GB2365953A

GB2365953A - Supplementary heat exchanger arrangement for providing domestic hot water

Info

Publication number: GB2365953A
Application number: GB0116525A
Authority: GB
Inventors: George Curtis
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-07-07
Filing date: 2001-07-06
Publication date: 2002-02-27
Anticipated expiration: 2021-07-06
Also published as: GB0116525D0; GB2365953B

Abstract

The arrangement includes a boiler 10 for heating central heating circulating water, a circulation pump 38 and means, which may be a pump 62 and one-way valves 58 and 68, for selectively diverting circulating water to at least one heat exchanger 64 to assist in the heating of a cold water supply 28 to provide a hot water supply 30. The heat exchanger may act to pre-heat a cold water supply to a combination boiler, or in conjunction with a conventional system boiler to heat cold water, or to post-heat hot water supplied from a combination boiler. The means for selectively diverting circulating water may be a pair of motorised valves. The heat exchanger may be located close to the point of hot water use. The heat exchanger may have a temperature control valve associated therewith which mixes hot water output from the heat exchanger with cold water. The arrangement may include a plurality of heat exchangers remote from the boiler located close to a point of hot water use.

Description

<Desc/Clms Page number 1> Heating Systems This invention relates to boilers, for domestic or commercial use. The invention is principally applicable to gas-fired boilers but could be used with other fuels. Central heating/hot water systems are mostly provided by three types of boiler installation: (1) "Conventional" boilers supply central heating by hot water pumped through a flow and return system by an external pump. Hot water supply is from a central indirect cylinder having a heating coil receiving hot water from the boiler either by a gravity system or by pump. (2) "System" boilers are essentially the same as conventional boiler but have the circulating pump and controls such as programmers integrated with the boiler in a single package.

(3) "Combination" or 11combill boilers combine a pumped heating flow and return with instantaneous "on demand" hot water supply.

Each of these has practical disadvantages.

With conventional and system boiler installations, it is necessary to maintain a relatively large volume of hot water in the indirect cylinder at all times when hot water is programmed to he available. Pipe runs to taps or appliances can be long and incur heat wastage. If a large amount of hot water is used, e.g. for a bath, the recovery time can be significant.

Combi boilers, in principle, provide greater efficiency. However, they control the temperature of the water delivered by varying the water flow. When the temperature of the cold water supply is low and the desired water supply temperature is high, this can lead to unacceptably low volumes being supplied.

The present invention seeks to provide improved central heating/hot water systems.

Accordingly, the present invention provides a central heating/hot water system including a boiler for heating central heating circulating water, a circulating pump, and a flow and return pipe and radiator system through which the circulating pump passes the circulating water; and including means

for selectively diverting said circulating water to a heat exchanger to assist in the supply of hot water.

In one form of the invention, the heat exchanger acts to pre-heat the cold water supply to the water heating path of a combi boiler.

In other forms of the invention, the heat exchanger is located close to the point of use. The heat exchanger may be used, in conjunction with a conventional or system boiler, to heat cold water. Alternatively, it may be used to superheat hot water from a combi boiler. In either case, it is preferred to associate the heat exchanger with a temperature control valve which mixes the hot water output from the heat exchanger with cold water.

The use of a remote heat exchanger in conjunction with a combi boiler has the added benef it of enabling the hot water system to be a vented system. More than one remote heat exchanger may be used, so that each tap or appliance is close to a heat exchanger. This is facilitated by the fact that the heat exchanger may be small enough to f it under a kitchen sink, for example.

The diversion of central heating circulating water may be ef f ected by a pair of motorised valves, or by means of an auxiliary pump and one-way valves. Such diversions may be initiated by a thermostat on the

remote heat exchanger, or by a demand for hot water indicated by the opening of a tap or appliance valve.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig.1 is a schematic diagram of a first embodiment of a heating system in accordance with the present invention; Fig.2 is a schematic diagram of a second embodiment of a heating system in accordance with the present invention; Fig.3 is a schematic diagram of a third embodiment of heating system in accordance with the invention; Fig.4 is a schematic diagram of a modification of the embodiment of Fig.3; Fig.5 shows a system similar to Fig.4 but used with a conventional boiler; and Fig.6 shows a system similar to Fig.4 but used with a system boiler.

Referring now to Fig 1, a combi-boiler shown generally at 10 is connected to a central heating system shown generally at 12 and a pre-heat system, in accordance with the invention, shown generally at

14, via a series of fluid supply conduits (which are detailed below).

The combi-boiler shown generally at 10 includes a gas burner 16, a primary boiler circuit shown generally at 18, a primary heat exchanger 20, a 3-port diverter valve 22, a hot-water circuit shown generally at 24, a gas input conduit 26 with an isolating valve 27, a cold water input conduit 28, a hot water output conduit 30, a heating flow conduit 32 with an isolating valve 33, a heating return conduit 34 with an isolating valve 35, a pressure relief valve 36 with a relief flow drain 37, and a first circulating pump 38.

The hot-water circuit shown generally at 24 includes a domestic heat exchanger 40 (i.e. a secondary or water-to-water heat exchanger) and a micro flow switch 42 which is connected into the cold water input conduit 28. The micro flow switch 42 senses the flow of water through the cold water input conduit 28. The boiler 10 further includes control means (not illustrated) such as programmable timers and thermostats, as will be well known to those of ordinary skill in the art.

In accordance with the invention, the boiler 10 is adapted by the addition of a second circulating pump 62 connected into the heating flow conduit 38, a further secondary (water -to -water) heat exchanger 64 adapted to transfer heat from water flowing through the heating flow conduit 32 to water flowing through

the cold water supply conduit 28, a by-pass conduit 66 interconnecting the flow and return conduits 32 and 34 and including a first non-return valve 68, which allows fluid flow only in the direction from the return conduit 34 to the flow conduit 32, and a second non-return valve 58 in the return conduit 34, downstream of the by-pass conduit 66 -in the return direction and allowing fluid flow only in the return direction.

The second circulating pump 62 operates in response to operation of the micro flow switch 42, as shall be described further below.

The apparatus of Fig. 1 has three modes of operation: a first operating condition in which the central heating is turned off, and the boiler operates only to supply hot running water on demand; a second operating condition in which the central heating is turned on and there is no demand for hot running water; and a third operating condition in which hot running water is supplied on demand whilst the central heating is turned on.

In the first operating condition, a hot water outlet tap (not shown) which is connected to the boiler shown generally at 10 via hot water output conduit 30, is turned on, causing cold water to flow into the heat exchanger 40 via cold water input conduit 28. The micro switch 42 opens a gas flow control valve 43 to activate the burner 16 (which combusts gas received via gas input conduit 26) and energises

the pump 38, in response to the flow of water through cold water input conduit 28 into heat exchanger 40.

Simultaneously, water is pumped through the first circulating pump 38 and around the primary boiler circuit 18, through a boiler outlet conduit 44 and into the primary heat exchanger 20 where the water is heated by the burner 16. The heated water then passes through a boiler output conduit 46, through the 3-port valve 22 (which operates in response to the micro flow switch 42 to allow water to flow from the boiler outlet conduit 46 into heat exchanger inlet conduit 48) and into the heat input side of the domestic heat exchanger 40. As the heated water passes through heat exchanger 40 via conduit 48, the cold water entering the domestic heat exchanger 40 via cold water input conduit 28 is heated in the heat output side of the heat exchanger 40, following which the heated water exits heat exchanger 40 via hot water outlet conduit 30, from where it proceeds to the selected hot water outlet tap (not shown) . Typically, there are a plurality of such hot water outlet taps connected to the boiler system 10.

In this first operating condition, the heated water flowing through heat exchanger 40 via heat exchanger input conduit 48 returns to the primary boiler circuit 18 from heat exchanger 40 via heat exchanger outlet conduit 50, pump 38 and conduit 44. The water is then re-heated in primary heat exchanger 20.

In said second operating condition, the central heating circuit shown generally at 12 is initiated via a central heating control means (not shown) such as a programmable timer. There is no demand for hot water via a hot water outlet tap in this second boiler operating condition. The initiation of the central heating circuit activates the burner 16 and the pump 38 in a similar way as under the first boiler operating condition. The pump 38 subsequently pumps water around the primary boiler circuit 18 through conduit 44, primary heat exchanger 20 (where the water is heated by burner 16), conduit 46 and through 3-port valve 22 (which in this second condition allows water to flow from conduit 46 into central heating output conduit 32), from where the heated water flows into the central heating system. The central heating system shown generally at 12 includes at least one radiator such as the radiator 54 shown in Fig 1. The heated water enters the radiator 54 via an input conduit 52 which is a first branch conduit from the flow conduit 32 which supplies heated water to the central heating system. The water returns to the primary boiler circuit 18 via radiator output conduit 56, heating return conduit 34, and non-return valve 58 (which only allows fluid flow in the return direction indicated by the arrow) . The water is then passed through the primary boiler 18 by circulating pump 38, conduit 44, primary heat exchanger 20 and conduit 46. The water is re-heated

in the primary heat exchanger 20 (by heat from the gas burner 16) before passing to the central heating system shown generally at 12 as before.

In said third operating condition, the central heating circuit shown generally at 12 has been initiated in a similar way as described with reference to the second operating condition and is assumed to have been running for a sufficient length of time to have heated the water in the central heating circuit 12 to some extent.

Switching on a hot water outlet tap in a similar way as described with reference to the first operating condition causes cold water to flow into the boiler 10 via cold water input conduit 28. This triggers the micro flow switch 42 which, in this third condition, again diverts the output flow through the 3-port valve 22 from conduit 32 to conduit 48, such that water flows from the primary boiler circuit 18 from conduit 46 through the domestic heat exchanger 40 as in the first operating condition.

However, in accordance with the present invention, the micro flow switch 42 also activates the circulating pump 62 which extracts heated water in the central heating circuit 12 through the by-pass conduit 66 and the non-return valve 68 and circulates the extracted water through the heat input side of the further heat exchanger 64. (The system may be arranged so that the second pump 62 operates in response to the micro flow switch 42

only when the central heating is turned on. Otherwise, the second pump 62 may operate also in the first operational condition. However, in that event the further heat exchanger 64 would serve no purpose since the water in the central heating circuit would not be hot.) In this way, cold mains water flowing through the heat output side of the further heat exchanger 64 from the cold water input conduit 28 is "pre-heated" by the hot water circulating in the central heating circuit 12 and flowing through the further heat exchanger 64 before this pre-heated water is passed to the domestic heat exchanger 40 inside the combi boiler 10, This enables the output flow rate of hot water through a hot water outlet tap (not shown) to be maintained under circumstances when the temperature of the water entering the boiler 10 via cold water input conduit 28 is reduced.

The invention has particular applications during the winter months or other periods of prolonged cold weather when the water entering the boiler via the cold water input conduit 28 is at a lower temperature than, for example, during the summer months. Under normal circumstances, it would be required to reduce the f low rate of hot water out of the hot water tap in order to maintain the desired output temperature of the hot water.

A typical boiler produces a temperature rise of 35'c at a flow rate of two gallons of water per minute

through the boiler. During the summer months, the temperature of the cold water entering the boiler via cold water input conduit may be approximately 15-180C. During the winter months, this may dip to as low as 5'C. Thus in order to maintain the same output temperature of the hot water, it is necessary to reduce the flow rate of water through the boiler. By pre-heating the water entering the boiler, the input temperature of cold water entering the heat exchanger 40 can be raised such that the flow rate of the water through the boiler may be maintained. Referring to Fig 2, there is shown a second embodiment of the invention which is substantially the same as the first embodiment shown in Fig 1. Components of the second embodiment which are similar to those of the first embodiment share common reference numerals.

The system of Fig 2 includes a combi-boiler shown generally at 10, the combi-boiler including a burner 16, a primary boiler circuit shown generally at 18, a primary heat exchanger 20, a 3-port diverter valve 22, a hot water circuit shown generally at 24, a gas input conduit 26, a cold water input conduit 28, a hot water output conduit 30, a heating output conduit 32, a heating return conduit 34, a pressure relief pipe 36 and a pump 38.

The hot-water circuit shown generally at 24 includes a heat exchanger 40 and a micro flow switch 42. The

pre-heat system shown generally at 14 includes a pump 62, a heat exchanger 64 and conduits 70, 72 connecting the pump 62 and heat exchanger 64 to the primary boiler circuit 18 via the 3-port diverter valve 22.

In a third boiler operating condition of the second embodiment of the present invention (similar to the third operating condition of the first embodiment), cold water entering the heat exchanger 40 via cold water input conduit 28 is pre-heated at heat exchanger 64 by hot water circulating through the central heating system 12 via pump 62, conduit 72, heat exchanger 64, heating output conduit 32, at least one radiator 54, conduit 56 and non-return valve 68.

The pre-heat system 14 of this second embodiment has all of its components contained within the casing of the boiler generally shown at 10, rather than having the components outwith the casing as shown in Fig 1. The first embodiment of Fig. 1 allows the invention to be applied to the conversion of an existing combi-boiler by means of a kit of parts comprising the further heat exchanger 64, the by-pass conduit 66, the second pump 62 and said f irst and second non-return valves 68 and 58. The second embodiment allows these components to be integrated into a new combi-boiler which is installed as a unitary assembly.

Referring now to Fig.3, this schematically illustrates a third embodiment of the present invention which differs from the past two embodiments (previously described with reference to Figs 1 and 2 wherein incoming cold water was pre- heated in the further secondary heat exchanger before passing through and being heated in the first secondary heat exchanger) in that incoming cold water first passes through the first secondary heat exchanger and is then post-heated in the further secondary heat exchanger by means of previously heated water diverted from the circulatory central heating circuit (i.e. in the third embodiment, tap water is post-heated by hot water diverted from the radiator (s) ) .

In the arrangement schematically illustrated in Fig.3, a conventional gas-fired domestic combi- boiler unit 100 receives combustible gas through a gas mains pipe 102 and cold water through a water mains pipe 104. Within the combi-boiler unit 100, gas delivered through the pipe 102 is controllably combusted in a primary (flame-to-gas) heat exchanger (not shown) , as in the preceding embodiments, to heat water in a closed-loop circulatory central heating circuit whose output from the combi-boiler unit 100 is via a delivery (flow) pipe 106, water being recirculated to the combi-boiler unit 100 via a return pipe 108. Outside the combi-boiler unit 100, one or more radiators (not shown) will be connected to the flow pipe 106 to receive heated water from the primary heat exchanger, the

radiator(s) also being connected to the return pipe 108 to return heat-depleted water to the primary heat exchanger wherein the recirculating water is re-heated. Water is pumped around this closed-loop recirculatory central heating circuit by means of a pump (not shown), as in the preceding embodiments, which may be located inside or outside the combi- boiler unit 100. The combi-boiler unit 100 also contains a first secondary (water- to -water) heat exchanger (not shown) , as in the preceding embodiments, having a heat input side and a heat output side. The heat input side of the first secondary heat exchanger is connected to the primary heat exchanger in parallel with the central heating flow and return pipes 106 and 108. The heat output side of the first secondary heat exchanger is connected to the incoming cold water mains pipe 104 to receive fresh cold water which is heated up in its passage through the heat output side of the first secondary heat exchanger by means of gas - combustion -produced heat from the primary heat exchanger received in the heat input side of the first secondary heat exchanger. The newly heated fresh mains water is delivered from the combi-boiler unit 100 by way of a hot running water output pipe 110. (Delivery of hot running water via the pipe 110 can be accomplished solely by means of water mains pressure, or the delivery of hot running water may be assisted by means of a water pump (not shown) which may be upstream or downstream of the first secondary heat exchanger,

and inside or outside the combi-boiler unit 100) Flow of hot running water is controlled by means of one or more outlet control taps, e.g. sink taps, bath taps, shower controls, etc, one of which is schematically depicted at 112. In accordance with this preferred form of the invention, a second secondary (water -to -water) heat exchanger in the form of a domestic heat exchanger 114 is fitted at a location which is physically close to the hot running water outlet control tap 112 (e.g. the heat exchanger 114 could be located underneath a hand basin (not shown) of which the tap 112 forms a part) The domestic heat exchanger 114 takes the form of a closed water tank 116 which forms the heat input side of the second secondary heat exchanger 114. Suspended within the tank 116 is a serpentine coil of pipe 118 which forms the heat output side of the second secondary heat exchanger 114. The pipe coil 118 is coupled to the hot running water circuit between the combi-boiler unit hot water output 110 and the tap 112 such that, while water in the hot running water circuit is hydraulically isolated from water in the recirculatory circuit of the heating system, boiler- heated water in the tank 116 transfers its heat to water within the pipe coil 118. The water tank 116 is connected by way of a feed pipe 120 to the central heating flow pipe 106 which delivers the newly heated water from the primary heat exchanger within the combi-boiler unit 100 to

radiator(s) in the central heating circuit. Water leaving the tank 116 of the heat exchanger 114 is returned to the central heating circuit by way of a pipe 122 connected to the return pipe 108. Immediately downstream of the point at which the tank feed pipe 120 is connected to the central heating delivery pipe 106, the delivery pipe 106 is fitted with a motorised two-port valve 124 (e.g. an electrically- controlled solenoid open/shut valve) . A thermostatic switch 126 is mounted on the outside of the water tank 116 such that the switch 126 senses the temperature of the water in the tank 116, the switch 126 being a change-over switch operating to open one circuit and to close another circuit in dependence upon whether the tank temperature is above or below a predetermined temperature or "setpoint". The thermostatic switch 126 has an input 128 which is connected by a first wire 130 to a first terminal ("permanent live") 132 in the combi-boiler unit 100. The thermostatic switch 126 has a first switched output 134 which is connected by a second wire 136 to a second terminal ("switched live") 138 in the combi-boiler unit 100. The thermostatic switch 126 has a second switched output 140 which is connected by a third wire 142 to the motor (solenoid) of the motorised two-port valve 124. An electrical return (neutral) connection from the motor (solenoid) of the valve 124 to a neutral terminal 144 in the combi-boiler unit 100 is omitted for clarity, as are appropriate earth connections

between various parts of the heating system and the combi-boiler unit earth terminal 146.

As well as the gas and water mains inputs 102 and 104, the combi-boiler unit 100 receives an electrical mains input (not shown per se) on the live /neutral/ earth terminals 132/144/146, as is well known in the art. The combi-boiler will include the usual programmable timer or the like for controlling the operation of the central heating system etc. The thermostatic switch input 128 is rendered live by way of the wire 130 from the live terminal 132. If the temperature of the water in the tank 116 (i.e. the temperature in the heat input side of the second secondary heat exchanger 114) is below the setpoint of the thermostatic switch 126, the switch 126 is in its "below setpoint" configuration, the first switch output 134 is connected to the switch input 128, and the second switch output 140 is disconnected from the switch input 128. In turn, the wire 136 causes the combi-boiler terminal 138 to become live, which switches on the supply of gas and operates the ignitor to light the main burner (not shown) of the primary heat exchanger; simultaneously, the wire 142 is not live and the valve 124 will be closed to prevent central heating water leaving the combi-boiler unit 100 by way of the flow pipe 106 from reaching the radiators, the hot water instead being forced down the feed pipe 120 to the tank 116 (eventually to return by way of the return pipes 122 and 108) . Consequently, the

temperature of water in the tank 116 tends to increase (at the expense of temporarily starving the radiators of heat) . Eventually, the temperature sensed by the thermostatic switch 126 will increase until it is sufficiently above the predetermined setpoint that the switch 126 changes over to its "above setpoint" configuration, causing the first switch output 134 to become disconnected from the switch input 128 and simultaneously causing the second switch output 140 to become connected to the switch input 128. In turn, the combi-boiler terminal 138 ceases to be live, and operation of the primary heat exchanger (including the combustion of gas) is no longer demanded by the switch 126 (combustion and heat output may continue, but under the control of radiator demands, as will subsequently be detailed) simultaneously, the switch output 140 becomes live (because it is now connected to the "permanently" live switch input 128) and the wire 142 transfers electrical power to the motorised valve 124 to open the valve 124 which terminates forced diversion of central heating water through the tank 116 and allows normal flow to the radiators (s) If the heat demand of the radiator(s) is sufficient, conventional thermostatic controls (not shown) e.g. room thermostat (s) , radiator thermostat (s) , etc, will cause the continued combustion of gas within the combi-boiler unit 100 despite the tank switch 126 being above its predetermined setpoint.

When the taD 112 is opened, mains water f lows through the combi-boiler unit 100 from the water mains pipe 104 to the hot running water output pipe 110, and such mains water flow causes a flow- sensitive switch (not shown) within the unit 100 to close and thereby operate the primary heat exchanger (including heat-generating combustion of gas) within the unit 100. The secondary heat exchanger within the combi-boiler unit 100 (i.e. the first secondary heat exchanger, and not the second secondary heat exchanger 114 downstream of and external to the unit 100) receives this newly-generated heat from the primary heat exchanger and heats up the fresh mains water flowing through the heat output side of the first (internal) secondary heat exchanger. (if necessary or desirable, flow of water through the heat input side of the first secondary heat exchanger can be assisted by a separate circulation pump) . Although the combi-boiler unit 100 may be physically remote from the newly opened tap 112 such that fresh mains water newly heated in the unit 100 is significantly delayed in reaching the tap 112, water currently leaving the tap 112 is almost instantaneously hot by reason of having been heated in passage throughout the pipe coil 118 immersed in the previously heated water in the tank 116 of the second secondary heat exchanger 114. Thus the second secondary heat exchanger 114 acts as a virtual "under sink" water heater but without the expense of a separate heat source (e.g. an electrical immersion heater) since it utilises heat

diverted from the radiator(s) of the recirculatory central heating circuit.

If sufficient hot running water is withdrawn through the tap 112 as to reduce the temperature sensed by the switch 126 below the predetermined setpoint temperature, the switch 126 will switch back to its "below setpoint" configuration, re-energising the terminal 138 and re-closing the valve 124. This will cause the primary heat exchanger to resume operation (or to remain in operation, if already operating) thereby to heat up the water recirculating through the central heating circuit which is forcibly directed through the tank 116 by reason of the closure of the valve 124. Thus the supply of heat to the second secondary heat exchanger 114 always takes precedence over the demands of the radiator (s) The bulk of water in the tank 116 provides a reservoir of heat such that the second secondary heat exchanger functions (to a certain extent) as a heat store rather than always as a heat exchanger with instantaneous equality of "heat in" with "heat out"; if relatively little water is withdrawn through the tap 112, the switch 126 may not revert to its "below setpoint" configuration. The third embodiment of the present invention (as depicted in Fig.3) can be provided as an all-new system, or converted from a pre-existing conventional central heating/hot water system employing a combi-boiler unit by the provision of a

kit of parts comprising a domestic heat exchanger (as the second secondary heat exchanger) and a motorised two-port valve, together with appropriate plumbing, wiring, and instructions.

As an alternative to the provision of a first secondary heat exchanger within the combi-boiler unit 100 for the indirect heating of running water, the incoming mains water could be fed through the primary heat exchanger (in a hydraulic circuit separate from the recirculatory central heating circuit) whereby the fresh mains water is directly heated.

The system shown in Fiq.4 is similar to that of Fig.3, and like parts are denoted by like reference numerals. Here, however, a temperature control valve 150 is interposed between the heat exchanger 114 and the tap 112. The temperature control valve is connected to the cold water supply 104 and mixes sufficient cold water into the stream of hot water f rom the heat exchanger 114 to ensure that a predetermined safe temperature is not exceeded. Also in Fig.4, in addition to the motorised valve 124 in the central heating flow line 106, a second motorised valve 152 is provided in the feed pipe 120. The valve 152 opens when the valve 124 closes, and visa versa. The system will operate with only one motorised valve, as in Fig.3, but without the second valve some circulation will occur through the

heat exchanger coil 118 whenever the central heating is operating.

Fig.4 includes an expansion vessel 154. This is only required in a sealed system, and then only if an existing system were operating close to the capacity of its existing expansion vessel before installation of one or more remote heat exchangers. A system similar to that of Fig. 4 may be used with conventional boilers, as in Fig. 5. In this case, however, there is no on-demand hot water from the boiler. The heat exchanger 114 is fed with cold from supply 104. The conventional boiler is shown at 200, and requires a separate circulating pump 202.

The system of Fig. 6 is identical to that of Fig. 5 but using a system boiler 300. Since the system boiler 300 has an internal circulating pump, no separate pump is shown.

Figs. 5 and 6 also illustrate the optional inclusion of an electrical immersion heater 210 in the domestic heat exchanger 114, providing a back-up heat source to the main boiler 200, 300. Typically, the immersion heater 210 may project into the interior of the tank 116 of the heat exchanger 114 from the top or side thereof as illustrated.

Similar immersion heaters could be incorporated into the heat exchangers 114 of the embodiments of Figs. 3 and 4.

The embodiments of Figs. 5 and 6 optionally also include thermostats 212 (preferably of the probe type having a sensor which projects into a conduit or vessel) on the cold inlet to the heat exchanger 114 for firing up the boiler 200, 300. Thermostats of this type are not required for combi-boiler systems.

The systems of Figs 3 to 6, may have more than one domestic heat exchanger 114. This may -be done so that each hot tap or appliance may have a heat exchanger nearby, thus minimising heat loss from long pipe runs, for example if the kitchen and bathroom are far apart. There may also be more than one heat exchanger at one location and connected together, to provide a greater hot water capacity in a modular manner.

Other modifications and variations can be adopted without departing from the scope of the invention.

Claims

Claims 1 A central heating/hot water system including a boiler for heating central heating circulating water, a circulating pump, and a flow and return pipe and radiator system through which the circulating pump passes the circulating water; and including means for selectively diverting said circulating water to at least one heat exchanger to assist in the supply of hot water.
2. A system as claimed in claim 1, wherein the boiler is a combi boiler and the heat exchanger acts to pre-heat a cold water supply to a water heating path of the combi boiler.
3. A system as claimed in claim 1, wherein the heat exchanger is located close to the point of hot water use.
4. A system as claimed in claim 1 or claim 3, wherein the boiler is a conventional or system boiler, and the heat exchanger is operable in conjunction with the conventional or system boiler, to heat cold water.
5. A system as claimed in claim 1 or claim 3, wherein the boiler is a combi boiler and the heat exchanger is operable to superheat hot water supplied from the combi boiler.

<Desc/Clms Page number 25>
6. A system as claimed in cla-Lm 4 or claim 5, wherein the heat exchanger has a temperature control valve associated therewith which mixes hot water output from the heat exchanger with cold water.
7. A system as claimed in any preceding claim, including a plurality of heat exchangers remote from the boiler, each of said remote heat exchangers being located close to a point of hot water use.
8. A system as claimed in any preceding claim, wherein the diversion of central heating circulating water is effected by a pair of motorised valves, or by means of an auxiliary pump and one-way valves.
9. A system as claimed in any preceding claim, wherein the diversion of central heating circulating water is initiated by a thermostat on the remote heat exchanger.
10. A system as claimed in any preceding claim, wherein the diversion of central heating circulating water is initiated by a demand for hot water indicated by the opening of a tap or appliance valve.