GB2369877A - Hot water supply systems - Google Patents

Abstract

A water heating apparatus comprises an insulated heat exchanger contained within an outer casing 3, together with connection means for connecting the heat exchanger in various configurations to a hot water supply system which includes a boiler heating a primary fluid. The heat exchanger transfers heat from the primary fluid to a supply of hot water, and includes a flow sensor 18 which senses a flow of hot water and actuates timing means for controlling the boiler. A conveniently located manual switch may also be provided for actuating the timing means. The casing may also contain expansion vessels 82 and a pump 80 for circulating the primary fluid and/or providing pressurised hot and cold water supplies. The heat exchanger may be connected alone or in series with a hot water cylinder to improve the performance of the system and provide a satisfying shower experience. The flow paths 6, 7 for the primary fluid and the water are preferably defined tubes 5 within tubes 4. Paths 6 and 7 are preferably of equivalent volumes. The volumes are preferably not substantially greater than that required to effect heat transfer.

Description

Water heating apparatus and hot water supply system

This invention relates to hot water supply systems.

A wide variety of systems are known for providing hot water supplies in houses, flats, mobile homes and the like, and these systems may broadly be grouped into two types, viz. demand type hot water supply systems, hereinafter referred to as"demand systems", and storage type hot water supply systems, hereinafter referred to as"storage systems", or combinations thereof.

Demand systems are those which heat water immediately prior to its use, and enjoy the advantage that, depending on the available supplies of cold water and heating energy, a flow of heated water may be drawn from the system for any required period of time without the temperature of the water reducing.

Demand systems typically comprise a heat exchanger for transferring heat directly from a heat source to a pressurized supply of water, which may be drawn from a water storage tank in a building but is typically drawn from the main water supply entering the building. A typical such system is the gas fired demand boiler, which senses the flow of water drawn from a tap or shower and activates a gas burner to heat the water as it passes through a heat exchanger within the boiler.

However, demand systems suffer from a number of disadvantages.

Fluctuations in the rate of flow of water through the heat exchanger commonly cause fluctuations in the temperature of the water drawn from the system. For example, a person enjoying a shower in one part of a building may find that the shower becomes abruptly colder when a person in another part of the

same building opens a hot water tap which is fed by the same demand system as the shower.

It is desirable for the heat exchanger in a demand system to be robust and durable. However, an increased mass of thermally conductive material, such as cast iron, whilst increasing the longevity of the heat exchanger will also absorb and release a greater amount of heat energy. This may cause an inconvenient delay in heated water reaching a tap or shower when drawing hot water from an already cold heat exchanger. Conversely, when water is drawn from such a heat exchanger shortly after a prior period of operation, the user may be scalded by the heat absorbed from the heat exchanger by the small volume of water which has lain briefly static therein. Various methods are employed to ameliorate these effects, such as the provision of thermostatically regulated valves for showers and taps.

However, the foregoing problems may be compounded by the buildup of scale within the heat exchanger, and may at their worst provide for the user a miserable shower experience.

It is therefore often preferred to provide a storage system rather than a demand system, which enjoys the advantage that heated water may be drawn from the system continuously or intermittently and at any desired flow rate without any sudden variation in temperature.

Storage systems represent a very common and traditional means of providing domestic hot water supplies, and commonly comprise a vessel for storing and heating water, typically in the form of an insulated copper cylinder, (hereinafter referred to as a"cylinder,") which is fed via a water supply pipe from a cold water supply, often in the form of a gravity feed cold water storage tank, and has a primary fluid heating means cooperating therewith. The primary fluid heating means is often a gas fired, oil fired or similar boiler which is arranged to heat a recirculated"primary"heat exchange fluid (hereinafter

referred to as "primary fluid. ") This primary fluid then flows through a heat exchanger in the form of a coil of tubing arranged within the cylinder to heat the water which is contained therein, the hot water flowing via a water supply pipe from the hot water outlet of the cylinder to supply the taps, showers and other points of demand.

However, storage systems suffer from the disadvantage that the rate of heat transfer between the primary fluid and the water may be relatively low, and the capacity of the cylinder is limited. The temperature of the hot water supply may therefore fall after a prolonged period of flow. Again, the problem may be exacerbated by the presence of scale around the heat exchanger.

It is known to provide a cylinder of increased size or a heat exchanger of increased surface area therewithin in order to increase the volume of heated water that may be drawn therefrom or to improve the"recovery time"of the cylinder. However, the efficacy of this approach is limited by the effectiveness of the heat exchanger and the available space for housing the cylinder.

The heat input to the cylinder may be controlled by a control system including a timing device set to operate at given times of the day. However, there may be no provision for the heat input to be responsive to the demand for heated water, other than by the provision of a manual control located at the timing device or boiler. Where the actual pattern of demand departs from the preset programming of the timing device, the user may therefore have to adjust the control system, which may be located for example in the kitchen, in order to procure additional hot water in the bathroom.

The component parts of a domestic hot water system may be replaced in order to improve its performance. However, it may be expensive and disruptive to remove cylinders, pipework and the like, which are often inaccessible without substantial building work and subsequent redecoration.

It is therefore the object of the present invention to provide a means whereby the performance of a hot water supply system may be improved.

According to the present invention there is provided a hot water supply system comprising a recirculated primary fluid conveying heat from a primary fluid heating means to a vessel for storing and heating water, characterised in that the said primary fluid and the said water flow through a heat exchange means which is substantially contained within casing means, the said casing means being separate from the said vessel and from the said primary fluid heating means, and in that the volume of water and of primary fluid contained within the said heat exchange means is not substantially greater than that required to effect heat transfer.

According to the present invention there is provided a hot water supply system comprising a recirculated primary fluid conveying heat from a primary fluid heating means to a heat exchange means so as to heat a supply of water flowing through the said heat exchange means, characterised in that the said heat exchange means is substantially contained within casing means, the said casing means being separate from the said primary fluid heating means, and in that the volume of water and of primary fluid contained within the said heat exchange means is not substantially greater than that required to effect heat transfer.

According to the present invention there is provided a water heating apparatus comprising a heat exchange means according to the hot water supply system as abovedescribed, characterised in that there are further provided connection means external to the said casing means whereby the said water heating apparatus may be connected to the said hot water supply system.

According to the present invention there is provided a water heating apparatus for connection to an existing hot water supply system, the said system including : a vessel for storing and heating water, at least two water supply pipes communicating with the said vessel, at least one heat exchanger contained within the said vessel, at least two primary fluid carrying pipes communicating with the said heat exchanger, and primary fluid heating means; the said heat exchanger containing a primary fluid and transferring heat therefrom to the said water contained within the said vessel ; the said water heating apparatus comprising a heat exchange means having at least a first fluid carrier and a second fluid carrier, and characterised in that the said heat exchange means is substantially contained within casing means so as to form a discrete unit, there being further provided connection means external to the said casing means for connecting the said first fluid carrier to at least one of the two said primary fluid carrying pipes, and the said second fluid carrier to at least one of the two said water supply pipes, such that the said primary fluid and the said water flow through the said heat exchange means and heat is transferred therebetween.

According to the present invention there is provided a water heating apparatus for connection to a hot water supply system, the said system including : at least two water supply pipes carrying water, at least two primary fluid carrying pipes carrying a primary fluid, and primary fluid heating means; the said water heating apparatus comprising a heat exchange means having at least a first fluid carrier and a second fluid carrier, and characterised in that the said heat exchange means is substantially contained within casing means so as to form a discrete unit, there being further provided connection means external to the said casing means for connecting the said first fluid carrier to at least one of the said primary fluid carrying pipes, and the said second fluid carrier to at least one of the said water supply pipes, such that the said primary fluid and the said water flow through the said heat exchange means and heat is transferred therebetween.

Preferably there are also provided sensing means cooperating with control means and electrical connection means for connecting to a control system of the said hot water supply system.

An illustrative embodiment of the present invention will now be described by way of example and with reference to the accompanying drawings in which : Figure 1 shows a side elevation of a water heating apparatus according to the present invention, with the casing partially cut away to show the inner parts thereof; Figure 2 shows a further side elevation of the water heating apparatus as seen from side A in Figure 1, again with the casing partially cut away; Figure 3 shows a cross-sectional view through X-X of the water heating apparatus as seen in Figure 1; Figure 4 shows a schematic diagram of a demand type domestic hot water supply system according to the prior art; Figure 5 shows the system shown in Figure 4 after the installation of the water heating apparatus shown in Figure 1; Figure 6 shows in the form of a flowchart the operation of the control means shown in Figure 5; Figure 7 shows the system shown in Figure 4 after the installation of the water heating apparatus shown in Figure 1 in an alternative configuration; Figure 8 shows a side elevation of an alternative embodiment of the water heating apparatus, again with the casing partially cut away;

Figure 9 shows the water heating apparatus shown in Figure 8 installed in the system shown in Figure 4, in a further alternative configuration ; Figure 10 shows a side elevation of a further alternative embodiment of the water heating apparatus, again with the casing partially cut away; and Figure 11 shows a side elevation of a further alternative embodiment of the water heating apparatus, again with the casing partially cut away.

The reference numbers refer to the same parts in each figure, and some duplicated reference numbers have therefore been omitted for the sake of clarity.

Referring to Figures 1,2 and 3, a water heating apparatus 1 comprises a heat exchange means 2 contained within casing means comprising an outer casing 3. The outer casing is shown cut away in Figures 1 and 2 to reveal the internal arrangements. The said heat exchange means takes the form of a pipe-inpipe arrangement, comprising an assembly of larger diameter pipes 4, each of which contains a smaller diameter pipe 5, the annular spaces between pipes 4 and their respective smaller diameter pipes 5 together defining a first fluid carrier 6. Pipes 5 together form a second fluid carrier 7 of substantially equivalent volume to the said first fluid carrier. The said pipes may be made for example from copper.

Pipes 4 and 5 are joined respectively by link sections 4'and 5'so that the said first and second fluid carriers are formed as a double inverted U-shape. The first fluid carrier 6 terminates at one of its two ends in a pipe connector 8 and at its other end in a pipe connector 9, which pipe connectors are arranged close to the base of the outer casing 3 and generally opposite each other. The second fluid carrier 7 terminates at one of its two ends in a pipe connector 10 which is arranged close to the base of the outer casing 3, and at its other end

in a feed pipe 11. The feed pipe 11 terminates in a pipe connector 12 which is arranged at the top of the outer casing 3.

The said pipe connectors together comprise connection means and may be for example brass compression fittings, or alternatively push-fit connectors to enable easy installation of the said water heating apparatus by connecting it to an existing hot water supply system as described hereafter. Alternatively for example the said connection means may be arranged as rigid or flexible tubes extending outwardly from the said outer casing.

The heat exchange means 2 is preferably thermally insulated by being substantially surrounded by thermally insulating material (not shown) such as a suitable insulating foam which fills the cavity 13 within the outer casing 3, and there is further provided electrical safety or bonding means comprising an earthing point 17 to which external earthing or bonding conductors may be attached and which is electrically connected to the said heat exchange means and to the said outer casing, if the said outer casing is made from an electrically conductive material.

A well known problem associated with hot water supply systems is caused by air which becomes trapped within the system to produce an airlock. The said heat exchange means is therefore provided with means facilitating the release of air which may become trapped within either of the said first or second fluid carriers.

The said first fluid carrier is equipped with an automatic air vent 14 of known design which is connected to all of the sections of the first fluid carrier 6 by connecting pipework 15. The said second fluid carrier is provided with an air release passage 16 which connects all of the sections of the said second fluid carrier to the feed pipe 11 close to the pipe connector 12. In order to prevent a significant volume of water from flowing through the air release passage 16 and therefore bypassing part of the second fluid carrier 7, the air release

passage is formed as a copper tube of small diameter which is locally compressed to provide a constriction 17 through which a very small amount of air or water may flow.

Many alternative designs of heat exchanger are well known, and it is to be understood that the heat exchange means 2 might equally well take any of a wide variety of alternative forms of heat exchanger. For example, the first fluid carrier might be formed as a single vessel just large enough to accommodate the second fluid carrier in the form of a helical coil of tubing contained therein. Alternatively for example the first and second fluid carriers might be formed as concentric tubes with ribs or other surface patterns to improve heat transfer therebetween.

The water heating apparatus 1 is also preferably of compact design, and the heat exchange means 2 is preferably formed so as to occupy the minimum necessary space, the outer casing 3 preferably being only large enough to accommodate the said heat exchange means together with other components and insulating material as described herein. A compact design will facilitate the installation of the water heating apparatus, for example adjacent a hot water cylinder, which is typically confined within a small space.

It is also important that the said heat exchange means does not contain a volume of water or of primary fluid greater than that required to effect heat transfer. The limited volume of water and of primary fluid allows effective operation of the said heat exchange means by ensuring a vigorous flow through the said first and second fluid carriers. The limited volume also enables the said water heating apparatus to be as small as possible so as to facilitate installation in the space available adjacent an existing cylinder, and enables the weight of the said water heating apparatus to be as low as possible in order to facilitate connection in the most convenient position, and possibly without the outer casing 3 resting on the floor, without straining the pipework which may partly or fully support its weight. The limited volume of

primary fluid within the said first fluid carrier is important in that it enables the said primary fluid to reach the required temperature in the shortest possible time; an additional volume of primary fluid would introduce unnecessary inefficiency and detract from the ability of the said water heating apparatus to respond rapidly to changes in demand.

The heat exchange means 2 is shown in the attached figures for illustrative purposes only, and one skilled in the art will readily conceive many alternative forms in which the said heat exchange means might advantageously be implemented.

According to a further aspect of the present invention, the water heating apparatus 1 is further equipped with sensing means, which sensing means may comprise a flow sensor 18 of known design which is arranged on the feed pipe 11 so as to provide an electrical signal indicating that water is flowing through the said second fluid carrier. Preferably the flow sensor 18 has a predetermined sensitivity such that a signal is provided only when the rate of flow therethrough exceeds a given level. The flow sensor 18 may comprise a flow switch for switching an electrical current in response to changes in flow.

A further well known problem of hot water supply systems is the phenomenon of unwanted heat transfer by the convection or circulation of hot water. It is therefore desirable that heated water should be prevented from flowing away from the heat exchange means 2 through the feed pipe 11 and back towards the cold water storage tank of the existing hot water supply system to which the said water heating apparatus is connected as described below. The flow sensor 18 is therefore preferably arranged so as to function as a one way valve and thus to prevent a significant flow of water through the feed pipe 11 in the unwanted direction.

It is desirable that the water heating apparatus 1 may be installed in any of a variety of positions and orientations, and the flow sensor 18 and other components are therefore preferably designed so as to function correctly when the main axis of the outer casing 3 is oriented at a variety of angles from the vertical. Alternatively the said water heating apparatus may be designed so as to be installed in a generally horizontal plane.

The said flow sensor is arranged to cooperate with a control means 58 via a suitable connection 59. Preferably the control means 58 is located within the outer casing 3, and comprises electronic control and switching means together with electrical connection means 60, comprising a plurality of electrical connection terminals, for connecting to a control system of the said existing hot water supply system. The said electronic control and switching means may conveniently be provided with a power supply via the said control system of the said existing hot water supply system.

Alternatively in a very simple embodiment the said control means may comprise only electrical connection means whereby the said sensing means may act as a switch to control the said control system of the said existing hot water supply system.

The said electronic control and switching means may include electrical relays for switching a mains voltage electrical current to control the said control system of the said existing hot water supply system, together with timing means and logic circuits for controlling the said electrical relays. The electrical connection means 60 may include means for connecting auxiliary sensing and control means external to the said outer casing 3, such as an auxiliary temperature sensing means and an auxiliary switching means, cooperating with the said electronic control and switching means.

The said control means may include one or more adjustable controls such as dials 61,62 which may be adjusted by the person installing the said water

heating apparatus, such as a plumber, together with indicating means such as a light emitting diode 63. The said sensing means may alternatively or additionally be arranged so as to sense the said primary fluid within the said first fluid carrier; the said sensing means may also include temperature or pressure sensing means. The control means 58 is adapted so as to control the said control system of the said existing hot water supply system according to the electrical output from the said sensing means, and an illustrative example of one arrangement of the said control means is described herebelow with reference to Figures 5 and 6.

Referring now to Figure 4, a conventional hot water supply system, hereinafter referred to as"the system", includes a vessel for storing and heating water, which is typically an"indirect"copper cylinder 41 with an outer insulating jacket (not shown), containing a heat exchanger 42 which comprises a coil of copper tubing, and having a cold water inlet 43 near its base through which inflowing cold water may flow into the said cylinder through a water supply pipe 44 under pressure from a source such as an elevated cold water storage tank 45. The water contained within the said cylinder is heated by the heat exchanger 42, and may be heated additionally or alternatively by a second heat source such as an electric immersion heater (not shown), and emerges from a hot water outlet 46 near the top of the said cylinder as hot water which supplies through a water supply pipe 44'one or more points of demand such as a shower 47. An expansion pipe 48 is provided to accommodate changes in the volume of the stored water and to enable air to escape from the system.

The heat exchanger 42 is connected by connection means 49'and 50'on the outer wall of the cylinder 41, respectively to an upper primary fluid carrying pipe 49 and a lower primary fluid carrying pipe 50, which pipes form a circuit

with a primary fluid heating means such as a gas fired or oil fired boiler 51, comprising typically a burner heating the said primary fluid as it flows through a jacket. The primary fluid heated by the boiler 51 flows through pipe 49 into the heat exchanger 42, is cooled by the water contained within the cylinder 41, and returns through pipe 50 to the boiler 51 where it is reheated and recirculated.

A control system is provided for controlling the boiler 51 and regulating the temperature of the water within the cylinder 41, and comprises a controller 55 and an electrical thermostat 56 which senses the temperature of the water within the cylinder 41 and passes this information to the said controller via wiring 57. The said controller 55 may be located on the boiler 51 or in any other position, and its component parts, which may include timing means and other components, may be located together or in separate locations.

The system shown includes a so-called"header tank"52 which supplies additional primary fluid as it is required through a"filler"pipe 53, and a safety vent pipe 54 which accommodates changes in the volume of the said primary fluid. Various alternative arrangements of hot water supply systems are possible, including systems wherein the header tank 52 and filler pipe 53 are replaced by a pressurised expansion vessel. Similarly, the cylinder 41 and tank 45 may be replaced by a pressurised hot water storage vessel, various components of a hot water supply system may be integrated into a single unit, and various additional devices and features such as pumps, overflow pipes, valves, space heating systems and other components will typically be included in such hot water supply systems. For example, such systems will typically be integrated with central heating systems. It is to be understood that the water heating apparatus described above may be connected to a wide variety of different hot water supply systems, and one skilled in the art will readily appreciate the various modifications and additional components which will be required in making such a connection both safe and effective.

Referring now to figures 1 to 6 but especially to Figure 5, the said water heating apparatus is connected to an existing hot water supply system, shown here by way of example as"the system"shown in Figure 4, such that the primary fluid thereof, typically a recirculated body of water containing corrosion inhibiting additives, flows through the first fluid carrier 6 between pipe connectors 8 and 9, and the cold water supply to the cylinder 41 is arranged to flow first through the second fluid carrier 7 and feed pipe 11 between pipe connectors 10 and 12, before flowing into the cold water inlet of the said vessel. Preferably the system includes known means for reducing the formation of scale.

The water heating apparatus 1 is preferably arranged so that the said pipe connectors are positioned so as to facilitate easy connection to the said system. Thus pipe connectors 8 and 9 are arranged generally opposite each other so that on installation, they may be connected by the said plumber between the lower primary fluid carrying pipe 50 supplying the heat exchanger 42 and the connection means 50'of the said heat exchanger provided on the wall of the cylinder 41 and close to the base thereof, by cutting a section from the said pipe 50 and connecting the pipe connectors 8 and 9 respectively to the cut ends of the said pipe 50, or alternatively, respectively to the cut end of the said pipe 50 and to the said connection means 50'. The water heating apparatus 1 will then conveniently occupy a generally upright position adjacent the cylinder 41 with pipe connector 12 uppermost and pipe connector 10 at the base, and any air which collects in the inverted U-shape of the first fluid carrier 6 will be vented through the automatic air vent 14.

The cold water supply pipe 44 may similarly be cut by the said plumber and the second fluid carrier 7 connected via pipe connector 10 to the cold water inlet of the said cylinder via suitable pipework, which may be part of the existing cold water supply pipe, and connected at its other end via pipe

connector 12 to that remaining part of the existing cold water supply pipe 44 which is connected to the cold water storage tank 45. The cold water supply pipe 44 will typically tend generally downwards from the elevated cold water storage tank 45 to its connection with the cold water inlet 43 of the cylinder 41. Any air which becomes trapped in the inverted U-shape of the second fluid carrier 7 will therefore flow through the air release passage 16 and leak past the flow sensor 18 to escape upwards through the cold water supply pipe 44 into the cold water storage tank 45.

The pipe connector 8 may be connected closer to the heat exchanger 42 and the pipe connector 9 closer to the boiler 51, so that when the pipe connectors 10 and 12 are connected as described below, the flows of fluid within the said first and second fluid carriers have opposite directions so as to maximise the rate of heat transfer therebetween.

Preferably the said first fluid carrier is connected to the lower primary fluid carrying pipe 50, so that the inflowing water entering the cylinder 41 through the cold water inlet 43 is preheated by the heat exchange means 2, but the said primary fluid is not cooled by the said inflowing water within the second fluid carrier 7 until it has passed through the heat exchanger 42.

In this configuration, the heat exchanger 42 is maintained at its maximum temperature in order to more readily heat the water contained within the cylinder 41 to the required temperature. However, during periods of increased demand for hot water, the said inflowing water entering the cylinder will be preheated by the heat exchange means 2 and will therefore be more quickly raised to the required temperature by the heat exchanger 42, resulting in a satisfying shower experience 69.

The said heat exchange means is rendered more effective by the fact that all of the said inflowing water is made to move over the surface of the first fluid carrier 6 through the second fluid carrier 7, as compared with the heat

exchanger 42 of conventional design which heats a much larger body of stored hot water, only some of which is brought into close contact with the said heat exchanger as it moves less vigorously by means of convection, which may result in an insufficiency of adequately hot water during periods of extended demand, leading to an unsatisfying shower experience 68.

The effectiveness of the said system may be further improved by the greater difference in temperature between the first and second fluid carriers, which increases the rate of heat transfer. The said water heating apparatus may be configured as above so as to return the said primary fluid to the said boiler at a lower temperature than was typical of the prior art system. The burner of the said boiler may therefore fire for a greater proportion of the time in order to maintain the temperature of the said primary fluid at the level set by the temperature sensing means within the boiler, and the rate of heat input into the system will therefore increase to match the rate of heat transfer. If necessary, the said primary fluid may be circulated by a pump as provided within the outer casing 3 according to an alternative embodiment below, in order to achieve the required rate of heat transfer from the said boiler to the said hot water.

The operation of the said water heating apparatus is enhanced by connecting the said control means 58 to the controller 55 of the existing hot water supply system by means of wiring 64 connected to the electrical connection means 60, so that the boiler 51 may be actuated thereby when hot water is drawn from a point of demand such as a bath or shower, thus heating and circulating the said primary fluid and ensuring that heat transfer takes place within the heat exchange means 2 whilst water is flowing therethrough into the cold water inlet 43 of the cylinder 41. In the embodiment shown, the demand for hot water is sensed by a flow sensor 18; it might alternatively be sensed for example by a temperature sensor or a pressure sensor.

The said control means also offers the further advantage that the said boiler or equivalent heat source is made to respond to the user's demand for hot water, in addition to any timing means incorporated in the said controller 55.

Thus for example if a user should require a shower at an unforseen time of day, when the boiler 51 is turned off by a timer in the controller 55 in order to save fuel, the boiler will be actuated by the said control means in order to maintain the temperature of the hot water drawn from the shower 47 and ensure the satisfying shower experience 69.

In order to prevent the boiler 51 from being actuated unnecessarily by a small volume of hot water drawn by a user, for example to fill a basin or to wash their hands, the said sensing means is arranged as described above so as to be insensitive to a flow of less than a predetermined rate.

In an alternative embodiment of the invention, an adjustable sensitivity control is provided whereby the sensitivity of the said flow sensing means may be adjusted by the said plumber. The said adjustable sensitivity control might comprise for example an adjustable valve means (not shown) arranged in parallel with the said sensing means so as to locally bypass it, and accessible from outside the said outer casing 3.

In addition, the said control means 58 may further comprise an adjustable timing means whereby the boiler 51 will be actuated only after hot water has been drawn off by a user at a sufficient rate of flow and for a sufficient length of time to indicate that a bath or shower is being used. The said adjustable timing means may be adjusted by means of the dial 61 by the said plumber, and may be adjustable within a range of, for example, from 15 seconds to 2 minutes.

The operation of the said adjustable timing means and/or other components may be indicated by indicating means such as the light emitting diode 63, in order to assist the said plumber in making the required adjustments.

The control means 58 may also include a boiler timing means which may be adjustable by the said plumber by means of the dial 62, which may have a range of, for example, from 5 minutes to 30 minutes. The dial 62 is adjusted to ensure that the boiler will not be caused to"cycle"wastefully for too short a time to adequately heat the said primary fluid, but will not run for longer than necessary. All of the abovedescribed adjustable means might alternatively be provided so as to be readily adjusted by the user of the said hot water supply system, but are preferably designed so as to be adjusted only by one skilled in the art, thereby ensuring that the satisfying shower experience 69 is untroubled by technical concerns.

The boiler 51 will typically remain inactive until the electrical thermostat 56 indicates that the temperature of the water in the cylinder 41 has fallen below the desired level, and there may therefore be a delay before the boiler can be actuated by the control means 58, which is connected to the controller 55 so as to leave the electrical thermostat 56 in control of the boiler, for example by being connected in series with the said electrical thermostat 56.

In order to enable the said control means to actuate the boiler as soon as the said boiler timing means is actuated, but to ensure that the maximum water temperature inside the cylinder 41 is still maintained at a safe level for the user, an auxiliary temperature sensing means such as an auxiliary thermostat 65 of known design may also be installed by the said plumber, for example on the outer wall of the cylinder 41 adjacent the said electrical thermostat 56, and connected to the said electrical connection means 60 of the said control means 58 by wiring 66. The said auxiliary thermostat is adjusted by the said plumber to operate at a higher temperature than the electrical thermostat 56, and the said control means is so arranged that the output from the said boiler timing means is dependent on the said auxiliary thermostat so that the boiler 51 is actuated by the said control means only if the temperature of the water in the cylinder 41 is below the temperature to which the auxiliary thermostat

65 has been adjusted. The control means 58 is then connected to the controller 55 so as to bypass the electrical thermostat 56, for example by being connected in parallel with the said electrical thermostat 56.

The boiler 51 may therefore be reliably but safely actuated by the control means 58 even though the water in the cylinder 41 is at the desired temperature, in order that the said inflowing water may be preheated as soon as the said adjustable timing means has timed out, and thereby ensuring that an adequate flow of hot water at the required temperature can be maintained for the duration of the said satisfying shower experience 69.

In the event that a user wishes to enjoy a shower or bath at an unforeseen time when the water in the cylinder 41 is insufficiently hot, it may be inconvenient to operate a manual control which will typically be provided on the controller 55 in order to actuate the boiler 51 to ensure a supply of hot water prior to commencing the shower or running the bath. According to a further aspect of the present invention there is therefore further provided an auxiliary switching means which is operable by the said user, such as a momentary contact electrical switch 67, which may be protected against the ingress of moisture, connected by suitable connection means 70 to the electrical connection means 60 of the control means 58 and located in a position remote from the said water heating apparatus and conveniently adjacent the bath or shower 47. The said control means 58 may be arranged so as to actuate the boiler timing means on actuation of the switch 67 by the user.

In order to facilitate safe installation of the said auxiliary switching means in a location convenient to the user, the control means 58 may further comprise a safety isolated low voltage electrical supply to which the said auxiliary switching means is connected via suitable electrical connection terminals of the electrical connection means 60.

Figure 6 shows a sequence of events exemplifying the operation of the said control means in controlling the boiler 51 or an equivalent heat source in the installation shown in Figure 5.

When a user draws a flow of hot water of sufficient volume from a point of demand, such as the shower 47, the said adjustable timing means is triggered by the flow sensor 18 and the light emitting diode (LED) 63 flashes to indicate that the said adjustable timing means has been actuated.

If the flow is of sufficient duration the said adjustable timing means times out and actuates the said boiler timing means, which is indicated by a steady light from the LED 63.

The said boiler timing means actuates the boiler for a predetermined period of time, dependent on the operation of the auxiliary thermostat 65 if fitted, or otherwise of the electrical thermostat 56.

Alternatively the said boiler timing means may be actuated by a momentary signal from the switch 67.

Referring now to Figure 7, the water heating apparatus shown in Figure 1 is shown installed in the system shown in Figure 4 in an alternative configuration.

The said second fluid carrier is connected to the water supply pipe 44' between the hot water outlet 46 and the shower 47 and other points of demand, the water heating apparatus 1 then raising the temperature of the hot water leaving the cylinder 41 to the desired temperature for use. In this configuration, the said primary fluid carrier is preferably connected to the upper primary fluid carrying pipe 49 in order that the said heat exchange means 2 may raise the temperature of the said hot water flowing therethrough

to the maximum temperature of the said primary fluid, before the said primary fluid is cooled within the heat exchanger 42 by contact with the water within the cylinder 41. The arrangement of the said heat exchange means 2, and especially of the said means facilitating the release of air, may be adapted for installation in this alternative configuration so that the said first and second fluid carriers and the said pipe connectors are placed in their optimal positions for easy connection by the said plumber. In this embodiment the said water heating apparatus may be regarded as effectively converting a storage type hot water supply system into a demand type hot water supply system, whilst advantageously retaining the cylinder 41 together with any additional heat source contained therewithin such as an electric immersion heater.

Temperature regulating means may be further included according to known designs of demand type hot water supply systems. For example, where the temperature of the said primary fluid may reach a scalding level, it may be desirable to include thermostatic regulating means within the outer casing 3 so as to limit the maximum temperature of the hot water flowing to the shower 47 or other points of demand.

In a less preferred alternative configuration the said water heating apparatus may be connected to the said system such that the said pipe connectors 8 and 9 are connected by suitable pipe joint means, such as"tee"connectors, respectively to the upper primary fluid carrying pipe 49 and the lower primary fluid carrying pipe 50, so that the first fluid carrier 6 of the heat exchange means 2 is arranged in parallel rather than in series with the heat exchanger 42.

Referring to Figure 8, there is shown a further alternative embodiment of the present invention wherein a water heating apparatus 90 is constructed as shown in Figures 1,2 and 3, the reference numbers shown corresponding to the same parts as shown in the earlier figures, but is further provided with pump means for inducing a flow through the second fluid carrier 7. The said

pump means comprises an electrically powered pump 80 communicating with the feed pipe 11 and arranged between the pipe connector 12 and the second fluid carrier 7, and provided with a power supply via a cable 81 connected to the control means 58. The pump 80 is automatically controlled, for example by flow sensing and/or pressure sensing means such as the flow sensor 18, and functions as a"shower pump"to increase the flow of hot water from a shower or other point of demand in a hot water supply system to which the water heating apparatus 90 is connected. The running speed of the said pump 80 may be adjustable by the said plumber by means of an additional dial (not shown) located on the control means 58.

An additional pump means may also be provided for inducing a flow of water between two additional pipe connectors (not shown) arranged externally to the outer casing 3. The said additional pipe connectors may then be connected by the said plumber to a cold water supply pipe leading to the cold water taps, shower mixer valves and the like serving those points of demand which are supplied with hot water by the pump 80. The said additional pump means will preferably be driven together by the same electrical motor as the pump 80, the pump 80 then comprising a single electrical motor driving two separate impeller assemblies as is known in the art. This ensures that the pressure of the hot and cold water supplies at each point of demand is approximately equal.

Alternatively or additionally, pump means may be arranged in communication with the first fluid carrier 6 so as to induce a flow of primary fluid when the said primary fluid heating means, such as boiler 51 is actuated. Where the said hot water supply system relies on convective or"gravity"circulation to induce a flow of primary fluid, the said pump means may induce a more vigorous flow and hence convert a"gravity"system into a"pumped"system and thereby increase the rate of heat transfer.

The said pump means may be actuated by a change in temperature, pressure, flow rate or other variables relating to the said water and/or the said primary fluid, by means either of the said sensing means and the control means 58 or of other suitable sensing and control means.

The water heating apparatus 90 shown in Figure 8 further provides expansion means for accommodating changes in the volume of the water within the second fluid carrier 7, comprising a pressurised expansion chamber 82 of known construction, which may comprise a chamber containing a body of pressurised air separated from the said water by an elastic membrane, and which is contained within the outer casing 3 and arranged to communicate with the second fluid carrier 7.

Additional expansion means and/or safety pressure relief means (not shown), such as an additional pressurised expansion chamber and/or a safety valve arranged to open under conditions of excess pressure and/or heat, may also be provided for accommodating the expansion of the said water and/or primary fluid within the said first and/or second fluid carriers. The said expansion and safety pressure relief means facilitate the safe connection of the water heating apparatus 90 to a hot water supply system wherein no expansion pipe or safety vent pipe is provided to accommodate changes in the volume of the said water and/or the said primary fluid, and a wider range of possible configurations is therefore available to the said plumber when installing the said water heating apparatus, for example as described below with reference to Figure 9.

Referring to Figure 10, in a further alternative embodiment the water heating apparatus 91 is constructed as shown in Figure 8 but is additionally equipped with a cold water outlet pipe connector 83 which is arranged externally to the outer casing 3 and communicates with the outlet side of the pump 80 between the pump 80 and the second fluid carrier 7, so that part of the flow of cold water induced by the pump 80 passes directly to the pipe connector 83, and

part passes through the second fluid carrier 7. The water heating apparatus 91 may be installed by the said plumber so as to provide a pressurised supply of cold and of hot water from a single input cold water supply connected to the pipe connector 12. If the pump 80 is designed as a suction pump, the said input cold water supply may be an unpressurised water supply, such as a tank of water connected to the pipe connector 12 by means of a suction pipe. In this embodiment the water heating apparatus 91 may be installed for example in a dwelling lacking a pressurised mains water supply, such as a caravan or the like.

Referring now to Figure 9, according to a further configuration, the water heating apparatus 90 shown in Figure 8, incorporating the said additional expansion means and/or safety pressure relief means (not shown), is shown connected to the hot water supply system as shown in Figure 4, in place of the cylinder 41, which is removed together with the electrical thermostat 56 and wiring 57 by the plumber installing the said water heating apparatus. The reference numbers correspond to the same parts as shown in Figures 1 to 8.

The expansion pipe 48, the safety vent pipe 54, the filler pipe 53 and the header tank 52 shown in Figure 4 have been removed, converting the said system from an"open"system to a"sealed"system. Additional safety measures (not shown) may have been included by the said plumber in order to effect the said conversion, together with means facilitating periodic replenishment of the said primary fluid from a mains pressure water supply.

Alternatively, the supply of cold water via the water supply pipe 44 may be provided directly from a mains pressure water supply instead of from the cold water storage tank 45 as shown. Where the said system includes a said cylinder and a said cold water storage tank, the said plumber may therefore install the said water heating apparatus in order to facilitate the removal, both of the cylinder 41 and of the cold water storage tank 45, converting the said system to use the same boiler 51 but provide the said hot water supply by

means of a connection from the water supply pipe 44 directly to the said mains pressure water supply.

The said water heating apparatus may therefore enable the said plumber to overcome a problem of insufficiency of water pressure resulting from an insufficiently elevated cold water storage tank 45, by replacing the said cylinder, which will typically be incapable of safely resisting the pressure of a mains pressure water supply, with the said water heating apparatus, wherein the said second fluid carrier is preferably arranged so as to withstand the higher pressure thereof.

Alternatively, the water heating apparatus 90 may be connected to a hot water supply system which does not include a vessel for storing and heating water, the system again being arranged for example as shown in Figure 9.

Alternatively the system shown in Figure 9 may for example comprise part of a central heating system, wherein the said primary fluid which is heated by the boiler 51 and circulated to radiators in order to heat a dwelling, is diverted by means of suitable additional pipework,"flowshare"valves or the like, to flow through the first fluid carrier 6 and hence to heat the said hot water supply.

The said water heating apparatus 90 functions in a similar way to the water heating apparatus 1 described above with reference to Figure 7, the said hot water supply system functioning as a demand type hot water supply system.

The pump 80 is controlled by the flow sensor 18 and the control means 58 to induce a flow of hot water as required to the shower 47 or other points of demand and thereby to enhance the satisfying shower experience 69.

Alternatively the pump 80 may be omitted from the said water heating apparatus, or may be disconnected or otherwise disabled, where the said water heating apparatus is intended to be supplied with the said mains pressure water supply directly from a mains pressure water supply pipe or "rising main"supplying the building in which the said hot water supply system is installed.

The control means 58 is connected and functions in a similar way to that described above with reference to Figures 5 and 6. The function of the auxiliary thermostat 65 may be performed by one or more temperature sensors (not shown) arranged so as to sense the temperature of the said water and/or primary fluid, and connected to the control means 58 so as to control the boiler 51 and/or the said pump means. The said temperature sensors may be arranged within the outer casing 3, and/or located remotely from the said water heating apparatus 90 on either or both of the primary fluid carrying pipes 49 and 50 and/or water supply pipes 44'and 44, and connected to the electrical connection means 60.

Referring now to Figure 11, a water heating apparatus 92 is constructed similarly to the water heating apparatus 91 in Figure 10, the pump 80 being equipped with separate first and second impeller assemblies driven by a single electric motor. The first impeller assembly is arranged so as to induce a flow of cold water as described above with reference to Fig. 10, part of the flow of cold water induced by the pump 80 passing directly to the pipe connector 83, and part passing through the second fluid carrier 7. During installation, the said plumber may elect to blank off the pipe connector 83 if a pumped supply of cold water is not required.

The said second impeller assembly is arranged between an additional pipe connector 9'and the first fluid carrier 6, the pipe connector 9 being also connected directly to the said first fluid carrier as shown in previous embodiments. The said plumber may elect to connect the additional pipe connector 9'to a primary fluid carrying pipe of the said system and blank off the pipe connector 9. In this case the said primary fluid will flow through the said second impeller assembly. The pump 80 may be actuated by the control means 58 when the flow sensor 18 senses that hot water is drawn from a point of demand, so as to induce a flow of primary fluid and of water simultaneously. Alternatively or additionally the control means 58 may be

arranged so as to actuate the pump 80 when the said boiler is actuated. Both the said first and second impeller assemblies are arranged so as recirculate the water or primary fluid contained therein without causing damage.

The said plumber may alternatively elect to connect both of the pipe connectors 9 and 9'together, for example by means of a tee joint, to the said primary fluid carrying pipe. In this case the flow of primary fluid will be largely unaffected by the said second impeller assembly.

An additional pressurised expansion chamber 93 of known construction is contained within the outer casing 3 and arranged to communicate with the first fluid carrier 6, accommodating changes in the volume of the said primary fluid.

The said plumber, by means of installing the said water heating apparatus together with such additional safety pressure and temperature relief and gauge means as may be required by the hot water supply system into which the said water heating apparatus is installed, may thus convert the said system from an"open"system to a"closed"system.

The control means 58 of the water heating apparatus 1,90, 91 or 92 may further provide an immersion heater switching means whereby an electric immersion heater contained within the said vessel may be controlled, for example by connecting it to the said electrical connection means 60. The said immersion heater switching means will preferably comprise an electrical relay and may include separate power supply connection means. The said control means may thereby control and coordinate all of the available heat sources according to the said sensing means cooperating therewith. For example, the said flow sensor may include a first stage flow sensing threshold value and a second stage flow sensing threshold value, so as to actuate both the boiler 51 and the said immersion heater during periods of exceptionally heavy demand for hot water, for example in the event that the said plumber is invited to share the said satisfying shower experience 69.

The above embodiments are described for illustrative purposes only, and it is to be understood that the invention is not limited to the embodiments herein described, but may be practised in many other ways without departing from the spirit and scope of the following claims. Many further configurations, advantages and embodiments of the present invention will become evident to one skilled in the art upon perusal of the foregoing description and accompanying drawings.

Claims (39)

1. A hot water supply system comprising a recirculated primary fluid conveying heat from a primary fluid heating means to a vessel for storing and heating water, characterised in that the said primary fluid and the said water flow through a heat exchange means which is substantially contained within casing means, the said casing means being separate from the said vessel and from the said primary fluid heating means, and in that the volume of water and of primary fluid contained within the said heat exchange means is not substantially greater than that required to effect heat transfer.

2. A hot water supply system comprising a recirculated primary fluid conveying heat from a primary fluid heating means to a heat exchange means so as to heat a supply of water flowing through the said heat exchange means, characterised in that the said heat exchange means is substantially contained within casing means, the said casing means being separate from the said primary fluid heating means, and in that the volume of water and of primary fluid contained within the said heat exchange means is not substantially greater than that required to effect heat transfer.

3. A water heating apparatus comprising a heat exchange means according to claims 1 or 2, characterised in that there are further provided connection means external to the said casing means whereby the said water heating apparatus may be connected to the said hot water supply system.

4. A water heating apparatus according to claim 3, characterised in that the said heat exchange means contains substantially equivalent volumes of said water and said primary fluid.

5. A hot water supply system according to claim 1 wherein the said primary fluid flows in series from the said primary fluid heating means to the said heat exchange means, returning from the said heat exchange means through a heat exchanger within the said vessel to the said primary fluid heating means.

6. A hot water supply system according to claim 1 wherein the said primary fluid flows in series from the said primary fluid heating means to a heat exchanger within the said vessel, returning from the said heat exchanger through the said heat exchange means to the said primary fluid heating means.

7. A hot water supply system according to claim 1 wherein cold water flows through the said heat exchange means, into the said vessel.

8. A hot water supply system according to claim 1 wherein water flows from the said vessel, through the said heat exchange means to points of demand such as showers or taps.

9. A water heating apparatus for connection to an existing hot water supply system, the said system including: a vessel for storing and heating water, at least two water supply pipes communicating with the said vessel, at least one heat exchanger contained within the said vessel, at least two primary fluid carrying pipes communicating with the said heat exchanger, and primary fluid heating means; the said heat exchanger containing a primary fluid and transferring heat therefrom to the said water contained within the said vessel ; the said water heating apparatus comprising a heat exchange means having at least a first fluid carrier and a second fluid carrier, and characterised in that the said heat exchange means is substantially contained within casing means so as to form a discrete unit, there being further provided connection means external to the said casing means for connecting the said first fluid carrier to at least one of the two said

primary fluid carrying pipes, and the said second fluid carrier to at least one of the two said water supply pipes, such that the said primary fluid and the said water flow through the said heat exchange means and heat is transferred therebetween.

10. A water heating apparatus for connection to a hot water supply system, the said system including: at least two water supply pipes carrying water, at least two primary fluid carrying pipes carrying a primary fluid, and primary fluid heating means; the said water heating apparatus comprising a heat exchange means having at least a first fluid carrier and a second fluid carrier, and characterised in that the said heat exchange means is substantially contained within casing means so as to form a discrete unit, there being further provided connection means external to the said casing means for connecting the said first fluid carrier to at least one of the said primary fluid carrying pipes, and the said second fluid carrier to at least one of the said water supply pipes, such that the said primary fluid and the said water flow through the said heat exchange means and heat is transferred therebetween.

11. A water heating apparatus according to claim 9 wherein the said connection means comprise connection means for connecting the said first fluid carrier to at least one of the two said primary fluid carrying pipes, and the said second fluid carrier to a water supply pipe carrying inflowing cold water to the said vessel.

12. A water heating apparatus according to claim 9 wherein the said connection means comprise connection means for connecting the said first fluid carrier to at least one of the two said primary fluid carrying pipes, and the said second fluid carrier to a water supply pipe carrying outflowing hot water from the said vessel.

13. A water heating apparatus according to claim 10 wherein the said connection means comprise connection means for connecting the said first fluid carrier to at least one of the two said primary fluid carrying pipes, and the said second fluid carrier to a mains pressure water supply pipe.

14. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided control means together with electrical connection means for connecting to a control system of the said hot water supply system so as to control the said hot water supply system.

15. A water heating apparatus according to claim 14 wherein there is further provided water sensing means cooperating with the said control means.

16. A water heating apparatus according to claim 14 wherein there is further provided primary fluid sensing means cooperating with the said control means.

17. A water heating apparatus according to claim 14 wherein there is further provided flow sensing means cooperating with the said control means.

18. A water heating apparatus according to claim 14 wherein there is further provided temperature sensing means cooperating with the said control means.

19. A water heating apparatus according to claim 14 wherein there is further provided timing means for actuating the said control means, the said timing means being actuated by flow sensing means for sensing a flow of water in the said second fluid carrier.

20. A water heating apparatus according to claim 14 wherein the said timing means is adjustable.

21. A water heating apparatus according to claim 14 wherein there is further provided boiler timing means actuated by the said control means and cooperating with the said electrical connection means to actuate the said primary fluid heating means for a predetermined period of time.

22. A water heating apparatus according to claim 21 wherein the said boiler timing means is adjustable.

23. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided means facilitating the release of air.

24. A water heating apparatus according to claim 23 wherein the said means facilitating the release of air comprise a tube of small diameter which is locally compressed to provide a constriction through which a very small amount of air or water may flow.

25. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided pump means for inducing a flow of said primary fluid.

26. A water heating apparatus according to claims 3, 9 or 10 wherein there is further provided pump means for inducing a flow of said water.

27. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided a pressurised expansion chamber for accommodating changes in the volume of the said primary fluid.

28. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided a pressurised expansion chamber for accommodating changes in the volume of the said water.

29. A water heating apparatus according to claim 14 wherein there is further provided auxiliary switching means located in a position remote from the said water heating apparatus, the said auxiliary switching means being operable by a user of the said hot water supply system and cooperating with the said control means to actuate the said primary fluid heating means.

30. A water heating apparatus according to claim 29 wherein the said control means further comprises a safety isolated low voltage electrical supply to which the said auxiliary switching means is connected.

31. A water heating apparatus according to claims 3 or 9 wherein there is further provided means for the connection of an auxiliary temperature sensing means, the said auxiliary temperature sensing means being located on the said vessel and sensing the temperature of the said water therein, there being further provided a control means together with electrical connection means for connecting to a control system of the said hot water supply system so as to control the said hot water supply system; the said auxiliary temperature sensing means cooperating with the said control means so as to control the operation of the said primary fluid heating means.

32. A water heating apparatus according to claims 3, 9 or 10 wherein the said heat exchange means is thermally insulated.

33. A water heating apparatus according to claim 14 wherein there is further provided immersion heater switching means whereby the said control means may control an electrical immersion heater which is connected to the said electrical connection means.

34. A water heating apparatus according to claims 3,9 or 10 wherein there is further provided pump means comprising at least two cooperating impeller assemblies for inducing simultaneous flows of said primary fluid and of said water.

35. A water heating apparatus according to Claim 26 wherein there is further provided an additional connection means cooperating with the said pump means so as to provide a pressurised supply of cold water.

36. A water heating apparatus according to claims 3,9 or 10 wherein the said casing means is thermally insulated.

37. A water heating apparatus according to claims 1,2, 3,9 or 10 wherein the said vessel is a hot water cylinder.

38. A water heating apparatus according to claims 1,2, 3,9 or 10 wherein the said primary fluid heating means is a boiler.

39. A water heating apparatus according to claims 9 or 10 characterised in that the volume of water and of primary fluid contained within the said heat exchange means is not substantially greater than that required to effect heat transfer.