GB2413842A

GB2413842A - A heat exchange unit utilising waste water to heat cold mains water

Info

Publication number: GB2413842A
Application number: GB0503271A
Authority: GB
Inventors: Matthew Rutherford
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-05-07
Filing date: 2004-05-07
Publication date: 2005-11-09
Anticipated expiration: 2024-05-07
Also published as: GB0503271D0; GB2413841B; GB0410170D0; GB2413841A; GB2413842B

Abstract

A heat exchange unit for installing above a shower tray 'ST' comprising a housing having an upper surface 21 upon which a person stands, a conduit divided into two or more parallel conduits 13a - 13e communicating mains water connected between a mains water supply and the water inlet of a shower unit and the conduits 13a - 13e being located in at least one channel 4a - 4e communicating waste water. The housing of the unit has a bottom surface positioned on one or more load bearing supports 129, which may be installed using a levelling tray (120, fig 21) to produce strips or pockets of cement bedding compound, putty or catalysed resin that space the unit from the shower tray to permit the wastewater to flow to a drain. Once the load bearing supports have set hard the levelling tray (120) may be removed. Alternatively the unit may be installed without the aid of a levelling tray (figs 24 and 25). The upper surface 21 may be supported on vertical ribs 9 which may be integral with the housing. Adjustable spacer bars (50, fig 10 and 124, fig 21) may be located around the edge of the housing and levelling tray (120). The housing may be supported on height adjustable legs. A cleaning device (80, figs 16 - 18) for the conduits 13a - 13e may be provided.

Description

1 24 13842

TITLE

Heat-exchange units

DESCRIPTION

Technical Field

The invention relates to heat-exchange units, and in particular to heatexchange units that use wastewater to heat cold water from the mains supply.

Background Art

It is known to use heat-exchangers to reclaim heat from domestic wastewater. Heat cxchangers are particularly suitable for use with conventional types of shower where the wastewater can be used to heat cold water from the mains water supply thereby saving power or increasing flow. Although the pre-heated cold water can be used for any purpose, it is usually supplied directly to the water-heater unit of an electric shower or to the cold water inlet of the mixer valve of a mixer shower. The term "mains water supply" is used throughout this patent specification and is intended to include water supplied via a cistern or from any other appropriate source and not just water supplied directly to domestic, commercial and industrial establishments from the water mains.

One of the main reasons why such heat-exchangers are not more widespread is the problem of installation. There is normally sufficient space underneath a conventional bath to fit a heat-exchanger but it can be expensive to install separately and there are problems gaining access for maintenance and repair. An example of a heat-exchanger of this type is shown in United Kingdom Patent Application 2385785. Wastewater from the bath 3 flows down a drain conduit 2 and through the heat-exchanger l. At the same time, cold water from the mains water supply 4 flows along a supply conduit through the heat-exchanger l to the water-heater unit 6 of an electric shower. By pre-heating the cold water in the heat-exchanger l before it reaches the water-heater unit 6, less energy is needed to heat it tr, the desired temperature. - 2

Additional problems are encountered if the heat-exchanger is to be installed in a fitted shower cubicle because of the limited amount of space available underneath the shower tray. It is therefore usually more convenient to make the heat-exchanger an integral part of the shower tray itself or locate it downstream in the drain. The heat exchanger shown in United Kingdom Patent Application 2295666 is located underneath a shower tray and has a spiral heat-exchange conduit 2. Wastewater flows down the drain 5 in the centre of the shower tray and through the heat-exchange conduit 2. At the same time, cold water is supplied from the mains water supply to the water-heater unit of an overhead shower through a supply conduit 1. Part of the supply conduit l is disposed inside the heatexchange conduit 2 so that heat can be exchanged between the wastewater and the cold water. IJnited States Patent 4821793 discloses a heatexchanger that can be retrofit on top of an existing bath or shower tray. A cover 12 provides a surface on which a person can stand when taking a shower andis mounted on a number of supports 13, 14, 15,23and24. Aswastewater flows along the bath or shower tray towards a drain 34 it is made to follow an extended and tortuous path created by the supports. Heat from the wastewater is therefore transferred to cold water from the mains water supply flowing through a serpentine heat-exchange conduit 16. The heat-exchanger of United States Patent 4821793 may suffer from problems because of the need to maintain a seal between the cover 12 and the surface of the bath or shower tray.

In view of the problems of installation mentioned above, there is a particular need for a heat-exchange unit that is self-contained, cheap and which can be easily and conveniently installed to existing shower trays. However, there is also a general requirement for a heat-exchange unit that is more efficient, reliable and easier to maintain than existing heat-exchangers.

Summary of the Invention

A comparison heat-exchange unit that does not form part of the claimed invention comprises a heat-exchange conduit that is connectable between a mains water supply and a water inlet of a domestic or commercial appliance, and two or more parallel channels for receiving wastewater, wherein the heat-exchange conduit is divided into - 3 two or more parallel conduits with each of the parallel channels receiving at least one parallel conduit such that heat may be exchanged between the wastewater and mains water flowing through the heat-exchange conduit.

The term "domestic or commercial appliance" is intended to include infer alla shower units such as the water-heater unit of an electric shower and the mixer valve of a mixer shower, combination boilers, central heating appliances, washing machines and dishwashers.

The heat-exchange unit can be installed underneath a bath or an existing shower tray such that wastewater from the drain flows into the channels. The heat-exchange unit can be integrally formed as part of a shower tray such that the channels are formed in an upper surface of the shower tray and then covered by a lid on which a person can stand when taking a shower. Or it can be formed as a self-contained heat-exchange unit where the heat-exchange conduit is located in channels formed in a housing having an upper surface on which a person can stand when taking a shower. The lid or upper surface of the housing can be provided with a non-slip pattern of ridges and/or projections and preferably includes a drainage hole for allowing the wastewater to flow into the channels. The lid or upper surface of the housing is preferably removable to allow access to the heat-exchange conduit. The heat exchange conduit can also be removably located in the channels so that it can be taken out for maintenance and repair. The housing is preferably formed from a plastics material and is sufficiently strong and rigid to take the weight of an adult person.

It will also be readily appreciated that the heat-exchange unit can be used to reclaim some of the heat from the wastewater produced by washing machines, dishwashers, and other domestic and commercial appliances.

The wastewater available for use in shower tray applications typically has a maximum head ot a few centimetres and this places fixed limits on the length of the flow path of the wastewater. Normally, this would limit the length of the heat-exchange conduit, and this will tend to limit the surface area of the conduit and hence the rate at which - 4 heat-exchange takes place. This problem might be overcome by arranging for the heatexchange conduit to have greater length by meandering its path within the wastewater channel. However, a meandering heat-exchange conduit tends to be more difficult to clean than one of straighter path, is likely to be more expensive to manufacture due to the greater number of bends, and also tends to require a wider wastewater channel in which to be located. Particularly because of the low head driving the wastewater flow, a wide channel will tend to cause problems with the distribution across the free section the channel of the wastewater flow (alluded to in more detail later). Another way of achieving greater heat-exchange area without increasing the length of the heat-exchange conduit is to arrange that the cross-section of the heat-exchange conduit has a greater perimetral length. On a heat-exchange conduit of circular cross-section this must be achieved by increasing the diameter of the heat-exchange conduit. However, a larger diameter heat-exchange conduit is more difficult to bend, and must be thicker-walled (hence more expensive) to withstand the applied internal pressure. Similarly, a heat-exchange conduit of non circular cross-section is less efficient than one of circular cross-section at resisting internal pressure and more difficult to bend. Also, the largerperimeter heat-exchange conduit is likely to take up more space, and hence lead to a less compact overall installation.

The comparison heat-exchange conduit preferably overcomes these problems by dividing the wastewater flow into a number of separate parallel channels. The effective flow path length is therefore equal to the length of each of the channels. The separate channels are preferably supplied with wastewater from a common plenum channel. The channels may also discharge into a common drainage channel.

The heat-exchange conduit is also divided into two or more parallel conduits so that each conduit is preferably located in a separate channel. However, it will be readily appreciated that each of the channels can accommodate two or more parallel conduits.

The effective flow path length is therefore substantially equal to the length of each of the individual parallel conduits. This can be useful if the heat-exchange unit is used - 5 in areas where the available pressure drop of the mains water supply across the heat exchange conduit is considerably less than normal.

For good heat transfer el'ficiency, it is generally preferred that the heat exchange area is as large as possible. In conventional heatexchangers this is normally achieved by making the heat-exchange conduit as long as possible. It will be readily appreciated that dividing the heat-exchange conduit into two or more parallel conduits does not affect the total heat exchange area and the heat transfer efficiency of the comparison heat-exchange unit is maintained. It is also generally preferred that the flow velocity of the wastewater is as high as possible. The flow velocity is determined by the ratio of the volumetric flow rate to the cross-sectional area for flow. 1\ small cross sectional area provides the required high flow velocity for a fixed volumetric flow rate and also reduces the likelihood of "dead regions" of low flow velocity developing in the channels that would lower the efficiency of the heatexchange unit. However, the head of wastewater required to drive the flow through the channels increases rapidly with the flow velocity of the wastewater. Therefore, if the cross-sectional area is too small then the wastewater will not flow through the channels until an unacceptably high head of wastewater has been established. This might cause the wastewater to "back up" upstream of the heat-exchange unit or flood over the walls of the channels.

If all the parallel conduits are located in a single channel then there is a risk that the absolute flow variation of the wastewater would vary significantly across the section of the charmer because of its relatively large width. This might lead to "dead regions" and reduce the efficiency of the heat-exchange unit. The comparison heat-exchange unit preferably overcomes this problem by locating each of the parallel conduits in a separate channel, preferably supplied with wastewater from a common plenum channel and discharging to a common discharge channel. This tends to ensure that the flow of wastewater through each of the channels is a controlled (preferably equal) fraction of the total flow. Moreover, the width of each individual channel only needs to be sufficient to receive a single parallel conduit and this means that the absolute flow variation of the wastewater can be controlled and minimised. - 6

Another way of providing a large heat exchange area is to increase the diameter of the parallel conduits beyond the minimum required for mains water pressure drop considerations. However, it will be readily appreciated that increasing the cross sectional area of the heat-exchange conduit will reduce the flow velocity of the mains water for a fixed volumetric flow rate. It is important that the flow velocity of the mains water is as high as possible, commensurate with an acceptable pressuredrop, so that good heat transfer efficiency is obtained. The flow velocity is therefore preferably maintained by locating a flow insert in the heat-exchange conduit (i.e. in each of the parallel conduits) to reduce the cross-sectional area for flow. Direct contact between the outer surface of the flow insert and the inner surface of the parallel conduit is preferably kept to an absolute minimum to maximise the wetted area.

The Row insert can be hollow with a sealed end or barriers to prevent the mains water from passing along the flow insert. Pressure equalising holes or apertures can be provided in the flow insert to maintain a pressure balance between the inside of the flow insert and the space between the flow insert and the parallel conduit so that it is subject to minimal pressure-induced mechanical stress or loading.

The inserts also promote heat transfer efficiency by controlling the flow of mains water through the heat-exchange conduit so that each parallel conduit receives a controlled (preferably equal) fraction of the total flow.

To obtain maximum heat transfer efficiency, it is normally preferred that the wastewater and the mains water flow in opposite directions (i.e. the heat-exchange unit uses counter-flow techniques).

The parallel conduits can be fluidly joined together at an upstream region by an inlet manifold connectable to the mains water supply and at a downstream region by an outlet manifold connectable to the water inlet of a domestic or commercial appliance.

However, it will be readily appreciated that the parallel conduits can also be fluidly - 7 joined together by any other suitable means. One possible alternative includes providing two or more pipe loops having an aperture at each end and which are fluidly joined together by a connector joint that is brazed into position. A conventional T joint can be used to fluidly connect an upstream region of one of the pipe loops to the mains water supply and a downstream region of one of the pipe loops to the water inlet of a domestic or commercial appliance.

The heat-exchange conduit and the separate channels for the wastewater preferably follow a substantially serpentine path. The number of parallel conduits that can be accommodated in a given area depends on how many times the heat-exchange conduit sweeps back and forth. For example, a three-sweep configuration has an N-shaped path and a four-sweep configuration has an M-shaped path. The three-sweep configuration allows for more parallel conduits than the four-sweep configuration and is therefore more suitable for situations where the wastewater is flowing through the channels at higher volumetric flow rate.

lSach of the parallel conduits can be formed from a single length of pipe that is bent the required number of times. It is also possible for each of the parallel conduits to be formed from single lengths of straight pipe that are joined together by individual U shaped connector pieces or by straight connector manifolds so the mains water follows a substantially serpentine path. This avoids the expense of having to bend a single length of pipe and in the case of the straight connector manifolds eliminates wasted space caused by the minimum bend radius. However, this means that the separate channels for the wastewater must also be straight and this can create turbulence as the wastewater impacts into the end of each channel and reduces the flow velocity. A high flow velocity is best maintained by turning the wastewater Irom one direction to another along a bend radius.

The heat-exchange unit can incorporate a cleaning device to remove soft scale, scum and other debris from the outside surface of the heatexchange conduit. If the heat exchange unit has a removable lid or upper surface then cleaning can be carried out manually using a cloth or sponge but this is generally unpleasant and it is difficult to - 8 clean all the way around the heat-exchange conduit unless the heat-exchange conduit can be lilted out of the at least one channel. The cleaning device allows the hcat exchange conduit to be cleaned in location so that no lifting or manipulation of the heat-exchange conduit is necessary. 'I'he cleaning device is therefore easy and convenient to use. A single cleaning device can be provided for all of the parallel conduits but it is generally preferred that each parallel conduit has its own individual cleaning device.

The cleaning device can be operated to slide along the outer surface of the parallel conduit or parallel conduits to remove the soft scale, scum and other debris. The cleaning device preferably includes an aperture sized and shaped to receive one of the parallel conduits and the part of the aperture that contacts the outer surface of the parallel conduit can be formed as a scraper or brush element. The cleaning device preferably includes a carriage that the user can grip to slide the cleaning member along the parallel conduit. The cleaning device can also be mechanically operated so that direct access to the cleaning device and the heatexchange conduit is not required.

It will be appreciated that a single aperture may have a tendency to jam on the parallel conduit when the cleaning device is operated. The cleaning device therefore preferably includes a pair of axially aligned apertures sized and shaped to receive one of the parallel conduits.

To prevent the cleaning device from restricting the flow of wastewater through its associated channel, the heat-exchange unit preferably provides a space upstream or downstream of the channels proper where the or each cleaning device can be located when not in use. The cleaning device can also be constructed in such a way that it can be clipped or positioned around the parallel conduit or parallel conduits prior to use and then removed.

The scraped debris can be washed out of the channels using a water nozzle. The water nozzle can also be used to wash the outer surface of the parallel conduits as they are cleaned. The water nozzle can be connected to the mains water supply and controlled by a shut-off valve. If the heatexchange unit has a removable lid or upper surl;ace and each parallel conduit has its own cleaning device then the water nozzle can be manually operated and inserted into an aperture in the top of the carriage where it is then used as a handle to slide the cleaning device along the parallel conduit. It will be readily appreciated that this also means that water is continually delivered to the precise place where the cleaning is taking place.

Alternatively, the water nozzle and the cleaning device may be provided together as an integral unit. The cleaning device would be clipped or positioned around the heat exchange conduit prior to use and then removed. This would have the advantage that the user would not have to maintain engagement of the water nozzle with the cleaning device.

The present invention provides a self-contained heat-exchange unit for installation above a shower tray having a drain, the heat-exchange unit comprising a box-like housing and a heat-exchange conduit that is connectable between a mains water supply and a water inlet of a shower unit and is located in at least one channel formed in the housing for receiving wastewater such that heat may be exchanged between the wastewater and mains water flowing through the heat-exchange conduit, wherein the housing has an upper surface on which a person can stand when taking a shower and a bottom surface that in use is positioned on one or more load-bearing surfaces and is spaced apart from the shower tray such that the wastewater can flow from the housing to the drain.

Although the comparison heat-exchange unit described above does not form part of the claimed invention, certain technical features (in particular those relating to the wastewater channels and the heat-exchange conduit) are also applicable to the claimed invention.

All the structural and functional parts of the heat-exchange unit are contained within the box-like housing to form a self-contained and fully integrated unit that can be easily retrofitted above an existing shower tray and connected to the mains water - lo - supply. Moreover, the heat-exchange unit is reliable and cheap to manufacture.

Installing a self-contained heat-exchange unit above an existing shower tray has the advantage that if for any reason the wastewater "backs up" and overflows the housing then it will simply flow straight into the shower tray and down the drain. The housing can preferably also be lifted out of the shower tray so that the shower tray can be properly cleaned. The housing might be hung on a peg or placed on a shelf within the shower enclosure, for example.

The upper surface is preferably supported by vertical ribs that are formed as an integral part of the housing and act as structural members to increase the strength and rigidity of the housing and transmit applied loads to the shower tray. The housing is preferably formed from a plastics material and must be sufficiently strong and rigid to take the weight of an adult person. The height or depth of the housing is preferably kept to a minimum so that the position of the user is not raised too far above the existing shower tray.

The upper surface of the housing preferably takes the form of a removable lid to allow access to the heat-exchange conduit for maintenance and repair. The lid can be releasably secured to the rest of the housing using clips, screws or any other suitable mechanical fixing. The upper surface can be provided with a non-slip pattern of ridges and/or projections.

The heat-exchange conduit is preferably connectable between a mains water supply and the water inlet of a shower unit using flexible conduits so that it can be easily installed and disconnected for maintenance and repair. The flexible conduits are connected to the fixed pipe work carrying the mains water supply and can pass through a slot in the upper surface of the housing where they are connected to the ends of the heatexchange conduit. Alternatively, the flexible conduits are connected outside the housing to fixed connector pipes that pass through the slot and are connected to, or integrally formed with, the ends of the heatexchange conduit. The flexible conduits can be of extended length, each having a part distal from the housing that is tensioned between two fittings that are fixed to the wall of the shower - 11 enclosure to keep the flexible conduits in place. The flexible conduits can be released from one or both of the fittings when the heat-exchange conduit needs to be manipulated or if the lid of the housing needs to be removed. The slot will usually be cut or formed when the heat-exchange unit is installed and may be covered to prevent the passage of wastewater.

The heat-exchange conduit is preferably divided into two or more parallel conduits each of which is located in a separate channel for receiving wastewater. The channels are preferably defined by the vertical ribs that support the upper surface of the housing, but may alternatively be defined by a separate insert positioned between the vertical ribs.

It will be readily appreciated that the level of wastewater in the channel or channels should preferably be high enough to completely cover the heat-exchange conduit but not so high as to spill over the vertical ribs.

The width of the at least one channel can be altered to accommodate seasonal variations in the flow velocity of the wastewater, for example. The width of the at least one channel can be altered manually by operating a knob or lever (perhaps calibrated according to the seasons of the year), or automatically by monitoring the level of wastewater to make sure it stays within predetermined limits. One way of controlling the width of the at least one channel is to provide an insert between the vertical ribs that can be moved laterally to widen or narrow the channel.

The wastewater in the channel or channels preferably flows into a common drainage channel that includes a drainage hole to allow the wastewater to flow out of the heat exchange unit. An adjustable wastewater level control device such as a gate, weir or dam is preferably located in the drainage channel upstream of the drainage hole to selectively control the level of wastewater in the channels and make sure it stays within predetermined limits.

The gate can be adjusted to provide an opening of predetermined width. The gate can be controlled to automatically adjust the width of the opening. One way of doing this is to provide a float to monitor the level of wastewater in the channels and then increase the width of the opening if the float rises and decrease the width of the opening if the Boat falls. The float can be located in a separate compartment that is in fluid communication with the channels so that the level of wastewater in the compartment is the same as that in the channels. A float can also be used to automatically alter the width of the at least one channel (see above).

The gate can also be controlled manually by operating a knob or lever (perhaps calibrated according to the seasons of the year). Similar forms of control can be applied to adjust the height of the weir or dam.

if a weir or dam is used then a small secondary drainage hole can be provided in the drainage channel upstream of the weir or dam so that any wastewater left in the channel or channels when the shower is turned off can flow out of the heat-exchange unit. This prevents harmful bacteria and algae building up in the at least one channel if the shower is not used for a long period of time.

in contrast, the gate provides an open exit path for the wastewater and allows debris to flow out of the heat-exchange unit through the drainage hole.

It will be readily appreciated that shower trays are very seldom flat and never level.

However, flow issues dictate that the heat-exchange unit must be level to within a small tolerance il it is to operate properly.

The housing is located on load-bearing supports that extend between the shower tray and a bottom surface of the housing. An advantage of this type of support is that the supports are in compression, and are not normally visible to the shower user. Such supports can be integrally formed as part of the bottom surface of the housing or formed separately and secured to the bottom surface of the housing using conventional means. Alternatively, the load-bearing supports can take the form of - 13 strips of a bedding compound such as mortar or putty that is mixed soft and then sets hard. The advantage of this is that the bedding compound will deform to match the exact profile of the shower tray (including any non-slip pattern of ridges and/or projections) and still provides sufficient support for the housing when it has set hard.

In every case it is important that gaps or channels are maintained between the bottom surface of the housing and the shower tray so that wastewater can flow from the self- contained heat-exchange unit to the drain of the shower tray.

Also, in every case it is advantageous if the supports are provided between the housing and the shower tray in a controlled pattern, preferably closely-spaced over the bottom surface of the housing, as this controls and increases the amount of support provided to the housing. The increased support results in the housing being less stressed by applied load, consequently allowing it to be of more lightweight construction and hence cheaper and less bulky.

The present invention also provides a method of installing a selfcontained heat exchang,e unit above a shower tray having a drain, the method comprising the steps of positioning the self-contained heatexchange unit on one or more load-bearing supports such that the wastewater can flow from the self-contained heat-exchange unit to the drain. The load-bearing supports transmit the weight of the user from the upper surl;ace of the housing, through the structure of the housing, to the shower tray.

The self-contained heat-exchange unit can be placed on bedding compound strips such as mortar or putty or catalysed resin that is mixed soft and sets hard.

A levelling tray can be used to install the self-contained heat-exchange unit to make sure it is level within a certain tolerance. 'I'he base of the levelling tray is formed with a number ol' apertures or slots in positions that are calculated to provide the necessary amount of structural support for the self-contained heat-exchange unit. A pair of grooves can be provided in an upper surface of the base of the levellingtray. When filecd with water, the grooves can be used as a guide to indicate whether or not the - l4 levelling tray is positioned level in the shower tray. The grooves are preferably substantially at right angles to each other but do not need to be connected.

Brackets are preferably located around the edge of the levelling tray for the mounting ol' adjustable spacer bars. Height adjustable legs are preferably provided in each corner of the levelling tray.

To install the self-contained heat-exchange unit, the levelling tray is placed in the existing shower tray and the height of the legs is adjusted until the levelling tray is level within a certain tolerance. The spacer bars are then adjusted until they contact the upstanding sidewalls of the shower tray so that the levelling tray is positioned laterally within the shower tray and is unable to move or rotate.

Flexible pockets are inserted into the slots and filled with a bedding compound such as mortar or putty that is mixed soft and sets hard. The flexible pockets contain the bedding compound so that it forms discrete strips of the correct length, width and thickness with the free surface of the bedding compound at the appropriate level to engage with the bottom surface of the housing. This prevents waste and makes sure the wastewater can flow freely from the drainage hole in the housing to the drain of the shower tray. The flexible pockets may be provided with a lip so that overfilling them with bedding compound automatically gives the appropriate level.

The heat-exchange unit is then placed directly on top of the base of the levelling tray.

Projections can be formed on the bottom surface of the housing of the heat-exchange unit so that they protrude though the apertures or slots in the base of the levelling tray and into the bedding compound to provide a good mechanical connection between the housing and the bedding compound. When the bedding compound has set hard, the heat-exchange unit and the levelling tray can be lifted away from the shower tray. It will be readily appreciated that the strips of bedding compound remain attached to the bottom surface of the housing and the levelling tray is removed and discarded. The heat-exchange unit can then be repositioned on top of the shower tray. To make sure the repositioned heat-exchange unit is correctly located within the shower tray, spacer - 15 bars can be located around the edge of the housing and adjusted until they contact the upstanding side walls of the shower tray. '['his adjustment is carried out before the heat-exchange unit and the levelling tray are lifted out of the shower tray.

Alternatively, both the heat-exchange unit and levelling tray are left in position on top -' f the shower tray once the bedding compound has set hard.

I'he self-contained heat-exchange unit can also be installed without a levelling tray.

The housing is placed in the existing shower tray and height adjustable legs provided in each corner of the housing are adjusted until the housing is level within a certain tolerance. Spacer bars can be located around the edge of the housing and adjusted until they contact the upstanding sidewalls of the shower tray to position the housing laterally in the shower tray.

Note that in all cases the spacer bars may be provided as items distinct from the housing, or may be formed continuously as part of the housing itself.

The drainage hole provided in the housing can be blocked with a bung or plug so that the housing can be filled with water to provide a useful indicator for levelling the housing. A number of graduations or markings can be provided on the side walls or vertical ribs of the housing so that the level of the water within the housing can be easily noted.

The base of the housing can be formed with a number of apertures through which a bedding compound such as mortar or putty that is mixed soft and sets hard can be introduced into flexible pockets. It is preferred that each flexible pocket communicates with a pair of apertures so that the bedding compound can be introduced into the flexible pocket through one of the apertures while the other aperture allows the displaced air to escape and provides an easy way of visually detecting when the flexible pocket has been completely filled. Each flexible pocket can be attached to the bottom surface of the housing by securing it over an annular flange surrounding each pair of apertures. This may be with an elastic band or the - 16 like. Alternatively, the rim of the flexible pocket may be firm enough to self-secure around the annular flange.

Several or all of the flexible pockets can be provided fixed into or continuously as part of a sheet. This would prefer several advantages, including that the sheet of pockets would be more easy to handle than individual pockets, and that the parts count is reduced.

projection can be formed on the bottom surface of the housing of the heatexchange unit within each of the annular flanges so that the projections protrude into the strips of bedding compound when the flexible pockets have been filled. This ensures a good mechanical connection between the bottom surface of the housing and the bedding compound.

Drawings Figure 1 is a top view of the casing tray and heat-exchange conduit of a self-contained heat exchange unit according to the present invention; Figure 2 is a top view of' the casing tray of the selfcontained heat exchange unit of Figure 1; Figure 3 is a detail perspective view of the casing tray of the self-contained heat cxchange unit of Figure 1 showing the drain hole and adjustable gate; Figure 4 is a top view of the heat-exchange conduit of the self-contained heat exchange unit of Figure 1; I'igure 5 is a top view of the casing lid of a self-contained heat exchange unit according to the present invention; Figure 6 is a cross-section view of the complete self-contained heat- exchange unit including the casing tray and heat-exchange conduit of Figure 1 and the casing lid of Figure 5; Figures 7A to 7D are perspective views of alternative ways of adjusting the width of the channels formed in the casing tray; I';igure 8 is a top view ol'an alternative casing tray; Figure 9 is a top view of an alternative heat-exchange conduit; Figure] O is a top view showing the self-contained heat-exchange unit installed in a shower tray; Figure 11 is a perspective view showing the self-contained heat-exchange unit installed in a shower tray and one way of fluidly connecting the heat-exchange conduit to the mains water supply and the water inlet of a shower unit; Figure 12 is a detail view of the installation of Figure 1 1; Figure 13 is a perspective view showing the self-contained heat-exchange unit installed in a shower tray and an alternative way of fluidly connecting the heat exchange conduit to the mains water supply and the water inlet of a shower unit using a fitting; Figure 14 is a detail view of the fitting of Figure 13; Figure 15 is a perspective view showing how the self-contained heat-exchange unit can be lifted out of the shower tray; Figure 16 is a perspective view of a cleaning device; - 18 Figure 17 is a top view showing how the cleaning device of Figure 16 can be used to clean the parallel conduits of a heatexchange conduit; Figure 18 is a view showing how the cleaning device can be used in combination with a water nozzle; Figure 19 is a top view of an alternative heat-exchange conduit; Figure 20 is a cross-sectional view of the alternative heat-exchange conduit of Figure 19; Figure 21 is a top view of a levelling tray for use in the installation of the self contained heat-exchange unit according to the present invention; Figure 22 is a side view showing the self-contained heat-exchange unit in the process of being installed above an existing shower tray and showing the levelling tray of Figure 21; Figure 23 is a cross-sectional view of the installation of Figure 21; Figure 24 is a top view of the base of a self- contained heat exchange unit that can be installed without a levelling tray; and Figure 25 is a cross-sectional view of the base of the self- contained heat exchange unit of Figure 24.

With reference to Figures 1 to 6, a self-contained heat exchange unit includes a casing tray 2, a heat-exchange conduit 10 and a casing lid 20. As described in more detail below, the heat-exchange unit is installed above an existing shower tray having a drain and the heat-exchange conduit 10 is connected between the mains water supply and the water- heater unit of an electric shower. The heat-exchange unit uses the wastewater produced when a person takes a shower to pre-heat cold water from the mains water supply. The pre-heated water is then supplied directly to the water-heater unit of the electric shower.

The casing tray 2 is made of a rigid plastics material and has a number of vertical structural ribs 3. The structural ribs 3 also act as flow guides and define five serpentine chaimels 4a to 4e for receiving the wastewater produced when the electric shower is in use. The structural ribs 3 support the casing lid 20, increase the strength - 19 and rigidity of the casing tray 2 and transmit applied loads (i.e. the weight of the person standing on the casing lid) directly to the shower tray.

The heat-exchange conduit 10 includes an inlet pipe] 1 that is fluidly connected to the mains water supply. Cold water from the mains water supply is supplied from the inlet pipe 11 to an inlet manifold 12 where it is divided equally between five parallel conduits 1 3a to 1 3e, each of which is received in a respective one of the wastewater channels 4a to 4e. The cold water flows through the parallel conduits 13 as shown by the arrows in Figure 4 and is heated by the wastewater flowing through the channels 4. An outlet manifold 14 receives the pre-heated water from the parallel conduits 13 and supplies the pre-heated water to an outlet pipe] 5 that is fluidly connected to the water-heater unit of the electric shower. A flow insert 16 (see Figure 6) is located in each of' the parallel conduits 13 to reduce the cross-sectional area and maintain a high flow velocity.

A removable casing lid 20 is made of a rigid plastics material and located over the casing tray 2. The casing lid 20 has an upper surface 21 on which a person can stand when taking a shower and downwardly extending sidewalls 22. A drainage hole 23 allows wastewater to flow through the casing lid 20 into a plenum channel 5 of the casing tray 2 upstream of the channels 4. A water-trap (not shown) may be provided between the drainage hole 23 and the plenum channel 5 to prevent odours from passing back through the hole. The wastewater then flows into and through the channels 4 as indicated by the arrows in Figure 2 until it reaches a drainage channel 6.

A drainage hole 7 is located in the drainage channel 6 so that the wastewater can flow out of the casing tray 2 and down the drain of the shower tray. A gate 8 is also located in the drainage channel 6 upstream of the drainage hole 7 and allows the flow of wastewater through the drainage hole to be selectively controlled to make sure the level of wastewater in the channels 4 is such that the parallel conduits 10 are fully immersed at all times. The gate 8 can be adjusted to provide an opening of varying width. The width of the opening can be manually or automatically varied by adjustment means (not shown) depending on various parameters such as the electrical power of the shower, the preferred water temperature of the person taking the shower - 20 and seasonal variations in the temperature of the mains water supply. A water-trap (not shown) may be provided downstream of the drainage hole 7 to prevent odours from passing out of the casing tray 2.

Vertical reinforcement ribs 9 provide additional strength and rigidity to the casing tray 2 and fill in the area formed by the minimum bend radius of the heat- exchange conduit 10.

It will be noted that the wastewater and the cold water from the mains water supply flow in opposite directions as shown by the arrows in Figures 2 and 4.

Figures 7A to 7D show flour different ways of varying the width of the channels 4 of the casing tray 2 to accommodate changes in the flow velocity of the wastewater. In Figure 7A a channel insert 30 is provided on either side of the structural rib 3 and releasably secured using spring clips 31 (only one of which is shown). The channel inserts 30 are spaced apart from the structural rib 3 by spacer blocks 32 that can be provided in various widths. It will be readily appreciated that a channel insert 30 may also be provided on either side of the adjacent structural rib 3' such that the two facing channel inserts can be moved closer together or further apart to vary the width of the channel 4 between them. In Figure 7B adjustable cams 33 are used in place of the spacer blocks 32 and can be rotated to selectively move the channel inserts 30 away l'rom the structural rib 3. This eliminates the need to provide a number of different spacer blocks.

In Figure 7C the base of each channel insert 34 is provided with studs 35 that engage with angled slots 37 in the casing tray 2. Facing flow channel inserts 34 can be moved along the slots 37 to vary the width of the channel between them.

A further alternative is shown in Figure 7D where a separate channel insert tray 40 of rigid plastics material is located within the casing tray 2. The channel insert tray 40 has fixed hollow walls 41 that define channels 42 of narrower width and into which the structural ribs 3 are received. The top surface of each of the structural ribs 3 is - 21 provided with an array of raised projections 3a that engage with corresponding apertures 43 in the top surface of the associated hollow wall 41.

An alternative casing tray and heat-exchange conduit are shown in Figures 8 and 9.

The casing tray 102 is made of a rigid plastics material and has a number of structural ribs 103 that act as flows guides and define twenty straight channels 104 for receiving the wastewater. The channels 104 are divided into a first set of six channels 104a, a second set of seven channels 104b and a third set of seven channels 104c by an extended pair of structural ribs 102a and 102b.

The heat-exchange conduit 110 includes an inlet pipe 111 that is fluidly connected to the mains water supply. Cold water from the mains water supply is supplied from the inlet pipe 111 to an inlet manifold 112 where it is divided equally between a first set of six parallel conduits 113a, each of which is received in a respective one of the first set of wastewater channels 104a. A first connector manifold 114 receives the partially pre-heated water lrom the first set of parallel conduits 113a and divides it equally between a second set of seven parallel conduits 113b, each of which is received in a respective one of the second set of wastewater channels 104b. A second connector manifold I I 5 receives the partially pre-heated water from the second set of parallel conduits 113b and divides it equally between a third set of seven parallel conduits 113c, each of which is received in a respective one of the third set of wastewater channels 104e. An outlet manifold 116 supplies the pre-heated water from the third set of parallel conduits 113c to an outlet pipe 117 that is fluidly connected to the water-heater unit of the electric shower.

Once again, It will be noted that the wastewater and the cold water from the mains water supply flow in opposite directions as shown by the arrows in Figures 8 and 9.

Figure 10 shows how the heat-exchange unit is installed above an existing shower tray ST. The shower tray ST is larger than the outer dimensions of the heat-exchange unit and adjustable spacer bars 50 are therefore located on the sides of the casing tray 2. Suitable slots (not shown) are provided in the sidewalls 22 of the casing lid 20 to - 22 accommodate the spacer bars 50. The spacer bars 50 prevent the heat-exchange unit t'rom moving or rotating within the shower tray ST. A rounded contact pad 51 is provided on the end of each spacer bar 50 to provide point contact with the upstanding sidewalls W of the shower tray ST. The spacer bars 50 are adjustable and can be cut to the appropriate length when the heat-exchange unit is installed. The installation of the heat-exchange unit is described in more detail below.

As shown in Figures 11 and 12, the heat-exchange conduit 10 is fluidly connected to the mains water supply and the water-heater unit WH of an electric shower using sinall bore piping P that is clipped to the wall of the shower enclosure and hidden by a cover (not shown). The small bore piping P terminates in a connector block CB and flexible conduits 60 are used to connect the connector block CB to the inlet pipe 11 and outlet pipe 15 of the heat-exchange conduit 10 with quick-release couplings 61.

These allow the flexible conduits 60 to be disconnected quickly and easily from the heat-exchange unit so that the casing lid 20 can be removed for maintenance and repair. The connector block CB may contain a valve so that, if necessary, the heat exchange conduit 10 can be isolated from the mains water supply.

With reference to Figure 5, the flexible conduits 60 can be fluidly connected to connecting pipes 62 without the need for quick-release couplings 61. 'the connecting pipes 62 pass through a slot 63 in the casing lid 20 so that the casing lid can be easily removed for maintenance and repair. The slot 63 can be covered to prevent the passage of wastewater through the slot and into the casing tray 2.

An alternative way of fluidly connecting the heat-exchange conduit 10 to the mains water supply and the water-heater unit Wl-I of an electric shower is shown in Figures 13 to 15. Extended flexible conduits 70 are used in place of the small bore piping and are tensioned to keep them flat against the wall of the shower enclosure by means of a pair ol'f'ittings 71 (only one of which is shown in Figure 13). A lower part 70a of the flexible conduits below the fitting 71 is not in tension. A fixed part 72 of each fitting 71 is secured to the wall of the shower enclosure using conventional means and a connector part 73 is secured to the flexible conduits 70. The connector part 73 is - 23 retained by the fixed part 72 to keep the flexible conduits 7() in tension and can be released as shown in Figure 15 so that the heat-exchange unit can be lifted out of the shower tray ST. This allows the shower tray ST to be properly cleaned and maintained.

A cleaning device 80 will now be described with reference to Figures 16 to 18. The cleaning device 80 is used to remove soft scale, scum and other debris from the outside surface of the parallel heat-exchange conduits 13. As shown in Figure 17, a separate cleaning device 80 is provided for each parallel conduit 13. However, a single cleaning device could also be used to clean all of the parallel conduits.

The cleaning device X0 has an upper carriage part 81 and two downwardly extending cleaning parts 82. Each of' the cleaning parts 82 has a circular aperture 83 that is sized to receive a parallel conduit 13. The edge or rim 84 of each aperture 83 is formed as a scraper element that contacts the outer surface of the parallel conduit 13. A water nozzle 85 is connected by a flexible conduit to the connector block CB and controlled by a shut-off valve (not shown). To clean one of the parallel conduits 13, the casing lid 20 is removed and the water nozzle 85 is inserted into an aperture 86 provided in the carriage part 81 of the cleaning device. The shut off valve (not shown) is then opened to allow water from the mains water supply to flow out of the end of the water nozzle 85 and onto the outer surface of the parallel conduit 13. The water nozzle 85 is then used as a handle to slide the cleaning device 80 along the parallel conduit 13 so that the full length of the parallel conduit is scraped clean. Any debris removed by the cleaning device 80 is flushed down the channel 4 and out of the heat-exchange unit through the drainage hole 7 provided in the bottom of the casing tray 2.

Figures 19 and 20 show an alternative heat-exchange conduit 90 having three pipe loops 90a, 90b and 90c that are fluidly connected together at opposite ends by a connector joint 92 that is brazed in position. A conventional Tjoint 93 can be used to fluidly connect an upstream region of one of the pipe loops 90b to an inlet pipe 94 and a downstream region of one of the pipe loops 90c to an outlet pipe 95. - 24

The self-contained heat-exchange unit can be installed on compound strips using a levelling tray 120 as shown in Figures 22 to 24. The levelling tray is made of a rigid plastics material and has a predetermined thickness that corresponds to the minimum acceptable thickness of the compound strips. A number of apertures or slots 121 are provided in the levelling tray 120 in positions that are calculated to provide the necessary amount of structural support for the heat-exchange unit. The area of the levelling tray 120 surrounding each of the slots 121 is raised slightly to provide a relief 122 (see Figure 23). The base of the levelling tray 120 also includes a pair of connected cross grooves 124. When filled with water, the cross grooves 124 can be used as a guide to make sure the levelling tray 120 is positioned level within a certain tolerance in the shower tray ST.

Brackets 125 are located around the edge of the levelling tray 120 for the mounting of spacer bars 126. Adjustable legs (not shown) are provided in each corner of the levelling tray 120.

To install the self-contained heat-exchange unit, the levelling tray 120 is placed in the existing shower tray ST and the height of the legs is adjusted until it is level within a certain tolerance. The spacer bars 126 are also adjusted until they contact the upstanding sidewalls W of the shower tray ST to position the levelling tray 120 laterally within the shower tray. Flexible pockets 127 are then inserted into the slots 121 and filled with a bedding compound 128 such as mortar or putty that is mixed sot's and sets hard. The relief 122 around each of the slots 121 allows the flexible pockets 127 to be filed to the correct level because any excess bedding compound can be accommodated in the gap between the bottom surface of the casing tray 2 and the levelling tray 120. 'I'he flexible pockets 127 contain the bedding compound 128 so that it forms discrete strips 129 of the correct length, width and thickness to support the hcat-cxchange unit. This prevents waste and ensures that the wastewater can flow freely from the drainage hole 7 in the casing tray 2 to the drain ol' the shower tray ST.

Once the levelling tray 120 is properly in position, the heat-exchange unit is placed on top of the levelling tray so that projections 130 formed on the bottom surface of the - 25 casing tray 2 protrude through the slots 121 and into the bedding compound 128 as shown in Figure 23. When the bedding compound 128 has set hard, the heat exchange unit and the levelling tray 120 are lifted out of the shower tray ST and the Icvelling tray is removed. If necessary, the levelling tray 120 can be broken up to facilitate its removal. The strips 129 of bedding compound 128 remain attached to the bottom surface of the casing tray 2 because of the good mechanical connection between the bedding compound and the projections 130. lithe heat-exchange unit can then be repositioned inside the shower tray. To make sure the heat-exchange unit is repositioned correctly after it has been lifted out of the shower tray ST, spacer bars 50 (see Figure 10, for example) provided around the edge of the casing tray 2 can be adjusted so that they contact the upstanding sidewalls W of the shower tray while the heat-exchange unit is supported on the levelling tray 120.

The strips 129 of bedding compound transmit the weight of the user to the shower tray ST. Because the number and placing of the strips can be controlled, it can be provided that the user's weight is transmitted to the shower tray by a direct path through the casing tray 2. This keeps (especially the bending induced) stresses in the casing tray 2 to an absolute minimum.

'l'hc self-contained heat-exchange unit can also be installed without a levelling tray as described with reference to Figures 24 and 25. Firstly, the heat-exchange unit is placed in the existing shower tray ST and height adjustable legs (not shown) provided in each corner of the casing tray 2 are adjusted until the heat-exchange unit is level within a certain tolerance. Spacer bars 50 located around the edge of the casing tray 2 are adjusted until they contact the upstanding sidewalls W of the shower tray ST to position the heat-exchange unit laterally in the shower tray.

The drainage hole 7 in the casing tray 2 is blocked with a bung or plug (not shown) and the casing tray is filled with water to provide a useful indicator for Icvelling the heat-exchange unit. A number ol' graduations or markings (not shown) are provided on the sidewalls of the casing tray 2 or the vertical structural ribs 3 so that the level of the water within the casing tray can be easily noted. - 26

A number of apertures 140 are formed in the bottom surface of the easing tray 2 and arranged in pairs. An annular flange 141 surrounds each pair of apertures 140 and a flexible pocket 142 is secured to each flange with an elastic band 143 before the heat exchange unit is placed in the shower tray. A bedding compound such as mortar or putty that is mixed soft and sets hard is introduced into the flexible pocket 142 through one of the apertures 140. Air that is displaced by the introduction of the bedding compound can escape through the other aperture and this other aperture provides an easy way of visually detecting when the flexible pocket 142 is completely full.

Projections 144 are formed on tile bottom surface of the easing tray within the annular flange 141 so that they protrude into the bedding compound 145 when the flexible pockets 142 are filled. This ensures a good mechanical connection between the bottom surface of the easing tray 2 and the bedding compound 145. The bedding compound is allowed to set hard to provide discrete strips of the correct length, width and thickness needed to support the heat-exchange unit. - 27

Claims

1. A self-contained heat-exchange unit for installation above a shower tray having a drain, the heat-exchange unit comprising a box-like housing and a heat exchange conduit that is connectable between a mains water supply and a water inlet of a shower unit and is located in at least one channel formed in the housing for receiving wastewater such that heat may be exchanged between the wastewater and mains water flowing through the heat-exchange conduit, wherein the housing has an upper surface on which a person can stand when taking a shower and a bottom surface that in use is positioned on one or more load-bearing supports and is spaced apart from the shower tray such that the wastewater can flow from the housing to the drain.

2. A self-contained heat-exchange unit according to claim I, wherein tee ur.,oer surface is supported by vertical ribs.

3. A self-contained heat-exchange unit according to claim 2, wherein the vertical ribs are l'ormed as an integral part of the housing and act as structural members to increase the strength and rigidity ol'the housing.

4. A self-contained heat-exchange unit according to claim 2 or claim 3, wherein the heat-exchange conduit is divided into two or more parallel conduits each of which is located in a separate channel for receiving wastewater.

5. A self-contained heat-exchange unit according to claim 2 or claim 3, wherein the heat-exchange conduit is divided into two or more parallel conduits and two or more parallel channels are formed in the housing with each of the charnels receiving at least one parallel conduit.

6. A sel l:contained heat-exchange unit according to claim 5, wherein each channel receives two or more parallel conduits.

7. A self-contained heat-exchange unit according to any of claims 4 to 6, wherein the channels are del'ined by the vertical ribs. - 28

8. A method of installing a self-contained heat-exchange unit according to any of claims l to 7 above a shower tray having a drain, the method comprising the steps of positioning the housing on one or more loadbearing supports such that the wastewater can flow from the housing to the drain.

9. A method according to claim 8, wherein the housing is placed on compound strips of mortar or putty or catalysed resin that is mixed soft and sets hard.

l O. A self-contained heat-exchange unit according to any of claims l to 7, wherein spacer bars are located around the edge of the housing.

11. A self-contained heat-exchange unit according to claim 10, wherein a number of apertures are formed in the bottom ol the housing and the housing is supported on height adjustable legs.

12. method of installing a self-contained heat-exchange unit according to claim l l above a shower tray having a drain, comprising the steps of: securing flexible pockets to the bottom of the housing so that each of the flexible pockets can be filled with a bedding compound of mortar or putty or catalysed resin that is mixed soft and sets hard through an associated one ol the apertures formed in the bottom of the housing, locating the housing in the shower tray, adjusting the height of the legs until the housing is level to within a certain tolerance, adjusting the spacer bars to position the housing laterally within the shower tray, tilling the flexible pockets with bedding compound, and allowing the bedding compound to set hard.

13. A Ievelling tray when used in the installation of a self-contained heat exchange unit according to claim 10 above a shower tray having a drain, the levelling tray - 29 having a base in which a number of apertures or slots are formed, spacer bars located around the edge of the levelling tray and wherein the levelling tray is supported on height adjustable legs.

14. A method of installing a heat-exchange unit according to claim 10 above a shower tray having a drain using a levelling tray according to claim 13, the method comprising the steps of: locating the levelling tray in the shower tray, adjusting the height of the legs until the levelling tray is level to within a certain tolerance, adjusting the spacer bars to position the levelling tray laterally within the shower tray, inserting a flexible pocket into the apertures or slots so that each of the flexible pockets can be filled with a bedding compound of mortar or putty or catalysed resin that is mixed soft and sets hard through an associated one of the apertures or slots formed in the base ol'the levelling tray, filling the flexible pockets with bedding compound, placing the housing on top of the levelling tray such that projections formed on the bottom surface of the housing protrude through the apertures or slots in the base of the levelling tray and into the bedding compound, and allowing the bedding compound to set hard.

15. A method according to claim 14, further comprising the steps of: lifting the housing and the levelling tray out of the shower tray, removing the levelling tray, and repositioning the housing in the shower tray supported by the bedding compound.

16. 1\ heat-exchange unit substantially as herein described and with rel'erence to the drawings.