GB2262593A

GB2262593A - An apparatus for and method of providing hot sanitary water

Info

Publication number: GB2262593A
Application number: GB9126764A
Authority: GB
Inventors: David Beale
Original assignee: INTER ALBION Ltd
Current assignee: INTER ALBION Ltd
Priority date: 1991-12-17
Filing date: 1991-12-17
Publication date: 1993-06-23
Anticipated expiration: 2011-12-17
Also published as: GB9126764D0; GB2262593B

Abstract

An apparatus for providing hot sanitary or domestic water includes a storage vessel (11) having an inlet in communication with a supply of primary water from a boiler (1) and a mixing valve (14), which is in communication with the storage vessel (11) and with the supply of primary water from the boiler and which is adapted to mix the primary water from the storage vessel (11) with water from the direct supply of primary water, and a heat exchanger (6) to effect heat exchange between the mixed primary water and a supply of sanitary water which flows in thermal contact with the primary water in the heat exchanger (6). A 3-way valve (9) directs hot water alternatively to the sanitary system or to a central heating system (4) in response to a signal from a flow detector (10) in the sanitary system supply line (5). <IMAGE>

Description

AN APPARATUS FOR AND A METHOD OF PROVIDING HOT SANITARY WATER The invention relates to an apparatus for and a method of providing hot sanitary water.

Conventionally, a system for providing hot sanitary water for use by a user may be combined with a central heating system, a common boiler being employed to provide the heat for both systems. This is achieved by arranging the boiler to heat up primary water which is fed to either the central heating system, or, when sanitary water is required, is diverted to the water heating system where the primary water undergoes heat exchange with sanitary water. A flow valve is arranged in the sanitary water system so that when sanitary water is drawn off through a tap, a three-way valve directs the primary water to the flow through the water heating system. The commonly used wall-mounted gas combination boiler units are of this type.

A disadvantage of such units is tha when no central heating is being utilised, (as is the case particularly in summer months) each time hot sanitary water is required the boiler, which is activated only on the draw-off of sanitary water, must start from a cold condition. There is therefore a significant delay before the primary water is hot enough to produce sanitary water at a reasonable temperature. In addition, factors such as pre-scavenging of the combustion chamber, high water content or heavy metal content all serve to augment the delay, which in some boilers can be as long as one and a half to two minutes.

One solution which has been proposed is to incorporate into the water heating system a storage vessel which retains a volume of hot primary water which is circulated to heat the system on initial draw-off of sanitary water. A problem exists in that, in order to reduce the volume of the storage vessel to retain a convenient size, the primary water is generally stored at a particularly high temperature. This is both wasteful of heat, and gives the disadvantage that, as the storage vessel is being recharged after draw off of sanitary water, the excessively hot water must be circulated through the heat exchanger, which can give rise to serious limescale deposits in the heat exchanger which thereby significantly reduce its efficiency.A further problem which can arise (during the first 15 to 30 seconds of draw-off cold water) is that cold primary water in the system mixes with the stored primary water and lowers its temperature, thereby reducing its usefulness particularly in the first 30 seconds.

The present invention seeks to overcome the above problems.

According to the present invention there is provided an apparatus for providing hot sanitary water comprising; a storage vessel adapted to communication with a supply of primary water from a boiler; mixing valve means adapted to communicate with both the supply of primary water, and said storage vessel, and to mix primary water from the storage vessel with water from the supply of primary water; and a heat exchanger arranged to effect heat-exchange between the mixed primary water and sanitary water.

By mixing hot stored water from the storage vessel with water from the boiler, which on start up will be cold, hot sanitary water can be obtained very rapidly after the initial start up of the boiler.

Preferably, the mixing valve means are adapted to control the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

The mixing valve means may be adapted to control the temperature of mixed primary water by control of the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

Preferably, said mixing valve means is adapted to mix the primary water from the storage vessel with water from the supply of primary water in a relative proportion which maintains the temperature of mixed primary water substantially constant during warm up of the boiler from an initially cold condition.

The apparatus may define a path therein for the mixed primary water which by-passes the heat exchanger, with by-pass valve means provided which are operable to divert the mixed primary water from flowing through the heat exchanger to flow through the by-pass path when the temperature of mixed primary water reaches a first predetermined value.

This ensures that should the temperature of primary water exiting the heat exchanger rise to the first predetermined value (which could occur if less than maximum water was being drawn off) then excessively hot primary water does not pass through the heat exchanger, and any sanitary water flowing will be limited in its maximum temperature.

Preferably, flow detection means are provided to detect the flow of sanitary water, and a temperature sensor is located within the storage vessel, and control means are provided, which control means are arranged to stop the supply of primary water when both no flow of sanitary water is detected, and the temperature of primary water in the storage vessel is at or above a second predetermind value. This allows recharging of the storage vessel with hot primary water once sanitary water is no longer being drawn off. An electric (e.g. positive temperature coefficient) heater may be arranged to provide heat for the water stored in the storage vessel.

The control means may be further arranged to switch the boiler to a low heat output condition when both no flow of sanitary water is detected, and when the temperature of primary water in the storage vessel is below the second predetermined value.

Preferably, the mixing valve means comprise a valve provided with a pair of opposed valve ports arranged to receive primary water from the storage vessel and from the supply of primary water respectively, and are each provided with respective valve plates which are fixed to a common support rod, the valve plates being movable between a first position at which the ratio of primary water from the storage vessel to primary water from the supply thereof is a maximum, and a second position at which this ratio is a minimum. The mixing valve means may include a thermosensitive motor connected to the valve plates and adapted to move the position of the valve plates in response to a change in temperature of mixed primary water leaving the heat exchanger, or, alternatively, in response to a change in temperature of santiary water.The thermosensitive motor comprises a memory alloy or a wax filled capsule or other thermosensitive actuator.

Preferably, the by-pass valve means includes a first by-pass valve arranged at an outlet of the heat exchanger having a valve plate which is connected to the thermosensitive motor such that when the mixing valve is in its second position, on a further increase in temperature of mixed water, the first by-pass valve plate is forced to move by the thermosensitive motor, to close the heat exchanger outlet. The apparatus may include a second by-pass valve which is arranged in the by-pass path and is adapted to be opened by the water pressure when the heat exchanger outlet is closed by the first by-pass valve.

Preferably, the apparatus comprises a housing to which primary water inlet conduit means is connected through which primary water is supplied from the boiler, the storage vessel being arranged above the housing, and further comprising a conduit extending from within the housing to a position adjacent the top of the storage vessel, with the mixing valve means being arranged at a lower end of the conduit so as to mix primary water from the housing with primary water which has passed from the storage vessel down the conduit. By drawing the water from the storage vessel which is to be mixed with the primary water specifically from the upper region of the storage vessel, the warmest water in the storage vessel is utilised.

The primary water inlet conduit means may extend into the housing where an opening into the housing is provided, and include a riser portion extending upwardly into the storage vessel to a position adjacent the top thereof, inlet valve means located at the opening being adapted to direct inlet water either into the storage vessel via the upwardly extending riser portion or through the opening into the housing. Preferably, the inlet valve means is adapted to direct inlet primary water up into the storage vessel via the upwardly extending riser portion when the temperature of inlet water exceeds a third predetermined value, and comprises a thermosensitive motor. This third predetermined temperature is preferably the temperature at which the inlet primary water from the boiler is sufficient to provide the full output to the heat exchanger.Thus, as soon as the inlet primary water temperature is sufficient to provide this full output, the inlet valve means directs the inlet primary water directly to the top of the storage vessel, from where it is taken directly down the conduit to the mixing valve, thereby reducing mixing of this water with other possibly cooler water in the housing, and maintaining the temperature stratification of water in the storage vessel. A further advantage is that during recharging of the storage vessel hot inlet water is discharged at top of the storage vessel, forcing cooler water at the base of the storage vessel to return via the by-pass path to the boiler.

The return of the cool water minimises the risk of premature boiler shut-off.

As an alternative to a thermosensitive motor, the mixing valve means, inlet valve means and by-pass valve means may be adapted to operate on a timed sequence which is initiated on initial draw off of sanitary water.

According to a further aspect of the present invention there is provided a method of providing hot sanitary water comprising the steps of mixing primary water supplied from a boiler with primary water from a storage vessel, and effecting heat exchange between the mixed primary water and a supply of sanitary water arranged to flow in thermal contact with the primary water.

Preferably, the primary water from the storage vessel and water from the supply of primary water are mixed together in a controlled proportion. The temperature of mixed primary water may be controlled by control of the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

Preferably, on initial flow of sanitary water, primary water is supplied from a cold boiler substantially at ambient temperature, and primary water from the storage vessel is at a temperature substantially above ambient temperature, the relative proportions of primary water from the boiler mixed with the primary water from the storage vessel being adjusted so as to maintain the temperature of the mixed primary water substantially constant as the boiler heats up from the initially cold state. The primary water from the storage vessel is preferably drawn off from an upper region of the storage vessel.

Primary water may be prevented from undergoing heat exchange with the sanitary water by being passed through a flow path which by-passes the heat exchanger if the temperature of mixed primary water reaches a first predetermined value.

Preferably, on cessation of flow of sanitary water, primary water is continued to be supplied from the boiler until the temperature of water in the storage vessel reaches a second predetermined value. Furthermore, on the cessation of flow of sanitary water, and while primary water is still being supplied from the boiler, the boiler may be switched to a low heat output condition.

Preferably, primary water from the boiler is supplied to an upper region of the storage vessel when the temperature of the inlet water is at or above a third predetermined temperature, and is supplied to a housing below the storage vessel and in communication therewith when the temperature of the inlet water is below the third predetermined temperature, from where it can flow into the mixing valve and into a base of the storage vessel, provided the temperature of mixed primary water is below the first predetermined value.

Embodiments of the present invention will be described, by way of example only, with reference to the accompanying drawings in which; Figure 1 shows schematically a combined central heating system and water heating system; Figure 2 is a schematic cross-sectional view through a part of a first embodiment of a water heating apparatus in accordance with the invention; and, Figure 3 is a schematic cross-sectional view through a part of a second embodiment of a water heating apparatus in accordance with the invention.

Figure 1 illustrates schematically a combined central heating system and water heating system, comprising a boiler 1 which is connected to both a sanitary water heating system and 2 central heating system 3. The central heating system 3 includes components such as heating radiators 4 which are distributed throughout a building for providing space heating. During operation of the central heating, primary water from boiler 1 is directed through heating radiators 4.

A sanitary water supply circuit 5 is connected to a mains supply of sanitary water and has a plurality of sanitary water outlets (not shown) at for example wash basins, baths, showers etc. The sanitary water heating system 2 includes a water/water heat exchanger 6 which comprises a series of primary water passages (not shown) which are in intimate contact with a helical portion 7 of sanitary water circuit 5, such that heat is transferred from the primary hot water from the boiler to the sanitary water passing through the heat exchanger 6.

A pump 8 is located to effect circulation of the primary water through the boiler 1. A three-way valve 9 is arranged to direct the primary hot water flow through either the central heating system 3 or to the sanitary water heating system 2. Flow detection means comprising a pressure switch or flow switch 10 is incorporated in the sanitary water circuit 5. A control system (not shown) is arranged to receive a signal from the pressure switch, and to cause the valve 9 to shut off flow through the central heating system 4 and to open flow through the hot water heating system 2 on the initial draw-off of sanitary water from circuit 5.

The water heating system 2 includes a primary water storage vessel 11 located upstream of the water/water heat exchanger 6. The water heating system 2 also includes a direct flow-path 12 by means of which a proportion of primary water from the boiler 1 can flow directly to the heat exchanger 6 without passing through the storage vessel 11. A by-pass path 13 is provided so that primary water may alss by-pass the heat exchanger 6.

A mixer valve 14 is adapted to allow mixing of primary water flowing from the storage vessel 11, and primary water flowing directly from the boiler 1. By-pass path 13 is provided with a valve 56 which is arranged to open as a further valve 15, sited at the exit of the heat exchanger 6, is closed.

A first embodiment of a part of the water heating system 2 is illustrated in detail in cross-section in Figure 2. The apparatus includes a housing 16 which is divided into an upper chamber 17 and a lower chamber 18 by partition 19. Inlet water conduit means comprise a water inlet pipe 20 through which water is supplied from the boiler 1 (not shown in Figure 2) which extends into the upper chamber 17 of the housing 16 and, connected thereto, a riser pipe 21. The riser pipe 21 is provided with an opening or port 32 into the upper chamber 17, with an inlet valve 22 being provided so as to close this port 32 or the riser pipe 21, as discussed in more detail below.

An outlet pipe 55 is connected to the lower chamber 18 of the housing 16, through which pipe 55 water is returned to the boiler 1. The storage vessel 11 (of which only the lower portion is shown in Figure 2) is situated above the housing 16 and is connected thereto by clamping ring 23. The upper chamber 17 of the housing 16 communicates with the contents of the storage vessel 11 through an annular orifice 24 defined between a neck portion 25 of the storage vessel 11, and a spreader plate 26 of the storage vessel 11. The riser pipe 21 extends upwardly through the spreader plate 26 towards an upper region of the storage vessel 11. The storage vessel 11 may be a standard storage tank, for example of capacity 11 to 12 litres.An electric heater 27 which may be a positive temperature coefficient heater is located within the upper chamber 17 below the neck of the storage vessel, at the side thereof remote from the inlet pipe 20. This heater 27 is a low power heater, for example 150 to 200 watts, which supplies heat to counteract the heat losses from the storage vessel which occur during periods when no water is being drawn off from the storage vessel 11. A temperature sensor 28 is located within the storage vessel 11 close to the neck of the storage vessel 11 to detect the temperature of water at the bottom on the vessel.

Inlet valve 22 comprises a disc 29 covering a port 30 and a disc 31 covering the port 32. The discs 29,31 are joined by a rod 33. The rod 33 is supported on a mounting with a thermosensitive motor 34 such as, for example, a temperature-sensitive spring arranged so as to move the assembly of discs 29,31 and rod 33 downwardly in response to a temperature increase above a certain value, so as to close port 32 and open port 30. The use of a memory alloy is particularly advantageous as the thermosensitive motor 34 in that such an alloy can actuate at very specific temperature.

A counter spring 35 is arranged about the rod 33 which urges the assembly of discs 29,31 and rod 33 upwardly.

A conduit 36 extends upwardly substantially axially from the upper chamber 17 of the housing 16 to a position close to the top of the storage vessel 11. The lowermost end of the pipe 36 is connected to the mixing valve 14. The mixing valve 14 includes opposed inlet ports 37 and 38, which ports are in communication with the pipe 36, and with the upper chamber 17 respectively. Ports 37 and 38 are closed by valve plates 39, 40 respectively, which are connected to each other by a rod 41 which supports the plates at a fixed separation from each other. Both ports 37 and 38 include stops (not shown) to limit the upward and downward movement of the plates 39,40 and rod 41, and to thereby limit the extent to which the ports 37 and 38 can be closed by their respective plates. A spring 42 biases the assembly of plates 39,40 and rod 41 downwardly.

A valve outlet 57 leads to a heat exchanger inlet pipe 43, which receives the blend of water from the storage vessel 11 entering via pipe 36 and port 37, with water which has passed directly from the water inlet pipe 20, through port 32 of valve 22, and port 38 of valve 14. The heat exchanger inlet pipe 43 is connected to the water/water heat exchanger 6 which for example includes a hot primary water conduit (not shown) between heat exchanger inlet 44 and outlet 45. The sanitary water system 5 includes a helical section of piping 7 in contact with the hot primary water conduit such that heat is transferred from the primary hot water to the sanitary water in the heat exchanger.

The heat exchanger outlet 45 is connected to outlet pipe 46 which enters the lower chamber 18 of the housing via a valve 15. Valve 15 includes a valve port 47 and valve plate 48.

The valve plate 48 is connected through a rod 49 and a thermosensitive motor 50 to the rod 41. A spring 51, which is substantially stiffer than spring 42, biases the valve plate 48 upwardly, thereby biasing the valve 15 in an open condition.

The thermosensitive motor 50 is a device which changes its dimensions in response to changing temperature, such as a wax-filled capsule. The arrangement of the valve plates 39,40 and rod 41, along with valve plate 48 and springs 42 and 51 is such that in response to increasing temperature, the assembly of plates 39,40 and rod 41 are caused to move upwardly by the thermosensitive motor, against the downward biasing of the spring 42, and once in the uppermost position (in which the plate 39 contacts a stop provided at the port 37) further temperature increases result in the wax filled capsule forcing the plate 48 downwardly against the force of the spring 51, to close the port 47 of the valve 15.

The partition 19 between upper and lower chambers 17,18 of the housing 16 is provided with an aperture 52 which defines a by-pass path 13 and which is closed by a by-pass valve 56 having a valve plate 53 and which is biased into a closed position by a valve spring 54. When the flow through the heat exchanger is arrested by closing of valve 15, the water pressure in the system is sufficient to cause opening of the by-pass valve 56 so that water can circulate between inlet pipe 20 and outlet pipe 55 whilst by-passing the heat exchanger 6 entirely.

By arranging the thermosensitive motor 50 in the lower chamber 18 the valves 14,15 are controlled in response to the temperature of primary water leaving the heat exchanger 6 through outlet pipe 46. It should be noted that a particular temperature at the heat exhanger outlet 45 can be associated with a particular temperature of primary water at the heat exchanger inlet 44, since, when sanitary water is flowing through the heat exchanger 6, a generally constant temperature difference exists across the heat exchanger 6.

The complete apparatus including the water storage vessel 11, housing 16 and heat exchanger 6 are enclosed in a layer of insulating material, of for example 40 to 45 mm thick, to reduce heat losses.

The operation of the water heating system incorporating the apparatus according to the invention is now described, starting from a condition in which the boiler 1 is off, and the storage vessel 11 is full of hot water at a temperature which is significantly above that at which the sanitary water is required. For example, it may be the case that sanitary water is required at about 60 C, and the stored water is at 0 about 90 C, at least at the top of the storage vessel 11, falling in temperature to about 800 towards the bottom of the storage vessel 11.

On the opening of a tap in the sanitary water system 5, the flow switch 10 detects the flow of sanitary water, and the control means causes the three-way valve 9 to move in to a position where the central heating system 3 is by-passed (if it is not already in that position), and water from the boiler 1 can then only flow through the water heating system 2. The control means also initiates the start up of the boiler 1, and pump 8 which causes the water to flow through the water heating system 2.

In the initial state, the thermosensitive motor 34 of the inlet valve 22 is located in cold water and is therefore contracted. Port 32 is open, whilst port 30 is closed. The thermosensitive motor 50 is also located in cool water, and the mixer valve 14 is therefore in its lowermost position in which the upper port 37 is in its most open position, and the lower port 38 is in its most closed. The stop provided at the port 38 ensures that the ports are not fully sealed off, but that the initial flow through the ports is arranged to be predominantly through the port 37, with a small flow through the port 38, for example, 80% through port 48, and 20% through port 50. Valve 15 is fully open, whilst valve 14 is fully closed.

On the start up of the boiler 1 and circulation of water, the inlet valve 22 directs water via port 32 into the upper chamber 17 of the housing 16, from where it can pass both to the mixer valve 14 and directly to the base of the storage vessel 11 through orifice 24. The water entering the water inlet 20 is at ambient temperature, for example 200C in summer. Water in the storage vessel is at about 800 to 0 mixer valve 90 C. The mixer valve 14 blends flows from the water inlet 20 and storage vessel 11, for example in the proportion 80% to 20%, such that water is supplied to the heat exchanger 6 at a preselected temperature, for example 750C, which is somewhat above that at which the sanitary water is required.The circulation of the primary water at this preselected temperature through the heat exchanger ensures heating of the sanitary water to the required 600C. By the arrangement described the most part of the cold water sitting in the boiler 1 and pump 8 and connecting pipework is fed into the base of the storage vessel 11 in a way which inhibits mixing up with the stored hot water, and the hot stored water is thereby directed immediately to the heat exchanger 6 to give almost instant hot water. In conventional storage systems this "sitting" cold water both mixes with stored water and passes through the heat exchanger at temperatures too low for adequate sanitary water heating.

As the boiler 1 heats up, the water entering the water inlet 20 will become hotter, thereby tending to increase the temperature of the water supplied to the heat exchanger 6 and thereby to the sanitary water. The thermosensitive motor 50 detects the increase in temperature of water exiting the heat exchanger 6, and forces the valve plates 39,40 upwardly, thereby decreasing the proportion of water taken from the storage vessel 11 (passing through port 37), and increasing the proportion of water directly from the inlet 20 (via the ports 32 and 38) in order to maintain the temperature of water supplied to the heat exchanger 10 at the preselected value, of about 75 0C. For example, at a time of 30 seconds from the 0 start up, it may be the case that water at 80 C from the storage vessel 11, and 300C directly from the water inlet 20 is mixed in a proportion 60% to 40% by the mixer valve 14.

The proportion of water from the boiler not taken into the mixer valve is directed into the bottom of the storage vessel 11 via orifice 24, in such a way as not to mix too vigorously with stored hot water.

As draw-off of sanitary water, and circulation of primary water, continues, the water in the storage vessel 11 will become cooler, since the fresh water from the boiler is being added, initially at 200C, compared to the 80-900C at which the water has been stored. The storage vessel 11 is arranged so that the velocity of incoming water at the bottom of the storage vessel is minimised to thereby minimise mixing of the fresh relatively cool water with the stored water. The spreader plate 26 assists in this. A stratification of water at different temperatures within the storage vessel 11 will exist, and by drawing off the water from the top of the storage vessel 11 through the pipe 36, the period of time for which relatively hot water is available from the storage vessel 11 is maximised.

After a further period of time, the water supplied from the boiler 1 is becoming still hotter, whilst water from the storage vessel 11 will be decreasing in temperature. The thermosensitive motor 50 of the mixer valve 14 will move the valve plates 39,40 still further upwards against the spring 42. This can occur until the valve assembly reaches the furthest upward extent of its travel, at which point the upper valve plate 39 engages a stop at the port 37, and the proportion of water flowing from the storage vessel 11 is minimised.

There may be a period during draw off of sanitary water, when the water leaving the storage vessel 11 has been reduced in temperature by the incoming cooler water from the initial throughput from the boiler 1, and the temperature of water directly from the boiler 1 is still insufficient to allow mixing of the two flows to achieve the preselected temerature (for example 750C) for input to the heat exchanger 6. There will then be a short period in which the sanitary water will be available at a temperature below the preferable 60 C.

However, by appropriate choice of the storage vessel capacity, primary water flow rate, and boiler output, any such period can be minimised to a number of seconds only, or eliminated altogether.

Further, since at temperatures lower than design in pipe 43 the boiler is under utilised and the boiler temperature will rise.

It is arranged that, by appropriate selection of the capacity of the boiler and heat exchanger, once both the boiler and the water in the storage vessel have reached their maximum temperatures the heat extracted from the heat exchanger prevents the temperature of water passing therethrough from rising excessively. In this situation the heat exchanger is taking virtually all the heat output from the boiler.

As a further precaution against the effects of reducing temperature in the storage vessel 11 it is arranged that when the water from the boiler 1 in pipe 20 reaches the point where it is sufficient for providing full output from the heat exchanger 6, the thermosensitive motor 34 of the valve 22 operates to close port 32 and open port 30. Boiler water is thereby directed immediately up riser pipe 21 to the top of the storage vessel 11 from where it flows down pipe 36. Thus, as soon as is possible, the body of water in the storage vessel 11, which may be at a lower temperature than is required in the heat exchanger 6 is essentially by-passed.

The apparatus also provides a means by which the overheating of the heat exchanger 6 is prevented when the sanitary water is no longer being drawn off. If the draw-off of sanitary water is stopped, and the temperature of water in the storage vessel 11 is at or above the temperature required for operation of the system from a cold boiler start, as detected by the temperature sensor 28, then the control means will shut down the system, the boiler I and pump 8 being switched off.

Simple electronic processing means can be provided as the control means for switching off the boiler and pump in response to the detected temperature. If, on cessation of draw-off of sanitary water, the water in the storage vessel 11 is below the preselected temperature (for example 80 to 0 90 C) required for operation of the system from a cold boiler start, further hot water is required to be circulated through the storage vessel 11 to recharge it with hot water.

As primary hot water is circulated through the heat exchanger, with no circulation of sanitary water, the temperature of water leaving the heat exchanger will tend to increase. The thermosensitive motor 50 of the mixing valve 14 will move the valve plates 39,40 to their uppermost position (if not already there) and will thereafter move the valve plate 48 downwardly against the stiffer spring 51, thereby closing the heat exchanger outlet pipe 46 to stop circulation of primary water through the heat exchanger 6. The water pressure in the system will then force the by-pass valve 56 to open so that primary water by-passes the heat exchanger entirely, thereby preventing overheating of the heat exchanger 6.Primary water is continuously circulated, passing up riser pipe 21 (valve 22 having port 30 open, and port 32 closed) and down through the storage vessel 11 (assuming that is that the temperature of incoming water is sufficient to supply the full heat exchanger load if this was operative), until the temperature sensor 28 registers that the preselected temperature (for example 0 80 C) has been reached, at which time, provided there is still no draw-off of sanitary water, the control means shuts the system down, the boiler 1 and pump 8 being stopped.

Overheating of the heat exchanger 6 is thereby prevented, and to the eventual build-up of limescale deposits in the heat exchanger avoided. An important feature of this recharging process is that the hot water enters the storage vessel 11 at the top thereof via riser pipe 21, displacing cool water from the bottom of the storage vessel 11 to return to boiler 1 via port 52 and outlet pipe 55. This ensures that good stratification is maintained within the storage vessel. It also ensures that the water being returned to the boiler is the coldest water in the apparatus, which minimises the risk of possible premature shut-off of the burner of the boiler 1, which could otherwise occur if water which was not the coldest in the apparatus was returned to the boiler 1.

A second embodiment of an apparatus for providing hot sanitary water is now described with reference to Figure 3 of the drawings. This second embodiment includes many of the features of the first embodiment, but represents a simplification of the first embodiment. Thus, only the differences between this embodiment and the first embodiment are described, and those parts which are also employed in the first embodiment are identified by the same reference numerals. The major difference of the second embodiment is that valve 22 and riser pipe 21 of the first embodiment are omitted. Thus, inlet pipe 20 opens directly into the upper chamber 17.In addition, the by-pass path 13 is defined by a conduit 60 which extends from the heat exchanger inlet pipe 43, from a location adjacent the outlet of the mixer valve 14, directly to the lower chamber 13 with the valve 56 located at the opening of the conduit 60. A further difference is that the spring 42 of the first embodiment is replaced by a spring 61 located above valve plate 39 and which acts downwardly on the assembly of plates 39,40 and rod 41.

In operation, the apparatus functions in a generally similar manner to that of the first embodiment. On initial start up of the boiler 1, and circulation of water, water entering the upper chamber from the inlet pipe 20 flows both directly to the base of the storage vessel 11 and to the mixer valve 14, as is the case with the first embodiment. However, in contrast to the first embodiment, once the water has reached a temperature sufficient to provide full output to the heat exchanger, water continues to flow both directly to the mixer valve 14 and to the storage vessel 11, in the absence of the arrangement of riser pipe 21 and valve 22.

A further difference of operation is that during the recharging process, when no sanitary water is being drawn off, and no primary water flows through the heat exchanger, the water passing through by-pass valve 56 is a mixture of water which has passed upwards from the base of the storage vessel 11 to the top thereof, and then down the pipe 36 (a minor proportion), with water directly from the inlet pipe 20 (a major proportion). Thus the arrangement does not maintain the temperature stratification to the extent of the first embodiment. Any risk of premature burner shut-off can be reduced by appropriate burner control.

Although the first embodiment allows more sophisticated temperature control of supply of sanitary water, both embodiments allow provision of near-instantaneous hot sanitary water, with subsequent conditioning and direction of primary water to maintain output sanitary water at or near a desired temperature, whilst additionally allowing by-passing of the heat exchanger when the storage vessel is being recharged with hot water. Furthermore, the arrangements described provide particularly simple mechanical means for effecting the mixing and possible by-passing to obtain delivery of near instant hot sanitary water at a required temperature.

It will be appreciated by persons skilled in the art that various modifications of the arrangement and of individual components are possible. For example, as an alternative to a wax filled capsule for the thermosensitive motor 50, a temperature sensitive spring or wire, for example a bi-metallic or metallurgically preconditioned wire, or a memory alloy, or a liquid filled system may be utilised. It will also be appreciated that the configuration of valves may be replaced by separately controlled individual valves provided at the respective ports. Each of these could be electronically controlled according to the temperature sensed at the heat-exchanger outlet, or at any other appropriate position in the apparatus.

The embodiments described above use valves which are opened and closed in response to a detected temperature or temperature change of primary water. It is also possible to provide valves which are controlled on a timed sequence.

Since the system parameters are predetermined, or are at least substantially predetermined within given ranges, the valves can be arranged to open and close at particular times calculated from the initial draw-off of sanitary water. The valves may be hydraulically controlled. Alternatively, a combination of valves operating on a pretimed sequence, and those responding to detected temperatures can be used.

Moreover, the thermosensitive motor 50 of the mixer valve 14 serves to detect changing load imposed by the sanitary water and to condition the flows and routes of primary water in response. Precisely the same function and responses could be achieved with the thermosensitive motor 50 immersed in the sanitary water outlet.

Claims

CLAIMS:

1. An apparatus for providing hot sanitary water comprising; a storage vessel adapted to communicate with a supply of primary water from a boiler; mixing valve means adapted to communicate with both the supply of primary water, and said storage vessel, and to mix primary water from the storage vessel with water from the supply of primary water; and a heat exchanger arranged to effect heat-exchange between the mixed primary water and sanitary water.

2. An apparatus according to claim 1, wherein said mixing valve means are adapted to control the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

3. An apparatus according to claim 1 or 2, wherein said mixing valve means are adapted to control the temperature of mixed primary water by control of the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

4. An apparatus according to any preceding claim, wherein said mixing valve means are adapted to mix the primary water from the storage vessel with water from the supply of primary water in a relative proportion which maintains the temperature of mixed primary water substantially constant during warm up of the boiler from an initially cold state.

5. An apparatus according to any preceding claim wherein a path for the mixed primary water is defined therein which by passes the heat exchanger, and wherein by-pass valve means are provided which are operable to divert the mixed primary water from flowing through the heat exchanger to flow through the by-pass path when the temperature of mixed primary water reaches a first predetermined value.

6. An apparatus according to any preceding claim wherein flow detection means are provided to detect the flow of sanitary water, and a temperature sensor is located within the storage vessel, and wherein control means are provided, which control means are arranged to stop the supply of primary water when both no flow of sanitary water is detected and the temperature of primary water in the storage vessel is at or above a second predetermined value.

7. An apparatus according to claim 6 wherein the control means are further arranged to switch the boiler to a low heat output condition when both no flow of sanitary water is detected, and when the temperature of primary water in the storage vessel is below the second predetermined value.

8. An apparatus according to any preceding claim wherein the mixing valve means comprise a valve provided with a pair of opposed valve ports arranged to receive primary water from the storage vessel and from the supply of primary water respectively, and each provided with respective valve plates which are fixed to a common support rod, the valve plates and support rod being movable between a first position at which the ratio of primary water from the storage vessel to primary water from the supply thereof which is mixed together is a maximum, and a second position at which this ratio is a minimum.

9. An apparatus according to claim 8 wherein the mixing valve means includes a thermosensitive motor connected to the valve plates and adapted to move the position of the valve plates in response to a change in temperature of mixed water leaving the heat exchanger.

10. An apparatus according to claim 8 wherein the mixing valve means includes a thermosensitive motor connected to the valve plates and adapted to move the position of the valve plates in response to a change in temperature of sanitary water.

Il. An apparatus according to claim 9 or 10 wherein the thermosensitive motor comprises a memory alloy or a waxfilled thermosensitive capsule.

12. An apparatus according to any one of claims 1 to 8 wherein the mixing valve means and by-pass valve means are adapted to operate on a timed sequence which is initiated on initial draw off of sanitary water.

13. An apparatus according to any one of claims 9 to 11 wherein the by-pass valve means includes a first by-pass valve arranged at an outlet of the heat exchanger having a valve plate which is connected to the thermosensitive motor such that when the mixing valve is in its second position, on a further increase in temperature of mixed water, the first by-pass valve plate is forced to move by the thermosensitive motor, to close the heat exchanger outlet.

14. An apparatus according to claim 13 wherein the by-pass valve means further includes a second by-pass valve which is arranged in the by-pass path and is adapted to be opened by the water pressure when the heat exchanger outlet is closed by the first by-pass valve.

15. An apparatus according to any preceding claim, comprising a housing to which primary water inlet conduit means is connected through which primary water is supplied from the boiler, the storage vessel being arranged above the housing, and further comprising a conduit extending from within the housing to a position adjacent the top of the storage vessel, with the mixing valve means being arranged at a lower end of the conduit so as to mix primary water from the housing with primary water which has passed from the storage vessel down the conduit.

16. An apparatus according to claim 15 wherein the primary water inlet conduit means extends into the housing where an opening into the housing is provided, and includes a riser portion extending upwardly into the storage vessel to a position adjacent the top thereof, inlet valve means located at the opening being adapted to direct inlet water either into the storage vessel via the upwardly extending riser portion or through the opening into the housing.

17. An apparatus according to claim 16 wherein the inlet valve means is adapted to direct inlet primary water up into the storage vessel via the upwardly extending riser portion when the temperature of inlet water exceeds a third predetermined value.

18. An apparatus according to claim 17 wherein the inlet valve means includes a thermosensitive motor.

19. An appratus according to any preceding claim wherein a positive temperature coefficient heater is arranged to heat the water stored in the storage vessel.

20. An apparatus for providing hot sanitary water substantially as hereinbefore described with reference to Figure 2 or 3 optionally in combination with Figure 1 of the accompanying drawings.

21. A method of providing hot sanitary water comprising the steps of mixing primary water supplied from a boiler with primary water from a storage vessel itself supplied from the boiler, and effecting heat exchange between the mixed primary water and a supply of sanitary water arranged to flow in thermal contact with the primary water.

22. A method according to claim 21 wherein the primary water from the storage vessel and water from the supply of primary water are mixed together in a controlled proportion.

23. A method according to claim 22 wherein the temperature of mixed primary water is controlled by control of the relative proportions of primary water from the storage vessel and water from the supply of primary water mixed together.

24. A method according to any one of claims 21 to 23 wherein, on initial flow of sanitary water, primary water is supplied from a cold boiler substantially at ambient temperature, and primary water from the storage vessel is at a temperature substantially above ambient temperature, the relative proportions of primary water from the boiler mixed with the primary water from the storage vessel being adjusted so as to maintain the temperature of the mixed primary water substantially constant as the boiler heats up from the initially cold state.

25. A method according to any one of claims 20 to 24, wherein primary water from the storage vessel to be mixed with the supply of primary water is drawn off from an upper region of the storage vessel.

26. A method according to any one of claims 21 to 25 wherein, primary water is prevented from undergoing heat exchange with the sanitary water, by being passed through a flow path which by-passes the heat exchanger if the temperature of mixed primary water reaches a first predetermined value.

27. A method according to any one of claims 21 to 26 wherein, on cessation of flow of sanitary water, primary water is continued to be supplied from the boiler until the temperature of water in the storage vessel reaches a second predetermined value.

28. A method according to claim 27, wherein on the cessation of flow of sanitary water, and while primary water is still being supplied from the boiler, the boiler is switched to a low heat output condition.

29. A method according to any one of claims 21 to 28 wherein inlet primary water from the boiler is supplied to an upper region of the storage vessel when the temperature of the inlet water is at or above a third predetermined temperature, and is supplied to a housing below the storage vessel and in communication therewith when the temperature of the inlet water is below the third predetermined temperature, from where it can flow into the mixing valve and into a base of the storage vessel, provided the temperature of mixed primary water is below the first predetermined value.

30. A method of providing hot sanitary water substantially as hereinbefore described with reference to Figure 2 or 3, optionally in combination with Figure 1 of the accompanying drawings.