ABLUTIONARY INSTALLATIONS

This invention relates to ablutionary installations. The invention has particular, but not exclusive, application to showers, especially electric showers in which a supply of water is heated as it passes through a heater tank containing at least one electric heating element. Electric showers of this type are often referred to as instantaneous showers because the water is heated to a desired temperature on demand at the time of use of the shower.

A problem with electric showers is the poor perceived performance due to low flow rates. Electric showers work by varying the flow of water over one or more electric heating elements contained in a heater tank - the lower the flow rate, the higher the change in temperature - and seasonal fluctuations in the temperature of the mains cold water supply have a significant effect on the flow rates that can be achieved to obtain a desired water temperature. Thus, during the summer months the temperature of the mains cold water supply may be around 15 to 20°C, or even higher, but can drop to around 5°C or less during the winter months. As a result, to achieve the same outlet water temperature throughout the year, a much lower flow rate is required during the winter months to compensate for the lower temperature of the incoming mains cold water. For example, during the winter months, the user could experience flow rates lower than 3 litres/minute compared to flow rates of up to 11 litres/minute during the summer months.

The flow performance of an electric shower can be improved by increasing the power rating of the heating elements but even here there are limitations on the maximum power rating can be employed. Currently the limit is 10.8 kW and the performance during the winter months is still

poor with flow rates less than 4 litres /minute. It has been proposed to improve the performance of an electric shower by using the wastewater from a bath/shower tray to pre-heat the incoming mains cold water supply to the heater tank allowing the electric shower to be operated at higher flow rates. However, pre-heating the cold supply with the wastewater can lead to unstable operation of the electric shower. Thus, for a given power setting, as the electric shower is operated, the warm waste water increases the temperature of the inlet water to the heater tank which then increases the temperature of the outlet water from the heater tank which means that the waste water temperature is also increased which in turn further increases the temperature of the inlet water to the heater tank and so on. This increase in temperature will continue until an unsafe showering temperature is reached or the user adjusts the setting of the electric shower. However changing the setting of the electric shower will affect the temperature of the inlet water to the heater tank and so on. Furthermore, during summer months when the temperature of the mains cold water supply is higher and higher flow rates are required, problems can arise if a sufficiently high flow rate cannot be obtained to achieve a safe showering temperature.

The present invention has been made from a consideration of the foregoing problems and disadvantages.

According to one aspect of the invention, there is provided a shower system comprising a thermostatic electric shower and a heat recovery unit for pre-heating a cold water supply to the shower by heat exchange with wastewater from the shower.

By employing a heat recovery unit with a thermostatic electric shower, the shower responds automatically to changes in the temperature of the

cold water supply to maintain substantially constant a selected water temperature. In this way, pre-heating the cold water supply does not cause the temperature of the outlet water discharged by the shower to increase gradually as the shower is operable to compensate for the pre- heating of the cold water supply. As a result, the user selected safe showering temperature will be maintained and the inconvenience of having to keep adjusting the shower settings manually while showering is avoided.

Preferably, the heat recovery unit includes a heat exchanger for transferring heat from the wastewater to the cold water supply. In a preferred embodiment, the heat exchanger is a plate heat exchanger providing a large surface area for heat transfer between the wastewater and cold water supply. Other forms of heat exchanger may be employed.

Preferably, the heat recovery unit includes a wastewater overflow bypassing the heat exchanger. The overflow allows a flow of wastewater higher than the maximum flow through the heat exchanger to be accommodated.

Preferably, the heat recovery unit includes means for controlling flow of waste water through the heat exchanger to adjust heat exchange with the cold water supply. For example, a flow modulating valve may be employed to control the flow of wastewater through the heat exchanger. The valve may prevent flow of wastewater through the heat exchanger if pre-heating of the cold water supply is not required, for example during the summer when the temperature of the cold water supply is much higher than in winter.

Preferably, the shower includes a heater tank containing at least one electric heating element for heating water flowing therethrough and a control system operable in response to a temperature sensor monitoring outlet and/or inlet water temperature for adjusting one or both of the flow rate and/or power input to the heater tank to maintain a selected water temperature substantially constant.

According to another aspect of the invention, there is provided a method of operating an electric shower comprising the steps of providing a supply of cold water to a heater tank containing at least one electric heating element for heating the water, supplying heated water from the heater tank to an outlet, collecting water discharged from the outlet, passing the collected water through a heat exchanger to pre-heat the cold water supply to the heater tank, providing a temperature sensor for monitoring water temperature into and/or out of the heater tank, and controlling heat input to the cold water in the heater tank to achieve and maintain a selected outlet water temperature substantially constant.

The heat input to the cold water in the heater tank may be controlled by adjusting the flow rate of the cold water and/or by adjusting the power setting of said at least one heating element.

According to yet another aspect of the invention, there is provided an ablutionary installation comprising an instantaneous water heater for supplying water having a desired temperature to at least one outlet, a heat recovery unit for pre-heating a cold water supply to the water heater by heat exchange with water discharged from the outlet, and means for controlling the water heater to maintain substantially constant the desired water temperature.

The power supply to the water heater may be gas or electric. Preferably, the water heater has one or more electric heating elements in a heater tank for heating water flowing through the tank.

Preferably, the control means includes a temperature sensor for monitoring the water temperature to or from the heater tank and is operable to control operation of the water heater to maintain substantially constant the desired water temperature by adjusting the flow rate of the water and/or power setting of the power supply in response to the detected water temperature.

According to a still further aspect of the invention, there is provided a heat recovery unit comprising a heat exchanger for transferring heat from a first fluid to a second fluid, and an overflow for the first fluid by- passing the heat exchanger whereby the first fluid can flow through the heat exchanger or the overflow.

Preferably, the heat recovery unit is arranged to receive wastewater from an ablutionary appliance such as a shower and pre-heat a water supply to the shower, usually a cold water supply, by heat transfer between the wastewater and the water supply in the heat exchanger.

Preferably, the overflow is designed to ensure that excess wastewater can escape without passing through the heat exchanger. For example, when a shower is installed over a bath, the overflow allows the bath to empty in a reasonable time when used for bathing.

Preferably, a filter is provided upstream of the heat exchanger to remove hair or debris carried by the wastewater to prevent blockage of the heat exchanger and maintain the performance of the heat exchanger.

Preferably, the heat exchanger is a plate heat exchanger and the flow of wastewater is preferably split into two or more streams for passage through the heat exchanger.

Other features and benefits of the different aspects of the invention will be apparent from the following description with reference to the accompanying drawings in which :-

Figure 1 is a schematic view of an electric shower installation embodying the invention; and

Figure 2 is a view of the heat recovery unit shown in Figure 1.

Referring first to Figure 1, an electric shower installation is shown comprising a wall mounted control unit 1 having an inlet (not shown) connected to a water supply pipe 3 and an outlet 5 connected by a flexible hose 7 to a handset 9.

The handset 9 is mounted in a parking socket 11 of a bracket 13 slidably mounted on a wall mounted riser rail 15 to allow the height of the handset 9 above a shower tray 17 to be adjusted. The handset 9 has a spray head 19 for discharging water in a spray according to the layout of nozzles (not shown) in the spray head 19. The spray head may be adjustable to select different combinations and/or types of spray nozzles to vary the spray pattern and/or type.

The water supply to the control unit 1 is pre-heated by heat exchange with wastewater from the shower tray 17 in a heat recovery unit 21 described in more detail later with reference to Figure 2 of the drawings. In this

embodiment, the control unit 1 has a rotatable control knob 23 for setting the power input to a heater tank (not shown) connected between the water inlet and water outlet connections of the control unit 1, and a rotatable control knob 25 for selecting the outlet water temperature.

A temperature sensor (not shown) is arranged to monitor the outlet water temperature from the heater tank and an electronic control system (not shown) is operable to compare the sensed outlet water temperature with the user selected outlet water temperature and adjust a flow regulator (not shown) to alter the flow rate through the heater tank to maintain substantially constant the user selected outlet water temperature for a given power setting.

In this way, the selected water temperature is maintained even with varying temperature of the inlet water going to the control unit 1 via the heat recovery unit 21. Combining heat recovery to pre-heat the water supply with thermostatic control of the selected water temperature allows the following advantages to be obtained :-

1. Using a lower kW rated thermostatic electric shower to achieve the same performance as a conventional higher kW rated electric shower. This will allow the customer to have reduced electricity bills and the capability to have a shower that performs like a conventional higher kW electric shower even if their electrical supply or consumer unit is not capable of supplying the required current for a conventional higher kW electric shower.

2. Using a high kW rated thermostatic electric shower to achieve a flow rate performance that is unachievable with a conventional

high kW electric showers. This will allow the customer to experience a powerful shower even in winter.

The electronic control system may respond to detection of an outlet water temperature higher than a pre-determined value to prevent the user being scalded by discharge of water above a safe showering temperature. The control unit may include a display to provide the user with a visual indication of the water temperature.

Referring now to Figure 2, the heat recovery unit 21 is shown in more detail and comprises a heat exchanger 27 and a wastewater manifold 29. In this embodiment, the heat exchanger 27 is a plate heat exchanger but it will be understood the invention is not limited to plate heat exchangers and that other forms of heat exchanger could be employed.

The plate heat exchanger 27 has two normally separated fluid flow paths defined by plates (not shown) of metal or other material having a high thermal conductivity and providing a large surface area for heat transfer between fluids flowing through the heat exchanger 27. In this embodiment, the cold water supply to the control unit 1 passes through one fluid path and the wastewater from the shower tray 17 passes through the other fluid path thereby pre-heating the cold water supply to the control unit 1.

The heat exchanger 27 has an inlet 31 at one end for connection to a mains cold water supply pipe 33 (Figure 1) and an outlet 35 at the other end for connection to the cold water supply pipe 3 (Figure 1) connected to the control unit 1. The manifold 29 has an inlet chamber 37 for connection to a waste pipe 39 (Figure 1) for wastewater from the shower tray 17, typically via a waste trap (not shown) connected to the outlet

from the shower tray 17, and an outlet chamber 41 for connection to a waste pipe 43 (Figure 1) for discharge of wastewater to a drain (not shown) .

The waste trap may incorporate a filter to collect hairs and other debris in the wastewater that could cause a blockage in the heat exchanger 27. The filter may be of any suitable type and may be removable via the outlet in the shower tray for cleaning. In a modification (not shown) the filter may be incorporated into the heat recovery unit 21 upstream of the heat exchanger 27 to prevent blockage of the heat exchanger 27 by hairs or other debris. The filter may comprise a mesh screen and may be removable for cleaning. Where a filter protects the heat exchanger 27, means may be provided to prevent flow of water through the heat exchanger 27 when the filter is not fitted. In this way, if the filter is removed for cleaning and the shower operated without replacing the filter, hairs or other debris in the wastewater cannot become trapped in and block the heat exchanger 27.

The inlet chamber 37 is connected by pipes 45,47 to a pair of inlets 49 (one only shown) on opposite sides of the heat exchanger 27 at the same end as the outlet 35. The outlet chamber 41 is connected by pipes 51,53 to a pair of outlets 55 (one only shown) on opposite sides of the heat exchanger 27 at the same end as the inlet 31. The inlet and outlet chambers 37,41 are also directly connected to each other by an overflow duct 57 that passes over the top of the heat exchanger 27 and by-passes the heat exchanger 27. The inlet and outlet chambers 37,41 and overflow duct 57 may be plastic mouldings that are joined together for example by ultrasonic welding.

In use, when the shower is switched on, water from the cold water mains supply passes through the heat exchanger 27 to the control unit 1 where it is heated as it flows through the heater tank before passing to the handset 9 where it is discharged as a spray. The water discharged from the handset is collected in the shower tray 17 and passes in the waste pipe 39 to the inlet chamber 37 where it is split into two streams that are delivered to the wastewater inlets 49 of the heat exchanger 27. The wastewater flows through the heat exchanger pre-heating the supply of cold water to the control unit 1 before leaving the heat exchanger 27 in two streams via the wastewater outlets 55 that are re-combined in the outlet chamber 41 before flowing to the drain.

As shown, the arrangement of the inlets and outlets is such that the cold water and wastewater flow through the heat exchanger 27 in opposite directions thereby improving heat transfer from the wastewater to the cold water. Splitting the wastewater into two streams for connection to separate inlets on opposite sides of the heat exchanger 27 produces a more uniform distribution of the wastewater flowing through the heat exchanger reducing the occurrence of hot or cold spots within the heat exchanger and further assists efficient heat transfer from the wastewater to the cold water. Splitting the wastewater into two streams also enables higher flow rates through the heat exchanger that also improves heat transfer from the wastewater to the cold water.

Pre-heating the cold water in this way, reduces the heat input required in the heater tank to raise the temperature of the water to the selected showering temperature allowing a higher flow rate to be achieved which improves the performance of the shower, in particular the spray produced when the water is discharged from the handset is improved. If the flow of wastewater is higher than the heat exchanger 27 can cope with, the

overflow duct 57 allows the excess flow to by-pass the heat exchanger 27 and prevents the wastewater backing up and filling the shower tray 17. For example, high flow rates may occur during summer when the temperature of the incoming cold water is higher than in winter. High flow rates may also occur when the shower is mounted over a bath and the bath is used for bathing in the normal manner. In this mode, when it is desired to empty the bath, the flow rate of wastewater is higher when draining the bath than when showering and the overflow duct 57 allows the wastewater to drain rapidly from the bath.

The cold water supply to the heat exchanger 27 keeps the flow path on one side of the heat exchanger filled with water at all times and the wastewater connections between the heat exchanger 27 and the manifold 29 are arranged so that, when there is no flow of wastewater, the wastewater flow path through the heat exchanger 27 remains filled with wastewater. In this way, air is prevented from being trapped in the flow paths that could form pockets restricting flow of cold water and wastewater through the heat exchanger. By keeping the flow paths through the heat exchanger filled in this way, efficient flow of wastewater and cold water through the heat exchanger 27 and thus heat transfer to the cold water is maintained.

In a modification (not shown) , heat transfer from the wastewater to the cold water may be controlled in response to the temperature of the incoming cold water supply and/or in response to user adjustment of the power input and/or temperature settings of the control unit 1. For example, in summer when the incoming cold water supply is much warmer, pre-heating the cold water may raise the temperature of the cold water to a level at which the control unit cannot provide a flow rate high enough for the selected power setting to achieve the selected water

temperature. This could result in discharge of water that is hotter than selected by the user.

In one arrangement, the heat recovery unit 21 may include a valve operable to control the flow of wastewater through the heat exchanger 27 to control heat exchange with the cold water to achieve a desired level of pre-heating of the cold water. In some cases, the valve may prevent flow of wastewater through the heat exchanger altogether so that the cold water is not pre-heated and the wastewater is directed to drain through the overflow duct 57.

In another arrangement, the heat exchanger 27 may be provided with a cold water by-pass and a valve operable to control the flow of cold water through the heat exchanger 27 to control heat exchange with the wastewater to achieve a desired level of pre-heating of the cold water. In some cases, the valve may prevent flow of cold water through the heat exchanger altogether so that the cold water passes directly to the control unit through the by-pass and is not pre-heated.

In both arrangements, the valve may be controlled by the electronic control system in response to the sensed temperature of the cold water and/or the settings of the control unit 1.

It will be understood that the invention is not limited to the embodiment above-described.

For example, the electronic control system may be arranged to adjust the flow regulator to alter the flow rate through the heater tank to maintain substantially constant the user selected outlet water temperature for a given power setting in response to a temperature sensor arranged to

monitor the inlet water temperature to the heater tank. In this arrangement, an outlet temperature sensor may also be provided to monitor the outlet water temperature to ensure the selected outlet water temperature is achieved and maintained.

The electronic control system may provide an indication of the outlet water temperature to the user via a suitable display on the control unit, for example an LED display of temperature. The electronic control system may include a memory for storing preferred shower settings that can be selected by any suitable means such as push buttons on the control unit. The memory may store (log) data relating to the operation of the shower, for example selected and actual water temperatures, operating times, power settings, flow rates etc. The data may be accessed locally, for example via a suitable port for connection to a laptop, palm top or other suitable hand held device. Alternatively, or additionally, the data may be accessed remotely, for example via a wireless link, to allow remote monitoring of the shower. Data logging may assist a service engineer to identify and correct any fault or malfunction of the control unit. Data logging may also be desirable for certain installations, for example in a healthcare establishment.

In the above-described embodiment, the flow rate through the heater tank of the control unit is adjusted in response to the temperature of the cold water supply and pre-heating is used to increase the flow rate for a given power setting. It will be understood, however, that pre-heating could also be used to allow the power setting to be reduced if an acceptable flow rate is achieved thereby reducing power consumption with associated cost saving for the user. For example, the electronic control unit may adjust the power setting to maintain the desired outlet water temperature for a given flow rate. Alternatively, the electronic control system may

adjust the power setting and flow rate in combination to maintain the desired outlet water temperature.

Although the heat recovery unit has been described for pre-heating a mains fed cold water supply to a thermostatic electric shower, it could be adapted to pre-heat a gravity fed cold water supply to a thermostatic electric shower via a booster pump or integral pump where required to boost the pressure of the cold water supply.

Moreover, while the heat recovery unit has been described in combination with a thermostatic electric shower, it could be used in other types of installations where pre-heating a cold water supply could be beneficial. For example, it could be used to pre-heat the cold supply of a mixer shower for mixing hot and cold water to provide water having a desired temperature. By pre-heating the cold supply to a mixer shower, the hot water demand of the shower is reduced with resulting cost savings. The mixer shower may be non-thermostatic but is preferably thermostatic.

Furthermore, while the heat recovery unit has been described for pre- heating a cold water supply to a thermostatic electric shower with wastewater from the shower, it could be used to pre-heat cold water to any appliance with warm water from the same or a different appliance. For example, where warm water is available from any source, such as a water cooling system, the heat recovery unit could be used to heat water for one or more showers or other appliances with warm water from the cooling system.

Other applications of the invention will be apparent to those skilled in the art.