GB2531023A

GB2531023A - Improvements in water heating systems

Info

Publication number: GB2531023A
Application number: GB1417728.1A
Authority: GB
Inventors: Cumming Alisdair
Original assignee: BDR Thermea Group BV
Current assignee: BDR Thermea Group BV
Priority date: 2014-10-07
Filing date: 2014-10-07
Publication date: 2016-04-13
Also published as: GB201417728D0

Abstract

A hot water supply system 1 comprises a heater 10 for heating a heat exchange fluid and a primary heat exchanger 22 which receives heat exchange fluid from the heater and supplies heated water to a hot water outlet 24. A secondary heat exchanger 46 receives heat exchange fluid from a heat store 20 and supplies heated water which is mixed with water from a cold water supply 26 at mixing valve 54. A flow meter 66 measures flow rate of water at the hot water outlet 24. The amount of water flowing from the secondary heat exchanger 46 through the mixing valve 54 is controlled depending on the flow rate measured by flow meter 66. A space heating system (100, Fig. 2) may be connected to heater 10 with heat exchange fluid pumped from heat store 20 to the space heating system by a pump (108, Fig. 2). Hot water may recirculate from outlet 24 depending on a signal from temperature sensor 68. The system may be operated in no-flow rate, low-flow rate or high-flow rate conditions.

Description

Improvements in Water Heating Systems

Field of the Invention

This invention relates to a water heating system. Particularly, the invention relates to improvements to increase efficiency and safety of a water heating system.

Background to the Invention

There is a continuing need to increase the efficiency of heating systems due to customer demand and increasing environmental and financial implications. In particular, there is a problem of satisfying a peak demand, for example which may occur in large residential buildings such as a hotel at certain times, such as in the mornings when residents wash, take showers, etc. In the past, in order to satisfy this peak demand, either a very large boiler, which is rated for maximum expected demand, must be used or a very large hot water tank is required. The water in this large hot water tank can be heated when the boiler has spare capacity to do so but once the hot water in such a large tank is depleted, it can take a long time for the boiler to heat the water once more.

Prior art document GB2458137 discloses a heating system comprising a heater and a local heat exchange system which is remotely located from the heater and is controlled by temperature sensors. In the prior art, a tank having heated water and a secondary heat exchanger is used to supplement the heating capacity of a primary heat exchanger at peak demand and the water in the tank can be reheated when the heater has spare capacity, i.e. when non-peak demand.

The present invention has therefore been devised with the foregoing in mind, and seeks to provide an improved water heating system that overcomes or ameliorates disadvantages of the prior art, or provides a useful alternative.

Summary of the Invention

According to a first aspect of the present invention there is provided a hot water supply system comprising: a hot water outlet; a heater for heating a heat exchange fluid; and a heat exchange system. The heat exchange system comprises: a primary heat exchanger adapted to receive heat exchange fluid from the heater, and having a passage for flow of water to be heated by said heat exchange fluid with an outlet connected to said hot water outlet; a heat store storing heated heat exchange fluid and connected to said heater; a secondary heat exchanger adapted to receive heat exchange fluid from the heat store, and having a passage for flow of water to be heated by said heat exchange fluid and an outlet for heated water; a mixing valve having a first inlet connected to the outlet of said secondary heat exchanger and a second inlet connected to a cold water supply, the mixing valve adapted to selectively vary an amount of heated water and an amount of cold water provided to the primary heat exchanger; and a flow meter for measuring a flow rate of water provided at said hot water outlet. The system is configured to vary an amount of water provided through the mixing valve from the secondary heat exchanger in dependence on the measured flow rate.

The hot water supply system may further comprise a controller for controlling the mixing valve to vary the amount of water provided through the mixing valve from the secondary heat exchanger in dependence on the measured flow rate.

The hot water supply system may further comprise a space heating system connected to the heater for supply of heat exchange fluid from the heater to space heaters.

The hot water supply system may comprise a plurality of heaters for heating the heat exchange fluid. Each of the plurality of heaters may have one or more connections for supplying heat exchange fluid to the primary heat exchanger, to the heat store and to the space heating system. The hot water supply system may further comprise a dump pump for pumping heat exchange fluid from the heat store into the space heating system.

The, or each, heater may comprise a fuel fired boiler At least one of the heaters may include a heat exchanger for recovering heat from flue gases by heating water to be provided to the hot water outlet. The water to be provided to the hot water outlet may be provided to the passage for flow of water to be heated in the secondary heat exchanger The hot water system may further comprise a recirculating flow path for water flow from the hot water outlet back to the passage for flow of water to be heated in the primary heat exchanger. The hot water system may further comprise a temperature sensor for sensing the temperature of water at the hot water outlet, wherein the temperature sensor provides a signal to a valve to close so as to stop flow of heat exchange fluid through the primary heat exchanger when the temperature exceeds a predetermined threshold According to a second aspect of the present invention there is provided a method of operating a hot water supply system that comprises: a heater for heating a heat exchange fluid; a primary heat exchanger; a heat store storing heated heat exchange fluid; a secondary heat exchanger; a mixing valve having a first inlet connected to the outlet of said secondary heat exchanger, a second inlet connected to a cold water supply, and an outlet connected to said primary heat exchanger; and a flow meter measuring a flow rate of water provided at a hot water outlet. The method comprises: based on the measured flow rate, adjusting the mixing valve to selectively vary an amount of water heated by said secondary heat exchanger entering the first inlet of the mixing valve and an amount of cold water entering the second inlet of the mixing valve, wherein the water heated by the secondary heat exchanger is heated using heat exchange fluid from the heat store.

The method may further comprise, based on the measured flow rate, operating the system in one of: a) a no flow rate condition; b) a low flow rate condition in which heat exchange fluid is heated by the heater and provided to the primary heat exchanger, and adjusting the mixing valve to provide only cold water entering the second inlet of the mixing valve to the primary heat exchanger; and c) a high flow rate condition in which heat exchange fluid is provided from the heat store to the secondary heat exchanger to heat water provided to the first inlet of the mixing valve, and in which heat exchange fluid is heated by the heater and provided to the primary heat exchanger, the mixing valve being adjusted to provide water entering the first inlet of the mixing valve to the primary heat exchanger.

When in the no flow rate condition or in the low flow rate condition and a temperature of the heat exchange fluid in the heat store is below a predetermined threshold, the method may further comprise circulating heat exchange fluid from the heat store through the heater to re-heat the heat-exchange fluid before returning it to the heat store.

The method may further comprise supplying heat exchange fluid from the heater to space heaters of a space heating system. The method may further comprise pumping heat exchange fluid from the heat store into the space heating system.

The heater may comprise at least one fuel fired boiler. The method may further comprise recovering heat from flue gases of the fuel fired boiler by heating water to be provided to the hot water outlet. The water to be provided to the hot water outlet may be further heated in the secondary heat exchanger.

The method may further comprise recirculating water flow from the hot water outlet back to the primary heat exchanger. The method may further comprise sensing the temperature of water at the hot water outlet, and stopping flow of heat exchange fluid through the primary heat exchanger when the temperature exceeds a predetermined threshold.

It is an advantage that embodiments of the invention provide a system that can be controlled according to, and in response to, a measured demand for hot water. It is a further advantage that, in embodiments of the invention, hot water is instantly ready to be supplied to the hot water outlet when there is a demand. This avoids the situation where a user has to wait for cold water to pass through the system before heated water begins to flow. It is a further advantage that the hot water supply system can be integrated with a space heating system in a manner that alleviates problems with such systems. It is a further advantage that, in embodiments operating a multiple heater system, the heaters can be used together or separately for different load conditions.

Further advantages of the invention will be apparent from the discussion of the embodiments below.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a schematic view of a hot water supply system having a heat exchange system; Figure 2 shows a schematic view of a hot water supply system, similar to that shown in Figure 1, in combination with a space heating system; Figure 3 shows a schematic view of a multiple heater combined hot water supply and space heating system having a heat exchange system; Figure 4 shows a schematic view of an alternative arrangement of a hot water supply system having a heat exchange system in accordance with another embodiment.

Description of the embodiments of the invention

With reference to Figure 1, there is shown a hot water supply system I which comprises a heater system 10 and a heat exchange system 14. The heater system 10 comprises a primary circuit outlet 16 for delivering a heat exchange fluid, typically heated water, to the heat exchange system 14 and a primary circuit inlet 18 to which the heat exchange fluid is returned. Although in the depicted embodiment one heat exchange system 14 is shown, in other embodiments the heater system 10 may be connected to two or more heat exchange systems.

Heating system 10 is typically a fuel-fired system, comprising, for example, one or more gas boilers, As shown in Figure 1, the system also includes a gas saver heat exchanger 51, which is used to recover heat from the exhaust gases of the heater system 10.

Hot water for use in, for example, a hotel, school, commercial building, domestic residence or other similar establishment, is provided through the heat exchange system 14. Cold water is also provided via a cold water supply 26. The heat exchange system 14 comprises a heat store 20, a primary heat exchanger 22, hot water outlets 24, a cold water outlet 26, a heat exchange fluid inlet 28 and a heat exchange fluid outlet 30. A primary circuit pump 31 is provided between the heater system 10 and the heat exchange system 14 for circulating the heat exchange fluid through the heat exchange system 14. The heat store 20 and the primary heat exchanger 22 are connected in parallel to the heat exchange fluid inlet 28 and the heat exchange fluid outlet 30. The heat exchange fluid inlet 28 is connected to the primary circuit outlet 16 of the heater system 10 and the heat exchange fluid outlet 30 is connected to the primary circuit inlet 18 of the heater system 10 thereby forming part of a primary circuit of the heater system 10.

The heat store 20 is a thermally insulated vessel, which stores the heat exchange fluid typically at a temperature of about 85°C, and may typically have a capacity of about 250 litres, although it may be any capacity as required. The heat store 20 comprises a heat exchange fluid inlet 38 and a heat exchange fluid outlet 40. The heat exchange fluid inlet 28 of the heat exchange system 14 is connected to the heat exchange fluid inlet 38 of the heat store 20 and the heat exchange fluid outlet 40 of the heat store 20 is connected to the heat exchange fluid outlet 30 of the heat exchange system 14. A valve 74 is located between the heat exchange fluid inlet 28 and the inlet 38 of the heat store 20.

The primary heat exchanger 22 comprises a first inlet 42 and a first outlet 44. The heat exchange fluid inlet 28 is connected to the first inlet 42 of the primary heat exchanger 22 and the first outlet 44 of the primary heat exchanger 22 is connected to the heat exchange fluid outlet 30. The primary heat exchanger 22 also includes a second inlet 62 and a second outlet 64 for passage of water to be heated in the primary heat exchanger 22.

The heat exchange system 14 further comprises a secondary heat exchanger 46 having, on one side, a first inlet 48 and a first outlet 50 for passage of heat exchange fluid from the heat exchange fluid outlet 40 of the heat store 20 and back to the heat exchange fluid inlet 38 of the heat store 20. There is a pump 47 for pumping the heat exchange fluid through the secondary heat exchanger 46. On its other side, the secondary heat exchanger 46 has a second inlet 52 and a second outlet 53 for passage of water to be heated by the secondary heat exchanger.

The heat exchange system 14 further comprises a temperature regulator valve 54 with a first inlet 56 for receiving water from the second outlet 53 of the secondary heat exchanger 46, and a second inlet 58 for receiving water the cold water inlet 36. An outlet 60 of the temperature regulator valve 54 is connected to the second inlet 62 of the primary heat exchanger 22. The second outlet 64 of the primary heat exchanger 22 is connected to the hot water outlets 24.

Located between the outlet 60 of the temperature regulator valve 54 and the second inlet 62 of the primary heat exchanger 22 is a flow rate sensor 66. The flow of water running through the flow rate sensor 66 is dependent on the demand at the hot water outlets 24. As will become apparent from the discussion below, the location of the flow rate sensor could be at any location where the total flow rate of water to the hot water outlets can be measured. For example, the flow rate sensor 66 could be located at an upstream location, as long as it measures only the flow rate of water passing through the system to the hot water outlets 24.

Located between the second outlet 64 of the primary heat exchanger 22 and the hot water outlet 24 is a temperature sensor 68. The temperature sensor 68 measures the temperature of the hot water leaving the second outlet 64 of the primary heat exchanger 22. In communication with the temperature sensor 68 is a safety valve 70 which is located in the flow path of the heat exchange fluid through the primary heat exchanger. The safety valve 70, as will be described later, is used to shut off the flow of the heat exchange fluid through the primary heat exchanger 22. The safety valve 70 is shown located on the outlet side between the first outlet 44 of the primary heat exchanger 22 and the heat exchange fluid outlet 30, but may be located on the inlet side of the primary heat exchanger.

Hot water from the second outlet 64 circulates around a hot water loop 25, with the hot water outlets 24 branching off from the loop 25. Only two hot water outlets 24 are shown in Figure 1, although in practice there could be three or more hot water outlets 24, or only one hot water outlet 24. There is a hot water return pump 72 positioned in the hot water loop 25 for circulating the hot water around the loop 25 and back to the second inlet 62 of the primary heat exchanger 22.

Cold water is provided direct from the cold water main supply 34 to the cold water outlet 26. Cold water is also supplied into a heat exchange system inlet 36 from a cold water main 34. A line from the cold water inlet 36 passes to and through the gas saver heat exchanger 51 In use, the heater system 10 heats the heat exchange fluid, which is pumped around the primary circuit by pump 31 to top up the heat store 20 with heated heat exchange fluid and/or to transfer heat to the hot water supply via the primary heat exchanger 22 to provide heated water at the hot water outlets 24.

In response to a demand for hot water to be provided at the hot water outlet 24s, cold water is supplied to the heat exchange system 14 from the cold water main 34 via the cold water inlet 36 and is heated at the primary heat exchanger 22. Alternatively, or additionally, cold water from the cold water inlet 36, which in the depicted embodiment has passed through the gas saver heat exchanger 51, passes through, and is heated by the secondary heat exchanger 46 using heat exchange fluid from the heat store 20.

It will be appreciated that embodiments may do away with the gas saver heat exchanger 51, such that cold water is supplied directly to the secondary heat exchanger 46 from the cold water inlet 36. Heat exchange fluid, typically at a temperature of 85°C flows from the heat exchange fluid outlet 40 of the heat store 20, through the pump 47, and through the secondary heat exchanger 46. The warmed heat exchange fluid flows in through the first inlet 48 of the secondary heat exchanger 46 and out through the first outlet 50 of the secondary heat exchanger 46. The pump 47 can be turned off to stop flow of the heat exchange fluid through the secondary heat exchanger 46.

This warmed water is then directed through the mixing valve 54, where it may be mixed with cold water direct from the cold water inlet 36 before passing through the primary heat exchanger 22. The temperature regulator valve 54 has an associated temperature sensor, which measures the temperature of the water leaving the temperature regulator valve 54. The temperature regulator valve 54, depending on how the temperature measurement compares with predetermined values, allows different proportions of cold water from the cold water inlet 36 and warmed water from the secondary heat exchanger 46 to pass through and be mixed in order to maintain a predetermined temperature of the water flowing to the primary heat exchanger 22.

The flow rate sensor 66 measures the flow of water passing through the flow rate sensor 66, which is determined by the demand for hot water at the hot water outlets 24.

As described later, the measurements from the flow rate sensor 66 are used to determine how the system is run.

The hot water return pump 72 is used to continually circulate the water through the primary heat exchanger 22 so the water in the pipes is always hot. This means hot water is instantly ready to be supplied to the hot water outlets 24 when there is a demand. This avoids water having cooled in the pipes which could lead to the user having to wait for the cold water to pass through the system before heated water begins to flow.

When there is not a high demand for hot water at the hot water outlet 24, the heating capacity of the primary heat exchanger 22 may be sufficient to meet this demand on its own. In this situation the system does not switch on pump 47, so no heat is provided to the secondary heat exchanger 46. Cold water from the inlet 36 passes through the gas saver heat exchanger 51, through the secondary heat exchanger 46 (but without receiving any heat from it), to the inlet 56 of temperature regulator valve 54. The water then passes through to the second inlet 62 of primary heat exchanger 22 from which it receives the heat required to raise its temperature to the required temperature at the hot water outlets 24. Also, at times of no, or very low demand for hot water at the hot water outlets 24, the temperature of the heat exchange fluid in the heat store 20 may be maintained at the required temperature (e.g. 55°C) by opening valve 74 so that fluid is circulated from the heat store outlet 40, through the heater system 10 and into the heat store 20 through inlet 38.

When there is a high demand for hot water at the hot water outlets 24, warmed heat exchange fluid from the heat store 20 is pumped through the secondary heat exchanger 46 using the pump 47. The secondary heat exchanger 46 warms the water passing through the secondary heat exchanger 46 (which has already been warmed slightly by being passed through the gas saver heat exchanger 51). The warmed water flowing out of the second outlet 53 of the secondary heat exchanger 46, which may or may not have been mixed with cold water from the cold water inlet 36 at the temperature regulator valve 54, passes into the second inlet 62 of the primary heat exchanger 22. The heat exchange fluid, heated by the heater system 10, enters through the first inlet 42 of the primary heat exchanger 22 and out through the first outlet 44 of the primary heat exchanger 22. Heat is transferred in the primary heat exchanger 22 and the water flowing out of the second outlet 64 of the primary heat exchanger 22 is thus heated in the primary heat exchanger 22 and then supplied to the hot water outlets 24 as required.

The heater system 10 heats the heat exchange fluid unless both valve 70 and valve 74 are shut. When valve 70 is open, heated heat exchange fluid flows through the primary heat exchanger 22. As described above, this may be when there is not a high demand, such that only the primary heat exchanger 22 needs to be used to meet the hot water demand, or when there is a high demand and both the primary and secondary heat exchangers are used with heat exchange fluid flowing through the primary heat exchanger 22 and also circulating through the secondary heat exchanger 46 from the heat store 20. Valve 74 remains shut in these situations and the heat store 20 is not topped up with heat exchange fluid from the heater system 10.

However, when there is no demand for hot water at the hot water outlets 24, then the system can be used to top up the heat store 20. Valve 70 can be shut so that there is no flow of heat exchange fluid through the primary heat exchanger 22. Pump 47 is off in this configuration. If the temperature of the heat exchange fluid in the heat store 20 drops below some predetermined value (due to having been used in the secondary heat exchanger during a high demand period), then valve 74 can be opened so that heat exchange fluid circulates through the heater system 10 and back to the heat store 20.

Also, when the demand for hot water at the hot water outlets 24 is low, the flow of heat exchange fluid from the heat store 20, through the secondary heat exchanger 46 can be stopped by stopping pump 47 from running. Valve 74 may be opened in this condition. This allows the heater system 10 to continually top up the heat store 20 with heat exchange fluid heated from the heater system 10. This means all available heat exchange fluid from the heater system 10 is used to restore the heat exchange fluid in the heat store 20 to its required temperature. Thereafter, when there is a higher demand once more, pump 47 can begin running again (valve 74 being shut) and the warmed heat exchange fluid from the heat store is available to pre-heat the water in the secondary heat exchanger 46, before it is passed through the primary heat exchanger 22.

In addition, at low demand, if the heat store 20 is fully topped up with heat exchange fluid from the heater system 10, in addition to pump 47 being turned off, valve 74 is shut. This means the heat exchange fluid will only be circulating through the primary heat exchanger 22.

The operation of the systems as described above may be controlled by means of a controller, such as a computer or microprocessor device. As will be described in more detail below with reference to Figure 4, signals from the flow rate sensor 66 and temperature measuring devices (e.g. thermocouples, not shown) may be sent to the controller (not shown in Figures 1 to 3). The controller in turn sends signals to open or close valves, such as valves 70, 74, to adjust the position of the mixing valve 54, to switch on or off pumps 31, 47, 72, and to switch on or off the boiler, or other fluid heating device of the heater system 10. Note, however, that the systems described above could be implemented by other means, such as with the use of a system of relays and switches, with or without a controller.

The flow rate sensor 66 monitors the amount of water flowing to the second inlet 62 of the primary heat exchanger 22. The flow of water is dependent on the demand for hot water at the hot water outlets 24. The readings from the flow rate sensor 66 are used by the controller to decide how the heat exchange system 14 is run. When the flow of water is above a certain predetermined value then the system is run as described above for high or peak demand. When the flow of water is below a predetermined value then the system is run as described above for low or non-peak demand.

Table I below gives some examples of the different conditions of operation of a system of the type described above, assuming an input water temperature (at main supply 34) of 10 degrees and a circulating temperature of 60 degree (available at hot water outlets 24).

TABLE I

Flow rate Pump Pump Valve Valve Temp at Condition 1/mm 31 47 70 74 meter 66 /° C o on off closed open undefined No demand -store 20 below set temp.

0 off off closed closed undefined No demand -store 20 at set temp. (85C) 0 -31 on off open closed undefined Low demand -boiler providing heat via primary ___________ _______ _______ _______ _______ __________ heat-exchanger 31 -62 on on open closed 35 High demand -using energy from store 20 to provide additional heat via secondary heat-exchanger The temperature sensor 68 measures the temperature of the hot water leaving the second outlet 64 of the primary heat exchanger 22 (typically between 55°C and 60°C).

If this temperature is above a certain predetermined value, e.g. typically between 60°C and 65°C at which it is too hot to be safe for use at the hot water outlet, then the temperature sensor 68 sends a signal to the valve 70 (or to the controller, which in turn sends a signal to the valve 70) to shut off the flow of heat exchange fluid through the primary heat exchanger 22, In this condition the heater system 10 may still operate to heat the heat exchange fluid to maintain the temperature in heat store 20, so it is available when there is increased demand for hot water. Once the temperature of the water, as measured by the temperature sensor 68, reduces to below a certain predetermined value (typically between 50°C and 55°C) the valve 70 will reopen and the heat exchange fluid will recirculate through the primary heat exchanger 22 and heat up the water to be supplied to the hot water outlets 24 once more. Having a single temperature sensor 68 located directly after the second outlet 64 of the primary heat exchanger 22, avoids the need for numerous temperature safety devices at each tap or outlet connected to the hot water outlets 24, can be avoided.

In another embodiment, and shown in Figure 2, there is provided a combined hot water supply and space heating system 2, which, in addition to supplying heat exchange fluid to the heat exchange system 14, also supplies heat exchange fluid to a space heating system 100. The heat exchange system 14 and reference numerals are the same as previously described. The space heating system 100 comprises a space heating inlet 102 and a space heating outlet 104. Additionally, there is a dump pump 108 located between the heat exchange fluid inlet 38 of the heat store 20 and the space heating inlet 102. The space heating inlet 102 is connected to the primary circuit outlet 16 of the heater system 10 and the space heating outlet 104 is connected to the primary circuit inlet 18 of the heater system 10 thereby forming part of a primary circuit of the heater system 10. There is a valve 106 connected between the primary circuit outlet 16 of the heater system 10 and the space heating inlet 102.

The valve 106 is used to cut off the supply to the space heating system 100 whilst not affecting the supply to the heat store 20 and primary heat exchanger 22. This may be due to either: no demand for space heating: or, if there is such a high demand for hot water at the hot water outlet 24 that the heater system 10 needs to supply all available heated heat exchange fluid to the heat store 20 and/or the primary heat exchanger 22.

In these cases no heat exchange fluid will be supplied to the space heating system 100. It is envisaged that such occasions of high demand for hot water will occur infrequently and for relatively short durations. Normally space heating has a slow rate of change in response to changes in the rate or temperature of heat exchange fluid supplied. This means that the short interruption to meet peak hot water demand does not adversely affect the temperature of the spaces being heated, and may not even be noticeable to people in those spaces.

The dump pump 108 is not turned on in normal use of the combined hot water supply and space heating system 2 but can be used to dump all the heat exchange fluid stored in the heat store 20 into the space heating system 100 if required. This may be required on starting up the space heating system 100 from cold, as there will be a large volume of heat exchange fluid which is at a relatively low temperature in the space heating system 100. This heat exchange fluid at a low temperature would then enter the primary circuit and would then affect the ability of the primary heat exchanger 22 to heat up the hot water to the correct temperature. This problem is alleviated by dumping all, or most of, the heated heat exchange fluid stored in the heat store 20 into the space heating system 100.

As with the embodiment of Figure 1, the operation of the systems in this embodiment may be controlled by means of a controller, such as a computer or microprocessor device, as described below with reference to Figure 4. In addition to the signals that are sent to and from the controller as described above with reference to the embodiment of Figure 1, the controller sends signals to open or close valve 106 and to start or stop dump pump 108. Thermostats or other space heating sensor/signalling devices may be used in the heated spaces to provide signals to the controller. Note, however, that the above embodiment could be implemented by other means, such as with the use of a system of relays and switches, with or without a controller.

In another embodiment, and referring to Figure 3, there is provided a combined hot water supply and space heating system 3 comprising a plurality of heaters 210, 211, 212. The components and layout in the heat exchange system 14 and the space heating system 100 are the same as in the previous embodiments so the reference numerals have been kept consistent. Each heater 210, 211, 212 is connected to the heat store 20, the primary heat exchanger 22 and the space heating system 100 in the same manner as heater system 10 in the previous embodiments. Also, each heater 210, 211, 212 has a corresponding gas saver heat exchanger 251. The heaters 210, 211, 212 may have the same capacity or have different capacities depending on requirements. Also, although in this embodiment three heaters are shown, in other embodiments, there could be more or fewer heaters.

There is provided an inlet manifold 214 which supplies heated heat exchange fluid to the space heating system 100, the heat store 20 and the primary heat exchanger 22.

Heater 210 has a primary circuit outlet 216, heater 211 has a primary circuit outlet 218 and heater 212 has a primary circuit outlet 220. The inlet manifold 214 is connected to the primary circuit outlets 216, 218, 220 of each heater 210, 211, 212 via connection points 222, 224, 226 respectively each with a respective in-line pump 221, 223, 225.

Also, the inlet manifold 214 is connected to the heat exchange fluid inlet 38 of the heat store 20 via a connection point 228 and the manifold 214 is connected to the space heating inlet 102 via a connection point 230. A return manifold 232 is provided which accepts heat exchange fluid from the space heating system 100, the heat store 20 and the primary heat exchanger 22 and returns the heat exchange fluid to the primary circuit inlets 234, 236, 238 of each heater 210, 211, 212. A valve 240 is located in the inlet manifold 214, between the connection point 224 for heater 211 and the connection point 226 for heater 212. Another valve 242 is located in the inlet manifold 214 between the connection point 226 for heater 212 and the connection point 228 for heat store 20. The valve 106 is provided between the connection point 230 for the space heating inlet 102 and the space heating inlet 102. A further valve 244 is located in the inlet manifold 214 between connection points 222 for heater 210 and the connection point 228 for the heat store 20.

In use, if all valves 70, 74, 106, 240, 242, 244 are open then each heater 210, 211, 212 can supply heated heat exchange fluid to the primary heat exchanger 22, heat store 20 and the space heating system 100. If valve 70 is shut, all heated heat exchange fluid flow from the heaters 210, 211, 212 to the primary heat exchanger 22 can be stopped.

If valve 74 is shut, all heated heat exchange fluid flow from the heaters 210, 211, 212 to the heat store 20 can be stopped. If valve 106 is shut, all heated heat exchange fluid flow from the heaters 210, 211, 212 to the space heating system 100 can be stopped. Valve 240 can be shut so that only heater 211 is able to supply the space heating system 100 and cannot supply the primary heat exchanger 22 and heat store 20. Valve 242 can be shut so that only heaters 211, 212 can supply the space heating system 100 and cannot supply the primary heat exchanger 22 and heat store 20.

Valve 244 can be shut so that only heater 210 is able to supply the primary heat exchanger 22 whilst one or both of the other heaters 211, 212 can supply the heat store 20 (depending whether valve 230 and valve 242 are open). In addition, if any of the heaters 210, 211, 212 fails then the system can still operate and even if two fail then there can still be hot water and space heating (even though at a lower rate).

Table 2 sets out the options for each of the valves being open or closed.

TABLE 2

Diifl1 q106 v240 v242 v70 v74 V244108 frt heaters supply to the primery heat excuanger 22 ___ 2!L ° 0fl Off 0 aUheaters supply to the heat store 20 jif on or; on on on off all heaters supply to the space heating system 100. Jfl, Oil 0ff off q__.9!! ill heaters supph; to space heating system iUfl dump the heat store 20 ________ on on jfl off off on on Two beaters supply to primary heat exchcriger 22 ind Ito the space heating system 100 on off aa_.. ca_ ° ° One heater supplies to primary heat exchanger 22 and two heaters supphJ to the space heatirp system 100 _________ on on ott on off:Ofl heater supplies to the space. hc sting system 100 and one neater supplies to the heat store 20 and one heater supplies to the pnmary hrdt xchaqe on off tn on on off In conventional systems, when there is a multipie heater system. all the heaters feed into a large common manifold. Each of the loads (domestic hot water. space. heating, tank heating) all take heat exchange fluid water from the common manifold A problem adses when, for example. the space heating system starts. The space heating bystem instanUv takes large volumes of hot water from the manifold and dumps large volumes of cold water into the manifold system This then stops the hot water circuit and tank 1.0 circuit from woikirig correctly as the man:foid water is too cold. In the embodiment of f:!9ure 3 described above, the valve syste,m allows the splitting up of the inlet manitoki 214 so that healers 210. 211, 212 can all he used together for one load or separately for different loads. When the system calls for space heating then just ous heater. e.g. heater 211, can be used to aet the space heating system IOU up to temperature and lOt affect the heating of the domestic hot water etc As with the embodiments of Figures 1 arid 2, the operation of the systems in this embodiment may be controfled by means of a controller, such as a computer or microprocessor device, as described below *IIII refernnce. to Figure 4. In addition to the signals that are sent to and from the controller as desonbed above with reference to the embodiments of Figi.res 1 and 2, the controller sends s.ignal.s to control the opening and. closing of the valves 240., 242,. 244, to stop or start pumps 221, 223, 225 and to start or stop heaters 210, 211, 212. Note1 however, that the systems described above could be implemented with the use of a system of relays and switches, with or without a controller.

Figure 4 is a schematic block diagram of an embodiment of a control system for controlling the heater system 10 and heat exchange system 14, as previously described. The control system includes a controller 400, which may be a computer, process controller or the like, and includes a processor 402 and configurable memory 404 storing software instructions and data that are used by the processor. The control system also includes a number of input channels 406 into which data signals from measuring devices in the heater system 10 and heat exchange system 14 are fed.

These signals include, but are not limited to, a signal indicative of the measured flow rate of water through the flow sensor 66, and signals from temperature sensors, such as thermocouples, indicative of the water or heat exchange fluid temperatures at various places in the system. The control system 400 also includes output channels 408 over which signals are provided to control operation of components of the heater system 10 and heat exchange system 14, as described above. These signals include, but are not limited to, a signal for controlling the position of the mixing valve 54, signals to open or close valves, signals to switch on or off pumps, and signals to switch on or off the boiler(s), or other fluid heating device(s).

Claims

CLAIMS: 1. A hot water supply system comprising: a hot water outlet; a heater for heating a heat exchange fluid; a heat exchange system comprising: a primary heat exchanger adapted to receive heat exchange fluid from the heater, and having a passage for flow of water to be heated by said heat exchange fluid with an outlet connected to said hot water outlet; a heat store storing heated heat exchange fluid and connected to said heater; a secondary heat exchanger adapted to receive heat exchange fluid from the heat store, and having a passage for flow of water to be heated by said heat exchange fluid and an outlet for heated water; a mixing valve having a first inlet connected to the outlet of said secondary heat exchanger and a second inlet connected to a cold water supply, the mixing valve adapted to selectively vary an amount of heated water and an amount of cold water provided to the primary heat exchanger; and a flow meter for measuring a flow rate of water provided at said hot water outlet, wherein the system is configured to vary an amount of water provided through the mixing valve from the secondary heat exchanger in dependence on the measured flow rate.
2. The hot water supply system of claim I further comprising a controller for controlling said mixing valve to vary the amount of water provided through the mixing valve from the secondary heat exchanger in dependence on the measured flow rate.
3. The hot water supply system of claim 1 or claim 2 further comprising a space heating system connected to the heater for supply of heat exchange fluid from the heater to space heaters.
4. The hot water supply system of any preceding claim, comprising a plurality of heaters for heating the heat exchange fluid.
5. The hot water supply system of claim 4, wherein each of the plurality of heaters has one or more connections for supplying heat exchange fluid to the primary heat exchanger, to the heat store and to the space heating system.
6. The hot water supply system of any of claims 3 to 5, further comprising a dump pump for pumping heat exchange fluid from said heat store into said space heating system.
7. The hot water supply system of any preceding claim, wherein the, or each, heater comprises a fuel fired boiler.
8. The hot water supply system of claim 7, wherein at least one heater includes a heat exchanger for recovering heat from flue gases by heating water to be provided to the hot water outlet.
9. The hot water supply system of claim 8, wherein the water to be provided to the hot water outlet is provided to said passage for flow of water to be heated in said secondary heat exchanger.
10. The hot water supply system of any preceding claim, further comprising a recirculating flow path for water flow from said hot water outlet back to said passage for flow of water to be heated in said primary heat exchanger.
11, The hot water supply system of claim 10, further comprising a temperature sensor for sensing the temperature of water at said hot water outlet, wherein the temperature sensor provides a signal to a valve to close so as to stop flow of heat exchange fluid through the primary heat exchanger when the temperature exceeds a predetermined threshold.
12. A method of operating a hot water supply system that comprises: a heater for heating a heat exchange fluid; a primary heat exchanger; a heat store storing heated heat exchange fluid; a secondary heat exchanger; a mixing valve having a first inlet connected to the outlet of said secondary heat exchanger, a second inlet connected to a cold water supply, and an outlet connected to said primary heat exchanger; and a flow meter measuring a flow rate of water provided at a hot water outlet, the method comprising: based on the measured flow rate, adjusting the mixing valve to selectively vary an amount of water heated by said secondary heat exchanger entering the first inlet of the mixing valve and an amount of cold water entering the second inlet of the mixing valve, wherein the water heated by the secondary heat exchanger is heated using heat exchange fluid from the heat store.
13. The method of claim 12, further comprising, based on the measured flow rate, operating the system in one of: a) a no flow rate condition; b) a low flow rate condition in which heat exchange fluid is heated by the heater and provided to the primary heat exchanger, and adjusting the mixing valve to provide only cold water entering the second inlet of the mixing valve to the primary heat exchanger; and c) a high flow rate condition in which heat exchange fluid is provided from the heat store to the secondary heat exchanger to heat water provided to the first inlet of the mixing valve, and in which heat exchange fluid is heated by the heater and provided to the primary heat exchanger, the mixing valve being adjusted to provide water entering the first inlet of the mixing valve to the primary heat exchanger.
14. The method of claim 13, wherein when in the no flow rate condition or in the low flow rate condition and a temperature of the heat exchange fluid in the heat store is below a predetermined threshold, circulating heat exchange fluid from the heat store through the heater to re-heat the heat-exchange fluid before returning it to the heat store.
15. The method of any of claims 12 to 14, further comprising supplying heat exchange fluid from the heater to space heaters of a space heating system.
16. The method of claim 15, further comprising pumping heat exchange fluid from said heat store into said space heating system.
17. The method of any of claims 12 to 16, wherein the heater comprises at least one fuel fired boiler.
18. The method of claim 17, further comprising recovering heat from flue gases of the fuel fired boiler by heating water to be provided to the hot water outlet.
19. The method of claim 18, wherein the water to be provided to the hot water outlet is further heated in said secondary heat exchanger.
20. The method of any of claims 12 to 19, further comprising recirculating water flow from said hot water outlet back to said primary heat exchanger.
21. The method of claim 20, further comprising sensing the temperature of water at said hot water outlet, and stopping flow of heat exchange fluid through the primary heat exchanger when the temperature exceeds a predetermined threshold.
22. A hot water supply system substantially as described herein with reference to the accompanying drawings.