Electric water heating system

Abstract

The water heating system (2, figure 1) is for an ablutionary device, e.g. shower, and comprises a flow controller 6 and an electric water heater (4, figure 1). The flow controller has an inlet 22 that

Description

The present application relates to an electric water heating system, specifically an electric water heating system for an ablutionary device. The ablutionary device may be 5 a shower or tap (faucet). Electric showers generally use an instantaneous (or continuous flow) water heater of the type in which a supply of water is heated as it passes through a heater tank to provide a source of hot water on demand. The heater tank receives an input supply of cold mains 10 water which is heated by one or more heating elements before being output to a shower outlet such as a handset. In such instantaneous water heaters, for a given power input to the heater tank, the temperature of the outlet water is determined by the flow rate of the water through the 15 heater tank. Control of the flow rate may therefore be used to achieve and maintain a selected outlet water temperature while the power input to the heating elements is kept constant. For example, if an increase in outlet water temperature is required the flow rate through the heater tank is decreased. 20 One drawback of this is that changes in the temperature of the input supply of cold water can cause variations in the outlet water temperature. The supply water temperature may change because of different ambient temperatures at different times of the year. For example, the supply water may be significantly colder during a UK winter compared to the summer. This means that the user must change the temperature setting throughout 25 the year to achieve the same outlet water temperature. Moreover, as the outlet temperature is affected by changes in the supply water temperature a calibrated numerical temperature scale cannot be provided for the temperature control of the shower. Typically, a non-graduated scale is provided instead which simply allows the temperature to be set between “cold” and “hot”. This makes it difficult for a user to set 30 their desired temperature. A further cause of changes in input supply water temperature is if an electric water heater is used with a waste-water heat recovery device (WWHR device). Such devices transfer heat from waste-water from the shower to the input supply of cold water using 35 a heat exchanger. The increase in temperature of the input water supply provided by the WWHR device is not however constant - at the beginning of a period of use of the shower the inlet water temperature will increase until the WWHR device reaches steady state operation. If the outlet water temperature is set by the user (via the flowrate) when the shower is first turned on it will be set according to a lower inlet water temperature 5 compared to that which will be reached once the WWHR system is running in steady state. As the supply water temperature increases there is a risk of a dangerously high water temperature being reached which could scald the user. A general problem to be addressed therefore is how to more effectively control an 10 electric water heater for an ablutionary device such as a shower in situations where a change in supply water temperature may occur. In a first aspect, the present application provides an electric water heating system for an ablutionary device as defined in claim 1. 15 The second flow regulator may be configured to adjust the flow rate of water from the C\j outlet of the flow controller being supplied to the water heater in use such that water heated by the water heater at the predefined heating power has a constant, or near constant, temperature at varying supply water temperatures. CM 20 -y—— This may have a number of advantages including: i) allowing the user to keep the temperature set point the same despite changes in supply water temperature at different times of the year; ii) adjust for changes in supply water temperature when the electric water heating system is used with a WWHR device which may cause a variation in the 25 supply temperature as the ablutionary device is being used (e.g. as it reaches steady state operation); and iii) a calibrated numerical temperature scale may be provided for a user input device with which the desired set point temperature is set. The second flow regulator may be controlled solely based on the supply water 30 temperature e.g. it may function independently of any user input. The flow controller may be arranged to provide an outlet water temperature of the water heater which varies by no more that ±2°C over a range of supply water temperature between 5°C and 20°C. This may provide suitable control over a typically expected 35 range of supply water temperatures. The predefined heating power may be up to approximately 11 kW and more specifically may be in the range between 7 kW and 11 kW. The second flow controller may be arranged to provide a change in flow rate provided by the flow controller between 50% 5 and 90%. This change of flow rate may allow suitable control of the temperature so that it is kept constant or near constant over a typical range of supply water temperatures. More specifically, the heating power may in the range 7.5 kW to 10.8 kW. 10 More preferably, the second flow controller may be arranged to provide a change in flow rate from the outlet between 56% and 81%. Even more preferably, the second flow controller may be arranged to provide a change in flow rate from the outlet between 65% to 70%, preferably 67%. 15 For example, where the second flow controller is arranged to provide a change in flow rate provided by the flow controller between 65% and 70%, this may allow a single flow controller to be used with water heaters having a range of different predefined heating powers. The second flow controller may be tailored to the average heating power of the range of heating systems with which it is to be used. This may reduce the number of 20 different types of components that are required to manufacture the water heating system (e.g. a different second flow controller is not needed for each heating power). For example, the heating power may be in the range of 7 kW and 1 IkW, or chosen from a group of discrete power values within that range 25 The second flow regulator may comprise a thermally responsive element arranged to expand or contract in response to changes in water temperature to control the flow of water through the second flow regulator. The flow controller may comprise an inlet chamber in fluid communication with the 30 inlet. The inlet chamber may be in fluid communication with the first and second flow regulators. The thermally responsive element may be located within the inlet chamber. This may allow the second flow regulator to quickly respond to changes in supply water temperature. The second flow regulator may be biased towards a closed state. This may allow it to return to a closed state after contraction of the thermally responsive element. The electric water heating system may further comprise an input device arranged to 5 receive a user input of a desired water outlet set point temperature of the ablutionary device. The input device may comprise a control dial and a calibrated numerical temperature scale. The input device may indicate a numerical value of the set point temperature. This may 10 only be possible by using the second flow regulator to compensate for changes in supply water temperature which would otherwise make any temperature indication or scale inaccurate. The water heater may be an instantaneous electric water heater. 15 The ablutionary device may be an electric shower. One or both of the first and second flow regulators may comprise a core member and an associated seal member. An outer surface of the core member may be co-operable with 20 the seal member. The core member may be formed with a plurality of axial grooves in its outer surface to define a plurality of orifices through which fluid can flow through the respective flow regulator. The grooves may be arranged so that, as the core member is axially displaced relative to the associated seal member, the total cross-sectional area of the orifices changes to change the flow rate through the flow regulator. 25 Each of the plurality of grooves may be formed with a tapered end. At the tapered end the grooves may reduce in width and depth until the point at which it terminates. The tapered end may reduce noise caused by water flowing through the offices, while maintaining accurate flow control. 30 The tapered ends may be located at the end of the grooves closest to the seal member when the core member is in a closed position. The electric water heating system may be mechanically controlled. In other words, the 35 first and second flow regulators may be mechanically rather than electronically controlled. This may allow the electric water heating system to be used with lower cost ‘mechanical’ electrical showers. According to a second aspect there is provided a plumbing system, comprising: 5 a shower comprising the electric water heating system of the first aspect or any of the statements above, the electric water heater of the electric water heating system being in fluid communication with an outlet of the shower to supply heated water thereto; and a waste-water heat recovery device arranged to receive waste-water from the 10 shower, the waste-water heat recovery device comprising a heat exchanger arranged to transfer heat from the waste water to a supply of cold supply water, wherein an outlet of the waste-water heat recovery device is in fluid communication with the inlet of the flow controller of the electric water heating system to provide a supply of heated water thereto. The electric water heating system of the present application may be particularly advantageous when used with a waste-water heat recovery (WWHR) device because it can compensate for changes in the supply water temperature as the WWHR device reaches steady state operation. This may otherwise result in excessively high 20 temperature water being supplied to the ablutionary device which can cause scalding. The core members having tapered grooves described above may be used with other types of flow controller, such as one without the second flow regulator. 25 The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied to any other aspect. Embodiments of the invention will now be described, by way of example only, with 30 reference to the accompanying drawings: Figure 1 shows a schematic front view of an electric shower comprising an electric water heating system; Figure 2 shows a schematic cross-sectional view of a flow controller of the water 35 heating system of Figure 1; Figure 3 shows a schematic cross-sectional view of the flow controller of Figure 2 at a first supply water temperature; Figure 4 shows a schematic cross-sectional view of the flow controller of Figure 2 at a second supply water temperature, which is hotter than the first supply temperature; 5 Figure 5 shows a close-up view of a user input device of the electric shower of Figure 1; Figure 6 shows schematic view a plumbing system comprising the electric shower of Figure 1 and a waste-water heat recover device; and Figure 7 shows two perspective views of a core member used in the flow regulators of 10 the water heating system of Figure 1, the core member being shown from two alternative angles. 15 20 Figure 1 shows a schematic view of an electric water heating system 1 provided in an electric shower 2. Flow of water is shown by the arrows in Figure 1. The electric water heating system 1 generally comprises a water heater 4 and a flow controller 6. The water heater 4 is configured to heat a supply of water at a predefined heating power using a heating tank 8. Within the heating tank 8 is located a series of heating elements 9 (more generally one or more heating elements 9). Electrical power is provided to the electrodes so that the water within the heating tank 8 is heated. The water heater 4 is an instantaneous (or continuous) water heater arranged to heat water as it flows through the heating tank 8 so that an on-demand flow of hot water is provided. Any suitable arrangement of electrodes may be used in order to heat water as it passes through the heating tank. 25 The electric shower 2 comprises a wall mounted shower unit 10 in which the water heating system 1 is located. The shower unit may be located within a shower enclosure or next to a bathtub. An outlet 12 of the heating tank 8 is fluidly coupled to a flexible hose 14, which is arranged to supply heated water to a shower handset 16. In other embodiments other arrangements of electric shower may be provided. For example, the 30 water heating system 1 may be located separately at a location away from the shower rather than being in a unit mounted with a shower enclosure. In some embodiments, the shower handset may be replaced with, or provided with additional, fixed shower heads (e.g. a fixed overhead shower head). Referring again to Figure 1, the water heater 4 is in fluid communication with the flow controller 6. The flow controller 6 provides an input supply of water to the heating tank 8 of the water heater 4 so that it can be heated. The flow controller 6 is configured to receive an input flow of water via an inlet 18 of the electric shower 2. The flow 5 controller 6 is arranged to control the rate of water flow from the shower inlet 18 to the water heater 8. The inlet 8 may be fluidly connected to a mains cold water supply of a plumbing system to provide the supply of water. Alternatively, the inlet 8 may be fluidly connected to a waste-water heat recover device (WWHR device) as will described later. 10 The electric water heating system 1 is configured to heat water using a predefined heating power. The water heater 4 supplies a fixed electric power to the heating elements 9 within the heating tank 8. In some embodiments, one or more discrete predefined heating powers may be used. To vary the temperature of water output by the water heater 4 the flow of water through the heating tank 8 is varied, rather than varying the electrical 15 power. The flow' of water through the heating tank 8 is varied by the flow controller 6 to control the temperature. For example, if a reduction in water temperature from the handset 16 is required the flow' rate of water through the heating tank 10 is increased. The flow rate is decreased to increase the water temperature. 20 As shown in Figure 1, the electric water heating system 1 further comprises an input device 20 which allows the user to input a desired temperature for the output water from the shower. In the present embodiment, the input device comprises a control dial (e.g. a rotary dial) via which a desired water outlet set point temperature for the shower may be set. In other embodiments, other input devices may be used such one or buttons or 25 switches, or a touch screen. The input device 20 is operatively connected to the flow controller 6 so that the flow controller can adjust the flow rate of water being supplied to the heating tank 8 according to the temperature set point. The input device 20 allows the temperature to 30 be adjusted by an adjustment of the flowrate through the heating tank 8. Further details of the flow controller 6 are shown in Figure 2. The flow controller 6 comprises an inlet 22 arranged to receive water from the inlet 18 of the electric shower I. The water supply is generally cold mains water (or water heated by a WWHR device). 35 The water supplied to the flow controller 6 has a supply water temperature. The flow controller 6 further comprises an outlet 24 arranged to provide a supply of water to the water heater 4 as described above. The inlet 22 and outlet 24 are formed by apertures in a housing or body 26 of the flow controller 6. 5 To control the rate of flow of water between the inlet 22 and outlet 24 the flow controller 6 comprises a first flow regulator 28 and a second flow regulator 30. The first flow regulator 28 is operable to control the rate of flow between the inlet 22 and the outlet 24 according to a desired output water temperature of the water heater 4. The first flow regulator 28 is operably coupled to the input device 20 such that the rate of flow can be 10 adjusted according to the temperature set point set by the user. The second flow regulator 30 is thermostatically controlled. It is arranged to control the rate of flow between the inlet 22 and the outlet 24 in response to a change in the supply water temperature. 15 The second flow regulator 30 is arranged to control the rate of flow between the inlet 22 and outlet 24 independently of the first flow regulator 28. Only the first flow regulator is user controlled. The second flow regulator may be controlled solely based on the inlet water temperature e.g. it may function independently of any user input. 20 The second flow regulator 30 is configured to adjust the flow rate of water from the outlet 24 being supplied to the water heater 4 in use such that water heated by the w ater heater 4 at the predefined heating power has a constant, or near constant, temperature at varying supply water temperatures. This allows the flow rate of water flowing through the heating tank 8 to be adjusted to compensate for changes in supply water temperature. 25 This allows the heated water to remain at a constant or near constant temperature at varying times of the year despite changing supply water temperature. Referring again to Figure 2, the flow controller 6 comprises an inlet chamber 32 in fluid communication with the inlet 22. The inlet chamber 32 is in fluid communication with 30 the first and second flow regulators 28, 30. Water flowing into the flow controller 6 is divided into a first flow path and second flow path downstream of the inlet chamber 32, each flowing through a respective one of the first and second flow regulators 28, 30. The flow controller 6 comprises an outlet chamber 34 in which water from the first and second flow paths is recombined before flowing out of the outlet 24. Each of the first and second flow regulators 28, 30 comprises one or more core members (which may be each referred to as a flow core) each arranged to engage with a respective seal member to control the rate of flow through the respective flow regulator. The first flow regulator 28 comprises a pair of co-axial core members 36a, 36b mounted on a 5 rotatable control spindle 38. The first flow regulator 28 further comprises a pair of seal members 40a, 40b. Each of the seal members 40a, 40b is arranged to surround and contact the outer surface of an associated one of the core members 36a, 36b. A mechanical linkage is provided between the spindle 38 and user input 20 so that the flow rate is mechanically controlled (rather than being electronically controlled). 10 The core members 36a, 36b are formed with a plurality of axial grooves (described in more detail later) in their outer surface which is co-operable with the associated seal member 40a, 40b to define a plurality of orifices (not shown) through which fluid can flow from the inlet chamber 32 to the outlet chamber 34. The seal members 40a, 40b 15 may comprise O-rings made of elastomeric material which may be located in annular grooves on an inner surface of the housing 26. The core members 36a, 36b are joined C\j together to form a unitary tubular component which is mounted on the spindle 38. The core members 36a, 36b are axially adjustable in response to rotation of the spindle 38 to adjust the axial position of each core member 36a, 36b relative to the associated seal 20 member 40a, 40b. The spindle 18 is operatively coupled to the user input 20 so that the flow rate (and hence temperature) can be adjusted by the user. Each core member 36a, 36b is similar and the grooves are constructed so that, as the core member 36a, 36b is axially displaced relative to the associated seal member 40a, 25 40b, the total cross-sectional area of the orifices and thus the fluid flow rate changes. In this embodiment, the grooves are arranged so that the flow through the orifices of the first core member 36a matches the flow through the orifices of the second core member 36b for each adjusted position of the unitary component formed by them. 30 The flow controller 6 is arranged to split the fluid flow from the inlet chamber 32 into two streams marked A and B. One stream A passes through the first core member 36a and the other stream B passes through the second core member 36b. The core members and seal members are arranged so that the flow through the first core member 36a is in the opposite direction to and matches the flow through the second core member 36b. Downstream of the first flow regulator 28 both flows re-combine upstream of the outlet chamber 34. The pair of core members 36a, 36b in the present embodiment are arranged such that 5 the first flow regulator is forced balanced. In any adjusted position of the core members 36, 36b the flow rate is maintained constant by radial deformation of the seal members 40a, 40b to vary the size of the orifices in response to change in pressure of the incoming fluid. Furthermore, by arranging the flows through the core members in opposite directions and matching the flows, the pressure drop across the seal members 40a, 40b 10 is the same and the forces on both seal members 40a, 40b are equalised. As a result, out of balance operating forces tending to cause the spindle 38 to rotate, and / or which have to be overcome to rotate the spindle 38 are reduced or eliminated. In this way, the axial position of the core members 36a, 36b relative to the seal members 40a, 40b for any selected flow rate is maintained and adjustment of the flow rate is facilitated resulting 15 in a smooth, reliable operation of the user input 20 to control the flow rate. C\j Referring again to Figure 2, the second flow regulator 30 comprises a core member 42 arranged to engage with a respective seal member 44. The core member 42 and seal member 44 of the second flow regulator 30 are similar to the first and second core 20 members 36a, 36b and seal members 40a, 40b of the first flow regulator 28 and operate in a similar way. Only one core member 42 and associated seal member 44 are provided in the second flow regulator 30 such that it is not force balanced. The flow controller 6 is arranged to split the flow of water from the inlet chamber 32 to 25 the outlet chamber 34 between first and second separate flow paths marked as X and Y in Figure 2. The first flow path X includes the first flow regulator 28 and the second flow path Y includes the second flow regulator 30. The first and second flow paths are combined at the outlet chamber 34 so that a single flow Z is output through the outlet 24. 30 As discussed above, the first flow regulator 28 is adjusted by user input setting the desired outlet water temperature. The flow rate through the first flow regulator is adjusted according to the user input to change the rate of flow through the heating tank 8 and hence set the temperature of the water provided to the shower handset 16. The 35 rate of flow through the second flow regulator 30 is adjusted according to the temperature of the water supplied to the flow controller 6. The flow rate of the combined first and second flow paths is therefore adjusted according to the supply water temperature. 5 To adjust the flow rate according to the supply water temperature the second flow regulator 30 comprises a thermally responsive element 46. The thermally responsive element 46 is arranged to expand or contract in response to changes in water temperature to control the flow of water through the second flow regulator 30. The second flow regulator comprises an actuator 48 such as a spindle on which the core member 42 is 10 mounted. The thermally responsive element 46 may be a component containing a filler such as wax arranged to sense the temperature of the water it is in contact with. The thermally responsive element 46 is coupled to the actuator 48 so that the position of the core member 42 is adjusted relative to the seal member 44 responsive to expansion / contraction of the thermally responsive element 46. The position of the core 15 member 42 is mechanically controlled using the thermally responsive element and actuator 48 rather than it being electronically controlled. CM As can be seen in Figure 2, the thermally responsive element 46 is located within the inlet chamber 32. It is therefore in thermal contact with water flowing into the flow 20 controller 6 and can adjust the flow through the second flow controller responsive to changes in the supply water temperature. The second flow regulator 30 further comprises a biasing member 50 arranged to bias the second flow regulator 30 towards a closed position. The biasing member 50 is 25 arranged to bias the core member 42 towards a fully closed position relative to the seal member 44 in which no water flows through the second flow controller 30. This allows the core member 42 to move towards and return to a closed position when the thermally responsive element contracts. The biasing member comprises a coiled spring in the described embodiment. Other types of biasing member may however be used. 30 The flow controller 6 shown in Figure 2 is mechanically controlled. In other words, the first and second flow regulators are mechanically rather than electronically controlled using mechanical actuators. This may allow the flow controller to be used with lower cost ‘mechanical’ electric showers which do not have an electronic controller. The thermally responsive element 46 described above is however only one example of how the second flow regulator 30 may be adjusted responsive to changes in supply water temperature. In other embodiments, the second flow regulator 30 may comprise at least one temperature sensor such as a thermistor arranged to sense the temperature of the 5 water supplied to or flowing through the flow controller 6. An actuator such as an electric motor operable under the control of a controller such as a microprocessor may then be provided to adjust the position of the core member 42 relative to the seal member 44. The first flow regulator may additionally or alternatively be electrically controlled in some embodiments 10 Operation of the flow controller 6 is illustrated in Figures 3 and 4. These Figures show the flow controller 6 of Figure 2 receiving supply water at two different temperatures. Only key components of the flow controller 6 in Figures 3 and 4 have been labelled for clarity. It will be understood that the same components as described above in connection 15 with Figure 2 are present in Figures 3 and 4. C\j Figure 3 shows a situation in which the flow controller 6 is receiving a supply of water at a temperature of 5°C. The user has set a shower water temperature of 40°C via the user input control 20. The flow of water through the first flow regulator 28 is set to 4.4 20 litres per minute (LPM) by adjustment of the position of the core members 36a, 36b of -y—— the first flow regulator 28. The second flow regulator 30 is in a closed position at which no water flows through it. The flow rate of water at the outlet 24 of the flow controller 6 is therefore also 4.4 LPM, which is supplied to the heating tank 8 as described above. At this combination of flow rate, supply water temperature and predetermined heating 25 power of the water heater 4 the water is heated to the desired temperature of 40°C. Figure 4 shows a situation in which the supply water temperature has increased from 5°C to 19°C This may be because of a difference in temperature in which the shower is being used - for example, the supply water temperature may be 5°C in the winter and 30 19°C in the summer when temperatures are higher. Figures 3 and 4 in this example represent different operations of the shower between which the user has left the shower set point temperature the same as they still wish the shower outlet water to be at 40°C. Alternatively, the change in supply water temperature may be caused by the presence of a WWHR device downstream of the shower 2 as will be described later. In that case, 35 Figures 3 and 4 may represent different stages of the same period of use of the shower. For example, Figure 3 may represent a situation when the shower is first turned on and the temperature of waste-water is not yet sufficient to allow any significant level of heat to be transferred from the waste-water to the supply water. In this example, Figure 4 represents a later situation in the same period of use when the WWHR device has 5 reached steady state operation and the supply water is being heated to 19°C by transfer of heat from the waste-water. In Figure 4 the rate of flow of water through the second flow regulator 30 is adjusted in response to the change in supply water temperature. The thermally responsive element 10 46 senses the change in the temperature of water flowing through the flow controller 6 and adjusts the position of the core member 42 relative to the seal member 44. As can be seen in Figure 4, the element 46 has expanded in Figure 4 moving the core member 42 downward against the action of the biasing member 50. 15 In the presently described example, the rate of flow through the second flow regulator 30 increases from zero in Figure 3 to 3.3 LPM in Figure 4. The flow rate of water at the outlet 24 is therefore 7.7 LPM (the combined flow rate through the first and second flow regulators 28, 30). At this combination of flow rate equal to 7.7 LPM, supply water temperature of 19°C and the same predetermined heating power of the water heater 4 20 the water is still heated to the desired temperature of 40°C. The flow rates and temperature given above are to be understood as one example only, with the change in flow rate provided by the second flow regulator 30 being calibrated according to the specific system with which it is being used. For example, the change 25 in flow rate provided by the second flow regulator 30 may be chosen according to the electrical power of the water heater 4. The electric water heating system 1 of the present application may have a predefined heating power up to approximately 11 kW. The second flow controller may be arranged 30 to provide a change in flow rate from the outlet 24 between 50% and 90%. More specifically, the heating power may in the range 7.5 kW to 10.8 kW and the second flow controller may be arranged to provide a change in flow rate from the outlet 24 between 56% and 81%. By providing a change of flow rate within these ranges a change in temperature of supply water between 5°C and 20°C may be adjusted for. By “change in 35 flow rate” we mean the percentage increase of the flow provided to the water heater from the outlet 22 by addition of flow through the second flow controller 30. In other words, the percentage change in flow rate is (z-x) / z* 100, where z is the flow rate in the outlet flow steam Z, and x is the flow rate in the first flow stream X defined above. 5 In some embodiments, the predetermined heating power of the water heater 4 is chosen from: 10.8, 9.8, 9.5, 9.0, 8.7, 8.5 or 7.5 kW. For example, the electric shower 2 may be manufactured with a heater power chosen from the list in the previous sentence. A range of showers may be manufactured with each having a heater power chosen from the group: 10.8, 9.8, 9.5, 9.0, 8.7, 8.5 and 7.5 kW so that a variety of showers can be 10 provided to meet specific implementations. The change in flow rate provided by the second flow regulator 30 may be tailored to the specific heater power. For example, it may be calibrated to each of the possible heater powers define above. An appropriate flow controller (e.g. having an appropriate core member in the second flow controller) may then be fitted to match the heater power during manufacture of a shower. This may 15 allow the optimum adjustment of the flow rate to more accurately control the temperature of the shower. CM In other embodiments, the same flow controller may be used for a variety of showers having different predefined heater powers (e.g. chosen from the group: 10.8, 9.8, 9.5, 20 9.0, 8.7, 8.5 or 7.5 kW, or with a range of 7 kW to 11 kW). For example, the flow controller may be calibrated to match the average predefined heating power of the different electric heaters it will be used with. In the presently described example therefore, the flow controller may be calibrated for a predefined heating power of 9.1 kW. This may correspond to providing a change in flow rate of 67%. 25 As discussed above the change in flow rate provided by the flow controller 1 may keep the output water temperature of the water heater constant or approximately constant despite changes in supply water temperature. In some embodiments, the flow controller may be arranged to provide an outlet water temperature of the water heater (and hence 30 of the shower 1) which varies by no more that ±2°C for a range of supply water temperature between 5°C and 20°C. This may be sufficient to provide suitable temperature control between winter and summer supply water temperatures. The variation of ±2°C may be achieved by using a change in flow rate at the outlet 22 between 56% and 81% as described above. More specifically, the variation of ±2 °C may be achieved with a change in flow rate at the outlet 22 of between 65% to 70%, preferably 67%. The electric water heating system 1 of the present application may advantageously allow 5 the input device to indicate a numerical value of the set point temperature. The adjustment of the first flow regulator can be calibrated by comparing the temperature of the water provided by the water heater 4 (at its predefined heating power) at the respective flow rate set by the user input 20. The user input device 20 may therefore comprise a calibrated numerical temperature scale via which the user can determine the 10 desired shower temperature. An example of this is shown in Figure 5, which shows a user input device 20 in the form of a rotary dial 20a with a temperature scale 20b surrounding it. In other embodiments, other types of user input device may be used. For example, the user input device 20 may be a display screen showing the set point temperature with buttons to increase and decrease the temperature. In yet other 15 embodiments, the buttons and display may be replaced with a touch screen. Providing such a calibrated numerical temperature scale may not be possible without the C\j adjustment of the flow rate suppled to the heating tank 8 by the second flow regulator 30. This is because the temperature of the heated water will otherwise depend too greatly on the supply water temperature, making any temperature scale too inaccurate. CM 20 Figure 6 shows the electric shower 1 of Figure 1 mounted within a shower enclosure 60. In this embodiment the electric shower 1 is connected to a WWHR device 62. The shower 1 and WWHR device form part of a plumbing system e.g. of a building in which the shower is located. The WWHR device 62 is fluidly connected to a drainpipe 64 25 which is arranged to carry waste-water collected on the shower tray 66 of the shower enclosure 60. The WWHR device 62 is arranged to receive a supply of cold mains water at a supply inlet 68. The supply inlet 68 is fluidly connected to a supply pipe of the plumbing system being used to supply water to the shower. 30 The WWHR device 62 comprises a heat exchanger 63 arranged to transfer heat from the waste-water to the supply of cold mains water. In the present embodiment, the heat exchanger 63 is a co-axial pipe-in-pipe heat exchanger in which hot waste-water flows through an inner pipe with cold supply water flowing through a surrounding outer pipe so that heat is transferred between them through the walls of the pipes. Other types of 35 heat exchanger may however be used, such as a flat or planar heat exchanger located within or below the shower tray. In other embodiments, the shower 1 may be an overbath shower with the heat exchanger located underneath a bathtub. Waste-water exists the heat exchanger 63 at an outlet connected to a waste pipe 70 via 5 which it flows to a drain or sewer. The clean water outlet 71 of the waste-water heat recovery device 62 is in fluid communication with the shower 1 via an input supply line 72. The input supply line 72 is fluidly connected to the inlet 22 of the flow controller 6 of the electric water heating system 2 to provide a supply of water thereto which is heated by the water heater 4. 10 As discussed above, the electric water heating system of the present application is advantageous when used in conjunction with a WWHR device as it can adjust the flow rate of the water supplied to the water heater of the shower to take into account the varying supply water temperature before steady state operation of the heat exchanger is 15 reached. C\j Figure 7 shows an embodiment of a core member 100 which may be used in the flow regulator or regulators of any embodiment described or claimed herein. For example, the core member 100 shown in Figure 7 may be used for the core members 36a, 36b of 20 the first flow regulator 28 and / or the core member 42 of the second flow regulator 30. I- The core member 100 is shown in Figure 7 from two different angles. As can be seen in the figures, the core member 100 comprises a plurality of grooves 102a-i, 104a-c. The grooves are arranged axially along the core member 100 (e.g. parallel to the axis along 25 which is moves) and are formed in its outer surface which contacts an associated seal member as described above. The grooves form a plurality of orifices through which flow can flow through around the core member 100. The grooves 102a-i, 104a-c are constructed so that, as the core member 100 is axially 30 displaced relative to the associated seal member, the total cross-sectional area of the orifices and thus the fluid flow rate changes. In the presently described embodiment, the core member 100 comprises a first series of grooves 102a-i which progressively change in axial length around the circumference of the core member outer surface. The change in length results in the number of grooves and thus the number of orifices 35 changing as the core member 100 is displaced to adjust the total cross-sectional area of the orifices. This allows the rate of flow of water to be adjusted by movement of the core member relative to the associated seal member. The longest groove 102a provides the lowest amount of water flow rate. 5 The core member 100 further comprises a second series of grooves 104a-c which are the same axial length as each other. The second series of grooves provide the maximum flow rate as further axial movement of the core member 100 relative to the associated seal member does not change the total cross-sectional area of the orifices formed by the grooves. 10 Each of the grooves 102a-i, 104a-c is formed with a tapered end 106 (only one of which is labelled in Figure 7). At the tapered 106 end each of the grooves reduces in width and depth until the point at which it terminates. The tapered end is provided at the end of the grooves closest to the seal member when the core member 100 is in a closed state. 15 The tapered ends 106 of the grooves is advantageous in reducing noise from the flow of water while maintaining accuracy of the flow rate control. Although all of the grooves are shown having a tapered end that may not be the case in all embodiments. In another embodiment, the core member 100 is provided with grooves of the same 20 length but variable cross-section in the axial direction so that the size of the orifices changes as the core member 100 is displaced to adjust the total cross-sectional area of the orifices. Alternatively or additionally, the core member 100 may be provided with a combination of grooves of different length and variable cross-section to provide any desired flow characteristics. In both of these cases, the grooves may also have a tapered 25 end 106. The flow controllers 28, 30 used in the electric water heating system 1 are to be understood as one example only. In other embodiments, the first flow regulator 28 may not be a flow balanced flow regulator having a pair of core members, but may instead 30 have a single core member so that it is similar to the second flow regulator 30. In other embodiments, the second flow regulator 30 may have a pair of balanced core members. In yet other embodiments, a different type of flow regulator may be used which does not use cooperating core members and seal members. For example, the flow regulators 35 30, 38 may be formed by valve members arranged to engage with tapered valve seats so that a change in flow rate can be produced. Although the flow regulators are shown as being mechanically controlled in the embodiments described above, they may alternatively be controlled by a motor and electrical controller. 5 The electric water heating system 1 of the present application has been described being used with an electric shower. It may be used more generally to supply any kind of ablutionary device. For example, the electric water heating system 1 may be used to supply a faucet (tap). The electric water heating system 1 may be supplied with water from a waste-water heat recovery device as shown in Figure 6, but may also be supplied 10 with un-heated mains water e.g. the WWHR device 62 in Figure 6 may be absent. The core member 100 shown in Figure 7 may be used in flow regulators other than that of the electric water heating systems described herein. For example, the core member having grooves in tapered ends may be used more generally with any kind of flow 15 regulator used to supply water to an ablutionary device. C\j According to another aspect, a flow controller for an ablutionary device is provided. The flow controller comprises: an inlet arranged to receive water from a water supply; an outlet arranged to provide a supply of water for use by the ablutionary device; and a 20 flow regulator operable to control the rate of flow between the inlet and the outlet. The flow regulator comprises a core member and an associated seal member (e.g. as shown in Figure 7 and described above). An outer surface of the core member is co-operable with the seal member. The core member is formed with a plurality of axial grooves in its outer surface to define a plurality of orifices through which fluid can flow through 25 the respective flow regulator. The grooves are arranged so that, as the core member is axially displaced relative to the associated seal member the total cross-sectional area of the orifices changes to change the flow rate through the flow regulator. Each of the plurality of grooves is formed with a tapered end. 30 Such a flow controller may be used in an electric water heater system such as that shown in Figure 1, but without the second flow regulator in the flow controller. The present application therefore also provides an electric water heating system for an ablutionary device, comprising: a water heater configured to heat a supply of water at a predefined heating power using one or more electric heating elements; and a flow controller 35 according to the aspect of the previous paragraph, the flow controller arranged to supply water to the electric water heater. The inlet of the flow controller is arranged to receive water from a water supply having a supply water temperature. The outlet of the flow controller is arranged to provide the supply of water to the water heater. The flow regulator is operable to control the rate of flow between the inlet and the outlet 5 according to a desired output water temperature of the water heater. Various modifications will be apparent to the skilled person without departing form the scope of the claims. The embodiments described above should be understood as exemplary only. Any feature of any of the aspects or embodiments of the disclosure 10 may be employed separately or in combination with any other feature of the same or different aspect or embodiment of the disclosure and the disclosure includes any feature or combination of features disclosed herein. CM

Claims

1. An electric water heating system for an ablutionary device, comprising:5 a water heater configured to heat a supply of water at a predefined heating powerusing one or more electric heating elements; anda flow controller arranged to supply water to the water heater, the flow controllercomprising:- an inlet arranged to receive water from a water supply having a supply 10 water temperature;- an outlet arranged to provide the supply of water to the water heater;- a first flow regulator operable to control the rate of flow between the inlet and the outlet according to a desired output water temperature of the water heater set by the user; and15 -a thermostatically controlled second flow regulator arranged to controlthe rate of flow between the inlet and the outlet independently of the first flow regulator and in response to a change in the supply water temperature,wherein the first and second flow regulators are arranged in parallel between the inlet and the outlet whereby a first flow path flows through the first regulator and a separate 20 second flow path flows through the second regulator.

2. An electric water heating system according to claim 1, wherein the second flow regulator is arranged to control the flow rate through the second flow path such that an outlet water temperature of the water heater which varies by no more that ±2°C over a 25 range of supply water temperature between 5°C and 20°C.

3. An electric water heating system according to claim 1 or claim 2, wherein the predefined heating power is up to 11 kW and the second flow controller is arranged to provide a change provided by the flow controller in flow rate between 50% and 90%.

4. An electric water heating system according to claim 3, wherein the predefinedheating power is the range between 7 kW and 11 kW.

5. An electric water heating system according to claim 3 or claim 4, wherein the second flow controller is arranged to provide a change in flow rate between 65% and 70%.5 6. An electric water heating system according to any preceding claim, whereinsecond flow regulator comprises a thermally responsive element arranged to expand or contract in response to changes in water temperature to control the flow of water through the second flow regulator.10 7. An electric water heating system according to claim 6, wherein:flow controller comprises an inlet chamber in fluid communication with the inlet;the inlet chamber is in fluid communication with the first and second flowregulators; and15 the thermally responsive element is located within the inlet chamber.

8. An electric water heating system according to any preceding claim, wherein the second flow regulator is biased towards a closed position.20 9. An electric water heating system according to any preceding claim, furthercomprising an input device arranged to receive a user input of a desired water outlet set point temperature of the ablutionary device, wherein:the input device is operably coupled to the first flow regulator such that the rate of flow can be adjusted according to the desired output water temperature of the water25 heater set by the user; andthe input device indicates a numerical value of the desired output watertemperature.

10. An electric water heating system according to claim 9, wherein the input device 30 comprises a control dial and a calibrated numerical temperature scale.

11. An electric water heating system according to any preceding claim, wherein the water heater is an instantaneous electric water heater.12 03 2412. An electric water heating system according to any preceding claim, wherein one or both of the first and second flow regulators comprises a core member and an associated seal member, wherein:an outer surface of the core member is co-operable with the seal member;5 the core member is formed with a plurality of axial grooves in its outer surfaceto define a plurality of orifices through which fluid can flow through the respective flow regulator; andthe grooves are arranged so that, as the core member is axially displaced relative to the associated seal member, the total cross-sectional area of the orifices changes to 10 change the flow rate through the flow regulator.

13. An electric water heating system according to claim 12, wherein each of the plurality of grooves is formed with a tapered end.15 14. An electric water heating system according to claim 13, wherein the tapered endsare located at the end of the grooves closest to the seal member when the core member is in a closed state.

15. A plumbing system, comprising:20 a shower comprising the electric water heating system of any preceding claim,the electric water heater of the electric water heating system being in fluid communication with an outlet of the shower to supply heated water thereto; anda waste-water heat recover device arranged to receive waste-water from the shower, the waste-water heat recovery device comprising a heat exchanger arranged to25 transfer heat from the waste water to a supply of cold supply water, wherein an outlet of the waste-water heat recovery device is in fluid communication with the inlet of the flow controller of the electric water heating system to provide a supply of heated water thereto.

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