanger apparatus is also connected to an expansion vessel 15. For the primary circuit 23 there is often a need for an expansion vessel 15, since the circuit is operated under pressure. The expansion vessel 15 may be of the type that also is the point where water is added to the system (in the same way as the water container in the car). By placing this just above the suction side of the pump 10 on the primary circuit 23, the water supply to the pump 10 is ensured when there is water in the vessel 15.
In order to illustrate the heat exchanger apparatus with reference to the true sizes of the various parts, rather than a schematic illustration, Figures 8 and 9 show a non-schematic drawing of a heat exchanger apparatus as described herein. The various parts have the same reference numbers and are in the same arrangement as shown in Figure 3, with the addition of an expansion vessel as shown in Figure 7. It will be seen that the pumps 7, 10 and the heat exchanger 11 occupy the same vertical space, which allows for a compact arrangement. Also, the three-way valve 5 is aligned with the pump 7 in the secondary circuit, which means that there is no need to lengthen the manifold 6 on that side. The pumps 7, 10 have inlets and outlets with a vertical flow direction, and this is in parallel with the flow direction from inlet to outlet on the heat exchanger 11.

Claims

A heat exchanger apparatus comprising:
a heat exchanger (11), the heat exchanger having a primary side and a secondary side, the secondary side having connections for a secondary side inlet (18) and a secondary side outlet (21), and the primary side having a connection for a primary side inlet (20; 19), wherein a first end of the heat exchanger has the connection for the primary side (20; 19) and one connection for the secondary side (18; 21), and wherein a second end of the heat exchanger has the other connection for the secondary side (21; 18);

a primary circuit pump (10) for propelling fluid through a primary circuit (23) from the primary side inlet to a primary side outlet (19);

a secondary circuit pump (7) for propelling fluid through the secondary side of the heat exchanger and through a secondary circuit (22) connected thereto from the secondary side inlet to the secondary side outlet; and

a secondary side manifold arrangement (8, 6) for connecting the secondary pump to the heat exchanger and to the secondary circuit;

wherein both the primary pump and the secondary pump are arranged in parallel with the line between the first end and the second end of the heat exchanger and each of the pumps have a pump inlet and pump outlet with inlet and outlet flow directions generally parallel to the line between the first end and the second end of the heat exchanger;

characterised in that the primary side of the heat exchanger has a connection for the primary side outlet (19; 20), and the second end of the heat exchanger has the other connection (19; 20) for the primary side;

in that the heat exchanger apparatus further comprises a primary side manifold arrangement (9, 12) for connecting the primary pump to the heat exchanger and to the primary circuit;

in that the primary circuit pump is for propelling fluid through the primary side of the heat exchanger to which the primary circuit is connected; and

in that the primary and secondary manifold arrangements each connect (9; 8) one connector (19; 20; 18; 21) of one side of the heat exchanger to an inlet or outlet of the respective primary or secondary pump, connect (12; 6) the second connector (20; 19; 21; 18) of said one side of the heat exchanger to the respective primary or secondary circuit (23; 22), and connect the respective primary or secondary circuit to the other of the inlet or outlet of the respective primary or secondary pump.
A heat exchanger apparatus as claimed in claim 1, wherein at least one of the manifold arrangements is split into two parts, a first part (9; 8) forming a coupling between the respective pump (10; 7) and the heat exchanger, and a second part (12; 6) forming couplings between the respective pump and the respective circuit (23; 22) and between the respective circuit and the heat exchanger.
A heat exchanger apparatus as claimed in claim 2, wherein the second part (12; 6) of the at least one of the manifolds comprises connectors (1, 2; 3, 4) for coupling to the respective circuit (23; 22), the connectors being aligned and facing in the same direction.
A heat exchanger apparatus as claimed in claim 3, wherein the connectors (1, 2; 3, 4) face away from the respective pump (10; 7) and are parallel with the line between the two ends of the heat exchanger.
A heat exchanger apparatus as claimed in any preceding claim, wherein each manifold arrangement is cast and/or machined.
A heat exchanger apparatus as claimed in any preceding claim, wherein the heat exchanger is an opposed flow heat exchanger, with the first end of the heat exchanger having an inlet (20; 18) for one side of the heat exchanger and an outlet (21; 19) for the other side, and the second end of the heat exchanger having an outlet (19; 21) for the one side and an inlet (18; 20) for the other side, such that one end of the heat exchanger will be a hot end, with maximum temperature on both sides, and the other end of the heat exchanger will be a cold end, with minimum temperature on both sides.
A heat exchanger apparatus as claimed in claim 6, wherein the heat exchanger apparatus is arranged, in use, so that the cold end is at the top of the heat exchanger.
A heat exchanger apparatus as claimed in claim 6 or 7, wherein the heat exchanger apparatus is arranged so that at least one of the pumps is connected to the cold end of the heat exchanger.
A heat exchanger apparatus as claimed in any preceding claim, wherein the apparatus includes a feedback conduit connecting the inlet (18) and outlet (21) of the secondary side of the heat exchanger and a three-way valve (5) for controlling the flow through and within at least one of the manifold arrangements (6).
A heat exchanger apparatus as claimed in claim 9, wherein the feedback conduit is formed as a part of the manifold arrangement.
A heat exchanger apparatus as claimed in any preceding claim, wherein:
the primary side outlet (19) of the heat exchanger is at the top of the heat exchanger, which is in use vertically oriented, and this is connected by a first part (9) of the primary side manifold arrangement to the primary circuit pump;

the outlet of the primary circuit pump connects via the second part (12) of the primary side manifold to the return for the primary circuit;

the second part of the primary side manifold also connects the primary circuit flow to the heat exchanger primary side inlet;

the secondary side inlet (18) of the heat exchanger is at the top of the heat exchanger and this is connected by the first part (8) of the secondary side manifold arrangement to the outlet of the secondary circuit pump;

the second part (6) of the secondary side manifold arrangement includes a feedback conduit connecting the secondary side outlet (21) of the heat exchanger to the inlet of the secondary circuit pump; and

the second part of the secondary side manifold arrangement also connects the secondary side outlet of the heat exchanger to the return for the secondary circuit, and connects the secondary circuit flow to the inlet of the secondary circuit pump;

wherein a three-way valve (5) controls the flow through the feedback conduit.
A heating system including a heat exchanger as claimed in any preceding claim, a combined heat and power device (13), and a heat load (14), wherein the heat exchanger is arranged to transfer heat from the primary circuit, which is the cooling circuit of the combined heat and power device, to the secondary circuit connected to the heat load.