GB2376517A

GB2376517A - Energy recovery system

Info

Publication number: GB2376517A
Application number: GB0109833A
Authority: GB
Inventors: Lubor Schiller
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-21
Filing date: 2001-04-21
Publication date: 2002-12-18
Anticipated expiration: 2021-04-21
Also published as: GB0109833D0; GB2376517B

Abstract

A shower 18 is provided with heated water with part of its heat derived from waste heat. The waste heat results from the water after it is used in the shower. A heat exchanger is mounted below the shower and cold water is suppled through a pipe 36 to a combined heater and pump unit 14. The hot waste water exits a shower tray 34 at drain 40 and circulates around the cold water pipe to transfer heat to it before it is discharged. The pipe 36 may be coiled, serpentine, or bent to be accommodated within the shower tray. The heat exchanger may alternatively be located below a bath or hand basin or in washing machines, dishwashers, or multi occupation buildings to perform the same waste heat recycling function.

Description

Title: Energy recovery system Field of invention This invention concerns systems for recovering energy particularly heat from waste hot water. The invention is of particular application to domestic installations but is not limited to domestic situations and could be applied equally to commercial and industrial applications and may well be of particular relevance to hospitals, hotels, schools and multioccupation buildings such as apartment blocks.

Background to the invention For many applications such as personal washing, laundry washing and dishwashing, large quantities of water have to be heated in advance and after use are discarded whilst still relatively hot. This is particularly so in the case of showers, where the cascading hot water has little time to cool before it drains to waste from the shower tray.

Various proposals have been put forward to recover waste water for irrigation and prior to any such subsequent use the water has to be cooled. The heat energy is therefore lost and effectively wasted.

The heat in the waste water tends to be so-called low grade heat in that even from a shower situation, the temperature of the water will rarely be much in excess of 45-500C maximum.

The present invention seeks to recover at least some of the heat from the waste water from hot water utilisation processes, particularly washing and the like.

Summary of the invention According to the broadest aspect of the present invention, in a process in which a fluid is heated before being used in a process and thereafter goes co wasce with residual heat still in the fluid, at least some of the residual heat energy is transferred to incoming fluid before the latter is heated for use in the process, or in another process requiring heated fluid.

The invention is of particular application to processes in which heated fluid is not retained in bulk and drawn off as a hot fluid, but in which cool fluid is supplied for use in the process and is heated in transit shortly before being used in the process. Depending on the temperature difference between the cool fluid supplied to the preliminary in-line heater and the temperature of the waste fluid, so there will be a greater or lesser temperature differential between the hot waste fluid and the incoming cool fluid. The greater the temperature difference, the greater will be the transfer of heat from the waste fluid to the incoming fluid for any given transfer time.

One preferred application for the invention is a shower installation having a pump and in-line heater to which cold water is supplied and heated by the in-line heater before being supplied under pressure to the shower nozzle. Such arrangements are popular in domestic situations where the head of water available from the domestic hot water installation is otherwise generally inadequate to produce a good pressure at the shower head. The in-line heater is typically electrically powered and because a temperature rise of the order of 20-300C is typically required between the incoming cold water and the normally desired temperature of the water leaving the shower head, the in-line heater will have to consume large quantities of electricity in order to provide for the desired temperature rise, and typically 8 kilowatt heaters are required.

The main problem with such installations is that flow rate and shower head temperature are inter-related. The faster the flow, the lower the temperature rise in the fixed heat output in-line heater and with 8 kilowatts being typically the maximum load which is sensible to consider in a domestic installation of this nature, the temperature rise particularly in cold weather when the incoming domestic cold water is possibly less than 10 C can result in a very lukewarm shower unless the flow rate is throttled back very considerably.

By retrieving the heat in the waste water from the shower and in accordance with the invention, transferring some of that heat to the incoming cold water feeding the in-line heater, so the temperature of the water supplied to the heater will be raised and the continuous heat output provided by the electrically powered in-line heater will enable the flow rate to be increased whilst maintaining the same shower head temperature or will allow a higher temperature to be achieved at the shower head for a constant flow rate.

In one embodiment of the invention, a heat exchanger is provided having primary and secondary circuits and the waste water from the shower tray passes through the primary circuit before going to waste and the incoming cold water from the domestic cold water supply is forced to pass through the secondary circuit of the heat exchanger before being applied to the in-line heater and pump arrangement associated with the shower.

In one embodiment, the heat exchanger comprises an elongate housing containing a long length of tubing typically coiled so as to accommodate the length within the housing, and the interior of the housing constitutes the primary circuit and the coiled tube constitutes the secondary circuit of the heat exchanger, fluid connections being provided at opposite ends of the housing to provide for the inlet and exit of waste fluid and fluid connections be provided at opposite ends of the

coiled tube to allow cold water to be supplied thereto from a domestic cold water supply and to supply warmed water from the other end to the heater and pump assembly of the shower unit.

According Lo a preferred feature of The invention, the housing may be shaped and dimensioned so as to fit below a shower tray to utilise what is otherwise waste space below a shower tray. Thus whilst typically the heat exchanger housing would be a straight cylindrical unit, the available space below a shower tray may be such that the heat exchanger unit may be made in a number of different sections which can be interconnected to lie below different regions of the shower tray at angles relative one to the other so as to fit into recesses or cavities in the underside of the shower tray.

Alternatively the whole housing may be preformed so as to accommodate a large percentage, if not all, of the available volume below a shower tray, and is dimensioned and constructed accordingly.

Alternatively the heat exchanger unit may be formed from deformable material so that it is supplied in the form of a long length of flexible material which can be bent and twisted so as to fit into available cavities and recesses on the underside of a shower tray.

According to a further preferred feature of the invention, the heat exchanger unit may itself be incorporated into and be an integral part of the shower tray and the housing of the heat exchanger unit may be constructed at least in part from the floor and the wall of the shower tray in conjunction with additional wall sections which combine with the wall and floor of the shower tray to define one or more cavities within the shower tray within which the elongate and possibly coiled secondary circuit of the heat exchanger can be located and suitable connections to allow water to supplied to the coiled tube and drawn therefrom for supply to the heater and pump of

the shower unit are provided, possibly in the side walls of the shower tray if external connections are required or on internally facing cavity walls below the shower tray so that such connections can be hidden from view, and the waste from the drainage outlet of the shower tray is conveyed to one end of the cavity formed within the shower tray and is collected and drained to waste from the other end of the cavity, again with suitable connections being provided to the relevant part of the heat exchanger so formed within the shower tray structure.

A particularly preferred feature of the invention lies in the provision of a generally flat heat exchanger which extends over part or all of the shower tray above the drainage outlet, so that waste water from the shower passes over and around the heat exchanger before draining through the conventional drain out let of the shower tray. Fluid connections for connecting the cold water supply to the secondary circuit of the heat exchanger and for collecting heated cold water from the other end of the secondary circuit of the heat exchanger are provided and the latter serves to supply warmed water to the pump and heater of the shower unit.

A generally flat heat exchanger of this nature preferably includes a tortuous fluid path therethrough between the fluid inlet and fluid outlets so that there is a considerable dwell time for cold water within the generally flat heat exchanger before it is released to the pump and heater of the shower unit. Likewise by providing a relatively high resistance path to the water collected by the tray before it can reach the waste outlet, a significant dwell time can be obtained for warm water to remain in the shower tray in contact with the heat exchanger panel before it drains to waste, so as to optimise the transfer of residual heat from the warm water to the cold incoming water.

For hygiene reasons, it may be necessary for the heat exchanger

panel to be removable to enable the shower tray and the panel to be cleaned. To this end fluid couplings to the panel-like heat exchanger are preferably made in the form of snap connections or so-called quick release connections so that the

need or maL. can ije remove, Cj-eane ann. repj-ace winou Lne need for tools or expertise.

In accordance with a preferred feature of this particular aspect of the invention, the plumbing associated with the incoming cold water is preferably routed via the shower control valve so that when the latter is turned to an off position, the heat exchanger is isolated from the cold water supply so that upon removing the generally flat heat exchanger unit from the shower tray, no flooding will result. Any water in the pipework above the level of the shower tray will of course drain back through the appropriate fluid connector when the heat exchanger panel has been removed, but according to another aspect of the invention, any such back drainage can be accommodated within the shower tray by ensuring that the connection causes any such water to be directed into the shower tray itself so that it will drain in a normal way via the drainage outlet associated with the shower tray.

According to a further aspect of the invention, it is preferred that the cold water feed to the shower is not supplied at the mains pressure nor any direct connection is made to the cold water supply main to the property, but that the cold water feed should be derived from a storage tank at high level in the property in the conventional way. Plumbing the shower in this way has two advantages. In the first place the head of pressure of water supplied to the water inlet to the heat exchanger unit will be at a lesser pressure than that of the domestic supply mains serving the property but will be constant, and the temperature of the water from the storage unit (typically within the roofspace of the property), may itself be at a higher temperature than the cold water feed to the property from the water supply main, by virtue of the fact

that being located within a property such as a domestic residence, heat from the property will have filtered into the roofspace and will have raised the temperature of the cold water in the storage tank in the roofspace by a few degrees relative to the water of the supply main to the house. Again in cold weather, this can all assist in reducing the temperature rise which has to be achieved by the in-line heater in the shower unit and will further assist in improving the temperature of the water at the shower head for any given flow rate or allowing a higher flow rate to be enjoyed for a given temperature at the shower head.

Although the invention has been described in relation to showers in which the water is heated by an in-line heater, the invention is not restricted to that arrangement and using a twin cylinder storage system and two heat exchangers one in each cylinder, the waste water from a shower can be passed into a first cylinder to displace water already standing in the cylinder and a first heat exchanger within the first cylinder in combination with a pumped system transfers heat from the standing water in the first cylinder to a heat exchanger in a secondary cylinder to which cold water is supplied under pressure and which provides water to a shower head via a pump. By supplying an in-line heater and pump of a shower unit from the second cylinder, so the same advantages can be gained as described in relation to the heat exchanger units proposed to be incorporated with the shower tray and since the recovered hot water from the waste can itself stand for a considerable period of time within the first cylinder, a greater quantity of heat can be extracted from that water to be conveyed to the cold water in the other cylinder than might be possible using an in-line heat exchanger approach. Where such an arrangement is envisaged, a pump may be required to extract waste water from the shower tray to allow the waste water to be supplied to the first cylinder which may be located above the level of the shower tray.

One preferred embodiment of low profile generally flat heat exchangers comprises a coiled length of narrow bore tube arranged as a flat spiral which is adapted to be laid on the floor of the shower tray, or incorporated into the floor of the shower tray, and incoming cold wacer is forced co pass chrough the coil before it passes to the heater and pump of the shower unit, and water cascading from the shower head has to traverse a tortuous path around the spiral before it can pass through the drainage outlet of the shower tray.

The tortuous path may be formed by virtue of the coiled tube or by virtue of a spiral path formed as a profile in the surface of the shower tray and which generally conforms to the coiled pipe embedded within the shower tray immediately below the profiled surface.

In a typical arrangement, the surface of a shower tray is profiled to accommodate the cross-section of the coiled tube so that the profiling actually constitutes a ridge of shower tray material defining or containing the spiral passage for the incoming cold water. Thus in a particularly preferred embodiment of this concept, the shower tray is formed with a tortuous fluid passage (between inlet and outlet connections) within the material forming the shower tray, and in particular very close to, if not forming the surface of the tray, so that there is high thermal conductance between the surface of the tray and the interior of the passage so that fluid such as water passing through the passage will be warmed by hot water from the shower head cascading onto the surface of the shower tray and slowly traversing over the surface of the tray to the drainage point.

Arrangements such as envisaged are particularly applicable to shower trays in which the drainage outlet is generally in the centre of the shower tray. Where the drainage outlet is nearer to one side or in one corner, the pattern of the passage or flat spiralled tubing is simply changed accordingly so that the

path through which water arriving on the surface of the tray has to pass to the drainage outlet is appropriate having regard to the position of the outlet relative to the overall surface of the tray.

The invention is not limited to dedicated showers and shower cubicles with shower trays but can also be adapted to be incorporated into a shower unit associated with a bath. Here the waste from the bath is conveyed via a heat exchanger to the domestic waste supply and cold water which is to be supplied to the in-line heater and pump of the shower unit is passed through the secondary circuit of heat exchanger in exactly the same way as previously described and because of its location, the heat exchanger is conveniently located below and/or to the side of the bath, preferably hidden from view behind the conventional panelling applied around a bath.

Where such a heat exchanger is provided, all waste water from the bath whether arising from the shower or when a bath of hot water is emptied, a diverter valve may be provided such that if the shower is not operating, the heated cold water in the heat exchanger is transferred to a storage cylinder for use as warm water for supplying to the heater when the shower is subsequently used.

All references to cylinders herein are intended to mean fully insulated cylinders so that warm water stored therein will only lose heat at a very low rate due to the insulating properties of the material surrounding the cylinder.

The invention is also applicable to hand basins where the hot water supply to the basin is provided through an in-line heater. To this end a heat exchanger as described above is located in association with drainage from the hand basin so that incoming cold water feeding the in-line heater to the hot water outlet associated with the hand basin, has to pass through the heat exchanger and be warmed by exiting hot water

from the wash hand basin, to assist in raising the temperature of the hot water supplied to the basin at any given flow rate or allowing flow rate to be increased for any given temperature.

It will be appreciated that in most applications of the invention, the primary of the heat exchanger will not be in receipt of heated water until for example a shower has been operated for a few seconds, and hot water heated by the in-line heater is cascading onto the shower tray or bath and is draining to waste via a heat exchanger provided by the invention. Only when such waste hot water is flowing through the primary of the heat exchanger will the incoming cold water be warmed and the benefits of the invention be obtained.

To accommodate this, an automatic mixer valve may be provided so that if after the shower unit has been operating for perhaps one minute, and the temperature of the water being supplied to the in-line heater is now perhaps much greater than it needs to be to attain the desired temperature at the shower head for the given flow rate, cold water can be introduced into the stream feeding the shower head so as to maintain the temperature of the exiting water from the shower head at the desired temperature.

Alternatively and more preferably, a control is provided for reducing the electrical heat input in any such application in response to the exit temperature from the heater of the water supplying the shower head exceeding a given threshold.

The simplest form of control is to provide two heating elements, one main heating element and one supplementary element. When both elements are operating, maximum heat input is provided via the in-line heater to the water flowing to the shower head, and the maximum for any given flow rate from the shower head will be obtained. In the event that the temperature of the water flowing to the shower head exceeds a

given threshold, temperature operated switch means may be provided to remove power from the supplementary heater element and thereby reduce the temperature rise effected by the heater on the water flowing therethrough.

By using a temperature operated switch which has a low thermal capacity and therefore a short response time to changes in temperature, the supplementary heater can be switched in and out during the operation of the shower so as to maintain a substantially constant temperature quite automatically and without the user of the shower realising that this is happening.

Alternatively a solid state synchronous switch may be used to chop the alternating current waveform and reduce the mean power supplied to the heater in response to increasing temperature sensed by a thermostat sensitive to the temperature of the water being supplied to the shower head. Such an arrangement enables the electrical power to the heater to be controlled in a linear sense relative to the sensed temperature and a control system may be programmed to adjust the percentage of each waveform which is removed to accurately control the mean power input to the heater so as to increase the energy to the heater if the water temperature drops and reduce the mean power to the heater if the temperature rises above a preset temperature, determined by the user of the shower, or preset.

Applications for the invention are primarily in-line heated showers for use in domestic premises, hotels, swimming pools, schools and hospitals and the like. Other applications are for hand washing facilities in domestic, commercial, hospital and educational establishments or in public places such as airports and the like where hot water is generated by in-line heating.

The invention is also applicable to constant flow washing facilities such as dishwashing and in hospital applications. It is also applicable to washing machines which are supplied with cold water only and have in-line heaters for heating the

water to be used in the washing machine in the hot was processes. Some domestic washing machines are of this type, as are industrial units. In the case of domestic units, water reservoir means may be provided in or associated with the washing machine co store the hoc wale frutt one cycle for heating the cold water feed to the in-line heater during the next cycle requiring hot water within the washing machine. In the case of industrial units or multi-washing machine installations, the machines can be operated in tandem and the heat from the hot water exiting from one machine can be used to warm the incoming water feeding to another machine which at that time is calling for water. Where long gaps can exist between the operation of one machine and another, buffer storage reservoirs may be provided as described in relation to a single domestic washing machine installation.

The invention is also applicable to multi occupation buildings or large scale domestic heat recovery systems in which the waste water from all water utilising facilities within the building is forced to pass through the primary of a heat exchanger, the secondary of which forms part of a closed pump circuit for conveying heat derived from the waste hot water in the primary circuit to another heat exchanger in a water reservoir so that heat can be stored in the reservoir in the form of warm water which is then drawn off as required for supply as cold water feed to in-line heaters associated with water utilising facilities such as wash hand basins, showers etc in the building. Preferably a temperature sensitive control system is provided together with a control to the pump in the closed circuit so that water is only circulated between the secondary of the heat exchanger and the primary heat exchanger in the water reservoir when the temperature of the water in the primary circuit of the heat exchanger exceeds by more than a predetermined threshold, the temperature of the water in the reservoir. This is most simply achieved by providing temperature sensors in both locations and supply as an electrical signal information relating to the temperature

at each of the locations to a programmable control system which compares the electrical signals and generates a control signal to enable the operation of the pump when the temperature differential is greater than a pre-programmed threshold and to inhibit the operation of the pump in the event that the temperature differential is less than the pre-programmed differential.

The invention will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic elevation view of a bath and associated in-line heated shower incorporating a heat exchanger in accordance with the invention; Figures 2 and 3 are elevation and plan views respectively of a shower unit having a shower tray incorporating a heat exchanger in accordance with the invention; and Figures 4 and 5 are side elevation and plan views respectively of another shower unit in which a heat exchanger is mounted below the shower tray in accordance with the invention.

As shown in Figure 1, a bath 10 is located adjacent a wall 12 on which is mounted a pump and in-line water heater of a shower installation which includes a flexible hose 16 feeding a shower head 18 which is normally supported by a head carrier (not shown) attached to the wall.

The composite unit 14 will include controls for determining the flow rate and temperature of the water issuing from the head 18. Electrical power is supplied to the in-line heater and the pump within the unit 14 in manner known per se via a cable 20.

Cold water is supplied from a suitable supplier via a pipe 22 through the secondary circuit of a heat exchanger unit 24 located below or to the side of the bath 10 and the outlet from

the secondary circuit of the heat exchanger is connected to a second pipe 26 which supplies water to the input of the unit 14 for heating and pumping water to the shower head 18.

Water from the shower head cascades into the bath in use and vv il Li t-L Li-L Li J-. ii-L. L. L Uz :) t-- u drains from the bath in the conventional way via the drain outlet generally designated 28. Instead of passing straight to the drainage system, the waste is connected via a pipe 30 to the input of the primary circuit of the heat exchanger 24 and the outlet from the primary circuit is connected to the waste pipe 32 to convey the waste water to the drainage system.

In manner known per se, a trap is preferably provided between the drainage outlet 28 and the heat exchanger 24 although this is not shown in the drawing.

As described herein, hot water exiting from the bath and passing through the primary circuit of the heat exchanger 24 will tend to warm incoming cold water passing through the secondary circuit of the heat exchanger 24 so that the water supplied to the heater and pump in the unit 14 is at a higher temperature than it otherwise would have been. This enables water at a higher temperature to be delivered from the shower head 18 for a given flow rate or for the flow rate to be increased whilst maintaining the same temperature.

Figures 2 and 3 illustrate an application of the invention to a dedicated shower unit such as in a shower cubicle, in which a heat exchanger is incorporated as a flat spiral tube or passage in the shower tray. Similar reference numerals are employed throughout to denote common items, thus the shower head 18 is shown directing water towards the shower tray 34 and the shower head is supplied with heated water from a combined heater and pump unit 14. Cold water is supplied to the unit 14 via pipe 12 which is supplied from the centre of flat spiral passage formed in the tray best seen in the plan view of Figure 3 and denoted by reference numeral 36. The other end

of the spiral passage includes a connection 38 enabling it to be connected to a cold water supply such as a domestic cold water supply pipe.

Hot water cascading from the shower head 18 onto the shower tray 34 eventually finds its way to the drain hole 40 in the centre of the tray from where it exits and goes to waste in the normal way. In doing so the water has to traverse the spiral and the dwell time for the hot water on the surface of the tray is considerable giving opportunity for heat in the water to be transferred to cold water in the passage 36 before it reaches the drain hole 40. In this way the temperature of the incoming water supplied to the unit 14 via pipe 12 is increased and as before, the temperature of the water leaving the shower head 18 can be increased or the flow rate increased for a given temperature.

Figures 4 and 5 illustrate a similar arrangement to that shown in Figures 2 and 3 but in this case the heat exchanger is made of a number of individual sections joined in series and located below the shower tray. Each section comprises a cylindrical housing having an input and an output and a secondary circuit formed by a coiled tube and the input of the first of the secondary coiled tubes is supplied with cold water via pipe 42 and each secondary output is connected to the secondary input of the next heat exchanger in the series as by connecting pipes 44,46, 48 and 50 and the final secondary output is connected to the pipe 12 feeding the unit 14 comprising the pump and heater for supplying hot water to the shower head 18. In Figures 4 and 5 the shower tray is denoted by reference numeral 52 and as before includes a central drain outlet 40.

The heat exchange sections are denoted by reference numerals 54,56, 58,60 and 62 and the drain from the shower tray is connected to the input of the primary to the heat exchanger 62 and the output of each of the heat exchange sections is connected to the input of the next in the series as by pipes

64,66, 68 and 70. The final secondary output is connected to the domestic waste supply via pipe 72.

Although not shown, a trap such as a U-bend is provided between the drainage outlet 40 and the inlet to the exchange unit 62.

The shower tray is normally mounted with sufficient space therebelow to accommodate a U-bend and therefore it would not normally be necessary to raise the shower tray relative to a floor or sub-floor more than the installation requires to accommodate the heat exchange units. However if this is necessary, the shower tray may be raised on a plinth or platform so as to increase the space below the tray to accommodate the thickness of the heat exchange units.

Figure 6 shows a heat exchange unit such as may be incorporated in the drain outlet from a wash hand basin. The latter is denoted by reference numeral 74 and the normal drain outlet for the basin is denoted by reference numeral 76. A cylindrical canister 78 is secured to the drain outlet in a conventional way by means of the nut 80 and the interior of the canister 78 constitutes the primary of the heat exchange unit. The lower end of the cylindrical container 78 is blocked by an end wall 82 which is apertured centrally to accommodate an outlet pipe 84 which curves around at 86 to form a U-bend trap before proceeding vertically and horizontally to the normal drainage system.

The secondary circuit comprises a coiled tube typically or copper or other good thermal conductive material generally designated 88 which extends through the plate 82 and at its other end passes through an opening in the wall of the canister 78 to provide an outlet connection 90. Cold water is supplied to the inlet connection 92 at the lower end of the heat exchange tube 88 typically from the domestic cold water supply in the house or other building in which the washing hand basin is located, and water which is to be supplied to an in-line

water heater for supplying the wash hand basin is available from the upper end of the heat exchange tube via the connection 90 which is conveniently joined to a pipe feeding the in-line heater (not shown).

The invention will be of particular value in situations where such basins are in regular use such as in public places and in multi-occupancy buildings where one person after another uses the wash hand basin. It will be seen that by extending the pipe 84 to the same level as the top of the canister 78 before bending the pipe at 94, an extended U-tube assembly is formed and the canister 78 will remain substantially full of warm water from the bowl after the latter has been used. It will only be displaced by further warm used water when the bowl is next used. In this way the water in the pipe 88 will be warmed by heat transfer from the static waste water located in the canister and will be available for warming the cold water static in the coiled pipe 88 in the heat exchanger before the latter is displaced into the in-line heater and will also be available to heat any water flowing through the coiled pipe when the in-line heater calls for more water. It will thus be seen that if the basin is used frequently, and in succession, the water available for the in-line heater will always be considerably warmer than it would be if supplied directly from the cold water supply main and as with the examples given in relation to the shower facilities, the hot water available from the heater will be greater than would otherwise be the case for a given input of electrical energy or a higher flow rate for a given temperature can be attained.

Claims

C612/L

CLAIMS - "'''''''''''. I.. l. 1o... J 1. A system in which an incoming fluid is heated before being used in a process and thereafter goes to waste with residual heat still in the fluid, wherein at least some of the residual heat energy is transferred to incoming fluid before the latter is heated for use in the process, or in another process requiring heated fluid.
2. A system as claimed in claim 1 comprising a shower installation having an in-line heater to which cold water is supplied and heated by the in-line heater before being supplied under pressure to the shower nozzle, wherein heat is retrieved from the waste water from the shower and employed to heat the cold water supplied to the in-line heater, so the temperature of the water supplied to the heater will be raised.
3. A system as claimed in claim 2 wherein the heat supplied to the electrically powered in-line heater enables the flow rate to be increased whilst maintaining the same shower head temperature.
4. A system as claimed in claim 2 wherein a higher temperature is achieved at the shower head for a constant flow rate.
5. A system as claimed in any of claims 2 to 4 wherein a heat exchanger is provided having primary and secondary circuits and waste water from the shower tray passes through

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the primary circuit before going to waste and the incoming cold water from the domestic cold water supply is forced to pass through the secondary circuit of the heat exchanger before being applied to the in-line heater associated with the shower.
6. A system as claimed in claim 5 wherein the heat exchanger comprises an elongate housing containing a long length of tubing coiled or otherwise folded so as to accommodate its length within the housing, and the interior of the housing constitutes the primary circuit and the coiled tube constitutes the secondary circuit of the heat exchanger, fluid connections being provided at opposite ends of the housing to provide for the inlet and exit of waste fluid and fluid connections being provided at opposite ends of the coiled tube to allow cold water to be supplied thereto from a domestic cold water supply and to supply warmed water from the other end to the in line heater of the shower.
7. A system as claimed in claim 5 wherein the housing is shaped and dimensioned so as to fit below a shower tray.
8. A system as claimed in claim 7 wherein the heat exchanger housing is a straight cylindrical unit.
9. A system as claimed in claim 7 wherein the heat exchanger is constructed from two or more different sections which are interconnected to allow them to lie below different regions of the shower tray.
10. A system as claimed in claim 9 wherein the different sections are flexibly connected one to the other so as to fit into recesses or cavities in the underside of the shower tray.

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11. A system as claimed in any of claims 2 to 5 wherein the heat exchanger housing is preformed so as to accommodate a

large percentage, if not all, of the available volume below a z t" ll-L ii. L-L li-L shower tray, and is dimensioned and constructed accordingly.
12. A system as claimed in any of claims 2 to 5 wherein the heat exchanger unit is formed from deformable material, and is in the form of a long length of flexible material which can be bent and twisted so as to fit into available cavities and recesses on the underside of a shower tray.
13. A system as claimed in any of claims 2 to 5 wherein the heat exchanger is incorporated into and forms an integral part of the shower tray.
14. A system as claimed in claim 13 wherein the heat exchanger unit is constructed at least in part from the floor and the wall of the shower tray in conjunction with additional wall sections which combine with the wall and floor of the shower tray to define at least one cavity within the shower tray which constitutes a primary circuit of a heat exchanger and a tube which comprises the secondary circuit of the heat exchanger is located within the cavity.
15. A system as claimed in claim 14 wherein connections to the secondary circuit, to allow water to be supplied to the tube and drawn therefrom for supply to the heater are provided on the side walls of the shower tray.
16. A system as claimed in claim 14 wherein connections to the secondary circuit wholly within the shower tray so that the connections and pipework thereto can be hidden.

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17. A system as claimed in any of claims 14 to 16 wherein the waste from the drainage outlet of the shower tray is conveyed to one end of the cavity or series of cavities formed within the shower tray and is collected and drained to waste from the other end of the cavity or series of cavities.
18. A system as claimed in claim 17 wherein connections to the cavity or cavities and the shower drainage outlet and the waste are wholly contained within and below the shower tray so that the connections and pipework thereto can be hidden.
19. A system as claimed in any of claims 2 to 5 wherein a generally flat panel-like heat exchanger extends over part or all of the shower tray above the conventional drainage outlet therein, so that waste water from the shower passes over and around the heat exchanger before draining through the conventional drain outlet of the shower tray, fluid connections for connecting the cold water supply to and for collecting warmed water from the flat heat exchanger being provided, the latter serving to supply warmed water to the in line-heater of the shower unit.
20. A system as claimed in claim 19 wherein the generally flat heat exchanger includes a tortuous fluid path therethrough between the fluid inlet and outlet so that there is a considerable dwell time for cold water within the exchanger before it is released to the in-line heater.
21. A system as claimed in claim 19 or 20 wherein there is a tortuous path by which warm water collected by the tray from the shower head can pass to the shower tray waste outlet, so that a significant dwell time is obtained for warm water to

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remain in the shower tray in contact with the heat exchanger before it drains to waste, so as to optimise the transfer of residual heat from the waste warm water to the incoming cold water-
22. A system as claimed in any of claims 19 to 21 wherein the heat exchanger panel is removable to enable the shower tray and the panel to be cleaned.
23. A system as claimed in claim 22 wherein fluid couplings to the panel-like heat exchanger are in the form of snap or quick release connections so that the panel can be removed, cleaned and replaced without the need for tools or expertise.
24. A system as claimed in claim 23 wherein the panel is flexible and in the form of a mat around or through which the water can drain.
25. A system as claimed in any of claims 19 to 24 wherein incoming cold water is routed via the shower control valve so that when the latter is turned to an off position, the heat exchanger is isolated from the cold water supply to enable the heat exchanger unit to be removed from the shower tray without flooding occurring.
26. A system as claimed in claim 25 wherein water in the pipework above the level of the shower tray drains back into the shower tray when the heat exchanger is removed.
27. A system as claimed in any of claims 2 to 26 wherein the cold water feed to the shower is derived from a cold water storage tank some height above the shower head.

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28. A system as claimed in claim 1 comprising a shower installation which includes a twin cylinder storage system and two heat exchangers one in each cylinder, and wherein the waste water from a shower is passed into a first cylinder to displace water already standing in the cylinder and a first heat exchanger within the first cylinder in combination with a pumped system transfers heat from the standing water in the first cylinder to a heat exchanger in a secondary cylinder to which cold water is supplied under pressure and which provides water to a shower head via a pump.
29. A system as claimed in claim 28 further comprising a pump to extract waste water from the shower tray to transfer the waste water to the first cylinder.
30. A low profile generally flat heat exchanger for use in a system as claimed in any of claims 19 to 27 comprising a coiled length of narrow bore tube arranged as a flat spiral, adapted to be laid or incorporated into the floor of a shower tray, so that water cascading from the shower head has to traverse a tortuous path around the spiral before it can pass to and out of the drainage outlet of the shower tray.
31. A heat exchanger as claimed in claim 30 wherein the tortuous path is formed by virtue of the coiled tube.
32. A shower tray for use in a system as claimed in any of claims 2 to 27 herein a spiral path is formed as a profile in the surface of the tray which generally conforms to a coiled pipe embedded within the shower tray immediately below the profiled surface.

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33. A shower tray for use in a system as claimed in any of claims 2 to 27 wherein the upper surface of the tray is profiled to create a hollow water path within a ridge of shower tray material through which incoming cold water is caused to pass before proceeding to the in-line heater.
34. A shower tray as claimed in claim 33 in which the profile describes a tortuous fluid passage between inlet and outlet connections in the material forming the tray or in the surface of the tray, and the thickness of the tray material forming the ridge is selected so that there is high thermal conductance between the surface of the tray and the fluid passage so that water passing through the passage will be warmed by hot water from the shower head cascading onto the shower tray and slowly traversing over the surface of the tray before draining away.
35. A system as claimed in claim 1 comprising a shower unit having an in-line heater for warming cold water before it reaches the shower head, which shower is located over a bath, and wherein warm waste water from the bath is conveyed to waste via a heat exchanger and cold water which is to be supplied to the in-line heater of the shower unit is caused to pass through a secondary circuit of the heat exchanger.
36. A system as claimed in claim 35 wherein the heat exchanger is located below and/or to the side of the bath, so as to be hidden from view.
37. A system as claimed in claim 35 or 36 wherein heat from waste water from the bath whether arising from using the shower or when a bath of hot water is emptied, is employed to warm incoming cold water to the in-line heater of the shower,

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and a diverter valve is provided such that if the shower is not being used, the warmed water from the heat exchanger is transferred to an insulated storage cylinder for use as warm water for supplying to the in-line shower heater when the shower is subsequently used.
38. A system as claimed in claim 1 comprising a hand basin to which hot water is provided through an in-line heater, and a heat exchanger is located in association with the drain from the hand basin so that incoming cold water feeding the in-line heater to the hot water outlet associated with the hand basin, has to pass through the heat exchanger and is warmed by exiting hot water from the wash hand basin, to assist in raising the temperature of the hot water supplied to the basin at any given flow rate or allowing flow rate to be increased for any given temperature.
39. A system as claimed in any of claims 2 to 37 in which an automatic mixer valve is provided so that if after the shower unit has been operating for a selected period of time, and the temperature of the water being supplied to the in-line heater is greater than it needs to be to attain the desired temperature at the shower head for the given flow rate, cold water is introduced into the stream feeding the shower head so as to maintain the temperature of the exiting water from the shower head at the desired temperature.
40. A system as claimed in any of claims 2 to 37 in which a control is provided for reducing the energy input to the inline heater if the exit temperature from the heater of the water supplying the shower head exceeds a given temperature threshold.

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41. A system as claimed in claim 40 wherein the in-line heater includes two heating elements, one main heating element and one supplementary element and switching means for

switching off the supplementary heating element, such Lhat 44 L. L-L-L when both elements are operating, maximum heat is provided to the water flowing to the shower head, and temperature sensing means is provided which senses the temperature of the water flowing to the shower head, switch means responsive to the sensed temperature being adapted to switch off the supplementary element if the temperature exceeds a given temperature threshold.
42. A system as claimed in claim 41 wherein the switch means comprises temperature operated switch means and has a low thermal capacity and therefore a short response time to changes in temperature, so that the supplementary heater is switched in and out during the operation of the shower so as to maintain a substantially constant temperature automatically.
43. A system as claimed in claim 40 wherein the in-line heater element is supplied with electric current via a solid state synchronous switch which chops more or less of each alternating current waveform so as to reduce or increase the mean power supplied to the heater in response to increasing temperature sensed by a temperature sensor sensitive to the temperature of the water being supplied to the shower head, whereby the electrical power to the heater is controlled in a linear sense relative to the sensed temperature and a control system may be programmed to adjust the percentage of each waveform which is removed to accurately control the mean power input to the heater so as to increase the energy to the heater if the water temperature drops, and reduce the energy to the

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heater if the temperature rises above a preset temperature threshold.
44. A system as claimed in claim 41,42 or 43 wherein the temperature threshold is adjustable, is determined by the user of the shower, or is preset.
45. A system as claimed in claim 1 comprising a constant flow dish-washing facility.
46. A system as claimed in claim 1 comprising a washing machine which is supplied with cold water only and has an inline heater for heating the water to be used in the washing machine in a hot wash cycle, in combination with thermally insulated water reservoir means in or associated with the washing machine to store the hot water from a hot wash cycle for heating the cold water feed to the in-line heater during the next cycle which requires hot water.
47. A system as claimed in claim 1 comprising a plurality of washing machines each having an in-line heater for heating incoming cold water for a hot wash cycle, wherein the heat from the hot water exiting from one machine is used or stored in an insulated reservoir, subsequently to warm the cold water which is fed to the next machine which calls for water.
48. A system as claimed in claim 1 for a multi occupation building or large scale domestic heat recovery system in which hot waste water from all water utilising facilities within the building (or system) is forced to pass through the primary of a heat exchanger, the secondary of which forms part of a closed pumped circuit for conveying heat derived from the waste hot water in the primary circuit to another heat

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exchanger in a water reservoir, so that heat can be stored in the reservoir in the form of warm water which is then drawn off as required for supply as cold water feed to one or more in-line heaters associated with water utilising facilities in the building or system, which require hot water, such as wash hand basins, showers, washing machines and dishwashers.
49. A system as claimed in claim 48 which further comprises a temperature sensitive control system together with a control to the pump in the closed circuit so that water is only circulated between the secondary of the heat exchanger and the primary heat exchanger in the water reservoir when the temperature of the water in the primary circuit of the heat exchanger exceeds by more than a predetermined amount, the temperature of the water in the reservoir.
50. A system for recovering heat from waste water constructed arranged and adapted to operate substantially as herein described and with reference to the accompanying drawings.
51. A shower or wash basin facility with provision for recovering heat from waste water therefrom substantially as herein described and with reference to the accompanying drawings.